X70 High Strain Offshore Pipeline Girth Welding Process And Experimental Study Speciality:Material Processing Engineering

The large deformation of offshore pipeline caused by laying operation,wave and current surge and platform movement makes the pipeline connection girth weld bear large stress and become the weak link of the pipeline.Therefore,the performance of the girth weld determines the service life of the submarine pipeline.In this paper,the structure,strength and toughness of X70 high strain offshore pipeline and the structure and properties of joints under different welding processes were studied.In this paper,the mechanical properties and microstructure of X70 high strain offshore pipeline were studied.The results show that the longitudinal tensile strength,yield strength,elongation and yield ratio of X70 high strain offshore pipeline are 620 MPa,526 MPa,59%,0.84,648 MPa and 510 respectively MPa,the elongation is 29.5%,the yield strength ratio is0.78;the hardness value ranges from 200HV₁₀ to 215HV₁₀;Under the series of impact temperatures of 0?,-20?and-40?,the impact value can still be maintained above 300J.The crack sensitivity coefficient is 0.14,which indicates that it has good weldability.The X70 high strain offshore pipeline is composed of two-phase structure of polygonal ferrite and bainite,in which the content of polyhedral ferrite is about 52%,bainite is about 48%,and the grains are small and the content of non-metallic inclusions is low.In this paper,the full-automatic GMAW welding method was selected to study the influence of three kinds of row welding methods and eight kinds of high-strength welding materials on the performance of X70 high strain offshore pipe welding joint under the optimized heat input condition.The results show that two straight pull rows from the hot pass can avoid welding defects and ensure the quality of welded joints.The weld structure of eight kinds of welding materials is mainly composed of intragranular acicular ferrite+polygonal ferrite+a small amount of proeutectoid ferrite.Due to the different composition of the eight kinds of welding consumables,the proportion of various structures in the weld is different.The strength matching value of HS23,HS25 and HS28 is too high,and the minimum elongation of HS25 and HS28 is 15%and 17%,respectively,which fails to satisfy the test requirements.The hardness values of HS23 joint root welding and filler welding are 309HV₁₀ and 301HV₁₀ respectively,and the hardness values are higher than 300HV₁₀,which does not satisfy the requirements of welding test.The strength matching value of other welding materials and base metal is between25.4%and 37.6%.The weld has good strength and toughness,which can ensure the welding requirements of X70 high strain offshore pipeline.