Is Pressure Relief Device (PRD) creating another serious unsafe scenario?
Himat Khimani (Process Safety/Loss Prevention/Technical Safety)
Sr. Process Safety Design Engineer - [BE Chemical Engineering, CSP, PGDIS, CFSP, CFPS ]
While taking PRD credit as Safeguard / Independent Protection Layer (IPL) against overpressure protection, remember learnings from the process safety incidents.
?Pressure relief devices (Pressure Safety Valve / Rupture Disc / Pressure Relief Valve) are considered as the most reliable safeguard / IPL against overpressure protection. Normally, this is the last line of defense against an overpressure scenario to prevent catastrophic failure and loss of primary containment (LOPC). ?However, if IPL credit is taken without proper compliance of all associated critical aspects, it might not be an effective IPL / Safeguard but could lead to another serious unsafe scenario!!
Today, I would like to reiterate the serious risk of fire/explosion/toxic exposure caused by the discharge of the PRD. You may like to go through the link of CSB video / investigation report given against each incident learning. Use this learnings, while designing overpressure protection, making sure that PRD remain an effective IPL and not creating another unsafe scenario!
(A)? Flammable hydrocarbon discharge from the PSV to atmosphere caused multiple fire & explosion.
(1) In 2018, at EVAL plant of the Kuraray America, Inc. in Pasadena, Texas, release of hydrocarbon (Ethylene) from a Reactor PSV discharge to atmosphere, resulted fire/explosion. For more details about the incident refer CSB animation video link
?(2) On July 14, 2023, multiple explosions occurred in the Dow Louisiana Operations Glycol II Ethylene Oxide Finishing unit in Plaquemine, Louisiana. Hydrocarbon (EO) release from the reflux drum PSV to atmosphere resulted vapour cloud leading to fire/explosion. For more details about the incident refer CSB investigation update link
?(3) Texas BP refinery explosion – Distillation column PSV discharge to atmosphere through a vent stake causing multiple fatality and extensive property damage. For more details about the incident refer Texas BP Refinery explosion link
Learning: Never allow PRD discharge to atmosphere if it is creating another fire/explosion scenario.
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(B) PSV discharge to treating system?
Whenever PSV discharge is taken to treating / combustion system (flare, vent scrubber, TOX, etc.) ensure that it’s always available, reliable/designed for the worst case relief load during any relief scenario.
Bhopal Incident – PSV vent treating system was not designed adequately to handle worst case relief load and was also out of service causing toxic gas release to atmosphere causing thousands fatalities. CSB has published video on reflections on Bhopal after Thirty Years :CSB animation video link-Bhopal Incident
(C)?? Special situations :
(1) PSV installed on the system handling Metal Alkyl (TEAL) / Pyrophoric system, PSV discharge shall not be taken to common plant flare system but to be taken to separate burn pit with firewall
(2) PSV discharge containing polymer / monomer having high risk of polymerization and blockage of flare header shall be evaluated further for safe discharge. (Routing back to process, treating system, alternate protection like HIPPS for PSV elimination, etc.)
(3) Don’t mix PSV discharge from cryogenic/low temperature service and PSV discharge from system having water/steam/condensate, this could form ice/freezing of liquid in flare header / KO drum / flare seal system & have potential flare/vent header blockage risk. ???
(4) Design PSV discharge handling system considering worst case temperature, especially, against low temperature embrittlement. Cryogenic / low temperature liquefied gas handling system, could subject to low temperature due to auto refrigeration on depressurization. ?
Professional Process Safety Engineer
7 个月I suspect many assessments performed for PRDs discharging to atmosphere post Texas City may not be available in a company’s system of record. I’ve therefore found it useful to record this as a secondary scenario in the PHA, either confirming no safety consequence, or evaluating the risk to justify any risk reduction. I’ve often used the phrase the PRD is the last line of defence. However, for PRDs discharging to flare, the flare system is the last line of defence. The PHA needs to ensure it records all credible scenarios and captures relevant design features as IPLs, e.g. flame detection to mitigate flame out etc, with a rigorous assurance process to verify safeguards are in place and functioning.
Worley
7 个月Excellent information