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Importance of magnetic saturation effects in the detection of internal tube cracks by magnetic flux leakage
ND T Abstracts The Colonial Pipeline Company, of Atlanta, Georgia, now uses a magnetic flux leakage (MFL) method of nondestructive testing to ensure the integrity of its many miles of pipes and many aboveground storage tanks. This method was developed following concern over the structural soundness of storage tank bottoms, which can normally only be inspected when empty. A successful programme of leak detection is described which complies with current safety regulations. The inspection unit, which uses three different types of sensors, is described in operation. Test data can he used by a attached computer to produce drawings of tank plates and anomaly locations. This process has proved quick and accurate, using MFL to locate anomalies and ultrasonic techniques to verify and categorize defects.
HanasaM, K.; Tsukada, K. Computer tomography of a wire rope by m a g n e t i c flux leakage measurement 51263
Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, Sao Paulo (Brazil), 18-23 Oct. 1992. Vol. 2, pp. 750-754. Edited by C. Hallai and P. Kulcsar. Elsevier (1992) Using the data of magnetic flux leakage around a damaged rope which is magnetized up to the saturation in the longitudinal direction of the wire rope, an attempt has been made to prepare tomograms, which are based on the degree of damage that was obtained as the solution to an inverse problem which was solved by using a modified least square method with a restriction that the magnetic charge must not he negative. Examining the influence of the direction of the magnetic flux leakage measurement on the solution obtained, it is recommended to use z and theta directions when observation in two directions is available. 51005 Stanley, R.K. Imaging of m a g n e t i c flux leakage signals for high quality a s s e s s m e n t of oil field tubular p r o d u c t s Non-destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, San Paulo (Brazil), 18-23 Oct. 1992, Vol. 1, pp. 371-375. Edited by C. Hallai and P. Kulcsar. Elsevier (1992) A recently developed system is described in which transverse and longitudinal magnetic flux leakage (MFL), and gamma-ray wall thickness measurements made on pipe are transposed onto a 2-dimensional map, via multi-algorithm reduction of the raw data. In this paper the system and its advantages over conventional MFL systems are outlined and exemplified.
Pignotti, A.; Kohan, A. Importance o f m a g n e t i c saturation effects in the detection of 50996
i n t e r n a l t u b e c r a c k s b y m a g n e t i c flux leakage Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, Sao Paulo (Brazil), 18-23 Oct. 1992, Vol. 1, pp. 456-460. Edited by C. Hallai and P. Kulcsar. Elsevier (1992) A mathematical model is used to analyze the possibility of detection of cracks on the internal surface of steel tubes by the magnetic flux leakage technique. A linear model shows that the signal from an internal flaw is more than one order of magnitude weaker than that from a similar external defect. But the inclusion of nonlinear effects due to saturation of the magnetic induction for strong fields is found to greatly enhance the relative importance of the signal from the internal crack, in agreement with experimental findings.
Uetake, L; Ito, H.; Saito, T. The relation between measured value of magnetic flux leakage
50517
a n d s e n s o r size Nondestructive Testing Evaluation, Vol. 7, No. 1-6, pp. 347-359 (1992) The size magnetic sensor influences the detectability of defect and the evaluation of magnetic flux leakage quantity. However the relation between the sensor size and the measured value of magnetic flux leakage has not been clarified quantitatively so far. In the present report, five Hall elements of different sizes are used as the magnetic sensor and the value of the normal component of magnetic flux leakage is experimentally obtained on a structural steel with an artificial defect or a fatigue crack, the effect of the sensor size on the results are discussed, it is clearly shown that the measured value of magnetic flux leakage is large in a smaller sensor, and the influence of sensor size on the measured value of magnetic flux leakage is large in a smaller lift-off value. An experimental equation is proposed for the relationship among the magnetic flux leakage, sensor size, lift-off distance and defect size. It is also confirmed that the influence of sensor size on the measured value of magnetic flux leakage for a fatigue crack shows the similar tendency to that of artificial defects.
36
N D T & E International Volume 26 Number 1 1993
50237 Uetake, I.; Ito, H.; Saito, 7". Effect of sensor on results of m a g n e t i c flux leakage testing ( l s t Report) (In Japanese: English A b s t r a c t ) Journal of JSNDI, Vol. 40, No. 5, pp. 291-297 (May 1991) Although it can be expected that the size of a magnetic sensor influences the measured value of the magnetic flux leakage and therefore the detectability of defects, the sensor size effect has not been clarified quantitatively so far. In the present report, using five Hall elements of different sizes as the magnetic sensor the normal component of magnetic flux leakage is experimentally obtained on a structural steel with an artificial defect or a fatigue crack and the effect of the sensor size on the results are discussed. It is clearly shown that the value of the magnetic flux leakage measured with a smaller sensor tends to he larger, and the sensor size influences the measured value more extensively in case of smaller lift-off value. Experimental equation is proposed for the relationship between the magnetic flux leakage value, sensor size, lift-off distance, and defect size. It is also confirmed that the effect of the sensor size on the magnetic flux leakage value obtained for natural fatigue cracks is quite similar to that for artificial defects.
Laursen, P.; Atherton, D.L. Effects of line p r e s s u r e stress on m a g n e t i c flux leakage p a t t e r n s 49989
British Journal of Nondestructive Testing, Vol. 34, No. 6, pp. 285-288 (Jun. 1992) The defect-induced signals obtained from magnetic flux leakage (MFL) pipeline inspection tools are strongly dependent on stress induced in the pipe wall by the internal gas pressure. Precision MFL maps measured with and without 100 MPa tensile simulated line pressure stress are presented here and the changes are compared with stress concentrations around a near side pit.
Atherton, D 2~.; Dhar, A.; Hauge, C.; Laursen, P. Line stresses affect MFL defect indications 49973
Oil & Gas Journal, Vol. 90, No. 27, pp. 81-83 (6 Jul. 1992) The need to correct for the effects of bending and line-pressure stresses during high-resolution magnetic flux leakage (MFL) in-line inspection has long been recognized, The study described reports preliminary tests to correct for such stress effects, but further research on this phenomenon is needed. The large, complex effects of stress on MFL signals cannot yet be readily explained. While further research is strongly indicated, a number of guidelines for the current use of MFL tests under stress conditions are suggested. 48991 Tsuka_da_,K.; Hansaki, K.; Fujinaka, Y. A m a g n e t i c method to measure metallic cross-sectional area of c o r r o d e d steel wire a n d wire r o p e (In Japanese:, English
Abstract) Journal of JSNDI, Vol. 41, No. 1, pp. 18-26 (Jan. 1992) This paper describes a magnetic method to evaluate the deterioration of steel wire rope due to corrosion and/or almmion. The irregular change in the metallic cross-sectional area along a rope is measured in terms of the change in magnetic flux through cross section of the rope when it is magnetized longitudinally up to the point of saturation. Parallel Wire Strands containing standard flaws simulated by removing lengths of wire were inspected. The experiments shows that the method is more accurate in the determination of area loss of rope cross section than the conventional Hux Leakage Method. This method was then applied to artificially corroded wire specimens. The area losses measured magnetically along a corroded wire specimen agree with those obtained from the photographic examination of the cross sections. As the result of subsequent tensile breaking test for these specimens, it was found that the reductions in the tensile strength were nearly equal to the maximum losses in the cross-sectional are~
Matzkanin, G.a.; Teller, C.M.; Suhler, S.A. Application of magnetic flux leakage to the inspection of largediameter, multi-strand bridge cables
48750
NDT for Today's Applications, 1990 ASNT Fall Conference and Quality Testing Show, Seattle, Washington (United States), 18-12 Oct. 1990. pp. 42-44. A S N T (1990) Problems of deterioration caused by corrosion and fracture in the wires which form the steel cables of modem suspension bridges, are of enormous concert to structural engineers bec-an~ of the potentially catastrophic results of failure. Highly reliable nondeslructive methods are needed to inspect these multi-strand structures. This paper describes the Magnetic Perturbation Cable (MPC) System, which is based on extensive laboratory research of magnetic flux leakage detection techniques applied to large steel structures.
HanasaM, K.; Tsukada, K. Computer tomography of a wire rope by m a g n e t i c flux leakage measurement 51263
Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, Sao Paulo (Brazil), 18-23 Oct. 1992. Vol. 2, pp. 750-754. Edited by C. Hallai and P. Kulcsar. Elsevier (1992) Using the data of magnetic flux leakage around a damaged rope which is magnetized up to the saturation in the longitudinal direction of the wire rope, an attempt has been made to prepare tomograms, which are based on the degree of damage that was obtained as the solution to an inverse problem which was solved by using a modified least square method with a restriction that the magnetic charge must not he negative. Examining the influence of the direction of the magnetic flux leakage measurement on the solution obtained, it is recommended to use z and theta directions when observation in two directions is available. 51005 Stanley, R.K. Imaging of m a g n e t i c flux leakage signals for high quality a s s e s s m e n t of oil field tubular p r o d u c t s Non-destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, San Paulo (Brazil), 18-23 Oct. 1992, Vol. 1, pp. 371-375. Edited by C. Hallai and P. Kulcsar. Elsevier (1992) A recently developed system is described in which transverse and longitudinal magnetic flux leakage (MFL), and gamma-ray wall thickness measurements made on pipe are transposed onto a 2-dimensional map, via multi-algorithm reduction of the raw data. In this paper the system and its advantages over conventional MFL systems are outlined and exemplified.
Pignotti, A.; Kohan, A. Importance o f m a g n e t i c saturation effects in the detection of 50996
i n t e r n a l t u b e c r a c k s b y m a g n e t i c flux leakage Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, Sao Paulo (Brazil), 18-23 Oct. 1992, Vol. 1, pp. 456-460. Edited by C. Hallai and P. Kulcsar. Elsevier (1992) A mathematical model is used to analyze the possibility of detection of cracks on the internal surface of steel tubes by the magnetic flux leakage technique. A linear model shows that the signal from an internal flaw is more than one order of magnitude weaker than that from a similar external defect. But the inclusion of nonlinear effects due to saturation of the magnetic induction for strong fields is found to greatly enhance the relative importance of the signal from the internal crack, in agreement with experimental findings.
Uetake, L; Ito, H.; Saito, T. The relation between measured value of magnetic flux leakage
50517
a n d s e n s o r size Nondestructive Testing Evaluation, Vol. 7, No. 1-6, pp. 347-359 (1992) The size magnetic sensor influences the detectability of defect and the evaluation of magnetic flux leakage quantity. However the relation between the sensor size and the measured value of magnetic flux leakage has not been clarified quantitatively so far. In the present report, five Hall elements of different sizes are used as the magnetic sensor and the value of the normal component of magnetic flux leakage is experimentally obtained on a structural steel with an artificial defect or a fatigue crack, the effect of the sensor size on the results are discussed, it is clearly shown that the measured value of magnetic flux leakage is large in a smaller sensor, and the influence of sensor size on the measured value of magnetic flux leakage is large in a smaller lift-off value. An experimental equation is proposed for the relationship among the magnetic flux leakage, sensor size, lift-off distance and defect size. It is also confirmed that the influence of sensor size on the measured value of magnetic flux leakage for a fatigue crack shows the similar tendency to that of artificial defects.
36
N D T & E International Volume 26 Number 1 1993
50237 Uetake, I.; Ito, H.; Saito, 7". Effect of sensor on results of m a g n e t i c flux leakage testing ( l s t Report) (In Japanese: English A b s t r a c t ) Journal of JSNDI, Vol. 40, No. 5, pp. 291-297 (May 1991) Although it can be expected that the size of a magnetic sensor influences the measured value of the magnetic flux leakage and therefore the detectability of defects, the sensor size effect has not been clarified quantitatively so far. In the present report, using five Hall elements of different sizes as the magnetic sensor the normal component of magnetic flux leakage is experimentally obtained on a structural steel with an artificial defect or a fatigue crack and the effect of the sensor size on the results are discussed. It is clearly shown that the value of the magnetic flux leakage measured with a smaller sensor tends to he larger, and the sensor size influences the measured value more extensively in case of smaller lift-off value. Experimental equation is proposed for the relationship between the magnetic flux leakage value, sensor size, lift-off distance, and defect size. It is also confirmed that the effect of the sensor size on the magnetic flux leakage value obtained for natural fatigue cracks is quite similar to that for artificial defects.
Laursen, P.; Atherton, D.L. Effects of line p r e s s u r e stress on m a g n e t i c flux leakage p a t t e r n s 49989
British Journal of Nondestructive Testing, Vol. 34, No. 6, pp. 285-288 (Jun. 1992) The defect-induced signals obtained from magnetic flux leakage (MFL) pipeline inspection tools are strongly dependent on stress induced in the pipe wall by the internal gas pressure. Precision MFL maps measured with and without 100 MPa tensile simulated line pressure stress are presented here and the changes are compared with stress concentrations around a near side pit.
Atherton, D 2~.; Dhar, A.; Hauge, C.; Laursen, P. Line stresses affect MFL defect indications 49973
Oil & Gas Journal, Vol. 90, No. 27, pp. 81-83 (6 Jul. 1992) The need to correct for the effects of bending and line-pressure stresses during high-resolution magnetic flux leakage (MFL) in-line inspection has long been recognized, The study described reports preliminary tests to correct for such stress effects, but further research on this phenomenon is needed. The large, complex effects of stress on MFL signals cannot yet be readily explained. While further research is strongly indicated, a number of guidelines for the current use of MFL tests under stress conditions are suggested. 48991 Tsuka_da_,K.; Hansaki, K.; Fujinaka, Y. A m a g n e t i c method to measure metallic cross-sectional area of c o r r o d e d steel wire a n d wire r o p e (In Japanese:, English
Abstract) Journal of JSNDI, Vol. 41, No. 1, pp. 18-26 (Jan. 1992) This paper describes a magnetic method to evaluate the deterioration of steel wire rope due to corrosion and/or almmion. The irregular change in the metallic cross-sectional area along a rope is measured in terms of the change in magnetic flux through cross section of the rope when it is magnetized longitudinally up to the point of saturation. Parallel Wire Strands containing standard flaws simulated by removing lengths of wire were inspected. The experiments shows that the method is more accurate in the determination of area loss of rope cross section than the conventional Hux Leakage Method. This method was then applied to artificially corroded wire specimens. The area losses measured magnetically along a corroded wire specimen agree with those obtained from the photographic examination of the cross sections. As the result of subsequent tensile breaking test for these specimens, it was found that the reductions in the tensile strength were nearly equal to the maximum losses in the cross-sectional are~
Matzkanin, G.a.; Teller, C.M.; Suhler, S.A. Application of magnetic flux leakage to the inspection of largediameter, multi-strand bridge cables
48750
NDT for Today's Applications, 1990 ASNT Fall Conference and Quality Testing Show, Seattle, Washington (United States), 18-12 Oct. 1990. pp. 42-44. A S N T (1990) Problems of deterioration caused by corrosion and fracture in the wires which form the steel cables of modem suspension bridges, are of enormous concert to structural engineers bec-an~ of the potentially catastrophic results of failure. Highly reliable nondeslructive methods are needed to inspect these multi-strand structures. This paper describes the Magnetic Perturbation Cable (MPC) System, which is based on extensive laboratory research of magnetic flux leakage detection techniques applied to large steel structures.