COR-TEN®, corten, CorTen, and so on are alloys that contain Copper. Copper and aluminum are dissimilar metals and electrolytic contact of these metals will induce and accelerate corrosion of the aluminum. The severity of electrolytic corrosion depends upon many factors including the severity and frequency of electrolytic contact (accelerating factors); and the oxidation rate of the aluminum (which will help to retard corrosion).
Typically, corten is used on corrugated roofs which the aluminum bracket and roof surface have a separator (epdm or butyl). Because of this separator, customers are often choosing to use the brackets on the roof; however, it needs to be the customer’s choice. We have heard that this type of roofing has made it into the standing seam market, If it is used on a roof where an aluminum clamp is utilized, then there are some options.
Anodizing the clamps: In theory, anodized aluminum is sometimes postulated as an appropriate method to separate dissimilar metal, however it should be noted that when the anodized coating is broken (via surface scratching during packing, shipping or during and post installation), the scratch location is subject to accelerated corrosion.
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. And anodizing has been known to increase corrosion resistance and wear resistance of the given metal (in this case aluminum). What we are unable to speak for is how much will it increase corrosion resistance.
Mill finish with a separator: Depending on seam geometry a stainless-steel separator or EPDM pad can be used to separate the metals.
Stainless steel clamps: Stainless is compatible with corten; however, it will depend on the seam geometry as whether or not a stainless clamp can be fabricated.
Mill finish clamp: In general, when dissimilar metals come into contact then corrosion will take place, to what extent is reliant on many different variables. These variables will change from project to project as each application will have its own environmental conditions and issues; therefore, it is not in our scope to be able to test how long it will take or to what extent corrosion will occur. With all that said the climate could be such, or the application such that corrosion is not a concern for the given application. The aluminum clamps in direct contact with a dissimilar metal in the desert will perform differently than say in a marine environment. It depends on whether or not you care if the clamp corrodes, it will not affect the roof however.
Further to all of this keep in mind corten is an alloy that contains copper and is not a copper roof. This too will diminish the harm done to an aluminum clamp.
Created by: Shawn Haddock
Modified on: Wed, 13 Jun, 2018 at 3:39 PM
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