Predicting Pipe Deflection
Predicting Pipe Deflection
(OP)
I am trying to determine the deflection of a pipe between two supports. Does anyone have an equation that I could use to predict the deflection. I want to take the temperature, psig and saddles into account. I'm not asking for the answer just the way to find it.
Thanks
Thanks





RE: Predicting Pipe Deflection
The following is for Horizontal Pipe.
It is similar to find a deflection for a simply supported beam with uniform load distribution and or local forces as a valve, saddle and ... on it.
As far as i know in this case, deflection is not affected by internal pressure or temperature of the pipe.
Hope it helps,
Frank
Calgary
RE: Predicting Pipe Deflection
Predicting deflection of plastic or composite etc. pipes can be a much more complex procedure, as I believe the deflection of such pipe beams is much more time and temperature etc. dependent (and to do a good prediction job in such cases probably requires more intimate knowledge of the material, exposure conditions, and "long-term modulus(i)" etc. of the material(s). Incidentally, unlike e.g. metal pipes the long-term modulus of plastics might be only a very small percentage of a short-term or instantaneous modulus, sometimes requiring many supports/short support spacings for such materials.
RE: Predicting Pipe Deflection
Sag = 17.1 * (w * (L^4) / (E*I) (inches)
w = weight per foot of pipe+liquid+insulation (lbs/ft)
L = pipe span (ft)
E = modulus of elasticty (psi)
I = moment of inertia (in^4)
Most span tables are based on a maximum deflection of 5/8", which is intended to keep the natural frequency of the span above 4Hz and therefore less likely to resonate in the wind.
Oh and, temperature is a factor as it will affect your elastic modulus, especially at high temperatures.
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
RE: Predicting Pipe Deflection
RE: Predicting Pipe Deflection
RE: Predicting Pipe Deflection
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
RE: Predicting Pipe Deflection
RE: Predicting Pipe Deflection
Turn on your calculator and run the numbers. Ed gave you the equation above and you can go to B31.3, Appendix C, Table C-6, to look up the E (Young's modulus) for the material and temperature that you are using. Try different "E"'s in the Kellogg equation and see the difference. Not a great difference for some carbon steels but as an extreme example if you have aluminun ............
Reductions in Young's modulus (E) due to temperature can really cause a significant redistribution of loads over a pipe support (hanger) system especially when spring hangers are in use. That is why we always recommend that the hanger design case for high energy power plant piping systems be run with the hot Young's modulus (you must use the Young's modulus at 70 degrees to calculate the stresses though).
Regards, John.
RE: Predicting Pipe Deflection
RE: Predicting Pipe Deflection
I turned on my computer and ran a simple model with Caesar II software and changed the temperature from ambient to 650 degree C and there was no change in the deflection at the middle of the pipe.
This is a very good point to discuss this with COADE guys who develop this software.
Thank you.
RE: Predicting Pipe Deflection
You are right, I am wrong, I am sorry. I regret if I offened you.
regards, John.
RE: Predicting Pipe Deflection
I ran a simple A-106B model with AutoPipe software and changed the temperature from 70 to 750 degF. Provided I changed the default settings to use the hot modulus, there was a change in deflection 20%. For the model, the deflection went from -0.375” using 70 degF modulus to 0.445” using the 750 degF hot modulus. I am not a Caesar II user. Is there a setting to change the default to use the hot modulus in Caesar II? According to their web site, Caesar II version 5 gives “The ability to perform an analysis using the “hot” material elastic modulus.”
Regards
RE: Predicting Pipe Deflection
Yes, you are right. The similar setting is also available in Caesar II, but as you said, by default, this is not taken into account unless you clicked it in the settings.
Thank you again.
RE: Predicting Pipe Deflection
Where and which book is the euquation stipulated?
Thank you very much!
RE: Predicting Pipe Deflection
It's quite expensive to buy:
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TTFN
RE: Predicting Pipe Deflection
The equation in the Kellogg book is just a standard beam deflection equation. Nothing special about it just because it is in Kellogg. The whole set of such equations is in Roark's Formulas and in any number of other introduction to mechanics books. These text books come and go and a large number of them can be had on the cheap from various used (or overstocked) book sellers.
Regards, John.
RE: Predicting Pipe Deflection
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
www.waterhammer.bigblog.com.au