That's the job of your materials engineer to look at all the risks of internal and external corrosion.
Dry gas and pure liquids have no or low risk of internal corrosion. Wet gas or liquids with a lot of water, especially with CO2 or H2S can corrode a lot and calculations exist to calculate how much with and without inhibitor. Salty oxygebated water is particularly corrosive.
External corrosion risk is normally low with good coatings and CP.
More pipelines recently are being designed with zero corrosion allowance.
CA is a rather expensive blunt tool and more people are realising this I think.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
NACE Corrosion Data Survey is a good place to determine corrosion rate based on the fluid and the pipe material. It provides data tables for different pipe materials and their corrosivity to different chemicals/fluids.
