Post Weld Heat Treatment (PWHT)

Stress relief annealing in steel construction and pressure equipment construction

Post Weld Heat Treatment (PWHT) is an important heat treatment after welding. The process is used in steel and pressure equipment construction to reduce residual stresses in the material and increase the operational safety of welded components. PWHT is often prescribed in standards such as EN 10028-3, for example via the time-temperature parameter.

When is PWHT used?

After welding, high residual stresses occur in steel components, which can lead to cracking or deformation. Stresses are reduced by stress relief heat treatment (PSHT), and the mechanical properties in the weld seam and heat-affected zone (HAZ) are improved. PWHT is similar to tempering and is therefore also referred to as post-weld heat treatment.

Procedure and implementation

There are two types of heat treatment:

• Local PWHT: The weld seam is heated specifically with heating mats or induction – ideal for repairs or installed components.
• Complete PWHT: The entire component is treated in the oven to ensure even temperature distribution.

The heating and cooling rates, holding temperatures and holding times have a significant influence on the structural change of the steel. Parameters such as the Larson-Miller or Hollomon parameters are used to describe these relationships.

PWHT service at UnionStahl

UnionStahl offers its customers comprehensive support for post-weld heat treatment (PWHT) – from material consulting to process planning and documentation. With experienced partners and in-depth expertise, UnionStahl guarantees process-reliable solutions, standard-compliant results and lasting quality in use.