A magnetographic technique for inspection of containment welds through coatings : Liu, S.N. Electric Power Research Institute, Palo Alto, California (United States), NP-6834-D, 92 pp. (May 1990)

Abstract

The purpose of this project was to develop an inspection technique for typical nuclear plant containment welds that could detect cracks 6 mm (0.25 inch) long or longer through paint thicknesses up to 0.38 mm (0.015 inch). A magnetographic technique was developed for this purpose. This technique incorporates a flexible magnetic medium such as magnetic recording tape which is placed into contact with the component while a magnetic field is applied. The leakage field from a flaw magnetizes the tape, and the signal from the tape can be read by scanning a magnetic tape head over the tape. In this project, both magnetic tape and a commercial product with the brand name Magnafilm were investigated for this purpose. Experimental investigations using cracks produced by a proprietary welding process showed that the magnetic tape had insufficient sensitivity; however, the Magnafilm was to have sufficient sensitivity to satisfy most of the projects goals. The Magnafilm produced permanent visual images on the Magnafilm material itself, and it could also be scanned with a tape head to produce magnetographic signals. Results were obtained from longitudinal cracks in the crown and toe of the welds in flat and 90-degree weld specimen, and from transverse cracksmore » in the crown of the welds in the specimens. Using visual Magnafilm indications, cracks ranging in length from 5 mm (0.2 inch) to 28 mm (1.1 inches) were detectable through simulated paint thicknesses up to 0.38 mm (0.5 inch), with the exception of one 6-mm (0.25-inch) crack which was detectable through thicknesses up to 0.23 mm (0.009 inch). Based on these results, a preliminary inspection procedure for inspecting containment welds through coatings was developed. 7 refs.« less