Out of Service Does Not Mean Out of Danger

A quiet branch can change chemically

A dead leg is a section where process fluid remains with little or no flow. Depending on the material, stagnant inventory can polymerise, corrode, settle, freeze or form deposits. The risk cannot be judged from the condition of the flowing main line alone. Identify the material, inventory, temperature, time out of service and the specific degradation mechanism before deciding how to monitor, flush, drain, isolate or remove the branch.

In its investigation of the 2019 TPC Group Port Neches explosions and fire, the U.S. Chemical Safety Board found that a procedure for dead legs failed to capture temporary dead legs, including the one that ruptured. The CSB identified popcorn polymer hazards in high-purity butadiene service. These findings are material-specific; they do not mean every idle line will polymerise.

Review the configuration whenever service changes

When a duty or spare pump, exchanger, bypass or instrument leg is taken out of service, walk the connections against current drawings. Ask whether valves trap material, whether an inhibitor or circulation path remains effective, and whether the inspection plan covers the new configuration. Assign an owner and a review date for temporary arrangements. Apply management of change where required by the site's procedure.

Do not open or flush a suspect section casually. Unexpected pressure, reactive deposits or incompatible cleaning methods may increase the hazard. Use an engineered work plan, competent review and verified isolation before intervention.

A question for today's team

Which equipment currently out of service has retained process inventory, and where is the evidence that its stagnant sections were identified and controlled?