CUI of subsea pipelines

[newerbee]

Hi,

I am looking for information on Corrosion under insulation for subsea pipelines with cathodic protection. almost all the references I found are mentioning CUI of piping in above ground installations.

specifically, I am looking for some answers to the following subjects. For subsea use (buried 1m minimum in the seabed),

is CUI a problem? Is CP being shielded? can we assume oxygen concentration in the seabed the same in the water? how does temperature of steel effect corrosion rate?

thanks.

 

[SJones]

CUI, as a corrosion term, is related to atmospheric corrosion. Assuming that your interest is with wet insulation systems, the principal approach to ensuring coating performance, including behaviour under cathodic protection, is qualification using, for example, ISO 12736. Temperature and oxygen aspects of CP design are addressed in ISO 15589-2 or NACE SP0607.

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.

 

[newerbee]

Hi Steve,

thanks for the answer. my concern is coating disbondment for wet insulation systems. I am trying to understand whether CP works or shielding comes into play. as I understand seabed sediments may be deaerated but then how temperature effect corrosion if CP is shielded. or is there no CP shielding at all?

 

[Hongbo]

Interesting question! Not sure if the following points will be relevant.

CP will reach the area if there is a continuous ionic path (assuming electrical path is no question). However, CP could be attenuated or even made no working if there is a high IR built along the ionic path. In your case, since the electrolyte is high conductive seawater (smaller R) and it is deaerated (smaller requirement of CP current I), the IR may not be significant. If that is true, CP is still working in that area?

 

[SJones]

Disbondment will only be an issue if water permeates the insulation and the second barrier of the anti-corrosion coating is broken at the point where the water collects. How likely is water permeation through the system, bearing in mind that this will reduce the insulating properties upsetting the flow assurance people, and should have been ruled out during qualification work?

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.