Safety Alerts 12

Flare

• Header: Cold liquid and vapour release are sometimes heated to be above MDMT of CS piping, instead of using SS piping. Heater failure resulted in brittle fracture of CS piping. Local release and fire. Use SS piping

• Header: Prolonged flaring of Glycol Contactor HP gas and Slug Catcher wet gas led to hydrate blockage in HP flare header. pressurized it to 30 bar, twice 150# rating. Pockets in flare header accelerated blockage. Reverse rupture of Rupture Disks on seawater, used for cooling, sent gas to Seawater Caisson and Oil Production System. Bulk of the gas discharged overboard via Seawater Caisson which bubbled to surface, formed a vapour cloud that set off gas detectors, triggering a full blowdown of the production train to the blocked flare. Fortunately, thanks to prevailing wind the vapour cloud didn’t ignite over the vessel that could have sunk it due to buoyancy loss. Do not mix wet and cold streams in the same flare header with pockets

• Acid Gas Flare Header: Sulfur and Iron Sulphide deposits can form as a result of SO2 + H2S slow Claus reactions. Blocked up to 80% header flow area. Avoid routing SO2 streams to Acid Gas Header; add RDs upstream of PSVs in SO2 sources; spec blind SO2 maintenance vents. Inspect and remove blockage

• Seawater used for cooling. Seawater pump start-up surge burst RD and poured seawater into flare

• Header: Liquid accumulation in flare header pocket poured out during maintenance. Fire. Avoid pockets in flare headers

• Offshore: Subsea header to remote flare tripod forms U pocket that got filled with carried over and condensed liquid that poured out of flare tip during flaring. Burning liquid floated on sea surface and drifted towards platform

• Light hydrocarbon C5 condensate accumulating on water in Seal Drum was discharged to OWS with water. Large vapor cloud. Steam coil could have warmed, evaporated and sent it to flare

• KOD: Liquids carried at high velocity with gas dislodged internals - piping rupture/ local release/ fire

• KOD: High momentum liquid carried over knocked outlet elbow. Explosion and fire

• Flare Tip: Hot tapping in a steam line used for steam-assist, resulted in hot-tap metal shavings blocking parts of steam injection ring. Steam injection rate affected and led to smoking flare

• Explosions during plant start-up in Water Seal Drum/KOD. Probable cause: Natural gas added to enrich flared gas + inadvertent routing of hot air resulted in combustible mix + higher flash back velocity than stack/tip velocity. First explosion damaged WSD hat and its effectiveness. On 2 restarts, ineffective WSD resulted in explosions in KOD. Inject enrichment gas after WSD. Avoid hot air

• Molecular Seals: have choked by carbon from incompletely burned gases. WWW

• Molecular Seals: Syn Gas Compressor seal oil accumulation in mol sieve erupted as fireballs, fell to ground and caused secondary fires in a Methanol Plant (Karthikeyan, CEP, Jan 20)

• Molecular Seals: A small corrosion hole on top of mol sieve allowed air leak into flare stack and mild deflagration, noticeable by a whoomph sound (Karthikeyan, CEP, Jan 20)

• Refinery Flare Gas Recovery System: Incorrect suction pressure setting of compressor, resulted in vacuum, air ingress and mild deflagration, noticeable by a whoomph sound (Karthikeyan, CEP, Jan 20)

• Refinery Start-up. Column overhead drum LT failure. 370m³ of light HC liquid drained to flare. Flare KOD and WSD flooded blocking gas release to flare. PAH + sooty flame. Flare KOD LAH not functional. Flare KOD electrical pump inadequate. Standby steam driven pumps not operational. Check liquid relief scenarios and size Flare KOD per API

• Vent: Flame arrestors are subject to blockage with corrosion products etc. FA located on a cantilever boom in an offshore platform was plugged. No access to check, clean or replace. Tank started breathing via a sample hatch - a local release that ignited during hot work near the tank. Ruptured 2 tanks. Provide access to FA for periodical cleaning. Bypass with RD/ glycol seal are other options

• Vent: ¾” vent ball valve opened by falling debris. Flammable release. Fire. Cap or blind flange such vents

• Flare: Elevated flare with lighter than air flared gas can result in air suck-in and internal explosion

• Flare and Flare Structure: Excessive vibrations/shaking. Due to mixing of NH3 and CO2 rich gases in the presence of water - partial blockage at stack bottom

• Flare Stack: Internal explosion when purge gas failed. Good to monitor O2 level with O2 Analyser. WWW 

• Flare Stack: Initially purged with steam for maintenance. As it was difficult to turn a spec blind on a 35” header with escaping steam, switched to Nitrogen purge. The Nitrogen cooled the stack allowing air to suck in when the spec blind joint was opened. Explosion. Use Nitrogen only. WWW

• Vent Stack: Tip refractory debris + ice by condensate from the top steam ring, blocked the stack. WWW

• Guyed flare structure collapsed/leaned by 10°. 3m section buckled. Probable causes: Corrosion due to flare open drain line + Chlorides carried over from water seal pot. Localized holes in stack resulted in internal combustion and localized heating

• SDV internal stop failed, shearing valve seats. Debris damaged a downstream PSV. Simultaneous failure of SDV and PSV resulted in over pressurization. Avoid SDVs with internal stops; go for external stops

• Offshore Platform. Flare boom fell into the sea during installation. Installation forces and methods

Drain

• OWS: Heavy rains spread light hydrocarbons floating on top of water all around the plant. Potential ignition and explosion. Another case: Welding sparks in OSBL ignited HC in OWS, spreading fire. Box-in welding jobs over drains with fire resistant sheets and/or cover the drains below

• SWD: Oil/ condensate floating on top provide a continuous fire path around the plant along the SWD routing. During rainy season, SWD can overflow spreading flammables. Usually, flash fires that are self-limiting once the oil/ condensate layer is consumed. But may set up secondary fires that last longer

• Vented gas migrated along structural beams into MCC. Subsequent actuation of a pump relay blew MCC

• Drain valve on tank outlet did not close properly, due to sludge accumulation. Valve was not blinded. Resulted in large oil spill.

• Light ends in drained liquid may flash, chill and freeze water in the drain line blocking further drain flow. If operators assume that all the liquids are drained and leave the drain valve open, later the line may thaw and release hydrocarbon liquid and vapor. Fire and Explosion. See under Tanks and Refinery. Check for icing

• Temporary flexible fibre-reinforced rubber hose melted while draining hot oil; as oil was above its auto-ignition temperature, spray caught fire. Fatality

• Seawater entry into pipelines through open drain sump caisson system can cause leaks and failure. SRB and Microbiologically induced corrosion (MIC)

• H2 generated by depleted anodes inside caisson led to explosion. Vapor Corrosion Inhibitor added

• NaSH solution from spills during tanker unloading was collected in a pit connected to a sewer. H2SO4 was added to control pH of sewer flow to an Effluent Treatment Plant. H2S generated escaped via a gap in the sewer manhole. 2 fatalities and 7 injured. Study potential cross-contamination issues

• H2S release while transferring wastewater from a tank to a tanker truck by a vacuum pump. The H2S in the wastewater was supposed to be neutralized before transfer. There was no instrumentation to monitor H2S level in the wastewater. 1 fatality tanker driver

• API Separator: Carbon canisters to absorb hydrocarbon vapours got overheated and ignited the flammable mixture in the vent line. Nitrogen blanket/purge was insufficient. BP