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Up Topic Welding Industry / Inspection & Qualification / Preheat temperatures for pipe?
- - By Inspect1980 Date 04-20-2017 13:32
I know this is a dumb question. I am trying to put together a WPS for 16" Gr. b .844. I'm still waiting to see if it's 5L or 106. The WPS is for API 1104. Where can I find temperature requirements such as pre heat and max interpeass? Thank you.
Parent - - By jarsanb (***) Date 04-20-2017 16:02
It depends on what welding process/electrodes you'll be qualifying. If you're using cellulosic then you'll probably need an aggressive preheat maintenance as well. 

R 460.20307 Welding preheating.
In addition to the requirements contained in 49 C.F.R.ยง192.235, which is adopted by reference in R 460.20606, if preheating is required, then an operator shall monitor the preheat temperature to ensure that the required preheat temperature is reached before beginning, and is maintained during the welding operation.

Common preheat temps using EXX10's with heavy wall (.844) are typically north of 200F to maximize hydrogen diffusion but also minimize stress in the weld joints. How will you apply the heat, how will you maintain the minimum through the welding process are questions you would need to answer in the procedure. Holding 250F isn't as simple as it might sound without some pre-planning. If using low hydrogen electrodes/processes then this number can come down significantly - I've seen it specified when temps are below 50F to heat up to 70-150F, and at all times between 70-150F. In any case, since procedure qualification is required per API 1104, the minimum temps you establish are essential variables.

In this study commissioned by federal DOT, preheat was established at 250F.
Parent - - By Inspect1980 Date 04-20-2017 16:16
Thank you. It will be using E6010 root and E8010 fill and cap. Isn't there somewhere I should be able to get a definitive minimum preheat temperature?
Parent - - By jarsanb (***) Date 04-20-2017 16:34
Not that I'm aware of. Because you are qualifying the procedure, and need to prove acceptability, I think all you'll find are recommendations. I could be wrong. Lincoln Electric would be a good reference since they are heavily involved with welding processes and electrodes tailored to API 1104. That .844 wall is your concern.
Parent - - By jarsanb (***) Date 04-20-2017 16:40
Using the E8010 in a situation with the heavy wall you mentioned on possibly API 5L Gr. B or A106 goes against the grain as well. The push is to closely match the filler to the pipe grade as possible. Over-matching isn't always a good thing. These welds, depending on your preheat selection, could have a significant amount of stress in them. Anyway - good luck
Parent - By Inspect1980 Date 04-20-2017 17:58
Thank you. The choice of filler was not my call. That was pre defined in the request. It looks like we will require a preheat of 250.
- By 803056 (*****) Date 04-22-2017 14:24
API 1104 is not a cook book for how to weld. Like ASME B&PV code sections, it assumes the user has the expertise necessary to do the work. Experience, engineering judgement, experimentation, etc. come into play when developing the WPS. The WPS is qualified by testing to ensure it will produce welds that meet the minimum requirements of the standard.

The minimum preheat can be determined experimentally by the contractor or they can use information available from other sources such as AWS. I often use AWS as the starting point if the base metal is listed by the structural welding code as a prequalified base metal, if not listed, I  use the annex found in the structural welding. In the annex there is a alternate method of determining the minimum preheat based on the chemistry of the base metal used and the level of hydrogen control.

Once the minimum preheat is determined, the WPS is qualified using the preheat specified and it becomes the basis of the preheat specified by the WPS approved for production.

Good luck - Al
Up Topic Welding Industry / Inspection & Qualification / Preheat temperatures for pipe?

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