TWO NEW NDE TECHNIQUES FOR INSPECTION OF CONTAINMENT WELDS BENEATH COATINGS

INSPECTION OF PAINTED OR COATED CARBON STEEL SURFACES OFTEN INVOLVES THE REMOVAL OF THE COATING PRIOR TO INSPECTION, ESPECIALLY WHEN THE USE OF MAGNETIC PARTICLE TESTING (MT) IS REQUIRED. IN THE CASE OF EXAMINATION OF CONTAINMENT VESSEL WALLS IN NUCLEAR POWER PLANTS, THE REMOVAL IS TIME CONSUMING, RESULTING IN INCREASED RADIATION EXPOSURE TO WORKERS. IN ADDITION, THE REMOVAL MUST BE DONE WITHOUT CREATING AIRBORNE CONTAMINATION. IN THIS PROPOSAL, TWO NEW NDE TECHNIQUES ARE PROPOSED WHICH COULD LEAD TO IMPROVED INSPECTION METHODS AND ELIMINATE THE NEED TO REMOVE COATINGS. THESE METHODS WERE DEVELOPED FOR IMAGING OF CRACKS AND OTHER DEFECTS IN ALUMINUM, BUT SHOULD BE APPLICABLE TO CARBON STEELS AS WELL, WITH MODIFICATIONS. THESE TECHNIQUES INVOLVE THE USE OF MAGNETO-OPTIC IMAGING, WHICH PRESENTS DIRECT, REAL TIME IMAGES OF DEFECTS THROUGH THE PERTURBATIONS THEY CAUSE IN INDUCED MAGNETIC FIELDS WITHIN THE PART BEING INSPECTED, ANDA SIMILAR APPROACH USING HALL-EFFECT SENSORS TO DETECT THE MAGNETIC FIELD PERTURBATIONS. A NOVEL METHOD INVOLVING SHEET CURRENT INDUCTION FOR MAGNETIZATION OF THE COMPONENT IS USED WITH THESE TECHNIQUES. BOTH METHODS SHOULD BE LESS SENSITIVE TO LIFTOFF OR COATING THICKNESS SINCE THEY DEPEND ON THE FIELD STRENGTH AND NOT THE FIELD GRADIENT AS DOES MT.