Major causes of corrosion are accumulation of road salt, dirt, moisture or chemicals in hard-to-reach areas of the vehicle underbody or frame, and chipping, scratches and any damage to treated or painted metal surfaces resulting from minor accidents or abrasion by stone and gravel.
Once the protective coatings are abraded, even to a minor degree, these areas will be exposed to the caustic environment of road salts and other de-icing materials, as well as allow dirt and road debris to accumulate directly on the vulnerable substrate. Therefore, any damaged areas ought to be repaired as soon as possible to prevent spot corrosion from spreading.
Environmental conditions like dust control chemicals, sea air, industrial pollution and high humidity also play a role in accelerating the rate of corrosion. In addition, moisture and high temperature play an active role in corrosion to the parts of a vehicle which are not well ventilated to permit quick drying.
Many industry groups have done a good job identifying the problem of corrosion on vehicles, but a comprehensive guide for solutions has remained elusive, says TMC's Braswell.
In 2005, TMC's Future Truck Committee challenged industry manufacturers and suppliers to raise the bar when it comes to corrosion performance levels. In its position paper, "Recommendations for Corrosion Abatement," the Committee set the performance expectation that corrosion should not cause equipment users to replace any component during its useful life. Additionally, the Committee determined that commercial vehicle users should not need to perform any maintenance to prevent corrosion, other than normal, periodic washing.
TMC defined "useful" life as 10 years for a medium duty truck itself and 16 years for the truck cargo body. For heavy duty applications, useful life was defined as eight years for trucks and tractors; 16 years for trailers and converter dollies. In all cases, TMC recommended that manufacturers back up the corrosion performance expectations with a 100-percent parts and labor warranty.
In support of these expectations, TMC's Future Truck Committee called for improved laboratory tests that more accurately simulate today's operating environment, Braswell says. These tests also should feature provisions for testing electrical components while operating.
"TMC's report recognized that corrosion impacts the various zones of a vehicle differently," he says. "For example, the zone ‘from the road level to four feet above the road level' should have the greatest corrosion protection, as well as withstand impact by sand and stones that can compromise a coating's corrosion protection ability."
TMC's user expectations for corrosion durability were incorporated by the Society of Automotive Engineers (SAE) in its J2721, "Recommended Corrosion Test Methods for Commercial Vehicle Components," says Braswell. SAE 2721, now undergoing an update, offers improved test methods for assessing corrosion caused by the newer de-icing chemicals, as well as other impacts, such as drying, humidity, abrasive exposure and environmental variations.
Braswell notes that manufacturers and suppliers have developed new offerings and upgraded specs to help fleets fight corrosion, especially in the areas of brake rust-jacking, vehicle frames, wheels and fasteners and trailer and landing gear components.
In 2007, TMC created a new committee to carry on the fight against corrosion, the Corrosion Control Action Committee (CCAC). Earlier this year, the CCAC started gathering the work of several active TMC task forces and other materials, to develop a complaint, cause and correction manual for fleet managers and technicians to use in combating corrosion. The guide will feature three sections: identification and classification of corrosion types; means of preventing corrosion through specification; and corrosion-related maintenance and repair issues.
The effort is being lead by CCAC Chairman Todd Cotier, director of maintenance, Hartt Transportation. Plans are to have a well-developed draft for review, as well as an educational session on the complaint, cause and correction manual, at TMC's 2011 Annual Meeting in Tampa, Fla., February 8-11, 2011.