PWHT / Pre Heat Services

AMSYCO has more than 50 sets of PWHT equipment and qualified PWHT technicians who are experienced in providing various Heat Treatment services to the Oil, Gas, Petrochemical, Power, Desalination, Construction and Manufacturing Sectors.

AMSYCO specializes in local Post weld heat treatment of carbon steel and alloy steel piping welds by means of the electrical resistance method, in the form of ceramic heater pads and by using electricity as source of heating for stress relieving of weld joints. All heat treatment services are designed to minimize downtime, improve structural integrity, and enhance effective plant life. Additionally, depending on the mobility of the required equipment many of our heating processes can be applied on‐site or at your facility.


Preheating involves rising the temperature of the parent material locally, on both sides of the joint to a value above ambient. The need for preheat is 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 the 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.

During the welding process, the two metal pieces being joined are subject to extreme temperatures and can cause the crystalline structure of the metal to pass through various metallurgical phases. As a result, hardening (and embrittlement) of the metal can occur to varying degrees (usually dependent on carbon content). Heat treatment is designed to reduce the hardness in the heat affected zone of the metals and also increase ductility in these sections. Various pressure vessel codes contain the specifics regarding the procedures for post‐weld heat treatment.

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