Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Pipe Support Forces for Transient Flow

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I agree with what you have said, except that it seems to result in "no consideration of transient pressures" if a detailed transient pressure analysis is not done.  I would rather at least have a "minimum percentage of maximum operating pressure" as an unbalanced force, to ensure that at least some unbalance has been accounted for. 
 

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com

 


From: Mark D. Anderson PE [mailto:mark(--nospam--at)alaskaengineer.com]
Sent: Thursday, February 16, 2006 2:43 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Pipe Support Forces for Transient Flow

I believe the reason for the absence of minimum design forces/guidelines to quantify dynamic transients is that the problem(s) defy generalization. 
 
Rapid opening valves produce the same type of effects as rapid closing valves, and the transient characteristics depend on many factors, generally including rate of opening/closing, pressure differential, speed of sound in the fluid medium, distance between changes in piping direction (even though the problem is not one of fluid momentum), mass of the piping between changes in piping direction, presence of any surge attenuating components, etc.
 
A non-conservative "generality" is potentially dangerous...
 
Good field data to measure the pressure transient(s) is a luxury that is hard to beat, if you can live with the experience of getting it... 
 
Mark D. Anderson PE
Anchorage
----- Original Message -----
Sent: Thursday, February 16, 2006 10:39 AM
Subject: RE: Pipe Support Forces for Transient Flow

Since Rich Lewis brought up pipe support design, I have other questions related to design forces on pipe supports. 
 
It seems to me that a piping system with fully restrained pipe joints should not have any unbalanced external forces due to either internal pressure or flow, when under steady state flow conditions (except for vertical weight).  However, when rate of flow changes, such as due to valve closure, there will be a pressure wave in the pipe that will cause unbalanced forces at pipe bends - such as "water hammer" effects.  For major piping systems, detailed transient flow analyses can be performed using computer software.  But for many piping systems, such transient analyses are not performed. 
 
So the question is, if a detailed transient analysis has not been performed, do any standards or guidelines define a minimum design force to be applied to an anchor for a straight pipe run between two bends?  If the piping only undergoes thermal changes due to ambient temperature changes, there would only be minimal axial force due to friction of the supported piping.  But it seems to me that there should be some minimum recommended design force for the anchor to handle the unknown transient flow forces. 
 
The book "Piping Handbook" (Edited by: Nayyar, Mohinder L., 2000, McGraw-Hill) provides some useful discussion of flow transients and recommends that transient conditions be considered in pipe support systems.  But it stops short of recommending design forces where a transient flow analysis has not been performed.  So far, I have not found a good source of information for such design.  What do engineers who regularly do pipe support design do when given a piping system to design for but without unbalanced forces defined?
 
(Rich, I recently reviewed a piping system very similar to your arrangement, except that it did not include expansion loops.  The piping was shown to be supported from below on a steel frame - the pipe-to-frame support details were still being worked out.  I proposed a single anchor point near the middle of the straight run, but the above question came up about what force to design the anchor for.)
 
William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com