In article , J.B.Slocomb
wrote:

On Fri, 26 Apr 2013 21:15:06 -0400, Joe Gwinn
wrote:

In article , J.B.Slocomb
wrote:

On Fri, 26 Apr 2013 12:51:25 -0400, Joe Gwinn
wrote:

In article , Ed Huntress
wrote:

On Tue, 23 Apr 2013 09:40:16 -0400, Ned Simmons
wrote:

On Mon, 22 Apr 2013 12:27:00 -0400, Ed Huntress
wrote:

On Mon, 22 Apr 2013 07:59:29 +0700, J.B.Slocomb
wrote:

[snip]

As JB says, 316 stainless if you want it to be stain-free.

I didn't notice if this is for fresh water or salt, but if it is for
salt water use and it has any load on it, anything but 316 will
develop stress-corrosion effects that can drive you nuts. Even if
strength isn't an issue, a stressed piece of 304 in salt water will
probably get rust spots or streaks on it.

Sure you're not mixing up stress corrosion and crevice corrosion? Both
304 and 316 are prone to stress corrosion. 316 does resist crevice
corrosion and pitting better than 304.

Stress corrosion is blamed for rusting of sailboat rigging and similar
applications. It's not something I learned from materials science but
rather something I learned as a sailor. I don't know what the
mechanism is. But the story is that 304 gives problems, and 316 does
not. I've seen it, but the descriptions come from experieced boating
people I've known, not from materials scientists.


As far as cosmetic rust spots go in a marine environment, for stuff
out in the open and above the water line, the finish can make a bigger
impact on rust spotting than the the difference between 304 and 316.
It's tough to distinguish between 304 and 316 for parts that are
highly polished and not exposed to stagnant water.

I don't have experience with that, but I'll take your word for it.
Passivating and the quality of the steel are issues, too.

I have a very good book (reportedly a classic) on sailboat rigging:

"The Complete Rigger's Apprentice - Tools and Techniques for Modern and
Traditional Rigging", by Brion Toss, International Marine (a division
of McGraw-Hill), 1998.

The matter of corrosion of stainless steel fittings is discussed at
some length, starting on page 275. Basically, crevice corrosion is the
issue. The mechanism is lack of oxygen in confined spaces, such as
between a stainless steel fitting and the thing it is bolted or crimped
to.

The general solution is to fill such spaces with a compound he calls
"slush", which is composed of 6 parts stockholm tar, 3 parts boiled
linseed oil, 1 part Japan drier, and 1 part spar varnish. I assume
that this is a traditional recipe, handed down in one form or another
since the age of sail.

Also widely used is straight lanolin.

I developed a similar trick in the 1970s to slow automobile
battery-post corrosion down: I smeared the post and the inside of the
clamp with silicon dielectric grease, pushed clamp onto post, and
tightened. This ensured that the space between post and clamp was
filled with silicon grease, preventing wicking of acid into that space.
I should have patented it - now kits to do the same are in every auto
parts store. But it seemed too simple and obvious. I bet a thousand
people had the same experience.

The author also addresses stress corrosion and metal fatigue, largely
in the context of failure swaged connections between fittings and wire
rope. The general solution there is slush plus better mechanical
details.

Anyway, I'd recommend that people read this part of the book for the
practical experience and advice.


Joe Gwinn

Toss' book is indeed a classic but he does get all nostalgic about old
time stuff - in one part of the book he gets rather excited about
galvanized rigging - which will last providing that the rigger spends
longer wrapping and frapping and slushing with Stockholm tar and
whatnot than he did splicing :-)

You're right about that. He didn't see the reason to spend the money
on stainless, but he still told how to do it - he wasn't going to send
work away.


But stainless rigging really doesn't have a lot of problems with
crevice corrosion and all the other mystical stainless corrosions
except for the swedged terminals on the lower shrouds which tend to
crack around the cable probably due to corrosion between the cable and
the swedged fittings although the "screw together" terminals like
Norseman don't seem to have this problem.

He didn't trust stainless to just work, and talked about inspecting by
unbolting a few things and looking. He also was not worried about rust
stains, but advised to look for surface pitting with a strong light and
a magnifier. If there was any pitting, it had to be dealt with,
generally with slush (if soon enough) or replacement (if too far gone)
or failure would soon be upon us, most likely during a storm.

To be honest, I never found anything wrong with swedged stainless
rigging except for the cracks in the bottom shroud fittings. I
understand that insurance companies suggest that stainless rigging be
changed every ten years but I'm not sure of the reasoning. I did
replace all the rigging on my last boat, and it was likely more than
ten years old, and I noticed that cutting the old rigging cables
seemed to take more effort than cutting the new cable but I don't know
whether that was work hardening of the old cables or a different alloy
in the new :-)

Toss does discuss this. It's the accumulation of fatigue and various
kinds of corrosion slowly eating away at the safety margin. Not to
mention becoming brittle from work hardening. Everything looks OK, but
will break in a storm, just when it's most critical that it not break.

The steel has not likely gotten worse. Most likely, the cables are
work hardened, as you suspect. Another reason for periodic
replacement.


As for swaged fittings, he recommended dipping the wire end in lanolin
or the like before assembly and crimping, precisely to exclude salt
water from the interstices of the wire in the crimp barrel. This was
especially important in the Tropics.

That makes sense (I guess). I replaced the terminals with screw
together terminals and filled them full of 5200 before screwing them
together and sealant did squirt out around the cable but I don't know
how far it penetrated into the cable.

I assume that you mean 3M type 5200 sealant. This is listed for
fiberglass and wood, but 3M does not mention use for metal. I would
also guess that 5200 is too thick to penetrate through the wire rope.
So, there may be little protection in this, as the sal****er can wick
down the center of the rope.


I used this method for copper wire terminals on my car, only used
silicon grease, followed with a heat-shrink sleeve for mechanical
strength. This worked well at keeping road salt from destroying the
assembly.

All in all, I found Toss's book to be quite practical. And I don't
even own a boat, though I grew up with boats.

I found it to be very good reading and about the best instructions for
splicing, particularly braided rope, I've come across.

Oh yes. And I have made some braided eye splices to make a nylon rope
handrail for the basement stairs, which are too narrow for a
traditional handrail. Just like on a boat. Used marine hardware for
the attachment points as well, for the guaranteed strength (real
full-penetration welds, not slapdash partial resistance butt welds),
with the hardware screwed directly to the studs through the wallboard.


Joe Gwinn