Feared Corrosion Problem
Feared Corrosion Problem
(OP)
For a specific kind of valve used in the cooling system of locomotive diesel engines, 6061-T6 aluminum is being chosen for the material of the valve body for several good reasons. The question arises as to how best to aleviate the corrosion problems inherent in such an application. The cooling water, at 180ºF max, may or may not have corrosion inhibitors in it and may be hard water taken from local wells and streams. The valve body is connected by bolts and flanges to steel pipes. Electroless nickel is being considered as a coating but doing this to aluminum is complicated and costly. Hard anodize can serve as an insulator against galvanic corrosion with the steel pipes. The bolt threads do not touch the cooling water but they will make an electrical connection. How good is hard anodize against chemical corrosion with the water? The valve is expected to operate for 20 years. I would appreciate some words of wisdom from you folks.





RE: Feared Corrosion Problem
1. Anodize (sulfuric acid, ASTM B 580 Type A or B or MIL-A-8625 Type II)
2. Nickel acetate seal
3. Epoxy primer (2 coats of high-solids type MIL-PRF-23377 or MIL-P-53022)
4. Some type of water-resistant topcoat paint. Polyurethanes are typically used over epoxies when the coating will be exposed to direct sunlight. However, I am not sure about the long-term water resistance of typical PU coatings such as those specified in MIL-PRF-53039.
This type of system provides outstanding corrosion performance on aluminum components. It would insulate the surface from galvanic corrosion with the steel pipes. I would contact some paint vendors to discuss this type of application. You can obtain the MIL standards that I mentioned, along with the list of approved suppliers, by using the following link:
http://assist.daps.dla.mil/quicksearch/
Just substitute QPL for MIL-P to find the approved suppliers and contact info.
RE: Feared Corrosion Problem
RE: Feared Corrosion Problem
That said, I have seen parts treated as TVP suggests hold up very well. In the long term the limit will be the durability of epoxy at 180F in water. You will reach a service limit.
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RE: Feared Corrosion Problem
RE: Feared Corrosion Problem
RE: Feared Corrosion Problem
Ed is right, if you can avoid Aluminum, do so. If not, coat it with epoxy and electrically isolate it fo cut down on the galvanic coupling.