Hot-dipped zinc galvanizing has long been the ag industry standard for protecting steel trailer chassis from corrosion. That may be changing if a 1,000-hour study by Daubert Chemical is any gauge. Note: Daubert manufactures a competitive wax-based underbody coating.

No definitive comparative study had been done, according to Mike Duncan, Daubert’s vice president for technology. “So we decided to undertake formalized testing” following the American Section of the International Association for Testing and Materials standardized (ASTM B117) method known as salt fog testing to assess corrosion resistance of heavy-duty trailer chassis steel.

Salt spray testing is an accelerated corrosion test that approximates the long-term protective efficacy of a coating and its failure rate. The test pitted galvanized steel I-beams to I-beams coated with Daubert’s Nox-Rust 1210HP wax-based coating. The galvanized steel began shedding protective zinc coating within 1,000 hours of exposure.

The continuous salt spray exposure caused the galvanized sample to begin visibly shedding its protective zinc coating as zinc oxide, also known as white rust. In contrast, a wax-based coating repels water molecules and prevents that oxidation.

Using galvanized metals for trailer construction presents other problems, too, claims Duncan. Slider suspension boxes, wing plates, lighting brackets and the like often involve welding, grinding and drilling operations that can dislodge zinc coatings on galvanized steel. Once that protective zinc is removed, the steel substrate is vulnerable to corrosion due to both oxidation and galvanic reaction from contact with dissimilar metals.

In contrast to galvanization, a residual wax-based barrier material is retained even after machining of pre-coated stock has taken place. It also adheres to fresh welds and provides residual oxidation and galvanic suppression during the application of screws, bolts and other mechanical fasteners.

“The idea that corrosion can be avoided by building a trailer using galvanized components is a myth,” concludes Duncan. “You simply can’t take corrosion out of the equation with galvanized steel. But you can successfully manage corrosion on all exposed metals, including galvanized, very cost-effectively with hot-melt wax-based coatings.”

No comparison was made with powder or epoxy coatings.

Source: Daubert Chemical