We are currently designing a FRP piping system for a client to BS 7159 and a query re the SIF calculations has arisen.

The client is concerned that the SIF values as calculated by BS 7159 are too conservative.

Has anyone any suggestions re where else to look for "standard" SIF information for FRP piping components? (As much as FRP design can be called standard).

Any suggestions/recommendations would be appreciated.

You might want to take a look at the ISO standard for FRP systems -- ISO 14692. This standard has basically taken the flexibility and SIF equations directly from BS 7159 (since there seems to be no other publicly available information on FRP SIFs -- I know, I once spent $250 on a text that I thought might offer something along this line) and modified them slightly and/or limited the results, based on "experience".

For example, bend flexibility factors are limited to 3.0, based on experience. Bend SIFs (in all directions) are limited to 2.5, again based on experience. Pressure stress multipliers are defined as 1.0 for smooth bends, 1.3 for miters, in place of the potentially higher BS 7159 values. For tees, SIFs are limited to 2.3 (shades of CAESAR II's original assumptions way back in the late 1980s) and pressure stress mulitpliers are limited to 3.0.

In one of the project I have done , the vendor has provided the SIF to be considered for Tee & Elbow.

So you can try to get it fron the FRP vendor

Would be nice, however it is the vender who is the client is this case and he is the one who thinks the SIF's we are using are too high (even if he can't provide guidelines as to what he wants us to use instead).

As per UKOOA standard, for Bends SIF 2.3 is to be applied for all sizes and for Tees S.I.F = 1.0 is used. We are using the same for FRP piping stress analysis.


K.R.Srinivasan
Senior Stress Engineer
Technip/Malaysia
email:krsrini@pacific.net.sg

As per UKOOA specification, Part 3 section 6.3.3, SIF is determined as per BS 7159. While stress analysis is carried out as per BS 7159 or UKOOA, SIF should not be altered as specified in code . However, user entered SIF may be used while stress analysis is carried out as per B31.3. SIFs are normally provided by vendor. In absence of vendor data, the SIF values for elbow, reducer and tee are 2.3, 1.0 and 1.0 respectively may be used.
Regards,