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RE: Pipe Support Forces for Transient Flow

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Bill,
Very interesting point(s).
I do non't recall eactly but very few papers published in the ASME Applied Mechanics Journal.
In the past (in very early 1980) , I did analyze the system using three dimensional moment distribution based on the papers published in the ASME Applied Mechanics and  Pressure vessels and piping journal. Based on the published papers I did develop a rule of thumb, but my supervisor didn't like it. so I did longhand calculations using moment distribution method.
No computer erra, the would be a simple matter.
Himat

>>> ShermanWC(--nospam--at)cdm.com 02/16/06 2:39 PM >>>
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 

 


________________________________

	From: Rich Lewis [mailto:seaint03(--nospam--at)lewisengineering.com] 
	Sent: Wednesday, February 15, 2006 3:45 PM
	To: seaint(--nospam--at)seaint.org 
	Subject: Pipe Support Detail
	
	

	I read some about this subject in the archives but couldn't find
the answers to my questions.  I have a situation where I need to support
two 12" and one 14" diameter horizontal runs of water lines about 20
feet above the floor.  I am not able to hang them from the roof
structure so I need to design a frame to support them.  I will have
anchor frames at each end and an expansion loop in the middle.  Right
now I am looking at the typical intermediate frame supporting the pipes
about 23 feet on center, not the anchor frames.  I was considering a Tee
type frame or a vertical stick frame with outriggers to support the
pipe.  I prefer the Tee system because I could more or less balance the
loads across the top.  I was told if I could stack the pipes vertically
instead of horizontally side by side it would help with the expansion
loop.  Using a stick type frame with outriggers puts all the load
eccentric to the column on the same side.

	 

	I think what will influence my final decision will be the type
of connectors of the pipe to the frame.  There is no insulation on the
pipes.  As I see it I need some type of slide or roller connection to
allow the pipe to expand and not push the frame.  I looked at bare steel
friction sliding and decided it was too great to fight with the frame.
I looked up a sliding type pipe connection on the internet to set the
pipe on the top cross member of the Tee.  I was thinking that maybe if I
hung them from the beam instead of sitting on top I could have a swivel
hanger type connection.  If I use one of these though I would think I
need a swivel at the pipe bracket and at the beam hanger nut location.
I didn't see any like this.  As I see it, this would also put a slight
rotational moment around the support column.  I saw there are roller
type swivel connections.  This would take out the horizontal component
of the pure swivel.  Unfortunately there load carrying capacity was
lower than I need of about 3,500 pounds.

	 

	I'm looking for suggestions in two areas from engineers who have
experience in pipe support:

	1.	Is it better to have the supports sitting on a cross
beam or hung form a cross beam? 
	2.	What connection material would be recommended to allow
the pipe to move longitudinally relative to the support frame? 

	 

	Thanks for any insight.

	 

	Rich

	 


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