A. Soto

I presume your line is probably connected to reciprocating compressor.
The common and simplest practice is to simply model "Y" and "guide" with friction.
The Best practice depends on what data you can get from the vendor/supplier. If you get the stiffness values of lining material(fabrekka) you can model it as a blinear restraint with K1=stiffness of lining material and K2=default stiffness for steel provided your support is rigid enough.

If you can get the value of bolt tightning forces, then the same should be applied in above restraints.

Generally there are two types of hold down clamps. One which is described above packs the pipe in top half circumference. The other type is like just touches the pipe on the top and have large gaps in both sides(guiding directions). When thermal movements needs to be allowed e.g. near some bends, such type of clamps can be used. There will not be guide restraint in this type of clamps.