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Flaw growth monitoring as an aid to lifetime prediction
N DT Abstracts is used for the measurement of crack depth in metallic components. The geometric shape of the sample must be considered in order to minimize the error. A three-dimensional finite element method is also used to calculate the electric field. The accuracy is shown to be satisfactory by comparing the calculations with the experimental results. From the results of the computation, the influence of the geometric factors is discussed in detail.
techniques, using acoustic emission, ultrasonics and the potential drop method, were applied during cyclic thermal and mechanical loading of the cylindrical pressure vessel wall. Each technique is shown to be successful in detecting defects in specific type number of inspection.
Dobmann, G.; Brinette, R.; Weib, R. Condition monitoring and on-line surveillance of a pipe in a BWR large scale e a r t h quake experiment
42705
43500 Newman, J.; Jefferson, A.; Gregson, P J.; Pitcher, P.D. C a l i b r a t i o n of a pulsed potential crack monitor for use in
Proceedings of the International Conference on Monitoring, Surveillance and Predictive Maintenance of Plants and Structures, Taormina-Giardini Naxos, Sicily (Italy), 15-18 Oct. 1989, pp. 772-778. Italian Society for Nondestructive Testing Safety rules ask for special design of components of LWR's in order to avoid damage or failure. One design criterion is protection against earth quakes. The contribution refers to the development and application of a dc potential drop technique for the on-line surveillance and condition monitoring of a predamaged tube (starter notch at the inner side with a fatique crack) in a large scale primary circuit experiment in the German Nuclear Safety Research programme (HDR-Programme). It will be demonstrated that the technique can control the crack growing starting at the inner side of the tube by a potential drop application from the outside. For interpretation, software (analytical and FE-codes) is available. Progressive crack propagation can be observed and an alarm can be derived. The tube falls with leak before break.
fatigue crack growth studies Royal Aerospace Establishment, Farnborough, (United Kingdom), AD-A210 958/5/GAR, 21pp. (Apr. 1989) A pulsed direct currem is used to generate a potential drop as a function of crack length. Experimental values of potential drop and crack length have been obtained for three test-piece geometries: a centre crack specimen, a holed specimen (AGARD) and a compact tension specimen. Computed values have been generated using a Fortran program and are compared with the experimental results. Comments are made on the accuracy of the technique and its consequences on potential probe positioning for both short and long cracks.
Haugland, H.; Lovaas, S.; Underwater detection and monitoring of fatigue cracks on a d y n a m i c loaded K-node with internal stiffeners
43292
Proceedings of the Twentieth Annual Offshore Technology Conference, Houston, Texas (USA), 2-5 May 1988. Vol. 4, pp. 505-512 Fatigue of a K-node with internal stiffeners is performed using an hydraulic actuator. The test took place at the seabottom inshore at a waterdepth of 20 meters. During the test, crack initiation and crack growth were monitored using two different acoustic emission systems and a global potential drop method, the Electric Field Signature method. Several cracks developed, both on one of the internal stiffeners and also on the outside welds. Location of the cracks using the monitoring systems showed good agreement with conventional inspection methods like MP! and ACPD.
42392 Silk, M.G.; Whapham, A.D.; Hobbs, C.P. Flaw growth monitoring as an aid to lifetime prediction International Journal of Materials & Product Technology, Vol. 4, No. 3, pp. 215-231 (1989) As the inspection of any large engineering structure is likely to result in the identification of a flaw, this can cause problems in continuing operation unless a reliable alternative to repair or removal is available. An alternative option is to monitor the behaviour of the flaw over a period and to place direct limits on flaw growth. This approach has had little success in the past because the precision of the NDT techniques was so poor that flaws could be close to failure before growth was established. Now, however, both the time of flight diffraction (TOFD) technique and the alternating current potential drop (ACPD) technique might achieve precisions of 0.25 mm or better in estimating flaw growth. The monitoring approach can then be shown to have economic benefits without affecting the essential structural safety argument for the plant. This paper reviews the justification for monitoring and presents experimental flaw-monitoring data.
Pozzi, D.; Gabetta, G. Development of a potential drop technique for crack growth monitoring in aqueous environments
42981
Proceedings of the International Conference on Monitoring, Surveillance and Predictive Maintenance of Plants and Structures, Taormina-Giardini Naxos, Sicily (Italy), 15-18 Oct. 1989. pp. 21-28, italian Society for Nondestructive Testing Potential Drop is one of the most promising technique for obtaining a very precise information on the crack length variations. The system developed at CISE uses direct current with polarity inversion, and it is employed for crack monitoring on fracture mechanics specimens tested in aqueous environment up to 300 C under constant, monotonic and cyclic loads. To operate at high temperature and pressure, it has been necessary to solve a few problems related to the specimen insulation and to the signal transmission probes. The system sensitivity is very high and the first results are reliable and reproducible. The system, completely automatic, is able to monitor at the same time three specimens and is driven by a PC IBM System/2. This paper describes in detail the used system and the obtained results.
42162 Silk, M. Flaw growth monitoring for safer p l a n t Atom, No. 394, pp. 6-9 (Aug. 1989) The development of a new technique called flaw growth monitoring at the National Nondestructive Testing Centre at Harwell will lead to improved accuracy in the safety assessment of steel structures, including welds. The two key parameters are critical flaw size and the remaining life of the structure. Improved precision is reported for the alternating current potential drop and ultrasonic time of flight diffraction techniques. 41308 Tabachnik, V.P.; Fedorishcheva, E.E.; Chernova, G.S. Calculation of the magnetic parameters of a solid p r o d u c t in inspection by coercive force with the aid of a two-pole magnet Soviet Journal of Nondestructive Testing, Vol. 24, No. 4, pp. 229-235 (Dec. 1988) The article presents a method of calculating the magnetic conductivity of the inspected part of a massive product and magnetic potential drop on it. Calculation and experiment were carried out for steel 40Kh in the annealed and hardened state.
42975 Lugg, M.C. A C F M - a new NDT technique Metals and Materials, Volo 6, No. 3, pp. 142-144 (Mar. 1990) Recent progress in the theoretical modelling of magnetic fields has allowed the development of the ac potential drop (ACPD) crack sizing technique into a non-contacting form, known as ac field measurement (ACFM). This new NDT technique aims to combine the sizing capability of ACPD with the practical benefits that arise when electrical contact does not have to be maintained with the material being inspected. The technique is already being used for cracks in mild steel and development of a rapid scanning system using an array sensor is also under way. Other applications in hostile, corrosive or high temperature environments for materials testing are envisaged in the near future.
Hulsey, R.C.; Goolsby, A.D. Nondestructive crack depth measurement in internally weld overlayed clad pressure vessels 41145
Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1749-1752. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989. Quantitative crack depth measurements were investigated to evaluate the structural integrity of two pressure vessels with internal cracking in a weld overlay to ensure the vessels were operated within safe operating limits while obtaining maximum useful life. Eddy current, potential drop, and ultrasonic time of flight techniques were used in laboratory and field trials to prove the cracks were confined to the overlay material. The most reliable measurements were obtained using eddy current techniques after calibration on test standards which exactly simulated the vessels weld overlay metallurgy.
Deuster, G.; Brinette, R. Monitoring, surveillance and predictive maintenance of plants and s t r u c t u r e s 42815
Proceedings of the International Conference on Monitoring, Surveillance and Predictive Maintenance of Plants and Structures, Taormina-Giardini Naxos, Sicily (Italy), 15-18 Oct. 1989. pp. 414-420. Italian Society for Nondestructive Testing This paper presents results from a comparative study of three nondestructive inspection techniques under assessment as part of a German reactor safety program for lightwater reactor components. The three
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techniques, using acoustic emission, ultrasonics and the potential drop method, were applied during cyclic thermal and mechanical loading of the cylindrical pressure vessel wall. Each technique is shown to be successful in detecting defects in specific type number of inspection.
Dobmann, G.; Brinette, R.; Weib, R. Condition monitoring and on-line surveillance of a pipe in a BWR large scale e a r t h quake experiment
42705
43500 Newman, J.; Jefferson, A.; Gregson, P J.; Pitcher, P.D. C a l i b r a t i o n of a pulsed potential crack monitor for use in
Proceedings of the International Conference on Monitoring, Surveillance and Predictive Maintenance of Plants and Structures, Taormina-Giardini Naxos, Sicily (Italy), 15-18 Oct. 1989, pp. 772-778. Italian Society for Nondestructive Testing Safety rules ask for special design of components of LWR's in order to avoid damage or failure. One design criterion is protection against earth quakes. The contribution refers to the development and application of a dc potential drop technique for the on-line surveillance and condition monitoring of a predamaged tube (starter notch at the inner side with a fatique crack) in a large scale primary circuit experiment in the German Nuclear Safety Research programme (HDR-Programme). It will be demonstrated that the technique can control the crack growing starting at the inner side of the tube by a potential drop application from the outside. For interpretation, software (analytical and FE-codes) is available. Progressive crack propagation can be observed and an alarm can be derived. The tube falls with leak before break.
fatigue crack growth studies Royal Aerospace Establishment, Farnborough, (United Kingdom), AD-A210 958/5/GAR, 21pp. (Apr. 1989) A pulsed direct currem is used to generate a potential drop as a function of crack length. Experimental values of potential drop and crack length have been obtained for three test-piece geometries: a centre crack specimen, a holed specimen (AGARD) and a compact tension specimen. Computed values have been generated using a Fortran program and are compared with the experimental results. Comments are made on the accuracy of the technique and its consequences on potential probe positioning for both short and long cracks.
Haugland, H.; Lovaas, S.; Underwater detection and monitoring of fatigue cracks on a d y n a m i c loaded K-node with internal stiffeners
43292
Proceedings of the Twentieth Annual Offshore Technology Conference, Houston, Texas (USA), 2-5 May 1988. Vol. 4, pp. 505-512 Fatigue of a K-node with internal stiffeners is performed using an hydraulic actuator. The test took place at the seabottom inshore at a waterdepth of 20 meters. During the test, crack initiation and crack growth were monitored using two different acoustic emission systems and a global potential drop method, the Electric Field Signature method. Several cracks developed, both on one of the internal stiffeners and also on the outside welds. Location of the cracks using the monitoring systems showed good agreement with conventional inspection methods like MP! and ACPD.
42392 Silk, M.G.; Whapham, A.D.; Hobbs, C.P. Flaw growth monitoring as an aid to lifetime prediction International Journal of Materials & Product Technology, Vol. 4, No. 3, pp. 215-231 (1989) As the inspection of any large engineering structure is likely to result in the identification of a flaw, this can cause problems in continuing operation unless a reliable alternative to repair or removal is available. An alternative option is to monitor the behaviour of the flaw over a period and to place direct limits on flaw growth. This approach has had little success in the past because the precision of the NDT techniques was so poor that flaws could be close to failure before growth was established. Now, however, both the time of flight diffraction (TOFD) technique and the alternating current potential drop (ACPD) technique might achieve precisions of 0.25 mm or better in estimating flaw growth. The monitoring approach can then be shown to have economic benefits without affecting the essential structural safety argument for the plant. This paper reviews the justification for monitoring and presents experimental flaw-monitoring data.
Pozzi, D.; Gabetta, G. Development of a potential drop technique for crack growth monitoring in aqueous environments
42981
Proceedings of the International Conference on Monitoring, Surveillance and Predictive Maintenance of Plants and Structures, Taormina-Giardini Naxos, Sicily (Italy), 15-18 Oct. 1989. pp. 21-28, italian Society for Nondestructive Testing Potential Drop is one of the most promising technique for obtaining a very precise information on the crack length variations. The system developed at CISE uses direct current with polarity inversion, and it is employed for crack monitoring on fracture mechanics specimens tested in aqueous environment up to 300 C under constant, monotonic and cyclic loads. To operate at high temperature and pressure, it has been necessary to solve a few problems related to the specimen insulation and to the signal transmission probes. The system sensitivity is very high and the first results are reliable and reproducible. The system, completely automatic, is able to monitor at the same time three specimens and is driven by a PC IBM System/2. This paper describes in detail the used system and the obtained results.
42162 Silk, M. Flaw growth monitoring for safer p l a n t Atom, No. 394, pp. 6-9 (Aug. 1989) The development of a new technique called flaw growth monitoring at the National Nondestructive Testing Centre at Harwell will lead to improved accuracy in the safety assessment of steel structures, including welds. The two key parameters are critical flaw size and the remaining life of the structure. Improved precision is reported for the alternating current potential drop and ultrasonic time of flight diffraction techniques. 41308 Tabachnik, V.P.; Fedorishcheva, E.E.; Chernova, G.S. Calculation of the magnetic parameters of a solid p r o d u c t in inspection by coercive force with the aid of a two-pole magnet Soviet Journal of Nondestructive Testing, Vol. 24, No. 4, pp. 229-235 (Dec. 1988) The article presents a method of calculating the magnetic conductivity of the inspected part of a massive product and magnetic potential drop on it. Calculation and experiment were carried out for steel 40Kh in the annealed and hardened state.
42975 Lugg, M.C. A C F M - a new NDT technique Metals and Materials, Volo 6, No. 3, pp. 142-144 (Mar. 1990) Recent progress in the theoretical modelling of magnetic fields has allowed the development of the ac potential drop (ACPD) crack sizing technique into a non-contacting form, known as ac field measurement (ACFM). This new NDT technique aims to combine the sizing capability of ACPD with the practical benefits that arise when electrical contact does not have to be maintained with the material being inspected. The technique is already being used for cracks in mild steel and development of a rapid scanning system using an array sensor is also under way. Other applications in hostile, corrosive or high temperature environments for materials testing are envisaged in the near future.
Hulsey, R.C.; Goolsby, A.D. Nondestructive crack depth measurement in internally weld overlayed clad pressure vessels 41145
Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1749-1752. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989. Quantitative crack depth measurements were investigated to evaluate the structural integrity of two pressure vessels with internal cracking in a weld overlay to ensure the vessels were operated within safe operating limits while obtaining maximum useful life. Eddy current, potential drop, and ultrasonic time of flight techniques were used in laboratory and field trials to prove the cracks were confined to the overlay material. The most reliable measurements were obtained using eddy current techniques after calibration on test standards which exactly simulated the vessels weld overlay metallurgy.
Deuster, G.; Brinette, R. Monitoring, surveillance and predictive maintenance of plants and s t r u c t u r e s 42815
Proceedings of the International Conference on Monitoring, Surveillance and Predictive Maintenance of Plants and Structures, Taormina-Giardini Naxos, Sicily (Italy), 15-18 Oct. 1989. pp. 414-420. Italian Society for Nondestructive Testing This paper presents results from a comparative study of three nondestructive inspection techniques under assessment as part of a German reactor safety program for lightwater reactor components. The three
71