Corrosion rate of steel in seawater.

[SteveyB]

I have been searching through various standards with regards to determining a corrosion rate for steel in water. I basically have a component which is connected to the bottom of a turret on a FPSO made from ASTM A182 f22 (approx 30m below the surface at 30 deg C). The component has an epoxy paint system all over and is cathodically protected for the most part, except from a portion on the inside which has to be accounted for via an allowable corrosion allowance. I know this is dependant an numerous thing such as temperature, oxygen etc, but there must be some standard corrosion rates available for such an instance. Currently I have assumed an average rate of 0.15mm/yr. The only standard I have found of any use is a DNV position mooring chain standard but feel this is not particularly applicable due the material type. If anyone could offer any advice this would be much appreciated.

Thanks

 

[SJones]

The problem is: there is no standard seawater. That aside, if CP is not reaching the surface under consideration, then it is possibly occluded from the bulk seawater environment which could have a strong influence on corrosion rates. Comparison with data from the NACE Corrosion Engineer's Reference Book would suggest that 0.15 mm/year could be considered as conservative for several ocean locations. A paper that may be of use is:

R E Melchers, Modeling of Marine Immersion Corrosion for Mild and Low-Alloy Steels—Part 1: Phenomenological Model, Corrosion, Vol 59, (4), 2003, pp 319 - 334



Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[SteveyB]

Thanks for the reply I will take a look