Safety Alerts 18

Refinery

• Cracker: Stabilizer Reflux Drum was pumped out, depressurized 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. Ignited by a furnace. Fire and explosion. Icing on drain points is a warning sign. Drain lines may also get choked. BP

• Hydroformer: Air accidentally entered and mixed with circulating inert gas and Naphtha vapors. Ignited by hot recycle gas fired heater tubes. Detonation. BP

• HDT: 1.5m crack in reactor released hot Naphtha + H2. VCE. Damaged other units

• HDT: Vibrations by a recip compressor + piping expansion/contraction during hot and cold cycling, caused 1" globe valve plug to fall off. As the valve was not fully closed, H2 leaked but quickly dispersed

• HDT: Severe failure of Naphtha HDT HX shell. HTHA can occur in the so-called safe region of Nelson curve in API 941. Operating conditions can get severe than design. Avoid CS in HTHA service and go for Cr-Mo steel

• HDT: Workers were trying to stop hot Naphtha leak from a flange with Steam lance to keep Naphtha from catching fire. Hot naphtha ignited and explosion

• DHT: Recip type Recycle Gas Compressor. Each loading/ unloading valve had Instrument Air tubing for valve actuation and a gland leak collection tubing to flare. Identical tubing. During maintenance one of the IA and flare tubing got interchanged. On starting the compressor, gland leak stream with 95% H2 and 0.05% H2S reached the nearby Analyzer House via the IA tubing. Explosion. Use different types of tubes, color coding and different directions of rotation for IA and flare tubing

• HDS: During shutdown, reactor was neutralized and washed with a polythionic acid solution. It accumulated at the drain nozzle in reactor inlet / furnace outlet piping. On startup, hot HDS gas from furnace evaporated the water concentrating the Chlorine. Industrial water was used to dilute polythionic acid had high chlorides that was further concentrated. SCC (Stress Corrosion Cracking). H2 leak and local fire. The dilution water was changed to pure water to lower the Chlorine level

• HDS: Leak from a PG piping caused jet fire. Minimize additional tapping

• HDS: Restart. HX additional bolt tightening was done due to thermal expansion. Leak and explosion. Channel cover and parts hurled over 200m

• Benzene: During start-up, Hydrogen gas leaked from HX flange and fire. Insufficient tightening / hot-bolting

• Catalyst Dewaxing: During hot hydrogen regeneration of catalyst, an explosion occurred. Reactor outlet pipe failed at an elbow. Possible cause sulfidation corrosion from catalyst activation years ago. Wall thinning from corrosion + turbulent flow at the elbow

• HF Alkylation: Piping elbow corroded. Had a high Nickel and Copper content. Carbon steel with a higher % of Nickel and Copper corrodes at a faster rate than Carbon steel with a lower % in HF service. VCE. No SDV installed to remotely stop the leak

• HF Alkylation: Liquid Caustic Neutralizer was replaced with solid KOH. Plant upset sent a slug of HF into KOH tower. Exothermic reaction. Explosion and fire. BP

• HF Alkylation: While a fitter was cutting a line on a purged and isolated unit, a mixture of Sulfides and HF was released. Cloud. Nearby safety showers were not working. BP

• HF Alkylation: On opening a drain, initially nothing came out. Suddenly the blockage cleared and HF, hit the ground and splashed. Drain point was close to the ground. Add an extension to route drains away from the operator. BP

• HF Alkylation: Leak and cloud of HF and Butane. Steam used to push back, vaporized the acid and added to the cloud size. Do not use steam on HF leaks. BP

• Alkylation: Oxygen in solution in propane stream was ignited by Iron Sulfide. Fire. BP

• MEA column ruptured at a weld joint made 10 years back. No PWHT. Propane at 14 bar propelled the vessel. Resultant fire and BLEVE burnt other units

• BBU: Bitumen Blowing Unit or Oxidizer. Usually at 246-266°C with water and steam to control temperature and inert the vapor space. Was at 279°C due to low water/ steam. Resulted in thermal cracking, making the offgas to incinerator fuel rich. Incinerator temperature rose to 954°C, higher than normal 593°C and was tripped on TAHH. Repeated attempts to relight failed. Wrongly concluding that too much steam, steam flow was further reduced; vapor space became flammable. As the incinerator was lit, flash back to the oxidizer. Internal explosion spraying hot asphalt on workers. BP

• Sulphur: Accelerated corrosion of Claus Sulphur equipment when opened for maintenance - due to humid air. SOP to address 100% drainage of contents + plugged piping + molten Sulfur issues while operations hands over to maintenance contractors (LinkedIn)

• Sulphur: Tube rupture in the waste heat boiler, released H2S and SO2. Sulfidation or high-temperature Sulfidic corrosion thinned iron-containing materials over time due to Sulphur compounds and Iron reaction. Poor BFW treatment and monitoring resulted in deposits on tube surface and higher tube wall temperatures; increased metal loss from sulfidation corrosion. Add BFW in-line analyzers. CSB

• Water freezing and damaging valves/ gaskets/ flanges leading to leaks and fire; blocking drain lines and then thawing leading to HC release and fire. Many incidents

Petrochemicals

• Ethylene: Unstable. Decomposes to C + H2 + Heat. Reaction front along tops of pipes/ equipment. Tell-tale: Scorched paint on piping top. Heat release can cause rupture, release and fire. Past incidents at - Ethylene Dryers, Mol Sieves, as regen gas, Compression with O2 or N2 (diatomic gases heat up more in compression). Avoid initiators like O2, metal powder/dust, peroxides and mol sieve. Purge air/ N2 from vessels slowly with C2=. Monitor temperature and cool sieve beds before introducing C2=

• C2=: Leaked into steam line and reached space heater below control room and accumulated in the condensate drain inside the building. Building was destroyed

• C2=: Regeneration line. Temperature range (-) 17°C to 220°C. Atmospheric moisture condensed and evaporated cyclically. Led to Corrosion Under Insulation (CUI) and leak of 40% C2=. Foot traffic or stepping on insulated line damages external jacket

• C2=: Start-up. One of the reactors had a lower pressure than the other 3. Circulation of refrigerant to the HX inside the reactor caused C2= condensation and low temperature. Steam was introduced in reactor vessel jacket to warm up. C2= vaporized increasing pressure to PAH. Operator manually routed gas to flare; not enough and the RV popped - not routed to flare but vented to atmosphere. Ignited by a welding machine. Fire

• C2=: Refrigeration Compressors. Low mass rotating assembly. Discharge check valve failure resulted in high reverse rotation speeds. Multiple incidents. A few resulted in gas release and fire

• C2=: Exothermic runaway reactions are known in Acetylene converters, MAPD+H2, C4 Hydrogenation, PGH, Methanators, MTBE reactors, Adsorption beds etc. Number of incidents

• C2=: Pneumatically assisted NRV in Cracked Gas Compressor line failed. VCE. Similar, C3 Refrigeration system compressor discharge in another C2= Plant

• C2=: Fire at the base of Deethanizer column, due to flange leak at reboiler or relief header. Leaking C3= ignited by steam piping. Fire engulfed C2= and C3= columns. A vertical C3= storage tank exploded and 2 C3= tanks toppled. 5 C2=/C3= tanks collapsed and exploded. C2= column released its inventory

• C2=: Lightning strike caused black screen in Cracker Control Room. Poor grounding of cable shield wires. Compressor controls damaged by over-voltage. RV release. RV chattering cracked 2 compressor vent lines. Plant ran on last set points of controllers

• C2=: Cold Box Failure. Hole in an elbow downstream of a JT valve. localized erosion due to impingement + cavitation damage

• C2=: HDPE made by polymerizing C2= dissolved in isobutane. Settling polymer particles dropped into legs at the bottom of reactor pipes. They were periodically removed by closing an upper DEMCO (butterfly) valve and a bottom valve in a leg. Frequently the legs used to get clogged. After closing the DEMCO valve, the leg was removed and cleaned out. Pneumatic connections for opening and closing the valve were identical and were improperly reversed when last re-connected. As a result, when the switch in the control room was in closed position, a leg was removed without closing the DEMCO valve. Flammable gas release and explosion. Interlock or DBB and Different hose connections?