Thermal and residual stress distributions in butt fusion joints of HDPE pipes: FE simulation and experimental validation

Butt fusion welding is widely applied for connecting high density polyethylene (HDPE) pipes but may generate residual stresses in the welded joints, interfering the bearing capacity and the service life of the pipeline system. As a result, tensile tests of the weld joints and the base HDPE specimens have been performed for investigating the effects of welding parameters on the mechanical properties of the two types of specimens. In addition, the hoop residual stresses in the base material and weldments are measured through open ring method and blind-hole method respectively. The finite element (FE) model taking temperature-displacement coupling into consideration has been established based on elastoplastic constitutive equations to depict the residual stress distribution during the welding process. The results show that the maximum tensile yield strength of the welded joints can be achieved when the heating temperature is 230°C, heating time is 100s and welding pressure is 2.5MPa. The residual stress of the base material is tensile at the inner surface while it is compressive at the outer surface. The FE simulation reveals that the residual hoop stress at both the inner and outer wall of the pipe is maximized near the welding seam and manifests itself as tensile stress. Following the path of welding seam-heat affected zone-base material the residual stress first decreases to negative and then increases to remain steady as tensile stress and compressive for inner wall and outer wall respectively. Furthermore, the increase of heating temperature and heating time will increase the residual stress value.