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Glossary of Design FMECA Terms

 

Term	Definition
Action Plan	An action plan in a strategy development analysis identifies an asset’s failure mode and recommends an action to prevent the failure or mitigate its consequences. For example, MTA2 and SIF action types are condition-based maintenance, failure-finding maintenance, scheduled restoration or discard, modification or redesign, and no scheduled maintenance (run to failure). RBI analyses support actions such as inspections, strategy, and modification or redesign.
Condition-based Maintenance	A task that entails checking for potential failures so that action can be taken to prevent the functional failure or to avoid consequences of the functional failure.
Environmental Consequences	A failure mode or multiple failure has environmental consequences if it could breach any corporate, municipal, regional, national, or international environmental standard or regulation which applies to the physical asset or system under consideration.
Evident Failure	A failure mode whose effects become apparent to the operating crew under normal circumstances if the failure mode occurs on its own.
Failure Consequences	Failure consequences are the ways in which the effects of a failure mode or a multiple failure matter (evidence of failure, impact on safety, the environment, operational capability, direct and indirect repair costs).
Failure Effect	What happens when a failure mode occurs.
Failure-finding Interval	A failure-finding interval is the length of time that it is considered safe to wait before performing failure-finding maintenance. The interval is calculated or estimated based on the desired availability and the frequency of failure of the protective device or system.
Failure-finding Task	A scheduled task used to determine whether a specific hidden failure has occurred.
Failure Mode	A failure mode is a single event that causes a functional failure. For example, if a pump’s impeller becomes worn, the pump cannot convey liquid at the required rate. Failure modes are analyzed in maintenance task analysis (MTA2), reliability-centered maintenance (RCM2), and failure modes, effects, and criticality (FMECA) analysis along with the action plans that prevent or mitigate failures. Safety instrumented function (SIF) analyses examine the risk of failure in safety devices, the effects and consequences of failure, and ways to reduce risk by putting safety provisions in place. For risk-based inspection (RBI) analyses, the failure of concern is loss of containment of pressurized equipment items. Examples of failure modes are small hole, crack, and rupture.
Failure Mode Consequence Priority	A failure’s or failure mode’s consequence priority provides an indication of the relative importance of the asset failure. The larger the number, the greater the severity of the failure. The priority can be used to recommend root cause analysis for a failure or to determine the order of action plan implementations. Consequence priorities are assigned to failure modes during risk assessment. In failure evaluation, the consequence priority is used in the calculation that determines whether the failure is suitable for root cause analysis. APM assigns the consequence priority by comparing the information to a set of customer-defined rules. The consequence priority rules can be based on the failure severity, relative risk (risk analysis only), failure costs, downtime costs, downtime, or a combination. For example, the Extreme consequence priority could be assigned to failures or failure modes whose total severity is greater than 25 or failure costs are more than $25,000.
FMECA	A failure modes and effects analysis (FMEA) “is a method in which an item or a process is broken down into elements and, for each element in turn, failure modes and effects are identified and analysed. This is to identify any required improvements by eliminating adverse effects or reducing their likelihood or severity. The purpose of adding a criticality analysis [FMECA] is to enable prioritization of the failure modes for potential treatment.” (BS EN IEC 60812:2018, Failure modes and effects analysis, p. 14).
Function	What the owner or user of a physical asset or system wants it to do. See also Primary Function(s) and Secondary Functions.
Function Group	A function group is a way of identifying assets that are responsible for performing a particular function. For example, the “Pump Assembly” function group could be used to indicate the relationship between a centrifugal pump, 20 HP motor, and valves.
Functional Failure	A state in which a physical asset or system is unable to perform a specific function to a desired level of performance.
Hidden Failure	A failure mode whose effects do not become apparent to the operating crew under normal circumstances if the failure mode occurs on its own.
Hidden Function	A function whose failure on its own does not become apparent to the operating crew under normal circumstances.
Multiple Failure	An event that occurs if a protected function fails while its protective device or protective system is in a failed state.
No Scheduled Maintenance	A failure management policy that permits a specific failure mode to occur without any attempt to anticipate or prevent it. Also referred to as “Run-to-Failure”.
Non-Operational Consequences	A category of failure consequences that do not adversely affect safety, the environment, or operations, but only require repair or replacement of any item(s) that may be affected by the failure.
On-Condition Task	A task that entails checking for potential failures so that action can be taken to prevent the functional failure or to avoid consequences of the functional failure.
One-Time Change	Any action taken to change the physical configuration of an asset or system (redesign or modification), to change the method used by an operator or maintainer to perform a specific task, to change the operating context of the system, or to change the capability of an operator or maintainer (training).
Operating Context	The operating context is the circumstances in which a physical asset or system is expected to operate.
Operational Consequences	A category of failure consequences that adversely affect the operational capability of a physical asset or system (output, product quality, customer service, military capability, or operating costs in addition to the cost of repair).
P-F Interval	The PF interval is the time between the point at which a potential failure becomes detectable and the point at which it degrades into a functional failure.
Potential Failure	A potential failure is an identifiable condition indicating that a functional failure is either about to occur or is in the process of occurring.
Primary Function(s)	The function(s) which constitute the main reason(s) why a physical asset or system is acquired by its owner or user.
Protective Device or Protective System	A device or system which is intended to avoid, eliminate, or minimize the consequences of failure on some other system.
RCM2	RCM2 is the reliability-centered maintenance process practiced by Bentley APM consultants. One of the features of RCM2 that distinguishes it from other interpretations of the RCM philosophy is that cross-functional groups of users and maintainers perform the analyses. After training, these analysis teams apply the process to their assets to produce robust and cost-effective asset reliability programs.
Reliability Strategy Selection	Reliability strategy selection (RSS) analysis applies a set of criteria to an asset to determine the most appropriate plan for improving its reliability. The analysis team uses the Reliability Strategy Selection questionnaire to perform, document, and review analyses of system-level assets. Possible strategies are to implement (or continue) basic care, perform maintenance task analysis, perform RCM2 analysis, or escalate the asset risk to stakeholders for further consideration and action.
Run-To-Failure	A failure management policy that permits a specific failure mode to occur without any attempt to anticipate or prevent it. Referred to in APM as “No Scheduled Maintenance”.
Safety Consequences	A failure mode or multiple failure has safety consequences if it could injure or kill a human being.
Scheduled Discard	A scheduled task that entails discarding an item at or before a specified age limit, regardless of its condition at the time.
Scheduled Restoration	A scheduled task that restores the capability of an item at or before a specified interval (age limit), regardless of its condition at the time, to a level that provides a tolerable probability of survival to the end of another specified interval.
Secondary Functions	Functions which a physical asset or system has to fulfill apart from its primary function(s), such as those needed to fulfill regulatory requirements and those which concern issues such as protection, control, containment, comfort, appearance, energy efficiency and structural integrity.
Strategy Development Analysis	Strategy development analyses are methodologies for evaluating asset priority, defining asset functions, determining how failures occur (failure modes), evaluating the risk of asset failure, and preventing or mitigating the effect of failures. The varieties of strategy development analysis include: • Asset Prioritization Analysis • Current Practice Review (CPR) • Design FMECA • Reliability Strategy Selection (RSS) • Maintenance Task Analysis (MTA2) • Reliability Centered Maintenance (RCM2) • Risk-based Inspection (RBI) • Safety Instrumented Function (SIF) Analysis • Hazard and Operability (HAZOP) Analysis
Susceptibility to Failure Evaluations	Susceptibility to failure evaluation examines the asset’s non-age related degradation patterns. It can provide an alternative to probability of failure analysis for these failure modes. For example, susceptibility evaluation can be used to determine the vulnerability of atmospheric storage tanks to corrosion under insulation or stress cracking. The evaluation can result in recommended actions, susceptibility ratings, or both. Note: Susceptibility to failure evaluations are not supported in design FMECAs.
Time Between Failure	The length of time between failures (TBF) is used in three ways in APM strategy development analyses: • The time between occurrences of the failure (TBF) when inspections and/or preventative maintenance are performed. This value is recorded in failure statistics. • The estimated length of time between failures (ETBF) when no preventive maintenance is performed on the asset. This value is sometimes used to determine probability of failure in risk analysis. • Estimated time between consequences (ETBC) – The time between unexpected consequences or failures when inspections and preventive maintenance are performed on the asset. APM calculates the mitigated (or residual) risk using this value when maintenance feasibility is evaluated.