The following was recently
posted on one of the piping forum web sites.
"Fitting to fitting welding is not permissible;
a pipe shall be (placed) between fittings."
(Posters
name withheld)
This is an example of wrong
information or wrongly interpreted information that has gotten started by some inexperienced
teachers/instructors in the past few years.
This specific statement is
totally incorrect when applied to 3" (80mm) and larger butt-weld fittings. Any butt-weld fitting or weld-neck flange can
be directly welded to any other butt-weld fitting or weld neck flange without the
need for any extra piece of pipe (Pup piece) between them. It is just a butt-weld and if I cannot make a
butt-weld between these two round, beveled-end, schedule 40 carbon steel (fitting)
objects what if I need to join two other round, beveled-end, schedule 40 carbon
steel pipes. What do I put between these
two pipe objects? Yes! It does sound a
bit stupid.
For butt-weld fittings the only
exception to this is; when there is an overall dimension requirement that is
greater than the combined total dimensions of the two fittings.
The only fittings that
cannot be connected directly to each other are screwed or socket-welded elbow
and Tee fittings. Screwed and
Socket-welded assemblies do require pipe, a pipe nipple or a swedge nipple
between these fittings.
I suspect that someone,
somewhere was listening to instructions about the make-up of piping assemblies
for 2" (50mm) and smaller screwed or socket weld piping and then mistakenly
applied the instruction to all piping including large-bore butt-weld piping.
This is not the first time I
have seen this. Over the years I have
gotten many sketches via E-mail asking about some certain aspect of a piping layout. Some of these sketches have shown this same faulty
piping error. One such case showed a
common control valve station (manifold) which had 11 (eleven) extra and unnecessary
"Pup" pieces where butt-weld fittings could have and should have been welded
together. It was a waste of money.
When this is done at a point
where it is not required, it does nothing to improve the function of the pipe configuration. The only thing it does do is add cost to the
job. The added cost comes from both a
direct and an indirect factor.
The direct cost includes:
·
the cost of the pipe
·
the cost of
cutting the pipe and prepping the ends for welding
·
the cost welding
·
the cost of extra
NDE
·
the potential cost
of a bad weld discovered during hydrotest that needs to be cut-out and re-welded.
The indirect cost includes:
- the cost of the added space required for a
complex piping configuration when multiple pieces of "pipe" (Pup pieces)
are added between every fitting to fitting make-up.
I strongly urge all who read
this,
o
if you are doing
this then STOP! Ask yourself, Why am I
doing this?
o
If you know
pipers who are doing this then tell them to STOP! Ask them why are they doing this?
Why should I not do this is
that it is amateurish, wasteful and improper piping.
Fitting-to-Fitting Welding of Piping
Re: Fitting-to-fitting make-up of piping
