TWI Technical Literature Review 22952
By Marcello Consonni
Repair by welding of a metallic component may be required during original fabrication, following in-service inspection or during planned maintenance operations. In some instances a post-weld heat treatment (PWHT) is required according to the fabrication specification. A PWHT is applied to a welded component with the main purpose of reducing the residual stresses produced by welding; at the same time, some tempering of the HAZ is obtained. However, its application may be impractical, potentially unsafe for the structure or personnel, and/or non-cost effective in a repair situation. In such cases, it may be possible to apply a modification or repair by using a welding procedure designed to effect tempering of the heat-affected zone (HAZ) produced by the repair itself, hence waiving the need for a PWHT. Such techniques are commonly referred to as 'temper bead welding', and it is also known as 'controlled deposition', 'half-bead welding' and 'butter bead welding' (see definitions in Section 2). The expression 'temper bead' is commonly used to refer to these techniques collectively and will be used throughout this review.
As noted by Brett (1986 and 1995) in a brief history of the technique, the approach was first used as early as 1965 in the former Soviet Union for the repair of Cr-Mo-V castings without a subsequent PWHT. This method has been successfully applied through the years on numerous steel components during fabrication as well as in-service.