Rust/Oxidisation

[david_e]

What is the best way to remove the light oxdisation that occurs on the threads of bottle screws etc and also on the strands of the rigging where it is swaged into the fitting.

Obviously not wanting to remove it in a way which will make it worse in the future.

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[tcm]

hi david.

These deck fittings are almost certainly stainless 316, and as such are not plated, but solid "stainless steel 316" all the way through. Yiour boat is nearly new, so the tarnishing simply should not happen - it is because of faults in manufacture that the surface layer shows rust - cleaning or polishing with carbon steel materials (wire wool etc) could have caused it for example.

First you need to get rid of the rust, then clean and repasivate the surface so that the chromium in the metal forms nice erm chromium oxide on the surface, and not iron oxide (i.e rust)

To get rid of the rust, use (say) a brass brush on a thread, or praps a plastic panscrub on flatter surfaces. Then, use something along the lines of whatever is recommended by anopol.co.uk to re-passivate the surface layer and it should never rust again.

Vyv_cox is resident metallurgist hereabouts and may know of other products.








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[DepSol]

Once you have got rid of the oxidisation then usee T-9 to once a month to stop it happening again. A light spray is all it takes.


<hr width=100% size=1>Dom

2003 is going to be a good year for me

 

[vyv_cox]

It doesn't look very good but it's pretty much harmless. What you are seeing is crevice corrosion in tiny laps, cuts and surface imperfections in the cut threads and the drawn wire. Passivation of stainless steel in a plentiful supply of air takes place without any intervention by us, that's what makes it stainless. Inside these little imperfections it is not possible to get enough air in to passivate the stainless steel, so it remains active. Unfortunately the galvanic potentials of active and passive S/S are some way apart, so cells are set up when the two are connected by water.

The best solution is to eliminate the water. A good layer of grease works well but the crew complain when it gets over their hands, clothes and the sheets (of the sails, not the bed!) I find that Waxoyl is very good for this, it dries hard and is hydrophobic. I have some that came in an aerosol spray, bought at a car parts shop. A method I have used for swaged shroud fittings is to heat the fitting with a hot gun and to melt No.3 grease into the socket. This fills it very well and keeps the most vulnerable part of the shroud corrosion free. Any other hydrophobic spray would help on threads.

On smooth fittings it will help to polish with an abrasive cleaner. Even on wires this treatment should help but it will never be possible to clean up threads by these means.

The only rider to this is that it applies more to 316 (A4) stainless steels. 304 (A2) is just as corrosion resistant, but it has a greater tendency to form corrosion pits in chlorides. A pit forms its own little crevice and galvanic cell, so more severe corrosion can happen.

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[david_e]

Thank you, most detailed - obviously a good grounding in engineering obtained at some time



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[david_e]

Thanks Vyv, whilst I have a hot gun, not sure if I fancy doing this on my pride and joy somehow. Will get some Waxoyl this lunchtime when nip down for lettering for lifering from motorfactors, hopefully that should suffice.

It begs the question, should this be covered under the bennytoe warranty?

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[tcm]

Re: warranty

You can certainly try - I did, quite successfully. They didn't replace the parts, but did give them a good polishing and treatment, and no more rusty bits.

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