Bypassed Relief Valve During a Maintenance Management of Change Gap
Vinit Pandey · Published 29 June 2026
This entry illustrates a representative incident pattern seen across the process industries. It does not describe a specific named company or disclose any client-identifying information.
In short: This lesson shows how an informally tracked temporary bypass of a pressure relief valve during maintenance was never restored before startup, leaving a high-pressure vessel without overpressure protection for several weeks.
- Relief Valve Removed for Service
- Temporary Bypass Installed
- Informal Tracking Only
- Startup Without Restoration
- Vessel Unprotected
- Near-Miss Pressure Excursion
What Happened
During a planned turnaround, a pressure relief valve was removed for routine servicing and a temporary spool piece was installed to allow the line to remain in service.
The temporary bypass was tracked only on a whiteboard in the maintenance shop, not in the site's formal Management of Change or safety-critical equipment override register.
The unit was restarted after the turnaround with the relief valve still off-line; the gap was only discovered three weeks later during a routine safety-critical equipment audit, after a transient pressure excursion had already occurred without protection.
Root Causes
- No formal, auditable register existed for tracking safety-critical equipment temporarily out of service — reliance on informal communication between shifts and crews.
- Pre-startup safety review (PSSR) checklist did not explicitly require verification that all safety-critical instrumentation and relief devices removed during the turnaround were restored.
- Time pressure to restart the unit ahead of a contractual production deadline reduced the rigor applied to the PSSR.
Lessons
- Every safety-critical device taken out of service, however temporarily, needs a formal override/bypass record with a named owner and a mandatory restoration step before startup — never an informal or verbal tracking method.
- PSSR checklists must include an explicit, itemised cross-check against the turnaround's safety-critical equipment override register, not a general 'is the unit ready' sign-off.
- Schedule pressure is a recognised precursor to PSSR shortcuts — sites with strong PSM maturity build in an explicit authority to delay startup when checklist items are incomplete.
Technical Takeaways
- PSSR is a core OSHA PSM / CCPS RBPS element specifically because pre-startup is where deferred maintenance items are most likely to be missed.
- A pressure vessel without its design relief device has no demonstrated overpressure protection — the LOPA/SIL credit assigned to that relief device is void for the entire bypass period.
- Safety-critical equipment override registers should be reviewed at every shift handover, not only at startup, to prevent exactly this kind of multi-week gap.