某X70管道环焊缝裂纹成因分析

Cause Analysis of Girth Weld Crack in A X70 Pipeline

某在役输气管道在检测时发现环缝焊根部存在裂纹缺陷。为了研究该环焊缝裂纹的成因及扩展,对含裂纹的焊口进行了外观检测、无损检测、焊缝的力学性能测试、缺陷处宏观及微观形貌观察、裂纹成因分析。结果表明,由于焊缝根部成型质量较差,根部易形成应力集中,在外力作用下,首先以脆性断裂方式在焊缝根部形成延迟裂纹,并以韧性断裂方式持续扩展。

Crack defect was detected at girth weld root of an in-service X70 gas pipeline. In order to analyze the cause and propagation of the girth weld crack, the appearance inspection, nondestructive testing, mechanical property tests of the weld, metallographic observation and SEM analysis of the defect were conducted. The results show that stress concentration is easily formed at the root due to poor forming quality of the weld root. Under the action of external stress, a delayed crack is firstly formed at the weld root in brittle fracture mode, then it continues to propagate in ductile fracture mode.