Is anyone aware of a Code or standard that states the minimum acceptable length of a pup piece or spool piece or minimum distance between 2 welds? Boilers and just piping in General.
What Big Inch said - that is the only rational standard that I know of.
Three different companies in Ft. McMurray told me "well, 18 inches of course" when I asked. And when I pursued the reason I only got a "well I dunno, that's the way it has always been" or "well that is the smallest length to which the contractor could set his pipe cutter" or the variation "smallest length that fit in the bevel grinder rig". I reckon one explanation is as bad as the others. Some of the USA oil companies say not less than one nominal diameter but that does not cover very small bore piping when you consider the "keep the HAZ's from overlapping" rule. Of course at those diameters they use a lot of socket welds.
This was my answer to a related question on another forum.
The question: What is a Pup Piece?"
My answer: What is it? Okay let's see if we can answer this question once and for all. In piping we all know we have two basic situations; one is Fitting-to-Fitting and the other is not Fitting-to-Fitting. With the first, there is nothing between one fitting and another except the weld. Therefore we call it "Fitting-to-Fitting or "Fitting make-up" With the second, the required overall dimension does not allow for Fitting-to-Fitting configuration. We then have an ELL, gap, ELL or ELL, gap, Reducer, ELL or ELL, gap, Flange or ELL, gap, reducer, flange or some combination of standard fittings BUT not Fitting-to-Fitting. There is that short gap between two of the fittings. This is an all too common natural occurrence in piping design. This short gap is where a piece of pipe must be placed (cut, beveled, fitted and welded) to connect the two fittings that don't touch. The short piece of pipe is called a "Pup" piece. The piece of pipe or "Pup" can be pretty much any length however when it gets to be around a foot in length it is no longer called a "Pup". A long piece of pipe is just a piece of pipe. The really short ones are called a "Pup". The only restriction for the length pf a "Pup" piece is common sense or a company imposed minimum length. This minimum length is defined in different ways by a Lead Design Supervisor or company and there is no absolute Code restriction or commonality. Individual pipers or a company minimum may consider the pipe wall thickness, the weld bevel, the heat effected zone, or the real or perceived ability of the shop to make a weld. There is no magic rule and there is no common industry standard. In referring to the proximity of butt welds in pipe. This question has been asked many times. The answer is the piping Codes do not provide specific guidance. In this situation, you must use engineering judgment such as, locate the butt welds as far apart as possible to avoid overlapping weld "heat affected zones" and stress concentration effects. For girth weld spacing, a criterion that has been used for many years is: the greater of 2 inches or 4 times the wall thickness. You might also want to talk to a good Welding Engineer as it could be dependent on the actual welding process. If this is for proximity of weld joints to one another there could be other concerns--again the Welding Engineer could help you.
I have generally used the criterion posted by pemmpiper. However I know some companies that require clamps to be used for all pipe welding, specifying minimum pup sizes that take into account the space required to fit clamps. Regards, Bill
How wide do you think an HAZ is going to be? To answer the very first question:
BS 2633 Class I Arc Welding Of Ferritic Steel Pipework For Carrying Fluids
as alluded to in the 'rule of thumb' thread I referenced and which also finds itself transliterated into at least one major's specification for welding of PIPING whereas that same major would demand one pipe diameter for PIPELINES.
And, whilst we are at it: BS 4515-1 Specification For Welding Of PIPELINES....., clause 11.1 'toe to toe distance not less than four times the pipe thickness'
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Pipe Spools / Pup min. lengths