Godina / Year 2013 ZAGREB Rujan / Listopad Broj / No 10 Sadržaj / Content 1 2 Poruka predsjednice /A Message from the President Poruka urednika /A Message from the Editor Lovre KRSTULOVIĆ-OPARA: APPLICATION of THERMOGRAPHY in ANALYSIS of FATIGUE STRENGTH of MATERIALS and STRUCTURES Lovre KRSTULOVIĆ-OPARA: PRIMJENA TERMOGRAFIJE u ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA 3-11 12-17 Dubravko MILJKOVIĆ: ENGINE MONITORS for GENERAL AVIATION PISTON ENGINES CONDITION MONITORING 19-23 Petar SMILJANIĆ: ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 24-31 Radovi održani na savjetovanju MATEST 2011: Dubravko MILJKOVIĆ: MISFUELING DETECTION WITH TWO OFFSETED CAPACITIVE FUEL SENDERS 32-38 Predstavljamo vam: CROATIAINSPECT 39-41 NDT WEEK in ZAGREB MATEST 2013 The Preliminary Program: CERTIFICATION 2013 42 43 44-45 HDKBR Centar za obrazovanje HDKBR Centar za certifikaciju MATEST 2013/ poster session 46 47 47 Pomoć u radu: Goran DRAGIČEVIĆ RJEŠENJE za POZICIONIRANJE ULTRAZVUČNIH APARATA 48 Izdavač: HDKBR Hrvatsko društvo za kontrolu bez razaranja Publisher: CrSNDT The Croatian Society for Non Destructive Testing Direktor / Director: mr.sc. Miro Džapo Tajništvo/Secretariat: HIS, Petra Berislavića 6. 10000 Zagreb, RH Tel: +385 (01) 60 40 451 Fax:+385 (01) 61 57 129 E-mail: hdkbr@hdkbr.hr, Website: www.hdkbr.hr Kontakt/Contact: Nina Bukovšak Izdavački odbor: Prof.dr.sc. Vjera Krstelj (Glavni urednikr) Dr.sc. Dubravko Miljković (Izvršni urednik) Dr.sc. Dario Almesberger Prof.dr.sc. Nenad Gucunski Mr.sc. Irena Leljak Prof.dr.sc. Lovre Krstulović Opara Bojan Milovanović, dipl.ing.građ. (mag. aedif.) Mag.Nenad Nikolić Suradnici: Mag. Ivan Smiljanić (tehnička podrška) Prof. Marina Manucci (eng. lektor) Prof. Davor Nikolić (hrv. lektor) Sandro Bura (priprema za tisak) Nina Bukovšak (distribucija) HDKBR Info izlazi četiri puta godišnje/ distribucija 300 kom/broj CrSNDT journal is published four times a year/circulation 300 each journal Godišnja pretplata 300 kn / 4 issues per year 40 Euro Časopis je besplatan za članove HDKBR-a The yournal is free for CrSNDT members HDKBR Info možete pratiti na www.hdkbr.hr An online version is available DOSTAVA PRILOGA HDKBR poziva članove i sve koji imaju materijale interesantne čitateljima ovog časopisa da ponude priloge. Znanstveni i stručni radovi će biti recenzirani od strane međunarodno priznatih eksperata. Za reprodukciju publiciranih radova i izvadaka treba osigurati dozvolu. Tekstovi i mišljenja autora u časopisu ne moraju biti u suglasju sa stavovima HDKBR-a i uredništva. Uredništvo ne nosi odgovornost za pogreške i propuste autora radova. PAPER SUBMISSION CrSNDT invites contributions that will be interesting for readers of HDKBR info Journal. Technical papers submitted are peer-reviewed by an Internationaly recognised experts. Permition should be obtained for reproduction of individual artlices and extracts.the Articles and views expressed in the publication are not necessarily in line with CrSNDT, editor and editorial. No liability is accepted for errors or omission. OGLAŠAVANJE/ADVERTISEMENT Cijena oglašavanja/The cost for advertising is: Stranica/Page in yournal Cijena za 4 broja /Cost for 4 numbers per year Zadnja/The last page (cover page A4 size) 8000 kn 1080 Euro or 1380 $ (US) Unutarnja/Inside pages (A4 size) 4000 kn 540 Euro or 690 $ (US) Unutarnja/Inside pages (A4/2 size; half page) 2000 kn 270 Euro or 395 $ (US) Cijena oglasa u samo jednom broju iznosi pola cijene godišnjeg oglašavanja. The price of advertisement published (in only one journal number) is half of the yearly cost. Poruka predsjednice Poštovani čitatelji, drage kolegice i kolege, s radošću i veseljem vas pozivamo da se uključite i pomognete svojom prisutnosti u nastojanju HDKBR-a da bude dio međunarodne “NDT” zajednice, doprinoseći tako unapređenju znanja, poboljšanju obrazovanja u našoj profesiji i općenito boljoj i pouzdanijoj primjeni nerazornih metoda u osiguravanju kvalitete i sigurnosti proizvoda i usluga. Za manje od mjesec dana u okviru značajnih međunarodnih sastanaka i putem razmjene informacija, mišljenja i znanja na konferencijama MATEST 2013 i CERTIFICATION 2013, u okviru tjedna koji smo nazvali: NDT week in Zagreb 7. - 12. listopada 2013. pruža se prilika svakom sudioniku da dopuni svoja znanja, ovaj put posebno o razvoju sustava obrazovanja i certifikacije, te da sudjelovanjem i osobnim primjedbama doprinese unapređenju sustava obrazovanja i certifikacije za osoblje koje primjenjuje nerazorne metode ispitivanja. O programu savjetovanja i predavačima koje ćete imati prilike upoznati saznajte na stranicama ovog broja časopisa, a više na www.certification2013.com. Iskreno se zahvaljujemo svim članovima koji su godinama sudjelovali u radu naše udruge te je svojim znanjem i zalaganjem doveli do današnje razine razvoja, kada s ponosom obilježava 50 godina uspješnog djelovanja. Zahvaljujemo se također međunarodnoj NDT zajednici koja je uvijek i na svim razinama s velikom pažnjom i prijateljski prihvaćala naše sudjelovanje. Sve vas s radošću očekujemo u Zagrebu. A message from the President Dear readers, dear colleagues, it is with great joy and pleasure that we may invite you to participate and help us by your presence in the efforts of CrSNDT to be part of the international “NDT” community, contributing thus to the improvement of knowledge, enhancement of education in our profession and generally to better and more reliable application of non-destructive methods providing quality and safety of products and services. In less than a month, as part of significant international meetings and through exchange of information, attitudes and knowledge at the Conferences MATEST 2013 and CERTIFICATION 2013, during a week that we have entitled NDT week in Zagreb 7-12 October 2013 every participant will have the opportunity to improve their knowledge, this time separately about the development of the education and certification systems, and to contribute by personal attendance and participation in discussions to the improvement of the education and certification systems for the personnel applying non-destructive testing methods. Please, find more information about the Conference Programme and about the presenters you will have the opportunity to meet, on pages of this Journal, and even more at www.certification2013.com. We would like to thank most sincerely all the members who have been participating in the activities of our society, CrSNDT, for so many years, and whose knowledge and efforts have made it possible to reach the today’s level of development, when we proudly celebrate the 50th anniversary of successful operation. We would also like to thank the international NDT community who has always and at all levels with great attention and friendliness accepted our participation. With great pleasure we are looking forward to meeting you in Zagreb. Prof. Vjera Krstelj, Ph.D. 1 Poštovani čitatelju, željeli bismo uvrstiti naš časopis u Scopus bazu podataka, što bi dalje doprinijelo ugledu i važnosti časopisa. Scopus (u vlasništvu Elseviera) najveća je baza sažetaka i citiranosti recenzirane istraživačke literature iz područja znanosti, tehnologije, medicine, društvenih znanosti, umjetnosti i humanističkih znanosti koja pruža sveobuhvatan pregled svjetske znanstvene produkcije. Baza podataka sadrži 21.000 naslova od preko 5.000 međunarodnih izdavača, uključujući 20.000 časopisa (od toga 2.600 časopisa s otvorenim web-pristupom). Da bi uspješno uvrstili časopis u bazu, napravili smo i neke korake koji olakšavaju uvrštenje. Časopis sad ima vlastitu, odvojenu web-adresu unutar društva s novim izgledom, opisom i etikom tiskanja. Pripremili smo i naputak za autore da bi postigli bolju ujednačenost grafičkog izgleda objavljenih radova i olakšali posao našem tehničkom uredniku. Vaše sudjelovanje u časopisu od presudne je važnosti. Ako imate kakav zanimljiv i kvalitetan znanstveni ili stručni rad, pošaljite nam ga za uvrštenje u sljedeće brojeve časopisa. Dear reader, Our current goal is to be included in the Scopus database which would further contribute to the prestige and importance of the journal. Scopus (owned by Elsevier) is the largest abstract and citation database of peer-reviewed research literature in the fields of science, technology, medicine, social sciences and Arts & Humanities. It delivers a comprehensive overview of global scientific output. Database contains 21,000 titles from more than 5,000 international publishers with 20,000 peer-reviewed journals (including 2,600 open access journals). For journal to be successfully included in the database we have made some steps to facilitate the listing. Journal now has its own, separate, web address within the society with a new look, description and ethics of publication. We have prepared instructions for authors to achieve greater graphical uniformity of published paper and to make life easier for our technical editor. Your participation in the journal is welcome. If you have interesting scientific and professional paper, please send it for inclusion in the next issues of the journal. S poštovanjem / Sincerely dr. sc. Dubravko Miljković Izvršni urednik/Handling Editor 2 Lovre KRSTULOVIĆ-OPARA, Fakultet elektrotehnike, strojarstva i brodogradnje, Sveučilište u Splitu, R. Boškovića 32, HR-21000 Split, www.fesb.hr/kk, lovre.krstulovic-opara@fesb.hr ABSTRACT - Thermography is becoming more and more relevant method in industry and as a research tool. It is an accepted method in many fields where non-destructive testing is carried out. In this paper focus was on evaluation of stress concentrations and fatigue of metal structures. Three thermographic methods: Thermoelastic stress analysis, Risitano method and acquisition of plastification zone and fracture propagation, are addressed and compared with results of classical cyclic testing of Al2024 alloy specimens. Specimens with three types of stress concentrator are used; 3 mm triangular notch, R3 mm circular notch, and a hole with 6 mm diameter. All thermographic methods showed high level of coincidence with classical fatigue tests. Thermoelastic stress analysis provides first stress invariant field for cyclic loaded sample, revealing stress concentrations near notches. Risitano method, from thermal dissipations at various levels of cyclic load, estimates dynamic strength of materials. Fast cooled middle-wave infrared cameras enable locating and tracing material plastification and fracture propagation. The outcomes of all evaluated methods are in accordance with each other. Keywords: Thermoelastic stress analysis, Risitano method, plastification, fracture propagation, fatigue, cyclic loading 1.INTRODUCTION Infrared thermography is nowadays an accepted non-destructive testing (NDT) method. It is applied as passive and active method, as described in our previous work [1-3]. Active thermography is used in NDT of composite polymer materials. Passive thermography is a method used in analysis of materials and structures, e.g. fatigue strength estimation. Passive thermography can also be used in evaluation and detection of plastification and fracture propagation. When used in estimation of fatigue limit it can be considered an NDT method due to the fact that fatigue strength can be estimated without destroying a single specimen. Fatigue strength estimation is generally based on destructive testing of specimens or whole sections of structure with the goal of predicting the fatigue limit of cyclic loaded structures. Detection and prevention of stress concentrations, as the main source of fracture initialization, is mostly limited to numerical simulations or experimental measurements with methods such as strain gauges, photoelasticimetry, etc. The realistic visualization of structure’s stress or strain distribution is hardly achievable with the majority of NDT methods. Strain gauges are applicable for dynamic strain measurements, providing reliable results, but with the drawback of enabling readings only in locations of application. The current development, sensitivity and price of IR thermograpy equipment enabled several thermographic approaches to become popular and accepted as an NDT tool. In the field of dynamic testing the Thermoelastic Stress Analysis (TSA) [3-12] enables a full field visualization of surface stress distribution (the method provides first stress invariant). The estimation of fatigue strength is possible by several passive thermography methods such as Risitano method [13, 14] or Meneghetti method based on energy dissipation [15, 16]. With these methods it is possible to significantly reduce, or completely avoid destruction of test specimens, which reduces the time and cost of fatigue testing. 3 APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES 1.INTRODUCTION Lord Kelvin found that elastically deformed bodies generate temperature changes when loading is applied, where tension causes cooling, while compression causes heating. In zones of stress concentrations these effects are more pronounced. For the case of metals, e.g. steel or aluminium, these changes are few milligrades, while for the case of plastic deformations changes are of several grades Celsius. These thermal changes, characterized by significant heat generation, enable detection and estimation of plastification zone propagation, crack propagation or final rupture scenario. The described IR-based methods are applicable to all structural materials, where applicability depends on the surface emission characteristics. Good emission coefficient can always be achieved by the application of high emissivity paint, e.g. Nextel Velvet-Coating 881-21 [17] with emission coefficient of 0.95, Figure 1. In this paper an overview of three methods is given, where the described methods enable visualization of stress distribution, estimation of fatigue limit and detection of plastification or fracture propagation. The obtained results are compared with classical fatigue testing (S-N diagrams). The used specimens are made of aluminium alloy Al2024 with cross section of 20x4 mm and cyclically loaded (r=Fmin/Fmax=0) with loading frequency of 20 Hz. The test specimens are machined with stress concentrators in the form of 6 mm hole, V shape notch (3mm in depth) and semi-circular notch (R3 mm). The cross section of the notched zone is the same for all specimens (14x4 mm). Figure 1 - Experimental setup and specimens with stress concentrators (V notch, semicircular notch and hole) 4 Although all described methods are fully applicable to reinforced polymer composites, only aluminium alloy will be addressed herein. Polymer composites are characterized by significantly lower thermal diffusivity so that the evaluation of such materials is for some of the methods possible even with LW thermal cameras based on micro-bolometric detectors. Due to the high thermal conductivity, high thermal diffusivity and low thermal capacity, metal specimens are characterized by fast thermal changes requiring detection with cooled MW thermal cameras based on photonic detectors. These cooled MW cameras enable acquisition with frame rates of over 700 Hz., where the limit is not due to the technology of detector, but due to the rate of data transfer to computer. Fast cooled MW detectors enable sharp images of dynamic occurrences (20 Hz cyclic loading rate for described examples), which is not the case for micro-bolometric LW detectors. The results presented here are provided by cooled MW camera FLIR SC 5000, with image resolution of 320x256 pixels and sensitivity of 0.02 K. Currently on the market there are similar cameras with double resolution, same sensitivity, but with lower frame rate. For the reduced image size the frame rate is increased up to over 700 Hz. The IC camera used herein, for the full image resolution (320x256 pixels), enabled frame rates of around 150 Hz. 2.EVALUATION OF STRESS DISTRIBUTION BASED ON THERMOELASTICITY In 1850 Lord Kelvin described the thermoelastic effect based on the fact that the applied load causes thermal changes of objects. In 1915 Compton and Webster conducted the first experimental proof, while in 1967 Belgen provided the first non-contact measurements [18]. With the development of non-contact IR measurement technology method became of particular scientific interest. In 1982 the first images were provided by Ometron SPATE 8000 instrument, where several hours were needed for the acquisition of ∆T = −α T (σ + σ 2 ) ρ Cp 1 , (1) where α is coefficient of thermal expansion, T is room temperature, ρ specimen density, Cp thermal capacity at constant pressure, while σ1 and σ2 are principal stresses. Supposing that coefficients α, T, ρ and Cp are constant for the observed specimen, equation (1) provides direct relation between increase in temperature and first stress invariant (the sum of principal stresses, where for the body surfaces 3rd principal stress σ3=0). Relation (1) holds for adiabatic condition (no gain or heat loss), which is satisfied for fast load changes (around 10 Hz). Thus, the method requires acquisition with fast cooled MW cameras, cyclic specimen loading of approximately 10 Hz (although loading can be reduced to 3 Hz) and sufficiently high level of stress changes. Load can be generated by magnetic field, ultrasound, or dynamic load actuator as described herein. When acquiring images of a cyclically loaded specimen (Figure 1) at load frequency of 20 Hz, cyclical heat flashes are recorded (Figure 2). In zones of stress concentrations these flashes are stronger. The cyclically loaded specimen in Figure 2 provides images of stress distribution, where cooler zones are zones with higher tensile stresses. As the camera frame rate was set up to 50 Hz (camera system enables higher frame rates), the set of images in Figure 2 demonstrate the problem of capturing the moment of highest loading. Figure 2 - Thermal flashes of cyclic loaded specimen (loading frequency of 20 Hz) Even when the moment of highest loading is captured, relation (1) will not provide realistic results. To obtain the precise reading of the first stress invariant, an additional hardware component, the so called Lock-In, is required. The Lock-In provides information about applied loading (e.g. the load cell signal) and integrates it with thermal set of images enabling correct stress distribution based on relation (1). Figure 3 illustrates on an example of fillet welded test specimen [19] the difference between raw image and image obtained after Lock-In image processing. Figure 3 - Raw image and stress distribution after Lock-In image processing 5 APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES stress distribution. The SPATE 8000 was based on a single thermal detector (thermal diode) and set of synchronized moving prisms providing surface thermal scan. In 1994 the introduction of digital focal point array technology enabled by instrument Stress Photonic the stress distribution acquisition within a few minutes. The TSA method is based on the thermoelastic relation: APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES Although a very reliable method, the TSA is not so common in literature. The limitations of the method are that cyclic loading is required, the loading must achieve a certain stress level, and the method requires relatively expensive cooled LW camera. The examples of the method are available in references [6, 20-23]. The TSA method is a full field NDT method providing visualization of stress distribution for the whole observed body surface. The method is similar to the method of photoelasticimetry, with the difference in result in the form of the first stress invariant. 3.EVALUATION OF FATIGUE LIMIT BASED ON THE RISITANO METHOD The Risitano method [13, 14] is based on the fact that at the beginning of cyclic loading, a small increase in specimen’s temperature occurs. The increase is stabilized after a few loading cycles, remaining constant until rupture (constant supposing there is no increase in temperatures of the whole experimental setup). A few cycles before rupture, there is significant increase in specimen’s temperature, followed by temperature drop after rupture. Figure 4 depicts the increase in temperature during the first load cycles of specimen with V-shaped notch, and sudden increase in temperature for the last loading cycles before rupture (example of 4 kN cyclic loading). This effect is similar to the effect of stress-strain hysteresis that can be observed for the first few loading cycles and the last few cycles before rupture during standard fatigue cyclic test. This hysteresis disappears at the beginning and reappears close to the end of fatigue test. Contrary to classical fatigue test, where several test specimens are needed, the Risitano method enables estimation based on a single test specimen, where final specimen rupture can be avoided. Fatigue limit is estimated from the fact that for a certain amount of load there is no temperature increase. The method is simple and applicable using LW 6 micro-bolometric cameras. When applied with more sensitive MW cooled cameras, due to the higher acquisition sensitivity, small thermal fluctuations appearing from elastic loading-unloading thermoelastic effect require additional smoothing of temperature data readings. The upper diagram in Figure 5 displays raw temperature data. The lower diagram in Figure 5 displays the smoothed curve that enables easier data evaluation. Thermal fluctuations in the upper diagram are thermal flashes illustrated in Figure 2. LW micro-bolometric cameras do not need such data processing due to the fact that sensitivity and frame rate of such cameras are much lower. Figure 4 - Increase, stabilization and final increase of specimen’s temperature Figure 5 - Thermal fluctuation and smoothed thermal diagram acquired by LW cooled IR camera During elastic cyclic loading tension causes cooling, while compression causes heating of the test specimen according to relation (1). Significant heat generation appearing in zones of yielding enables recording the whole plastification process. Materials with high thermal capacity and low conductivity enable use of LW micro-bolometric cameras. Metals require acquisition with cooled LW cameras. Figures 6-8 depict sequences of plastification initialization, propagation and final rupture. Temperature differences between upper and lower part of specimens are caused by heat flow due to the thermal difference of grips, where lower grip is connected to hot hydraulic piston and the upper one is connected to the cooler load cell. Figure 6 - Propagation of plastification zone until rupture for V-notched specimen Figure 7 - Propagation of plastification zone until rupture for specimen with hole Figure 8 - Propagation of plastification zone until rupture for specimen with semicircular notch 5.COMPARISON OF IR-BASED METHODS WITH CLASSICAL CYCLIC FATIGUE TESTS To demonstrate the capabilities of IR-based methods the obtained results are compared with classical fatigue test for specimens in Figure 1. The S-N diagrams (stress vs. number of cycles) providing relation between the level of sinusoidal cyclic loading and the achieved number of cycles in the logarithmic scale are depicted in Figures 9-11. Symbol “x” in diagrams symbolizes the moment of specimen failure, while the red lines are the mean values for cases where several specimens are loaded with the same cyclic load. Cycling was performed on servo-hydraulic dynamic testing load frame Instron 8800 50 kN at the frequency of 20 Hz. Due to the limited number of available specimens the number of three specimens per each load case has not been achieved. Although partial, S-N diagrams do show material fatigue resistance, making them comparable to the results obtained by addressed IC-based methods. Figure 9 - S-N diagram for V-shaped notch 7 APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES 4.EVALUATION OF PLASTIFICATION AND RUPTURE PROPAGATION APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES Figure 10 - S-N diagram for specimen with hole Figure 11 - S-N diagram for semicircular notch Figure 12 . Stress distribution of V-notched, semicircular notched and specimen with hole at 8 kN cyclic loading The TSA enables visualization of stress distribution for all analyzed specimens. Figure 12 depicts stress distribution for maximal cyclic load level of 8 kN (corresponds to nominal stress of 143 MPa). Stress scale shows maximal stress appearing for V-shaped notch (94.26 MPa), while semicircular notch has minimal stress, which is comparable to S-N diagrams, where the lowest fatigue resistance characterizes a V-notched specimen. The specimen with hole has slightly lower fatigue resistance than the semicircular notched specimen, which is comparable to maximal stresses in Figure 12 (48.87 MPa for specimen with hole, 42.97 MPa for the semicircular notched specimen). Figure 13 - Stress distribution for specimen with hole and semicircular notched specimen at cyclic loading of 16 kN The thermo elastic effect becomes stronger at higher loadings. Thus, it is not only necessary to achieve the required loading frequency, but the loading level as well. In Figure 13 the stress distribution of V-notched specimen is not displayed as the specimen already ruptured for the loading lower than 16 kN (286 MPa). The Risitano method is based on recording the specimen’s temperature for cyclic loaded specimen at different loading levels. Figure 14 depicts the mean temperature of the measured area (blue quadrilateral) for 6,000 cycles of sinusoidal loading at the frequency of 20 Hz. Camera frame rate was set to 50 Hz. Although higher frame rates 8 Figure 17 - Time diagram of mean temperature for test area of semicircular notched specimen Figure 14 - Time diagram of mean temperature for test area Thermal diagrams in Figures 15-17 depict thermal increase during 6,000 loading cycles for different load levels at the frequency of 20 Hz, where the ratio of load extremes was r=Fmin/Fmax=0. The initial temperature level depends on the specimen’s room temperature and does not influence the method as only relative thermal increase during the test is observed. For each case the thermal increase is higher for higher loading levels. The rupture is characterized by sudden increase in temperature, followed by temperature drop after rupture. Diagrams in Figures 18-20 are thermal increases of mean temperatures displayed in Figures 15-17. At the point where the line defined by linear approximation reaches zero the thermal increase is nominal maximal stress, that is: for V-notched specimen 44 MPa, for specimen with hole 123 MPa, and for semicircular notched specimen 126 MPa. These results correspond to the results of maximal stress obtained by the TSA method at the same level of loading (Figure 12), where maximal stress is observed for V-notched specimen (94 MPa), while for specimen with hole it is 49 MPa, and for semicircular notched specimen it is 43 MPa. When comparing the results of the Risitano method with the maximal nominal stress in S-N diagrams (Figures 9-11), maximal nominal stresses obtained by the Risitano method correspond to the results obtained in S-N diagrams. As fatigue tests on load frame have not exceeded 106 cycles, the obtained results cannot be fully compared, but the trend of stress concentrator influence is clearly visible. To make more precise predictions, reaching 107 load cycles is required. Figure 15 - Time diagram of mean temperature for test area of V-notched specimen Figure 16 - Time diagram of mean temperature for test area of specimen with 6 mm hole Figure 18 - Thermal increase vs. load level increase and linear approximation of V-notched specimen 9 APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES are possible, high frame rates will result in unnecessary increase in the collected data. The length of the recorded sequence depends on the temperature stabilization period. In thermal diagrams in Figures 4, 1417, the thermal drop before the beginning of cycling (Figure 15) is caused by initial tension. APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES Figure 19 - Thermal increase vs. load level increase and linear approximation of specimen with hole Figure 20 - Thermal increase vs. load level increase and linear approximation of semicircular notched specimen During the Risitano method testing only three specimens ruptured, which is significantly lower than 23 specimens required for S-N diagrams that did not provide final results of maximal nominal stresses. The testing time required for all specimens evaluated by the Risitano method was several hours, while S-N curves required two weeks of load frame testing. 6.CONCLUDING REMARKS In this paper an overview of the application of IR-based methods to estimate fatigue resistance, stress concentrations and fatigue strength for metal specimens is presented. All three described methods, i.e. the TSA, the Risitano method and recording of plasticity and crack propagation, are fully applicable on polymer composites. When evaluating metals, i.e. materials with high diffusivity, LW micro-bolometric cameras can only be used in the Risitano method. The TSA requires cooled MW camera, additional Lock-In hardware component, and corresponding data processing software, 10 which increases the equipment price. These prices have remained constant over the last few years. There have been no significant changes in technology, except that for the same price a camera with double image resolution can be obtained. Double image resolution for the methods addressed here is not necessary, and the increasing image resolution decreases the camera frame rate, which is an important issue. During the last decade several companies that produced MW cameras and image processing software based on Lock-In approach (e.g. Agema, Cedip) have been bought by bigger global companies, mostly oriented towards LW camera market, causing a stagnation of research and applications in the field of TSA. Except for some academic research work, there have been no major steps forward in industrial applications. This particular area of research and development still enables new approaches and can be of great scientific interest. With regional stagnation in industrial research and development, the research in IR-based methods stagnates as well, which keeps the prices of MW thermal cameras high. The TSA enables visualization of stress field for object surface, thus enabling the estimation of stress concentrations. When comparing three addressed specimens, it can be concluded that the one with semicircular notch is characterized by the lowest stress concentration and the highest fatigue limit. This has been confirmed by classical fatigue tests, i.e. S-N diagrams. The results obtained by the Risitano method correspond to the results of fatigue tests. Fast cooled MW cameras enable evaluation of plasticity and crack propagation including specimen rupture. These observations can be compared with the TSA, where if the zone of fracture initialization corresponds to stress concentration zones, it proves that the stress concentration is the cause of rupture. If this is not the case, then the cause of rupture can be found in material drawbacks or the machining method. The TSA, the Risitano method and the acquisition of plastification and fracture 7.References [1] Krstulović-Opara, L., Domazet, Ž., Klarin, B., Garafulić, E.: The Application of IR Thermography to the NDT and Thermal Stress Analysis, HDKBR info, no. 6/7, 17-22, 2012. [2] Krstulović-Opara, L., Klarin, B. , Garafulić, E. and Domazet, Ž.: Application of gradient based IR thermography to the GRP structures inspection, Key Engineering Materials, Vols.488-489, 682685, 2011. [3] Krstulović-Opara, L. , Klarin, B., Neves, P., Domazet, Ž.: Thermal imaging and Thermoelastic Stress Analysis of impact damage of composite materials, Engineering Failure Analysis, vol. 18, 713–719, 2011. [4] Lesinak, J.R., Boyce, B.R.: A high-speed differential thermographic camera, SEM conference, 1995. [5] Lesinak, J.R., Bazile, D.J., Boyce, B.R., Zickel, M.J.: Stress intensity measurement via infrared focal plane array, ASTM conference, May 1996. [6] Haldorsen, L.M.: Thermoelastic stress analysis system developed for industrial applications, Ph.D. Thesis, University of Aalborg, Institute of mechanical engineering, 1998. [7] Lesinak, J.R., Boyce, B.R., Howenwater, G.: Thermoelastic measurement under random loading, SEM conference, June 1998. [8] Boyce, B.R.: Steps to modern thermoelastic stress analysis, ATEM Conference, Ube, Japan, July 1999. [9] Honlet, M., Boyce, B.R.: Full-field thermoelasticity. A new generation of an optical method showing directly effects produced by mechanical strains, 15th WCNDT, Roma, Italy, 2000. [10] Dulieu-Barton, J.M., Quinn, S.: Thermoelastic stress analysis of oblique holes in flat plates, Int J Mech Sci, vol. 41, 527–46, 1999. [11] Boyce, B., Lesniak, J.: Unique applications of thermoelastic stress analysis, Spring SEM conference, 1999. [12] Lesniak J, Bartel B.: An elevated-temperature TSA furnace design, Exp Techniques, 20(2):96, 1999 [13] La Rosa, G., Risitano, A.: Thermographic methodology for rapid determination of the fatigue limit of materials and mechanical components, International Journal of Fatigue, vol. 22, 65-73, 2000. [14] Fargione, G., Geraci, A., La Rosa, G., Risitano, A.: Rapid determination of the fatigue curve by the thermographic method, International Journal of Fatigue, vol. 24, 11-19, 2002. [15] Meneghetti, G.: Analysis of the fatigue strength of a stainless steel based on the energy dissipation, International Journal of Fatigue, vol. 29, 81-94, 2007. [16] Minak, G.: On the Determination of the Fatigue Life of Laminated Graphite-Epoxy Composite by Means of Temperature Measurement, Journal of Composite Material, vol. 44, 2010. [17] Tang-Kwor, E., Matteï, S.: Emissivity measurements for Nextel Velvet Coating 81121 between -36 °C and 82 °C., High Temp.-High Press., vol. 33, 551-556, 2001. [18] Boyce, B.R.: Steps to Modern Thermoelastic Stress Analysis, ATEM Conference, July 1999, Ube, Japan,1999. [19] Pirsić, T. , Krstulović-Opara, L , Domazet, Ž.: Thermographic Analysis of Stress Distribution in Welded Joints, The European physical journal. EPJ Web of Conferences, 6, 07004-p1 - 07004p6, 2010. [20] Medgenber, J., Ummenhofer, T.: Assessment fatigue damage in low-carbon steel using lock-in thermography, 8th Int. Conference on Quantitative infrared Thermography (QUIRT 2006), June 28-29, Padova, Italy, 2006. [21] Lin, S.-J., Quinn, S., Matthys, D.R., New, A.M., Kincaid, I.M., Boyce, B.R., Khaja, A.A., Rowlands, R.E.: Thermoelastic Determination of Individual Stresses in Vicinity of a NearEdge Hole Beneath a Concentrated Load, Experimental Mechanics, vol. 51, 797-814, 2011. [22] Cavaliere, P., Rossi, G.L., Di Sante, R., Moretti, M.: Thermoplasticity for the evaluation of fatigue behavior of 7005/Al2O310p metal matrix composite sheets joined by FSW, International Journal for Fatigue, vol. 30, 198-206, 2008. [23] Lesinak, J.R., Boyce, B.R.: A High-Speed Differential Thermographic Camera, SEM Conference, 1995. 11 APPLICATION OF THERMOGRAPHY IN ANALYSIS OF FATIGUE STRENGTH OF MATERIALS AND STRUCTURES propagation are reliable approaches to estimation of fatigue resistance and stress concentration enabling assessment of materials and structures. The presented methods are dynamic, non-destructive (except fracture propagation) and non-contact methods. The examples demonstrated the ability of IR thermography as a reliable NDT and experimental mechanics tool. PRIMJENA TERMOGRAFIJE U ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA PRIMJENA TERMOGRAFIJE U ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA Lovre KRSTULOVIĆ-OPARA, Fakultet elektrotehnike, strojarstva i brodogradnje, Sveučilište u Splitu, R. Boškovića 32, HR-21000 Split, www.fesb.hr/kk, lovre.krstulovic-opara@fesb.hr SAŽETAK – Termografija, kao nerazorna metoda, ima sve veću primjenu u istraživanjima i industriji. U radu je prikazana primjena termografije u procjeni koncentracije naprezanja te zamora materijala i konstrukcija. Na primjerima uzoraka s koncentratorima naprezanja prikazana je primjena termografije u analizi metalnih materijala. U tu svrhu uspoređeni su rezultati klasičnih ispitivanja na umarlici s tri termografske metode: termoelastičnom analizom naprezanja, Risitanovom metodom te metodom praćenja širenja zone plastifikacije i loma. Termoelastičnom analizom naprezanja na ciklički opterećenim uzorcima dobiva se raspodjela naprezanja te koncentracije naprezanja na površini materijala. Risitanova metoda na temelju mjerenja porasta temperature ciklički opterećenog uzorka s porastom opterećenja predviđa dinamičku čvrstoću uzorka. Zbog velike disipacije topline u zoni plastifikacije i pukotine, brze srednjovalne kamere omogućuju praćenje tijeka plastifikacije i širenja pukotine. Opisane metode primjerene su za dinamička ispitivanja, nerazorne su i beskontaktne te ne utječu na rezultate ispitivanja. Ključne riječi: termoelastična analiza naprezanja, Risitanova metoda, plastifikacija, propagacija pukotine, zamor, cikličko opterećenje 1.UVOD Infracrvena termografija u širokoj je primjeni kao nerazorna metoda ispitivanja materijala, bilo kao pasivna bilo kao aktivna termografija, o čemu je pisano u nekim našim prethodnim radovima [1-3]. Aktivna termografija igra značajnu ulogu u nerazornom ispitivanju kompozita. Pasivna termografija ima značajnu ulogu u analizi materijala i konstrukcija, a jedno bitno područje primjene jest evaluacija pogonske čvrstoće konstrukcija, točnije određivanje dinamičke čvrstoće materijala, odnosno konstrukcija. Termografija je primjenjiva metoda u analizi loma, dok se u analizi zamora i procjeni dinamičke čvrstoće može smatrati nerazornom metodom s obzirom da je procjenu moguće provesti bez loma ispitivanog materijala, odnosno uzorka. Analiza na zamor materijala i konstrukcija uglavnom podrazumijeva razarajuće ispitivanje uzoraka, odnosno čitavih segmenata konstrukcija s ciljem utvrđivanja životnog vijeka dinamički opterećenih konstrukcija. Otkrivanje i izbjegavanje koncentracija naprezanja, kao najčešćeg uzroka otkazivanju konstrukcija, uglavnom se ograničava na numeričko modeliranje i simuliranje opterećenja te mjerenje nekom od metoda eksperimentalne analize 12 naprezanja poput metode elektrootpornih mjernih traka (tenzometri), fotoelastičnosti i sl. Realni prikaz stanja raspodjele naprezanja, odnosno deformacija, na čitavoj površini ispitivanog objekta teško se dobije. Tenzometri daju pouzdane informacije i primjereni su dinamičkim ispitivanjima konstrukcija u eksploataciji, no manjkavost im je što očitavaju deformacije samo na mjestu lijepljena tenzometra. Infracrvena termografija relativno je novija metoda, razvoj koje je omogućio razvoj kvalitetnijih i cijenom pristupačnijih digitalnih detektora. Ako se razmatraju tipična ispitivanja u pogonskoj čvrstoći, termografija u okviru metode termoelastične analize naprezanja (Thermoelastic Stress Analysis – TSA) [312] omogućuje prikaz raspodjele sume glavnih naprezanja po čitavoj površini opterećenog tijela. Utvrđivanje dinamičke čvrstoće pojedinog materijala moguće je metodama poput Risitanove metode [13, 14] ili Meneghettijeve metode [15, 16], temeljene na disipaciji energije. Ovim metodama moguće je bitno smanjiti broj potrebnih uzoraka za ispitivanje, odnosno ispitivanje se može svesti samo na jedan uzorak, što nije slučaj kod klasičnog ispitivanja na zamor koje iziskuje cijeli niz ispitivanja i epruveta. Slika 1. (vidi strana 4) Iako su opisane metode u potpunosti primjenjive na polimerne kompozite, ovdje će se komentirati samo primjena na metalima. Polimerne kompozite karakterizira daleko veća toplinska tromost (manja toplinska difuzivnost) te je za njihovu evaluaciju u nekim metodama moguće koristiti i dugovalne mikrobolometarske kamere. Zbog svoje velike toplinske vodljivosti i malog toplinskog kapaciteta (velika difuzivnost), metale karakteriziraju brze promjene temperature te su za njihovu evaluaciju nužne brze hlađene srednjovalne kamere. Za razliku od mikrobolometarskih dugovalnih kamera, srednjovalne kamere omogućuju akvizicije od preko 700 Hz. Ovo omogućuju detektori koji se temelje na tehnologiji fotonskog izbijanja, gdje granicu u brzini akvizicije ne predstavlja sam detektor nego prebacivanje signala u računalo. Brzi detektori i pri ovim velikim frekvencijama opterećenja (20 Hz u korištenim primjerima) osiguravaju oštre snimke, što kod mikrobolometarskih kamera nije slučaj. Kamera korištena u ovdje prikazanim primjerima je srednjovalna hlađena kamera Flir SC 5000, rezolucije 320x256 piksela i osjetljivosti 0,02K. Trenutačno su na tržištu i kamere dvostruke rezolucije, iste osjetljivosti, no brzina akvizicije u punoj je rezoluciji manja. Ograničavanjem kadra (polja aktivnih piksela kamere) povećava se brzina akvizicije do vrijednosti preko 700 Hz. U punoj rezoluciji (320x256 piksela) brzina je akvizicije oko 150 Hz. 1.EVALUACIJA NAPREZANJA METODOM TERMOELASTIČNOSTI Još 1850. god. lord Kelvin opisuje termoelastični efekt, odnosno činjenicu da pod djelovanjem sila dolazi do promjene u temperaturi tijela. God. 1915. Compton i Webster provode prvi eksperimentalni dokaz, a 1967. Belgen vrši prva beskontaktna mjerenja [18]. Metoda dobiva na značaju kada se razvila tehnologija beskontaktnih mjerenja putem termokamera. Godine 1982. dobivaju se prvi snimci uređajem Ometron SPATE 8000, a za akviziciju naprezanja bilo je potrebno nekoliko sati s obzirom da se uređaj temeljio na samo jednom detektoru (diodi) i setu pomičnih zrcala koja su sinkroniziranim radom omogućivala prenošenje temperature s cijele površine uzorka. God. 1994. uređajem Stress Photonic, odnosno razvojem digitalnih detektora s nizom piksela, omogućena je akvizicija raspodjele naprezanja u nekoliko minuta. 13 PRIMJENA TERMOGRAFIJE U ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA Još je lord Kelvin ustanovio da je karakteristika elastično deformiranih tijela da djelovanjem opterećenja dolazi do promjene temperature, pri čemu vlačno naprezanje izaziva lokalno pothlađivanje, a tlačno lokalno zagrijavanje tijela. Na mjestima gdje su naprezanja veća i ove su promjene veće. Promjene temperature za tipične konstrukcijske materijale poput čelika i aluminija iznose nekoliko desetinki stupnja Celzija ili Kelvina. Kod naprezanja i deformacija kod kojih dolazi do plastičnih deformacija i lomova materijala temperature su znatno više, nekoliko desetaka stupnjeva, pa termografija omogućuje praćenje načina plastifikacije i širenja pukotine sve do loma konstrukcije ili uzorka. Navedene metode primjenjive su na gotovo svim konstrukcijskim materijalima, a mogućnost primjene uglavnom ovisi o stupnju emisivnosti površine, što se lako rješava bojanjem bojama visokog stupnja emisivnosti (u radu je korištena boja Nextel Velvet-Coating 881-21 [17], koeficijenta emisivnosti 0,95, slika 1). U ovom članku bit će dan pregled tri metode kojima se omogućuje procjena raspodjele naprezanja, određivanje dinamičke čvrstoće te praćenje tijeka plastifikacije i širenja pukotine. Rezultati će se usporediti s klasičnim ispitivanjem na zamor u koju svrhu su aluminijske epruvete (legura Al2024) dimenzija poprečnog presjeka 20x4 mm opterećivane vlačno sinusoidno (frekvencija 20 Hz, r=Fmin/Fmax=0). Na epruvetama su izrezani koncentratori naprezanja u obliku rupe u sredini promjera 6 mm te u obliku polukružnog (radijus R3 mm) i V koncentratora (dubina utora 3mm). Na mjestu koncentratora površina poprečnog presjeka za sve je uzorke ista. PRIMJENA TERMOGRAFIJE U ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA Osnova je metode jednadžba termoelastičnosti: −α T (σ + σ 2 ) ∆T = ρ Cp 1 , (1) gdje je α koeficijent temperaturne ekspanzije, T sobna temperatura uzorka, ρ gustoća, Cp toplinski kapacitet pri konstantnom tlaku, a σ1 i σ2 glavna naprezanja. Uzme li se da su koeficijenti α, T, ρ i Cp za jedan promatrani uzorak konstantni, jednadžba (1) daje izravnu vezu između prirasta temperature i invarijante naprezanja (suma glavnih naprezanja, gdje je na površini tijela σ3=0). Jednadžba (1) vrijedi samo za adiabatsko stanje (nema dovođenja ili odvođenja topline), što nije moguće postići, no ako su promjene naprezanja dovoljno brze (oko 10 Hz) zadovljen je uvjet adiabatičnosti. Dakle, potrebna je brza hlađena srednjovalna kamera, uzbuda od približno 10 Hz (iako su moguće i uzbude od 3 Hz), te dovoljni iznos energije (naprezanja) da bi detektor zabilježio učinak. Uzbuda može biti magnetno polje, ultrazvuk i dinamičko opterećenje što je ovdje slučaj. Promatra li se dinamički opterećeni uzorak (slika 1) pri frekvenciji uzbude od 20 Hz, vide se uzastopni toplinski bljeskovi (slika 2). Na mjestima gdje su naprezanja veća, veći su i toplinski bljeskovi. Slika 2 prikazuje snimak vlačno dinamički opterećenog uzorka, pri čemu hladnije zone predstavljaju mjesta s većim vlačnim naprezanjem. Kako je frekvencija kamere namještenja na 50 Hz (kamera omogućuje i veće frekvencije), niz slika upravo demonstrira problem da je teško kamerom zabilježiti trenutak maksimalnih naprezanja. Slika 2. (vidi strana 5) I kada bi se snimilo maksimalno naprezanje, korištenjem jednadžbe (1) dobila bi se prevelika odstupanja od realnih iznosa naprezanja. U cilju kvalitetnog računanja sume glavnih naprezanja potrebno je koristiti hardversku komponentu, tzv. Lock-in, kojom se vrši spajanje na signal uzbude (mjerna doza kidalice), te se uz softversku obradu cijelog niza snimaka vrši obrada, a korištenjem jednadžbe (1) dobiva 14 raspodjela naprezanja na površini tijela. Slika 3 prikazuje primjer ispitne epruvete kutnog zavara [19], gdje je na prvom termogramu neobrađeni snimak kamere, a drugi termogram predstavlja obradu uz pomoć Lock-in hardverske komponente. Slika 3. (vidi strana 6) Iako vrlo pouzdana metoda, TSA se relativno rijetko koristi te je vrlo malo objavljenih radova na primjerima primjene TSA. Razlog je tomu što je nužno ostvariti promjenjiva naprezanja, što ta naprezanja moraju biti dovoljnog iznosa da bi IC kamera zabilježila učinke i što je metoda ograničena na skupe srednjovalne hlađene kamere. Primjeri primjene metode mogu se pronaći u referencama [6,20-23]. Metoda je nerazorna i predstavlja tzv. „Full field method”, metodu punog polja koja omogućuje vizualizaciju raspodjele naprezanja po površini. Slična je metodi fotoelasticimetrije, s razlikom da je rezultat suma glavnih naprezanja. 2.ODREĐIVANJE DINAMIČKE ČVRSTOĆE RISITANOVOM METODOM Risitanova metoda [13, 14] temelji se na činjenici da prilikom započinjanja cikličkog opterećenja uzorka dolazi do blagog rasta temperature. Porast se nakon par ciklusa stabilizira te temperatura ostaje konstantna sve do loma, zanemari li se rast temperature cijelog mjernog sustava. Neposredno pred lom temperatura naglo raste. Slika 4 prikazuje, za slučaj trokutnog koncentratora, porast temperature na početku cikliranja te nagli skok temperature neposredno pred lom (slučaj opterećenja od 4 kN). Efekt je sličan efektu kad se ciklira uzorak u umaralici pri ispitivanju na zamor, gdje prvih par ciklusa u dijagramu sila-pomak (naprezanje-deformacija) postoji histereza koja nakon par ciklusa iščezava te se pojavljuje neposredno pred lom. Za razliku od klasičnog ispitivanja gdje je potrebno slomiti čitav niz epruveta, Risitanova metoda omogućuje ispitivanje na samo jednom uzorku, gdje se za zadane Slika 4. (vidi strana 7) Slika 5. (vidi strana 7) 3.EVALUACIJA TIJEKA PLASTIFIKACIJE I ŠIRENJA PUKOTINE Pri elastičnim deformacijama vlačna naprezanja izazivaju pad temperature, a tlačna rast temperature prema jednadžbi (1). U plastičnom području zbog tečenja materijala i znatnog oslobađanja toplinske energije (nekoliko desetaka stupnjeva), IC kamerom moguće je zabilježiti proces plastifikacije uzorka. Za materijale s velikim toplinskim kapacitetom i malom vodljivosti (niska difuzivnost) moguće je korištenje dugovalnih mikrobolometarskih kamera. Za metale nužne su brze hlađene srednjovalne kamere. Na slikama 6-8 niz termograma prikazuje zonu početka tečenja te širenje pukotine sve do loma epruvete. Razlika u temperaturi između gornje i donje polovine epruvete uslijed je toplinskog toka između donje toplije čeljusti (spojena na hidraulički klip) i gornje hladnije čeljusti (spojena na mjernu dozu). Slika 6. (vidi strana 7) Slika 7. (vidi strana 7) Slika 8. (vidi strana 7) 4.USPOREDBA METODA S KLASIČNIM PRISTUPOM ODREĐIVANJU DINAMIČKE ČVRSTOĆE U cilju prikaza mogućnosti termografije u procjeni zamora provedeno je klasično ispitivanje na zamor epruveta sa slike 1. S-N dijagrami, odnosno iznosi sinusoidnog vlačnog naprezanja prema broju ciklusa do loma prikazani su u logaritamskom mjerilu slikama 9 - 11. Oznakama „x” u dijagramima označava se lom, a crvenim oznakama prikazane su usrednjene vrijednosti za slučaj kad je nekoliko epruveta ciklirano s istim iznosom opterećenja. Frekvencija cilkiranja na servo-hidrauličkoj pet tonskoj dinamičkoj kidalici (umaralici) Instron 8800 50kN je iznosila 20Hz. Zbog dostupne količine uzoraka nisu za sve iznose opterećenja provedena uobičajena tri ispitivanja na lom, no dijagrami pokazuju trend i usporedivi su s kasnijim rezultatima opisanih IC metoda. Slika 9. (vidi strana 8) Slika 10. (vidi strana 8) Slika 11. (vidi strana 8) Termoelastičnom analizom naprezanja dobiva se raspodjela naprezanja na uzorcima s trokutnim, polukružnim i kružnim koncentratorima. Slika 12 prikazuje raspodjelu naprezanja za maksimalni iznos opterećenja od 8 kN (odgovara naprezanju 143 MPa). Skala naprezaja pokazuje da se maksimalna naprezanja javljaju za trokutni koncentrator (94,26 MPa), dok polukružni koncentratori imaju najmanju razinu 15 PRIMJENA TERMOGRAFIJE U ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA priraste opterećenja IC kamerom bilježe prirasti u temperaturi uzorka. Pri tom do loma epruvete ne mora nužno doći. Iz trenda porasta i činjenice da se traži naprezanje pri kojem porasta nema, slijedi dinamička čvrstoća materijala odnosno ispitnog uzorka ili dijela konstrukcije. Metoda je jednostavna i primjenjiva na dugovalnim mikrobolometarskim kamerama. Kod primjene na preciznijim hlađenim srednjovalnim kamerama, zbog veće osjetljivosti, kamera bilježi sinusoidne skokove temperature te je potrebno zaglađivanje krivulje kako bi se lakše očitali podaci. Gornji dijagram na slici 5 prikazuje signal dobiven kao srednju vrijednost očitanja u području koncentratora. Donji dijagram na slici 5 predstavlja obradu signala (filtriranje) s ciljem lakšeg očitanja porasta temperature. Toplinski skokovi na gornjem dijagramu slike 5 toplinski su bljeskovi prikazani slikom 2. Potreba za ovakvom obradom podataka ne postoji kod dugovalnih kamera s obzirom da kamere ne uspijevaju zabilježiti kolebanje topline, kako radi osjetljivosti, tako radi frekvencije akvizicije i tehnologije detektora. PRIMJENA TERMOGRAFIJE U ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA naprezanja, što je u skladu s rezultatima S-N dijagrama gdje se vidi da najnižu dinamičku čvrstoću ima trokutni kondenzator. Okrugli koncentrator (rupa u sredini) ima nešto nižu dinamičku čvrstoću od polukružnih koncentratora, što odgovara maksimalnim očitanim naprezanjima na slici 12, odnosno 48,87 MPa za rupu u sredini, prema 42,97 MPa za polukružne koncentratore. Slika 12. (vidi strana 8) Pri većem je opterećenju termoelastični učinak izraženiji, što ukazuje na činjenicu da nije samo dovoljno postići frekvenciju, već treba postići i određeni iznos naprezanja kako bi se termoelastični učinak uočio. Na slici 13 nije prikazan trokutni koncentrator jer je već pri iznosima opterećenja od 16 kN (286 MPa) došlo do loma epruvete s trokutnim koncentratorom. Slika 13. (vidi strana 9) Risitano metoda se sastoji u snimanju temperature uzorka koji se ciklira na umaralici (kidalici). Na slici 14 prikazan je dijagram srednje temperature ispitnog pravokutnog polja za 6000 ciklusa sinusoidnog opterećenja frekvencije 20Hz. Frekvencija snimanja kamere iznosila je 50 Hz. Iako su moguće veće frekvencije snimanja, za ovu vrstu analize za to nema potrebe jer bi količina podataka bila prevelika. Period dužine snimanja se odabire na način da dođe do stabilizacije porasta temperature. Na dijagramima temperatura (slike: 4, 1417), pred sam početak sinusoidnog cikliranja (slika 15) vidljiv je pad temperature. Do pada temperature nastaje prelaskom iz nultog opterećenja u vlačno opterećenje cikliranja, koje zbog prije opisanih razloga izaziva pad temperature. Početna temperatura ispitivanja određena je lokalnim temperaturnim uvjetima u laboratoriju i nije bitna za metodu ispitivanja jer se prati samo porast temperature obzirom na porast opterećenja. Na svim dijagramima vidljivo je da je porast temperature veći za veće iznose opterećenja. Sam lom karakterizira nagli skok u temperaturi, nakon kojeg slijedi hlađenje slomljenog uzorka, što više nije predmet ispitivanja. Slika 15. (vidi strana 9) Slika 16. (vidi strana 9) Slika 17. (vidi strana 9) Dijagrami na slikama 18-20 predstavljaju temperaturne priraste očitane s dijagrama na slikama 15-17. Linearnom aproksimacijom definiran je pravac čije sjecište s nultim porastom temperature predstavlja dinamičku čvrstoću koja za trokutni koncentrator iznosi 44 Mpa, za provrt u sredini 123 MPa, a za polukružni koncentrator 126 MPa. Ovo odgovara usporedbi iznosa maksimalnih naprezanja dobivenih TSA metodom za isti stupanj opterećenja (slika 12), gdje je maksimalno naprezanje za trokutni koncentrator 94 MPa, za rupu u sredini 49 MPa, a za polukružni koncentrator 43 MPa. Uvrste li se vrijednosti dinamičke čvrstoće dobivene Risitanovon metodom u S-N dijagrame (slike 9-11), iznosi dinamičkih čvrstoća odgovaraju očekivanim vrijednostima iz S-N dijagrama. U klasičnim ispitivanjima umaralicom broj cilkusa uglavnom nije nadilazio milijun ciklusa (106 ciklusa), no trend je vidljiv. Za preciznije određivanje dinamičke čvrstoće trebalo je provesti ispitivanja reda veličine 107 ciklusa. Slika 18. (vidi strana 10) Slika 14. (vidi strana 9) Slika 19. (vidi strana 10) Temperaturni dijagrami na slikama 15-17 prikazuju snimanje temperaturnog porasta za 6000 ciklusa opterećenja i razne stupnjeve sinusoidnog opterećenja frekvencije 20 Hz, pri čem je odnos ekstrema opterećenja r=Fmin/Fmax=0. Slika 20. (vidi strana 10) 16 Ono što je bitno jest da su se Risitanovom metodom polomile samo tri epruvete, što je daleko manje od priloženih S-N dijagramima gdje su polomljene 23 epruvete, s tim da 5.ZAKLJUČAK U prethodnim poglavljima dan je pregled primjene termografije kod procjene zamora i pogonskih opterećenja metalnih konstrukcija. Sve tri opisane metode; TSA, Risitanova metoda te praćenje propagacije plastifikacije i pukotine, u potpunosti su primjenjive kod kompozitnih materijala. Za slučaj metala, odnosno materijala velike difuzivnosti, dugovalne mikrobolometarske kamere jedino se mogu primijeniti u Risitanovoj metodi. Za TSA metodu potrebno je uz hlađenu srednjovalnu kameru imati i hardverski Lock-in dodatak te pripadajući softver, što sve dodatno poskupljuje cijenu opreme. Prateći cijene na tržištu nema vidljivih pomaka u tehnologiji dostupnih srednjovalnih kamera, osim u dvostrukoj rezoluciji. Dvostruka rezolucija za opisane metode nije bitna s obzirom da se dvostrukom rezolucijom gubi brzina akvizicije (frekvencija kamere). Cijene opreme u posljednjih se desetak godina nisu promijenile, odnosno ostale su iste. Kupnjom tvrtki koje su razvijale ovu vrstu srednjovalnih kamera i pripadajućih softverskih aplikacija (Agema, Cedip) od strane multinacionalnih tvrtki orijentiranih ka tržištu dugovalnih mikrobolometarskih kamera došlo je do zastoja u razvoju softvera i metoda mjerenja. Osim usamljenih znanstvenih radova uglavnom nema većih pomaka u industrijskoj primjeni. Ovo je područje vrlo široko i još dovoljno neistraženo te ima smisla i dalje istraživati mogućnosti razvoja opisane metode. Opadanjem istraživanja i primjene u industriji šire regije došlo je do usporavanja tempa razvoja opisanih metoda, što drži tržište srednjovalnih kamera ograničenim, a time cijene opreme ne padaju. TSA metoda omogućuje prikaz raspodjele sume glavnih naprezanja po površini te time i procjenu koncentracije naprezanja. Usporedbom triju uzoraka zaključuje se da uzorak s polukružnim koncentratorom ima najmanje naprezanje, a samim time i najveću dinamičku čvrstoću, što potvrđuju i klasična ispitivanja na zamor. Isto vrijedi i za Risitanovu metodu kojom su se, uz znatnu uštedu vremena i broja uništenih uzoraka, dobila rješenja koja se također podudaraju s klasičnim ispitivanjima na zamor. Brze hlađene srednjovalne kamere omogućuju i dobro praćenje širenja zona plastifikacije te nastanka pukotine i loma. Prikazom posljednjih kadrova neposredno pred lom može se odrediti gdje nastaje inicijalna pukotina te je usporediti s TSA. Ako se lokacije poklapaju, koncentracija naprezanja uzrok je loma, a ako se ne poklapaju, razlog lomu treba tražiti u greškama materijala i obradi uzoraka. TSA, Risitanova metoda i praćenje plastifikacije pouzdani su pristupi u procjeni zamora i koncentracije naprezanja konstrukcija. Metode su dinamičke, nerazorne (s iznimkom praćenja loma) i beskontaktne. Uz navedene metode, kao i ostale metode primjene termografije za nerazorna ispitivanja, termografija se dokazala kao pouzdana i primjenjiva metoda eksperimentalne analize naprezanja. 17 PRIMJENA TERMOGRAFIJE U ANALIZI POGONSKOG OPTEREĆENJA KONSTRUKCIJA dinamička čvrstoća nije određena zbog nedovoljnog broja podataka i što se samo za polukružni koncentrator poštovalo pravilo od barem tri epruvete za jednu razinu opterećenja. Vrijeme ispitivanja za Risitanovu metodu iznosilo je par sati, dok je za klasično umaranje na umaralici potrošeno dva tjedna rada kidalice (kidalica nije bila stalno opsluživana). 18 ENGINE MONITORS for GENERAL AVIATION PISTON ENGINES CONDITION MONITORING ABSTRACT – Classical engine gauges give very basic information about engine operation and condition. With graphical engine monitors is now possible to have substantially more diagnostic information available in a timely and usable manner. This information may provide better and more efficient engine operation. It can also detect most impeding engine problems. Keywords: engine monitor, aircraft, piston engine, general aviation 1. INTRODUCTION Vast majority of general aviation aircrafts (popularly known as small private airplanes) are powered by gasoline piston engines. The main source of engine information available to pilot are several gauges indicating cylinder head temperature (CHT), exhaust gas temperature (EGT), engine rotational speed (RPM, tachometer), fuel flow, oil temperature and oil pressure, Figure 1. These gauges give very basic information about engine condition. E.g., single CHT and EGT gauge gives an average of each cylinder’s head and exhaust gas temperature. Engine monitor, [1], [2], replaces this older method of viewing of only one temperature at time with precise multi- cylinder engine monitoring of EGT and CHT less important parameters. Such engine monitors cover much more engine data then basic gauges in a cockpit (about dozen of parameters that are also recorded and can be analyzed later). By monitoring engine parameters it is possible to detect minor engine problems before they become large ones. This device augments diagnostic possibilities of classical boroscope inspection, engine oil analysis and magnetic chip detector (detection of metal particle – engine debris). 2. AIRCRAFT PISTON ENGINE Piston engine is a heat engine designed to convert energy into rotational mechanical motion. It uses reciprocating pistons to convert pressure into a rotating motion. Typical main four strokes of the petrol internal combustion engine are intake, compression, power and exhaust strokes, as shown in Figure 2. Piston aircraft engine is not very efficient at converting energy contained in a fuel to a mechanical energy, Figure 3. Figure 1 Classical gauges for monitoring of aircraft piston engine (CHT, EGT, RPM rotation speed, FF - fuel flow, oil temperature and oil pressure) temperature plus myriad of other more or Figure 2 Four strokes of the petrol engine 19 ENGINE MONITORS for GENERAL AVIATION PISTON ENGINES CONDITION MONITORING Dubravko MILJKOVIĆ, HEP, Zagreb, CROATIA, Phone: (1)6113032; dmiljkovic@hep.hr ENGINE MONITORS for GENERAL AVIATION PISTON ENGINES CONDITION MONITORING engine can be run at temperatures that will significantly reduce the life of some of its parts and there is no automatic system or computer to prevent or limit engine damage, [5]. Excessive EGTs and/or CHTs cause engine damage on a regular basis. 2. GRAPHICAL ENGINE MONITOR Figure 3 Distribution of energy contained in fuel in a piston engine, adopted from [3] Only about one-third of the energy contained in Avgas is converted into useful energy to the propeller, [3]. Roughly half the fuel’s energy is wasted out the exhaust pipe (if no turbocharger is provided). The remaining one-sixth is transferred to the cooling air passing over the cylinder fins and through the oil cooler. Quality of the combustion process can be assessed by monitoring the temperatures of exhaust gases. Diminished efficiency of the combustion process indicates various engine problems like low compression, nonuniform fuel distribution, faulty ignition, and clogged injectors, [4]. An aircraft engine, as one shown in Figure 4, does not have a detonation detector, oxygen sensor or a computer to control timing or fuel/air mixture based on throttle position, temperatures, detectors or sensor inputs (FADEC equipped aircraft piston engines are still very rare). If a pilot chooses, an aircraft Figure 4 Lycoming IO-320 (four cylinder fuel injection engine commonly used on Cessna 172 aircraft) 20 Engine monitor is advanced and accurate piston engine-monitoring instrument that improves the pilots understanding of engine operation, [1-5]. Temperatures are shown graphically as bars on the display of an engine monitor, Figure 5. Each column in the bar on a display is composed of a stack of segments. The total height of each column represents the EGT while the missing segment in the column represents the CHT. In addition to graphically displaying EGT and CHT temperatures, the instrument continuously displays Turbine Inlet Temperature (TIT) on turbocharged engines. Figure 5 Engine monitor with bar graph display (Insight Avionics, older GEM 603) For twin engine aircraft special variants of engine monitors are developed that simultaneously monitor and show parameters of both engines on a display of a single instrument, [6], Figure 6. New products often have color display with separate columns for EGT and CHT, [7], Figure 7. Monitored engine Figure 6 Engine monitor with bar graph display for twin engine aircraft (JPI EDM 760) % HP % Horse Power MAP Manifold Pressure RPM Revolutions Per Minute TIT Turbine Inlet Temperature EGT Exaust Gas Temperature CHT scale It must be measured separately as it is not simple function of separate EGTs. Temperature probes are illustrated in Figures 8-10, and its mounting in Figure 11. CHT Cylinder Head Temperature Cylinder I.D. box indicates which cylinder temperatures are shown in the digital display Figure 7 Engine monitor with separate bars for EGT and CHT (JPI EDM 830) Figure 8 CHT Probe parameters (available in JPI EDM 830) are shown in Table 1. Similar parameters are also available in other modern engine monitors Table 1 Monitored engine parameters (JPI EDM 830) Parameter EGT CHT Description Exhaust Gas Temperature Cylinder Head temperature OIL TEMP Oil Temperature 1 OIL PRES Oil Pressure 1 TIT 1 TIT 2 OAT IAT CRB Turbine Inlet Temperature 11 Turbine Inlet Temperature 2 1 Outside Air Temperature Compressor Discharge Temperature 1 Intercooler Air Temperature 1 Carburetor Air Temperature 1 CDT - IAT Intercooler cooling CDT RPM Rotations Per Minute MAP Manifold Pressure % HP % Horse Power CLD CHT Cooling Rate 2 DIF EGT Span 3 FF Fuel Flow 1 1 optional, 2fastest cooling cylinder, 3difference between the hottest and coolest EGT Separate temperature probes are implemented for each cylinder. Cylinder Head Temperature probe is fitted to the cylinder head’s thermowell. Exhaust Gas Temperature is measured with a probe that penetrates the exhaust stack a few inches from the cylinder. Turbine inlet temperature is measured by a probe mounted in the exhaust inlet leading to the turbocharger. Figure 9 EGT Probe Figure 10 TIT Probe Figure 11 Mounting of temperature probes, adopted from [4] 3. OPERATING MODES Engine monitor typically has monitoring and lean operation mode. 3.1. MONITORING MODE In monitoring mode there is percentage view and normalized view, [1, 4-8]. Percentage view easily discerns EGT differences across all cylinders. In normalized view EGT temperatures are displayed with all column peaks initially set to the same half-height. This is useful for trend analysis as it is possible to compare current engine operation to prior engine operation. 21 ENGINE MONITORS for GENERAL AVIATION PISTON ENGINES CONDITION MONITORING EGT scale 3.2. LEAN OPERATION MODE ENGINE MONITORS for GENERAL AVIATION PISTON ENGINES CONDITION MONITORING Leaning is a process of adjusting fuel/air ratio, [1], [2]. Adjusting the mixture is necessary combustion diagnosis and monitoring of all critical temperatures. Data shown on a display help diagnose mixture, timing, compression, oil consumption and other engine phenomena that can be used for early detection of engine problems. Documentation accompanying engine monitors, [1, 4, 6-8], gives advices what to verify (e.g. uniform rise in EGT with application of mixture) and what to be alert for (e.g. high or uneven EGT or CHT, cooling rate CLD) for various flight phases of operation: Taxi Run up Take off, Climb and Full Throttle Operation, Cruise (leaning) and Descent. Figure 12 Various relationships between the mixture, fuel flow and engine power, adopted from [4] because during the flight engine operates at various altitudes and corresponding air pressures. It restores a significant amount of engine power and hence improves aircraft performance. Leaning process can be performed by monitoring EGT temperature. As the mixture is leaned, EGT rises to a peak temperature and then drops as the mixture is further leaned, [1, 4-8], Figure 12. The best operating mixture for aircraft engines is in the vicinity of this peak (lean of peak or rich of peak). Engine monitors are equipped with the leaning find mode that helps identify the first cylinder (in case rich of peak) or last cylinder (if case lean of peak) to reach peak EGT during a leaning process. When this mode finds the leanest cylinder it is not necessarily the hottest cylinder, but the cylinder that has peaked, [4], [6], [7]. In all flight phases pilot must strictly observe the red-line temperature limits imposed for CHT, EGT and TIT during takeoff, climb and high-performance cruise power operation, [9]. Engine monitors have custom predefined (but also custom adjustable) alarm limits set to encompass all flight regimes, Table 2. Values for alarm limits are determined from engine producer documentation. Default alarm limits are set to encompass all flight regimes. When a parameter falls outside of its normal limits, the digital display will flash with the value and abbreviation of the alarming item. 4.1. SHOCK COOLING Shock cooling is an excessively rapid decrease in temperature of cylinders that may happen during descent with idle engine power setting. Damage from shock cooling often manifests itself as stuck valves and cracked cylinders. By observing CLD parameter it is possible to operate an engine in a fashion that avoids rapid cooling of cylinder and associated damage. Table 2 Default Engine Monitor Alarm Limits Measurement CHT 4. COMON FAULTS DIAGNOSTICS Engine monitor is useful during all flight phases. Its benefits are apparent to pilots even while aircraft is still on a ground (during taxi, run up and take off). Benefits include 22 OIL TIT CLD DIF MAP Default Low Limit 90 °F 32 °C Default High Limit 450 °F 230 °C 230 °F 110 °C 1650 °F 00 °C -60 °F/min -33 °C/min 500 °F 280 °C 32 inch Hg DIAGNOSTIC FAULT PATTERNS Engine diagnostic charts in accompanying documentation contain examples of various bar patterns shown on a display and corresponding symptom, probable cause and recommended action that can help diagnose and solve engine problems. Patterns shown in Figures 13 and 14 illustrate just two engine problems. There are about 15 bar graph patterns in diagnostic charts, [1, 4, 6-8]. • Decrease in EGT of one cylinder may be caused by intake valve not opening fully or faulty valve lifter 5. CONCLUSION The graphic engine monitor is the essential tool for modern engine management. It improves the pilot’s understanding of engine operation and removes guesswork from engine management. Figure 15 Example from engine monitor log 50% Figure 13 Intake valve or valve filter • EGT and CHT are not uniform in case of dirty fuel injectors or fouled plugs 50% Figure 14 Dirty fuel injectors or fouled plugs 4.3. DATA LOGGING Engine monitor automatically records engine parameters during each flight. Example of one part of engine log (raw data) is shown in Figure 15. Recorded data can be downloaded with cable, wireless connection or memory card for later analysis using software, [10], installed on a PC for sophisticated graphical analysis as illustrated in Figure 16. This also includes plotting the trends of user selected measurements and generating flight summary. Analysis software may also include engine monitor simulator that simulates operation of engine monitor display based on engine data logged in previous flights. Suspicious data logs can be sent to a mechanic or engine manufacturer for further clarification. Figure 16 Graphical representation of engine parameters during one flight. Upper curves show main data (EGT, CHT, TIT), lower curves show optional data (CLD, OILT, FF, RPM, MAP) Simultaneously it increases reliability of piston engine, flight safety and operational economics. With its diagnostic capabilities many impeding failures can be detected. Engine leaning with built in leaning find function is crucial for optimum performance with benefits in improved fuel economy, reduced maintenance costs, and extended engine life. 6.REFERENCES 1. Graphic Engine Monitor Data Logging System, Insight Avionics, USA, 1995 | 2. Bush M., EGT Myths Debunked, Cirrus Pilot, Vol. 5, No. 7, July/August 2010 | 3. Bush M., Understanding CHT and EGT, Cessna Pilots Association, April 2009 | 4. Pilot’s Guide: Engine Data Management, EDM-700, EDM-800, EDM-711 Primary, J. P. Instruments, California, USA, 2007 | 5. Roberts R., The Pilot’s Manual for Leaning and Diagnosing Engine Problems, Electronic International, Oregon, USA, 2004 | 6. Pilot’s Guide EDM760 Twin, JPI, California, USA, 2005 | 7. Pilot’s Guide EDM730, EDM-830, EDM-740, JPI, California, USA, 2005 | 8. Ultimate Bar Graph Engine Analyzer (UBG-16) Operating Instructions, Electronic International, Oregon, USA, 1997 | 9. Lycoming Operators Manual, Lycoming, USA, March 1973 | 10. Pilot’s Guide, EzTrends, J. P. Instruments, 2006 23 ENGINE MONITORS for GENERAL AVIATION PISTON ENGINES CONDITION MONITORING 4.2. ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 Petar Smiljanić, ALSTOM HRVATSKA, Karlovac, Hrvatska Ivan Smiljanić, Hrvatsko društvo za kontrolu bez razaranja, Zagreb, Hrvatska SAŽETAK Ispušno kućište, koje je dio kombiniranog sustava plinskih turbina GT 24 i GT 26, zaštićeno je od visokih temperatura posebnom oplatom. Oplata je izrađena od limova austenitnog čelika koji se spajaju „montažnim” zavarenim spojevima. Takvi zavareni „V”-spojevi moraju biti redovito kontrolirani zbog visokih radnih temperatura kućišta i dinamičkih naprezanja kojima su podvrgnuti tijekom rada. Na određenim pozicijama ti spojevi nisu dostupni s obiju strana, nego samo s „čeone”, te se stoga mogu ispitivati samo ultrazvučnom metodom. Osim problema dostupnosti zavara javlja se i problem grubozrnate strukture zavarenog spoja, odnosno anizotropnosti ispitivanog materijala što otežava ispitivanje. Ultrazvučno ispitivanje u ovakvim uvjetima zahtijeva poseban pristup, kao i posebnu dodatnu opremu (etalone), što je detaljnije objašnjeno u ovom radu. 1. UVOD Slika 1. Kombinirani proces plinske turbine GT 24 /GT Plinske turbine GT 24, odnosno GT 26 (sl. 1) dizajnirane su kako bi mogle djelovati u kombiniranom procesu koristeći prirodni plin kao primarno gorivo. Dio takvog kombiniranog sustava, koji se nalazi između kućišta turbine i ispušnog difuzora, jest ispušno kućište. Njegova je funkcija usmjeravanje ispušnih plinova iz niskotlačnog dijela turbine u ispušni difuzor, pri čemu također podupire i montažu krajnjeg ležaja turbine. Kućište je podijeljeno na gornju i donju polovicu, a obje se sastoje od vanjskog i unutarnjeg kućišta povezanih izoliranim rebrima (sl. 1). Osnovna struktura zaštićena je od vrućih ispušnih plinova (preko 600 °C) oplatom kućišta ispod koje je izolacija za zaštitu kućišta od pregrijavanja te zbog izbjegavanja gubitka toplinske energije sadržane u ispušnim plinovima. 24 Predmet ultrazvučnog ispitivanja u ovom su slučaju „montažni” zavareni spojevi s podložnom trakom kanala i poklopaca kanala oplate ispušnih kućišta GT 24 /GT 26. Oplata je izrađena od limova debljine 8 +/- 0,5 mm, a materijal je X 6 CrNiTi 18/10 (austenit). Oplata je podvrgnuta visokim dinamičkim naprezanjima i vrlo visokim temperaturama, što su otežani radni uvjeti, te se radi toga provodi ispitivanje u svrhu otkrivanje grešaka neprovarenog korijena, nepotpunog protaljivanja osnovnog s dodatnim materijalom (greška naljepljenja), zarobljenog oksida na skošenjima pripreme te pukotina u tijeku izrade i kasnije u tijeku eksploatacije. Te greške su one koje je zapravo moguće detektirati ovom metodom, odnosno tehnikom ispitivanja, s obzirom na specifične uvjete pod kojima se ispitivanja i provode. Treba obratiti pozornost na dvije činjenice pri ovakvom ispitivanju. Prva je ta da je ispitivani materijal austenitni čelik koji je anizotropan, te koji svojom grubozrnatom strukturom ograničava prolaz ultrazvučnih valova kroz materijal zbog raspršenja velikog dijela energije tih valova. Dok je gubitak ultrazvučne energije kroz osnovni materijal (koji je gotovo izotropan) vrlo mali, dendritna struktura samog zavarenog spoja znatno pogoduje većim gubicima. Razlika takvih gubitaka između osnovnog materijala i zavarenog spoja u ovom slučaju iznosi oko 75%. Iz toga razloga potrebno je pomno odabrati vrstu sonde, kao i njezinu frekvenciju (odnosno valnu duljinu valova kojima se ispituje grubozrnata struktura), a treba voditi računa i o vrstama grešaka, odnosno njihovim lokacijama, koje se u takvom slučaju mogu detektirati (problem detekcije grešaka unutar samoga spoja). Drugi problem ovog ispitivanja proizlazi iz činjenice da je riječ o montažnim zavarenim „V”-spojevima koji su fizički dostupni samo s jedne strane (čeone). Naša iskustva pokazuju da je za provedbu ispitivanja dobro koristiti sljedeće norme: - za ultrazvučno ispitivanje zavarenih spojeva - EN 1714 - za ultrazvučne razine ispitivanja - EN 1712 - za karakterizaciju grešaka - EN 1713 - za kriterij prihvatljivosti - ISO 5817 25 ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 Slika 2. Ispušno kućište turbine: 1 - izolacija, 2 - osnovna struktura, 3 - oplata 2. PROVEDBA ISPITIVANJA ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 2.1. Ispitivano područje Slika 3. Skica zavara oplate Zahtjev za ispitivanje je sljedeći: ispituju se „V”-zavareni spojevi s nadvišenjem br. 1 i br. 2 (sl. 3) kanala 1 ÷ 10 (ukupno 20 zavara) te zona utjecaja topline po 10mm sa svake strane zavarenog spoja. Kao što je i u uvodu naznačeno, osnovni je materijal austenitni lim debljine 8 +/- 0,5 mm. Kvaliteta površine mora biti takva da omogući pouzdano ispitivanje te se radi toga u području skeniranja trebaju odstraniti sve nečistoće: prskanje dodatnog materijala, ostaci toplinske obrade, neravnine i slično. Detaljnije skice presjeka rebra, kao i ispitivanog područja dane su na slikama 4 i 5. Slika 4. Rebro, presjek (crvenom oznakom naznačeno je zumirano područje koje prikazuje slika 5) 26 2.2. Postupak ispitivanja Ispitivanje će se provesti prema EN 1714 [4] – metoda 3, koja definira osjetljivost ispitivanja. Oprema koja se koristi za izvedbu ovog ispitivanja je sljedeća: - ultrazvučni aparati s mogućnosti podešavanja frekvencija 1 ÷ 10 MHz, vertikalnom linearnošću u granicama +/- 2 dB i horizontalnom linearnošću < 2% - ispitna sonda MWB 70, frekvencije 4 MHz - kontaktno sredstvo: gel ZG-F ili ulje - etaloni: • K2 – za baždarenje mjernog područja prema normi EN 27963 [1] • EGH 1 – za određivanje osjetljivosti ispitivanja, izrađen prema zahtjevu iz EN 1714 [4] (sl. 6) – materijal ovog etalona istovjetan je kao i ispitna pozicija (X6 CrNiTi 18/10) – sadrži središnji reflektor of 1 mm te reflektor od 2 mm (dio skošenja pripreme zavara) • EGH 2 – etalon za karakterizaciju indikacija, s provarenom podložnom trakom (sl. 7) • EGH 3 – etalon za karakterizaciju indikacija, za neprovareni korijen 2 ÷ 3 mm (sl. 8) Navedeni etaloni EGH 1, EGH 2 i EGH 3 dizajnirani su od strane tehnologa koji provode nerazorna ispitivanja. Dizajn sadržava detaljne nacrte sa svim potrebnim dimenzijama, kao i materijal za koji je nužno da bude istovjetan s materijalom ispitivanog objekta. Dizajn etalona EGH 1 temelji se na normi EN 1714 koja definira osjetljivost ispitivanja. Svrha je etalona EGH 2 i EGH 3 da budu podloga za karakterizaciju navedenih indikacija koje je ovim postupkom moguće otkriti, a koje mogu biti pokazatelji postojećih pogrešaka. Za izradu etalona napravljen je naputak za tehnološki proces koji omogućuje kvalitetnu izradu etalona. 27 ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 Slika 5. Zavareni spoj kanala i poklopca ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 Slika 6. Etalon EGH 1 Slika 7. Etalon EGH 2 Slika 8. Etalon RGH 3 Mjerno područje je 100 mm. Ono se podešava na K2 etalonu, tako da prvi signal sa r = 25 mm postavimo na 25 hds (horizontalni dijelovi skale) i 80% VE (visina ekrana), a drugi signal na 100 hds. Zbog razlike u ultrazvučnim brzinama materijala etalona i materijala oplate prvi signal sa 25 hds treba postaviti na 28 hds. Naime brzina transverzalnih ultrazvučnih valova u materijalu etalona K2 (čelik) veća je od brzine istih valova u austenitnom materijalu, što ima za posljedicu razliku u vremenu prolaza vala za upravo 3 hds-a na mjernom području od 100 mm. Referentna osjetljivost ispitivanja proizlazi iz norme EN 1714 i EN 1712. Prema metodi 3 određivanja referentne osjetljivosti za kutne sonde ≥ 70° i debljine ispitivanja 8 ÷ 15 mm koristi se etalon s utorom dubine 1 mm (EGH 1) za izradu krivulje referentne osjetljivosti ispitivanja (DAC krivulja) (sl. 9). Slika 9. DAC krivulja referentne osjetljivosti 28 Slika 10. Signali od podložne trake Uvođenjem ultrazvučne energije (skicirano zelenim strelicama) do greške neprovarenog korijena s naznačenih pozicija sonde dobivaju se karakteristični signali prikazani na sl. 11. Slika 11. Pozicije uvođenja ultrazvučne energije (etalon EGH 3) Slika 12. Maksimalni signal na 21,5 mm ultrazvučnog puta (7,3 mm dubine) s pozicije skeniranja p/2. Ehodinamika signala je 16 ÷ 25 mm ultrazvučnog puta (5,5 ÷ 8,5 mm dubine). Slika 13. Maksimalni signal na 64,5 mm ultrazvučnog puta (22,1 mm dubine) s pozicije skeniranja 3/2 p. Ehodinamika signala je 60 ÷ 68,4 mm ultrazvučnog puta (20,6 ÷ 23,4 mm dubine). Uvođenjem ultrazvučne energije (skicirano zelenim strelicama) do greške naljepljenja s naznačenih pozicija sonde dobivaju se karakteristični signali kao na sl. 14. 29 ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 Na sl. 10 prikazani su signali dobiveni skeniranjem sa strana kanala, međutim treba voditi računa o tome da signali od podložne trake nisu uvijek prisutni, a ovise o položaju trake u odnosu na oplatu kao i neprovarenosti zavarenog spoja trake i oplate. Ehodinamika signala je 41 ÷ 47 mm ultrazvučnog puta (12 ÷ 16 mm dubine). ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 Slika 14. Pozicije uvođenja utrazvučne energije (etalon EGH 1) Slika 15. Maksimalni signal na 36,3 mm ultrazvučnog puta (12,4 mm dubine) s pozicije skeniranja između p/2 i p. Ehodinamika signala je 32,1 ÷ 39,4 mm ultrazvučnog puta (11 ÷ 13,5 mm dubine). Slika 16. Maksimalni signal na 88,4 mm ultrazvučnog puta (28,5 mm dubine) s pozicije skeniranja između 3/2p i 2p. Ehodinamika signala je 77,4 ÷ 91,4 mm ultrazvučnog puta (26,5 ÷ 31,3 mm dubine). 4. ZAKLJUČAK Dobivene ultrazvučne signale u tijeku ispitivanja, potrebno je procijeniti s obzirom na njihovu visinu i karakter: - treba razmotriti sve signale čija je visina veća od 33% visine DAC krivulje (-10 dB od referentne razine) - zabilježiti sve signale bez obzira na njihovu dužinu ako dosežu visinu -2 dB referentne razine. Prema ISO 5817 za klasu zavara C, sve indikacije dužine (l) u odnosu na debljinu (t) nisu prihvatljive ako su zadovoljena dva uvjeta: - l ≤ t i visina signala iznad je referentne razine - l > t i visina signala je -6 dB od referentne razine (tj. 50% DAC krivulje) Ako su ultrazvučne indikacije okarakterizirane kao planarne (pukotine, greške naljepljenja i neprovarenog korijena), tada je to primarni kriterij za prihvaćanje ili odbacivanje. Indikacije čija visina signala prelazi 30% DAC krivulje (-10 dB od referentne razine), a okarakterizirane su kao planarne, nisu prihvatljive. Opisana ultrazvučna tehnika ispitivanja u ovom postupku zavarenih „V”-spojeva oplate ispušnog kućišta plinske turbine GT 24 /GT 26 pokazala se pouzdanom u otkrivanju pogrešaka zavara i to neprovarenog korijena, nepotpunog protaljivanja osnovnog s dodatnim materijalom, tj. greške naljepljivanja zarobljenog oksida na skošenjima pripreme i pukotina. Ispitivanje se provodi prema EN 1714 - metoda 3, ali je potrebno koristiti: 30 Ovako primijenjena tehnika ispitivanja pokazuje dobre rezultate i uz činjenicu da je ispitivani materijal austenitni čelik (X 6 CrNiTi 18/10). 5. LITERATURA [1] EN 27963 - Welds in steel - calibration block No.2 for ultrasonic examination of welds [2] EN 1712 - Non-destructive testing of welds – Ultrasonic testing of welded joints [3] EN 1713 - Non-destructive examination of welds - Ultrasonic examination of weld joins – Acceptance levels [4] EN 1714 - Non-destructive examination of welds - Ultrasonic examination of weld joins [5] ISO 5817 - Welding - Fusion-welded joints in steel, nickl, titanium and their alloys (beam welding excluded) – Quality levels for imperfections [6] V. Krstelj „Ultrazvučna kontrola - odabrana poglavlja“, Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, 2003. 31 ULTRAZVUČNO ISPITIVANJE OPLATE ISPUŠNIH KUĆIŠTA PLINSKIH TURBINA GT 24/GT26 1) ultrazvučni aparat s mogućnosti podešavanja frekvencija 1 ÷ 10 MHz, vertikalnom linearnošću u granicama +/- 2 dB i horizontalnom linearnošću < 2% 2) ispitnu sondu MWB 70 (4 MHz) 3) za baždarenje mjernog područja etalon K2 (prema normi EN 27963) 4) za karakterizaciju indikacija izrađene etalone EGH 1 (prema zahtjevu iz EN 1714), EGH 2 i EGH3 pri čemu je važno da su etaloni napravljeni od istovjetnog materijala, odnosno da imaju ista svojstva s obzirom na prijenos ultrazvučne energije. Također treba voditi računa da dimenzije etalona odgovaraju stvarnom ispitivanom objektu. MISFUELING DETECTION WITH TWO OFFSETED CAPACITIVE FUEL SENDERS Dubravko, MILJKOVIĆ, HEP - Croatian Electricity Company, Zagreb, CROATIA, Contacts – mob: +385 98 9825602, e-mail: dmiljkovic@hep.hr ABSTRACT - Misfueling of a general aviation aircraft with a Jet Fuel instead of an Avgas can have dire consequences. In this paper simple non-destructive testing method is proposed using two capacitive fuel senders that are vertically displaced in a fuel tank by a small distance to detect such situation. Method is based on different readings for the same fuel level in a tank (as fuel senders are displaced). Each fuel has different dielectric constant. In case of correct fuelling difference between these readings will always fall within narrow fixed interval. MATEST 2011 1. INTRODUCTION Misfueling is the introduction of an improper fuel into an aircraft’s tanks. The consequences of misfueling can range from the benign (fuel system drainage) to the expensive (engine replacement) to the disastrous (engine failure shortly after takeoff), [1]. Misfueling is always potentially very serious event. The greatest danger for most general aviation pilots occurs when a gasoline (Avgas) engine is serviced with jet fuel (often know to general population as kerosene, but with commercial names Jet fuel A, A1, B, Avtur etc.). Most commercial turbine engines can be run on avgas within the limits listed in the Pilot Operating Handbook. However the gasoline engines cannot be run on jet fuel. If not supplied with fuel of a certain octane rating, a gasoline engine will stop working, be damaged or destroyed by detonation. Many practical aspects of misfueling prevention by conventional procedures for aviators are described in great detail in [1]. In this paper simple method is proposed using two capacitive fuel senders that are vertically displaced in a fuel tank by a small distance (i.e submerged to different depth in fuel) to detect such situation. Method is based on different readings for the same fuel level in a tank. Each fuel has different dielectric constant. In case of correct fuelling difference between these readings will always fall within narrow fixed interval. However in case of a misfueling, due to different dielectric constant of a mixture or layering of different fuels (before they mix) with different dielectric constants and capacitive fuel senders vertically submerged to different depths in different fuels, difference between readings will fall outside of the acceptable interval. In the later case warning will be issued and additional probe of fuel should be preformed. A lightly contaminated fuel (FAA test find it up to 6% volume mixture of Jet Fuel in Avgas acceptable for lean rating but still unacceptable for rich rating) would pass through with little or no detriment to engine. Requirement for accuracy of capacitive senders is proposed based on tolerable mixture. 32 1.1 DIELECTRIC CONSTANTS OF AVIATION FUELS Dielectric constants of aviation fuels are presented in Table 1 and Figure 1, [2]. Table 1 Dielectric constants of aviation fuels Fuel Avgas Jet A, A1 Jet B Fuel 20 Avgas1,96 2,13 Jet A, A1 Jet B2,06 Temperature (°C) Temperature (°C) 2040 4060 1,96- 2,10 2,07 2,13 2,10 2,03 2,00 2,06 2,03 60 2,07 2,00 MATEST 2011 Jet fuel A and A1 have about 10% higher dielectric constant than Avgas. Figure 1 Dielectric constant vs. temperature for typical aircraft fuel at 400 Hz (adopted from [2]) 1.2 DIELECTRIC CONSTANT OF THE FUEL MIXTURE Dielectric constant of the fuel mixture can be determined by following equation: where k = pk 1 + (1 − p )k2 (1) k is the dielectric constant of mixture k1 is the dielectric constant of fuel 1 k2 is the dielectric constant of fuel 2 p is the volume part of fuel 1 in mixture, 0 < p < 1 33 1.3 PRINCIPLE OF CAPACITIVE FUEL SENDER Capacitive fuel sender is based on tubular capacitor probe where fuel becomes dielectric, as shown in Figure 2, from [3]. Principal of operation is based on the difference in the dielectric properties of air and fuel, and described in great detail in [2]. At different fuel levels, different values of capacitance are measured and therefore the level of fuel can be determined. AC current is used in a process. As dielectric constants vary a little with temperature, better capacitive fuel includes thermal compensation. Device itself is without any movable or flexible parts. Advantages of capacitive fuel senders are high precision, high reliability and good cost performance. MATEST 2011 Figure 2 Fuel level sensor schematic Theoretical capacitance of cylinder probe in vacuum is C= where is q 2πε o L = V ln (b a ) (2) L – length of probe a – Outer radius of probe inner tube b – Inner radius of probe outer tube In a real life capacitance of a probe Cp consists of two parts: the effective capacitance CPeff developed across the dielectric gap between the electrodes and the stray capacitance CPstr developed between the tube and other items like adjacent structure. The overall dry capacitance is expressed as CPdry = CPeff + CPstr (3) When the probe is fully submerged in a fuel of dielectric of k its capacity is CPfull = kC + CPstr (4) CPfull = (k − 1)CPeff + CPdry (5) Peff When the probe is partially submerged in a fuel of dielectric of k, where n is normalized value between 0 and 1, its capacity is expressed by CnPfull = n(k − 1)CPeff + CPdry 34 (6) The change in capacitance CpnΔ from air to partial submersion is CPn ∆ = CnPfull − CPdry (7) CPn ∆ = n(k − 1)CPeff (8) Electronic circuits supplied with the capacitive probe provide that a change in probe capacity is transformed to the output voltage proportional to the fuel level in a tank (e.g. 0 – 5 V range), where is r proportionality constant: U out = rC P n ∆ + U base (9) After correct calibration Ubase is set to 0 and output voltage is expressed by U out = rC P n ∆ (10) Method uses two displaced capacitive fuel senders with temperature compensation. They are submerged into fuel to different depth, as shown in Figure 3. First probe is submerged almost to the bottom of the fuel tank, while second probe is offseted (displaced) by 25% of the full tank fuel level (without some small amount of fuel under the first probe and bottom of the fuel tank). For the particular fuel level in a fuel tank readings from both senders will differ for a constant value (actually, readings will fall within narrow interval). If the fuel level in tank is greater than 25% of full capacity both probes will be submerged in fuel. Fuel senders have temperature compensation (due to slight change of dielectric constant of Avgas with temperature). Offset value of 25% was chosen arbitrary as a compromise between precision and necessary fuel level. Figure 3 Fuel tank with two capacitive fuel senders submerged to different depths (the diameter of fuel senders is enlarged in comparison with the tank for clarity purpose) If we assume that CPeff is same in both fuel probes the capacity change from empty tank in the first probe is CPn ∆ ,1 = n(k − 1)CPeff (11) 35 MATEST 2011 2. METHOD The capacity change from empty tank in the second probe is CPn ∆ , 2 = (n − 0.25 )(k − 1)CPeff (12) The capacity change between two probes is then CP∆ = CPn ∆ ,1 − CPn ∆ , 2 (13) CP∆ = 0.25 (k − 1)CPeff (14) MATEST 2011 The output from fuel senders is voltage change proportional to change in capacitance: U out ,1 = rC P n ∆ ,1 U out , 2 = rC P n ∆ ,2 (15) (16) ∆U = U out ,1 − U out , 2 (17) ∆U = r (CPn ∆ ,1 − CPn ∆ , 2 ) (18) ∆U = 0.25 r (k − 1)CPeff (19) where is Uout,1 - the output voltage from the first fuel sender Uout,2 - the output voltage from the second fuel sender With the correct fueling difference ΔU will remain constant regardless of the fuel level within a tank (once the tank is full over 25% and both probes are submerged). However in case of misfueling, dielectric constant k of the mixture will change and so will difference ΔU. Differences in values of dielectric constants of different fuels are not very large, actually values are quite similar. For that reason it is necessary to detect subtle changes in ΔU. ( ) ∆U Avgas = 0.25 r k Avgas − 1 C Peff (20) ∆U Mix = 0.25 r (k Mix − 1)CPeff (21) where is ΔUAvgas - the difference between outputs of two fuel senders submerged in Avgas ΔUMix - the difference between outputs of two fuel senders submerged in fuel mixture (Avgas and Jet Fuel). 3. RESULTS OF CALCULATIONS FOR FUEL MIXTURES In real application the precision class of fuel senders should be considered. If α is the relative errors then the following relation is valid for Avgas (1 − α )U out ,1 − (1 + α )U out , 2 < ∆U Avgas < (1 + α )U out ,1 − (1 − α )U out , 2 36 (22) and the following for the case of mixed fuels: (1 − α )U out ,1 − (1 + α )U out , 2 < ∆U Mix < (1 + α )U out ,1 − (1 − α )U out , 2 (23) When considering the ratio ΔUMix / ΔUAvgas in worst case scenario both relative errors in ΔUAvgas will be the opposite direction of both relative errors in ΔUMix. 0,25 r (k Mix − 1)CPeff ( ) 0,25 r k Avgas − 1 CPeff (1 − 4α ) < 0,25 r (k Mix − 1)CPeff ∆U Mix (1 + 4α ) < ∆U Avgas 0,25 r k Avgas − 1 CPeff ( ) (24) Table 2 Dielectric constants for various Avgas and Jet Fuel A1 fuel mixtures, ratio kMix-1 / kAvgas-1 and minimal required accuracy class for fuel senders to detect ratio for a particular fuel mixture Fuel volume mixture Required accuracy class kMix-1 Dielectric constant Avgas -------for fuel senders (% Jet Fuel A1 (%) (20° C) (%) kAvgas-1 precision accuracy) 100 0 1,9600 1 95 5 1,9685 1,0089 0,2 94 6 (FAA tolerance)* 1,9702 1,0106 0,2 90 10 1,9770 1,0177 0,2 80 20 1,9940 1,0354 0,5 70 30 2,0110 1,0531 1 60 40 2,0280 1,0708 1 50 50 2,0450 1,0885 2 40 60 2,0620 1,1063 2 30 70 2,0790 1,1240 2 20 80 2,0960 1,1417 2 10 90 2,1130 1,1594 2 0 100 2,1300 1,1791 2 max volume part of Jet Fuel in Avgas as suggested by tests performed by FAA (for real application please do check this data) * 4. DISCUSSION As already mentioned there is just slight difference between the dielectric constant of correct fuel (Avgas) and the dielectric constant of improper fuel (mixture of Avgas and Jet fuel). Therefore method must be very sensitive to these subtle changes in dielectric constant. That requires quite precise capacitive fuel senders (accuracy class 0,2). However, such fuel senders are today commercially available under moderate price (few hundred USD), particularly when considering application. Capacitive probe diameter should be large enough (25 mm) to allow fuel mixing not just within a tank but also within the fuel probes. Fuel probes span across most depth of the fuel tank and integrate dielectric constant of fuel at various 37 MATEST 2011 k Mix − 1 (1 − 4α ) < ∆U Mix < kMix − 1 (1 + 4α ) (25) k Avgas − 1 ∆U Avgas k Avgas − 1 Here is assumed that α << 1 and Uout,1 is close to Uout,2 (actually Uout,2 is, when tank is full, 33% less than Uout,1, but here is still considered close), and worst case relative error is for more precise consideration about ±3.5 α. Dielectric constants for various Avgas and Jet Fuel A1 fuel mixtures, ratio kMix-1 / kAvgas-1 (and hence ΔUMix / ΔUAvgas ) with minimal required accuracy class for fuel senders to detect the ratio for particular fuel mixture (using ±4 α error) are presented in Table 2. levels within a tank, not just at one point (what could be achieved with e.g. small capacitive probe placed at the bottom of a tank). Due to inherent sensitivity to change of dielectric constant method may encounter problems if fueled with Avgas that contain some additives (i.e. slightly different variants of Avgas may available at different refueling locations). These changes in dielectric constant must be somehow known in advance. Method will easily detect fuel contaminated with water (water has high dielectric constant of around 80). MATEST 2011 5. CONCLUSIONS Proposed idea could be a valuable approach for detecting misfueling of general aviation aircraft. It could be simple integrated into existing airplanes, replacing the old (unreliable) type of floating fuel sender. By employing two commercially available high precision offseted (displaced) fuel senders with temperature compensation it detects misfueling by detecting a change in dielectric constant of the fuel. Fuel senders are submerged into fuel to different depths and hence give different output voltages. The difference between these voltages is constant regardless of the fuel level. In case of msifuelling this difference shifts from its usual narrow range of values. Use of two fuel senders also gives redundant setup for measuring fuel level within a tank. This paper is just theoretical basis, for the real application extensive experiments would be needed, including process of initial mixing of fuels, influences of various fuel levels in the tank (e.g. full tank, three quarters and half tank) after misfueling, influences of fuel additives, effect of filling the fuel probes from the bottom and diffusion of fuel mixture within the probe (need for the sufficient probe diameter). 6. REFERENCES 1. AOPA Safety Brief No 4: Misfueling, http://www.aopa.org/asf/publications/SB04.pdf (PDF, accessed October 9, 2011) 2. Roy Langton, Chuck Clark, Martin Hewitt, Aircraft Fuel Systems, Wiley 2009, UK 3. Shenzhen, High accuracy capacitive fuel sensor, http://joint-tracking.com/Upload/ PicFiles/2010.7.20_9.28.8_9083.pdf (PDF, accessed October 9, 2011) 38 U ovom broju predstavljamo CROATIAINSPECT. vam dugogodišnjeg kolektivnog člana, društvo T k a l č i ć e v a 7 / I V, 1 0 0 0 0 Z a g r e b , w w w. c r o a t i a i n s p e c t . h r ( 01/4874777 2 01/4873728 : info@croatiainspect.hr Direktor i član Uprave Mario Štambuk, dipl. ing., ujedno je i potpredsjednik HDKBR-a. Osnovna je djelatnost tvrtke kontrola kvalitete, nadzor u provođenja ispitivanja te osiguravanje kvalitete opreme koja se koristi u naftnoj industriji, počevši od opreme za istraživanje i proizvodnju do opreme za transport, preradu i skladištenje nafte i plina. Uprava Croatiainspecta smještena je u samom centru Zagreba u Tkalčićevoj 7, pa je g. Štambuk i najbliži susjed HDKBR, stoga je ovaj intervju iznimno brzo i lako dogovoren. Budući da je naša djelatnost kontrola kvalitete, razvija se suradnja s društvom u više područja. U samim počecima, a ove godine smo uspješno proslavili 40. godišnjicu naše tvrtke, osim obrazovanja naših inspektora bila je i značajna suradnja na zajedničkim projektima uvođenja nerazornih metoda u kontrolu kvalitete i razrada postupaka za potrebe ispitivanja bušotinske opreme. Također treba naglasiti da su naši inspektori u okviru društva pratili i surađivali u razvoju kontrole bez razaranja (KBR-a) i na taj način lakše izvršavali inspekcijske nadzore. Iskustva koja smo stjecali u okviru našeg posla po cijelom svijetu, gdje smo imali prilike vidjeti i upoznazi se s najsuvremenijom opremom za kontrolu cijevi i zavarenih spojeva elektromagnetskim i ultrazvučnim tehnikama, prenosili smo i dijelili s kolegama u Hrvatskom društvu za kontrolu bez razaranja. Ultrazvučna kontrola zavarenog spoja cijevi sa spiralnim zavarom Magnetska kontrola UV-česticama u liniji proizvodnje Naravno da je neizostavno područje u kojem također surađujemo sustav osiguranja kvalitete kao i praćenje relevantnih normi iz tog područja. U posljednje vrijeme, otkako sam član Upravnog odbora HDKBR, rado se odazivam na europske i svjetske konferencije, tako da sam imao čast i zadovoljstvo biti jedan od predstavnika HDKBR-a na konferencijama u Valenciji i Durbanu. 39 PREDSTAVLJAMO VAM Na kojem se području zasniva suradnja Croatiainspecta s HDKBR-om? PREDSTAVLJAMO VAM Durban, Svjetska konferencija KBR 2012. Ovdje moram naglasiti da sam posebno bio očaran i ponosan dobrodošlicom domaćina, predstavnika EFNDT-a i ICNDT-a, nama u HDKBR-u, duboko uvjeren da je to zahvaljujući Vama, našoj dugogodišnjoj predsjednici, Vašem predanom radu te suradnji s međunarodnim organizacijama. Kako ste zadovoljni s obrazovanjem Vaših inspektora u području KBR-a u našem društvu? Teško je objektivno odgovoriti na ovo pitanje s obzirom da sam kao član Upravnog odbora i sam odgovoran za rad i djelatnost društva. Moram međutim istaknuti da je organizacija obrazovanja i sustav certifikacije znatno poboljšan, kao i kvaliteta i opseg predavanja i materijala. Kao korisnik usluga Društva, iako je poboljšana frekvencija organizacije tečajeva, još uvijek nije u potpunosti prilagođena zahtjevima nas iz privrede koji moramo često vrlo brzo i tržišno reagirati. Znajući i da su mogućnosti organiziranja obrazovanja djelomično ograničene, naime HDKBR ima određeni program tečajeva, a s druge strane upoznati smo s potrebama obrazovanja i izvan Hrvatske, možda bi se problem mogao riješiti onlineobrazovanjem. Razmatram tu ideju i vjerujem da ću ako nađem dovoljno argumenata predložiti tu ideju Centru za obrazovanje. 40 Molim Vas da nam se sada osobno predstavite zbog naših čitatelja koji nisu imali prilike upoznati vas do sada. Stalnim usavršavanjem na različitim tečajevima, bavio sam se i kontrolom bez i sa razaranjem, auditima proizvođača, kontrolama označavanja, pakiranja, utovara i istovara robe te ostalim aktivnostima inspektora strojarske opreme. Ovlašten sam inspektor Aramca, naftne kompanije Saudijske Arabije, za što sam osim referenci i poznavanja engleskog jezika trebao položiti poseban ispit o znanjima iz područja materijala, zavarivanja, ispitivanja bez razaranja i poznavanja relevantnih normi. Brzo sam napredovao i postao voditelj poslova, pomoćnik direktora pa do sadašnje funkcije člana Uprave. Od 2001. do 2011. uz postojeći posao obavljao sam i poslove Predsjednika uprave Adriainspekta i direktora Tehničke poslovnice. za kontrolu kvalitete i kvantitete robe i trgovačku djelatnost Cargo Superintendence and Trade Company, Ciottina 17b, 51000 Rijeka, Croatia, http://www.adriainspekt.hr Glavna djelatnost Tehničke poslovnice upravo je pružanje usluge ispitivanja nerazornim metodama, najčešće u riječkom okrugu u RN Rijeka, TE Rijeka, brodogradilištima 3. maj, Viktor Lenac, Kraljevica, Janaf i ostalim pogonima. Adriainspekt posjeduje laboratorij s opremom za nerazorna ispitivanja, certiificirano osoblje, a od prošle godine ima i uređaj za digitalnu radiografiju. Također ima poslovnicu za kontrolu nafte i derivata te poslovnicu za rude i poljoprivredu. U razdoblju mog rada u Adriainspektu suradnja s HDKBR-om bila je dvostruka jer sam uključio obje tvrtke, odnosno kolege u kontroli bez razaranja iz obiju tvrtki. Mislim da je važno napomenuti da sam dugogodišnji član TO 135 za kontrolu bez razaranja pri HZN. Kolega Štambuk, imate li Vi možda neko pitanje koje želite uputiti kolegama u kontroli bez razaranja? Nemam pitanje, ali bih želio iskoristiti prigodu i pozvati sve naše kolegice i kolege da nam se pridruže i budu aktivni sudionici u tjednu „NDT week in Zagreb”, europske konferencije o obrazovanju, certifikaciji i normizaciji, CERTIFICATION 2013 kao i MATESTA 2013, međunarodne konferencije HDKBR-a, koji ove godine obilježava 50. obljetnicu. Ovu prigodu da u Zagrebu imamo tako važan skup na kojem će se okupiti stručnjaci u kontroli bez razaranja iz cijeloga svijeta ne smije se propustiti. Kolega Štambuk, hvala na Vašoj podršci HDKBR-u. 41 PREDSTAVLJAMO VAM Na FSB-u diplomirao sam 1984. godine i već prije obrane diplomskog rada zaposlio se i počeo raditi kao inspektor, premda mi je moj mentor, cijenjeni prof. Šurina, ponudio mjesto na katedri Automatika u strojarstvu. Stječući praksu kao mladi inženjer/inspektor, najprije u inspekciji proizvodnje cijevi u Željezari Sisak, naučivši osnove tehnologija proizvodnje, kontrole i zahtjeva API-normi, vrlo brzo počeo sam raditi i slične inspekcije po cijelome svijetu. Tako sam prošao sve renomirane proizvođače cijevi, opreme za istraživanje i proizvodnju, te transport i skladištenje od Amerike do Japana. Mnoge stvari vidio sam u funkciji daleko prije nego su se pojavile kod nas. Tako naprimjer sustav osiguranja kvalitete, današnji HRN EN ISO 9001, u Sumitomu (Japan) bio je u primjeni još 1985., dok je kod nas prvi skup na tu temu koji smo mi organizirali pod pokroviteljstvom HGK-a bio održan nekoliko godina kasnije, a još je prošlo par godina do početka certifikacije sustava. NDT WEEK in ZAGREB NDT WEEK in ZAGREB 7-12 October 2013 2013. godine HDKBR obilježava 50 godina kontinuiranog djelovanja u promociji i potpori razvoja primjene nerazornih metoda u ispitivanju, kontroli kvalitete i tehničkoj dijagnostici. Godine 1963. bila je to samo skupina entuzijasta svjesna važnosti uvođenja kontrole kvalitete i metoda koje to mogu osigurati. Danas HDKBR s ponosom najavljuje TJEDAN KBR-a u ZAGREBU u kojem će s nama biti mnogi cijenjeni stručnjaci iz Europe i svijeta. Croatian Society of Non-Destructive Testing, (HDKBR - local abrivation) is celebrating 50 years of permanent activity in promoting and supporting R&D and implementation of NDT and Technical Diagnostic. In the year 1963, it was just a group of enthusiasts starting to implement NDT in Quality system. We proudly invite you to NDT WEEK in ZAGREB. Many of renown scientists and experts from Europe and wider will be with us working on NDT, nowdays an unavoidable proffession. Monday 07.10.2013. P.M. ECEC meeting Tuesday 08.10.2013. ECEC & ICEC joint meeting* EFNDT & ICNDT Certification executive Committee Wednesday 09.10.2013. MATEST 2013 09:00-10:00 Opening MATEST 2013 10:30-18:00 ISO / TC 135 / SC 7 / WG9 meeting* 10:30-18:00 EFNDT BoD meeting* 10:00-13:00 16:00-18:00 EFNDT WG 5 meeting 19:30-22:00 Reception: HDKBR 50th annievrsary MATEST 2013 Conference program continuing Thursday 10.10.2013. CERTIFICATION 2013 09:00-11:00 Opening 11:30-17:00 Session 1: ICNDT Regional groups 11:30-17:00 17:00-18:30 Session 2A: National Societies; Education Qualification & Certification Session 3: EFNDT and ICNDT MRA; Signature ceremony Friday 11.10.2013. CERTIFICATION 2013 13:00-15:30 15:30-17:00 Session 2B: National Societies; Education, Qualification & Certification Session 4: Quality system, Methods, Laboratory; Different sectors approach Session 5: Competence / Training syllabuses Session 6: Safety & Security 17:00-17:30 Conclusions & Closing 19:00-22:00 Conference dinner 09:00-10:30 11:00-13:00 Saturday 12.10.2013. 09:00-12:00 EU Leonardo project meeting* *Sastanci samo uz poziv/ *meetings by invitation only 42 16:00-18:00 EU Leonardo project meeting* MATEST 09.10.2013. 08:00 - 09:00 Registration 09:00 - 10:30 OPENING 09:00 - 09:20 Miro Džapo: Opening 09:20 - 09:40 Nenad Gucunski: Robotic Platform RABIT for Conditional Assessment of Contrete Bridge Decks Using Multiple NDE Technologies 10:00 - 10:30 10:30 - 14:00 10:30 - 10:45 10:45 - 11:00 11:00 - 11:15 Dario Almesberger: NDT Methods in Exploration Works on the Structure of Arena in Pula Coffee break SESSION 1 Lovre Krstulović, Endri Garafulić: Željko Domazet: Termography Image Processing Techniques Zoran Bičanić, Saša Bratko, Danko Dobranović: Experience in Applying Infrared Thermography in Gas Leak Detection Berislav Nadinić, Fran Jarnjak: Overview of Advanced UT Techniques 11:15 - 11:30 Sanja Rakljašić: Experience in Applying Phased Array in Inspection of Welds on Small Dimensions Tubes 11:30 - 11:45 Zvonimir Ivković:Tracebility of NDT key documentation required by PED 97/23 EC 11:45 - 12:00 Bruno Breka: Possibility of Achieving Requested Image Quality in Case When Standard Requirements can’t be Achieved 12:00 - 12:15 Tomislav Andrić: Future Development of NDT Activities in Shipyard Brodotrogir 12:15 - 12:30 Vladimir Zado: Ispitivanje zavarenih spojeva priključaka na poklopac reaktorske posude ultrazvučnom metodom/ Testing of reactor vessel head nozzle J groove welds by ultrasound 12:30 - 12:45 Dragica Krstić, Martina Pavec, Zdravko Schauperl: Characterization of Foxing Stains in Eighteenth Century Books 12:45 - 14:00 Lunch 14:00 - 15:15 SESSION 2 14:00 - 14:15 Ivana Banjad Pečur: Istraživanja u građevinarstvu pomoću ispitivanja bez razaranja/ Research in civil engineering using non-destructive testing 14:15 - 14:30 Roberto Rinaldi: The experience of ITC about certification: CM or NDT? 14:30 - 14:45 Noam Amir: Non-invasive inspection of Heat Exchanger Tubes 14:45 - 15:00 Mark Nel: The basic of TOFD 15:00 - 15:15 Mark Nel: The basic of Phased Array 15:15 - 15:30 Predrag Dukić: Risk base assesment 16:00 - 16:15 Dubravko Miljković: Statistical Properties of Aircraft Piston Engine Monitor –CM Data 16:15 - 16:30 Mladen Vrebčević: Akreditiranje tijela za certificiranje osoblja 16:30 - 18:00 POSTER SESSION 43 MATEST 2013 09:40 - 10:00 The Preliminary Program: CERTIFICATION 2013 09:30 – 11:30 09:30 – 09:45 09:45 – 10:00 10:00 – 10:15 10:15 – 10:30 10:30 – 11:00 11:00 – 11:30 11:30 – 14:30 11:30 – 11:45 11:45 – 12:00 12:00 – 12:15 12:15 – 12:30 12:30 – 12:45 12:45 – 13:00 13:00 – 14:30 14:30 – 17:00 14:30 – 14:45 14:45 – 15:00 15:00 – 15:15 15:15 – 15:30 15:30 – 15:45 15:45 – 16:00 16:00 – 16:15 16:15 – 16:30 16:30 – 16:45 16:45 – 17:00 17:00 – 18:00 44 CERTIFICATION Day 1, 10.10.2013. OPENING Vjera Krstelj: Opening Lecture Patrick Fallouey: EN ISO 9712 – Succesfull merging; What’s after? Hajime Hatano: The activities of ISO/TC 135 Giusseppee Nardoni: Academia NDT international in Competence support Questions and Discussion Coffee break SESSION 1: ICNDT REGINAL GROUP Matthias Purschke: EFNDT Certification Agreement – Why to an European Certificate? John Zirnhelt, Sharon Bond, PK Yuen: Qualification and Certification in Canada Norikazu Ooka: Introduction of NDT Training course for Asia Pacific Region and Activities of Task Group meeting being conducted by JSNDI extra budget Ir. Sajeesh K Babu: NDT Personnel Certification updates in Asia Pacific Region Patrick Brisset: IAEA activities related to NDT personnel training and certification Questions & Discussion Lunch SEASSION 2A: NATIONAL SOCIETIES: Education, Qualification, Certification Biserka B. Brezak: Accreditation; National, Regional and Worldwide approach Miro Džapo: Qualification and Certification in Croatia Gerhard Aufricht, Roman Wottle: Experience with the professional, modular NDT-Certification in Austria Emilio Romero, Radolfo Rodriguez: The training and certification of NDT personnel in Spain, past, present and future Bento Alves, Claudia Almeida, M.Jose Teixeira: RELACRE, the authorized Qualification Body for NDT in Portugal – Current Situation and Main Challenges Pavel Mazal, Bernard Kopec: Certification of NDT personnel in the Czech Republic – situation and perspectives Matt Gallagher, Philip Picton, David Gilbert: An integrated education programme for NDT proffesionals Vasil Nichev, Mitko Mihovski, Aleksander Skordev: Education and Certification in Bulgaria. Specific approach Questions & Discussion Coffee Break SEASSION 3: EFNDT and ICDNT MRA Mike Farley / ICNDT – Patric Fallouey / CEN – Hajime Hatano /ISO EFNDT and ICDNT MRA - Signature ceremony - 09:15 – 09:30 09:30 – 09:45 09:45 – 10:00 10:00 – 10:15 10:15 – 10:30 10:30 – 10:45 10:45 – 11:00 11:00 – 12:15 11:00 – 11:15 11:15 – 11:30 11:30 – 11:45 11:45 – 12:00 12:00 – 12:15 12:15 – 12:30 12:30 – 13:45 12:30 – 12:45 12:45 – 13:00 13:00 – 13:15 13:15 – 13:30 13:30 – 13:45 13:45 – 15:00 15:00 – 17:00 15:00 – 15:15 15:15 – 15:30 15:30 – 15:45 15:45 – 16:00 16:00 – 17:00 45 The Preliminary Program: CERTIFICATION 2013 09:00 – 11:00 09:00 – 09:15 CERTIFICATION Day 2, 11.10.2013. SESSION 2B: NATIONAL SOCIETIES: Education, Qualification, Certification Milan Škrlet: Standardisation in Quality system in Croatia Goran Sofronić, Dragana Kuzmanović, Davor Gruber: Accreditation, Qualification and Certification of NDT personnel in Serbia Goran Sofronić, Dragana Kuzmanović, Davor Gruber: Accreditation, Qualification and Certification of NDT personnel in Serbia Ekaterina Cheprasova: Russian Society for NDT’s Automated System of NDT Specialists Training Şinasi Ekinci: NDT Training and Certification in Turkey Joseph Pessach: Qualification and Certification system in Israel João Rufino: Qualification and Certification in ABENDI; Brazilian Association of NDT and Inspection Coffee break SESSION 4: Quality system, Methods, Labaratory; Different sectors approach Theobald O.J. Fuchs, Frank Sukowski, Christian Schorr, Tobias Schön, Stefan Schröpfer, Ulf Hassler, Thomas Hofmann, Nils Reims: High-Energy 3-D X-ray Tomography for Container Inspection Ferenc Fücsök, Balázs Hámornik, Ferenc Marcsó: Experiences of the proficiency tests in the Hungarian Association for NDT Sergej Kolokolnikov, Antony Dubov: Certification scheme based on ISO 9712:2012 of NDT personnel for MMMM Mykhail Kazakevych, Migoun Nikolay: Certification of product families for penetrant testing Elena Nicheva: Education and qualification requirements for NDT personnel at NPP Kozloduy Coffee break SESSION 5: Competence / Training syllabuses Ralf Holstein, Rainer Link: ISO 9712 Level 3 Certification: A Skeptical Approach Radolfo Rodriguez, Emilio Romero: Proqualint, LEONARDO DA VINCI programme. Development of NDT study materils in diferent languages. Ir. Sajeesh K Babu: Comparison of training syllabuses in NDT Prsonnel Certification István Skopál: Competence control without “significant interruption” John Thompson: The ICNDT Electronic Examination Question Book Lunch SESSION 6: SAFETY and SECURITY Kurt Osterloh, Gerd-Ruediger Jaenisch, Daniel Kanzler: How to approach rare events Isaac Einav: See the invisible–innovative technology as tool for safety and quality Davor Zvizdić: University approach to Safety and Security Ivica Prlić: Security, Education, Qualification, Certification Closing TEČAJEVI za KVALIFIKACIJU i CERTIFIKACIJU Program tečajeva je razrađen u skladu sa potrebama industrije, te kandidati mogu odabrati pohađanje tečajeva u skladu sa svojim obavezama. Više od ovdje ponuđenih termina može se dogovoriti, kao i održavanje tečajeva u tvrtki, kada za to ima potrebe. HDKBR Centar za obrazovanje PLANIRAJTE i REZERVIRAJTE ODMAH Kandidati za tečajeve 3. stupnja trebaju osim gore navedenog dostaviti životopis u kojem treba navesti iskustva u kontroli kvalitete. Zamolbe za pohađanje 3. stupanaj dostavljaju se najkasnije do 15. listopada 2013.g. Kandidati koji su završili studij na sveučilištu, veleučilištu ili visokoj školi, tehničkog ili prirodoslovno-matematičkog usmjerenja stiču pravo na skračeni program obrazovanja za glavnu metodu - 3 stupanj. Stupanj Termini održavanja Ultrazvučna kontrola UT1 14.10.-25.10.2013. Magnetska kontrola MT2 25.11.-28.11.2013. Vizualna kontrola VT1 02.09.-04.09.2013. Penetrantska kontrola PT2 16.09.-19.09.2013. Ultrazvučna kontrola UT2 02.12.-13.12.2013. Radiografska kontrola RT2 04.11.-15.11.2013. Opći dio; 3 stupanj VT3 PT3 MT3 UT3 RT3 11. mjesec Metoda Glavna metoda; 3stupanj 9. mj, 10. mj VAŽNA OBAVIJEST Polaznici tečajeva od 1.1.2013. godine osiguravaju obrazovanje i mogućnost certifikacije u skladu sa zahtjevima nove norme HR EN ISO 9712 ČLANSTVO u HDKBR-u Obavještavamo sve članove da je u tijeku izdavanje iskaznica za 2013. godinu. Iskaznice će primiti samo članovi HDKBR-a koji su uplatom članarine za 2013. godinu ili drugim osnovom stekli članstvo. Obzirom da članovi ostvaruju popust pri certifikaciji, te dobivaju časopis HDKBR Info i druge obavijesti iz Tajništva HDKBR-a, važne za vaš profesionalni život, molimo vas da provjerite jeste li osigurali članstvo. Svi koji žele izbjeći gubitak vremena na uplatu od 100 kuna svake godine mogu to učiniti jednokratno za više godina i pri tome ostvariti popust. Uplatom članarine za tri godine u iznosu od 200 kn ili uplatom članarine za pet godina u iznosu od 400 kn. Tajništvo HDKBR 46 STJECANJE UVJERENJA Za stjecanje uvjerenja za određenu metodu, stupanj obrazovanja i područje ispitivanja treba: - dostaviti prijavnicu, -uspješno završiti tečaj obrazovanja u HDKBR Centru za obrazovanje ili u centru obrazovanja priznatom od strane HDKBR Centra za certifikaciju, -potvrdu o radnom iskustvu i obavljenom očnom pregledu. Za stjecanje uvjerenja za ispitivanje tlačne opreme prema članku 13. Pravilnika PED 97/23/EC treba: - dodatno obrazovanje u trajanju od jednog dana u HDKBR Centru za obrazovanje. Cijena izdavanja certifikata po osobi: 150 eura + PDV, u što je uključeno i obrazovanje u HDKBR Centru za obrazovanje. Za svaku dodatnu metodu cijena uvjerenja je 100 eura + PDV. Metoda Stupanj Vrijeme Vizualna kontrola VT1 Vizualna kontrola VT2 Magnetska kontrola MT2 28.11.2013. Penetrantska kontrola PT2 19.09.2013. Ultrazvučna kontrola UT1 25.10.2013. Ultrazvučna kontrola UT2 13.12.2013. Radiografska kontrola RT2 15.11.2013. 3. stupanj: VT3,MT3,PT3,UT3,RT3, 13.12.2013. Listopad 2013. Članovi Društva imaju popust od 10 %. HDKBR Centar za certifikaciju CENTAR za CERTIFIKACIJU Više o certifikaciji na www.hdkbr.hr ili telefonski u tajništvu HDKBR-a. POSTER SESSION Branko Jagodić, Zlatko Horvat Iskustva u ispitivanju zavarenih spojeva sitnozrnatih čelika/ The experiance of steel weldings Gordan Polonijo Ispitivanje zavarenih spojeva na “Cutter Suction Dredgeru” i “Suction Hopper Dredgeru”/ Experiance in NDT of Cutter Suction Dredgeru and Suction Hopper Dredgeru Tamara Topić Iskustva uvođenja nerazornih ispitivanja u programe obrazovanja; program veleučilišta/ The experiance of launching NDT in high education; college programs Ivan Gabrijel, Bojan Milovanović, Ivana Pečur Banjad, Nina Štirmer Primjena IC termografije za ispitivanje betonskih konstrukcija /Using IR thermography as a NDT method for testing concrete structures Ivan Gabrijel Mikan Slijepac Mladen Bošnjaković, Krunoslav Jukić, Josip Jukić MATEST 2013/ poster session 09.10.2013; 16:30-18:30 MATEST 2013 Praćenje očvršćivanja betona metodom akusto-ultrazvuka/Monitoring of concrete hardening using acousto-ultrasonic method Iskustva u ispitivanju radnih kola vodenih turbina/ The experiance of NDT of water turbines Zahtjevi za ispitivanje zavarenih spojeva tlačne opreme prema EN i ASME / Examination requirements for welds in pressure equipment according EN and ASME standards 47 POMOĆ U RADU; Goran Dragičević, Brodosplit Za časopis uredio: Ivan Smiljanić RJEŠENJE ZA POZICIONIRANJE ULTRAZVUČNIH APARATA 'Krautkramer USM 25' I/ILI 'Krautkramer USM 35' POMOĆ U RADU Slika 1. Ultrazvučni aparat Krautkramer USM 35 Ultrazvučni aparati Krautkramer USM 25 i Krautkramer USM 35 pouzdani su i često korišteni modeli aparata, koje posjeduje mnogo NDT ispitivača diljem svijeta, kao i na našim prostorima. Međutim kod njih postoji jedna slaba točka, koja postaje očita tijekom dužeg korištenja ovih aparata. Nakon određenog vremena (kraćeg nego što bi se očekivalo) pozicioneri ručice gube svoju funkciju, zbog pucanja na mjestima gdje su najtanji. Mjesta nastanka oštećenja prikazana su crvenim strelicama na slici 1. Jednostavno i zanimljivo rješenje nudi nam kolega Goran Dragičević, zaposlenik Brodosplita. Slika 2. Nacrt pozicionera ručice. Slika 3. Slika sastavnih dijelova pozicionera ručice Prvi korak predstavlja izrada kapice od meke plastike za brtvila. Bolje bi rješenje bilo da se kapice izrade od tvrde gume, ali takva bi opcija bila isplativa samo pri izradi u tvornici jer je izrada kalupa za lijevanje najskuplja stavka. Drugi korak sastoji se od jednostavnog navlačenja istih kapica na pozicionere, kako je prikazano na slici 2. Za jasniju predodžbu na slici 3 dan je i prikaz sastavnih dijelova ovakvog pozicionera. Nadamo se da će vam ponuđeno rješenje biti od koristi te zahvaljujemo kolegi Dragičeviću što je svoj patent podijelio s nama. Ovom prigodom potičemo i sve vas na sličnu razmjenu ideja koje nam olakšavaju svakodnevne radne aktivnosti. 48 49
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