Reliability engineering glossary
Comprehensive terminology reference for asset integrity, risk-based inspection, reliability engineering, and governance. 149 terms defined with industry context and cross-references.
Showing 149 of 149 terms
A
Action Lifecycle
The progression of an action item through defined stages from creation to closure: Open (created, assigned), In Progress (work started), Completed (work finished, pending verificat...
ALARP(ALARP)
As Low As Reasonably Practicable — a principle requiring that residual risk be reduced to the lowest level that is reasonably achievable, balancing the cost and effort of further r...
API 510
Pressure Vessel Inspection Code — covers in-service inspection, repair, alteration, and rerating of pressure vessels.
API 570
Piping Inspection Code — provides requirements for the inspection, repair, alteration, and rerating of in-service metallic and fiberglass-reinforced plastic piping systems.
API 571
Damage Mechanisms Affecting Fixed Equipment in the Refining Industry — a comprehensive catalogue of over 60 damage mechanisms that can affect refinery and petrochemical equipment.
API 579-1/ASME FFS-1(API 579)
Fitness-For-Service standard — provides quantitative engineering assessment procedures for evaluating flaws, damage, and degradation found in pressurized equipment.
API 580
Risk-Based Inspection standard — provides guidance on developing and implementing a risk-based inspection program for fixed equipment in the hydrocarbon and chemical process indust...
API 581
Risk-Based Inspection Technology — provides the quantitative methodology for calculating probability of failure (PoF) and consequence of failure (CoF) for pressurized equipment.
API 653
Tank Inspection, Repair, Alteration, and Reconstruction standard — covers the inspection, repair, alteration, and reconstruction of steel aboveground storage tanks built to API 650...
Approval Gate
A checkpoint in a governed workflow where an authorized person must review and explicitly approve before the process can proceed to the next stage.
ASME B31.3
Process Piping Code — prescribes requirements for materials, design, fabrication, assembly, erection, examination, inspection, and testing of piping systems for process plants, inc...
Asset
A physical item of plant, equipment, or infrastructure that has value to an organization and is subject to management decisions regarding its acquisition, operation, maintenance, m...
Asset Condition
The current state of an asset's physical integrity and functional capability, as determined by inspection, monitoring, and operational data.
Asset Hierarchy
A structured, multi-level organization of assets that reflects the functional and physical relationships between equipment items, from the site level down to maintainable component...
Asset Lifecycle
The complete span of an asset's existence from initial conception through design, procurement, construction, commissioning, operation, maintenance, modification, and eventual decom...
Asset Register
A comprehensive, structured inventory of all physical assets within an organization's scope of responsibility, containing essential information for each asset including unique iden...
Asset Tag
A unique identifier assigned to each physical asset within a facility, typically following a structured naming convention that encodes the equipment type, process area, and sequent...
Audit Trail
A chronological record of system activities, decisions, and data changes that provides documentary evidence of the sequence of events that have affected a specific operation, proce...
Availability
The proportion of time that an item is in a state to perform its required function under given conditions, assuming that the required external resources are provided.
B
B-Life
The time by which a specified percentage of a population is expected to have failed, derived from the Weibull distribution parameters.
Bathtub Curve
A graph of the hazard rate versus time that describes the typical life cycle of a population of items, characterized by three distinct phases: (1) Infant Mortality — a decreasing f...
C
Change Request
A formal document initiating the Management of Change process, describing the proposed change, its justification, the affected equipment and systems, the assessment of potential ha...
Compliance Evidence
Documentary proof that an organization's practices conform to applicable regulatory requirements, industry standards, or internal procedures.
Condition Indicator
A measurable parameter that provides information about the current health or degradation state of an equipment item.
Condition Monitoring
The process of monitoring a parameter of condition in equipment (vibration, temperature, pressure, flow, oil quality, acoustic emission, electrical properties) to identify signific...
Condition Monitoring Location(CML)
A designated, permanently marked point on equipment where thickness measurements or other condition assessments are taken at regular intervals.
Consequence of Failure(CoF)
A measure of the impact resulting from an equipment failure, encompassing safety (personnel injury/fatality), environmental (release to atmosphere/ground/water), production (lost t...
Corrective Action
An action taken to eliminate the root cause of a detected nonconformity, failure, or undesirable situation to prevent its recurrence.
Corrosion Allowance(CA)
Additional wall thickness added to the minimum required thickness during the design phase to compensate for expected material loss due to corrosion, erosion, and other degradation...
Corrosion Circuit
A group of equipment items and piping segments that are exposed to the same process environment and are therefore expected to experience the same corrosion or degradation mechanism...
Corrosion Rate
The rate of material loss due to corrosion or erosion, typically expressed in millimeters per year (mm/yr) or mils per year (mpy).
Corrosion Under Insulation(CUI)
External corrosion of piping and equipment that occurs beneath thermal insulation, fireproofing, or other external coatings where moisture becomes trapped against the metal surface...
Critical Item
An equipment item, component, or system whose failure would result in unacceptable safety, environmental, or operational consequences.
Criticality Analysis
A structured evaluation to determine the relative importance (criticality) of equipment items based on the consequences of their failure.
Criticality Classification
The assignment of a criticality ranking (typically A, B, or C) to each equipment item based on the consequences of its failure across safety, environmental, production, and mainten...
Criticality Matrix
A structured evaluation framework used to determine the criticality classification of equipment by scoring its failure consequences across multiple dimensions (typically safety, en...
D
Damage Factor
A numerical modifier in the API 581 RBI methodology that quantifies the increased probability of failure due to specific active damage mechanisms.
Damage Mechanism
A specific process or phenomenon that causes degradation of material properties, leading to eventual failure of equipment.
Decision Journal
A structured log of significant engineering and management decisions made during the lifecycle of asset integrity programs.
Deferral
The postponement of a planned inspection, maintenance activity, or corrective action beyond its originally scheduled date.
Deferral Register
A centralized log of all deferred inspections, maintenance activities, and corrective actions, tracking the original schedule, the deferral justification, the approval chain, compe...
Degradation Mode
The specific pattern or form of material deterioration resulting from active damage mechanisms.
Design Conditions
The maximum temperature, pressure, and other parameters for which equipment is designed and rated.
Detection
A rating of the ability of current controls to detect the failure mode or its cause before the failure reaches the end user or causes harm, scored on a scale of 1 (almost certain d...
E
End of Life(EOL)
The point at which an asset can no longer perform its intended function safely, economically, or in compliance with applicable standards, and must be decommissioned, replaced, or s...
Engineering Decision Record(EDR)
A formal document that captures the technical basis for a significant engineering decision, including the problem statement, the options evaluated, the analysis performed, the sele...
Equipment Class
A categorization of equipment items by their generic type, construction, and function.
Equipment Type
A more specific classification within an equipment class that distinguishes items by their design configuration, operating principle, or application.
Erosion
The removal of material from a surface by the mechanical action of impinging particles, liquid droplets, cavitation, or high-velocity fluid.
Escalation Chain
A predefined hierarchy of responsibility that determines who is notified and in what order when an issue exceeds the authority or capability of the current handler.
Evidence Pack
A curated collection of compliance evidence, documentation, and records assembled to demonstrate conformance to a specific requirement, support a specific decision, or respond to a...
External Corrosion
Corrosion that attacks the outer surface of equipment and piping, caused by exposure to atmospheric moisture, chemicals, soil (for buried piping), or water trapped under insulation...
F
Failure Cause
The underlying reason or mechanism that initiates the process leading to a failure mode.
Failure Effect
The consequence of a failure mode on the operation, function, or status of the item and the system.
Failure Mode
The specific manner in which a component, subsystem, or system fails to perform its intended function or performs it in an unintended way.
Failure Mode and Effects Analysis(FMEA)
A systematic, proactive methodology for evaluating a process, product, or design to identify all possible failure modes, determine their effects on system performance, rank them by...
Failure Mode, Effects, and Criticality Analysis(FMECA)
An extension of FMEA that adds a criticality analysis step to quantify the combined frequency and severity of each failure mode's consequences.
Failure Rate(Lambda)
The average number of failures per unit of time for a population of items, typically expressed as failures per hour, per year, or per million hours.
Failure Reporting, Analysis, and Corrective Action System(FRACAS)
A closed-loop process for systematically reporting failures, analyzing their root causes, implementing corrective actions, and verifying that those actions effectively prevent recu...
Fault Tree Analysis(FTA)
A top-down, deductive analysis technique that uses Boolean logic (AND/OR gates) to model the combinations of events that can lead to an undesired top event (typically a system fail...
Fishbone Diagram
A cause-and-effect analysis tool (also called Ishikawa diagram or cause-and-effect diagram) that visually organizes potential causes of a problem into major categories branching fr...
Fitness-for-Service(FFS)
An engineering assessment methodology used to determine whether equipment with identified flaws, damage, or degradation can continue to operate safely and reliably for a defined fu...
Functional Location
A position in the asset hierarchy that describes a function or location within a technical system, independent of the specific physical equipment installed at that position.
G
Governance Event
A discrete, auditable event in the lifecycle of a governed artifact (asset, risk, MOC, inspection) that records a decision, approval, status change, or significant action.
Governed Artifact
Any entity within the asset integrity management system that is subject to governance controls — formal creation, modification, approval, and audit trail requirements.
H
I
IEC 60812(IEC 60812)
International standard for Failure Mode and Effects Analysis (FMEA) — provides procedures for performing FMEA and FMECA across hardware, software, processes, and services.
Immutable Record
A data record that cannot be altered, deleted, or overwritten after creation.
Infant Mortality
The early-life period of a component or system characterized by a higher-than-normal failure rate that decreases over time (Weibull beta < 1).
Inspection Confidence
The degree of certainty that the inspection data accurately represents the current condition of the equipment.
Inspection Effectiveness
A qualitative rating of the probability that an inspection activity will correctly identify and characterize the damage present in the inspected equipment.
Inspection Interval
The time period between successive inspections of an equipment item, determined by the RBI risk ranking, the remaining life, and applicable code requirements.
Inspection Strategy
The comprehensive plan that defines what to inspect, how to inspect, when to inspect, and what to look for on each equipment item.
Integrity Circuit
A broader grouping than a corrosion circuit that encompasses all equipment sharing common integrity management requirements, not limited to corrosion.
Integrity Operating Window(IOW)
Defined limits for process variables (temperature, pressure, flow, composition, pH, chloride content, etc.
Internal Corrosion
Corrosion that attacks the internal surface of equipment and piping, caused by the process fluid and operating conditions.
ISO 14224
Petroleum, petrochemical and natural gas industries — collection and exchange of reliability and maintenance data for equipment.
ISO 31000
Risk Management standard — provides principles, a framework, and a process for managing risk.
ISO 55000
Asset Management standard — provides an overview, principles, and terminology for the management of physical assets.
L
Lessons Learned
Knowledge gained from experience — both positive (what worked) and negative (what went wrong) — that is documented, disseminated, and applied to improve future performance.
Lessons Library
A searchable repository of lessons learned from across an organization, indexed by equipment type, damage mechanism, failure mode, process area, and other relevant categories.
Life Cycle Cost(LCC)
The total cost of acquiring, owning, operating, maintaining, and disposing of an asset over its entire lifecycle, expressed in present-value terms.
M
Magnetic Particle Inspection(MPI/MT)
An NDE method for detecting surface and near-surface discontinuities in ferromagnetic materials.
Maintainability
The probability that a failed item can be restored to operational condition within a specified period of time when maintenance is performed under stated conditions using prescribed...
Management of Change(MOC)
A systematic process for evaluating, approving, implementing, and documenting changes to process equipment, technology, procedures, or organizational structure that could affect sa...
Material Specification
The formal designation of the material of construction for an equipment item, specifying the alloy composition, mechanical properties, heat treatment, and applicable material stand...
Mean Distance Between Failures(MDBF)
The average distance traveled or cycles completed between consecutive failures, used for equipment where usage is measured in distance or cycles rather than operating hours.
Mean Time Between Failures(MTBF)
The average time between consecutive failures of a repairable system or component, calculated as the total operating time divided by the number of failures during that period.
Mean Time To Failure(MTTF)
The average time from the start of operation until the first failure of a non-repairable item, or the average time between replacement and next failure for items that are replaced...
Mean Time To Repair(MTTR)
The average time required to repair a failed item and restore it to operational status, measured from the point of failure detection to the point of verified restoration.
Minimum Required Thickness(t_min)
The minimum wall thickness required by the applicable design code to safely contain the operating pressure at the design temperature, considering the allowable stress of the materi...
Mitigation Action
An action specifically designed to reduce the probability or consequence of an identified risk.
Monte Carlo Simulation
A computational technique that uses random sampling from probability distributions to model the behavior of complex systems and estimate outcomes.
N
Nameplate Data
The technical information physically stamped or attached to equipment by the manufacturer, typically including: manufacturer name, model number, serial number, year of manufacture,...
Nominal Thickness
The wall thickness specified at the time of design and fabrication, before any in-service degradation.
Non-Destructive Examination(NDE/NDT)
A group of analysis techniques used to evaluate the condition of materials, components, and assemblies without causing damage or altering their serviceability.
NORSOK Z-008
Risk-Based Maintenance and Consequence Classification standard — establishes a systematic approach to maintenance optimization based on criticality and consequence classification o...
O
P
P-F Curve
A graphical representation of the degradation trajectory of an item from the point of initial potential failure (P) to functional failure (F).
P-F Interval
The time between the point at which a potential failure is first detectable (P — the onset of detectable degradation) and the point of functional failure (F — the point at which th...
Predictive Maintenance(PdM)
A maintenance strategy that uses condition monitoring data, analytics, and failure prediction models to determine the optimal timing for maintenance intervention.
Pressure Systems Safety Regulations(PSSR)
UK regulations (SI 2000 No.
Preventive Action
An action taken to eliminate the potential cause of a nonconformity or failure that has not yet occurred but is anticipated based on risk assessment, trend analysis, or lessons lea...
Preventive Maintenance(PM)
Maintenance performed at predetermined intervals or according to prescribed criteria to reduce the probability of failure or functional degradation.
Probability of Failure(PoF)
A quantitative or semi-quantitative measure of the likelihood that an equipment item will fail within a specified time period.
Process Hazard Analysis(PHA)
A thorough, organized, systematic approach for identifying, evaluating, and controlling hazards of processes involving highly hazardous chemicals.
R
Radiographic Testing(RT)
An NDE method that uses penetrating radiation (X-rays or gamma rays) to produce an image of the internal structure of a component.
Random Failure
A failure that occurs with approximately constant probability per unit time, independent of the item's age or accumulated operating time (Weibull beta approximately 1).
Redundancy
The provision of additional components, systems, or means beyond the minimum required for functional capability, intended to maintain system function when one or more components fa...
Reliability
The probability that an item will perform its required function under stated conditions for a specified period of time.
Reliability Block Diagram(RBD)
A graphical method for modeling system reliability by representing components as blocks connected in series, parallel, or complex configurations that reflect the functional relatio...
Reliability Event
A documented occurrence of equipment failure, degradation, or near-miss that is recorded in a reliability database for analysis.
Reliability Growth
The improvement in reliability achieved through systematic identification and elimination of failure causes over time.
Reliability-Centered Maintenance(RCM)
A systematic process for determining the maintenance requirements of a physical asset in its operating context.
Remaining Life
The calculated time until the wall thickness at a CML or the minimum measured thickness on a component reaches the retirement thickness, based on the current measured thickness and...
Remaining Useful Life(RUL)
The estimated time from the present until an equipment item reaches a condition where it can no longer perform its intended function safely and must be repaired, replaced, or retir...
Retirement Thickness
The minimum acceptable wall thickness below which equipment must be retired from service, repaired, or re-rated.
Risk Acceptance
A formal, documented decision to accept a specific risk without further treatment, based on a determination that the risk level is within the organization's risk tolerance criteria...
Risk Appetite
The amount and type of risk that an organization is prepared to seek, accept, or tolerate in pursuit of its long-term objectives.
Risk Assessment
The overall process of risk identification, risk analysis, and risk evaluation.
Risk Matrix
A two-dimensional grid that combines Probability of Failure (PoF) on one axis and Consequence of Failure (CoF) on the other to produce a visual risk ranking.
Risk Priority Number(RPN)
A numerical value that ranks the risk associated with a failure mode by multiplying three independently scored factors: Severity (impact of the failure), Occurrence (likelihood of...
Risk Ranking
A categorical classification (typically A through E) derived from the risk matrix that represents the combined probability and consequence of failure for an equipment item.
Risk Register
A structured repository that records all identified risks, their assessments (probability, consequence, risk level), treatment plans, residual risk after treatment, risk owners, re...
Risk Score
A numerical value representing the level of risk for an equipment item, calculated as the product of Probability of Failure and Consequence of Failure scores.
Risk Tolerance
The degree of risk that an organization is willing to withstand in pursuit of its objectives, expressed as specific thresholds or boundaries for different risk categories.
Risk-Based Inspection(RBI)
A methodology that uses risk assessment to prioritize and plan inspection activities for pressurized and other equipment.
Root Cause Analysis(RCA)
A systematic investigation methodology used to identify the fundamental underlying cause(s) of a failure, incident, or undesired outcome.
Run-to-Failure(RTF)
A deliberate maintenance strategy where no preventive or predictive maintenance is performed, and the item is allowed to operate until it fails, at which point it is repaired or re...
S
Safety Integrity Level(SIL)
A discrete level (SIL 1 through SIL 4) for specifying the safety integrity requirements of safety instrumented functions (SIFs).
Scale Parameter (Eta)(Eta)
The Weibull scale parameter (eta, also called characteristic life) that represents the time by which 63.
Severity
A rating of the worst potential consequence of a failure mode, scored on a scale of 1 (negligible) to 10 (catastrophic/hazardous without warning).
Shape Parameter (Beta)(Beta)
The Weibull shape parameter (beta, also written as b or k) that determines the form of the failure distribution and the nature of the failure rate over time.
Shutdown Scope
The defined set of inspection, maintenance, repair, and capital modification work items planned for execution during a plant shutdown or turnaround.
Stress Corrosion Cracking(SCC)
A damage mechanism involving the initiation and propagation of cracks in a material under the combined action of tensile stress (applied or residual) and a specific corrosive envir...
SudoGate
A Reliatic-specific re-authentication mechanism that requires users to confirm their identity before performing critical, irreversible, or high-consequence actions.
Susceptibility
The degree to which an equipment item is vulnerable to a specific damage mechanism, based on material of construction, process conditions (temperature, pressure, chemistry), design...
System Reliability
The reliability of a system composed of multiple interconnected components, calculated from the individual component reliabilities and their functional configuration (series, paral...
T
Technical Object
A specific physical piece of equipment identified by its manufacturer, model, and serial number, as distinct from the functional location it occupies.
Thickness Reading
A measured wall thickness value obtained at a CML using non-destructive examination techniques, typically ultrasonic thickness gauging.
Turnaround Planning
The comprehensive planning process for a major planned shutdown of a process unit or facility for inspection, maintenance, repair, and capital modification activities.
W
Wear-Out
The late-life period of a component or system characterized by an increasing failure rate over time (Weibull beta > 1), caused by progressive degradation mechanisms such as fatigue...
Weibull Distribution
A continuous probability distribution widely used in reliability engineering to model the time-to-failure of components and systems.