"Giant's mechanical integrity program did not effectively prevent repeated pump seal failures," CSB lead investigator Johnnie Banks said of CSB's findings. "Problems were addressed when equipment broke down, not in a preventive manner."
The incident occurred in the refinery's hydrofluoric acid (HF) alkylation unit. Alkylation is a standard oil refinery process that combines olefins with isobutane using a catalyst HF in this case to produce alkylate.
Alkylate, which is highly flammable, is used to boost the octane rating of gasoline.
Operators Believed Pumps Were De-Pressurized
The CSB investigation found that the day before the incident, alkylation unit operators performed a regularly scheduled switch of the alkylate re-circulation pumps in the iso-stripper section of the akylation unit. When operators attempted to put the spare pump in service, they discovered that it had a leaking mechanical seal and that it would not rotate.
The spare pump was scheduled for maintenance the next day. To isolate the pump for work, plant personnel, using a valve wrench, turned a shut-off valve connecting the pump to a distillation column to what they believed was the "closed" position. CSB investigators determined that the valve actually was open.
An operator disconnected the pump's vent hose to verify that no pressure was in the pump, and witnessed some alkylate flow through the hose. After the flow subsided, he believed the pump had been de-pressurized and was ready for removal.
CSB's study concluded that the vent line was plugged, not de-pressurized.
Plant Operator was Seriously Burned
As the mechanics were removing the pump, alkylate was suddenly released at high pressure and temperature, producing a loud roar that was audible throughout the refinery, according to CSB. One of the mechanics was blown over an adjacent pump and broke his ribs.
About 30 to 45 seconds after the initial release, the first of several explosions occurred. The plant operator was covered in alkylate that quickly ignited and seriously burned him. Other personnel suffered burns and eye injuries.
"The design of the valve wrench made it easy to remove and re-position onto the valve stem in different directions, and this led to a potential hazard because operators sometimes determined whether the valve was open by its wrench position, rather than the valve position indicator," Banks said. "In this incident, the valve wrench collar had been installed in the wrong position. Operators depended on the wrench position and mistakenly determined the valve was closed."
CSB also found that the valve had been modified in the past to replace a hand wheel method of opening and closing it with a bar-type hand wrench. If company officials had performed a management-of-change analysis before modifying the valve, they could have recognized the hazard of identifying the valve position that this modification caused, according to CSB.
In addition, Giant operators did not effectively verify that the pump involved in this incident had been isolated and de-pressurized before beginning to remove it, CSB found.
Management-of-Change Analyses Urged
Under the "Lessons Learned" rubric of the CSB report, the agency urges:
- Management-of-change analyses for any valve modifications;
- Effective lockout/tagout programs to ensure equipment has been isolated, de-pressurized and drained; and
- Proper mechanical integrity programs to prevent breakdown maintenance.
The report says Giant should have determined the cause of the frequent alkylate re-circulation pump malfunctions and implemented a program to prevent them.
"Proper mechanical integrity programs and effective management-of-change analyses are essential components of safe operations at any refinery," CSB Board Member John Bresland said. "The board plans to disseminate this case study to other refineries and trade organizations to help make incidents like the one at Giant less likely to occur in the future."