Expansion Joints required? 1

[hvacpiper]

First off,I'm a long time lurker,first time poster.I have to say I really appreciate all the information I've gleened from the discussions on this board.

I am a piping installer,generally I do alot of larger size commercial HVAC,institutional and industrial process pipe.

I seem to end up with alot of "cookie cutter" engineered drawings,that will show runs of pipe,with an expansion loop drawn somewhere in the middle of the run,anchors are shown,but nothing is dimensioned.It seems to me that no calculations were done,and the loops were just drawn in as a C.Y.A. type thing....


Onto the question... Why would chilled water lines require expansion loops?(these lines are 6" A53,100' straight run,plus a few elevation offsets that operate @40F ,are installed at @60F and all equipment connections are via flex connections)...even on identical HW lines that operate at 180F,I question the need.The specs on this particular job,conform to ASME B31.9,but after looking through B31.9,I couldn't find any hard numbers,relating to expansion.Even if the force on the equipment was supposed to be zero...I don't see the need.This isn't superheated steam in a nuke plant...

Again,I'm not a contractor,I'm just a dumb pipefitter wondering if this is lazy engineering,or I'm missing something.The amount of money spent on these "expansion loops" would pay my salary for a few weeks ...at least.

 

[sspeare]

FOR: Dimensions of Expansion Loops - see this link for the required dimensions & capacity of expansion loops for steel pipe:

http://www.engineeringtoolbox.com/steel-pipe-expansion-loop-d_1069.html

FOR: Expansion Coefficient - see this link for the thermal expansion, or contraction, per 100 feet of steel pipe:

http://www.engineeringtoolbox.com/steel-pipes-temperature-expansion-d_38.html

I agree that the thermal movement (contraction) for CHILLED water will be "small", since the delta T is only 20 degrees: from 60 degree installation to 40 degree operation. And yes, the designer should still calculate this "small" chilled water movement, and put values into the Exp Joint Schedule. But I disagree with your statement that HOT water at 180 degrees would not require expansion loops. The designer has to look at the system and decide how to handle the thermal movement. Sometimes I can accomodate the movement by taking advantage of the flexibility of the piping system. But, sometimes the piping flexibility is not enough, and I have to call for expansion loops. Each job is unique; you can't just say you "question the need" if you don't have the facts.

Finally, you might want to visit

http://pipeng.com

because there are several on-line expansion and stress calculators at that site. If you run a few problems, you'll get a sense of the stresses created by restraining pipes too much - inother words, not allowing for expansion. I highly recommend you visit this site.

Hope this helps. Good luck!

 

[Duwe6]

And keep in mind that the 'basic length' of your pipeline was established at whatever ambient temp was the day the last [tie-in] weld was made. If your system was built in winter, use 35 or 40°F for that temperature.

Thus, as sspeare said, there will be 140 to 145°F of thermal growth. At 200-ft, this will be 2 inches of growth at 70,000 psi times the area of your pipe wall. 3"NPS Sch40 = 70ksi x 2.228 sq-inches = 156,000 pounds.

Your hot water line has the force to smash a hole in a robust wall. Put in some 90° ells for expansion relief.

 

[hvacpiper]

Thanks for the links,I frequent engineeringtoolbox quite a bit..I need to spend some time looking at pipeng.com

I didn't mean to infer that 180f water isn't hot enough to require expansion consideration.I understand there are considerable forces at work here...

Is it common practice to place expansion loops in piping systems without calculations?Obviously during the engineering phase of a job,every twist and turn of the piping is not known,(particularly in congested ceiling spaces of modern day buildings)So who in turn is responsible for maintaining adequate tolerences for thermal growth? The engineer,the designer...the installer?

 

[sspeare]

In my opinion, the Engineer is responsible. Full disclosure: I'm an Engineer, a P.E., mechanical. This type of question comes up all the time in my ofice. I say "show them on the drawings", but the bean counters squeal that we "can't spend any hours!" And so it goes .......

The expansion loops should be drawn as a "standard detail", along with a Loop Schedule that calls out the specific dimensions for each loop: EL-1, EL-2, etc. Each loop should be indicated somehow on the piping plans. The loops don't necessarily have to all be DRAWN on the plans; it can be difficult to show them at 1/8" scale. But they can all be called out as, for example: "provide EL-1 here, see Detail Sheet xxx for dimensions."

Unhappily, it is common to leave out the detail and say on the drawings "contractor to provide all expansion loops and compensation, as required." I don't like seeing it done that way, but it happens because of the bean counters who sign the paychecks.