Dose a welded splice have to be 12" from the end, or is that only if the end gets welded, or maybe this is a myth?
Is the 12" to keep the HAZ away from a welded connection? Dose it pertain to plate as well as shapes? Where, in what code is this, if it is so?
Ahhhh...the infamous 12" pup, 2 times (or 3X) pipe diameter minimum pup, illegal pup length, etc debate. Never have seen it directly addressed in any code. Sometimes it is defined in site specific documents. A couple of issues do arise from using too short of a splice though.
1) The only really severe consequence of using short pups is overheating the pup beyond maximum inner-pass temperature. There just isn't enough mass to conduct away all that heat.
2) When using short pipe pups, as often happens in pump tie-ins and valve stations, both ends need to be tacked and welded together or run the risk of warping the free end of the pipe out of round.
3) And finally. It just looks unprofessional. (Refer to Industry Standards debate in the forum archives)
Hi guys,
AWS D1.1 Clause 5.22.3.1 - No two girth welds shall be located closer than one pipe diameter or 3 ft, whichever is less.
Regards,
Shane
Shane,
I havn't D1.1 before me so I'll ask you: doesn't the clause end with a phrase like " .......... whichever is less, IF AT ALL POSSIBLE" or something similar?
Don't any of the ASME B31's say the same thing, even with other words?
In my 35 years of project engineering, either in erection or design, I've seen many times the need to reduce that distance because it was impossible to keep it.
Giovanni S. Crisi
Sao Paulo - Brazil
The code paragraph Shane posted is the only one I know of. And in all the years I've been around this industry I have never seen any definitive study stating there is any problem with short pups. They are engineered in all of the time. It just doesn't look good but it is done every day and especially with expensive alloys when you start getting to the end of the job and buying more full joints would be very cost prohibitive.
For SHAPES:
I use 1' min splices in the shop just so that I have room to UT from two directions, especially if the main member is less than a foot too short due to a customer revision or saw mistake. I just get them to add on a whole foot if the piece is (ie. 4") too short, because they will cut to the correct length after I have UT'd the joint anyway. Gives me wiggle room...LOL
Keep in mind that Pipe may be a whole different ball game....I don't know.
I deal with pressure vessels and we are also iffy about toe to toe distances on welds, which is more or less the same discussion. From a stress distribution point of view it should be kept in mind that a weld is a discontinuity and therefore a stress raiser. Having to many of these close together is not a good idea, especially if you are expecting expansion contraction on piping. Another issue although I don’t think as important (depend on which professional you speak to) is flow of the medium in the pipe, root penetration can cause turbulence which in turn my lead to some form of erosion corrosion, again too many of these too close together is not good.
Something to consider
Main concern with turbulence caused by root penetration is when they're close to a flowmeter. The turbulence will interfere with the meter operation.
Giovanni S. Crisi
Sao Paulo - Brazil
Hi All!
Just to add to Giovanni's post, in typical power generation situations, proximity of weld roots (discontinuities) can cause turbulence within the media (High Pressure Steam), which will enhance the erosion effects of high pressure steam! I have seen this personally and it is quite dramatic when failure occurs! It can cut through steel quite easily!
Regards
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