Know Which Bolts Hold the Pressure Boundary

What the incident teaches

On 27 July 2021 at the LyondellBasell La Porte Complex in Texas, contractors were assigned to remove an actuator from a plug valve during repair work. They removed bolts they believed belonged to the actuator connection. Those bolts actually held a pressure-retaining valve cover. The plug was expelled and a hot acetic acid mixture escaped. The U.S. Chemical Safety Board (CSB) reported that two contractors died and two other workers were seriously injured.

The lesson is not merely to tell workers to be more careful. The CSB identified both valve design that permitted confusion and inadequate work conditions, procedures and training. Similar errors had occurred elsewhere. A system that depends on an individual recognising unfamiliar fasteners by appearance alone leaves a serious failure mode in place.

Define the pressure boundary before defining the job

A valve can be closed and still contain hazardous pressure on one side. Before removing an actuator, gearbox, bracket or cover, the team should identify the exact valve model and assembly, the connected inventories, and which components retain pressure. Use the manufacturer’s information and approved plant drawings, then verify the installed equipment in the field. Generic sketches and assumptions based on similar valves are insufficient when a component’s function is uncertain.

The work pack should identify the specific fasteners to be removed, the components that must remain intact, the isolation boundary, how zero energy will be proven, and the hold point before the first fastener is loosened. If the pressure boundary cannot be positively distinguished or the required safe state cannot be established, stop and obtain engineering and operations review.

Build a stronger barrier than a verbal warning

Engineering and procurement teams should consider designs that make pressure-retaining fasteners difficult to mistake for actuator fasteners. Where installed equipment has a known ambiguity, assess whether physical differentiation, durable identification, a dedicated removal procedure and independent field verification are needed. Labels help, but they do not substitute for a safe equipment design or a proved isolation.

Supervisors should bring operators, maintenance workers and contractors into the same pre-job review. Confirm the exact scope and valve identity at the equipment. Record the agreed safe state and responsibilities. Treat an unexpected bolt pattern, drawing mismatch, residual pressure or unplanned change in scope as a stop point, not a cue to improvise. Site procedures and competent engineering judgement must determine the specific controls.

A question for today’s team

Before the next valve or actuator job, can we show on the actual equipment which fasteners retain pressure, which ones are in the approved removal scope, and what evidence proves the boundary is safe?