Safety Alerts 11

Piping

• Glued Insulating Gasket: For cathodic isolation of a C2/C3. Glue between stud bolt washers and isolation sleeves extruded on sunlight, weakening the bolted joint. Failed and released gas. After cleaning off the glue, bolts maintained original torque

• Insulation Flanges: Avoid inadvertent painting or removal. Keep a caution board. BP

• Small Bore Pipe: (1) Vehicle impact ripped off a drain valve in liquid C3= line and (2) Toppled LPG Cylinder ripped off LPG small bore filling line. Fire and explosion

• Small Bore Pipe: branch off from large pipes have failed in a number of places. Poor support. Usually in compressor or pipe discharge lines. Vibrations. Avoid

• Small Bore Pipe: Many small bore pipes fail by fatigue as they are free to vibrate. Small valves have been knocked open or have vibrated open. WWW

• Utility Hose: No NRV at vessel UC nozzle. Attempt to purge vessel without depressurizing, ruptured N2 hose as the vessel was at 18 bar. Expecting operators to attach a check valve to the hose may not work

• Hoses: Are frequently connected and disconnected. Not stored properly. Frequent flexing makes failure likely

• Hoses: Mix-up. LPG hose used for NH3 failed. SS hose instead of Hastelloy C used in chlorine service failed

• Foam Debris: Dried foam choked foam chemical: water mix proportioning valve. Flush after every use

• Mismatched/ locally procured gasket O ring failed. Gas plant fire. Remember space shuttle Challenger explosion due to O ring failure

• Poor quality plate. Vessel failed under hydrotest

• DGA column 36” line hydrotested at 1,915 psig. Poor quality gasket good for 1,160 psig broke at 1,500 psig. HP water jet with broken gasket hit a worker on his face

Relief

• Ensure atmospheric relief (open vent) discharges are to a safe location and are safe. Discharges can be toxic or may result in VCE (Vapor Cloud Explosion) (1) Methyl isocyanate discharge (2) Flammable chemicals VCE (3) Ethylene vapor (4) Methyl Mercaptan from a storage tank; poisonous liquid methyl mercaptan pump relief close to grade; Nitrogen discharge below pipe rack; Chlorine discharge below operating platform (5) Tetrahydrofuran vapors and (6) Isomerization unit vent stack

• PSV: Inlet pipe in Debutanizer was plugged with polymer. High pressure events deformed the inlet piping, as PSV was unable to relieve. Butadiene is known to polymerize when concentrations build-up in dead legs like PSV inlet piping. Flush continuously or insert a RD in protected vessel to avoid build-up

• PSV: Inlet flange had minor leaks. When PSV started simmering, the stud nuts fell off. Release and fire

• PSV: High discharge velocity/ momentum ρv², led to tail pipe failure, gas release and local fire. In another case, led to auto-closing of discharge LO valve. Note: High velocity in tail pipes do not occur during group loads but when a PSV/BDV alone opens with low backpressure. Support tail pipes properly

• PSV: Quench column PSV opened on Cooling Water failure. PSV vibrations led to failure of bolted flanges. Local release and explosion, shutting steam to cracker furnace tubes. Loss of steam resulted in cracker furnace tubes rupture and release of quench oil. Quench oil pool fire below a cracker damaged 4 cracker furnaces 

• PSV: Steam RV outlet had condensate accumulation. No drain or weep hole. When RV opened, water hit and damaged the tail pipe. WWW

• PSV: Cavern Gas Storage. MOC used good for screwed/ bolted application. Welding caused microscopic changes and corrosion cracks. Some PSVs ruptured and making the caverns inoperable

• RD + PSV: Leakage thru upstream RD led to higher backpressure on RD and hence over pressurisation of the protected vessel. Monitor downstream pressure of RD regularly. Add PG/PAH

• RDs can prematurely fail. RD on Cooling Water (CM) failed due to pressure surge when CW pump was started, sending CW to flare

• Failed RD on HX routed hot oil to flare, resulting in Flare KOD LAHH/PSD + gas release. High velocity relief gas impact on hot oil in the relief header led to water hammer damage of flare piping. Consider premature/ latent failure of aged RDs in relief system design

• Bonnet vents of conventional RVs are plugged while in service. Bonnet vents of balanced bellows RV should not be plugged and should be left open to atmosphere. Take care. Difficult to know RV type by external appearance

• HX with NH3 in shell taken out on maintenance. PSV inlet closed. HX steamed out. Liquid NH3 vaporized and HX burst

• PSV chattering: Offshore Slug Catcher. On ESD gas outlet SDV closed before inlet SDV closed, leading to a blocked outlet. The large sluggish PCV responded slowly resulting in all the 3 PSVs popping. PCV progressive opening reduced the flow to PSV, resulted in chattering; after 20 seconds of chattering PSV bellows failed leading to local release

• PCV: Removed flare PCV without outlet isolation. Flare gases released locally. Fire - injury and death