Reliability
Reliability in the design context Weibull Analysis
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•
•
•
Practical testing
Trends
Beta trends
Real data for numerical work
• Weibull examples
Failure rate
Early-life failure
Wear out
Mid-life failure
Time in service
Failure rate
Falling values suggesting initial defects x Rising values suggesting wearing out o x
o x x
Time in service
o o o
Failure rate
β>1
Β<1 β=1 Time in service
Failure modes and effects analysis
System/equipment:
Analyst:
Dwg no,:
Date:
Issue:
Ref: Example
Sheet 1 of 1
Item/Component
Failure mode
Local failure effects
System failure effects
Symptoms
Rectification
Corrective action
Seal
Scored or damaged
Relief valve leaks
Hydrocarbon gas leaks from system and pressure falls
Noise of leaking gas.
Pressure reduction
Replace valve
Piston seal
Leaking or damaged (e.g. chemical reaction)
Pressure above piston drops and relief valve opens spuriously Hydrocarbon gas spuriously vented from system Spurious opening of relief valve
Replace valve
Choose materials resistive to chemical attacks, etc.
Piston liner
Scored or damaged
As above
As above
As above
As above
Abrasion resistive materials for piston lining Shipping spring
Weakened, worn or fatigued
Reduction in downwards force on piston may cause spurious, intermittent opening of relief valve As above
As above
As above
Choose material with suitable fatigue characteristics Supply tube
Leakage at connections
Reduction in supply pressure to pilot valve will cause increase in pressure required to activate relief valve
Hydrocarbon gas allowed to rise to a higher pressure than specified. May be critical Gauges indicate unrelieved pressures
Replace valve
Ensure connections are clean and adequately sealed Pilot valve
(i) Leakage
(ii) Valve seized shut
Greater pressure required to activate relief valve
Pilot valve unable to activate opening of relief valve
As above
As above
Gauges indicate dangerously high pressures As above
•
•
•
•
Practical testing
Trends
Beta trends
Real data for numerical work
• Weibull examples
Failure rate
Early-life failure
Wear out
Mid-life failure
Time in service
Failure rate
Falling values suggesting initial defects x Rising values suggesting wearing out o x
o x x
Time in service
o o o
Failure rate
β>1
Β<1 β=1 Time in service
Failure modes and effects analysis
System/equipment:
Analyst:
Dwg no,:
Date:
Issue:
Ref: Example
Sheet 1 of 1
Item/Component
Failure mode
Local failure effects
System failure effects
Symptoms
Rectification
Corrective action
Seal
Scored or damaged
Relief valve leaks
Hydrocarbon gas leaks from system and pressure falls
Noise of leaking gas.
Pressure reduction
Replace valve
Piston seal
Leaking or damaged (e.g. chemical reaction)
Pressure above piston drops and relief valve opens spuriously Hydrocarbon gas spuriously vented from system Spurious opening of relief valve
Replace valve
Choose materials resistive to chemical attacks, etc.
Piston liner
Scored or damaged
As above
As above
As above
As above
Abrasion resistive materials for piston lining Shipping spring
Weakened, worn or fatigued
Reduction in downwards force on piston may cause spurious, intermittent opening of relief valve As above
As above
As above
Choose material with suitable fatigue characteristics Supply tube
Leakage at connections
Reduction in supply pressure to pilot valve will cause increase in pressure required to activate relief valve
Hydrocarbon gas allowed to rise to a higher pressure than specified. May be critical Gauges indicate unrelieved pressures
Replace valve
Ensure connections are clean and adequately sealed Pilot valve
(i) Leakage
(ii) Valve seized shut
Greater pressure required to activate relief valve
Pilot valve unable to activate opening of relief valve
As above
As above
Gauges indicate dangerously high pressures As above