Abstract
This study deals with an industrial case which consists in the Post Weld Heat Treatment (PWHT) of a butt weld of two shells of large diameter, high thickness and great length constituting parts of pressure equipment.
The limited local heated length is the source of local thermal gradients in the longitudinal direction because of the existence of transitions between hot and cold parts at the ends of the heated zones. These local thermal gradients generate residual stresses which are distributed in the so called “Heated Zone”, including the zone of the weld to be relieved named “Soak Band”, but also in the transition zones on either side of the heated zone, which we refer to as the “Gradient Control Band”.
The stress relief being carried out at a keeping average temperature of 615°C and according to a well-defined thermal cycle in time (heating and cooling rate and keeping duration), the evolution of the thermomechanical stresses due to the thermal cycle is calculated using a combination of the laws of plasticity and creep of the material of low alloy type 16MND5.
The plasticity and creep laws being fixed, and the residual stresses being determined for a reference heating configuration, the effect on the residual stresses of a simple variation in the extent of the thermal insulated zones are evaluated.
