Tank Material Innovations Extend Trailer Service Life

This story appears in the April 29 print edition of Transport Topics.

As tank fleets replace their long-lived trailers, they are turning to vehicles that take advantage of several innovations in recent years to increase strength, reduce weight, resist corrosion and better protect products, according to carriers and manufacturers.

Dan Furth, president of the National Tank Truck Carriers in Arlington, Va., said new tank trailers cost about $100,000 and can last 20 years or longer, depending on the type of service they see.

One of the key innovations that fleets and manufacturers said can make trailers both more durable and lighter is a stainless steel alloy called “lean duplex” that initially became popular because it had a price advantage over traditional stainless alloy.

Now that price advantage has largely diminished, but carriers and manufacturers said that in addition to durability and weight advantages, lean duplex steel reduces corrosion and protects the contents of the tank better than older tankers.

Chuck Boudin, director of equipment compliance for technical services at Quality Carriers Inc., said the higher tensile strength of lean duplex stainless steel (LDSS) allows tanks to better resist damage to loads caused by accidents on the road.

“In the case of a rollover event, the shell of the lean duplex tank will sustain impact loads [at a rate that is] 33% higher than a [conventional] tank,” Boudin said.

He also said that, because of its ability to resist corrosion, he expects his LDSS tanks could last for more than 30 years. For his traditional tanks, that durability drops to 20 to 25 years.

QCI is a unit of Quality Distribution Inc., based in Tampa, Fla., which ranks No. 38 on the Transport Topics Top 100 list of the largest U.S. and Canadian for-hire carriers. QCI operates more than 600 cargo tanks and hauls everything from water to sulfuric acid. The carrier initially added just a few lean duplex tankers to the fleet shortly after the product was introduced in 2006. The fleet has 230 of them today.

Wabash National Corp.’s Walker Group Holdings LLC, based in New Lisbon, Wis., supplies stainless steel products for the dairy, chemical, food and beverage transportation industries, among others.

John Cannon, vice president of engineering for the Walker Group, said he expects 10% of the new hazardous materials tanks sold in 2013 to be made of LDSS.

“This dynamic is occurring when the economic advantages of [LDSS] are not pronounced, like in 2007,” he said. “In the coming decade, I expect the adoption rate [of LDSS] will be greater than 10%.”

“We offer it, but the response has been mixed,” said Peter Weis, chief engineer for refrigerated trailer maker Polar Corp., based in Holdingford, Minn. “How many we sell, in part, depends on what is happening with commodities; lean duplex can take some expense out depending on the cost of commodities,” he added, “but now there is not much difference in the cost of lean duplex and the cost of 316 stainless steel,” which is used in traditional tanks.

“Until customers realize that there might be a cost savings or benefits, we won’t see a lot of growth,” Weis said. “I think, in the future, the use will pick up as word gets out about it.”

In addition to its strength, lean duplex steel reduces corrosion in trailers, according to Brenner Tank LLC. The Fond du Lac, Wis., manufacturer, a unit of the Walker Group, introduced LDSS to the North American market in 2006.

“Tank trailers are being kept longer than ever, and fatigue cracks [which can lead to corrosion] develop over the tank trailer’s continuous cycles of going over bumps where the tip of the welds compress, expand and compress again,” Cannon said.

“To whatever extent we can preclude the possibility of those fatigue cracks when the carriers have their annual inspections, they can rest assured that the unit is going to be able to stay in service,” he added.

The Houston-based National Association of Corrosion Engineers said corrosion costs the trucking industry $900 million a year.

For tank trucks hauling food products, catering to shippers can present their own special problems. Temperature control, particularly, is another asset enhanced by LDSS.

One reason for Weis’ growth optimism is Polar’s customers that ship food products. LDSS allows Polar “to make the barrel thinner, and it has good heat properties,” Weis said.

“Customers seem to be more interested in the heat properties,” he added, and LDSS “can reduce buckling from heat.”

The experience of LCL Bulk Transport — a family-owned company based in Green Bay, Wis., with 160 tanks hauling food-grade products across North America — confirms Weis’ observation.

LCL requires its tanks to have in-transit heat lines for some applications because the carrier mainly hauls chocolate.

“Different types of chocolate and oils must maintain a certain level of temperature to maintain liquidity,” said Hans Schaupp, LCL’s president.

Failure to keep loads at their proper temperature can result in the need to reheat solidified products, refusal to accept the load, extensive cleaning of units with solidified “heel,” expensive disposal of excess heel and time delays, Schaupp said.

Heel is solidified residue that occurs when certain products are not kept at the proper temperature in the tank.

To reduce heel and improve the offloading of product, Brenner developed the Shaker Tank — a patented specialty trailer that uses a vibration system to dislodge heel. The Shaker Tank decreases unloading and cleaning time, the company said.

“In addition, the driver does not have to stand on top of the tank to squeegee the product out of the tank,” Schaupp said.

Being able to get more product out of the tank results in less wasted product, less water used and less wastewater, he added.

Another factor to consider when buying a tanker trailer — which carriers and manufacturers said is an essential consideration — is precisely matching the tank to the load it will be carrying.

“If a load has a high concentration of calcium chloride [used for refrigeration], it needs to be put in a lined or coated piece of equipment rather than in a stainless steel tank,” Quality Carriers’ Boudin said.

The type of lining or coating is based on the concentration and temperature of the material to be hauled. U.S. Department of Transportation lining options include rubber, fiberglass and resin-based Kynar coating.

If calcium chloride is put in a stainless steel tank, pitting probably will occur, Boudin said.

“Pitting is another form of corrosion. Once a tank is pitted, it is harder to clean,” he said. “Some customers won’t reload a pitted tank because they feel they would be taking a chance of contaminating the new load.”

In addition, if the pit hole goes below the minimum thickness requirements, it no longer conforms to DOT code and can’t be used to haul hazardous materials.

Material and product design changes continue to evolve, so tank manufacturers also are looking at ways to improve their manufacturing processes.

For example, Polar has invested in new design and manufacturing technology that includes high-definition plasma and laser cutting tables, robotic welding cells and other advances.

“The new software and machinery are tightly integrated so information flows smoothly from our engineering group to the [computer numerical control] machinery in our plants,” Weis said. “The result is more precise measurements and cuts, which means better fit-ups and welding.”

Tank manufacturers also have to respond to changes in tractors and truck chassis. Recent emissions-reduction equipment has added several hundred pounds to tractors and trucks.

“Increasingly, customers want us to help them regain that lost ground, but not at the expense of structural integrity,” Weis said, adding that the use of lean duplex trailers can reduce their weight by 700 pounds, compared with a traditional DOT 407 tank.

“I am surprised there has not been more interest in [LDSS] for that reason,” Weis said, “but unlike the food industry, which likes to maximize payload, the chemical industry is more focused on batches, and the receiving tanks can only hold so much payload.”