I beleive FRP/GRE/GRP Vessel Vendor provides nozzle allowable forces and moments.

Is there any code or standard to calculate Nozzle allowable forces and moments on FRP/GRE/GRP vessels with respect to size and pound rating?

Does one need to perform any code checks as per BS 7159?

Could somebody define the code checks required while performing FRP/GRE/GRP pipe stress analysis.

Can CAESAR-II perform buried FRP/GRE/GRP pipe stress analysis?

Please be aware that GRE piping material behaviour is not same as Crabon steel. It is very important to get the GRE vendor involved at the earliest in the project.

AWWA M 45, UKOOA and ISO 14692 will give a good insight into the Codal requirements and the related issues.

There are plenty of discussions on this topic in this forum.

Yes CAESAR II can perform a flexibility analysis using FRP/GRE pipe according to either BS7159 or UKOOA.

As stated above, you need to get a vendor involved with this to obtain the proper material characteristics.