Pipe Support Spacing 1

[dcarr82775]

We have a project where we need to provide frames to support some 8" and 12" schedule 40 pipes. Based on the existing framing I want to install the frames at 15'-6"o.c.. The pipes can easily span the distance, but I believe there is a code requirement on spacing of supports. The Mech Engineer on the project claims there are no such rules. Anybody know what the requirements are, if any? thanks

 

[SlideRuleEra]

For industrial applications with steel pipe, unless piping codes have changed (on this subject) in recent years, there are NO specified pipe support spacings. This is because there are so many factors, such as the location and rating of valves, fittings, pipe wall schedule, etc., that any "required" span could be either too long or too short, depending on the details.

The pipe installation companies, such as Grinnell, have long published technical books and (voluntary) guidelines on the subject. To quote from page 158 of "Piping Design and Engineering", Fifth Edition (1976) by ITT Grinnell Industrial Piping, Inc:

"No firm rules or limits exist which will positively fix the location of each support on a piping system. Instead, the engineer must exercise his own judgment in each case to determine the appropriate hanger location."

http://www.SlideRuleEra.net

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[westheimer1234]

typical pipe rack has 20 ft distance between bents..
so 15'-6" is more than ok.. 8" dia pipe can span more than that..

dont step on other disciplines scope of work.. pipe stress/design will tell you if support distance is too long..

 

[dcarr82775]

Thanks sliderule and westheimer. The mech eng doesn't want anything to do with the support racks, so came to us. I just looked at gravity load stresses (plus some thermal changes) in the pipe (with water) and things looked fine at 15'6, just could have sworn there were rules.

 

[smb4050]

You don't state what the pipes will be carrying, if it's a pressure pipe or gravity flow or an interior or exterior installation.

westminster 1234's comments about other disciplines scope is good advice particularly about the pipe stress, so don't indirectly assume that responsibility. Ditto on Sliderule Era's comments, my copy of Grinnell is the catalog PHDE-96. ASHRAE & ASME both address "supporting elements" requirements. ASME B31.1 table 121.5 lists "Suggested Pipe Support Spacing" for water or steam-gas-air service. For water service, it lists 19' for 8" pipe, and 23' for 12" pipe.

Normally what dictates support location is allowable deflection and concentrated loads (valve banks). In some applications, seriously bad things can happen if liquid ponds in a pipe. Ammonia refrigeration piping supports were 7' centers based on ANSI/IIAR requirements. Steam piping is another animal all to itself, so don't go there unless you've done it before. Generally for exterior applications the pipe has sufficient lateral rigidity from bends, valve banks and headers that the pipe actually supports the stands. What I was taught is standard practice is to assume the pipes are full of water when designing the pipe stands, and empty when for wind loads. Of course you have know if that would adequate for your application. ASCE 7.15 addresses requirements for seismic piping attachments. If I recall correctly from the Grinnell catalog, recommended maximum movement for pipe hangers, parallel to the pipe, is 7 degrees, but that needs to be verified. For gravity piping, the stands need to accommodate post construction adjustments.

For trapeze type stands, don't forget to check the deflection of the horizontal support.

 

[smb4050]

I found it, recommended movement for rod hanger is 4 degrees.

 

[ToadJones]

In short, the span of the pipe has to come into play in the design of the pipe --> meaning the support spacing should be given to you by the pipe designer.

 

[Gumpmaster]

MSS SP 58 is another often quoted reference. It has several tables of maximum recommended support spacings.

 

[aswierski]

I deal with this all the time. I typically set my spans based on the following:

1. Assume pipe to be uniformly loaded simple beam.
2. Limit the allowable stress that the pipe would see due to its own dead weight, including fluid (or hydrostatic test conditions where applicable) and insulation to one half of the maximum allowable stress [fb = 0.5Fb]. From this you can get your allowable span.
3. Find maximum deflection [y = (5wL^4)/384EI]. Limit the deflection to 1/4 of the nominal pipe size or 1 inch, whichever is less.
4. The max span should be the lesser value obtained from Step 2 and Step 3.

Note that these steps do not account for any valves (or any other concentrated loads, for that matter) or thermal expansion. For thermal expansion I always refer to our pipe stress engineer and/or pipe stress analysis reports.

Now, to answer your question, I have never seen anything limiting the spans of supports other than the calculations I listed above. (FYI, most of my work is pertains to industrial sites.)

 

[aswierski]

If any of you want, I can forward on a spreadsheet I developed that gives me max spans. Let me know if you do and I'll post it.

 

[dcarr82775]

Thanks for all the responses. There are (2)12"(hot water) and (2)8" (cold water) pipes supported on frames bolted to a concrete wall at 10'o.c.. We need to move the pipes off the wall in a couple of places to allow for some other work. All the valves and such are still mounted to the concrete wall so we just need to support the pipes/water/insulation. I did calcs similar to aswierski described and things work fine at 15'(15'-6 in my original post was a typo, the floor framing is spaced at 7'-6"o.c.). It is just a lot more work to put the frames in at 7'-6".

Thanks all

 

[JLNJ]

Any closer together it will be more efficient to put them twice as far apart and run beams between the supports.

I like greater spacing and beams running bewteen supports for several reasons:

- You can add intermediate members when they need to run a small line (such as a condensate line or electrical conduit).
- The beams help with stability bewteen supports and you might not nned to consider the columns cantilevered.
- Fewer foundations.

 

[JStephen]

We had a project long ago where we had some 18" pipes vertically unsupported for about 75'. They met all the stress criteria that way, but were vibrating in the wind, which was something we hadn't thought of. I doubt this would happen if the pipe was normally full, but something to consider otherwise.