I agree with a lot of the responses I see. It is true that API 1104 does not have a time lapse between passes or how many passes have to be put in before a weld is left to cool. The best place to look is the written welding procedure or the Owner's (or engineering firm's
![razz :razz:](/f2/epx.png)
) specification. I have found that on higher yield pipe the more passes before the weld is allowed to cool, the better. If I was allowed to contribute to the procedure or the specification I would require that for pipe of API 5L-X60 and higher at least three passes be completed before welding is interrupted. I would include breaks, lunch time, and the end of the day in that requirement as well. Any time welding would be interrupted, three completed passes minimum.
Now, what do we do before we resume welding? Preheat the entire weld thoroughly, not just the skin, let it soak all the way through, and maintain the preheat until the weld is complete. Big pipe, when you are jumping from side to side completing the welds after the third pass, as in later in the day or the next day, preheat to the required temperature and maintain it till the weld is complete. Preheat anytime the welding is interrupted.
As far as delaying the completion and the preheating of the weld I also have an opinion. Most of these pipeline welds are made with cellulosic electrodes that do contain some moisture if they are SMAW (stick) welded. The moisture disassociates in the welding arc and leaves some hydrogen in the weld. Delaying the completion of the weld allows some of the hydrogen to escape over a prolonged period. This is also why preheating and maintaining preheating is so important. It allows the weld to stay hot to warm longer to allow some of the hydrogen to escape.
I have heard of some Owners requiring "delayed" procedures, procedures where root beads and hot passes are left for several days, of up to seven days before the weld is completed then destructive testing the welds to qualify the procedure. This is fine and if I was working for that Owner as an inspector I would comply with that requirement from the Owner although I might not agree with it. Just keep my mouth shut and my eyes open.