Pipe Support Friction Factors 3

[DSB123]

Just wanted to bring this old one up again.
Friction Factors for pipe supports where a pipe shoe sits on steelwork. Nearly everyone uses a friction factor of 0.3 for steel to steel contact. How can this be correct for pipe systems running along pipe racks or outside where we all know that maintenance is not what it used to be. The general friction factors for steel to steel are for static friction are around 0.72 to 0.74 and for sliding friction the values are quoted as 0.57. So I ask what is the justification of using 0.3 for pipe stress analysis ? Does the pipesupport "know" it is a pipe support therefore the maximum frictional load cannot be greater than 0.3 times the perpendicular load ? No is the answer so come on the Pipe Stress guys out there make a justification for using 0.3 in your pipe stress analysis when before movement occurs a load of 0.72 times the perpendicular load needs to be achieved and to keep the pipe moving a loading of 0.57 times the perpendicular load needs to be maintained?

 

[DSB123]

Whoa,
Even Peng uses a friction factor of 0.3 in Figure 4 and a friction factor of 0.4 in Figure 1. So even Mr Peng seems to suggest in this brief paper that friction factors vary!!!! End of debate I think!!!!

 

[TGS4]

I think that you will find significant agreement between what I have written above and LC Peng's paper. (Perhaps in the far distant past I have read his work and simply absorbed it into my engineering philosophy ).

 

[DSB123]

Agree TGS4 but as you can see there are those amongst us that think friction factor is 0.3 NOT 0.4 or 0.5 etc but must be 0.3 always!!!!

 

[BigInch]

Or effectively 0.1

Learn from the mistakes of others. You don't have time to make them all yourself.

 

[DSB123]

With PTFE of course!!! otherwise in your dreams!!!

 

[TGS4]

Actually, if you read LC Peng's paper, he also states that in some instances, a zero-friction case may be the governing case (particularly around rotating equipment or other nozzle-load sensitive equipment).

I have always agreed that a range of coefficients must be examined. And a single value, whether it is 0.3 or 0.72 does not encompass the true understanding of how friction effects piping systems.

 

[DSB123]

TGS4,
I agree TGS4, I always run an analysis with friction and one without to ensure worst cases are covered. Perhaps we should all use the effective value of 0.1 proposed by BigInch then we would not require any low-friction (PTFE/PTFE or PTFE/SS) supports anymore!!! (Only joking )
Friction modelling is only guesswork at the best of times. My original point/question was to get a feeling of what others use for the friction factor but it seems most just "fit the blinkers" and use 0.3!!!