Direct Welding of Fittings to Flanges (ASME)

There may be some close-coupled situations that could prevent installing some of the flange bolts.

Fitting-to-Fitting

By James O. Pennock and Dave Murphy

The following statement was made in a communication about welding two fittings directly to each other. This situation also applies to a fitting welded to a weld-neck flange or two weld-neck flanges welded together.

"Fitting to fitting welding is not permissible; a (piece of) pipe shall be (placed) between (all) fittings."

This is an example of someone giving 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 cost of additional insulation and heat losses.

· the cost of adding another potential leak point even if the weld passes initial NDE and hydro.

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? Because it is amateurish, wasteful and improper piping.

That "rule" is especially crazy in shipboard situations, where compactness may be of the essence.

Also don't forget that in pump suction piping, it is usually advised to have a straight pipe of length = 6 x diameter before entering the pump.

I'm surprise to hear these words for the second time at that forum. I decide with a full power of my mind that there is no any restrictions to weld any fitting directly to any other one or to a flange. And nothing in piping nor pressure vessel ASME codes nor standards which forbidden welding of fittings directly into each other nor to a flange.

Go ahead and do what you want, and only don't forget to consider the rules of ASME IX related to WPS's, PQR's and WPQ's.

go ahead weld. just as much as possible use same type of material. if not just make sure the welder knows the preparation and welding rod to use.

Thanks a lot everyone!

There is no restriction on doing so. The reason why a piece of pipe is recommended to put in between two fittings is due to following reasons: 1) When fitting to fitting is welded, and due to any reason a crack has developed in weld found during Radiographic Testing, has to be removed by cut-out of Weld Joint, according to API 1104. Cutting weld out by Oxy-Acetylene Torch would spoil both fitting, if not being careful by torch cutting. Plus it would take much longer time to remove old weld up to heat affected zone. When you grind off too much from the heat affected zone you loose perfection in fitting measurement and lead to make gap, if you have pair of flange the end. When you have piece of pipe welded in between two fittings, you can mount 'cutting and beveling' machine on pipe and can remove old weld precisely without loosing measurement of pipe fitting. 2) When you make final tie-in of welded spool with flanged joint at the end, it provides flexibility in the segment to pull two spool together with least stress on the weld joint. 3) Spool with pipe piece in between two fitting endures much easier to operational fatigue such expansion contraction due to heat and cold. 4) Fitting to fitting weld mandates selection of electrodes which produces fine grain in the weld deposit or otherwise heat treatment is required for high pressure piping assembly. 5) Possibility of leak through mechanical joint is higher in spool with fitting to fitting weld.

6) When repairable defect is detected in fitting to fitting weld, repair is difficult in small diameter pipe and lead to cut-out the weld and bring you to situation as in para 1). A. W. Siddiqui