Study On Safety Assessment Of Circumferential Weld For The High-Nb X80 Steel Pipe

The new generation pipeline steel of the high-Nb X80 is used increasingly because of the high toughness and good weldability. At the same time, as a typical pipe welded structure, the welded joints are the weakness location.This is mainly because there inevitable welding defects,residual and inhomogeneous microstructures and poor mechanical in the welded joint zone.With the development of the engineering practice and the fracture mechanics, people don't required that the structure should not contain any welding defects, gradually use the principle of the "fitness for purpose" to assess the influence of the welding defects on the structures. This movement not only take into account of the economic cost of the structure, but also provide the theoretical basis for the safe performance of the structure.In this study, through the Crack Tip Open Displacement (CTOD) tests conducted under zero of 10 degree according to the requirements of the standard of BS7448,in which a strandard TPB (three point bending) shape was accepted,the values of CTOD were obtained for the circumferential weld joint and the axial weld joint in the different welding process.The different crack direction is studied for the circumferential weld joint.One is the embedded flaw,the other is the surface.Based on the tensile test results of base metal and weld metal including Hobart and JC-30,the failure assessment curves of respective levels were created.The standard BS7910 was applied to assessment for circumferential weld joint for the China-made high-Nb X80 pipeline steel tube with embedded flaw and surface flaw at the weld toe in a given crack size and load. The results of the assessment showed that all assessment points are located within the failure lines of analysis.The study provide a reference for the application of the high-Nb X80 in China...