First off which code are you using for your buried piping?
Second, it probably doesn't matter because all codes require you to calculate the stresses the pipe is under during operation.
One of those stresses is thermal expansion.
Therefore it is required. Now how detsailed you make tht analysis is a different question and that will depend on your routing, your design, the material, the soil, the installed temperature etc etc.
The pipeline design codes have simple calculations for retrained and un restrained pipe.
If you have a process fluid of 45C, experience tells me that there shouldn't be a bi general issue, but you're getting close to the limit where it might be in a particular location where other stresses or bending occurs.
So, IMHO, your opening sentence "Pipe stress analysis is required for process piping under temperature having significant expansion" is not correct. Stress analysis is required for ALL process piping, but if there is no large expansion then there shouldn't be a big issue and you might be able to do it quite simply and in a straightforward manner.
just noticed your discrepancy - title says 48C, post says 45C. which is it??
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.