This term indicates the preheating keeping at the same temperature or higher temperature after the welding is completed.
The main scope is activating the diffusion phenomenon in order to facilitate the hydrogen release from the joint and thus prevent the risks of cold cracking.
The most typical application is the treatment of high-strength C-Mn steels and low-alloy steels, which are more exposed to the risks of hydrogen cracks after welding.
Unlike the preheating, proper instructions about preheat maintenances are not often found in the manufacturing technical standards: rather, it is an integral part of maker specification, based on established practices.
Considering the purposes of the preheat maintenance, when a succeeding PWHT is also required, the maintenance of preheat temperature remains essential if the PWHT cannot be carried out right after the welding operation.
Similarly, a preheat maintenance does not exempt from a proper stress relieving heat treatment.