Corne,

We have chosen B31.3 from the beginning, and I see that people are still using it for plastic pipe so I want to continue using this code, moreover we are using academic version so only B31.3 available.

I found that your previous comments are right, for plastic piping systems, we have to check the following (according to Chapter 52, Structural Engineering, National Engineering handbook):

1, bending stress < (HDB/FS)*T = HDS*T with T is temperature derating factor

2, deflection < allow. 0.5% span for PVC and 1 inch for another plastic pipes. But the above allowable deflection seems no reasonable because it should be dependent on the pipe diameter and thickness?

3, Hoop stress < HDS

The long-term and short-term strength and modulus are applied differently for each cases depending on the load is long-term or short-term.

Please correct me if I am wrong.

Thanks.