7/27/2019 The Hazards of Dead Legs

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The Hazards of Dead Legs

Dead legs are sections of process piping that have been isolated and no longer maintain a flow of liquidor gas. They are often formed in industrial process piping as processes are changed or modified. Deadlegs have been the cause of several industrial incidents, especially during the winter months.

Dead Leg Danger

In February 2007 an oil and gas refinery witnessed the destruction in its de-asphalting unit caused by aforgotten dead leg in the process piping for liquid propane. Valves were used to isolate a section ofprocess piping when the process sequence was changed; however, a foreign object prohibited one ofthe valves from closing completely. As a result, moisture from the processing of the liquid propaneleaked through the valve into the dead leg. Weather conditions during February were below freezing forfour days, which was long enough for the moisture to freeze and rupture the piping. Once the

temperature rose above freezing, the ice melted, allowing liquid propane to flow from the rupturedpiping into the dead leg. This quickly formed a vapor cloud that was carried by the wind to an ignitionsource nearby. The Chemical Safety Board, which investigated the accident, said, The accidentresulted in multiple injuries, damage exceeding US$50 million and reduced operation for nearly ayear.

Recommended Procedures for Dead Legs

As a result of this accident and others, the U.S. Chemical Safety Board recommended several changesto the American Petroleum Institute (API)standards that address the hazards of dead legs. The

Chemical Safety Board recommends that any industrial or chemical facility consider the following forprocess piping containing hazardous materials:

Develop a written freeze protection program to ensure that process piping and any dead legs are

properly protected. This would include installation of a heat trace or insulation around piping exposed toweather conditions, as well as routine determinations of mechanical integrity.

Conduct periodic inspections to identify and maintain dead legs. This should include inspection and

maintenance of associated valve systems or isolating devices and mechanical integrity testing.

Implement a management of change program to ensure hazard evaluations are conducted when a

change in process equipment or technology is proposed. A management of change program is adocumented approach to requesting, evaluating risk, planning and implementing a change to a process,

equipment, control technology or system. It requires the review and approval of a multidisciplinary team(including operations; engineering; and environmental, health and safety management) to ensure thatpotential hazards are not missed, all required documents are maintained, and communication andtraining are provided to all personnel affected by the change.

The refinery accident demonstrated the importance of reviewing the potential for dead legs whenprocess piping is changed. It also shows the damage that could be experienced if dead legs are notproperly maintained or removed. Process piping should be continually evaluated, and Piping andInstrumentation Diagrams (P&IDs) should be properly maintained with necessary updates or revisions.These simple tasks will go a long way toward preventing a major incident.

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