When a badly corroded upper coupler assembly on a tank trailer caused a roll-over several years ago, Elvin Knollman began thinking of ways to prevent that insidious and almost invisible damage.
Elvin Knollman tests an Encapsulated Upper Coupler by pumping in air, then listening for leaks caused by cracks or rust damage. If it holds air, it's sound inside, he says. Photo by Tom Berg.
Elvin Knollman tests an Encapsulated Upper Coupler by pumping in air, then listening for leaks caused by cracks or rust damage. If it holds air, it's sound inside, he says. Photo by Tom Berg.

The answer to the internal corrosion problem, he eventually decided, was to seal the structural members to keep water-borne salt from getting inside. The result is his Encapsulated Upper Coupler, which he is patenting and having manufactured for sale to truck operators and to trailer builders, if they're interested.

In September he took examples to the Technology & Maintenance Council's Fall Meeting in Pittsburgh, and presented the product at a session discussing corrosion -- a hot topic at TMC meetings. That's where I met him, and subsequent e-mails and phone calls convinced me to drive over to Indiana to see him.

Knollman has no engineering education but a lot of mechanical ability that came from his growing up on a beef-cattle farm and helping his family keep machinery running, he related last weekend at his small fleet headquarters near Greensburg in southeastern Indiana. His tankers haul gasoline, jet fuel and other petroleum products; the one that rolled over had diesel fuel aboard, and some of it spilled into a roadside ditch in Ohio.

He was faced not only with a loss of the trailer but with an expensive environmental cleanup bill. However, he proved that the wreck was caused not by driver error but by rusting of L-channel members inside the upper coupler. The coupler bowed against lateral forces caused by sloshing of the cargo during a low-speed turn; this accentuated the roll effect and allowed the trailer to go over, taking the tractor with it.

He still has the damaged coupler for display in his clean and orderly garage. A settlement from insurance and the trailer's builder paid that cleanup bill instead. But he doesn't necessarily blame the trailer's maker.

"The coupler was probably entirely adequate when Heil built the tanker back in 1989," he said. "What's changed is the salt" used by highway departments to deice roadway pavement. Like other truck operators, Knollman knows that calcium- and magnesium chloride deicers are far more aggressive than traditional sodium chloride, and the accident, in June 2008, was one result.

Salt, Water and Time

Upper couplers consist of a bottom plate of strong steel that's supported by steel channels welded to it. The kingpin is welded or bolted to the center of the structural frame. The box has an open top facing the bottom of the trailer's nose, so moisture carrying road salts and debris can get in over the box's upper edges.

It can be inspected by looking for external cracks and bulges which might indicate weakening inside, but internal damage is otherwise invisible unless the coupler is removed from the trailer.

For his encapsulated product, Knollman covers the coupler by solid-welding an additional plate made of 1/4-inch Grade 80 steel over the top of the box. This also strengthens the device. He has two basic versions: The "fully encapsulated" type's plate covers the entire box, and the "partially encapsulated" design uses two smaller plates that cover the structural members, leaving fore and aft areas open. Moisture in them drains off through holes in the bottom plate.

Into the sealed enclosure he pours several gallons of glycerine that sloshes among the steel members, protecting their surfaces by absorbing water that can condense inside. Knollman told me the additional top plate and the glycerine fill add about 25 pounds to the trailer. One customer uses drained motor oil instead, he said. A drain plug is turned out to check for presence of rust debris, and a Shrader valve allows pressure-testing of the enclosure.

"This is how you inspect it," Knollman said during a quick demonstration using an encapsulated coupler under the nose of one of his own tankers. "With compressed air." He pumped in 17 psi -- 15's enough -- and let it sit. Then he listened for any leaks that might be caused by cracks or interior corrosion. He heard none, and after a few minutes put his gauge on the valve and saw that it still registered 17 psi. "It's holding air. That means there's no damage inside."

He motioned at the old but still very clean trailer and said, "Today they have electronic anti-rollover devices. This right here," now pointing to his corrosion-resistant coupler, "is an anti-rollover device, too."

Upper couplers today last seven to 10 years, and then have to be repaired or replaced. Many fleets sell or trade off their trailers sooner than in former years to rid themselves of the corrosion problems, Knollman said. He figures his Encapsulated Upper Coupler will add at least three years, and maybe more, to a trailer's useful life. He has formed a company called LGM (the initials of his three children's first names) to market the product.

"It's getting a lot of interest" from other tanker operators as well as one large fleet that runs dry vans, he said. It's now standard with a recently formed tanker manufacturer and another is leaning toward it. Large manufacturers aren't interested because it's not something they invented, he lamented. But he has designs for major-brand tank trailers and can adapt it to other trailer types.

The "OE-style" product with the shorter cover costs about $150 more than a standard coupler on a new trailer. The fully encapsulated design costs a little more. Aftermarket prices range from $548 to $660, with discounts for volume purchases.

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