black iron pipe for electrolytic derust tank?

Depends on what you mean by a "coating", Nate. If it is coated with an elastomer, then that could be an issue. If it is just coated with rust or such, it should not cause a problem.

As long as the coating can pass current, then you are okay.

I'm not sure what it's coated with, is why I'm asking :) I know that it's Schedule 40, in a scrap bin, and black in color.

Actually, galvanized should probably work OK, now that I think about it, I'll see if there's any of that in the bin.

nate

Zinc / iron should work similar to a corrosion protection system that is not only galvanic but has impressed current. Iron normally has a positive charge and oxygen negative. Combine the two and it makes rust. The object is to reverse the current flow. Zinc, being more electomotive postive than iron, means the iron ends up with a net negative charge and the iron is protected. The zinc burns up rather quickly though. It sounds like a fun experiment. The hotter temp the better. For normal rust removal I use phosphoric acid, rinse with water, dry, then coat with vinyl phosphate.

The activity of zinc or steel make no real difference when you use an impressed current process. A cheap galvanized nipple from the hardware store would work, but of course you to (1) keep this electrode from contacting the tank and (2) you run into trouble with current "throwing" on complicated shapes.

How do you apply the "vinyl phosphate"? Do you use a catalyst?

Oops. Thanks for catching that. I meant v.acetate and wrote v.phosphate. Clean with phos.acid then coat with Loctite Extend spray.

I did corrosion monitoring of underground structures for several years. We found that impressed current was great when it worked correctly, but overall they were not very reliable.

Thanks. That fits a lot better. I worked with cathodic protection for a while during the time my employer was exploring this market. If everything were designed properly, and if the soil and implemented electrode system were as they should be, then they did work well.

We finally got out of it because it just didnt fit within our business model.

You forgot "and properly maintained." People put the things in, and they expect them to run forever without any inspection or electrode replacement.

--scott

Very true. I always felt there was a better way to do it, but nobody wanted to hear about it. You know the story "This is the way we have always done it and we aren't going to change now".