API 1104, preheat/interpass/PWHT req.

Date 06-14-2003 16:42

hi everybody

As per API 1104 Welding code for and design code ASME B31.4 / 31.8

1- What is the requirements and limitation for preheat? is there any table same as per ASME 31.3 ?
2- what is the limitations (min. or max.) for interpass temperature should be or should it be mentioned in WPS?

Note: Welding design code is ASME B31.4 ad ASME B31.8. This is for 30" oil pipeline with wall thick. 25 mm (1") and the material API 5L X65.
I will appriciate for your reply.
Best regards.

By George-kh (**)

Date 06-20-2003 09:48

As you mentioned ASME is used for design. So I guess you just have to follow API 1104 for welding.
1 – There’s not any table to suggest preheating in API 1104.
According to API 1104, 1999 – 5.4.2.13: A decrease in the specified minimum preheat temperature constitutes an essential variable. But according to ASME you are allowed to decrease preheat up to 100F.
2 – Instead of interpass temperature, time between passes is mentioned in API 1104. According to API 1104, 1999 – 5.4.2.8: An increase in the maximum time between completion of the root bead and the start of the second bead constitutes an essential variable.
However, I suggest you not to interrupt your welding from start to completion. Because your material is thick enough and has a relatively high strength and it’s prone to hydrogen induced cracking. Especially, if your filler is cellulosic one.

By NDTIII

Date 06-20-2003 12:58

I'd like to help you answer this question, if I may.
First of all if you are welding an oil line your design code should be B31.4. B31.8 is for gas transmission lines. API 1104 is only for procedures, welding, fabricaiton , NDE, etc. 1104 tells you how to weld the pipeline, but B31.4 gives you supplemental requirements for various facilites.
Your preheat and interpass temperatures can be found in ASME B31.4 paragraph 434.8.8 and is only required for steels having a carbon equivalent in excess of 0.32% (heat analysis) or a carbon equivalent (Carbon + 1/4 MN) in excess of 0.65% (heat analysis) unless other variables or conditions require preheat. In this case, if preheat is required it must be done so with a qualified procedure. B31.4 doesn't specify an actual interpass temperature (min or max). Only that it must be considered and used during procedure qualification.
Now if you are tying into a facility that falls under B31.3, that is a completely different code. There will be PWHT requirements on the plant side but not on the pipeline side.