Investigators from the U.S. Chemical Safety Board completed their two-day assessment of the May 20 fire at the Valero St. Charles refinery and returned Tuesday to Washington, D.C. No further CSB investigation of the incident is planned.
According to CSB and Valero study, at approximately 11:30 p.m. on Saturday evening, a 12-inch overhead pipe ruptured in the refinery's Distillate Hydrotreater, a unit that uses hydrogen to remove sulfur from a hydrocarbon feedstock.
The pipe normally operates at a pressure of approximately 600 pounds per square inch. The rupture of the pipe caused a loud report and began releasing flammable gaseous hydrocarbons at a temperature high enough to cause spontaneous ignition. No personnel were present in the unit when the pipe rupture occurred.
The Valero fire brigade extinguished the ensuing fire at around 1:30 a.m. No employees or emergency responders were injured. Air monitoring at the perimeter of the refinery did not detect elevated concentrations of any hazardous chemicals.
The CSB investigative team examined the Distillate Hydrotreater unit and the fire-damaged equipment, which was confined to an approximately 100-foot square section of the unit. Two fan-type heat exchangers were destroyed by the fire along with an approximately 50-foot section of piping; electrical conduit was also damaged by radiant heat. No blast damage was observed.
Valero personnel cooperated fully with the CSB team. CSB Lead Investigator John Vorderbrueggen said, “Valero has assembled an incident investigation team to identify the proximate causes and, more importantly, any management system deficiencies that contributed to the incident. Valero management has committed to sharing the recommended corrective actions and program improvements throughout the company's global refining operations.”
While cautioning that the cause of the pipe rupture at Valero has not been determined, CSB Board Member Gary Visscher noted there have been a number of past instances of corrosion-related failures in refinery hydrotreater units. Mr. Visscher said, “While this incident fortunately caused no injuries, it is important to carefully maintain the integrity of piping that contains hazardous substances through rigorous inspection and testing.”
The CSB is an independent federal agency charged with investigating industrial chemical accidents. The agency's board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in safety management systems, regulations and industry standards.