One of the biggest is none other than the S.S. United States. Like many liners of her day, she was built with a steel hull and an aluminium superstructure to lower her center of bouyancy.A rubber seal was placed between the superstructure and hull to prevent galvanic corrosion, but over time, the rubber has rotted away. It is my understanding (but I could be wrong) that this will need to be resolved along with a possible repowering should she ever be returned to service.-James Hefner Hebrews 10:20a Surviving World Steam Project

I'm quoting Dave again, because another aspect of this discussion has just come to mind. While not implicitly stated in the references I cited, it would appear that Galvanic corrosion does not only occur where the two dissimilar metals touch each other; given the presence of two dissimilar metals and moisture to form a current path, the more anodic metal will corrode wherever the electrolyte comes in contact with it. This is basically how the sacrificial magnesium anode rod protects your hot water heater from corrosion, and it protects the whole wetted part of the shell, not just the fitting it's threaded into. Therefore, one possible reason for the plentiful corrosion Dave mentions may be the presence of both steel and aluminum in the same moist environment.

> This is probably why EMD didn't use aluminum to begin with. Which raises the question in my mind; what did AT&SF, CB&Q, and others who used stainless steel for side panels do to overcome this? I'm assuming, of course, that they did not use stainless steel for the vertical frame components which the side panels attached to, or did they?

I believe that there were some rebuilt Pittsburgh PCC cars that used Alucobond material to replace rusted-out portions of the outer skins.

EMD didn't use aluminum because AL is expensive relative to steel. Remember that EMD came up with an in-house substitute for plymetal in the form of a sandwich of two steel sheets with a corrugated inner steel section.Don't think that galvanic action is a concern with stainless and carbon steel.Doesn't the NKP 190 have s/s sidesheets ?

I don't think there are enough of these locomotives in captivity for anyone to have had experience with them. I know that the entire nose of the E-5 at IRM is a welded stainless fabrication, but I have no idea if the structure behind it is stainless or carbon steelI was rather hoping that someone with experience in restoring Budd passenger cars (and for that matter, the stainless clad CorTen P-S cars, too) would chime in here, as they involve all the same issues, but are much more common. And yes, the issues are there. Take a look at the pages on side sill defects on the Illinois Transit Assembly web site at:http://www.iltransit.com/sidesill.htmlI will hazard a guess as to what the builder's philosophy was:Steel and stainless are much further toward the passive end of the scale than aluminum is. Therefore, while there will eventually be problems, they will develop more slowly.When aluminum is used, it is typically the 'show' metal, and the effects of the corrosion will be noticed early. Where stainless is used, the more passive metal is the 'show' metal, and the framing behind it can quietly corrode away un-noticed for years.Galvanic corrosion is only going to happen if the dissimilar metals are continuously wet. On a piece of equipment in service, the air streaming by will tend to dry it quickly, and keep it dry.All equipment is designed with a service life in mind. If our product remains trouble free for thirty years, the customer has gotten his money's worth, and has no reason to complain.Contrast this with the conditions historic artifacts face:Most are on their second or third 'service life'. In fact, some may have been sitting still, unmoved, for more than one service life. The Pioneer Zephyr is a good example. Any little pinhole in the sealing of the joints will let in literally gallons of water over that period of time. That water will then stay and turn the interior into a terrarium. In addition, it is our intention that the item last not for thirty years, but forever. At least, as preservationists, that should be our intention.

I don't see the connection between passenger cars and carbody-type diesel locomotives.Passenger cars are meant to be 'waterproof', i.e, water is not supposed to infiltrate the passenger space. Of course, that doesn't mean it doesn't penetrate the outer skin. Carbody type locomotives are not waterproof (nor were they meant to be)-as there are too many openings in the form of louvers, shutters and so on. When they are operating, the engineroom is at a slight negative pressure-with lots of air movement. By way of example, a number of the FL-9's that were rebuilt by ABB in the early 90's were found to extensive structural corrosion in the side trusses and required some extensive (and expensive) repairs. Contrast this with an Alco/GE FA-1 that was 10 years older. There was no evidence of full penetration of rust through structural members. The side truss structure of the Alco utilized much heavier members.None of this stuff was meant to last forever-anybody check out the Parthenon these days ? Dave K