Just wondered if people know why krabs turn to jelly in a very short space of time if you leave them on a hanger down a cave.

Its chemistry innit. I cant be arsed to go into the nitty gritty chemisty of it (to do with + charges and - charges and electrons and oxidation an all that ting)

but basically if you put two different metals in contact together in a corrosive (oxidizing i.e rusting) environment then one will corrode in preference to the other and corrode faster.

So if your hanger is stainless steel (basically iron Fe2+) and your crab is aluminium (Al3+) then the aluminium will react with oxygen and water much faster than the steel which will hardly corrode at all.

Thats why it is very important to avoid leaving aluminium alloy (nearly all) krabs on insitu hangers

Clearly systems where all the components are stainless steel are the best. EG P bolt with a stainless mallion. but failing that - steel mallions on steel hangers.

I suppose you could leave an old ali krab on the hanger too, just to act as a sacrificial anode.
i.e. let it sit there and rot in-order to preserve the steel mallion - just a thought.

[/chemistry lesson]

suppose you could leave an old ali krab on the hanger too, just to act as a sacrificial anode.
i.e. let it sit there and rot in-order to preserve the steel mallion - just a thought.

Click to expand...

would that work?

cool

I suppose it would.

I know that most ships have blocks of Magnesium or aluminium bolted to the hull so that they corrode instead of the steel hull.

You would have to look carefully at the metals involved.

I pulled a ring hanger out recently - sleeve an all. noticed back in the pub that the ring and sleeve where not too badly corroded - but the cone that would have been captive within the sleeve had compeletely gone. :shock:

I wish some one would tell landrover about this !

Great, all alli body pannels but where ever steel is bolted to it it has reacted and blown all the paint from the alli, little or no rust though on the steel !

Its a age old problem with dis simular metals

Stainless steel is the way to go hard wearing and non ferous