Heat Treatment Systems
Pre-Welding Heat Treatment
Preheating involves raising the temperature of the parenmaterial locally, on both sides of the joint to a value above ambient. The need for preheat in usually determined by the pertinent fabrication code and verified by the weld procedure qualification test. Preheat may be required as an aid to welding for one of four basic reasons;
To control the rate of cooling
To control the diffusion rate of hydrogen in a welded joint.
To reduce thermal stresses.
Compensation for heat loss.
Post-Welding Heat Treatment
Metallurgical changes are very beneficial in that they reduce the high hardness of the as-welded structures, improving ductility and reducing the risks of brittle fracture. Post weld heat treatment has mandatory significance governed by the national standards and codes, as well as being required to offer acceptable component life in onerous environments. As with preheat , the alloying content of the steel is related to the significance of heat treatment temperature.
Benefits of Post Weld Heat Treatment
Reduced residual stresses.
Improved metallurgical structure.
Improved corrosion resistance.