Study On SSCC Performance Of Welded Joint Of X65 Pipeline Steel Based On Nickel-based Welding Material And Carbon Steel Welding Material

Based on the general properties of austenitic stainless steel,Arc625 nickel alloy welding of X65 steel pipe for butt welding is used innovatively,Explored to replace the traditional welding materials using the welding material,the possibility of improving H₂ S stress corrosion cracking?SSCC?of welded joints in oil and gas pipelines by a large margin.In this paper,we mainly study SSCC performance of A,B,C,D four joints,which,class C joint is obtained by adopting welding materials Arc625.A,B,D three kinds of joints using carbon steel welding consumables.The differences of microstructure,mechanical properties,electrochemical corrosion properties,hydrogen permeation ability of four kinds of pipeline steel welded joints were compared.?1?Microstructure observation and mechanical property analysis of A,B,C and D four kinds of joints show that:?1?Base metal: The base metal of the four kinds of joints is composed of massive ferrite,retained austenite and a small amount of needle ferrite,the tissue is uniform and the corresponding hardness value is in the low level,and kept in the 165-180 HV.?2?HAZ: The grain size of fine grain zone in the heat affected zone,and the coarse grain region of the coarse grain zone appeared different degree of grain coarsening,the HAZ coarse grain zone of two kinds of joints B and D contain a large amount of coarse martensite and retained austenite.Large amounts of carbides precipitated along the grain boundaries,greatly deteriorated the joint performance,and the hardness value was increased in the 170-220 HV range.?3?Weld: In the welded joints,the root of the weld of A,B and D three kinds of joints are oriented growth of columnar ferrite distribution between the needle ferrite,the weld is fine uniform needle ferrite structure,the overall hardness is slightly higher than the base metal.The microstructure of weld of the C joint was composed of a large number of dendritic cells and the cytoplasm of cells,and the local hardness value was over 300 HV.?4?The yield strength: Tensile strength and elongation of the tensile specimens are decreased due to the uneven microstructure and the microstructure of the welded joints.In which the mechanical properties of C joints were best.?2?The electrochemical corrosion test results of B and C two kinds of joints are indicated: The corrosion current density and corrosion rate of the weld joint of the C type joint is smaller than that of the B type.Two types of joints in the heat affected zone and base metal polarization curves almost coincide,the corrosion current density and corrosion of their equivalent.The hydrogen permeation test results of B,C,D three kinds of joints and base metal are indicated: The hydrogen permeation curves are analyzed and evaluated J?L?Dapp,capp and NT of B,C,D and base metal,the results showed that J?L,Dapp of base metal are minimum,the value of capp and NT maximum.J?L?Dapp of C joint maximum,the value of capp and NT minimum.The welded joint used nickel alloys showed strong ability of hydrogen permeation.?3?The SSCC properties of four kinds of welded joints of A,B,C and D were tested.After 720 hours,found that the B type joint and the C type joint were cracked,and A type joint and the D type joint were in good condition.There is a deep corrosion groove in the fusion zone of the B type joint,and there are pores in the weld.A longer linear crack near the fusion line of the C type was observed,and the B was found that the cracking of the joints was flat,which showed that the cracking was dominated by anodic dissolution.And the crack of the C type joint has a small gap,which is caused by hydrogen deep metal.Further EDS energy spectrum analysis of the C joint is carried out,results show: It is found that the carbon element in the C type joint is smooth,the content of carbon element in the fusion zone near the crack is intense,which is caused by decarburization and carbon rich layer.Therefore,nickel and chromium in the distribution of the cracking of the C type joint is also a big fluctuation.?4?XRD phase analysis results of the base metal and the transition layer of A,B,C,D four kinds of welded joints are showed: There was no harmful phase found in the base metal and the transition layer of four types of welded joints.Mainly by the gamma and alpha phase.