Reliability

Good Essays
Topics: Valve, Leak, Pressure
Reliability in the design context Weibull Analysis





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

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