Corrosion of Aluminium fittings in Seawater

[knowkeys]

Has anyone got any experience of corrosion of Aluminium fittings in Seawater?

I know that Aluminium is used in anodes, so would expect a sacrificial "reduction" over a period of time.

The specific case is with Aluminium "ferrules" which terminate the end of wire ropes. The wire rope will be "touching" carbon steel pipe, although full electrical continuity may not be achieved. The internals will be filled with seawater.

We have seen cases of Aluminium "fizzing" away after days and other cases where the period is "months". This will obviously depend on the alloy used.

Any guidance on typical "life" and/or experience of this type of fitting would be appreciated.

Thanks
Steve

 

[rnd2]

You need zinc anodes. They are anodic to aluminium and will stop the aluminium corroding. This is well documented. However, they absolutely need to be in electrical contact with the aluminium.
Another alternative to zinc is magnesium but if you are in seawater go for zinc.

 

[unclesyd]

If you see any metal fizzing in saltwater you have a problem that needs to be corrected. A Zn andoe would fizz more than the Al, it would still protect the Al. You have stray currents, (probably DC) that need located and corrected.

Come back with a little more information on physical location and surroundings.

 

[jay165]

Be careful with magnesium. It is even more active than zinc and I've heard of a case were an explosion inside a tanker barge was caused by a build-up of H2 as a result of a magnesium anode electrolysis.