Post Weld Heat Treatment

[etrobal]

we need to install (asap!) a tee connection. however, the tee welds will require pwht (as the thickness is 25.4mm) but we don't have the time as the plant shutdown cannot be extended.

what we did is that we tapered the ends of the tee connection (three ends) to a thickness where pwht will not be needed and proceeded with the weld connection. needless to say, we did not do any pwht on the three welds.

is the tapering of the thickness to forego the pwht allowed? with the tapered butt ends of the tee, the heat affected zone (haz) is thus reduced to a thickness where pwht is no longer needed. am i correct on this haz?

is there a code or a standard that says so? is this good engineering practice? what might be the consequences of our action?

our design pressure is 2.14 mpag while design temperature is 216degC. the tee size is 30-inch diameter with a wall thickness of 25.4mm.

 

[BigInch]

What code?
What's the remaining wall thickness after the taper?

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[etrobal]

sir BigInch, am looking for a code, standard or write up from a consultant, if there is one, that says that this is allowed or reasons why this should not be allowed.

sir, the resulting tapered thickness was at an average of 12.5mm while the legnth of the taper was approximately 50mm from butt ends.

thank you very much indeed sir.

 

[athomas236]

I think it would have been better to have looked at a code, standard or consultant's write up before you reduced the pipe thickness from 25mm to 12.5mm.

At the moment, you appear to have an unknown risk of failure.

Regards,

athomas236

 

[BigInch]

I don't understand how you need 25mm and then figure you can reduce the wall thickness to 1/2 of that. If the original selection was based simply on hoop stress, you're more than likely well over that limit now.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[etrobal]

sir biginch, thank you for your advices and comments. and everybody herein. thanks indeed. sir, the resulting taper was 0.625 of an inch and not half an inch as earlier posted to match the mating pipe wall thickness of 0.625-inch. will the taper affect the integrity of the double longitudinal welds of the tee? how will this affect the overall construction of the tee.

sir athomas236, indeed we should have done that and this. but the short notice we got on the plant shutdown and a short duration at that, we didn't have much choice but to use the available tee. thank you anyway. we do have an unknown risk of failure.

comments, advices, are very much welcome, negative or positive. feel free please. again, thank you very much.

 

[0707]

etrobal

If your connection is in carbon steel and the reduction of the thickness in the ends of your tee, withstands the maximum allowble operation service pressure of your system I think the pwht can be avoided taking in mind that the reduction in thickness of the tee should be as smooth as possible till reaching the thickness of connection pipes

regards

luismarques