Question about Galvanic Corrosion

Why do you need to use both types of steel?

one manufacturer offer a cilinder with that kind off steel

What environment will they be in where you expect galvanic corrosion? Water is needed for galvanic action, and if the environment will be dry (or at least not seaside), this shouldn't be a major problem. Otherwise, simply painting MAY help, but many grades of stainless don't like being deprived of oxygen. Also, what material is the shaft? You may be better off using a steel end cover. Talk to your cylynder supplier or manufacturer - they should be able to advise you on your application.

As long as the cylinder is not going to be immersed in water you should be OK. I'm assuming an outdoor application. There will be some steel loss at the mating surface of the two metals but internal wear in the cylinder will be the limiting factor over the life of the cylinder. As mentioned previously paint is an option.

The cylinder is to outdoor application, in conditión off relative humity 60%, 25ºC annual media, on a forest. I assuming the material of the cylinder dont have troubles during transportation and proof, but they gone to be expose 4 years and I need information if is possible a falifure

Unless this is being built for some disposable robotic machine never to be touched again then any cylinder should be built to allow easy field repair. If it will never be accessed again then what is the expected service life, and will it ever be exposed to conditions where galvanic action can occur? If the cylinder assembly is held together by external fasteners and end plates then the surface/edge abutment could be protected by a barrier gasketing material. Welding or threading the anchor end shut introduces unnecessary production and quality control issues. An example would be the high rate of weld failure between the jacket on a catalytic converter (stainless) and the exhaust pipe (steel) on any current in production automobile. In an environment with radical temperature extremes it would be prudent to keep the coefficients of thermal expansion among the components as close to each other as possible to prevent pieces from unthreading and leaking.

For operate one Hydarulic gate , we need one hydarulic cylinder. The gate is gone to be use for the derivation channel and the cylinder is gone to be out off water, exposed to atmosphere in a tropical zone (forest, over 25ºC, Relative Humity 60%). The gate and the cylinder is gone to be exposed almost 4 years on that enviroment and when we close the derivation channel never again we need the gate. we only can monut the gate and the cylinder when the channel is on construction. The principal data off the cylinder are: - Force 140 ton - Carreer 10 m on the bid document, indicates the cylinder body is on steel, and the end on stainess steel At the present one manufacture offer a cylinder with the initial materials, acording with bid documents, but we have douts about that, is for that reasson i need documentation about. The equivalents to ASTM norm off the materials are: - St52.4 DIN2448 eq. ASTM A440 - 25CrMo4 DIN17200 eq. ASTM A322

Personally, I'd worry more about the weld joint & heat affected zone - regarding regular corrosion (ie, rust). But, like stated above, it's nothing a good paint-job won't solve.

Galvanic corrosion of steel, from a practical standpoint, is only a problem when the galvanic couple is continuously immersed in a conductive electrolyte that contains oxygen. This application is merely outdoors. Paint should be fine.

Steel penstocks are paint inside with special paints that last for at least 10 to 15 years before need to be paint againg. Same happens with spillway and drum gates used at dams. Paint the cylinder with special paint and you get rid of the enviroment including the galvanic corrosion. I would worry more on the interface between the shaft and the atmosfere, so i will protect that end with, maybe, a grease boot. And will also grease the shaft (with an enviroment frendly grease). The botton line is to cover and to protect the entire mechanism with paint and grease. These should last you for years. Keep it simple =) Regards. Luis

Ok, We are going to paint the cilinder with han epoxic paint.

I work at the Panama Canal (Gatun and Madden Hydro Generating Stations) and as you know this is a rain forest area. We have been using this method in all our equipments for many years and has proven sucessfull. Good luck. Regards. Luis

Here is a link to an interesting site which helps to see which steels are compatible with others' and the effects and causes of corrosion. http://www.key-to-steel.com/Articles/Art60.htm

Here: http://www.engineersedge.com/corrosion/galvanic_co rrosion.htm and here: http://www.engineersedge.com/galvanic_capatability .htm