Cathodic Protection on Bulkhead (A572 Steel)

[craigmcg]

Hi hopefully this will be a straightforward question as this is not my field of practice:

I'm looking at a preliminary design of a sacrifical anode cathodic protection system for a sheet-pile bulkhead structure in brackish waters. The steel used will be A572 Gr.50 and will be coated with a thick coal-tar epoxy. The bulkhead needs to have a relatively long service life (>50 years), hence the dual methods of protection.

What I need to know the electrical potential of A572 Gr.50 (high strength low alloy) steel in reference to a copper/copper sulfate cell (a website or book reference to this would be great). I've read in the military that a mild steel will usually have a -850mV potential, is this correct?

Another quick question while I'm at it... The system calls for aluminum anodes to be used. Will the driving potential between the two metals in brackish waters be reliable? Or would zinc or magnesium make more sense under initial observation?

Thank you for your help. If there's any additional info needed please let me know.

 

[dik]

I'm currently digging into information using a combination coating and cathodic protection and am in the process of obtaining additional information on use of high build polyureas and polyurethanes for coating and using magnesium or aluminum as the sacrificial anode. I understand that for salt water applications that zinc is the preferred material. The problem with the use of the former materials is that they haven't been around long enough for a history of use.

A high build epoxy with glass has a history of about 40 years in marine environments.

We shy away from tar modified epoxy because it is possibly? a carcinogenic material, and is not currently used in our environs.

Dik

 

[SJones]

http://www.google.com/custom?domain...000000;GFNT:0000FF;GIMP:0000FF;FORID:1;&hl=en

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/