320 likes | 498 Vues
Where We Go Wrong In Vessel Design. Dick Hawrelak Presented to ES-317Y in 1999 at UWO. Introduction. 30% 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 Record.
E N D
Where We Go Wrong In Vessel Design Dick Hawrelak Presented to ES-317Y in 1999 at UWO
Introduction • 30% 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 Record • 6486 accidents. • 516 injuries. • 90 deaths.
OSHA Record Includes • Power Boilers • Water Boilers and Steel Tanks • Cast Iron Boilers • Pressure Vessels (poorest record)
Pressure Vessel Record • 1310 / 6486 accidents • 437 / 516 injuries • 73 / 90 deaths
Press Vessel Components • Shell • Head • Attachements • Piping • Safety Valves • Misc
PV Failure Causes • Operator error or poor maintenance – 149 / 933 • Faulty Design – 144 / 933 • Corrosion or erosion – 132 / 933 • Pressure control failure – 41 / 933 • Other – 420 / 933
PV Failure Types • Cracked – 403 / 1087 • Other - 298 / 1087 • Leakage – 163 / 1087 • Rupture – 158 / 1087 • Explosion – 22 / 1087 • Collapsed Inward – 15 / 1087
Obtain Data & Analyze • Search OSHA records On Internet - Google • Extract records • Create Excel Database • Sort and Filter data • Analyze Data
Personal Experiences • Based 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 89 • A-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.
Nozzles • Level 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 Site • Chemical Emergency Preparedness and Prevention Office web site at www.epa.gov/ceppo/acc-his.html • Check Rupture Hazard of Pressure Vessels. • Check Catastrophic Failure of Storage Tanks.
Ammonia Storage Tank Modification • Oil and Gas Journal, Dec 26, 1998 • Pressure storage in spheres • Removes bottom unloading lines. • Converts to overhead siphon system. • Excellent article on 4 process design options.
Internals • Impingement details not well designed. • Pump-out sumps act as dirt trap. • KO Pot internals not designed properly.
Design Pressure • Design Pressure not suitable for upset conditions.
Reactive Chemicals • P&IDs must be examined for reactive chemical possibilities.
Low Pressure API Tanks • Very 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 Options • Not well understood. • See BLOSS program for design options.
Flammable Storage Area • EO 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 Questions • What 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 Cont’d • What 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?
Summary • This 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.