Comparison of microstructure and properties of X80 girth weld joints welded by different flux-cored wire process conditions
In order to improve the reliability of the girth weld of the pipeline and ensure the safe and smooth operation,a comprehensive comparative analysis of the two X80 pipeline girth welds that have been put into use was conducted.The welding methods of the girth weld of the two X80 pipelines are flux-cored wire self-shielded welding(FCAW-S)and flux-cored wire gas shielded welding(FCAW-G),and the comparative analysis includes chemical composition,metallographic structure,hardness,tensile strength and Charpy impact test.The analysis shows that the weld metal had higher Ni and lower Cr and Mo than the base metal.The Al and N contents of FCAW-S weld are much higher than those of FCAW-G weld and base metal.In the grains of FCAW-S weld,the substructure size is large and the diversity of orientation is low.Compared with FCAW-G weld,the hardness of FCAW-S weld is higher,the yield strength is lower,and tensile strength is relatively close.It can be seen from a series of impact tests,the ductile-brittle transition temperature(DBTT)of FCAW-S weld is 12.2℃,which is 55.6℃ higher than that of FCAW-G.From the test results,it is concluded that the girth weld welded by FCAW-S has a high possibility of brittle fracture.
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