ANSI B 31.3

Start with what is in it, its temperature and its pressure.

You read the Process Piping Code (ASME B31.3) understand the terms and calculate the minimum required wall thicknes, in accordance with the instructions.

This, of course assumes that you know what piping material that you desire and the diameter of the pipe that you need.

The code equation that must be used is not anything that a 12 year old child cannot handle.....

What is your real question ?

In addition to all of the good information you have received on this post I would add that after (if) you determine the minimum applicable pipe wall thickness:

Determine/know the ambient conditions and environment you are installing the pipe in and account for abrasive, corrosion, and vibration damage from those conditions.

In many cases the wall thickness needs to be increased due to the environment of the application.