Concepts Tasks Settings Glossary of RBI Terms The following terms are used throughout the RBI analysis topics. For a full glossary of APM terms, see Glossary. 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. Barrier A barrier is a means of slowing or mitigating asset degradation. For example, coating, lining, and chemical treatment are used to slow corrosion in metal piping. Confidence Factor The confidence factor represents the analysis team’s faith in current maintenance or inspection practices to contain the failure mode’s risk. The higher the value, the greater the confidence. The confidence factor can adjust the inspection factor or likelihood of failure up or down. Consequence The way in which the effects of a failure mode matter (impact on health and safety, environment, or economic costs). 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. Criticality See Relative Risk. Damage Mechanism A damage mechanism is a general cause of problems or failures within process equipment. Examples of damage mechanisms are corrosion under insulation, brittle fracture, thermal fatigue, and heat damage. The Damage Mechanisms Library provides generic failure modes that the analysis team can browse and add to analyses. Degradation The reduction in the ability of a component to provide its intended purpose of containment of fluids. This can be caused by various deterioration mechanisms (e.g., thinning, cracking, mechanical). Damage or degradation may be used in place of deterioration. Degradation Category Degradation categories are used to facilitate searching and filtering data in APM. Categories are usually general, such as interior, exterior, mechanical, electrical, and so on. Degradation Location An inspection location is the area of the asset to be inspected for deterioration, for example, a specific elbow or joint on a piping segment. A location can also refer to a general area, such a location exposed to excessive moisture. Degradation Mechanism A degradation mechanism is the type of deterioration that could lead to asset failure. Examples are corrosion, erosion, mechanical failure, and pitting. Degradation Pattern The degradation pattern is the form that the general damage mechanism takes, for example, cracking or external pitting. Degradation Scope Degradation scope indicates in general terms the extent of the degradation, for example, general or localized. Scopes are used for reference and for searching and filtering data. Degradation Type For RBI analysis, three types of degradation are usually identified: • Age-related • Non-age-related • Strategy-based Demand Scenario A demand scenario is a situation that requires that an asset, such as a safety device, be put into operation. Examples of demand scenarios are fire, power failure, and blocked outlet. Downtime Downtime is a period of time or a percentage of a timespan that an asset is not functioning, usually as the result of either a failure or routine maintenance. Evaluation Group An evaluation group is an identifier that restricts consequence evaluation categories to specific asset types or damage mechanisms library entries. For example, a pop-up questionnaire that analysts use to evaluate the Health and Safety effects of a failure mode in an RBI analysis can display one set of questions for a Tank Roof asset and another set for a Tank Floor asset, depending on the evaluation groups assigned to the asset types and evaluation categories. Failure A failure is an event or state in which an asset cannot perform one or more of its required functions within the specified limits under specified conditions. A failure often requires that equipment be shut down and repaired. Failure Effect What happens when a failure mode occurs. For example, when a pump’s impeller becomes worn (failure mode), the flow through the pump declines until it no longer delivers liquid at the required rate. 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 Mode A failure mode is a single event that causes a functional failure. For risk-based inspection, the failure of concern is loss of containment of pressurized equipment. Examples of failure modes are “Sudden rapid fracture after stress” and “Corrosion due to moisture associated with atmospheric conditions”. Flow Flow is an aspect of the operating environment in which the damage mechanism is prone to occur. Examples are motionless-static and hydrodynamic. Inspection In the context of RBI, “inspection” refers to examination and/or testing to determine the physical and metallurgical condition of equipment in terms of fitness-for-service. Inspection Factor An inspection factor is the portion of the asset’s remaining life calculated for the current degradation rate to be used when calculating indicator collection dates. For example, an inspection factor of “0.5” means that the indicator reading should be collected at half of remaining life. The greater the confidence factor, the higher the inspection factor, meaning that the interval between inspections is greater. The inspection factor is based on the confidence factor, degradation type, consequence priority (criticality), and (optionally) integrity group of the failure mode. Inspection Factor Matrix In APM, an inspection factor matrix is generated to create one entry for each combination of degradation type, criticality, confidence factor, and (optionally) integrity group defined for the site. Each generated entry, called an inspection factor, can be assigned an inspection factor value, inspection strategy, inspection interval, or a combination of these. Inspection Interval An inspection interval is the period of time (usually years) between regularly scheduled inspections. Intervals are typically used with failure modes for assets prone to non-age related degradation, where process monitoring is more effective in avoiding degradation. A failure mode’s inspection interval is determined by a matrix that takes into account criticality, degradation type, confidence factor, and (optionally) integrity group. Inspection Strategy An inspection strategy describes the action to be taken (for example, detailed analysis or redesign) in response to the failure mode’s risk assessment, degradation type, and confidence evaluation. Inspection strategy can be specific to the asset’s material classification or type. Typically, inspection strategies are used with demand scenario risk assessment or when criticality is severe and confidence low. Integrity Group Integrity group is identified on asset types, providing an easy mechanism to group similar assets. For example, integrity groups can be created for piping systems, vessels, and heat exchangers. In risk analyses, integrity groups are used in inspection factor matrices to help determine a failure mode’s Inspection Factor, Inspection Strategy, and Inspection Interval as a result of confidence evaluations. Life Adjustment Factor A life adjustment factor is a portion of an asset’s by-design life span, for example, one tenth of its original estimated life. Typically, a life adjustment factor is used to estimate asset lining’s remaining life based on its condition at the time of inspection. This information is used to track the asset’s degradation. Load Type Load type is an aspect of the operating environment in which the damage mechanism is prone to occur. Examples are static stress, cyclic stress, and impact. Mitigation Limitation of any negative consequence or reduction in probability of a particular event Operating Context The operating context is the circumstances in which a physical asset or system is expected to operate. Operating Parameter Detailed information about an asset’s designed and actual performance, including unit of measurement, maximum and minimum measurements, measurement frequency, and indicators used to track parameters. An asset’s operating parameters combine to establish its operating window. Probability Extent to which an event is likely to occur within the time frame under consideration. The mathematical definition of probability is “a real number in the scale 0 to 1 attached to a random event”. Probability can be related to a long-run relative frequency of occurrence or to a degree of belief that an event will occur. For a high degree of belief, the probability is near one. Frequency rather than probability may be used in describing risk. Degrees of belief about probability can be chosen as classes or ranks like “Rare/unlikely/moderate/likely/almost certain” or “incredible/improbable/remote/occasional/probable/frequent”. Process Process is an aspect of the operating environment in which the damage mechanism is prone to occur. Examples are hydrogen, phosphoric acid, and carbon. Relative Risk Relative risk is one of the outputs from an asset prioritization analysis. It is the product of the probability of failure of an asset and the consequences of failure. Relative Risk = (Probability of Failure) x Sum (Consequence of Failure Scores) Risk Analysis Systematic use of information to identify sources and to estimate the risk. Risk analysis provides a basis for risk evaluation, risk mitigation and risk acceptance. Information can include historical data, theoretical analysis, informed opinions and concerns of stakeholders. Risk-based Inspection A risk assessment and management process that is focused on loss of containment of pressurized equipment in processing facilities, due to material deterioration. These risks are managed primarily through equipment inspection. 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. Technology A technology is a method or tool, such as ultrasonic testing or infrared inspection, used to determine the condition of in-service equipment to measure degradation. Temperature range Temperature range is an aspect of the operating environment in which the damage mechanism is prone to occur. 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. Usage Group Usage groups control the damage mechanisms library entries that are available to add to an RBI analysis. For example, if a usage group is specified in the analysis’ Failure Mode options, only entries assigned the same usage group are available for selection in the Browse Damage Mechanisms Library dialog.
