All piping stress engineers must be aware that while modeling supports or restraints in Caesar II input spreadsheet we have to enter the frictional co-efficient. The value of this co-efficient depends on the supporting surface material and surface roughness. During project bidding stage (ITB Document) the client generally provides the information regarding which friction factor to be used for which surface. Also every EPC organisation prepares their own guideline for using standard friction factor in case not available in ITB document. The following write up will try to provide an idea regarding which co-efficient of friction to be used in what situation. This can be used as a guide only. However project specific data or information will override any word mentioned here.
- Coefficient of friction factor depending upon the supporting interface (i.e, junction between Top of Steel and Bottom of Pipe or Bottom of Shoe/Cradle) shall be applied at all vertical restraint (+Y or Y supports) locations as mentioned below. But if ITB for any project provides separate data then those data shall be considered.
- Carbon Steel to Carbon Steel: 0.3
- Polished Stainless Steel to Polished Stainless Steel/Graphite: 0.15
- Teflon to Teflon/ Polished Stainless Steel: 0.10
- Concrete to Carbon Steel: 0.4
- Pipe to Roll Support: 0.01
- Teflon to Carbon Steel: 0.2
- There is various philosophy among EPC companies regarding the use of co-efficient of friction for guide and directional anchor supports. Some organisation prefer not to use any frictional co-efficient for horizontal supports. However if used the same can be taken from the above table (normally 0.3 is used if no special arrangement is made).
- No friction factor to be used while supporting using rigid hangers.
- In case when Sliding Plate is required, put the comment as “(PTFE/Graphite) Sliding Plate Required” and mention friction factor μ=0.1 /0.15 respectively depending on temperature” on stress sketch. Use Teflon (PTFE) Slide plate up to a Temp of 204 degree Centigrade, above which use graphite plate (up to 540 degree Centigrade).
- Normally the friction factor shall not be applied when modeling bottom type spring. But sometimes ITB document/Client could insist for friction modeling of bottom type springs, in that situation friction factor could be applied as per requirement.
- When the pipe/shoe is supported on the welded rod on the structure then friction factor of 0.25 shall be considered.
To know the actual effect of friction on piping stress analysis refer the article “Treatment of Support Friction in Pipe Stress Analysis” published by Mr L C Peng. Click here to download and read the same
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