TWI Frequently asked questions
It is an accepted practice that no more than two attempts are carried out.
However, much will depend on the type of material being welded and the process in use. If the material is known to be metallurgically 'sensitive' to heat input, which could result in degradation of both the HAZ and weld deposit, itthen becomes a question of complete removal of the welded joint and replacement with an inserted section.
Materials such as mild, low carbon and carbon-manganese steels, are considered to be very tolerant to heat input and may accept at least two or more re-weld operations. In the case of low alloy steels, re-welds will be governed bythe heat-treated condition in which they were supplied. For the Cr-Mo steels, up to two re-welds may be carried out, but consideration needs to be given to the post-weld heat treatment operations and possible resultant degradation ofthe welded joint.
With the 3xx series stainless steels, two re-welds may be tolerated, but in the case of the duplex and super duplex stainless steels, only one re-weld operation is advisable, and then with extreme care and control over the heatinput. Ideally, for these complex metallurgical materials, avoidance of any form of re-weld operation is favoured.
The aluminium alloys (5xxx) series can generally be regarded as a two re-weld operation but the (6xxx) series is far more sensitive to heat input and even a single re-weld operation is undesirable.
Of course when considering re-weld operations for what ever reason, consideration must be given to the following: material thickness, distortion problems, build up of residual stresses, and not forgetting the weldability rating ofthe material.
Copyright by TWI, 1999
