Hi oatty

To make the thing simple...

Since your pipe is going underground I guess temperature is quite less so there is no much movement expected at interface, I think consider the interface as Anchor. For the above ground piping provide additional flexibility ( May be add one additional elbow) to cover up interface movement accuracy.

You might attach sketch of above ground & underground piping mentioning Diameter, thickness, temperature & pressure to comment better for your particular case.

Regarding my previous statement, since underground & aboveground pipe is connected so if you only consider underground piping to find interface movement it will not be so accurate, because above ground piping also affect the interface movement.


Regards

Habib

Email habibur21@gmail.com