Magnetic Properties of Pipeline Steels are Variable

Magnetic or electromagnetic nondestructive inspection techniques for steel are ultimately limited by the fact that the magnetic properties of high strength steels used in pipelines vary considerably. Different samples of steels with similar mechanical specifications and properties can, and do, have very different magnetic properties. Furthermore large variations often occur over distances of as small as a few millimeters within a single sample depending on position, direction and conditions, particularly applied and residual stresses. Unfortunately these variations are typically most pronounced in high strength steels since these often have high residual stresses as a result of their having been heavily cold worked to enhance yield strength. Here we present examples illustrating the effects of some of these variations.