Failure Analysis of the Branch Connection Leakage on Primary Pipeline of the Primary Heat Transport System and the Maintenance Strategy Investigation for the Similar Connections Available to Purchase

An primary pipeline branch connection of the primary heat transport system leaked in Dec, 2007. Physical and chemical testing are conducted on the leakage location of the branch connection. The primary failure cause was concluded that transgranular stress corrosion cracking (SCC) on stainless steel side of the branch connection dissimilar metal weld lead to the leakage. There are total 8 similar pipelines in each unit of Qinshan III. The preventive repair strategies for this kind of pipelines are investigated. The similar defects could be detected with ultrasonic testing in the planned shutdown outage. The corresponding precaution condition establishing methods for the similar branch connections with 3 typical positions are investigated and defined. A maintenance strategy to repair the dissimilar weld on the branch connection was developed.