Safety Alerts 16

Refinery

• CDU: Pipe thinned by sulfidation corrosion rupture. Corrosion at a uniform rate over a larger area

• CDU: Incorrect MOC. Elbow failed. Pool fire. 3 days later, column structurally failed due to internal fire as a result of air ingress + pyrophoric material and oil in the column

• CDU: Earthquake toppled a 94m tall concrete chimney. Fire in CDU, reformer and tank farm

• CDU: Flashfloods filled SWD and spread HC around. Ignited by Coker furnace still cooling down. Fire in CDU and DCU. Similar in another refinery. Storage Tanks too exploded

• VDU: Vacuum residue pipe leak. Alloy pipe wrongly replaced by CS during maintenance

• VDU: Incorrect MOC in column branch. Leak and fire. Column fell on HX train

• VBU: Pump strainer maintenance. Block valve failure. Oil spill that auto-ignited and destroyed VBU. Fire spread by FW application

• DCU: Improper metallurgy caused hot oil above its AIT leak at pump discharge. Fire. Fatality

• DCU: Reverse rotation: On power failure, Delayed Coker feed pump reverse rotated, malfunction of its discharge check valve, under discharge pressure + 30 bar BFW injected to furnace coil to purge it. Pump and its motor damaged. Consider remote operated discharge valve for bigger pumps

• Coke Drum: Fire resulted from opening the top unheading valve of an active LP coke drum

• Fluid Bed Coker: CS piece inadvertently inserted in 5 Cr pipe. Erosion failure. Released liquids close to AIT. Fire. Additional pipes ruptured adding fuel

• FCC: Expander vibration resulted in safe shutdown. Leaking slide valve on reactor to regenerator led to loss of catalyst barrier. Steam purge to push hydrocarbon into downstream column led to steam leak towards Expander. Steam flow was reduced that unfortunately resulted in Hydrocarbon backflow into the air/ flue gas side and got ignited by ESP installed to reduce catalyst particle emission

• FCC: Shut down for maintenance. Due to erosion, slide valve failed to maintain a +ive catalyst bed barrier between reactor and regenerator. Air from regenerator travelled via reactor to downstream pipes with HC. Explosion. Debris punctured an asphalt tank 60m away. Asphalt poured out and spread. Ignited. Smoky fire in CDU and FCC units

• FCC: Debutaniser outlet didn’t open during a start-up while receiving from upstream Deethaniser. Operators routed Debutaniser Over-Head Drum flow to Wet Gas Compressor Inter-Stage Drum (ISD). On ISD LAHH, compressor tripped venting to flare. High liquid levels in Flare KOD, made worse by operators routing ISD liquids directly to flare. Flared gas + liquid broke an elbow. Vapor Cloud Explosion (VCE). Flare KOD pumps didn’t start on LAH

• FCC: Depropanizer overhead piping corrosion in elbow. C3+HC release. VCE. Blast toppled the fractionator and damaged FCCU and other units. Elbow downstream of ammoniated water injection point. Localized corrosion. Similar see Piping - Erosion Corrosion

• FCC: During shutdown oil was drained from a vessel used to separate heavy oil and solid catalyst. Vessel was steam purged. Hot oil was introduced before steam condensate (water) was drained. Led to rapid expansion, rupturing vessel and igniting oil

• FCC: Unstabilized gasoline pump tripped. Liquid routed to unit Flare KOD via PSV on high level. KOD liquid was drained to OWS (CBD route was defunct). Vapor cloud ignited by FCC furnace

• FCC: HC liquid continuously pumped into a process vessel with blocked outlet led to relief. Flare system was unable to cope, led to FCC Flare KOD outlet rupture that ignited

• FCC: C3/C4 gas recovery unit pipe rupture. VCE. Gas and FCCU destroyed

• FCC: Shut down for maintenance. Due to erosion, slide valve failed to maintain a +ive catalyst bed barrier between reactor and regenerator. Air from regenerator travelled via reactor to downstream pipes with HC. Explosion. Debris punctured an asphalt tank 60m away. Asphalt poured out and spread. Ignited. Smoky fire in CDU and FCC units

• FCC: Pump casing weld failure in C3= Splitter unit. C3= release. Explosion. Damage to FCCU

• HCU: Faulty level instruments. Gas blowby from HP Sep to LP Sep, whose relief valve was sized for fire only. LTs of LC and LAHH/LALL should track each other and give discrepancy alarm. Size PSVs for gas blowby, if applicable

• HCU: Stage 2 Reactor 3 outlet piping ruptured. High temperature ~ 1,400°F. Hot spot in bed 4. Reactor was not shut down and depressurised after crossing 800°F. Poor temperature inputs/ monitoring

• HCU: 2” H2 line at 208 bar failed at weld. Resulting flame impingement on reactor skirt. Reactor collapsed. Similar, H2 leak and fire. Damaged the main reactor. Similar, CS elbow rupture released H2 + HC. Explosion. HC release from column with extensive damages to HCU, HDS and H2 units 

• RFCC CO Boiler: Aqueous ammonia/ urea solution sprayed to convert NOx into N2 + H2O (SNCR – Selective Non-Catalyst Reduction process) caused external corrosion/ thinning of boiler tubes, as the solution did not vaporize as expected; dripping liquid droplets caused wet CO2 corrosion. Based on spray test, the spray nozzles were extended to avoid liquid dripping

• H2 Production: CO2 from shift reaction was absorbed by potassium carbonate solution. During maintenance, carbonate solution was withdrawn from its tank. This resulted in H2 flow from the absorption tower into the tank. High tank pressure. Explosion and Fire. Failure to isolate and/or purging the tower with N2

• H2 Production: SS pipe bypassing HTS converter - no flow pipe – ruptured. Water and KOH (from K promoter in SMR catalyst) accumulation in low point. SCC. Fire. SS replaced with 1¼Cr-½Mo

• HCU: Feed heater tube ruptured due to flame lick/ hot spot. 4’8” longitudinal split. Hot spots were wrongly assumed as burning scale. Early warning via smoky plume in stack tip + reducing Xs O2 in stack, due to additional fuel from leak. Failed to recognize that scales in SS347H tubes form at higher temperature (1,300-1,500 °F) c.f. ferrous tubes in other heaters. Optical pyrometer scan not used

• Cracker: Stabilizer reflux drum was pumped out, depressurised and purged in preparation for a shutdown. Residual light hydrocarbon vaporized, chilled, freezing water in the drain point. As no further drain liquid came out, operators assumed all liquid was drained and left the drain valve open by mistake. Later, the drain line thawed, and a large amount of liquid escaped and vaporized. The gas flashed at a furnace. Fire and explosion. Icing on drain points is a warning sign. Drain lines may also get choked. BP

• HDT: 1.5m crack in reactor, releasing hot naphtha + H2. VCE. Damaged other units. Bayernoil