Analysis for End-cracking of L80-3Cr Corrosion-resistant Oil Well Pipe

The reasons for the end cracking of the hot-rol led L80-3Cr oil well pipe are analyzed. As a result a conclusion is made as follows. The pipe-end cracking is identified as a type of brittle cracking. Owing to rather high cooling speed as employed during the pipe-end de-scaling process,massive brittle bainite structure is developed,which leads to poor crack propagation-resistance of the material. Furthermore during straightening process,rather high residual stress is produced with the pipe as remarkably bend-deformed due to inhomogeneous cooling. Thus in cased of bad sawing operation,the residual stress,during releasing process,gathers at burrs or breaks to eventually cause cracking of the pipe end. Accordingly improvement actions are proposed,i.e.,during hot rolling operation,trying as far as possible to avoid development of massive brittle bainite structure as caused by fast cooling of the pipe-end; strengthening management of the hot-rolling process to prevent occurrence of any pipe-end burr or sharp pit and break as may happen during the pipe sawing and conveying operations. Heat treatment has to be performed with in 24 h to pipes in any alloy type with rather low toughness like L80-3Cr.