Metals compatibility

[tangofour]

Perkins 4-108 engine. Water injector elbow on the exhaust manifold. Finaly dissolved after 20 years. Why? Aluminium Cast master piece. Cast iron elbow atttache to it with 2 S/S bolts. Steel blanking plate to other hole also attached with 2 S/S bolts.

A veritable battery when submersed in warm seawater.

Any suggestions on how to put the new bits together and avoid some of the effects?

 

[cliff]

[ QUOTE ]
Perkins 4-108 engine. Water injector elbow on the exhaust manifold. Finaly dissolved after 20 years. Why?

[/ QUOTE ]Don't know, I would have expected 1~2 years so at 20 years service life I would not complain. Cast Iron one on my engine is almost a "service item" (5 years if I am lucky).
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[Birdseye]

I'd second that. With cold salt water ebing injected onto a hot exhaust with corrosive combustion gasses you have done well

 

[vyv_cox]

I'm not quite understanding the relative proportions of your arrangement but if I assume the aluminium part to be more massive than the iron/steel bits, then this is an acceptable design. The aluminium is more electronegative than the other components but there is far more of it. It dissolves but protects the rest. 20 years seems more than reasonable to me: most Bukh manifolds last about three years if you are lucky.