RE: Friction Effects in Piping Systems

From: <Steve>
Date: Mon Apr 21 2003 - 05:39:00 EDT

Hi Kaustubh

I refer you to paragraph 119.7.3 of B31.1 - 1986:

"In calculating the flexibility of a piping system between anchor points, the system between anchor points shall be treated as a whole. The significance of all parts, such as supports or guides, including intermediate restraints introduced for the purpose of reducing moments and forces on equipment or small branch lines, shall be considered."

It sounds as if the company you are referring to must be referring to some other code; perhaps you could ask them which code complies with their suggestion.

Often the additional loads induced by support friction are very small in relation to the other loads. However they must be considered. In some cases, brief analysis may result in the engineering judgement that they may be ignored. In other cases a different conclusion may be reached.

The statement that friction forces (always) disappear after a time is incorrect. Proof is the handbrake in your car when parking on a hill. Viscous forces yes (in this case), friction no.

However I have had some concerns seeing considerable correspondence regarding the use of teflon and the like to reduce shoe friction coefficients. If a piping design needs the use of these low friction materials to perform as designed, then the robustness of the design appears questionable.

Unless the company is referring to some specific set of circumstances, and can validate, I would ignore their suggestion. Sounds like they may be trying to chisel external design charges.

Cheers

Steve McKenzie

-----Original Message-----
From: KAUSTUBH JOSHI [mailto:kvj@epc.ltindia.com] Sent: Monday, April 21, 2003 3:35 PM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] Friction Effects in Piping Systems

Hello All,

A few days ago, a world known consultancy & EPC company suggested us the following:

1. While performing the static analysis (flexibility analysis) of the piping systems, it is not necessary to consider the friction forces. The friction forces are short time generated loads, and act on the system during the thermal expansion. The friction forces diappears after the thermal movement of the piping. That's why friction should be excluded from static piping stress analysis (flexibility analysis).
2. There will be no friction at the guide side surfaces or the limit stops. The friction will be there only for the resting supports.

What are your views on these?

Regards,

Kaustubh

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Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Received on Mon Apr 21 05:39:00 2003