Please do a search on this forum regarding the FRP piping codes UKOOA, BS7159 and ISO14692 compared to B31.3. I have written about this extensively in other topics.

There are no FRP piping codes in CII that reference cross-country (buried) piping. Be careful when modelling such FRP piping, especially regarding the used coupling between pipe spools.

The difference in results between ASME and BS may be the bourdon effect, but also the way the code stress is calculated is different (check the CAESAR II quick reference guide).