Safety Alerts 20

LNG

• Closed blowdown valve resulted over-pressurization of an LNG plant HX that exploded

• Start-up warming up of an LNG line led to thermal expansion in a blocked-in piping. As its RV was isolated, line ruptured; released LNG ignited resulting in BLEVE, vapor cloud explosion, a fireball, a small secondary pool fire. Poor isolation and car seal procedures. Failure of temperature indicator alarms

• Leaking LNG, extremely cold, has caused fractured metal supports / plates in several incidents

• Tank failed and LNG overflew the dike. Vapor cloud ignition. Legs of adjacent tank failed. Significant destructions to the plant and adjoining area. Inner tank made of 3-1/2% Nickel - its low temperature properties, testing, weld procedures and radiographic examination. Use 9% Nickel. Inadequate dike volume. Dispersion and fire radiation on adjoining area. Heating of outer tank floor to avoid embrittlement. BP East Ohio Gas Company, Cleveland

• While repairing mylar liner, it ignited. Resulting fire increased the temperature and pressure in the tank to rise, dislodging its 150 mm thick concrete roof. BP

Hydrogen

• Hydrogen: Low mol weight gas, susceptible to flange etc. leaks. Faster upwards dissipation; ignition less likely. Highly flammable. Its high flame speed leads to faster burn-out. Tests have shown it is safer than gasoline fuel (https://hydrogen.wsu.edu/2017/03/17/so-just-how-dangerous-is-hydrogen-fuel/). Caution: Wider flammability range 4-74%. Low ignition energy 0.02 mJ Vs 0.29 mJ for natural gas. High pressure H2 release can spontaneously ignite without ignition sources, such as spark or hot surface. H2 flame is almost invisible. Hard to pin-point the source. It is odorless, colorless and tasteless - leaks are hard to sense. Indoor H2 leaks accumulate at ceiling level

• SMR Hydrogen production: Pipe believed to be empty was opened; high pressure H2 release that self-ignited. Strict isolation, verification, and hazard controls are essential

• H2 generated while charging batteries accumulated and blew the roof. Good ventilation a must

• Liquid H2 Storage: Tank exploded when Fire Water was sprayed on tank vent. Low temperature H2 formed ice and plugged the vent

• Electrolysis and H2 Storage: https://h2tools.org/lessons/ lists over H2 related incidents. A few are covered in other pages. (1) Sludge deposits in Electrolyser reduced electrolyte flow increasing cell temperatures and electrolyte concentrations. Led to severe corrosion/erosion damage of the electrodes and separators allowing H2 into O2 separator. Ignition and explosion. Fatality. Periodically test and monitor H2 and O2 gas purity analyzers + trip the plant on high impurity (2) Similar. Blockage in makeup water line led to low electrolyte levels in cells and higher O2 in H2. Ignition and explosion at H2 HP compressor outlet. Damaged HP H2 storage. Monitor/ trip on electrolyte level and gas purity (3) Check Valve Shaft Blow-Out due to H2 Embrittlement releasing H2 and HC. VCE (4) Failure of Inconel 600 rupture disks (5) Leak from liquid H2 pump near ground, unlike gaseous H2 that dissipates fast. Explosion (6) RV relief, horizontally vented - not flared - fire and explosion (7) Electrolyser was at 25% capacity. To maintain a high pH liquid, its liquid was sent to plant sump. It eventually reached the Electrolyser by design. Plant computer-controlled acid injection system was unable to cope-up. High pH electrolyte increased O2 and H2 concentration fell below UFL. Ignition and explosion. Gas concentration monitoring, alarms and trips. Operator training (8) Liquid H2 Storage Tank RD blew, venting cold H2. Vent tip fire. Firewater directed at the vent tip froze - super cold H2 and blocked the vent tip. As residual liquid H2 in the tank warmed up, tank ruptured. BLEVE. Do not use water in liquid H2 service

• Poor drum labelling lead to addition of KOH that led to H2 release. Gas detectors were not working. No vents on the reactors and poor building ventilation. Explosion

• HP H2 from 150 bar cylinders was used to regenerate Cat Reformer catalyst. Instead of the regular hose outlet fitted with a pressure regulator and RV, a bypass hose was used with blocked outlet. LP rated hose failed, H2 release and fire. BP

Ammonia

• HTHA: High Temperature Hydrogen Attack 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

• Primary Reformer: See under Fired Equipment

• Secondary Reformer: Fe2O3 deposits at WHB hot end. Internal refractory failure. Tubes creep failure

• CO2 Removal: Corrosion in coolers, condensers and reboilers. Due to (1) Inadequate concentration of anodic inhibitor (2) Hydrocarbons (3) High gas loading and/or frothing/ foaming (4) Formation of a Sulfide layer and (5) Galvanic interaction

• Methanation: Exothermic Runaway Reaction. Poor or aging catalysts in HT and LT Shift Converters lead to hi CO, that is not absorbed in CO2 Removal unit. High temperature in Methanator

• CO2: Explosion in CO2 piping to Urea plant. Presence of H2. Due to (1) Trip system disabled (2) H2 enriched gas entry (3) Nitrogen purge not effective and (4) Air leak formed an explosive mixture

• HP Ammonia Pump, feeding Urea plant. Tie rods of pump 3rd plunger failed and the plunger blown away. HP Ammonia release. Plant did not have any Ammonia sensor to automatically stop Ammonia fed to the pump and trip the pump. Advised proximity sensors to detect plunger likely failure; scheduled replacement of tie-rods and water curtain above the pumps

• Syn Gas: Compressors. Avoid Wet Gas Seals. Go for Dry Gas Seals. Use Duplex SS Coolers

• Syn Gas: Ribbon wound pressure vessels better than mono wall. Failure of expansion bellows of HX due to H2 attack. RV poor support led to piping failure and fire

• Syn Gas: Syngas leak from reactor outlet flange ignited. Inappropriate tightening torque on the bolts + temperature difference between the bolts and the flange

• Ammonia hose ruptured. Hose meant for LPG was wrongly used by the trucking company. Color code

• Ammonium Nitrate: AN was made neutralizing NH3 with HNO3. AN plant was shut down when HNO3 plant was down. Operators purged the HNO3 feed line first with air and then steam to prevent back flow AN into HNO3 feed line. Plant exploded killing 4 and injuring 18. Causes: AN can decompose, deflagrate and detonate at low pH levels, high temperature in a low density (gas bubbles) confined space in the presence of contaminants like Chlorides. Purging the HNO3 line could have lowered pH to 0.8 Vs 5.5 to 6.5 maintained during production. Steam sparging provided enough heat + low density air: steam bubbles. Chlorides were in the HNO3 feed. The pH probe present in the Neutralizer overflow line could not detect the lowered pH inside the vessel; any way the probe was defective for 2 weeks. Defective SOP. (1) Vessel should have been emptied and/or kept at a pH >6 (2) Unsupervised steam sparging and failure to monitor temperature (3) Operators were not aware of NH4NO3 hazards as no HAZID study. AIChE CEP

• Ammonium Nitrate: Massive explosion. A few causes - including chemical accident - Sodium Dichlorocyanurate mixed with AN spilled on stored AN

• Ammonium Nitrate: Wooden storage depot fire detonated AN stored in wooden bins

GI Structures

• Electrochemically treated Zinc in galvanized steel can produce H2 that get stored under pressure in structural supports without drain or weep holes. Drilling, cutting etc. can produce an easily ignited gas jet