The Boating Forum - Passivation of SS parts

I have a short question. Recently had some SS parts welded. They will be contact with SW. The welds have been ground and polished.

Do the parts also need to be passivated or will they be OK?

Thanks in Advance,

TSA

Even though they have been ground and polished, they will be much more corrosion resistant if you passivate them. They'll be even better if you electropolish them, which also makes them look like they've been chromed. In my world, any stainless that I've worked on gets passivated before it goes on the boat. You can do a pretty good job of home passivation with a 10% nitric acid bath., but then you face the problem of what to do with the bath after you've used it.......

Kern:

Thanks. What about edges on trim tabs that have been cut with a grinder or dremmel tool.....passivate those too?

Usually you only have a problem when the steel from cutting tools gets imbedded into the stainless. Grinding and sanding is not a problem, but drilling and filing is. If the Dremel tool is steel, you best sand out any place it touched.

You can neutralize a 10% nitric acid solution with a box of baking soda. Add it slowly. It will fizz up. When the fizz stops, it is not nitric acid anymore.

Yeah, but.............That can be done, but adding bases to acids is not for the timid. The acid (Hn03) will combine with and be neutralized by the baking soda (NaHCO3), but you are dealing with some pretty strong stuff. Reagent grade Nitric, which is what you need for passivating, is well into the "fuming" range. It needs to be stored away from things that can corrode, even though it is in a plastic container. If you are going to neutralize it with baking soda, I'd suggest pouring the acid into water to dilute it first and then adding the baking soda. I'm pretty comfortable with chemicals, but I would not be happy trying to neutralize 10% nitric by pouring in bicarbonate of soda........................

If you buy nitric acid, be prepared to have your name go onto some interesting "lists" maintained by the Kevlar Cowboys.

As much as I enjoy 3 am no-knock raids, I think I would just polish it and buff it and be done with it.

Thanks for the replies.

I actually have 5 lbs of powdered citric acid laying around that I use to control tree frogs. I think I will mix up a solution and dip the parts in it for 30 minutes. Might try a scrap piece first just to see how it fairs.

Your best bet is to have them passivated then electropolished. Max protection...

CMP