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Risk Assessment of Catastrophic Failures of Pumps Resulting from Isolated Running

Risk Assessment of Catastrophic Failures of Pumps Resulting from Isolated Running

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Risk Assessment of Catastrophic Failures of Pumps Resulting from Isolated Running

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  1. Risk Assessment of Catastrophic Failures of Pumps Resulting from Isolated Running by J. Wayne Chastain

  2. Potential Concern • Centrifugal Pump in Operation • Full of Fluid • Suction and Discharge Closed or Plugged • BLEVE of Pump

  3. Pump Isolation Concern • Risk • Process Hazard Analysis • Actual Data at Tennessee Eastman • Quantitative Risk Assessment • Additional Controls

  4. Typical Spared Pump

  5. Pump Isolation Concern • "The potential exists for operator error to result in a pump being started in an isolated condition (with suction and discharge valves closed). If this occurs, the pump could be overpressured and fail causing injury to personnel in the area and damage to additional equipment."

  6. Consequence • Injury to personnel • Class B – Lost Time Injury • Class C – Hospitalization • Class D – Severe Injury • Release of Flammable Liquid • Class B – Less than 10,000 lb • Class C – More than 10,000 lb

  7. Controls • Trained Operators • Operating Procedures • Emergency Response • Deluge Protection • Area Electrical Classification

  8. Controls • Trained Operators • Operating Procedures • Emergency Response • Deluge Protection • Area Electrical Classification

  9. Are the controls adequate? • Other safeguards: • Likelihood that the seal will fail and relieve the pressure • Likelihood that anyone is in the area when the pump fails • Likelihood that person is injured by shrapnel • Likelihood that other equipment is damaged and a release occurs • Likelihood that any flammable release is ignited

  10. Frequency of Occurrence • Eastman Chemical Company, Tennessee Eastman Division • ~7850 Centrifugal Pumps in Operation • Sized from <1 hp to >500 hp • 5 events in 14 years • 10-4.5 BLEVEs / pump-year

  11. Quantitative Risk Assessment • Fault Tree • Event Tree • Failure Modes Effects and Criticality Analysis • Layers of Protection Analysis (LOPA)

  12. LOPA Description • Simplified form of quantitative risk assessment • Uses order of magnitude categories for: • Consequence severity • Initiating event frequency • Likelihood of failure of Independent Protection Layers (IPLs) • Provides a numerical indication of adequacy of protective systems

  13. Benefits of LOPA • More objective basis for risk acceptability compared to qualitative techniques • Gives a basis for Safety Integrity Level (SIL) determination for Safety Instrumented System (SIS) design

  14. Tolerable Risk • Based on the types of consequences evaluated by the LOPA • Varies for different levels of consequence • May be dictated by governing authority or determined by individual companies

  15. Tolerable Risk for Life Safety • Individual Work Accident Risk • 1.5 x 10-4 per year (BLS 2003) • One method of determining an acceptable target is to provide an order magnitude "better" protection than industry average for a particular cause-consequence pair

  16. Government Tolerable-Risk Criteria Summary

  17. Possible Variables • Non Hazardous vs. Hazardous Materials (Toxic, Flammable, Reactive) • Plugging vs. Clean Services • Local vs. Remote Start • Automatic vs. Manual Start

  18. Example LOPA Table

  19. Explanation of Values • Simplification of approach by working in logarithmic values • Log (1 x 10-5) = -5 • Working with logs of values allows all manipulations to be handled by addition and subtraction • Accuracy is limited to the closest half order of magnitude value

  20. Explanation of Values

  21. Example LOPA Table

  22. Initiator • Operator Error • Initial error is in isolating a pump without immediately draining it • Secondary error is starting a pump that is isolated • Likelihood is increased if pump is started remotely • Accepted failure rate is 1 x 10-2 per opportunity • Events per year • Best estimate of opportunities for event to occur on a yearly basis • Only used when the initiating failure is per opportunities

  23. Example LOPA Table

  24. Enabling Events • Pump isolated • Must be expressed as a probability for consistent units • Value may vary depending on actual likelihood

  25. Example LOPA Table

  26. Layers of Protection • Criteria • Effective • Independent • Auditable • Seal Failure as Relief • Questionable as to its auditability • Given minimal credit • Will vary depending on seal type and maintenance

  27. Example LOPA Table

  28. Conditionals • Probability of ignition • 0 for releases caused by collision • 0 for releases close to fired equipment • -0.5 for releases in general process areas • -1 for releases in remote process areas • Probability of personnel in affected area • Varies depending on event, process, and location • Probability of severe injury • -0.5 for personnel in area of fire • -1 for personnel in area of shrapnel

  29. Example LOPA Table

  30. Differential • If value is 0 or positive then additional risk reduction is not needed • If value is negative, then additional risk reduction of that reliability may be warranted

  31. Additional Controls

  32. Safety Instrumented Systems • Shutdown pump when an isolated running condition is detected • Low power • High pressure • Valve position • High temperature • Flow

  33. High Pressure SIS

  34. Low Power SIS

  35. Conclusions • Qualitative risk assessment techniques like PHA can only give a "gut feeling" as to the need for controls to prevent pump isolated running and prevent the potential for BLEVE • LOPA can be used to determine when additional controls are needed and the required reliability of the controls

  36. Layers of Protection Analysis • Additional information on LOPA can be found in Layer of Protection Analysis: Simplified Process Risk Assessment, CCPS, 2001 (www.aiche.org/ccps) • LOPA class will be offered for Eastman personnel in January • ABS Consulting offers a LOPA class (http://www.abs-jbfa.com/lopa.html)