Effect of helix angle on residual stress in the spiral welded oil pipelines: Experimental and finite element modeling

Abstract This paper studied the distribution of weld residual stress in a spiral welded pipeline by finite element method (FEM) and experimental measurements, and the effect of helix angle on residual stress has also been investigated. Both the FEM and experiment results show that the residual stresses in HAZ are larger than those in weld. The error between FEM and experiment results is within 14%, proving that our FEM is correct. There is a peak-shape stress distribution through the weld thickness and the residual stresses in the inner surface are larger than those in the outer surface. Different helix angle has a different equivalent weld length along the hoop and axial directions, which generates different hoop and axial plastic strains, leading to different hoop and axial residual stresses. As the increase of the helix angle, both the radial and hoop residual stresses decrease, while the axial residual stresses increase. As the helix angle increases from 20° to 50°, the hoop stresses in HAZ decrease by 65%, while the axial stresses increase by 120%. The residual stresses are influenced by the pipe dimension (pipe diameter, thickness, weld profile), welding technology (heat input, welding speed) and material grade. When the helix angle is between 40° and 45°, both the hoop and axial residual stresses are reduced to the minimum. The most suitable helix angle is suggested to design around 40°–45°.