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The measurement of surface crack inclination in metals using AC electric fields
N DT Abstracts 40895 Hayashi, M.; Sonoda, S. Portable P D M surface c r a c k detection system Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands) 23-28 Apr. 1989, Vol. i, pp. 512-514. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989 A portable PDM (Potential Drop Method) surface crack detection system has been developed. The system is 5kg in weight and fits into an attache case, making it hand-carryable. With this system, surface crack configurations can be easily inspected at fabrication locations or plant sites with an accuracy of +-0.3ram in depth. Since the system can he easily extended, pipe cracks and reductions in pipe thickness can be monitored on-line.
instrumentation, for improving existing solutions and for evaluation of new
ideas. 40501 Gibson, G.P. Evaluation of the A.C. potential drop method to determine J-crack resistance curves for a pressure vessel steel Engineering Fracture Mechanics, Vol. 32, No. 3, pp. 387-401 (1989) An evaluation has been carried out of the a.c. potential drop technique for determining J-crack growth resistance curves for a pressure vessel steel. The technique involves passing an alternating current through the specimen and relating the changes in the potential drop across the crack mouth to changes in crack length occurring during the test. The factors investigated were the current and voltage probe positions, the a.c. frequency and the test temperature, in addition, by altering the heat treatment of the material, J-crack resistance curves were obtained under both contained and non-contained yielding conditions. In all situations, accurate J-R curves could be determined.
40714 Pelioux, R.M.; Peltier, J.M.; Zilberstein, V.A. Creep testing of 2.25 Cr-I Mo welds by DC potential drop technique Journal of Engineering Materials and Technology, Vol. ! 1 I, No. l, pp. 19-20 (Jan. 1989) Creep damage in weldments has been studied at the Massachusetts Institute of Technology. The method is based on monitoring the change in voltage across a preselected short section of a test specimen and relating this change to the local creep strain rate and creep damage. This technique is likely to be especially useful in older fossil-fuel power plants in falling high temperature piping. The experimental procedures and results are described. The potential drop technique is found to he useful in estimating remaining life in fossil-fuel plants.
Lugg, M.C.; Shang, H.M.; Collins, R.; Michael, D.H. The measurement of surface c r a c k inclination in metals using AC electric fields 40360
Journal of Japanese Society for Non-Destructive Inspection, Vol. 37, No. 9A, pp, 841-842 (Sep. 1988)
Journal of Physics D: Applied Physics, Vol. 21, No. 12, pp. 1814-1821 (14 Dec. 1988) The AC potential drop technique is widely used in non-destructive testing for sizing surface-breaking cracks in metals but, in order to find the through-thickness penetration of a crack, its inclination to the surface is needed as well as its size. By modelling the electric field around an inclined crack in the extremes of both large and small skin depth, it is shown in this paper that the asymmetry in the voltage signal across the crack can be used to find the angle of inclination. Experimental results obtained from a range of metals confirm the theoretical findings.
40522 Pennick, A.M.; Rogers, L.M. Monitoring c r a c k growth in full scale RPV plate weldments by
LB.
40710 Hayashi, M.; Sonoda, S. Study on detection of thickness reduction by DC potential drop
method
40321
Kavalyauskas, R.A.; Rakauskene, B.K.; Sidaravichyus,
Effect of d a r k potential drop of electroradiographic plates on the radiographic sensitivity Soviet Journal of Nondestructive Testing, Vol. 24, No. 3, pp. 182-185 (Mar. 1988) The effect of dark potential drop on the radiographic sensitivity upon long exposure is determined experimentally and by analysis of the kinetics of the potential drop of electroradiographic plates.
acoustic emission Proceedings of the 16th European Working Group on Acoustic Emission Conference, London (United Kingdom), 13-18 Sep. 1987, pp. 2906-2925. Edited by C.B. Scruby and R. Hill, Proceedings of the 4th European Conference on Non-Destructive Testing, London (United Kingdom), 13-17 Sep. 1987, Vol. 4, Pergamon Press, 1988 Results are presented of acoustic emission measurements during the tensile testing of a 1220 x 1640 x 50ram thick carbon steel plate containing a full penetration butt weld along the centreline. The weld had a central machined notch with crack initiation slits at each end. Stress was applied along the full length of the plate, normal to the weld. During testing, the plate was subjected to a series of fatigue cycles which simulate in-service shutdowns of a reactor. This was followed by a small number of cycles at higher stress, designed to cause extension of cracks at either end of the notch. The specimen was also monitored by closed circuit television, strain gauges, AC potential drop, and extensometers. The objective of the (AE) acoustic emission monitoring was to detect the onset of crack growth from both ends of the initiation slot before it was evident at the surface and subsequently to trace its development. The acoustic emission indications of crack growth preceded both the visual and acpd (alternating current potential drop) results, with which good correlation was subsequently obtained as the cracks advanced.
Materials Engineering Associates, Inc. Second CSNI workshop on ductile f r a c t u r e test methods 40239
Proceedings of the Second CSNI Workshop on Ductile Fracture Test Methods, Paris (France), 17-19 Apr. 1985. NUREG/CP-0064 (CSNI Report No. 105) pp. 41-54 (Aug. 1988). Results obtained show that it is possible to use the DC potential drop method to determine the J-R curve of austenitic stainless steels with good precision compared to the interrupted loading method. This method seem s, however, slightly conservative concerning J values for the onset of crack growth. Crack extension can he easily correlated with potential drop using a linear relationship for limited values of crack growth. The partial unloading method can lead to overestimates of J values for the onset of crack extension due to lack of precision in compliance measurements. The detection of crack initiation by acoustic emission seems to be difficult. Results obtained show that J values, corresponding to a change in the acoustic emission rate, are related to a macroscopic crack extension and that acoustic emission events cannot be directly related to crack extension values. However, further investigations must be done using other signals like cumulative peak amplitudes or cumulative area under peaks.
40515 Haugland, H.; Lovaas, S.; Otteren, A. U n d e r w a t e r crack detection test of different monitoring methods d u r i n g fatigue of a steel-node Non-Destructive Testing, Proceedings of the 4th European Conference, London (United Kingdom), 13-17 Sep. 1987. Vol. 4, pp. 2709-2717. Edited by J.M. Farley and R.W. Nichols. Pergamon Press, 1988 Structural monitoring methods are tested in 20 meter water depth outside NUTEC in Bergen, Norway. Acoustic emission, using transducers and hydrophones and a global potential drop method, (the electric field signature method), were used for detection and localization of several fatigue cracks which occurred during fatiguing of a steel T-node. The results are compared with conventional NDT-methods, such as MPI (Magnetic Particle Inspection) and ACPD (Alternating Current Potential Drop). Also different stain sensors were tested. The paper will also discuss stability of sensors. The objective of the work is to replace diver based inspection in deep water and also to develop equipment to monitor an already detected defect. This practical experiment has disclosed problems with elements in monitoring systems, signal to noise ratio in different situations - and size levels of crack detection. All results are of significance for specification of offshore
40179 Livingstone, F.; Kilpatrick, I.M. On-line fatigue crack growth m o n i t o r i n g in externally pressurised vessels using the a l t e r n a t i n g c u r r e n t potential drop (ACPD) technique Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7B, pp. 1531-1540. Edited by D.D.Thompson and D.E. Chimenti, Plenum Press, 1988. At ARE (Dunfermline) fatigue tests are carried out on internally stiffened, welded steel cylindrical pressure vessels. These vessels are constructed from high yield strength quenched and tempered steels with full penetration butt and T-butt welds. Continuous on-line monitoring was therefore highly desirable not only to reduce overall testing time but also to provide data on the effect of any interruptions to the fatigue cycling. This paper describes the advances made in the application of an on-line crack
72
instrumentation, for improving existing solutions and for evaluation of new
ideas. 40501 Gibson, G.P. Evaluation of the A.C. potential drop method to determine J-crack resistance curves for a pressure vessel steel Engineering Fracture Mechanics, Vol. 32, No. 3, pp. 387-401 (1989) An evaluation has been carried out of the a.c. potential drop technique for determining J-crack growth resistance curves for a pressure vessel steel. The technique involves passing an alternating current through the specimen and relating the changes in the potential drop across the crack mouth to changes in crack length occurring during the test. The factors investigated were the current and voltage probe positions, the a.c. frequency and the test temperature, in addition, by altering the heat treatment of the material, J-crack resistance curves were obtained under both contained and non-contained yielding conditions. In all situations, accurate J-R curves could be determined.
40714 Pelioux, R.M.; Peltier, J.M.; Zilberstein, V.A. Creep testing of 2.25 Cr-I Mo welds by DC potential drop technique Journal of Engineering Materials and Technology, Vol. ! 1 I, No. l, pp. 19-20 (Jan. 1989) Creep damage in weldments has been studied at the Massachusetts Institute of Technology. The method is based on monitoring the change in voltage across a preselected short section of a test specimen and relating this change to the local creep strain rate and creep damage. This technique is likely to be especially useful in older fossil-fuel power plants in falling high temperature piping. The experimental procedures and results are described. The potential drop technique is found to he useful in estimating remaining life in fossil-fuel plants.
Lugg, M.C.; Shang, H.M.; Collins, R.; Michael, D.H. The measurement of surface c r a c k inclination in metals using AC electric fields 40360
Journal of Japanese Society for Non-Destructive Inspection, Vol. 37, No. 9A, pp, 841-842 (Sep. 1988)
Journal of Physics D: Applied Physics, Vol. 21, No. 12, pp. 1814-1821 (14 Dec. 1988) The AC potential drop technique is widely used in non-destructive testing for sizing surface-breaking cracks in metals but, in order to find the through-thickness penetration of a crack, its inclination to the surface is needed as well as its size. By modelling the electric field around an inclined crack in the extremes of both large and small skin depth, it is shown in this paper that the asymmetry in the voltage signal across the crack can be used to find the angle of inclination. Experimental results obtained from a range of metals confirm the theoretical findings.
40522 Pennick, A.M.; Rogers, L.M. Monitoring c r a c k growth in full scale RPV plate weldments by
LB.
40710 Hayashi, M.; Sonoda, S. Study on detection of thickness reduction by DC potential drop
method
40321
Kavalyauskas, R.A.; Rakauskene, B.K.; Sidaravichyus,
Effect of d a r k potential drop of electroradiographic plates on the radiographic sensitivity Soviet Journal of Nondestructive Testing, Vol. 24, No. 3, pp. 182-185 (Mar. 1988) The effect of dark potential drop on the radiographic sensitivity upon long exposure is determined experimentally and by analysis of the kinetics of the potential drop of electroradiographic plates.
acoustic emission Proceedings of the 16th European Working Group on Acoustic Emission Conference, London (United Kingdom), 13-18 Sep. 1987, pp. 2906-2925. Edited by C.B. Scruby and R. Hill, Proceedings of the 4th European Conference on Non-Destructive Testing, London (United Kingdom), 13-17 Sep. 1987, Vol. 4, Pergamon Press, 1988 Results are presented of acoustic emission measurements during the tensile testing of a 1220 x 1640 x 50ram thick carbon steel plate containing a full penetration butt weld along the centreline. The weld had a central machined notch with crack initiation slits at each end. Stress was applied along the full length of the plate, normal to the weld. During testing, the plate was subjected to a series of fatigue cycles which simulate in-service shutdowns of a reactor. This was followed by a small number of cycles at higher stress, designed to cause extension of cracks at either end of the notch. The specimen was also monitored by closed circuit television, strain gauges, AC potential drop, and extensometers. The objective of the (AE) acoustic emission monitoring was to detect the onset of crack growth from both ends of the initiation slot before it was evident at the surface and subsequently to trace its development. The acoustic emission indications of crack growth preceded both the visual and acpd (alternating current potential drop) results, with which good correlation was subsequently obtained as the cracks advanced.
Materials Engineering Associates, Inc. Second CSNI workshop on ductile f r a c t u r e test methods 40239
Proceedings of the Second CSNI Workshop on Ductile Fracture Test Methods, Paris (France), 17-19 Apr. 1985. NUREG/CP-0064 (CSNI Report No. 105) pp. 41-54 (Aug. 1988). Results obtained show that it is possible to use the DC potential drop method to determine the J-R curve of austenitic stainless steels with good precision compared to the interrupted loading method. This method seem s, however, slightly conservative concerning J values for the onset of crack growth. Crack extension can he easily correlated with potential drop using a linear relationship for limited values of crack growth. The partial unloading method can lead to overestimates of J values for the onset of crack extension due to lack of precision in compliance measurements. The detection of crack initiation by acoustic emission seems to be difficult. Results obtained show that J values, corresponding to a change in the acoustic emission rate, are related to a macroscopic crack extension and that acoustic emission events cannot be directly related to crack extension values. However, further investigations must be done using other signals like cumulative peak amplitudes or cumulative area under peaks.
40515 Haugland, H.; Lovaas, S.; Otteren, A. U n d e r w a t e r crack detection test of different monitoring methods d u r i n g fatigue of a steel-node Non-Destructive Testing, Proceedings of the 4th European Conference, London (United Kingdom), 13-17 Sep. 1987. Vol. 4, pp. 2709-2717. Edited by J.M. Farley and R.W. Nichols. Pergamon Press, 1988 Structural monitoring methods are tested in 20 meter water depth outside NUTEC in Bergen, Norway. Acoustic emission, using transducers and hydrophones and a global potential drop method, (the electric field signature method), were used for detection and localization of several fatigue cracks which occurred during fatiguing of a steel T-node. The results are compared with conventional NDT-methods, such as MPI (Magnetic Particle Inspection) and ACPD (Alternating Current Potential Drop). Also different stain sensors were tested. The paper will also discuss stability of sensors. The objective of the work is to replace diver based inspection in deep water and also to develop equipment to monitor an already detected defect. This practical experiment has disclosed problems with elements in monitoring systems, signal to noise ratio in different situations - and size levels of crack detection. All results are of significance for specification of offshore
40179 Livingstone, F.; Kilpatrick, I.M. On-line fatigue crack growth m o n i t o r i n g in externally pressurised vessels using the a l t e r n a t i n g c u r r e n t potential drop (ACPD) technique Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7B, pp. 1531-1540. Edited by D.D.Thompson and D.E. Chimenti, Plenum Press, 1988. At ARE (Dunfermline) fatigue tests are carried out on internally stiffened, welded steel cylindrical pressure vessels. These vessels are constructed from high yield strength quenched and tempered steels with full penetration butt and T-butt welds. Continuous on-line monitoring was therefore highly desirable not only to reduce overall testing time but also to provide data on the effect of any interruptions to the fatigue cycling. This paper describes the advances made in the application of an on-line crack
72