Comprehensive inspection of refrigerated ammonia storage tank welded joints by the metal magnetic memory technique and conventional NDT methods

摘要

Refrigerated ammonia storage tanks (RAST) are hazardous industrial facilities, where accidents with severe consequences occur. Defects of welded joints are one of the main reasons of RAST accident occurrence. Due to this, during the technical inspection, special attention is paid to quality control of welded joints. The use of non-destructive testing (NDT) for defect detection is essentially important as it can be used to assess the integrity of such critical steel structures as storage tanks. Among the several NDT techniques available, acoustic emission (AE) can supply valuable information assessing structural integrity, detecting flaws and leaks in base metal and welded joint. However, assessing structural integrity usually includes other NDT techniques (e.g., visual examination, ultrasonic testing, dye penetrant test) additionally to AE, providing complementarity between different NDT techniques. Nevertheless, conventional NDT methods are aimed at detecting only the defects that occurred during manufacturing and operation and do not assume stress-strained state (SSS) assessment. The metal magnetic memory (MMM) technique is a passive magnetic one that is recommended to be applied for SSS assessment in accordance with guidance documents. A flaw detectability relation between UT and MMM techniques is observed.