Local Pipe Stress on Saddles
Local Pipe Stress on Saddles
(OP)
We have 10 thru 20 diameter (GA 10 = 0.135") pipes filled with water and supported at 8 ft OC. I am concerned with the local and bearing stresses at the supports (Clevis Hangers & Saddles)
Roark's Formula for Stress and Strain (page 642) has a formula to check these local strsses but I dont feel comfortable with it. Is there something that I should be aware or check besdies the local stresses?
S = k(P/t2) ln (R/t)
P = Load
t = thickness
R = Radius
k = 0.02-0.00012(beta-90) for R/t < 50
k = 0.03-0.00017(beta-90) for R/t > 28
Roark's Formula for Stress and Strain (page 642) has a formula to check these local strsses but I dont feel comfortable with it. Is there something that I should be aware or check besdies the local stresses?
S = k(P/t2) ln (R/t)
P = Load
t = thickness
R = Radius
k = 0.02-0.00012(beta-90) for R/t < 50
k = 0.03-0.00017(beta-90) for R/t > 28





RE: Local Pipe Stress on Saddles
- is there some failure mechanism that is not reflected by the stresses you are calculating?
- do you think the equation is incorrect or unconservative?
- unusual loading or geometry?
RE: Local Pipe Stress on Saddles
Design of Ductile Iron Pipe on Supports
http://www.dipra.org/pdf/pipeOnSupports.pdf
Zick
http://www.codeware.com/support/papers/zick.pdf
RE: Local Pipe Stress on Saddles
RE: Local Pipe Stress on Saddles
RE: Local Pipe Stress on Saddles
You could do what a number of piping engineers/designers do and ignore it. Remember pipe support makers sell you the supporting components, which are load rated, but do not guarantee that when using these components that you are not going to cause overstressing in the pipe - most pipe designers I have come across do not grasp this fact. If you can get hold of the very good book by van Laan covering pipe supports there are sections in there which promote formulae (actually from Roark) for calculating "local" stresses around supports. From what I remember in the example there is a typo so be careful. Anyway very thin wall as you have is vulnerable to buckling and ovalisation as a poster above has indicated. If you are that concerned why not "model" a section in FE. The time to build a simple model is not exhaustive if you have the software.
RE: Local Pipe Stress on Saddles
Also ASCE 79 (power penstocks) for similar (but more comprehensive) analysis & design (large power penstocks).
Bednar (pressure vessels) also has a good section.
For your small pipes, I would just use AWWA M11.
For very thin pipes (ducting), the ducting manual gives a conservative view of these stresses.
RE: Local Pipe Stress on Saddles
Whomever designed the piping system had no sense of piping sizes or codes. (however, he may have been an HVAC designer...)
Specifically, to which code was this system designed to ?
If you have 20"OD pipe with 0.135 wall thickness, you have, essentially, ductwork filled with water.
The thinnest piping schedule in common usage is schedule 5S.... and for 20 inch OD, Schedule 5S is 0.188 inches.
Thank god there is no pressure in this system !! ( or....gulp... is there ??/?)
-MJC
RE: Local Pipe Stress on Saddles
Process pipe for a water treatment plant. Therefore, B31.3