Broke a bolt

I snapped a stanchion bolt the other day! 1/4" stainless steel machine screw actually.
Starboard stanchion by the cockpit. Forward inboard bolt.
The stanchions get abused sometimes, people grabbing them or the lifelines while docking. This one was leaning forward an inch off of vertical, but seemed sturdy enough.
I had the lifelines loose and was pulling on it (aft) - not all that hard! to straighten it up - And something went POP! Pretty loud too
Inspecting it, it was pretty obvious what had happened, so I dug the bolt out and replaced it.
This bolt (machine screw actually) had some serious corrosion issues. (See the attached photos)
There is quite a bit of old damage on the mating surfaces. That's the dull gray part. And quite a bit of sealant over the old damage!
The bright metal tab seems to be the place where it broke. There was NOT A LOT of metal there!
I have recently learned that there is an aluminum plate buried in the deck lay-up where the stanchions are attached.
What say ye? Was this 20 years of dissimilar metal corrosion? (4 photos) http://www.home.earthlink.net/~capri26/bolt.htm
As soon as possible, ALL of the stanchions are going to be pulled and re-bedded.
--

Richard Lamb
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wrote:

You'd expect the aluminum to lose in a galvanic couple with SS. There are several other corrosion mechanisms that affect SS in marine environments. Google:
crevice corrosion stress corrosion cracking chloride stress corrosion cracking
for a few possibilities which are, in my opinion, more likely than galvanic corrosion in this case.
Carbide precipitation is another possibility, but that would be a result of faulty manufacturing of the fastener. On the other hand, I have seen what I'm pretty sure was carbide precipitation in the tubing in a couple bow pulpits, so it's not out of the question.

--
Ned Simmons

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Ned Simmons wrote:

I've heard of crevice corrosion and stress corrosion cracking, but the third one, chloride stress corrosion cracking, I had not heard of before. Interesting.. but I doubt we have had that kind of environment onboard the boat. :) At least I hope not!
My photos are the limit of my camera. Aperture priority (about f 3.5) in macro mode - zoomed all the way out (about 1/4" x 1/4" frame size).
Certainly not 500 X by any stretch of the imagination).
The suspect surfaces look more granular/pitted than fractured.
But if we could zoom in 300 X to 500 x would it look like these?
http://www.atclabs.com/Photos/300%20series%20SS%20Pitting%20Corrosion.%20BSE.jpg
http://www.atclabs.com/Photos/300%20series%20SS%20SCC%20Area%202.jpg
Or a simple overload mechanism?
http://www.atclabs.com/Photos/300%20series%20SS%20Overload.jpg
Well, whatever it was, that screw mess it up for the whole bunch. They ALL are getting pulled and replaced!
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Richard Lamb
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A company I worked for had a product made from 316 stainless steel. Often the product was submerged in a marine enviromment continuously.
A customers returned some with some M3 threaded holes in the body "stripped". The screws looked ok, just the holes were "stripped". Turned out it was crevice corrosion. We learnt something new that week!
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Dennis wrote:

I'm going to use real BOLTS when they get changed...
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Richard Lamb
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Stainless does okay in fresh salt water, but not in stagnant salt water. The stagnant salt water does not have oxygen which is essential to keep the stainless with an oxide layer. I am no expert but you might consider Monel bolts.
Dan
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snipped-for-privacy@krl.org wrote:

Absolutely true. the process is called passivating and can occur only with the presence of oxygen. Monel sounds good, but its gets expensive. but anyone with a big boat must have a lot of money :)
John
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John wrote:

Not necessarily, John.
And she's not THAT big anyway...
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Richard Lamb
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Are bronze fasteners available? I know monel is nasty stuff to work, but bronzes usually aren't.
Stan
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The aluminum would be the loser if it was electrolytic corrosion. Probably chloride corrosion. Stainless steel -isn't-, at least when it comes to sea water. You get inter-granular corrosion, basically chunks fall out, how big depends on the alloy's grain structure. And checking bolts would probably be a good idea, I'm told a beeswax- pitch mixture makes a good goop for threaded hardware exposed to seawater. Hope the stub wasn't hard to get out.
Stan
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snipped-for-privacy@prolynx.com wrote:

Thanks, Stan.
No, It came out with finger power and a long socket. Just getting the socket on it was the hard part.
I can't inspect what's in the hole until I can remove the stanchions completely and dig out all the old sealant.
What kind of "beeswax/pitch mixture" would that be?
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Richard Lamb
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wrote:

Like you already know *everything* on a saltwater boats corrodes and breaks. Good sealant really helps, we use tubes and tubes of that white silicone sealant from the Marine boat supply. I'll get the name if you need it.
I've seen pics of your boat. You got life easy. I waste my windy days working on a 20 year old commercial fishing boat.
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Karl Townsend wrote:

Temptress is 20 years old too, Karl!
But we sail purely for the pleasure of it.
The difference is - who pays whom for what!
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Richard Lamb
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wrote:

I'm surprised, she's been treated like a fine lady.

"Reel Smiles Too" heads out anytime there's $500 on the table, about 250 times a year. She's starting to look rode hard and put away wet.
Karl
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In article
snipped-for-privacy@prolynx.com wrote:

I read in a book on sailboat rigging that pure lanolin works well in protecting splices in stranded stainless steel wire. They also mentioned using pitch and beeswax, but lanolin was the best for inside the splice.
Joe Gwinn
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Probably the point is to cover the stressed parts with something waterproof that will stay that way. Cosmoline, heavy grease(lanolin qualifies!), tar, whatever. Just that some stuff is a little nicer to handle than others after applying.
As far as pitch and beeswax, it was an equal mixture. Pitch is pine tar in this case, not oil refining leftovers. Melt on a water bath and mix it up. If it's too hard, add more wax.
Stan
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wrote:

I believe that I'd pull all the bolts and I'd use something other then aluminum plate as a backer - I know, some of the commercial made yachts use it - but I've used waterproof plywood epoxied in place and, if I thought it necessary, capped with thin stainless plate, the stanchion well bedded with 5200 and the new bolts well coated too. It seems to last ands last. I'd also stop using all-thread (if that what they were) bolts and get proper bolts (the kind that only have threads where the nuts go :-) as they are stronger.
Another thing. Don't let people pull on the life lines when they get on and off. I even made some lovely lanyards, tied to the hand rails, with a crown knot and hung them over the lines for fat ladies to use to haul themselves aboard.
Cheers,
Bruce
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ARE YOU T-R-Y-I-N-G TO PISS ALL US SNOW SHOVELERS OFF!!!!!!!
Kidding of course, but no Key West Race Week for me this year either, so I'm grumpy.
No metallurgist here, but do you think these are OEM? There were certainly a lot of "stainless steel" screws used that were definitely NOT marine grade.
While I am impressed with how well the photos came out, it's a bit hard to tell from the pix how far below the surface the thread broke, but heed the other poster that suggested a bolt that is not full threaded so it has max strength, and use stainless as a backer. It also appears that these were standard heads, and not flat-head. That might put a bit more strain on things too, especially if the stanchion base has countersunk holes..
Take care.
Brian Lawson, Bothwell, Ontario.
XXXXXXXXXXXXXXXXXXXXXXXXXX
wrote:

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Brian Lawson wrote:

OEM, probably yes. Catalina installed them - but it was 20 years ago.
I do take your point, but what is "marine grade"? Is it anything like "aircraft quality"?
I think the wise thing for something like this is to buy known metals, not just what's _called_ that.

The break is about 1/8" above the top of the lock washer. The deck is about 5/8" thick there. So it broke just above the inside surface.

The stanchion base plates are not countersunk. More fastener options there.

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Richard Lamb
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On Sun, 30 Jan 2011 18:14:13 -0500, Brian Lawson

If it makes you feel any better, it got flat calm most of that week. Too hot also. If you ever do come down, go fishin' with me.
Karl
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