Analysis preheat effect on thermal cycle and residual stress in a welded connection by FE simulation

• FEA reveals temperature peaks follow reasonably the sequence of weld.
• At the inner surface of the welded pipe, tensile axial residual stress is serious.
• Preheat has major effect on thermal cycle, but on residual stress is not apparent.
• Change in essential WPS parameters can be investigated by FE simulation precisely.

Preheat effect on thermal cycle and residual stress was studied by employing a 3D finite-element method. A circumferential multi-pass butt weld of pipes based on ASME section IX was investigated and the experiment for thermal cycle validation was carried out. A spherical heat source density with a Gaussian distribution was employed and by an appropriate coordinate system, the rotation of electrode around the pipe was modeled reasonably. Sequentially coupled, thermal–mechanical analysis was applied using temperature-dependent thermo-mechanical behavior for material properties and the variation in peak temperature, cooling rate, and the axial residual stress due to the preheat effect were evaluated.The simulation results revealed that the pattern of final residual stress was influenced by the preheat temperature. However the thermal cycle experienced in the welding zone seems to be significantly affected by the preheat temperature.