[ww]

Echo11,

I’m agreeing with you. In my earlier post, I reached conclusions identical to yours. Designers do not have to add anything to the reference dimensions shown on butt weld fitting charts.

When I brought up the 1/8″ gap I was responding only to the idea that you don’t have to worry about weld gaps because its ONLY 1/8″. My point was that if 1/8″ WERE added to each weld, it could be a problem in some situations. In fact, 1/8″ is NOT added to each weld.

Wayne

[ww]

Thanks for your comments 11echo. I agree that in most situations the 1/8″ would be inconsequential but there are times when it matters. For example, if you have a run of fittings welded together with no pup pieces (as often occurs at control valve stations), and you accumulate 1/8″ at each weld, you could end up with a +3/4″ or more difference. This can make a real difference when you’re trying to fit piping into a tight spot, or even more so, when your new piping has to align with existing piping (eg a tie-in at an existing flange).

Wayne

[ww]

I stated clearly in my post that I have over 20 years of design experience so I’m not sure why you’re wondering what to believe. I presume the “junior” under my name is posted by the forum software and refers to my number of posts, not my experience. In any case, my experience has nothing to do with answering the question.

I appreciate your offer of help, but I don’t think you understand the intent of my question. I’m not obsessing over 1/8″ nor am I in a quandary about what to do about the vendor’s drawings. I was just curious if anyone else had any insight on how the weld gap is accounted for in dimensioning butt-welded fittings. I know that there is a gap between the welds and I also know that designers do not include this gap in their dimension calculations.

I got the answer to my question this morning when I spoke to one of the piping foremen at the refinery. Yes, there is a gap between the welds. This gap is accounted for by the pipefitters and adjustments are made accordingly. If they need to eliminate the gap to conform to the overall dimensions, they can do this by grinding down the end of each fitting by 1/16″. Some of the gap also goes away when the weld is made (the two fittings are drawn together).

In some cases, they may leave gaps between the fittings, and make up the difference by shortening a pipe spool.

So the bottom line is: 1) yes, there are gaps between the welds 2) butt-weld fitting charts do not account for these gaps 3) these gaps can be ignored by designers because they will be compensated for by the fabricators.

Wayne

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