TWI Industrial Member Report Summary 791/2004
D J Abson, Y Tkach, I Hadley, A Kelleher and F M Burdekin
Post-weld heat treatment (PWHT) is applied to steel assemblies primarily to reduce the risk of brittle fracture by reducing the level of tensile residual stresses and by tempering hard, potentially brittle, microstructural regions. For large steel assemblies in particular, PWHT can be an expensive operation, and there is thus an economic incentive to avoid PWHT, wherever possible. The report reviews exemptions from PWHT in several current codes, and considers the similarities and the differences between them, including maximum permitted thickness for as-welded conditions, the associated toughness requirements (in terms of the Charpy test) and what may be done to effect some rationalisation.
- To identify materials where there are grounds for seeking wider exemption from PWHT
- To compare and contrast the limiting thickness requirements above which PWHT is required and the associated Charpy test requirements
- To investigate the methods available for gaining exemption from PWHT,
- To demonstrate the use of fracture mechanics procedures to define minimum toughness requirements
- To identify whether a future programme of toughness testing and residual stress measurements on specific steels is needed to demonstrate a case for exemption from PWHT.