steel corrosion rates due to atmosphere exposure? 1

[MMagrane]

Hello,
I'm trying to figure out how external corrosion rates, on pipelines that are above-ground and exposed to the atmosphere (let's say a dry desert area, minimal humidity on a span), are affected by a protective coating such as paint. Yes, I do understand that it will slow a corrosion process down, but by how much? What would be a good prediction rate for that scenario besides the standard API rate:
rate = depth of anomaly/age of pipeline

All responses are appreciated! Thank you!

 

[stanweld]

In our pipeline system in dry desert locations, no corrosion was observed after 50 years exposure on painted pipe. Pipe was repainted at approximately 20 year intervals. Proper paint selection is paramount.

 

[unclesyd]

Checkout this post by strider6.

thread338-216863