Protection of Internal Surfaces with CP
Protection of Internal Surfaces with CP
(OP)
I've been looking hard at Oxygen corrosion for the last few weeks and I'm beginning to understand that internal Oxygen corrosion is a cathodic reaction just like the external reactions that people normally use CP to protect.
What I've been unable to determine whether an impressed-current CP system will protect against internal cathodic reactions like oxygen corrosion or MIC. Does anyone have an opinion?
David
What I've been unable to determine whether an impressed-current CP system will protect against internal cathodic reactions like oxygen corrosion or MIC. Does anyone have an opinion?
David





RE: Protection of Internal Surfaces with CP
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Protection of Internal Surfaces with CP
We tried this approach early on in the MIC wars to mitigate corrosion to SS heat exchangers. Our only measurable response came with using Lead anodes. Our particular flora/fauna was extremely sensitive to the Pb ion. This project did help with the MIC but was quashed by the environmental people.
We tried sacrificial anodes and impressed current in a large waste water storage tank. The project didn't pan out as our product composition never got to a steady state.
h
RE: Protection of Internal Surfaces with CP
On painted surfaces, such as underwater hulls and most tanks, the steel is painted, and CP is only needed to protect steel exposed by failed pait.
In most cases the internal surfaces of piping systems is unpainted. The "CP current" will tend to "short out", and its difficult to "project" current any distance down small diameter piping and tubing. In the cases of heat exchangers, its unlikely CP provides any benefit past a few inches of the tubes (of course, its often the first inch or two that is most likely to fail, also).
RE: Protection of Internal Surfaces with CP
David
RE: Protection of Internal Surfaces with CP
- what matters isn't the CURRENT, but the CURRENT DENSITY.
- the exterior of the pipe is probably painted, so all you need to protect is paint holidays and areas of paint damage.
- the inside of the pipe is bare.
- the equation for current density is "current / area".
- Increase the denominator (area) by 10^3 or 10^4, and you'll have the affect on current density.