Magnetic easy axis development in steel - the influence of manufacturing

Oil and gas pipelines often display a bulk magnetic easy magnetization dire ction, and this may influence results obtained during magnetic nondestructi ve evaluation. The origin of this magnetic easy axis is not well known. Ear lier work [L. Clapham, C. Heald, T. Krause, and D. L. Atherton, J. Appl. Ph ys. 86, 1574 (1999)] speculated that it was a result of residual stresses i ntroduced during pipeline manufacturing, specifically cold bending. This ar ticle reports a study in which a magnetic Barkhausen noise technique is use d to follow the development of a magnetic easy axis in a steel plate sample subjected to progressive amounts of cold bending. (C) 2000 American Instit ute of Physics. [S0021- 8979(00)04816-7].