Calcium and magnesium chlorides: Corrosion’s new bad guys
April 1, 2005
TAMPA, Fla. - There was a time that road salt was the great evil-doer blamed for corroding components, but new materials such as calcium chloride and magnesium chloride are proving to be even worse....
KEY WEAPON: Designing equipment with better draining can help prevent rust.
TAMPA, Fla. – There was a time that road salt was the great evil-doer blamed for corroding components, but new materials such as calcium chloride and magnesium chloride are proving to be even worse.
“The molecule is roughly half the size of its sodium cousin, so it can go in a lot more places,” says Greg Kinesey of Phillips Industries, which makes electrical connectors. Consider the seven-pin connector that’s open by design and regularly saturated with contaminants that come off the tire. “Even if you can wash it directly, it’s very difficult to get off.”
While road salt can be rinsed away with a power washer, the new materials need to be wiped clean with a brush or rag.
Compounding matters, magnesium and chloride attract water at lower levels of humidity, so once it finds its way into a crack or joint, it’s going to maintain the moisture that can accelerate corrosion, says David Alexander, project manager of a University of Idaho study examining the ice-clearing materials.
But even though the Colorado Department of Transportation concluded in May 2002 that magnesium chloride was more corrosive than road salt, that’s hardly slowed its use. Thirty-eight states and a growing number of Canadian jurisdictions are switching to the material because it’s simply more effective at clearing ice. The “chlorides,” after all, can be applied to a road surface several hours before a storm rolls into an area. Hate it? Want to see a switch back to salt? Tough.
The general public continues to demand clear roads, says Alexander. “With that level of service and salt comes corrosion.”
That leaves a greater emphasis on improving the coatings that protect components in the first place, panelists said during a recent TMC presentation on corrosion.
“A lot of the solutions are not ‘out there’ solutions,” insists John Repp, senior engineer with Corrpro Inc., which specializes in fighting corrosion. “They’re here today.”
Yes and no. While coating manufacturers are quick to suggest they have the ultimate solutions to corrosion woes, they complain that many OEMs have yet to incorporate them. The TMC has suggested that heavy-duty tractors should last eight years without requiring a replacement relating to corrosion, while trailers and dollies should last 16 years. Equally, the maintenance arm of the American Trucking Associations wants medium-duty trucks to last 10 years and their truck bodies to last 16 years.
“They have that beacon out on the night,” Ryder Systems group manager of maintenance services Jerry Thrift says of the recently unveiled goals. “Now (equipment manufacturers) know what we users are expecting…it doesn’t mean the industry is going to get out there all at once.”
For manufacturers, that can be a greater focus on the corners and crevices that will retain water, and designing “intelligent” drain holes that can drain as much water as possible instead of simply taking half-inch drill bits to expanses of steel, Repp says. They may also need to pay closer attention to restoring coatings damaged after materials are bent, formed, cut and welded during the assembly process.
“Material selection is probably one of the best methods of corrosion control,” he adds, noting how aluminum will sacrifice itself to protect the steel to which it’s attached.
Those who apply coatings of any kind need to be sure they’re properly preparing surfaces to meet manufacturer recommendations, he adds, referring to sources ranging from Material Safety Data Sheets to technical bulletins.
Meanwhile, promoters of different coatings (as well as the Technology and Maintenance Council) suggest common corrosion-related tests need to be updated. Phillips, for example, adds an electrical load to traditional tests since electricity can accelerate corrosion – and the blue circuit to power your anti-lock brakes is always live when the key is turned on.
“You deserve to buy components that have been tested to a higher standard,” Kinesey says.
Buyers, for that matter, need to consider equipment purchases and installation methods that offer added protection whenever possible, he added. For example, about 90 per cent of the moisture that attacks a seven-pin connector seeps around a cavity at the head of the connector.
“Rinse, brush and re-grease sockets and plugs with dielectric grease every six months. This is especially true on the tractor side,” he recommends, adding that socket gaskets can offer some added protection.
It’s a matter of considering all your weapons in the war against corrosion.