Job conditions, prevailing codes, high restraint, alloy level, WPS, or other considerations would normally dictate preheat and interpass temperatures, but since you're saying that the code and specification makes no mention of either, in general, the minimum preheat and interpass temperature for API 5L X70 in your posted thickness range is around 200 degrees Fahrenheit.
I would insist in "warm to the hand", but since Mr. Norris has suggested 200 F (about 95 C), I'll agree with him.
Hundreds of times I've read in the specifications (all specifications, not only Welding) the following phrase: "When two specifications apply to the same item, the stricter one shall be followed"; and 200 F is stricter than warm to the hand.
Giovanni S. Crisi
If the carbon content is less than 0.2 and the thickness is less than 12mm (.472), the minimum preheat and interpass temperature is 50 degrees Fahrenheit. If the carbon content is less than 0.2 and the thickness is more than 12mm, the minimum preheat and interpass temperature is 100 degrees Fahrenheit.
If the carbon content is more than 0.2, and the thickness is less than 12mm the minimum preheat and interpass temperature is 100 degrees Fahrenheit. If the carbon content is more than 0.2 and the thickness is more than 12mm, the minimum preheat and interpass temperature is 200 degrees Fahrenheit.
Professor Crisi,
Since we know the thickness is 21mm (.826) the minimum preheat and interpass temperature will either be 100 or 200 degrees Fahrenheit. Not knowing the carbon content, I suggested the stricter one.
Mr. Norris,
The nominal carbon content of 5LX 70 is 0.26%, so 200 F would be OK.
Now, there are two answers below recommending a higher temperature. It's up to Mr. Kulkarni to decide what to do.
Giovanni S. Crisi
Dear ALL
Thanks you all .... Feedback of you all has helped me to conclude preheating temperature to 100 degree C. Thanks a lot again ....
What does your client specify?
When we have welded X70, normally the client specifies a somewhat elevated preheat. In one instance, the client required preheat of 300F for X65 and above.
Charles
Hi All,
Am currently welding on pipe line parts for LNG pump staion in Holland,FCAW metal filled core and our preheat is minimum 150oC max 200oC, interpass max 250oC,thk 15mm-35mm and i think the grade is the same,will check and let you know.High preheat is to counteract lack of fusion problems
Cheers
AJ
I just finished work on a project in Colorado with similiar material the WPS called for a preheat of 200 to 250 degrees farenheit. But the problem with amount of heat was that most of the welders were getting excesive burn through on the root pass so the manufacturer dropped the preheat to 150- 175 degrees also with that much heat the you can have a hard time getting to fill and cap passes to stack.
The morning temps were around 10 to 15 degrees in the morning and warming to around 50 to 70 in the afternoon.
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