Application of Automated Eddy Current Techniques for Off-Shore Inspection

Abstract

Publisher Summary This chapter presents the application of automated eddy current techniques for offshore inspection. The nondestructive in-service inspections of the weld zones are necessary to detect fatigue cracks in an early state before they increase to a critical size. These cracks are resultant of high stress concentration factor and changes of the structural condition in weld area. The most applied techniques for the detection of cracks in weld seams of underwater constructions are the magnetic particle test methods and the ultrasonic technique. The advantage of the magnetic particle testing technique is the high detection capability in the indication of cracks in the weld seam and the simple evaluation of the results, but the disadvantage is the fact that the area to be inspected has to be cleaned accurately. The ultrasonic technique is applied easily in remote controlled manipulators and is often used in such systems. The main disadvantage of the ultrasonic technique is the complicated and permanent changing geometries of the three dimensional structure, leading serious problems in the evaluation of the signals. The chapter also presents the eddy current testing method. It is a traditional technique for the detection of surface cracks that is applied in offshore for a very short time, because the signals of weld seam roughness and the changes of magnetic permeability variation, and electric conductivity caused by the welding process superpose the crack signal that reduces the detectability of cracks. Experiments showed that an inspection of weld seams of offshore constructions by means of eddy current testing methods detects fatigue cracks with the same grade of reliability as the magnetic particle technique.