Pipeline - atmospheric corrosion rate? 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 desert area 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!

 

[pmover]

above ground pipelines are inspected periodically for corrosion, coating problems, etc., especially at the transition locations (where pipe enters/leaves the ground) or in contact with supports. the pipeline/ROW are inspected by aircraft, with any/all anomalies inspected by personnel soon thereafter. any pipeline crossings (arroyos, etc.) that have signs of recent rainfall, are inspected. basically, each pipeline company has internal guidelines/procedures incorporated with required DOT procedures/guidelines to ensure the safe and reliable operation of the pipeline.
sorry, i am not aware of any corrosion rates, per se. it does not mean there aren't any, i am not aware of any.

good luck!
-pmover

 

[gr2vessels]

The corrosion rate cannot be specified for generic cases, because the error/deviation can be significant. Regional studies over a period of time have generated certain data used for estimation of possible corrosion rate range, without guaranteeing those figures for corrosion rate predictions of a structure, pipe of plant equipment. You might have noticed that the environmental conditions tend to be variable and tend to defy any strict prediction. You could talk to relevant people in your area (a refinery, a gas distribution centre or the like) and ask what conservative figures they might use for corrosion rate predictions. Use your experience to predict what are your chances of avoiding holydays in the pipe coating, accidental break down of that coating applied on the pipe, likely to generate accelerated localised corrosion. Yes, this is practical theory. To answer you specific question, in accordance with the environmental conditions you have assumed (desert, dry, etc..);- you don't need any coating, because the carbon steel to corrode need moisture/water, oxygen and temperature. Since you have removed the moisture, there is no corrosion. Easy done, see? Maybe not, perhaps is something wrong with the assumption...
cheers,
gr2vessels