Nondestructive examination of welds through painted surfaces: Final report

A study was performed to develop reliable nondestructive examination techniques for detection of surface-open defects located under a surface coating on ferromagnetic materials. The magnetic particle test method (MT) alternating current (ac) yoke technique presently appears to be an optimum approach because of its technically straight-forward operational basis. A complementary technique uses the eddy current method with a differential type probe. The techniques were verified on both cracked samples and artificial flaws through varying thicknesses of real and simulated coatings. An analytical study of the MT yoke technique, experimental details and test data are presented. On the basis of the test results, recommended changes to ASME Section XI requirements are identified for consideration.