Frequently Asked Questions
There will certainly be variations in arc energy at different positions around a girth weld arising from the change in welding speed necessary to achieve satisfactory welding behaviour, in terms of adequate penetration, gap-filling, appearance etc. However, these variations should be associated with the position of welding and remain relatively constant at any particular point around the pipe. If there are concerns about the effect of this variation on mechanical properties, TWI suggests that when the pipe girth weld procedure is qualified, the mechanical test pieces be taken from positions at which the extremes of arc energy are noted. In this way the procedure as a whole will be qualified. This approach is similar to that taken in the UK standard - BS 4515 and in EN ISO 15614-1. The position of mechanical tests (e.g. impact, tensile) is such that they are taken from both low arc energy positions (6 and 12 o'clock) and high arc energy positions (3 and 9 o'clock), assuming a manual procedure. In practice, the variation in welding speed around a pipe should be similar for a mechanised process such as GMAW (MIG/MAG).
Practical working tolerances for arc energy can then be applied by adding the minus tolerance to the minimum arc energy noted and the positive tolerance to the maximum arc energy recorded.
BS 4515 Specification for welding of steel pipelines on land and offshore, 1996
EN ISO 15614-1:2004 Specification and qualification of welding procedures for metallic materials. Welding procedure tests for the arc welding of steels and nickel alloys.