Corrosion on maststeps, problematic?

[Franziska]

Hi,



Im looking at the attached mast with maststeps and I'm wondering if this is mostly esthetic or if its likely a big issue.



I'm not interested on the maststeps suitability, the rivets can be drilled out and reriveted with Tefgel.



I'm more wondering if this mast is likely to have structural issues from the corrosion visible on the steps. Thoughts?



We would take all fittings off, grid blast it, primer and Epoxy paint it than seal of with proper PU paint before attaching everything back the proper way (Tefgel, plastic washers...).

[nuku34]

From where I sit, its impossible to tell the extent of the underlying corrosion given the photo evidence. If it were me, I'd be scraping off that flacking paint, manually wire brushing the areas, and seeing what's actually going on.

You don't want to be welding up serious areas of corrosion; welding messes with the strength of the alloy.

I did exactly what you are contemplating with both the masts on my 12m Joshua ketch. Its a lot of work!

[Benz]

If there's pitting more than 1/32" deep once you blast all the stuff off, I'd be inclined to consult a rigger or surveyor who can lay eyes on it. I'd probably not worry too much though--look at the size holes they cut into masts for halyard exits without compromising the structure.
You might consider not having steps, unless you really need them--the less stuff fastened on the better, after all.

[GordMay]

It looks, to my failing eyesight, that your mast is powder coated [electrostatic spray paint deposition].

If so, it’s likely that the “corrosion” may [merely] be a failure of the paint system, [perhaps] due to dissimilar metal [Al & SS] corrosion*, at the mast steps. and [subsequent] oxidation of the aluminum.

When this occurs, a hard, white-coloured skin forms on its surface.
Unlike rust with steel or iron, this form of corrosion is non-destructive to aluminium, but the oxidation process leaves the metal surface looking unattractive.

The reasons for powder coat failure, are normally due to problems during the powder coating process, or the failure to isolate dissimilar metals.
Marginal or poor adhesion will lead to “scissions”, or breaks in the coating, which will invite moisture, and salt, to accelerate corrosion.

If something goes wrong during the process, the aluminium surface can end up with various issues:

Filiform corrosion – worm-like filaments appear under the powder coating finish, lifting it away from the metal, due to less effective pretreatment methods before applying the powder coating.

Orange peel effect – the finished surface is not smooth due to a faulty application of the powder coat

Failure of the powder coating to stick to the surface – because of either the insufficient pre-treatment or faulty application of the powder coating layer.

One solution is to touch up any damaged areas, with colour-matched liquid paint. This can work, where there has been fading due to oxidation, or where there are scratches or blemishes.

See also:
* “Why Can’t You Use Stainless Steel and Aluminum Together”
➥ https://www.albanycountyfasteners.co...inless%20steel.

[psk125]

Besides the corrosion issue, does it appear to anyone that the steps may have been installed upside down? It would make more sense to have the place where your foot goes to be flat and unencumbered by an upright that keeps you from being able to move your feet around.

[Benz]

Originally Posted by psk125

Besides the corrosion issue, does it appear to anyone that the steps may have been installed upside down? It would make more sense to have the place where your foot goes to be flat and unencumbered by an upright that keeps you from being able to move your feet around.

That bail is supposed to keep your foot from slipping off if the boat's heeling. Even the most low-profile folding mast steps usually feature an end nub to keep feet from sliding.

[BAD ORCA]

May i ask why people dont use aluminum machine screws drilled and tapped for attaching things to the mast?

[Benz]

Originally Posted by BAD ORCA

May i ask why people dont use aluminum machine screws drilled and tapped for attaching things to the mast?

Probably because stainless is so much easier to find, harder to strip, and stronger. But I've long thought that alloy fasteners, sized properly for load, would be far superior.

[JPA Cate]

I took a close look at the mast pic, Franziska, and I think I'm seeing two different things: the failure of the powder coat, and the failure to insulate the feet of the steps between the foot and the mast.

I expect you're going to have to remove the steps entirely (and they will resist if stainless screws were used) in order to see how bad the pitting underneath them is.

It is a sign the PO didn't know what he was doing. If the pitting isn't too deep, and you go ahead with the project, I'd make sure you put something physical to isolate the feet from the galvanic issue, like inner tube material, or the skinny silicone cutting board material, as well as using Duralac or similar on the screws.

@Benz: I've seen alloy (Oz speak for aluminum) rivets used to secure fittings to masts, but never screws. Would you feel comfortable trusting your life to aluminum screws? I've never used any.



Ann

[boatpoker]

Originally Posted by GordMay

When this occurs, a hard, white-coloured skin forms on its surface.
Unlike rust with steel or iron, this form of corrosion is non-destructive to aluminium, but the oxidation process leaves the metal surface looking unattractive.

Sorry Gord, if talking environmental oxidation, then yes I agree however, the issue here also involves galvanism which can be devastating to aluminum. The resulting aluminum oxide is not the hard harmless stuff of environmental corrosion but a powdery layer of degraded aluminum caused by galvanic reaction which could eat it's way through the mast.

[Bowdrie]

Originally Posted by JPA Cate

I took a close look at the mast pic, Franziska, and I think I'm seeing two different things: the failure of the powder coat, and the failure to insulate the feet of the steps between the foot and the mast.

I expect you're going to have to remove the steps entirely (and they will resist if stainless screws were used) in order to see how bad the pitting underneath them is.

It is a sign the PO didn't know what he was doing. If the pitting isn't too deep, and you go ahead with the project, I'd make sure you put something physical to isolate the feet from the galvanic issue, like inner tube material, or the skinny silicone cutting board material, as well as using Duralac or similar on the screws.

Yes, it's ALWAYS wise to have something between the interfaces.
I generally use 1/16th Neoprene, generously slathered with an aluminum anti-seize, same with fasteners.
You mentioned using an inner-tube, same thing, good to go.

[GordMay]

Originally Posted by boatpoker

Sorry Gord, if talking environmental oxidation, then yes I agree however, the issue here also involves galvanism which can be devastating to aluminum. The resulting aluminum oxide is not the hard harmless stuff of environmental corrosion but a powdery layer of degraded aluminum caused by galvanic reaction which could eat it's way through the mast.

Never say you're sorry, when you're right. [Canadians, like us, excepted.]
My answer was materially incomplete.
Thanks for the expansion/correction.

[Benz]

Originally Posted by JPA Cate

@Benz: I've seen alloy (Oz speak for aluminum) rivets used to secure fittings to masts, but never screws. Would you feel comfortable trusting your life to aluminum screws? I've never used any.



Ann

I absolutely would, if they were engineered properly. I use aluminum toggles (dogbones) on soft shackles all the time; A lot of rigging mast connectors, deadeyes, and such are alloy, and my mooring bitt is an alloy setup with an alloy crossbar, and a alloy pin holds the heel of the bowsprit in place.
Most rockclimbing gear is aluminum, and I trust my life to it all the time.
It would be a matter of using the correct alloy (7075, maybe) in the right size.

[GordMay]

Originally Posted by Benz

...
Most rockclimbing gear is aluminum, and I trust my life to it all the time.
It would be a matter of using the correct alloy (7075, maybe) in the right size.

Aluminum 7075 [vs 2024 & 6061]- Screws, Bolts & Nuts
➥ https://www.extreme-bolt.com/aluminu...olts-nuts.html

Typical Aluminum Mechanical Properties
Grade - Tensile Strength (PSI) - Yield Point (PSI) - Elongation - Brinell Hardness
2024 - 68,000 psi - 47,000 psi - 20 - 120
6061 - 45,000 - 40,000 - x - 95
7075 - 83,000 - 73,000 - 11 - 150

[thinwater]

Lose the steps. One more reason. Better if they had never been installed.