WATCHING a cargo tank suck-in was unquestionably the highlight of Brenner Expo '03, a one-day technology conference held earlier this year in Fond du Lac, Wisconsin. Almost 100 tank truck industry representatives were on hand for the suck-in.
The vacuum-induced cargo tank collapse followed lunch at Brenner Tank LLC's Fond du Lac plant. The event was such a hit that Brenner is offering a video ($20 donation requested) that can be shown in training classes to help explain to drivers, tank mechanics, and wash rack workers the dynamics of suck-ins and how to prevent them. The video was shot from several angles, including inside the tank, during the collapse.
“We've all heard about unplanned suck-ins of tank trailers in our industry,” said John Cannon, Brenner vice-president of engineering. “Our objective in the demonstration was to provide people with a window to the science of a suck-in. We wanted them to see firsthand what happens second-by-second when this unplanned phenomenon occurs. We believe this was the first time anyone in this industry did a suck-in demonstration.
“We hope a demonstration like this will help prevent some of the unplanned suck-ins. These events can occur at wash racks when the manhole cover is closed after cleaning and the tank is parked outside in freezing temperatures. Suck-ins happen when cargo is pumped off while the manhole cover is closed. During closed-loop unloading, someone forgets to open a valve on the air replenishment line. Whatever the cause, the end result is an expensive lesson.”
Old tank
The trailer selected for the demonstration was a 1966 Certified tank constructed of 12-gauge stainless steel. A pressure gauge was mounted on the street side of the tank to enable observers to monitor pressure differential. A 1984 Brenner vacuum trailer was used to suck the air out of the test unit.
The Certified tank trailer that was sucked in was donated by Jacob Press' Sons Inc, which has tank repair shops in Bridgeview and Joliet, Illinois. Diamond F, a Wisconsin liquid waste hauler, provided the vacuum trailer.
Shortly after the demonstration began, ripples formed in the Certified trailer's shell. Less than five minutes into the demonstration, the tank collapsed between the second and third set of stiffening rings and just ahead of the landing gear. Vacuum was at about four inches of mercury at that point.
“The collapse occurred in an area where spacing between the rings was at its greatest, and this was one of the points we wanted to make,” Cannon said. “Stiffening rings can't be more than 54 inches apart, and the closer they are, the better. In addition, rings should be spaced evenly.”
The demonstration also showed the importance of welded rings. Cannon explained that some tank trailers still have tension fitted stiffening rings or rings attached with adhesive.
Just to make the demonstration more interesting, Brenner invited those in attendance to guess when and where the collapse would occur on the tank trailer. Steve Hoffman, Archwood Protection Inc, correctly guessed four inches of mercury and the section between the second and third rings.