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SIF for buttwelds of pipe with different ODs

SIF for buttwelds of pipe with different ODs

SIF for buttwelds of pipe with different ODs

(OP)
I am working on a project in which there will be pipe welded together that have different ODs. The pipe to be welded is 30" OD x 1.306" WT to 31" OD x 1.806" WT which gives a constant ID but different OD. Table E-1 in ASME B31.8 gives the calculation for buttweld with an offset ID and constant OD but no indication for constant ID with offset OD. My question is how do I calculate the stress intensification factor for this?

Thanks.

RE: SIF for buttwelds of pipe with different ODs

I don't know about the SIF but I would like to know :
a). Why are you doing this?
b). What are the Operating conditions (pressure and Temperature)?

prognosis: Lead or Lag

RE: SIF for buttwelds of pipe with different ODs

(OP)
a.) It is for a riser and hang-off flange and the requirement is to maintain a constant ID for pigging purposes. A 3rd party is designing the hang-off flange and they are saying that they need the 31"OD for their design.
b.) Pressure is 3705psi and temperature is 60F.

RE: SIF for buttwelds of pipe with different ODs

I'm surprized that a constant ID is needed for pigging between those pipe components. Who told them they need constant ID?

What is being connected, a launcher barrel to the pipeline?

I'm guessing 60 ksi steel and the wall thicknesses don't match very well with B31.8 hoop stresses, but I don't know your corrosion allowance and I also have not checked what std walls are available in that pressure range to see if you have selected one of those, but all seem light unless the 31" is for DF =0.6. DF of 0.72 makes the 31 inch a bit thick for that, but as I recall, 0.72 is not the DF for platform work.

Why the 3705 psig design pressure? I would think it would be either 3700 (nice round number) or 3750 psig, the 2500 ANSI class pressure.

If you made a transition, you'd only have to grind off the outside wall of the 31". Since the B31.8 calcs are based on OD, you wouldn't have to do anything else. Why not tell them to do that. If you don't do something like that, that's going to look pretty funny anyway.

I don't believe the constant ID excuse for the pigs.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

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