Influence of strength of girth welded joints on axial bearing capacity of high strain submarine pipeline

For oil and gas pipeline based on strain design, strength of girth welded joints plays an important role in the axial deformation capacity.Finite element method, digital image correlation(DIC)tensile test and wide plate tensile test were used to study influence of strength changes in different regions of GMAW girth welded joints on the axial bearing capacity of high strain submarine pipeline with size of OD559×31.8 mm and grade of L485.The results showed that with the increase of strength of weld metal, the axial limit load and axial mean strain increased, and the failure position shifted from weld to heat affected zone(HAZ)and base metal.Due to small proportion of root welding metal and narrow HAZ, strength of root weld and HAZ had little influence on the axial ultimate load and axial average strain of pipeline in the case of overmatching.Under axial load, distribution of axial stress and axial strain in base metal, HAZ and undermatched weld was very uneven.Due to restraint effect of base metal and deformation strengthening of weld metal itself, tensile strength of undermatched welded joints was higher than that of all-weld metal, but deformation and yield were mainly concentrated in the weld, which easily led to failure of girth weld of pipeline.