Safety Alerts 3

Separators/ Vessels

• Nitrate Induced Cracking: Cooling water was poured to condense hot cyclohexane fumes leaking from a reactor. Water had nitrates that resulted stress corrosion cracking of a reactor. WWW

• MEA absorption tower: 1” SA 516 Gr 70 welded with full penetration submerged arc joints, but without post-weld heat treatment. Developed cracks. BLEVE

• Ethylene Plant: Depropaniser Feed Drum LT embrittlement. Normal t = 60°C. Transient start-up T < 0°C that could have flashed to < -10°C. Failure at an aged weld

• Nitrobenzene column start-up. Damaged trays led to poor separation and abnormally high nitrobenzene concentration in bottoms. Explosion. Plant damage and fatalities

• Quick Opening Doors may fail on repressuring. Refer to manufacturer's procedure for fastening method. Stay clear of doors when repressuring. If possible, avoid Quick Opening Doors

Storage Tanks

• Storage tank incidents are more in refineries (61%), followed by petrochemical plants (34%) and oil fields (5%). External floating roof > inner floating roof. Loading/unloading operations > grounding > static electricity

• Rapid filling: Crude Oil Tank didn’t overflow but excess vapor vented ignited by uninsulated hot piping. Piping manifold failure released additional oil to fire. F&G. Rate of tank filling

• Blending: Calculation error - excess Butane was blended with gasoline. Light ends vapor lifted and tilted the roof generating static or metal - metal sparks. Fire. Blending agitation may also generate static sparks in tanks. Blending in a closed circuit piping system under pressure is recommended. BP

• LPG tank: Inlet pipe ruptured. Gas cloud ignited by ground flare. BLEVEs of 4 spheres. Extensive fatality and loss

• LPG: Sample valve frozen. Leak and BLEVE. Add DBB in sample point

• LPG: Water drained from an LPG sphere. The second downstream valve got frozen and the first valve got plugged by hydrate. While trying to fully open the first valve, its handle came off. Leaking LPG cloud was ignited and LPG pool below the sphere caught fire. The uncooled top part of the sphere burst, knocking down an adjacent sphere, bursting it too. Route drain pipes away from the sphere. Keep 600mm minimum distance between the valves. Check for icing while draining. First valve should be ROV/ ESD. Insulate or mound the sphere. Add deluge water. Slope the ground below. Add BDV. Similar, a refinery LPG Sphere PRV failed to open and operators opened its drain valve, little realizing that vapor pressure on top will remain the same. Drain valve froze and liquid LPG ignited. BLEVE. Similar, sphere overpressurized and its PRV did not lift. Inlet line ruptured. Resulting flame heated an LPG sphere that BLEVEd. More spheres and tanks BLEVEd. WWW

• LPG: Internal ball float came loose and blocked RV inlet in tank top. Tank deformed. If the ball can block any of the tank top branches, protect with a metal cage or go for a different type level indicator. WWW

• LPG: Butane/ Butadiene low boilers condensed and pulled in vacuum when the ambient temperature is below 0°C. Design the tank for vacuum and/or recycle warm gas. WWW

• Liquified gas filled tanks overfilled ruptured on thermal expansion due to solar. 1948 - Tank car with DME (Dimethyl Ether) 200 fatalities + 4,000 injuries. 1978 - Propylene 217 + 200

• LNG Tank roll-over or water boil off in oil storage tanks. Rupture/ fire 

• Flame Arrestor: Fine gauze FA choked with sand and corrosion products, created vacuum and tank partially collapsed on product withdrawal. Check of FA regularly. Avoid fine gauze in FA. BP

• Hydrotest: Tank pulled vacuum and collapsed when its vent was covered with plastic bag for painting or honeycomb or plugged flame arrestor. Inspect vent before filling or emptying a tank

• Hydrotest: Fast filling with under sized vent, tank blew it’s top. Remember: Tank filling takes a long time. No short cut. Air can’t get out as fast as water can be pumped in

• Hydrotest: Tanks on soft reclaimed soil collapsed

• Hydrotest: LPG spheres collapsed due to CUI (Corrosion Under Insulation) of its legs. Good insulation and inspection windows on insulation to monitor CUI. Apply coatings on legs

• Weld in a tank containing C3 at -44°C failed. Wave of liquid propane swept over the dikes and inundated process area before igniting. Failed weld was a repair on a weld failure a year earlier. Suspect: Microbiological sulphate reducing bacteria from hydrotesting with sea water

• Roll-Over or Froth-Over: Refinery recovered oil storage tank fed with ballast water. Internal floating roof. Bottom water heated by steam coil. Automatic heating control changed over the years to manual control. Local TG + hand felt tank shell temperature was used to control steam flow. On top of water floated an emulsion layer that usually acted as a good insulator to the oil on top. Local TG malfunctioned setting off 6 control room temperature alarms - vertically arranged A to E. As alarms were considered unreliable, steam flow was maintained. The emulsion broke, heating oil resulting in vapor release. H2S and LEL gas alarms sounded in the tank farm

• Froth-Over: Hot Vacuum Oil accidentally transferred to a Slops tank with water-oil liquids. Froth-Over sank the internal floating roof and roof ruptured under internal pressure. BP

• Boil over: #6 fuel oil transfer from one tank to another. 180' dia tank. As the oil temperature was high, operators cut a tracing system to cool it. Next morning when they tried to manually gauge the tank, an explosion occurred, due to non-intrinsically safe lamps or static spark. The roof of the tank landed some distance away and severed some product lines, igniting a bund fire. Tank was under a full surface fire. As the site was remote + tank was on a hilly terrain, firefighting was limited. The only access road below the bund was on fire. The tank boiled over, with a 500' dia fire ball. The boil over pushed product over the top of the tank, creating a wave of burning liquid that went over the 20' high bund wall and travelled more than 1,300' downhill. This wave entered another bund and ignited another fuel oil tank. 160 killed and more than 500 injured. Destroyed a 500 MW and 1,200 MW power plants. Poor location of large inventory tank on a hill above the facility. BP

• Slop Tank: Steam heating coil. At 100°C, water-oil emulsion separation released boiling light ends. VCE. BP