Winter is here. As temperatures continue to drop, it’s important for chemical plants to be prepared for the unique safety challenges of subfreezing weather. Since 2001, the CSB has investigated two major accidents that resulted from water freezing inside process pipes.
Both accidents involved what are known as “dead legs.”
Dead legs are sections of piping without any flow of liquid. They are often created when existing processes are reconfigured. Dead legs are particularly vulnerable to the hazards of freezing.
Most recently, a massive fire occurred at a refinery near the town of Dumas in the Texas panhandle. The fire seriously burned three people, shut down the refinery for two months, and contributed to gasoline shortages hundreds of miles away. The fire occurred in a unit that used large amounts of high-pressure liquid propane. Years earlier, the unit had been reconfigured, creating a dead leg. The dead leg was blocked on one side by a valve that was later found to leaking Over time, small amounts of water, which were contained in the liquid propane, sank past the leaking valve and accumulated in the piping below.
On February 15, 2007, the temperature fell to six degrees Fahrenheit. The water froze, expanded, and cracked the pipe. The following day, the weather warmed up, the ice melted, and propane began jetting from the broken pipe. Fire engulfed the area, injuring workers and causing more than 50 million dollars in damage.
In February 2001, a similar accident occurred at a steel mill in Chesterton, Indiana.
This accident actually had its origins nine years earlier, when the mill disconnected a furnace that was fueled by coke oven gas. The 25-foot vertical pipe that once supplied gas to the furnace was left in place, with a closed, ten-inch valve at the bottom. It was a dead leg.
In the winter of 2001, water accumulated inside the dead leg and froze, cracking the valve. As a crew later began work to replace the valve, they were sprayed with flammable liquid gas condensate, which ignited. The fire killed 2 workers, and injured 4 others.
Both the water and the flammable liquid had condensed from the coke oven gas. The accumulation of liquids had accelerated because insulation had been removed from piping, and the drain lines in the gas system had become blocked with ice. These two serious accidents illustrate the importance of effective winterization programs at refineries, chemical plants, and other facilities that handle hazardous materials.
Dead legs need to be surveyed. Ideally they should be removed, or else permanently and effectively isolated from hazardous process streams. Piping that is susceptible to freezing needs to be identified and properly winterized. That can include insulation, or heat tracing.
Winterization is a simple concept. But the lack of winterization has caused serious accidents that have cost lives and inflicted huge property losses. Companies should establish formal, written winterization programs, and they should apply appropriate management of change techniques when piping or equipment is taken out of service.