Abstract: During the regular inspection of hydrogen storage tanks (three types of pressure vessels) of a power station, it was found that there were defects exceeding the allowed limit in the welding seams. Through a series of tests(including MT,UT, PAUT, TOFD, RT, etc.) and a series of repair(including defect repair, welding of repaired parts, heat treatment and post-heat treatment detection), in the end, it was found that there were still defects exceeding the allowed limit in the welding seam. After container inspection and comprehensive evaluation, the container is scrapped. A failure analysis was carried on for the over-limit defect. The failure analysis conclusion further proves that the inspection conclusion is correct.