Leak problem at Corpus Christi refinery known for months, CSB says
Vol . 27 Spring 2012
A leaking flange at a Corpus Christi, TX, refinery first detected at least five months earlier is being cited by U.S. Chemical Safety Board investigators as the cause of a March 5 hydrofluoric acid release.
The incident released between 300 and 500 pounds of highly corrosive and toxic HF. Absorption through the skin and underlying tissue can produce fatal cardiac arrest and inhalation damages the lining of the lungs.
“There were no injuries resulting from the accident but I would like to emphasize that the CSB takes any accident involving the release of HF very seriously,” said Johnnie Banks, lead investigator for the CSB team assigned to the incident.
Banks spoke Friday (March 16) during a press conference conducted by CSB in Corpus Christi.
The March 5 leak occurred due to the failure of the seal on a 12-inch flange on a process vessel in the refinery’s alkylation unit. Photos show that the flange turned a distinct red color from the leak.
“The paint on the flange turns red when it comes in contact with even a small quantity of acid,” Banks said. “Following a maintenance activity the flange is washed with a caustic solution which returns it to its original color so that subsequent leaks can be identified.”
To date, the CSB investigation has found that the March 5 release can be traced to leaks at this flange reported as far back as September 2011.
“In late January of this year, maintenance was performed on the flange, tightening the existing bolts, but the leak persisted,” Banks said. “Further maintenance was performed on Feb. 10 – over three weeks prior to the actual incident. At that time workers replaced the flange bolts and a work order was submitted to order a clamp to enclose the leak.”
The clamp was ordered as an alternative to shutting down the unit, he said. However, the proposed design of the new clamp was rejected three times over the next three weeks and it was not installed at the time of the March 5 release.
“On the day of the incident the leak from the piping flange on the 12-inch line worsened,” Banks said. “Process liquids containing hydrocarbons and about five percent HF were released in a steady stream which worsened through the late afternoon.”
Eventually, sensors detected the release and triggered the alkylation unit’s automatic water cannons, designed to capture airborne HF.
“Automatic water cannons are intended as the last line of defense in the event of a release of HF,” Banks said.
The water cannons were again activated by an HF release on March 10 and 11 as the refinery was restarting the unit, he said.
“The events that took place on March 10 and 11 were planned work activities and the company was aware that the water cannons might be triggered,” Banks said.
Although the two additional releases were small in quantity, the CSB is concerned that management accepted that the water cannons could be triggered, he said. This indicates that the facility is routinely using water cannons as release mitigation for maintenance activities.
“The facility’s continued reliance on the water cannons to control an HF release raises serious concerns regarding the facility’s management systems and control,” Banks said.
The March 5 incident is not the first time that the CSB has deployed investigators regarding an HF release at the facility. On July 19, 2009, an intense hydrocarbon flash fire resulted in a release of HF from the same process unit.
“The fire, which burned for several days, critically injured one employee and another was treated for possible HF exposure,” Banks said. The refinery reported to the Texas Commision on Environmental Quality that approximately 21 tons of HF was released from alkylation unit piping and equipment.
Since arriving on March 6, the CSB investigation team has conducted about 20 interviews, examined the accident scene and designed testing to estimate the total amount of process stream that was released to the atmosphere during the March 5 incident.
“The CSB’s investigators seek to identify the root cause of an accident,” Banks said. “As new information becomes available, we will keep the community, public officials and the industry informed.”