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.
(Just for interest's sake, Australian Standard AS 4458 specifies the following: "The
distance between the edge of two circumferential butt welds shall be not less
than four times the pipe wall thickness or 30 mm, whichever is the greater,
unless the first weld is post weld heat treated (PWHT) before the second
weld.")
Comment:
Most if not all Owner/Operator/Clients and Engineering Companies tend to have guidelines that they impose for their projects. Most of these were formed long ago and were based on the opinion of person in their company who had the power of position and who is now long dead. Today, logic and technology should be considered.
Minimum Pipe Spool Piece Between Welds
Re: Minimum pipe spool piece in between welds
