Sulfur X80 Pipeline Steel Under The Condition Of The Development Of The Submerged Arc Welding Flux

With the increasing demands for oil and gas resources as the development of the national economy,demands for X80high-grade pipeline steel are growing for its low costs and efficiency improvement. The development of oil and gas fields containing sulfur brings potential safety risks of corrosion destroy to the pipelines, which puts a higher demand on the strength and toughness,as well as the corrosion-resistance properties on the pipeline steel during the construction of pipeline.On the base of the performance of welded joints of X80pipeline steel, by optimizing the contents of agglomerated flux for pipeline steel, a kind of agglomerated flux used for X80pipeline steel submerged arc sulfur-containing conditions was developed. Fluorine alkali was determined according to the different characteristic of fluxes. Mn, Cu, Mo, Ni and rare earth oxide were chosen as alloying agents and the uniform design method was used to design the formula of agglomerated fluxes. Match the test fluxes with CHW-SG4wire of the Atlantic Welding Material Co., Ltd and optimized the formula combined with microstructure observation and mechanical properties tests of the deposited weld metal. SSRT test was used to study the effect of different fluxes on the stress corrosion susceptibility of weld metal; fracture morphology and EDS analysis were applied to explore the mechanism of the SCC resistance of welded joints.The experiments results show as follows:it can be ignored that the impacts to the process performance of flux made by the sodium tetraborate, manganese, copper, of Mo and Ni; affect the order of components of the homemade flux is fusedmagnesia, rutile, bauxite, fluorite. Compared with the weld welded by CHF102GX flux, content of Cr of the weld metal welded by homemade10-group flux is generally low; content of Mn of the experimental weld metal is quite except5#; the weld metal used the flux contained of Ti and B is contained high levels of Ti and B; the iron content is not very different. Anlysis the mechanical properties of X80pipeline steel weld matal and find that weld meet the yield strength as>551MPa in API standard except1#,2#,3#,6#,7#,8#,9#and10#flux welding of weld meet the AKV-20℃≥160J in API standard. The maximum of the hardness of experimental weld is HRC18.6, not more than HRC22which is the requirements resistance to HIC and SCC corrosion. Compared with SCC of the weld welded by5#,6#,7#and8#four groups flux,6#is not into gas as reference to other three groups, we can find SCC of order of the other three groups is7#<5#<8#; stress corrosion cracking tendency of7#weld specimens is not obvious, while stress corrosion cracking tendency of the8#weld specimens is obvious.