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  • Where We Go Wrong In Vessel Design

    Dick Hawrelak

    Presented to ES-317Y in 1999 at UWO

  • Introduction30% of large property damage losses are caused by failures in tanks, process drums and marine vessels.Average Trended Loss was $40.5MM for tanks alone.

  • 1984 U.S. National OSHA Record6486 accidents.516 injuries.90 deaths.

  • OSHA Record IncludesPower BoilersWater Boilers and Steel TanksCast Iron BoilersPressure Vessels (poorest record)

  • Pressure Vessel Record1310 / 6486 accidents437 / 516 injuries73 / 90 deaths

  • Press Vessel ComponentsShellHeadAttachementsPipingSafety ValvesMisc

  • PV Failure CausesOperator error or poor maintenance 149 / 933Faulty Design 144 / 933Corrosion or erosion 132 / 933Pressure control failure 41 / 933Other 420 / 933

  • PV Failure TypesCracked 403 / 1087Other - 298 / 1087Leakage 163 / 1087Rupture 158 / 1087Explosion 22 / 1087Collapsed Inward 15 / 1087

  • Obtain Data & AnalyzeSearch OSHA records On Internet - GoogleExtract recordsCreate Excel DatabaseSort and Filter dataAnalyze Data

  • Personal ExperiencesBased on 33 Years of Chemical Plant Design at Dow.

  • Incomplete Mass Balances

    Normal mass balance.Start-up, shut down or upset.Recycle conditions.Off-loading situations unplanned.

  • Residence or Hold-up Time

    Inventory logistics not well defined.Flammable or toxic inventories too high.

  • Containment

    Dyke dimensions do not meet codes.Drainage does not follow NFPA 15.Catastrophic failure overwhelms dyke walls.

  • Materials Of Construction

    Not suitable for corrosive fluid at high temperature.Not suitable for low temperature excursions.

  • Quantum Explosion - 7 June 89A-515-70 grade CS brittle failure of heat exchanger shell.Start-up, inlet flange leak, isolated exchanger and depressured to flare.30 minutes to failure. Two fatalities, seven serious burns, major damage to ethylene plant.

  • NozzlesLevel control nozzles in wrong location.Nozzles too small creating impingement on far wall.PSV nozzles not suitable for thrust.

  • Visit U.S. EPA CEPP Web SiteChemical Emergency Preparedness and Prevention Office web site at Rupture Hazard of Pressure Vessels.Check Catastrophic Failure of Storage Tanks.

  • Ammonia Storage Tank ModificationOil and Gas Journal, Dec 26, 1998Pressure storage in spheresRemoves bottom unloading lines.Converts to overhead siphon system.Excellent article on 4 process design options.

  • Typical Pressure Vessel

  • KO Pot Design

  • InternalsImpingement details not well designed.Pump-out sumps act as dirt trap.KO Pot internals not designed properly.

  • Design PressureDesign Pressure not suitable for upset conditions.

  • Reactive ChemicalsP&IDs must be examined for reactive chemical possibilities.

  • Low Pressure API TanksVery easy to bulge or suck-in resulting in loss of containment.PSV, pad de-pad settings very close.Floating roof explosion at Suncor in Sarnia. Roof hangs up on pump-out, air sucked into vapor phase, lightning ignites flammable vapor.

  • Breathing.Pumping and temperature change breathing not allowed for in combination.High breathing losses a cost and an environmental problem - Benzene tank.

  • Vapor Recovery OptionsNot well understood.See BLOSS program for design options.

  • Flammable Storage AreaEO storage bunkers located 1 mile from ISBL.3 independent means of checking quantity to prevent overfilling (dual LC, weigh scale & flow rate x time).Refrigeration to prevent polymerization, chart temperature.Dump contents to pond if runaway reaction takes place.

  • EO Storage

  • Toxic Storage

  • Possible Exam QuestionsWhat are three independent methods for preventing overfilling of a storage vessel.If a storage product can generate heat by polymerization at ambient temperatures, what safety measures should be considered?What are the main problems with fixed roof, low pressure API type storage vessels?

  • Exam Questions ContdWhat is one of the main problems with an API, floating roof storage tank in flammable service?What are the safety measures that should be taken for a large chlorine storage sphere to prevent a toxic gas release?

  • SummaryThis short list is indicative of some of the problems caused by poor engineering discipline in vessel design.Recommend you obtain a copy of the Chemical Plant Design programs and follow the procedures built into the vessel design spreadsheets.