New pressure vessel designs keep roads safer

Figure 1
These Exosent Engineering-fabicated cargo tankers have a low center of gravity, unlike more traditional tankers that people are likely to notice on U.S. highways. The cones that are part of the tanker design play a key part in reducing that center of gravity. Photos courtesy of Exosent Engineering.

When you find an engineer well-versed in the world of metal fabricating, you have found a rare person. The disconnect that often exists between the product designer and the metal fabricator, who makes that part a reality, doesn’t exist.

Yuval Doron is one of those people. He is a third-generation fabricator that stepped away, temporarily, from a 20-year fabricating career in 2008. He wrapped up his master’s degree in mechanical engineering at Texas A&M in College Station, Texas, in 2009 and co-founded Exosent Engineering with Andrew Duggleby in 2010.

He still lectures at Texas A&M, and until recently he was working Exosent Engineering’s four-roll plate rolling machine. He got the opportunity to jump back into fabricating when his company started fabricating a new design for pressure vessel transports in 2012. It’s a great example of what can happen when intelligent engineering meets fabricating expertise.

Starts With Engineering

Unlike many fabricating business stories, this one starts with drawings that needed to be brought to life.

“Instead of doing what’s already been done out there, we used our engineering skills and methodologies to find a way to improve designs in the pressure vessel world. We had found out that there was a need for pressure vessels that are safer in terms of reducing the potential for rollover,” Doron said.

If you have been on any major traffic artery, you’ve seen symmetrical cargo tankers attached to trucks. They are reminiscent of giant pills on wheels. They haul everything from milk to hazardous chemicals.

While that style of pressure vessel transport dominates U.S. roadways, different-style tankers can be found elsewhere in the world. In places like the U.K. and Australia, tanker designs that feature lower centers of gravity have begun appearing on roads in recent years. The reduced centers of gravity help to minimize the forces that might contribute to a tanker turning over as the truck driver is forced to contend with some unforeseen situation. (Anything with a high center of gravity relative to its width is less stable. The liquid in the tank that sloshes to the left during a right-hand turn or forward during a stop makes the vehicle even more unstable.)

You may think that tanker rollovers are caused mostly by impaired drivers or inclement weather, but research debunks that myth. According to a Cargo Tank Roll Stability Study, conducted by Battelle for the U.S. Department of Transportation in 2007, inattention and distraction are the causes for about 15 percent of cargo tanker rollover crashes, and pavement is dry in 85 percent to 95 percent of the rollovers studied. The biggest cause of these types of accidents is driver error, such as speeding, which is tied to 75 percent of cargo tanker rollovers.

If a tank with a low center of gravity can help keep the truck upright when a driver does make a poor decision while driving, why hasn’t this design been embraced in the U.S.? The answer has to do with the material and the way that material is formed to create the tanks.

Fabricating Makes It Happen

Doron has lectured at Texas A&M on the subject of computer-aided design (CAD) since 2012. He knows his way around design software.

Figure 2
Yuval Doron, co-founder of Exosent Engineering, poses with the company's four-roll plate roller from MG s.r.l.

He also knows how tanks with a low center of gravity were once embraced by industry in the early 20th century. That all changed as the steels got harder and fabricating the unique shapes, such as cones, became too difficult for many fabricators to pull off.

That knowledge and Doron’s CAD skill led Exosent to create the first generation of its low-center-of-gravity tankers (see Figure 1). The first one was fabricated in 2014. Doron not only had a hand in the design, but also the actual fabrication.

“I’ve been rolling steel since I was 13 years old,” he said.

Exosent uses a four-roll plate roller from MG s.r.l., an Italian manufacturer of sheet, plate, and section bending machines, to form the sections that make up the low-center-of-gravity tankers. This style of plate roller helps to deliver consistent bends because it has the ability to pinch the plate between the two motorized central rolls, which makes pre-bending and the bending through the whole plate section in one pass much easier to do. The plate is kept squared without slipping during the pre-bending and bending cycle thanks to the constant pinching of the central rolls. Doron said that Exosent is typically rolling plate sections that are 8 feet wide and between 5/16 to ½ inch thick (see Figure 2).

The plate roller also is capable of coning the plate, which is useful considering that 80 percent of the work fabricated by Exosent has that feature. The MG plate roller, according to the company, has rolls that are assembled on sealed bearings, which minimizes the applied force generated by the plate rolling. As a result, the machine’s side rollers have greater capacity to take on aggressive conical bending.

Having a skilled plate roller helps as well. Because the material is very strong—with the yield and tensile strength being very close—it can fracture in the plate roller if the operator is not careful.

“Not anyone can walk off the street and roll these sections,” Doron said, later adding that he’s never had to scrap a section that he rolled.

Looking Toward the Future

Doron said that the new tanker designs are generating good buzz in the industry and demand is growing for them. But it’s not just safety concerns that are driving the interest.

“We’re making changes where it has real value, not just in terms of safety, he said. “Our vessels, because of their shape, actually have a lower drag coefficient. So the trucks that pull our trailers see increased fuel economy. It’s substantial—over 17 percent in some cases.”

Exosent also is thinking smaller, at least when it comes to its next iteration of tanker design. This new, patented design is for small tanks that are mounted to the truck chassis, also known as bobtails in the trucking industry. Doron said the company introduced the design at a recent trade show and the response was encouraging.

Exosent is in the process of building a new 50,000-square-foot building, leaving its 22,000-sq.-ft. home behind. It currently has 25 employees.

It’s also looking at possibly adding automated welding to the shop floor in the coming months. It’s proving out the technology now at the university. For a company that designed and built its own submerged arc welding system and plasma cutting table, that shouldn’t be surprising. That’s what engineers with fabricating backgrounds do.

Exosent Engineering, www.exosent.com

MG s.r.l., https://mgsrl.com