Using reinforce plate to control the residual stresses and deformation during local post-welding heat treatment for ultra-large pressure vessels

Larger residual stresses and deformations are inevitably generated during local post-weld heat treatment (PWHT) for ultra-large pressure vessels, which may lead to cracking in weld joint. In this paper, a new control method with reinforced plate was proposed to prevent cracking during local PWHT for ultra-large pressure vessels. And the evolution of stresses and deformation during local PWHT and the reason of cracking were discussed. The results show that bigger inconsistent deformation along axial direction and larger axial stresses in weld toe are the main reason to cause cracking. The hoop, axial and maximum principal stresses in welded joint can be reduced by reinforced plate. And the maximum radial deformation during holding stage of PWHT was decreased by reinforced plate because of the decreased elastic and plastic strain. The maximum radial deformation was decreased by more than 50%. The inconsistent deformation at heating stage can be improved, so the stress concentration in weld toe resulting in cracking could be also improved. This work will provide a good guidance for the manufacture of ultra-large pressure vessels.