Stainless fasteners failure

AngusMcDoon

AngusMcDoon

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I have had a few stainless parts fail recently, all the same way, with a slowly developing crack until weakness causes plastic failure. Previously these have been in fairly mundane items like the main sheet system and have been no more than in inconvenience. Now I've had an important one fail - a bolt that connects one of the hinges to the hull on a folding trimaran. Fortunately the others took the load and no further damage was done.

Now we all know that stainless rigging degrades invisibly and should be replaced periodically, irrespective of what it looks like and how shiny it is. But now I'm wondering if all stainless fasteners in important systems on boats where failure could lead to a safety risk should be replaced. So rather than just replacing the one failed bolt should I replace all 50 of them? The cost is not too high at about £75 for load rated marked items.
 
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Yes replace them all, its what I would do after finding out what specification of stainless would be better. Perhaps the wrong specification has been used by the builder, so you just need to purchase the correct fastenings.
 
I'd say you have to replace at least all the load bearing bolts.

Sounds like the famous crevice corrosion, which I expect you're aware of; do you know what grade stainless these bolts are / were ?

I can't help thinking they may be being put under a side load, have looked at relatively old folding tri's like Telstars and winced at the loads involved, and no doubt by coincidence those bolts were showing surface rust ( at least ).
 
BlowingOldBoots said:
Yes replace them all, its what I would do after finding out what specification of stainless would be better. Perhaps the wrong specification has been used by the builder, so you just need to purchase the correct fastenings.
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I'm replacing just one immediately to get the boat going again and to make sure what I have ordered fits. I've asked the manufacturer for full specification but they are not known for prompt replies. I have also asked their opinion on replacing them all.
 
That picture is a coach bolt.
They tend not to be well made items, they are normally used in applications where they are well oversized for the loads involved.
Crevice corrosion is one thing, damaging fasteners on assembly is another. Tightening stainless bolts dry can cause galling of the threads, which I think can be the start of damage which leads to cracking.
IMHO, any stainless which is taking significant load should be assembled with either some sort of lubricant or some sort of loctite. This should help with both problems.

I would also go up a size if possible and go for quality having had one fail. Can you use proper bolts instead of coach bolts?
 
I can't quite see from your photo but it looks like fatigue, which would concur with your description of the event. Fatigue in bolts is invariably caused by undertightening but it is not possible to tighten an A4-50 to the ideal torque. If it is possible to buy this type of bolt in a stronger material I would certainly do so. In fatigue it is always recommended to replace all, assuming identical duty, when one fails.
 
lw395 said:
IMHO, any stainless which is taking significant load should be assembled with either some sort of lubricant or some sort of loctite.
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When buying new waterstays from the manufacturer Quorning they always arrive with the threaded end pre-greased. I have wondered why. This may explain it.

lw395 said:
I would also go up a size if possible and go for quality having had one fail. Can you use proper bolts instead of coach bolts?
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I can't go up a size, and a normal bolt would leave a head proud where it's not wanted. I can go up a strength grade though.
 
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You've been lucky enough to have a warning, I would heed it if I were you. You definitely need to replace all of them. You must buy good quality branded product with proper markings. It might pay to consider a different alloy or material.
 
savageseadog said:
You've been lucky enough to have a warning, I would heed it if I were you. You definitely need to replace all of them.
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I have just wandered down to the mechanical engineers' lair where I work, and when they had all stopped cringeing, sharp intakes of breath, going yikes, ouch and jeepers, they all agreed that it's time to replace the lot, and do it regularly.

I shall buy a box of 100 once I've confirmed that the 1 I have ordered fits.
 
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