Hmmm... I've never used it on carbon steel. Cool, I'll have to check it out. If it does apply a protective layer, I would think it does so by pre-corroding the top layers, similar to the galvanic coating on galvanized steel pipes and fittings.

I'd have to look more into it to know how durable the coating is, once it is scratched or worn, it would of course be useless.

Edit: you also have to check the permeability of the corrosion product coating. If it's too permeable it's also significantly less useful.

It's great for what it does and is a useful cleaning agent to prepare many types of stainless steel for a protective coating. However, you do have to be aware of the type of stainless steel you have before you use it. Off the rope of my head, I seem to recall that there are a few varieties of stainless that have additives that can react badly with the phosphorus... plus just plain impurities like chloride can potentially set up micro areas of intense corrosion.

I believe there are charts available with a Google search that can outline the compatability of different stainless steels with phosphoric acid.

I used to teach a corrosion course at my local college.

What best practices are they wanting to implement? Most companies take anti corrosion measures pretty seriously (at least the ones I am familiar with). Loss to corrosion costs money to replace, and failures due to corrosion cost a lot in potential damages to personnel, equipment, and fines I it causes environmental damages.

Keep in mind corrosion can't be stopped, only slowed.

Man, when I was in art school and learned about how crazy specific and controlled corporate colors were it blew my mind.