The Development Of Submerged Arc Welding Material For X70MS Pipeline Steel Of High Strength And Resisting H₂S Corrosion

According to the characteristics of X70 MS Pipeline Steel of high strength and resisting H2 S corrosion, the research of the corrosion mechanism of H2 S 、the influence of the alloy and microstructure for resisting H2 S corrosion was performed.The acicular ferrite and granular bainite for weld microstructure 、the alloy system and the composition range of the main alloy elements for the wire 、the slag content and basicity range of the flux were designed.The submerged arc welding wire NS1、 NS2、NS3、NS4with resisting H2 S corrosion and a optimization flux SJ101G4 for X70 MS Pipeline Steel of high strength and resisting H2 S corrosion were developed.The deposited metal in submerged arc welding with the wires in couple with the flux possesses quite high yield strength(≧510)、excellent toughness(AKV(-20℃)≧54)、the low hardness(HVmax≦213) and the excellent property of resisting H2 S corrosion.The cracks in the HIC test and the SSCC test were not occurred.Especially,when the force reaches 133%σs of the tensile stress, The cracks were also not occurred,so the property of resisting H2 S corrosion for the deposited metals meet the requirements of X70 MS pipeline steel.Furthermore,the butt joint welding test and the small batch in the laboratory using submerged arc welding wire and theoptimization flux were performed.the results shows that the welding processes were fine,the designed microstructures and excellent mechanical properties of welding joints were obtained,the fine property of resisting H2 S corrosion was also got. The wire is suitable for a wide range of welding speed,and when the welding speed is 2 m/min,the properties of welding joints meet the requirements of technical specifications of API SPEC 5L appendix H-acidservice conditions for PSL2 steel,the H2 S corrosion resistance of NACE TM0284-96 and NACETM0177-2005.