Safety Alerts 10

Compressors

• CO2 Compressor Suction Scrubber at 32-70 bar. Liquid level control stuck open. Gas blowby to drain system. Common in cold weather. Due to JT effect, CO2 reached (-) 34°C. Ice or hydrate formation plugged drain piping and pressure relief valve. Drain Vessel reached 39-49 bar and catastrophically ruptured. Drain Vessel did not have pressure, temperature, or level instruments. Scrubber liquid level and dump valve position were not recorded. Inadequate vessel and piping design, inadequate instrumentation and overpressure protection. PHA reviews considered Scrubber gas blowby to drain as an operational issue and not a safety problem; did not identify potential ice or hydrate formation and pressurization in the drain system. CSB

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

• C2= Plant. Cracked Gas Compressor. HP Stage 2” balance line (balances impeller thrust force) had cracks. Assumed due to long-term fatigue. Accelerometer tests showed natural frequency resonance at a small window of compressor operating speeds. Fixed with suitable supports. Include auxiliary piping in design reviews as done for main lines

• Isolation: After maintenance, isolation blinds were removed. Ethylene leaked thru the isolation valves into the compressor and the ethylene-air mixture ignited. WWW

• Water collected in the discharge check valve froze during severe frost, resulting in a blocked outlet when the compressor was cut-in. BP

Dehydration

• Small bore: Glycol Pump discharge ½" SS tubing upstream of tower SDV broke. Glycol, condensate, and gas sprayed onto the glycol reboiler and ignited

Sweetening

• HC separated in Rich DEA Surge Drum routed to unit Flare KOD. Pumped from KOD to Lean Amine Tank instead of Slop Tank, leading to HC accumulation in tank. Tank HAC (Hazardous Area Classification) didn’t factor it. Tank drained by a vacuum truck using an unearthed non-conducting hose. Explosion

• Pyrophoric: Wet spent metallic parts with water on opening a column/ tank in H2S service

Piping

• Piping failure is the cause of about 50% of leaks. Fatigue and/or inadequate flexibility. WWW

• Bend: Downstream of a flashing LCV eroded. HC release. Keep minimum 20D distance to bends after a LCV/PCV. Proppants/ sand in the fluid accelerate erosion. If a downstream separator is elevated to provide pump NPSH, install a check valve at its inlet, to prevent its emptying

• Bend: Thinning/ hole in Cold Box piping bend, after a liquid methane LV. Flashing and cavitation

• Bend: Wash water injected in Deethanizer feed. Water at gas velocity thinned piping bend. Gas release and explosion. Avoid bends immediately after such erosion-corrosion zone. Consider a spray nozzle for liquid injection with gas as atomizing fluid. Inspect downstream bends regularly

• Bend: Cold VGO injected into hot VGO+H2 downstream of HX preheat train. Downstream elbow at 2D (minimum 10D) failed. Fire. Inspect downstream bends and piping support regularly

• Elbow: Carbon Steel elbow wrongly inserted instead of alloy steel elbow in a high-pressure, high-temperature Hydrogen line. High Temperature Hydrogen Attack (HTHA) ruptured the elbow. H2 release. Ignition. Positive alloy verification is a must. Design out incompatible components being interchanged

• Low Temperature Embrittlement: Poor mixing of LT fluid into warm fluid. Keep minimum distance upstream of mixing point in HT line for HT/LT spec break

• Low Temperature Embrittlement: While service temperature may suit CS, auto-refrigeration on loss of pressure - venting/ blowdown can bring down metal temperature. MDMT issues

• Brittle fracture: CS piping during hydrotest. Manufacturer reduced Manganese to lower limit of piping codes - A106/A53 pipes + A105 flanges + A234 fittings. Ask for “Mn:C ratio > 5 and grain size <7”

• Brittle fracture: Threaded 3” cast iron Y strainer installed in a welded SS piping failed. Likely thermal expansion. Iso-butylene released. VCE

• Bellows: Fail due to poor installation or when not designed to applicable operating conditions. A bellow not designed for steam out failed. WWW

• Isolation: Pump RV removed but inlet was not blind flanged. Condensate discharge and fire

• Isolation: Cyclohexane leak and explosion. Earlier blamed on temporary patch up piping by plant personnel, without a design review. Now understood as caused by fugitive water into reactor that vaporized suddenly with a pressure surge. Management of Change procedure

• Isolation: While cutting a 30m vertical line from CDU fractionator to Naphtha Stripper, Naphtha was released. Stripper operating pressure was higher than static head of Naphtha in the vertical line and felt via a passing valve across LCV, upstream of the Stripper. Ignited by fractionator bottom bare area running above naphtha auto ignition temperature

• 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

• Isolation: Blind left in place corroded. 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

• 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 units, downstream units with large flammable inventory do not have extensive remote isolation valves to automatically or manually close from a safe location to minimize release. Avoidable escalations. After studying many incidents, CSB has recommended to API, EPA and OSHA to have them installed in downstream industries - CSB Safety Study No. 2024-01-H: ‘Remote Isolation of Process Equipment 

(1) To close a manual valve in a Naphtha tank feeding a fire, firefighters had to wade thru a mixture of water, foam and HC in the tank dike

(2) A pipe elbow ruptured releasing a large vapor cloud and explosion

(3) Small bore piping. Vehicle impact ripped off a drain valve in liquid C3= line

(4) PDA unit leak spread quickly. Major pipe rack carrying flammable hydrocarbons collapsed and added fuel to the fire. Some of the pipe rack structure columns were not fireproofed

(5) Fire in a storage tank with Naphtha and Butane blend spread to additional tanks

(6) Metal piece broke away from a 3" cast iron y-strainer in the isobutylene feed line to a batch reactor. Gas release. Operators manually closed valves, but VCE

(7) Butadiene polymerization when build-up in dead-legs. Popcorn polymer that exponentially expanded in a dead-leg ruptured the pipe. Butadiene release and fire

• Valve Open – Closed: Failure of handle, stem, ball or seat may indicate valve is closed when it is open

• Thermal Expansion: of a blocked in heat transfer oil line. Heat from steam tracing. Rupture. BP

• Water Hammer: Steam was introduced into cold pipe work that has not been drained. 24”- 30m pipe flew 800m away

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