Bruce wrote:

The acid treatment was "passivating".

My experience is that unless the stainless is polished to a mirror
bright finish you will get staining. All the bits have to be polished;
Assuming that it is a bolt on fitting the bolts and washers that are
exposed to sea water need to be polished.

I've been making things out of stainless and putting them on boats for
quite a number of years and I have found that if the part has all the
welds ground smooth (so the welding ripples don't show), no pin holes
or voids in the weld and then polished bright I seldom get staining.
If I don't do this I always get staining.

snip...
Bruce in Bangkok
(brucepaigeatgmaildotcom)


Hi Bruce,

I've just recently started building stainless
parts for my two sailboats. I'm using 316 SS and
316L SS exclusively and passivating with Citrisurf
which is a strong citric acid. It can also be
used for electropolishing, and I intend to try
using it for that in the future.

Google "Citrisurf". It is supposed to be better
and more environmentally friendly than nitric acid
paste. Several of the welders that post to
sci.engr.joining.welding have used it with good
results. I've only started using it about six
months ago, so the stuff I've built has not been
out in the salt spray long enough to tell how good
the passivation was.

Don W.