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Heat Treatment

Heat treatment involves raising the temperature of the parent material to a value above ambient on either side of a joint to be welded.

The need for preheat is normally determined by the relevant fabrication code and verified by the weld procedure. Preheat is normally required as an aid to welding, to drive out moisture, but can be required for other reasons:

  • To slow the rate of cooling in the heat-affected zone, reducing the risk of hardness and cracking.
  • To control the diffusion rate of hydrogen in the welded joint
  • To reduce thermal stresses
  • To compensate for heat loss.

Stress-relieving post-weld heat treatment (PWHT) is used when required by the fabrication specification code and verified by the WPS, in some cases being mandatory. It involves raising the temperature of the weld and the heat-affected zone, uniformly and in a controlled manner. The purpose of PWHT is primarily to reduce residues and the internal stresses caused by welding, quench-hardening or cold-working. It can also be beneficial in improving resistance to stress corrosion, cracking and brittle fracture. It improves the elasticity, ductility and strength of the material and enhances its machine-ability.

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Bluelimit was founded more than 30 years ago, primarily to provide inspection and testing services to the petro-chemical, oil and gas industries.

Today we offer a comprehensive non-destructive testing capability, applying our skills and experience to everything from traction engines to environmental renewables.

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