Stress redistributions during local Post Weld Heat Treatments (PWHT) are numerically studied for a multi-pass butt-welded pipe with mechanically unrestrained ends. The pipe material is a micro-alloyed C-Mn steel. Temperature and stress fields developed during welding and PWHT are determined from a FE-analysis where rotational symmetry is assumed. Use of heaters with a total axial width less than four times the pipe wall thickness is found to result in substantially different final stress fields than those obtained after a uniform (furnace) heat treatment. The tensile axial and hoop stresses on the inner pipe surface near the centre section of the weldment are considerably higher after a local PWHT. The differences were found to arise mainly during the cooling periods of the PWHTs.

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