Where We Go Wrong In Vessel Design
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.
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 www.epa.gov/ceppo/acc-his.htmlCheck 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.
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.