Stainless strength?

[mick]

Some years ago I replaced the stainless backstay/transom bolts, nuts, and washers. At the time I didn't know that I should have put sealant under the fittings. Every season I get rusty streaks leaking from this area. I intend to replace the bolts, etc. and this time bed them in, but will this corrosion have caused any significant weakening of the backstay fitting itself, which is a substantial piece of stainless steel?

 

[desertqueen]

Everything you ever wanted to know about stainless steel, and then some:

http://www.sandmeyersteel.com/

 

[mick]

Thank you, Priscilla. Just been watching aspects of Baltimore life in The Wire. Superb.

 

[matelot]

No one can give you a definitive answer to your question without examination of the fitting. That said I think it extremely unlikely that the fitting has been weakened by the surface staining that you descibe. But undo the bolts, remove the fitting and have a good pook at it to check.

Sounds to me as if the bolts you are using arent good enough - they shouldnt stain like that, sealant or no.

 

[vyv_cox]

It's crevice corrosion. Has nothing to do with the quality of the steel, it's an inevitable consequence of having a narrow crevice under a washer, bolt head, fitting etc, containing water. The passive oxide film doesn't form deep in the crevice, due to a reduced oxygen content. Active stainless steel has a different galvanic potential from the passive stuff that is present in the open air, so a cell is set up between them. Corrosion is the result.

The solution is to bed all such fittings and fasteners on a mastic bed.

 

[mick]

Thanks for all replies.

 

[desertqueen]

[ QUOTE ]
The solution is to bed all such fittings and fasteners on a mastic bed.

[/ QUOTE ]
Mastic bed ... that makes me think tile, could you explain this please?

 

[vyv_cox]

Sikaflex 291, or whatever is your favourite sealant. I never use silicones for any of these applications but it would do no harm. All you are trying to do is ensure that water does not get into the gap between a stainless component and something else. Put a good dollop on one of the surfaces and bolt it down, ensuring that sealant emerges all around.