Reducing Axial Temperature Gradient in Thick Wall During Local Heat Treatment of Pressure Vessels With Electromagnetic Induction

Post-welding heat treatment (PWHT) is a key manufacturing procedure of thick-walled pressure vessel. Local PWHT is thereby needed due to large size of pressure vessels. Different from module furnace heating and resistance heating, electromagnetic induction heating is a new heating technology with the merits of green and high heating efficiency. However, the axial temperature gradient is inevitably generated. Excessive axial temperature gradient can reduce the effectiveness of heat treatment and even result in material scrap. In order to reduce axial temperature gradient in thick wall during local heat treatment of pressure vessels with electromagnetic induction, the electromagnetic–thermal multifield coupling simulation was carried out on the thick-walled pressure vessel cylinder in this paper. The distribution of induced magnetic field, eddy current field, and temperature field in the electromagnetic induction heating process was explored in detail. The results show the influence of the number of cable turns, the width of outer wall insulation band, spacing between turns, and the current frequency on the axial temperature distribution. The increase of cable turns causes an increase in both heating rate and temperature difference. Larger insulation width of the outer wall and bigger spacing between turns can make the axial temperature higher and the uniformity better. Above 1 kHz, the lower frequency causes an improvement in the temperature and its uniformity. The recommended induction heating process parameters required by the cylinder were determined: 16 turns, 1460 mm in outer insulation width, 32 mm in spacing width, and 2 kHz current frequency.