Duralac paste needed with monel rivets?

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eddystone

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When I needed to remove the boom end cap (aluminium to aluminium) a couple of months ago, the guys at Aladdin's Cave where I bought the rivets told me you didn't need chromate paste with monel rivets. Now I'm not so sure - should I drill them out and do it again with paste this time?
 
Worth putting "Duralac" into the forum search-box! Not the first time the question has come up...I reckon it is worth acquiring some if adjacent metals will routinely get wet...

...but I expect people would more happily buy the tube of paste, if the manufacturers sold the stuff in quantities which relate to the rarity and smallness of their required use.

As it is there must be thousands of opened tubes in this country with hardly any of the contents squeezed out...certainly, I and others at my club fell into the belief that we couldn't do without it, nor count on our neighbours to have any. If I knew where my tube was, I'd gladly send it to you, to save yet another largely unnecessary outlay on this stuff.

The company called Plastic Padding put their hardeners in tiny tubes...that much Duralac would last me for ten years I'm sure...but I had to buy enough for several lifetimes. :(
 
eddystone said:
When I needed to remove the boom end cap (aluminium to aluminium) a couple of months ago, the guys at Aladdin's Cave where I bought the rivets told me you didn't need chromate paste with monel rivets. Now I'm not so sure - should I drill them out and do it again with paste this time?
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Preferable, Monel is a copper nickel alloy, but I'd not go to the trouble of drilling them out again.

I took the goose neck fitting off and refitted it about 30 years ago without using Duralac on the rivets. No problems as a result.
 
eddystone said:
When I needed to remove the boom end cap (aluminium to aluminium) a couple of months ago, the guys at Aladdin's Cave where I bought the rivets told me you didn't need chromate paste with monel rivets. Now I'm not so sure - should I drill them out and do it again with paste this time?
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Barium chromate paste is only needed with alloy to stainless or stainless in alloy - you'll find the manufacturers all use aluminium rivets for boom ends. The more up-market ones put an insulating collar under the head.
Aluminium rivets are rubbish in shear and stainless heads are usually so thin that they give way.
 
AngusMcDoon said:
...a tin containing over twice as much is cheaper than a toob...
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Having already bought a tube, assuming I can find it, I doubt I'll ever need more, but well done for showing that we needn't be ripped off.

I expect it's possible to buy a five-gallon barrel of Colgate for the price of a dozen tubes in Boots. :rolleyes:
 
dancrane said:
Having already bought a tube, assuming I can find it, I doubt I'll ever need more, but well done for showing that we needn't be ripped off.

I expect it's possible to buy a five-gallon barrel of Colgate for the price of a dozen tubes in Boots. :rolleyes:
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I've still got the tube of Duralac I bought in 1992; it's about half-full and I keep it in the 18v Makita drill box.
 
charles_reed said:
you'll find the manufacturers all use aluminium rivets for boom ends. The more up-market ones put an insulating collar under the head.
Aluminium rivets are rubbish in shear and stainless heads are usually so thin that they give way.
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Certainly not true for Seldén booms.
There is some good advise on page 67 of this document:
http://www.seldenmast.com/files/595-540-E.pdf
As I read it, there is no requirement for duralac or similar for monel rivets, but it should/could be uses for stainless fittings and/or screws.
 
The function of Duralac is to prevent galvanic corrosion. Since monel and aluminium occupy different positions in the galvanic series there is a possibility that corrosion could occur in the event that seawater lodged between them. There is even a case that it should be used between components with the same composition. Googling it finds lots of hits of course but this one seems to talk sense. http://intek-uk.com/index_htm_files/Duralac TDS.pdf
 
vyv_cox said:
The function of Duralac is to prevent galvanic corrosion. Since monel and aluminium occupy different positions in the galvanic series there is a possibility that corrosion could occur in the event that seawater lodged between them. There is even a case that it should be used between components with the same composition. Googling it finds lots of hits of course but this one seems to talk sense. http://intek-uk.com/index_htm_files/Duralac TDS.pdf
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That Duralac is promoted as "indespensable" by someone who produces/markets it is perhaps not so surprising.
If that was true, I think a major spars maker like Seldén would use it on every monel rivet put into aluminium and also strongly advice their customers to do so when (re)fitting something. But they don't, apparently. So I think the OP can trust the guys at Aladdin's.
 
BabaYaga said:
That Duralac is promoted as "indespensable" by someone who produces/markets it is perhaps not so surprising.
If that was true, I think a major spars maker like Seldén would use it on every monel rivet put into aluminium and also strongly advice their customers to do so when (re)fitting something. But they don't, apparently. So I think the OP can trust the guys at Aladdin's.
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Why do you think that stainless steel on aluminium, which everybody agrees should have a Duralac treatment, is different from monel on aluminium? Monel and 300 series stainless steels occupy almost exactly the same position in the galvanic series table, with a potential difference of between 0.7 and 0.9 volts. Aluminium masts and spars corrode badly around stainless steel fittings and fasteners that are unprotected, so why should monel be any different?
 
BabaYaga said:
That Duralac is promoted as "indespensable" by someone who produces/markets it is perhaps not so surprising.
If that was true, I think a major spars maker like Seldén would use it on every monel rivet put into aluminium and also strongly advice their customers to do so when (re)fitting something. But they don't, apparently. So I think the OP can trust the guys at Aladdin's.
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Look at the pictures, wonder why my rigger is using Duralac?
616AE372-43DC-4328-A061-537AA643253B-1429-0000010E25B956DD_zps790d7e2d.jpg


2D1DFDFF-A0E5-40DF-89F0-2BB00475EBD1-1429-0000010E7973EE40_zpsd4a7215d.jpg


CD89E32E-3C36-4FD1-B39E-74A61D366017-1429-0000010E724173DF_zps203bb902.jpg
 
vyv_cox said:
Why do you think that stainless steel on aluminium, which everybody agrees should have a Duralac treatment, is different from monel on aluminium? Monel and 300 series stainless steels occupy almost exactly the same position in the galvanic series table, with a potential difference of between 0.7 and 0.9 volts. Aluminium masts and spars corrode badly around stainless steel fittings and fasteners that are unprotected, so why should monel be any different?
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My understanding of the general agreement is that a stainless steel fitting on aluminium should be isolated, not necessarily by Duralac, but perhaps even better by a nylon gasket or similar (which quality fittings often comes supplied with).
The lack of such isolation is what I think can be seen in the pictures posted by knuterikt.
Duralac on monel rivets? Surely not harmful and likely beneficial to some extent. But the OP was asking if he should drill out the newly fitted monel rivets and put new ones in, this time with Duralac. IMO that would be unnecessary, for the reason already stated.
Why are monel rivets better than stainless? I have no idea, but if their ability to create corrosion in aluminium was equal I assume the spars manufacturers would use stainless, as it is cheaper probably just as strong.
 
knuterikt said:
Look at the pictures, wonder why my rigger is using Duralac?
616AE372-43DC-4328-A061-537AA643253B-1429-0000010E25B956DD_zps790d7e2d.jpg


2D1DFDFF-A0E5-40DF-89F0-2BB00475EBD1-1429-0000010E7973EE40_zpsd4a7215d.jpg


CD89E32E-3C36-4FD1-B39E-74A61D366017-1429-0000010E724173DF_zps203bb902.jpg
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The reason for this corrosion is the stainless not the monel. Monel will corrode aluminium but very very slowly after 20 years it will have removed some of the material but minimal. If you have already done it forget about it and rest easy. 98% of rivets in spars are not isolated as it's not necessary.
 
vyv_cox said:
Why do you think that stainless steel on aluminium, which everybody agrees should have a Duralac treatment, is different from monel on aluminium? Monel and 300 series stainless steels occupy almost exactly the same position in the galvanic series table, with a potential difference of between 0.7 and 0.9 volts. Aluminium masts and spars corrode badly around stainless steel fittings and fasteners that are unprotected, so why should monel be any different?
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My 15 metre aluminium mast is about 40 years old and made up in various sections being in 2 vertical U sections with 3 sheave joins all connected with monel rivets when original built. Later in life it has some stainless fittings added using aluminium rivets with no duralac. These stainless fittings showed extensive corrosion when modified the mast before fitting to my current boat, where the original monel rivets had no corrosion at all.

Don't know the answer and like you if the there is galvanic corrosion with aluminium and monel the lack of duralac over that time should show lots of corrosion but it does not so maybe there is something else at play between stainless and aluminium that is not in play between monel and aluminium.
 
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