The general starting point would be the either the paint manufacturer's recommendation or by you searching the paint datasheets on their websites for performance information:
for example.
Experience has dictated that, in general, the manufacturer's data really needs to be verified by appropriate performance testing which will take us down a different thread.
If you are insulating the pipe, review NACE RP 0198 to get guidance on the paint systems to be used. You can also get guidance from the eight parts of ISO 12944.
For your information, our company has tested and qualified the following system for atmospheric exposure in an arid environment:
1. Polyamide epoxy primer 50 microns
2. Polyamide epoxy hi build intermediate 100 microns
3 Aliphatic polyurethane topcoat 50 microns
Total DFT: 200 microns.
Thermal spray aluminium could also be an option for you.
Take a look at NORSOK M-501
Good luck
Steve
Steve Jones
Shell Iran Offshore Ltd, Dubai