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

• Brittle Fracture 

• Stress Cracking

• Corrosion Cracking

• Fatigue failure

• A much greater dimensional stability is obtained and maintained 

• The potential of stress induce cracking is reduced. 

• Metallurgical structure is improved.

• Strength of the Material and Life of the equipment is enhanced

• 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.

Our Services- On-Site Field Post Weld Heat Treatment (PWHT) services are used frequently in the following applications.

• Process Piping

• Power Piping

• Boiler and Vessel Repairs

• Nozzle Installations

Description of PWHT Unit

• Manufacturer of unit Weldotherm (Germany)

• Electric resistance Type heating unit

• Automatic temperature controllers and with a facility to record Temperature 6 points

• With 100 % duty cycle

• Three phase power input requirement with 50 Hz

• TRC (Temperature recorder channels) 6 in numbers

• Thermal Insulation

• Thermocouple attachment unit