Failure Mechanisms

A failure mechanism is the physical, chemical or other process that leads to a failure. It is a characteristic of the failure event that can be deduced technically, such as the visible, apparent or observed cause of the failure.

The failure mechanism should normally be related to a lower indenture level (subunit or maintainable-item level). In practical terms, the failure mechanism represents a failure mode at maintenance-significant item (MSI) level.

Due care is required so as not to confuse failure mechanism (describing the apparent, observed cause of failure) with failure cause (describing the underlying or “root” cause of a failure).

ISO 14224 prescribes the following best practice failure mechanisms:

Failure mechanism type	Failure mechanism	Description of the failure mechanism
Mechanical failure	Leakage	External or internal leakage, either liquids or gases: If the failure mode at equipment unit level is coded as “leakage”, a more causally oriented failure mechanism should be used wherever possible.
	Vibration	Abnormal vibration: If the failure mode at equipment level is vibration, which is a more causally oriented failure mechanism, the failure cause (root cause) should be recorded wherever possible.
	Clearance/ alignment failure	Failure caused by faulty clearance or alignment
	Deformation	Distortion, bending, buckling, denting, yielding, shrinking, blistering, creeping
	Looseness	Disconnection, loose items
	Sticking/seized/jammed	Sticking, seizure, jamming due to reasons other than deformation or clearance/alignment failures
	General mechanical failure	Failure related to a mechanical defect, but no further details known
Material failure	Cavitation	Relevant for equipment such as pumps and valves
	Corrosion	All types of corrosion, both wet (electrochemical) and dry (chemical)
	Erosion	Erosive wear
	Wear	Abrasive and adhesive wear, for example scoring, galling, scuffing, fretting
	Breakage	Broken, fractured, breached, cracked
	Fatigue	The cause of breakage can be traced to fatigue
	Overheating/burnt	Material damage due to overheating or burning
	Burst	Item burst, blown, exploded, imploded
	General material failure	Failure related to a material defect, but no further details known
Instrument failure	Control failure	Faulty or no regulation
	No signal/ indication/alarm	No signal, indication or alarm when expected
	Faulty signal/ indication/alarm	Signal, indication or alarm is wrong in relation to actual process; can be spurious, intermittent, oscillating, arbitrary
	Out of adjustment	Calibration error, parameter drift
	Software failure	Faulty or no control/monitoring/operation due to software failure
	Common cause/ mode failure	Several instrument items failed simultaneously, for example redundant fire and gas detectors; also failures related to a common cause
	General instrument failure	Failure related to instrumentation, but no further details known
Electrical failure	Short circuiting	Short circuit
	Open circuit	Disconnection, interruption, broken wire/cable
	No power/voltage	Missing or insufficient electrical power supply
	Faulty power/voltage	Faulty electrical power supply, for example overvoltage
	Earth/isolation fault	Earth fault, low electrical resistance
	General electrical failure	Failure related to the supply and transmission of electrical power, but no further details known
External influence	Blockage/plugged	Flow restricted or blocked due to fouling, contamination, icing, flow assurance (hydrates)
	Contamination	Contaminated fluid, gas or surface, for example lubrication oil contaminated, gas-detector head contaminated
	Miscellaneous external influences	Foreign objects, impacts, environmental influence from neighbouring systems
	General external influence	Failure caused by external events or substances outside the boundary, but no further details known

Also refer to Failure Mechanism Types.