Present Status of Inspection Technology and Standards for Large-Sized In-Service Vertical Storage Tanks

In order to assure reliable and safe operation of large-sized vertical storage tanks and find the hazardous defects during the operation, it is needed to regularly inspect and test the storage tanks. Current inspection technology for in-service storage tanks can be divided into online inspection technology and post-shutdown internal inspection technology. Online inspection technology mainly includes acoustic emission technique, guided ultrasonic wave technique, spot ultrasonic thickness measurement technique and ultrasonic thickness measurement technique using auto wall-climbing robot, etc., and post-shutdown internal inspection technology mainly includes magnetic flux leakage inspection technique, ultrasonic inspection technique, surface inspection technique and vacuum leak detection technique, etc. This paper introduces the inspection methods for large-sized vertical petroleum storage tanks adopted currently in China in order to judge the status of the storage tank according to the online inspection results, decide whether to cut down or extend post-shutdown internal inspection cycle or not and develop inspection and maintenance plan; and conduct post-shutdown internal inspection according to the cycle specified in the enterprise standard. This paper also introduces the development situation of codes for design, construction and erection, repair and retrofitting and inspection standards for large-sized vertical petroleum storage tanks.