[PSUBS-MAILIST] Stainless prop shaft

[Stephen Fordyce via Personal_Submersibles]

Hi Brian,
SS304 is the most common grade of stainless for general use, but SS316 is
the most common used in marine (and is usually what people mean when they
say "marine grade").  That said, the difference in performance is mainly
cosmetic for intermittent salt water use (ie. some very light
"tea-staining" rust), and I've used various bits of SS304 on my boat and
dive gear that are absolutely fine years later, although it all gets fresh
water washed after use.

For continuous exposure to salt water, or with crevices (ie. your thru hull
seals) likely to trap and hold salt water, SS304 is likely to eventually
corrode enough that it may eventually wear or cause the seals to develop
leaks.

I know at least sometimes the prop & propshaft on bigger boats is protected
from corrosion with an anode, which wouldn't be very practical on a thru
hull.  Possibly this explains why the one you have is 304.

Another thing I see at work all the time is contamination of any grade of
SS pipe with carbon steel dust from grinders, drill shavings, etc.  A piece
of SS you thought was clean left in the rain will develop nasty rust spots
overnight!  Important to store your SS away from carbon steel workshop
areas and/or cover it.

Cheers,
Steve

On Fri, Jan 9, 2015 at 7:59 AM, Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hi All,
>              I was given a stainless steel prop shaft which is about 1
> 1/2" in diameter, I have cut it up into 2" long pieces so they can be used
> as thru hull fittings for some of my rotating shafts that I will be using.
> I was always under the impression that the prop shafts were a highly
> resistant alloy of stainless and would be good for my application.  I
> recently was able to have someone do a spectral analysis of the metal and
> it showed that the material is 304 stainless.  I'm wondering if that will
> be good enough to use as a stainless fitting for a thru hull ?
>
> Brian
>
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