Post Weld Heat Treatment (PWHT) involves controlled heating and cooling of welded or machined surfaces to improve their chemical, mechanical, and metallurgical properties. Residual stresses from welding and machining can cause damage if not relieved. PWHT relieves these stresses and refines the microstructure of the heat affected zone to reduce cracking and improve strength. PWHT units use electric resistance heating and automatic temperature controllers to precisely heat and cool components based on their application, such as piping, boilers, and vessel repairs.

1. POST WELD HEAT TREATMENT
Introduction
Post Weld Heat Treatment (PWHT) is a controlled heating and cooling process performed after
welding/machining to improve the chemical / mechanical / metallurgical properties of weldment
/ machined surfaces, generally termed as Stress Relieving
Residual stresses in the weld and heat affected areas are likely to be present due to uncontrolled
heating and cooling. Residual stresses are stresses that are inside or locked into a component or
assembly of parts. The internal stresses are caused by thermal and /or mechanical processing of
the parts. Common examples of these are bending, rolling or forging also the thermal stresses are
induce by welding operation. These stresses may lead to swear damage to equipment and
environment if left as such. Also as a result of welding process the base material near the weld
metal and the heat-affected zones transform through various metallurgical phases, depending
upon the chemistry of the metals in their areas. Hardening occurs in various degrees, depending
mainly upon the carbon content. This is particularly very true in the heat - affected zone adjacent
to the weld metal deposit. Resultant stresses in case of welding are highest due to melting and
solidification
Presence of residual stress may to:
1. Brittle Fracture
2. Stress Cracking
3. Composition Cracking
4. Fatigue Failure
Advantages of PWHT:
1. A much greater dimensional stability is obtained and maintained
2. The potential of stress induce cracking is reduced
3. Metallurgical structure is improved
4. Strength of the material and life of the equipment is enhanced
5. Reduction in the risk of brittle fracture can be achieved by refining the HAZ microstructure.
Inspectest (Private) Limited has vast and rich experience in providing Inspection, Testing and
Certification services to various Industrial sectors all over Pakistan. To further facilitate our
valued Clients, we are pleased to offer our services in the field of Post Weld Heat-treatment.

2. Our Services- On-Site Field Post Weld Heat Treatment (PWHT) services are used
frequently in the following applications.
1. Process piping
2. Power piping
3. Boiler and Vessel Repairs
4. Nozzle Installations.
DESCRIPTION OF PWHT UNIT:
1. Manufacture of unit weldotherm
2. Electric resistance Type heating input
3. Automatic temperature controllers and with a facility to record temperature 6 points
4. With 100% duty cycle
5. Three phase power input requirement with 50Hz
6. TRC ( Temperature Recorder Channels ) 6 in numbers
7. Thermal Insulation
8. Thermocouple attachment unit.