Panel Discusses Chemical Tank Longevity
Feb 1, 2000 12:00 PM, mbt staff
IN 1997, loading personnel at BP Amoco chemical plants began noticing cracks in some of the stainless steel chemical trailers that were 10 years old or more. The discovery led to a corporate policy to reject any chemical trailer that was more than 10 years old.
Against that backdrop, shippers, carriers, and tank manufacturers discussed cargo tank longevity issues during the 1999 Cargo Tank Maintenance Seminar October 25-27 in Chicago, Illinois. The conference was cosponsored by National Tank Truck Carriers and the Truck Trailer Manufacturers Association.
"We became concerned when we started seeing double-conical tank trailers that had developed one- to two-inch cracks in the center area," said Mel Arterberry, BP Amoco. "We also found some cracks extending from the top by the manway to the bottom outlet. Fortunately, we didn't experience any leaks on the highway.
"These trailers had been built by various manufacturers and were operated by a number of carriers. They were transporting different products. The only common thread we found was that they had been built around the same time (1985-86). Based on these findings, we stopped loading tanks that were more than 10 years old."
Arterberry added that double-conical tanks weren't the only ones with cracking problems. Cracks also have been detected in rear-discharge, straight-barrel tanks in the same age range. The cracks were in the center area at about five and seven o'clock.
"While we have taken action, we believe more information is needed," he said. "We want to know what is happening to the tanks and why. We would like to see development of a database that can be shared throughout the industry. We hope the tank manufacturers are willing to participate."
Fleet View Carrier perspective came from Randy Hales, Miller Transporters Inc. He said that a recent review of 414 tank trailers in the Miller fleet that are 10 years or older turned up three with problems.
He pointed out that long life for a cargo tank starts with good specifications and maintenance. At the same time, shippers can significantly degrade tank life by loading the wrong types of products or loading products at the wrong temperatures.
"More damage is done by shippers through improper loading than by poor tank construction," Hales said. "We do our best to specify a tank for long life with a 10-gauge barrel and a 400 degrees F capability. We inspect tanks every 35,000 miles, which means most are checked at least three times a year."
Stainless steel chemical trailers are designed today for a 20-year life, according to John Cannon, Brenner Tank Inc. For the most part, the tank trailers are delivering the expected useful life. Ashland Chemical and BP Amoco are the only shippers that have adopted a tank age restriction.
He suggested that bottom loading might be a factor in the cracking of some double-conical tanks. Proper bracing of the outlet will help extend the life of the trailer.
Proper care is a key factor in achieving the full life of a chemical trailer. For instance, tanks in corrosive service should be passivated at least once a year. "Pitting can be the source of a crack," Cannon said. "A brand new trailer is most susceptible to pitting and other corrosion."
Stainless steel tanks should be cleaned as soon as possible after each load is delivered. Tanks should be thoroughly dried after cleaning. Corrosion can result if moisture remains.
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