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The Nypro chemical plant at Flixborough produced caprolactam, a key raw material for nylon, using a process that involved oxidation of cyclohexane — a highly flammable substance.
Cyclohexane was processed under high pressure (~150 psi) and elevated temperature (~150°C) in a series of six reactors connected by stainless steel pipework. The process had operated successfully for several years.
But when one reactor developed a crack, the chain reaction that would follow was not chemical — it was human.
On that afternoon, a pipe in the so-called “4-sidecut” line (an 8-inch high-temperature carbon steel pipe exiting the crude unit distillation tower) ruptured and released hot hydrocarbon/light gas oil vapour.
The rupture created a large vapour cloud which spread over the facility and into nearby community areas. Within approximately 90 seconds of release, ignition occurred, leading to a large fireball and subsequent fire.
The incident caused injuries to refinery workers (six or more), and many members of the public sought medical attention—nearly 15,000 residents in the surrounding area of Richmond reportedly sought treatment for breathing or exposure issues.
The cause: extensive corrosion—specifically sulfidation corrosion of carbon-steel piping that had been exposed to high-sulphur crude and service conditions beyond what the piping alloy or inspection regime was designed to handle.
There was normalization of deviation: although some internal experts had flagged sulfidation corrosion risks, recommendations for full inspection/replacement were repeatedly deferred/denied under cost or turnaround framing constraints.
The management of change (MoC) and risk assessment for the changed feedstock (higher sulfur crude) were inadequate. The system did not fully evaluate how service change increased corrosion rates and decreased remaining life of piping.
Response to the leak was delayed and lacked formal protocol: after the leak was noticed, there was a period of about 2.5 hours before rupture, during which leak location and mitigation were attempted—but the underlying structural failure progressed and no controlled shutdown preceded rupture.
The refinery is located in a densely populated urban neighbourhood. Community impacts were high, and internal emergency management (shelter-in-place, public warnings) were triggered but the incident highlighted proximity risks.
Corrosion mechanisms can be insidious: In steel plants, heavy equipment (pipes, ducts, refractory linings, molten metal transfer systems) can degrade due to conditions (temperature, chemistry) that may change—but original design may not assume those changed conditions.
Service change (e.g., different material, feedstock, process parameters) must be treated as a major hazard: when you change what a system handles, you also change the degradation rate of its barriers.
Ageing equipment and legacy materials require rigorous monitoring: For steel plants using older steel, high-temperature piping, boiler systems, converters etc, assume that older material specifications (low alloy, low silicon, minimal inspection regimes) may harbour hidden weakness.
Emergency response and community interface matter: The Richmond incident impacted many off-site people; similarly, large steel plants located near communities must evaluate off-site consequences of failures (e.g., dust, molten metal ejection, explosion of gas holder).
Ownership of safety and inspection recommendations must be clear: “Experts told us” is not enough—there must be accountability and tracking of inspection/maintenance recommendations and schedule of remediation.
The Richmond refinery fire demonstrates that barriers fail gradually until they catastrophically break — here, corrosion weakened what seemed like benign piping until it exploded, releasing a vapour cloud that ignited. For heavy industry, especially steel plants with molten streams, high temperature piping, and legacy infrastructure, the message is clear: vigilance on degradation, service change, and organisational response is non-negotiable.
“When a pipe is old, the hazard is not that it looks bad now—it’s that you don’t see the damage until it starts to leak.”