Stainless Scew Sets?

I'd be worried about electrolytic action, fitting stainless anything to a Land Rover - all those dissimilar metals wreak havoc with one another if you are not careful

Karen

On or around Mon, 12 Jun 2006 09:07:58 +1000, Karen Gallagher enlightened us thusly:

mind, you get that with ordinary steel. If you fit stainless direct to the alloy you're recommended to isolate 'em, e.g. with a bit of polythene sheet or similar, though.

Hi all,

Well three years ago I fitted stainless steeel bolts onto a Series 3 when I did a part rebuild, three years alter there is no rust and I live within sight of the sea. The new owner loves it as well. On Defender 110 not one bit of rust or corrosion when I used stainless steel bolts. The Chromium stops any rust.

I have a policy now when I replace a nut bolt or screw on my Disco it is always Stainless Steel.

On the series 3 the front bumper had to be removed a year later and I had used huge Stainless Steel bolts, it came off as though it had been put on the day before.

Go Stainless - lots of suppliers on e-bay. You do not say which vehicle you are fitting them to, series 3 and Defender can be a pain for the doors, lots of oil to soak the old nuts for a couple of days and then an impact driver I found helpul. Go for the stainless with Allen key heads they are excellent.

Yours

Andy

And the salt promotes chloride cracking in stainless steels.

Steve

Quite agree.

I had to have a mild steel bolt spark eroded out of my (horribly expensive) Keihan stainless exhaust for the R80. I was charged 60UKP to do it, but a new pipe would've been 180UKP (for one side). It had 'exploded' with rust, and was quite impossible to get out otherwise, and yes, I'd tried all the usual fixes: 'easy-out', welding a nut onto the stub and careful drilling.

The three other stainless bolts caused different damage, causing the exhaust brackets to corrode away in very short order, and necessitating some really awkward welding on the frame to replace them. All the problems were at the stainless/mild steel contact points.

Aluminium doesn't seem to have the same effect. The engine is still there, and the rest of the bike's frame.

Regards,

Simonm.

And the chromium promotes rust in the surrounding mild steel.

Regards,

Simonm.

I'm getting lost on some of the logic behind this thread....

Why would stainless steel promote any greater re-action on a mechanical fixing (against aluminium) than mild steel? The reasoning being suggested is the chromium content but don't many motorcycle engine casings use stainless screw sets on 'tricked up' machines? My motorcycle engine casings where fitted out with stainless screws sets 7 years ago but don't show any signs of re-action?

Regards, Dennis

I can't see why rust is ever an issue given the amount of sodding engine oil coating the entire underside of any of my landies. What a waste of money all that Waxoyl was...

I have used Stainless on all my doors and bonnet Series 2A hinges - 4 years they have been on and no probs at all.

just remember if you are replacing 8.8 with Stainless to go for A2 or higher.

hope this helps

gary

DB4 wrote:

A few years ago someone really knowledgeable answered this in this same forum; I kept their post, but sadly not their name, but here it is again anyway:

Aluminium corrosion Galvanic corrosion can occur when dissimilar metals are electrically connected in the presence of an electrolyte (i.e. conductive solution, e.g. salt water). Galvanic attack can be uniform in nature or localised at the junction between the alloys depending on service conditions. In such a process, one of the metals acts as cathode where oxygen is reduced and the second metal acts as anode that suffers corrosion (oxidation).

To predict the risk of corrosion and determine which metal will corrode in a given electrolyte, metals/alloys are classified following the corrosion potential (natural potential) they develop in contact with an electrolyte. The following table gives those potentials for some typical alloys/metals in contact with seawater at 25C - I know thats an unheard of sea water temp in the UK, but here in North Eastern Australia in mid winter the water temp has only just dropped below 22C.

The dissolution potentials of various metals in sea water are;

Graphite + 200 Stainless Steel - 100 Brass and copper - 350 Low-alloy steel - 600 Low-alloy steel and cast iron - 600 Aluminium alloys - 750 Zinc - 1000 Magnesium - 1600

This classification stays valid for many types of metals and liquids solutions that they might come into contact with. As a consequence, aluminium will corrode when contacted with stainless or normal steel (commonly used in road transport), or copper (sometimes). Aluminium will be protected in contact with zinc that corrodes instead of the aluminium.

In most cases (except in frequent contact with salty solutions), the combination "aluminium/steel" only generates a detrimental effect on the aesthetic appearance of the aluminium structure but not on the mechanical properties of the assembly. Indeed, aluminium corrosion in contact with common mild steel is very slow - years instead of minutes. This is why connections with steel chassis which are expected to last a long time are usually made using steel fasteners.

Without suitable precautions, the combination "aluminium/stainless steel" should be avoided taking into account the big difference of corrosion potential of both metals (-100 : -750). However, aluminium alloy components are often assembled using stainless steel bolts. It's important to remember that stainless steels have surfaces that can be passivated (eg washing in nitric acid) and this inhibits or eliminates galvanic corrosion until the oxide created at passivation is worn off by friction. Turning a nut onto a bolt can be sufficient at times.

In case of frequent immersion or wetting (e.g. inside road tankers or the bodies of Landrovers), aluminium and other metals should be isolated from one another to prevent aluminium corrosion (an elastomer gasket on flat surfaces and a grommet through holes or a specially formulated coating such as an epoxy resin with a glass filler which is hard enough to withstand friction).

Possible origins of galvanic corrosion in an older Landrover:

1. Steel bolts or rivets on aluminium panels
2. Aluminium body on a steel chassis
3. Stainless steel bolts or rivets on aluminium panels
4. Aluminium body on a galvanised steel chassis
5. Other bolt on accessories - bull bars, etc.
6. Multi-aluminium-alloy components (condenser, radiators, coolers, welded or brazed assemblies)

Possible effects near the metallic contacts

1 & 2 Less aesthetical appearance (the white powder of aluminium oxide) 3 to 6 Significant decrease in the thickness of aluminium components over short periods of time depending on the electrolyte strength - salt water, etc.

Prevention or Remedial Actions

1 to 5 Insulate dissimilar materials 3 & 4 Use stainless steel with passivated surfaces only if they oxicde will not be removed

1. Use special coatings for the application - no one coating will prevent all corrosion
2. Good corrosion design (choice of right combination of aluminium alloys)

If the insulation is not properly done, galvanic corrosion will often be combined with crevice corrosion.

I have quoted from various sources and books on corrosion and tried to bring it together.

Hope this helps.

Karen

On or around Tue, 13 Jun 2006 23:02:13 +0100, gary enlightened us thusly:

Looked into this once before - A2-70 is not quite as strong as 8.8; the 70 part is tensile strength in some units or other as is one at least of the

8s, you need a -80 stainless to be equivalent tensile strength. however, the tensile strength of an 8.8 bolt is rarely critical.

Very true - the cost goes up by some margin once you go above A2, but i would go for the cost of that for a suspension part or high load area that i would only fit an 8.8 to in the first place.

also i'm not sure if stainless is like high tensile? in that a bolt it

8.8 but the same size in an allan cap is 12.9! - any idea if its the same for stainless???? - i usually use allan caps for my builds.

gary

Aust> On or around Tue, 13 Jun 2006 23:02:13 +0100, gary

On or around Wed, 14 Jun 2006 17:45:59 +0100, gary enlightened us thusly:

you can get ordinary bolts in 12.9 as well, mind. not easily, I grant you.

here, more info:

second question down explains something I've had happen before now.

Thanks for the link, most interesting, as for the 12.9's yes you can get them but you usually have to order them, if you go for cap heads you get them as standard :-)

Gary

Aust> On or around Wed, 14 Jun 2006 17:45:59 +0100, gary