A change is in the air with outdoor temperatures dropping, which means chemical and other facilities need to be aware and prepared for the safety challenges posed by cold weather, such as water freezing and expanding, which can damage equipment or cause instrumentation to fail.
When the temperature drops, the freezing process begins, and materials expand. This can crack or break pipes and rupture or damage process equipment. Damaged equipment may not become evident until the temperature rises, the ice thaws, and a leak develops. More subtle hazards may also exist, such as the formation of a hydrate, where water chemically combines with a compound, forming a solid that can also block process piping. This can happen even above freezing temperatures.
Facilities’ process safety management programs, including hazard reviews, management of change (MoC) evaluations, pre-startup safety reviews, and operating procedures, should reflect a year-round focus on how low temperatures may affect piping and other equipment and instrumentation, said officials at the U.S. Chemical Safety Board (CSB), who released a cold weather update.
The following scenarios are a summary of three CSB investigations where ineffective freeze protection practices and programs were found to be the cause an incident. It also offers key safety lessons from these incidents, as well as additional freeze protection guidance and resources.
DuPont La Porte, Texas, Chemical Facility Toxic Chemical Release
In November 2014, a release of toxic methyl mercaptan killed four workers at a pesticide manufacturing company in La Porte, Texas. Days before the incident, water mixed with liquid methyl mercaptain in piping located in an outdoor area of the plant. Due to cold weather in the Houston area, this mixture formed a solid hydrate, which blocked the piping. Although the potential for this hazard was known, the piping was not heat traced (heat applied to pipes, tanks, instruments and associated equipment) or otherwise protected to prevent a solid hydrate from blocking flow. A company team developed a plan to clear the blockage by spraying hot water onto the pipes to melt the hydrate. To prevent piping thermal expansion hazards, this plan included opening valves from the liquid piping to a vapor vent piping system.
On November 15, 2014, workers worked through the night attempting to clear the hydrate blockage. Following a failed startup, workers paused to take a break. During the break, the plant experienced a different problem — high pressure in the vent piping. The company had long-standing issues with vent piping installed in 2011. To deal with these problems, workers had daily instructions to drain liquid from the vent piping inside the manufacturing building. On the night of the incident, not realizing the original hydrate blockage had cleared, and with valve positions now open between the liquid methyl mercaptan and vapor vent piping systems, two workers were killed when liquid methyl mercaptan drained from the open valves and filled the room with toxic vapor. One of those workers made a distress call and two additional workers died responding to that call.
Valero Refinery Propane Fire
In February 2007, a massive refinery fire occurred near the town of Dumas, Texas. 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, or a section of piping without any flow. Dead-legs are particularly vulnerable to the hazards of freezing. The dead-leg was blocked on one side by a valve that was later found to be leaking. Over time, small amounts of water that were contained in the liquid propane flowed past the leaking valve and accumulated in the piping below. On February 15, 2007, the outdoor air temperature fell to six degrees Fahrenheit. The water froze, expanded, and cracked the pipe. The following day, the weather warmed up, the ice melted, the propane ignited, and fire engulfed the area, injuring workers and causing more than $50 million in damage.
Bethlehem Steel Corporation Gas Condensate
In February 2001, an incident occurred at a steel mill in Chesterton, Indiana. This incident had its origins nine years earlier (1992), when the mill disconnected a furnace that was fueled by coke oven gas. The 25-foot pipe that once supplied gas to the furnace was left in place with a closed 10-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 two workers and injured four others. Both the water and the flammable liquid had condensed from the coke oven gas. The accumulation of liquids accelerated because insulation was previously removed from piping and drain lines in the gas system became blocked with ice.
Key Winterization Safety Lessons
These three serious accidents illustrate the importance of effective winterization programs at refineries, chemical plants, and other facilities that contain hazardous materials, such as:
• Dead-legs must be surveyed and, ideally, removed or permanently and effectively isolated from hazardous process streams.
• Equipment that is susceptible to ice or hydrate formation in cold weather should be identified and properly winterized, such as insulating or heat tracing.
• Companies should establish formal, written winterization programs and identify and control winterization hazards, such as ice and hydrate formation, through process hazard analyses, MoC evaluations, pre-startup safety reviews, and operating procedures.