All the welded parts that are subjected to high pressure whilst in operation require a further process of stress relieving and tempering.
This particular heat treatment is called post weld heat treatment (PWHT).
PWHT is a controlled heating cycle consisting of a heating phase, with a temperature gradient not exceeding 250 °C/h (482°F/h), a holding time of at least 1 hour at approximately 700°C (1292°F) and a controlled cooling to 300°C (572°F).
If the parts are too large or non-transportable and the process cannot be carried out in a furnace, induction heating is the best solution because the temperature difference between the inner and outer surfaces is reduced.
When the parts to be heated vary and are large in number, it is more advisable to use resistance heaters.