Stainless steel "dissolving" in electrocoat process into anolyte

[MIGGY]

We are having problems with anolyte for a electrocoating application. The colour of the anolyte (acetic acid) has changed from a normal pale yellow to a dark red/black colour. It is suspected that the 316 stainless steel anodes may be "dissolving" as high concentrations of Cr, Ni and Mo are found in the anolyte solution. A change of voltage has been tested through the anodes recently, could this be the source of the problem? Any other theories on the topic?

 

[mcguire]

316 stainless, if made anodic at a voltage that puts it in the transpassive region, will dissolve. What voltage is required is a function of the specific solution and it's temerature. Your hypothesis seems quite likely.

 

[TVP]

A good place to look for more information on this topic is the website for Products Finishing magazine, specifically the painting section. I highly recommend the site and the magazine (both available for free)-- articles, clinic, and forum are all very useful.

http://www.pfonline.com/paint/index.html

 

[TVP]

I gave you the wrong link in my previous email-- there is a separate "electrocoating" section from the "painting" section. Same stuff applies:

http://www.pfonline.com/ecoat/index.html

I found the following article on troubleshooting to be particularly useful:

http://www.pfonline.com/articles/079802.html