WHT is a controlled process in which a material that has been welded is reheated to a temperature below its lower critical transformation temperature, and then it is held at that temperature for a specified amount of time. It is often referred to as being any heat treatment performed after welding; however, within the oil, gas, and petrochemical industries, it has a specific meaning. Industry codes, such as the ASME Pressure Vessel and Piping Codes, often require mandatory performance of PWHT on certain materials to ensure a safe design with optimal mechanical and metallurgical properties.
The need for PWHT is mostly due to the residual stresses and micro-structural changes that occur after welding has been completed. During the welding process, a high temperature gradient is experienced between the weld metal and the parent material. As the weld cools, residual stress is formed. For thicker materials, these stresses can reach an unacceptable level and exceed design stresses. Therefore, the part is heated to a specified temperature for a given amount of time to reduce these stresses to an acceptable level. In addition to residual stresses, microstructural changes occur due to the high temperatures induced by the welding process.
The use of PWHT can help reduce any increased hardness levels and improve toughness and ductility to levels acceptable for design.
BIRAWA offer a full range of on site heat treatment services, to the power industry, oil and gas, fabrication and casting industries.
Working safely and closely to meet the clients specific procedures and requirements, to enable a quality service at a competitive cost.
Preheating the steel to be welded slows the cooling rate in the weld area. This may be necessary to avoid cracking of the weld metal or heat affected zone. The need for preheat increases with steel thickness, weld restraint, the carbon/alloy content of the steel, and the diffusible hydrogen of the weld metal.
To prevent the occurrence of cold cracks, also to reduce the violence in the HAZ, Lower the residual stress, Reduce the distortion.
Preheat before welding work done on the material, and at temperatures between 175 ~ 220Celcius done before welding.
Preheat process continues further along with welding until welding process is completed.
Electric furnace is necessary to cut the pipe work schedule. PWHT using Temporary Electric Furnace PWHT object can produce more, however it can be done following the recommendations on the rules of the ASME standard or the manufacturer's recommendations.
DRY OUT can also be done by Electric system, with engine capacity of Main Unit and Heater powerful it is possible to do DRY OUT, especially in re leaning castable is only part of the reactor or Refractory Coil Fired Power Plant located on the metal or factory.
We are able to serve the work of Internal and External firing with LPG fuel. Our engineers have the experience to do the work of Internal and External Firing large vessels or tanks sphere.