SS URD Transformer Corrosion Failure

[2banee]

Recently we've had a couple of stainless steel (409) subsurface transformer tanks corrode through and fail. The transformers are only 3.5 yr old. They're located in a concrete vault and have standing water around them pretty much 24/7. I'm not sure whether to install CP and/or change our spec to require a higher grade stainless steel tank construction. Water tests haven't pointed out anything abnormal:

CL 20 ppm
EC 4000 ohms/cm
pH 7.2 neutral

The soil conditions are corrosive to mildly corrosive. Does anyone have any suggestions or know of a corrosive engineering firm with experience in utility based corrosion of this nature???

 

[cuky2000]

Check if the corrosion resistance design for network transformer work for your application.
Network transformers for subway or vault applications are designed for frequent or continuous submerged operation with good record of accomplishment for corrosion resistance. Usually this type of transformer is designed with steel corrosion-resistant tank painted with black zinc chromate epoxy, oven cure and air dry.

 

[BJC]

Do a web search on "Stress corrosion". Stainless steel is not always the best material to use in wet or damp places.

 

[waross]

I see you have cross posted in Corrosion engineering. There goes one of my suggestions.
The other suggestion is the stainless steel forums. I suggest a message pointing to this thread or the thread in corrosion engineering rather than double posting. That makes everyone aware of the question but keeps the discussion in one place.
yours

 

[patrick7]

Sounds like the installation of some sort of cathodic protection may be in order.
I am not exactly sure (it has been a lot of years) but I believe that one tenth of of a milli amp will plate out seven pounds of cu. in a year.
I would look into protecting your investment.