Impact Of Repeat Repairing On Microstructure And Mechanical Properties Of X80 Steel Welded Joint

It can not be avoided to repair the weld during the welding process of oil and gas pipeline construction. Despite the general engineering standards had made some strict requirements for the repairing times, there were still in practice the phenomena of multiple repairing in engineering welding. Up to now, it is not so much for the research on changes of microstructure, chemical composition and mechanical properties of welded joints undergoing the multiple repairs, and so is even less for the welded joints of large diameter X80 steel pipeline.In this thesis, welded joints of a large diameter X80 pipeline experiencing the different repairing times(from 1 to 6 times) are prepared based on the practical engineering condition, and the systematic analysis are made for the macro- & micro-structures, the performances of joint tensile, hammer breaking of grooving joint, bending, low temperature impact and hardness data corresponding to the different repairing times.The analysis results show that the X80 welded joint can be repaired repeat for several times(≤6 times), and same times keep still their good mechanical properties, which can reach the needs of practical engineering, i.e. the X80 steel welded joints have a good repair-ability. The valuable reference testing data are provided in this thesis for the welding engineering of the large diameter X80 pipeline.