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WELDING CRACKS CAUSED UNION OIL BLAST FATAL TO 17

Cracks in an industrial pressure tank caused the explosion and fire that killed 17 people and caused $100 million in damage last year at the Union Oil Refinery in Romeoville, says a report issued Friday by the state fire marshal. The report, prepared by Packer Engineering Associates, found that a network of cracks formed in the brittle metal surrounding a weld that was made on the pressure tank in 1974, when a section of the tank was replaced.

”Eventually that network of cracks joined to form a huge 9-foot crack on the inside of the vessel,” said Deputy Fire Marshal Tom Ortciger. ”Pressure blew that 9-foot crack open like a zipper” and blasted the 30-ton vessel 3,400 feet into the air with 1.5 million pounds of thrust.

The 55-foot tank left in its wake a huge cloud of highly flammable propane and butane gas that immediately burst into flame, Ortciger said.

The cracks in the tank that caused the explosion were traced to faulty welding work, but the report did not issue any reprimands.

”The purpose of the investigation was not to assess blame, but rather to determine cause,” Ortciger said, pointing out that the fire marshal`s office has recommended changes in inspection procedures for such tanks.

After the explosion, Union Oil was cited by state and federal agencies for ineffective inspections of equipment on the site. The firm has denied the charges.

The explosion, which occurred July 23, 1984, was in a part of the plant where a raw material was processed into propane, propylene, butylene and butane.

The tank was installed at the refinery in 1969, according to the report prepared by Packer, a consulting firm and laboratory retained by the office of the fire marshal to study the blast. The tank was designed to remove hydrogen sulfide from propane and butane gas, a common procedure for gas sold commercially because hydrogen sulfide gives off a strong ”rotten egg”

stench.

Problems with the tank were noticed early in its use, the report says. In addition to the 1974 weld, a liner was installed in 1976 in the lower portion of the vessel to control hydrogen corrosion.

But Ortciger said it was the 1974 welding that caused the network of cracks. He explained that if metal to be welded is not properly preheated, or is heated after the weld, the surrounding metal becomes brittle. ”Such brittle metal is well known to be susceptible to cracking in a hydrogen-rich environment,” Ortciger said.

Even before the Packer report was issued, Ortciger said, the office of the state fire marshal suspected that weld cracks caused the blast.

On Sept. 4, Ortciger said, the fire marshal`s Board of Boiler and Pressure Vessel Rules updated its inspection guidelines covering such pressure vessels in an effort to avoid another explosion.

Previously, each company using pressure tanks had to have a staff of inspectors certified by the fire marshal`s office on hand to approve work on the vessels and was required to inspect them periodically.

Because of the Union Oil blast, the rules were modified so that the inspectors make up a separate department within a company`s structure.

”The inspectors cannot be part of the company`s financial management team or of their engineering division,” Ortciger said, ”and thus will not be subjected to any pressure from peers.”

Also, Packer has prepared a ”technical information bulletin” to be distributed to companies throughout the state and describing techniques for applying welds to the vessels.