Hello,
Required pipe wall thickness (schedule) is ALWAYS related to the design temperature and pressure (and it is also a function of the piping material and its Code allowable stress). Also, the choice of schedule depends upon whether the pipe is seamless or seam welded. So, the answer to your question is that there is no easy answer to your question.
If you had A-106, grade B carbon steel pipe and the service were saturated steam at 150 psig and 366 degrees F. then standard schedule pipe would be appropriate up to but not including NPS 30 (in the smaller diameters there would be a lot of margin for erosion, corrosion (internal and external), abrasion grooving and threading - you were considering those things were you not?). Then there is the issue of how your piping system will be fabricated. Will you use all standard fittings, and if so, what standard? If you fabricate a branch connection you will have to do some additional calculations. It would be best to seek the assistance of a good piping engineer.
Regards, John.
