Causes of Corrosion
For decades, sodium chloride (rock salt), calcium chloride, and magnesium chloride have been used for de-icing roadways. The presence of salt dramatically enhances the rusting of metals. Road debris, sand, gravel, and other deicing materials can damage trailers as well. These substances leave chips in the trailer’s coating and expose the underlying substrate to the corrosive environment.
Many trailer components are also vulnerable to galvanic corrosion caused by dissimilar metals making contact. A simple maintenance repair that pairs the wrong nut, bolt, or washer can create a corrosive response. Problems can also occur as a result of tightened fasteners, which can dislodge surface coatings, exposing reactive metals to one another and the elements. Areas on a trailer with high exposure to road-born moisture, such as around tires, are areas where corrosion is most likely to occur. Other important areas to inspect for corrosion on trailers include rear frames, gussets, rear underride guards, threshold plates, front aprons, upper couplers, landing gear brackets and braces, cross members, end clips, front under-structure, suspension, and axle assembly components, and any ledges underneath a trailer that allow debris to enter.
Roadway pretreating products such as calcium chloride and magnesium chloride are very corrosive and react even to low humidity. Because of this, these substances should be washed off a trailer as soon as possible after coming in contact with them. For example, if a trailer traveled over a road treated with these chemicals in Oklahoma, and concluded the trip in warm weather in Texas. Throughout the eight to ten-hour journey, these corrosive chemicals will continue to react even in low humidity until the trailer is thoroughly washed. To combat this, some of the nation’s largest fleets have implemented daily underbody wash procedures during winter months to prevent corrosive damage caused by the reaction of these two chemicals.
Preventing & Treating Corrosion
Today, trailer manufacturers can use a range of approaches to prevent corrosion when they build trailers. There are also various options on the market available for corrosion prevention on in-service trailers. Trailer manufacturers can fight corrosion on a trailer’s structural cross members with paint applications, two-step zinc and paint combinations, epoxy coatings, and construction methods using galvanized, stainless steel, or aluminum components.
For trailers already in-service, trailer technicians address corrosion issues by taking into consideration what type of corrosion-fighting method was initially used on a vehicle when making repairs. Some coatings and materials are more expensive, and some are more difficult to work with than others. In some instances, a touch-up job may be all that is necessary to slow down or stop the corrosion process.
In addition to several paint applications, galvanized aluminum and stainless steel are very effective in the fight against corrosion. This process applies a protective zinc coating to protect metals from rusting. The zinc prevents corrosive substances from reaching the underlying metal and, when scratched, serves as an anode for the exposed metal surface. Other kinds of protective coatings can also offer a feasible and long-term solution for corrosion control, without the issues inherent in soft film barriers and galvanizing methods. Polyureas and polyurethanes provide exceptional durability and chemical resistance, even in extreme weather. They are flexible and impact resistant and will not cut, peel, crack, or chip. These coatings are similar to spray-on truck bed liner material but have unique properties.
Once the end-user has purchased the trailer, they can take a few proactive steps to address corrosion. First, they should develop a habit of taking the extra time to wash, clean, and detail their trailer before storing it in a clean, dry, and protected environment. This will not only help keep the trailer looking good; it will prevent corrosion and increase the useful life of the trailer. As part of the cleaning process, trailers should be thoroughly cleaned before storing them, including under the floor mats in livestock trailers. Trailers with certain coatings can even be waxed once or twice per year with several automotive detailing products, subject to the trailer manufacturer's recommendations. Owners should conduct maintenance inspections regularly and have any corroded areas immediately addressed by professionals before the corrosion continues to spread. Just like in the used automobile market, taking care of trailers and preventing corrosion pays off when it comes to preserving the resale value of the trailer.
The NATM Safely Towing a Trailer brochure has been updated to feature a new section on corrosion prevention. Published in 2019, the brochure has expanded its maintenance section to educate end-users about their role in preventing rust. To order NATM products, visit www.natm.com/products.
For a list of NATM Associate Members that supply paints and other protective coatings, visit the NATM Online Buyer’s Guide at www.NATM.com. For more information regarding the manufacture of trailers, contact NATM Technical Director Colin Holthaus at Colin.Holthaus@natm.com or (785) 272-4433.