Safety Alerts 10

Piping

• Poor Isolation: Swinging spec blind or hammer blind. Valve passing led to gasoline leak/flashing and accumulation in tank pit. Operator overcame by fumes. VCE. Similar incident in an LPG plant. Use blinds, plugs or caps instead of relying on single valve closure. All valves leak

• Failure of handle, stem, ball or seat may indicate the valve is closed when it is open

• Poor Isolation: N2 header block valve not closed after completing LNG defrosting operation. Natural gas back flowed via N2 header into a control room where smoking was allowed. Explosion

• Poor Isolation: Blind left in place corroded thorough. Blind with short tag handle was left closed. Small bore branches were not isolated properly. Thin blind buckled under pressure and was difficult to remove. WWW

• Poor Isolation: HP gas piping was isolated by closing hydraulically operated valve. No spectacle blind was inserted. Loss of hydraulic oil resulted in the valve opening, gas release and explosion. WWW

• Poor isolation: Unlike upstream Oil & Gas industry, downstream industries do not have SDVs to automatically or manually close from a safe location to minimise release. After studying many incidents CSB has recommended to API, EPA and OSHA to have them installed in downstream industries

• Maintenance: Wrongly inserted a carbon steel elbow, instead of alloy steel elbow in a high-pressure, high-temperature hydrogen line. High Temperature Hydrogen Attack (HTHA) ruptured the elbow; released H2 ignited. Positive alloy verification is a must. Piping engineers may design out the possibility of incompatible components being interchanged

• Water hammer in steam lines: When steam is introduced into cold pipework that has not been drained. 24”- 30m pipe flew 800m away

• Water hammer in steam lines: Condensate accumulation upstream of a valve located in a pit. No upstream trap. When the valve was opened water hammer burst a branch, filling the pit with steam. WWW

• Water hammer in steam lines: Poor piping layout can result in steam-lock upstream of steam trap (condensate unable to reach the trap and drain). Resultant water hammer in the steam heating coils of a storage tank, burst the coil, boiled off tank contents and damaged its roof (JR Risko, ChE, May 24)

• Steam Traps: Bimetal traps subcool condensate. Difficult to maintain constant temperature. Accumulating condensate can corrode steam coils; on shutdown may freeze and split. Replace with float or thermostatic traps that avoid condensate accumulation (JR Risko, ChE, May 24)

• Need to specify pressure parts correctly and completely, rather than letting go off an incomplete specification hoping to catch up later. An improperly specified "flex pipe" ruptured while pressure testing

• Gear operated valve. Gas leaked via stem into gear operator. Its vent was painted over. Top plate blew off. In another incident natural gas was used to actuate its PRV. Corroded/ overpressurized and ruptured actuator blew off

• Long bolt or sandwich, or wafer valves: On flame impingement longer bolts expand rapidly and lengthen, allowing both gaskets to leak, adding more fuel to fire than standard flanges. Avoid

• 3 Part SS ball valve nuts cracked. Local release. Avoid lower grade SS 303/304. Use marine grade 316. Replace 3-part valves with solid block type

• HC piping trunnion support: Subject to localized corrosion and release. Inspect regularly

• Low Point Trap: Peroxide/ alcohol mix trapped in a 100m elevated piping decomposed and ruptured when pipe was steamed. Prior N2 purging was ineffective to remove the reactive chemicals. Operators missed the 2 low point drains ‘hidden’ in the pipe rack. Piping redone eliminating the pocket

• Dead legs /Pockets: Get corroded. During winter trapped water froze and cracked the piping; led to hydrocarbon release via a leaking valve. Conduct dead leg reviews/ Winterization checklist/ Freeze protection

• Dead legs / Pockets: Get corroded. 8” relief line failed and released 75 tonnes of flammable material. Avoid dead legs associated with vessel liquid outlets - LCV bypass, drain lines and low points

• Dead legs: API 570 “Components of a piping system that normally have little or no significant flow. Some examples include blanked (blinded) branches, lines with normally closed block valves, lines with one end blanked, pressurized dummy support legs, stagnant control valve bypass piping, spare pump piping, level bridles, pressure relieving device inlet and outlet header piping, pump trim bypass lines, high-point vents, sample points, drains, bleeders, and instrument connections. Dead-legs also include piping that is no longer in use but still connected to the process.” See Section 6.6.2 Dead leg inspection

• Dead end: HDS reactor outlet HX bank piping had a dead end that trapped process injection water containing NH4OH and chlorine. H2 leak. Explosion. Oil leak and pool fire. Regularly inspect and check wall thickness of dead end and low point piping

• Out of service - for 15 years - propane control station piping cracked. Fire. Refinery down. Isolate units/ equipment/ piping not in service, purge and blank off

• Chloride stress corrosion cracking: During pressure equalization, HP Compressor suction 16” ball valve bottom trunnion SS304 screw failed and trunnion ejected. Gas release

• Bypass line in RDS. NH4HS corrosion. Leak and fire

• Piperack structure: Were not fire-proofed. Collapsed and added fuel to fire

• Hydrogen Compressor Discharge Piping: cut thru by a bolt on adjacent support bracket of a temperature gauge. Watch during plant walks

• Insulation: That is soaked in oil can reduce its auto-ignition temperature and cause fire. Replace such insulation ASAP. WWW