Welding anodized aluminium mast

[Leonidas]

I had the mast down for routine inspection and found 2 vertical cracks about 10cm long one of them starting from a screw hole in the vicinity of the step. ( The mast is made by the now defunct Franspar and is stepped on the coachroof) . Rather than cropping this section, the spar technicians recommended to grind them out, put stop holes at the end and weld the cracks with Argon and then grind them to a smooth finish. I am concerned that the heat affected zone (in way of the welding) will destroy the anodizing which is still effective and may cause future problems.
There has been a suggestion of using duralac primer followed by top coats to cover the welded repairs and also the step so as to avoid direct contact between the mast extrusion and the step internally.
Any other recommendations as to how to mitigate this??

 

[krissteyn]

Next time you are in a big blow - you are going to be looking like a chicken with your head bobbing up and down checking to see if the mast is holding up.
At a time when you should be concentrating on safety and seamanship , you will be concentrating on those welds.
If you have any offshore tendencies - this is a clearcut case of replacement. If not a serious cruiser, well, you pays your money and you gets what you pay for...

my 0.02c Good luck kris

 

[lw395]

You might be able to get it re-anodised, but that probably involves a lot of dismantling.
Epoxy primer and two pack paint should work.
If both holes are close to the foot of the mast, it ought to be possible to reinforce this section beyond reasonable doubt.

 

[Jabs]

You can get a product to anodise a small area. It used to be called Alodine.

The surface will need to be spotlessly clean and free of oil.

I can help wondering if a new rig is the proper solution.

Tony.

 

[merlin3688]

Francespar is now Sparcraft, UK agents are Eurospars and Sailspar, if the section was still available sleeving could be possible. Reanodising would cost a lot as all fittings would need removing. Welding just the crack may make the section softer in that area, doubling up would be better in my opinion.

 

[William_H]

Welding mast

Masts are frequently welded at the base for a foot and near the top for halyard etc. In my case welded for about 1.5 metres from top down to taper it. Apparently with no problems. of course real strength is needed in the middle of the mast not so much at bottom or top. So strength should not be a problem.
The welding will damage anodising. Alodine is similar chemical treatment but intended as an undercoat for paint and looks bad in itself. (orrible brown streaky)
You might be far better off to add reinforcing around the base. Pop rivet it over the area. Use a section of mast material cut open. This has the necessary heat treatment.
A mast does have a huge downward pressure which can cause cracking around holes if they are too big or too many close together. As I found. good luck olewill

 

[Leonidas]

Francespar is now Sparcraft, UK agents are Eurospars and Sailspar, if the section was still available sleeving could be possible. Reanodising would cost a lot as all fittings would need removing. Welding just the crack may make the section softer in that area, doubling up would be better in my opinion.

Thanks for the suggestion.
The mast is in compression and all the load is vertical at the foot. I am concerned that I may be introducing additional weak spots by rivetting a doubling strip . Besides, I shall not be able to check if the repairs are holding . So perhaps a removable stainless steel clamp in way of the repairs maybe a better solution??

 

[Zen Zero]

Have you identified and eliminated the cause of the cracks?

A good weld should restore structural integrity to the mast but as you say, the weld and the area surrounding it will no longer be anodised, I'm not sure how much of a problem this is though since aluminium will anodise itself, and you can paint it. Another problem will be that the welded area will be of a different hardness to the rest of the mast and that will introduce stress concentration factors that could become the source of new cracks - solution: keep an eye on it.

That's about it really. Good luck!

 

[parbuckle]

I am not sure from your description the exact location of the splits but if they are at the very base maybe an extended shoe or would it be possible to make up a tabernacle of sorts that will support the lower end ,this will add strength and could hide any marks that the welding makes .
Most new masts over 40 ft long are joined by internal sleeves and dozens of pop rivets but the original section is used for sleeve so finding the same section would be the problem but could be the strongest fix.
Many masts have had welding work done on them , my mast had an 8ft taper cut in and welded during manufacture but I would want a professional mast building company to do the job.

 

[oldfatgit]

I think that you should be able to take some confidence in the welding repair, if it is done by a welder experienced in welding aluminium then, from an initial engineering point of view, it should be pretty strong. The problem, over the long term, will be protecting the repair from corrosion. The options are (1) to have the mast re-anodised, an industrial process which will work very effectively on all surfaces but is likely to be pretty expensive as it will entail shipping the mast to a factory, removing all non-aluminium and moving items before having the process carried out, (2) to carry out a local anodising repair which will require some specialist supplies and equipment and will not do any of the repair which cannot be reached, (3) prime with etching primer and paint the area which will be as effective as option (2) including not reaching any interior surfaces, and finally (4) smooth off and polish the exterior surfaces of the repair and repeat at regular (annual?) intervals.

Inside surfaces will, by their very nature, be sheltered from the elements and as long as they are not in a position where moisture and contaminants such as dirt and salt will be held then corrosion will proceed very slowly, but if corrosion is likely, then it will proceed fast and unseen.

Localised anodising repairs are carried out on aluminium aircraft sections and involve holding the electrolyte (sulphuric acid) in position over the area by some means and passing a low voltage current through it. Though the techniques are understood and require pretty cheap equipment, I have been unable to find any kits that one can buy to do the process oneself. To do a thorough job will require the area to be cleaned and degreased, anodised and then sealed. There is some small scale kit available at http://www.caswelleurope.co.uk/anodise.htm but this is all for immersion of the whole item. I may be mistaking but I suspect this option is not really viable.

Option (3) should be dead easy, just buy an appropriate spray on etching primer, mask off the area, prime and then top coat. If done neatly this should prove very effective and easy to maintain. It may be possible to prime and paint with a silvery grey colour which may be a close match to the anodised finish of the rest of the mast, but I'm no expert and expect that an obvious neat job my look better.

Option (4) is all about getting a smooth aluminium surface (which will not hold water or contaminants, and sealing the surface with a propriety polish. Probably just as easy as option (3) but should not stand out unlike paint.

I cannot find or think of any other options for you but good luck.

 

[merlin3688]

So perhaps a removable stainless steel clamp!
I would not fit anything that is stainless, you could make more of a problem with corrosian from dissimilar metals, still think sleeving is best option if you can find the same section.

 

[bogman]

aircraft type repair to mast

Unsure without pictures if this is possible but you could get a local sheetmetal person to fabricate a repair patch in marine grade aluminium. 5000 series or 6000 series. Fabricate the patch from one gauge thicker than the mast and ensure you have enough room for two rows of rivets. Pilot drill the patch and mast, remove the patch and clean up, drill to the exact finished hole size and deburr again use duralac or even Sikaflex between the mast and patch and properly install the pop rivets. The diameter of the rivets will be given by the size of the patch and mast. If the repair patch is a complex section it may need to be made from annealled aluminium and then heat treated but all possible.

If the rivets are 6.4mm then stagger the holes 4 x 6.4mm apart and make sure no hole is less than 2 x 6.4mm from an edge. Use these dimensions to size the basic patch.

If this is done properly it will last a very very long time as it is a basic aircraft non pressurised repair scheme.

Be careful not to drill any ropes or wires inside the mast.

 

[AntarcticPilot]

Others with more knowledge and experience will be able to comment on this, but I thought that aluminium is actually a highly reactive metal which on exposure to air forms a strong oxide layer (which is actually corundum, a very hard and chemically inert substance) on the surface, protecting it from further corrosion. Anodization merely makes the corundum layer thicker, and allows alternative finishes. For that reason, I've always regarded anodization as a cosmetic rather than a structural issue. After all, we don't usually bother touching up a scratch on an anodized spar.

Can one of the metallurgists on here confirm or deny this?

 

[oldfatgit]

Others with more knowledge and experience will be able to comment on this, but I thought that aluminium is actually a highly reactive metal which on exposure to air forms a strong oxide layer (which is actually corundum, a very hard and chemically inert substance) on the surface, protecting it from further corrosion. Anodization merely makes the corundum layer thicker, and allows alternative finishes. For that reason, I've always regarded anodization as a cosmetic rather than a structural issue. After all, we don't usually bother touching up a scratch on an anodized spar.

Can one of the metallurgists on here confirm or deny this?

Yep, you are correct, save where some other agent exacerbates the corrosive effect. The oxide layer is very thin and can, therefore, be easily breached particularly where corrosive conditions exist such as dissimilar metals or areas where sea water and dirt become trapped. A poor weld particularly if contaminated is bad news also. Corrosion may be slow however and even stop once the cause is removed unless stresses work the area leading to "stress-corrosion cracking". Aluminium is great because it is both light and for the reasons you outline, does not easily corrode. If conditions lead to corrosion, however, the same high reactivity of the metal that causes the protective layer can speed things up. Anodising helps by increasing the thickness of the protective layer which is also sealed as the final part of the process.

 

[Leonidas]

I think that you should be able to take some confidence in the welding repair, if it is done by a welder experienced in welding aluminium then, from an initial engineering point of view, it should be pretty strong. The problem, over the long term, will be protecting the repair from corrosion. uNQUOTE

Thanks for these helpful suggestions.

The proposed repairs will be as folows:

1.- The full penetration welding of the cracks ( 1 x10cm, 2 x5 cm long) will be carried out by coded welder using Aluminium series 6 electrodes , and will be ground smooth on completion.
2.- A shaped aluminium doubler about 10 cm wide, which will follow the profile of the mast will be welded around the base of the mast externally to reinforce the weldings and area of mast.
3.- On completion,after wire brushing, all weldings will be treated with suitable primer internally and externally and finished with a top coat of similar shade as that of the mast.

I think that should take care of it ????

 

[Zen Zero]

Others with more knowledge and experience will be able to comment on this, but I thought that aluminium is actually a highly reactive metal which on exposure to air forms a strong oxide layer (which is actually corundum, a very hard and chemically inert substance) on the surface, protecting it from further corrosion. Anodization merely makes the corundum layer thicker, and allows alternative finishes. For that reason, I've always regarded anodization as a cosmetic rather than a structural issue. After all, we don't usually bother touching up a scratch on an anodized spar.

Can one of the metallurgists on here confirm or deny this?

It's what I said earlier, "it anodises itself". I think the welding idea is a good one. The only thing is it will leave an area of different hardness (harder or softer depends 1 on how hard it was before (what temper it had) and 2 how quickly it cools after the weld).

Go for it!