Salt Water Testing for Galvanized Metal Strut
Thomas & Betts
Thomas & BettsMost metal strut systems are made of carbon steel, which requires plating, or galvanizing, usually with zinc, to protect the components from corrosion. Thomas & Betts (T&B), manufacturer of two lines of metal strut, Kindorf® and Superstrut™ channel systems, offers a selection of zinc galvanizing options, among them being a trivalent chromium finish applied over zinc, creating a chemically bonded, nonporous barrier, as well as its characteristic yellow color. T&B markets this finish as GoldGalv® plating for Superstrut channel systems and Galv-Krom® plating for Kindorf channel systems. The plating is applied after cutting and punching, which protects all surfaces of the finished product.
Another type of finish is pre-galvanized plating, which is a zinc coating that is applied by submerging steel components in molten zinc at the mill prior to fabrication.
Thomas & Betts conducted testing that compared the performance of zinc trivalent chromium plating with the pre-galvanized finish on metal strut. The test measured resistance to both red rust, which is oxidation and corrosion of carbon steel, and white rust, which is oxidation and corrosion of zinc. Both kinds of rust affect the service life of metal strut.
The samples of metal strut were taken from standard inventory and subjected to salt-fog testing in accordance with ASTM B117.
The results of the test indicated that strut plated with GoldGalv and Galv-Krom finishes took an average of 40 hours to accumulate white rust on the full sample and an average of 152 hours to accumulate red rust (three of these samples did not reach 5 percent of red rust after the 1,128 hours of the test was completed). In comparison, the pre-galvanized samples took an average of 16 hours to accumulate white rust and an average of 184 hours to accumulate red rust.
Photo courtesy of Thomas & Betts