Tin oxide corrosion in turbine and gear bearings

[BillSalvage]

The turbine and gear bearings of a marine propulsion set were found blackened and harder than expected. A surveyor said it could be caused by tin oxide corrosio. What is tin oxide corrosion? Any other ideas?

 

[nan2001]

This is visible by a black coating on the running surface.Normally water gets separated and are drained in turbines at regular intervals. The oils used in turbines have these properties. If too much emulsion takes place and left unattended, may lead to above corrosion. These u may find in diesel engine bearing too when percentage of water gets more and TBN value decreases.

 

[shipvibration]

tin oxide corrosion occurs in white metals.black(dark grey)surface layer attached to white metal.bright tin-antimony specks show on examination.
layer hardness: 350 VPS(vickers pyramid hardness)
orig white metal hardness:30 VPS (compare mild steel 130 VPS).
due to this hardness all soft bearing props r lost.if rust were to find its way in then, journal damage ensues rather than the bearing.
TO corrosion reduces clearances.in worst case blocks lubrication..high temp...seizure!!
factors causing TO corrosion: water ingress,extreme pressure additives(especially those based on chlorides),
white metal composition(cadmium addition helps)