API 580 Risk Based Inspection:

Terms and Definitions:


absolute risk
An ideal and accurate description and quantification of risk.
acceptable risk
A level of risk that is acceptable to the owner-user.
as low as reasonably practical
A concept of minimization that postulates that attributes (such as risk) can only be reduced to a certain minimum
under current technology and with reasonable cost.
Parts that make up a piece of equipment or equipment item. For example a pressure boundary may consist of
components (pipe, elbows, nipples, heads, shells, nozzles, stiffening rings, skirts, supports, etc.) that are bolted or
welded into assembles to make up equipment items.
An outcome from an event. There may be one or more consequences from an event. Consequences may range from
positive to negative. However, consequences are always negative for safety aspects. Consequences may be
expressed qualitatively or quantitatively.
corrosion specialist
A person who is knowledgeable and experienced in the specific process chemistries, corrosion degradation
mechanisms, materials selection, corrosion mitigation methods, corrosion monitoring techniques, and their impact on
pressure equipment
An activity that is both effective in resolving an issue (e.g. some form of mitigation) and is a financially sound use of
damage (or deterioration) mechanism
A process that induces micro and/or macro material changes over time that are harmful to the material condition or
mechanical properties. Damage mechanisms are usually incremental, cumulative, and, in some instances,
unrecoverable. Common damage mechanisms include corrosion, stress corrosion cracking, creep, erosion, fatigue,
fracture, and thermal aging.
damage (or deterioration) mode
The physical manifestation of damage (e.g. wall thinning, pitting, cracking, rupture).
damage tolerance
The amount of deterioration that a component can withstand without failing.
design premise
Assumptions made during the design (e.g. design life and corrosion allowance needed).
The reduction in the ability of a component to provide its intended purpose of containment of fluids. This can be
caused by various damage mechanisms (e.g. thinning, cracking, mechanical). Damage or degradation may be used
in place of deterioration.
An individual item that is part of a system. Examples include pressure vessels, relief devices, piping, boilers, and
Occurrence of a particular set of circumstances. The event may be certain or uncertain. The event can be singular or
multiple. The probability of an event occurring within a given period of time can be estimated.
event tree
An analytical tool that organizes and characterizes potential occurrences in a logical and graphical manner. The event
tree begins with the identification of potential initiating events. Subsequent possible events (including activation of
safety functions) resulting from the initiating events are then displayed as the second level of the event tree. This
process is continued to develop pathways or scenarios from the initiating events to potential outcomes.
external event
Events resulting from forces of nature, acts of God, sabotage, or events such as neighboring fires or explosions,
terrorism, neighboring hazardous material releases, electrical power failures, forces of nature, and intrusions of
external transportation vehicles, such as aircraft, ships, trains, trucks, or automobiles. External events are usually
beyond the direct or indirect control of persons employed at or by the facility.
Any location containing equipment and/or components to be addressed under this RP.
Termination of the ability of a system, structure, equipment or component to perform its required function of
containment of fluid (i.e. loss of containment). Failures may be unannounced and undetected at the instant of
occurrence (unannounced failure). For example, a slow leak under insulation may not be detected until a pool of fluid
forms on the ground or someone notices a drip or wisp of vapor. A small leak may not be noticed until the next
inspection (unannounced failure), e.g. slow leakage from buried piping or small leak in a heat exchanger tube; or they
may be announced and detected by any number of methods at the instance of occurrence (announced failure), e.g.
rupture of a pipe in a process plant or sudden decrease in pressure in the system.
failure mode
The manner of failure. For RBI, the failure of concern is loss of containment of pressurized equipment items.
Examples of failure modes are small hole, crack, and rupture.
Fitness-For-Fervice assessment
A methodology whereby damage or flaws/imperfections contained within a component or equipment item are
assessed in order to determine acceptability for continued service.
A physical condition or a release of a hazardous material that could result from component failure and result in human
injury or death, loss or damage, or environmental degradation. Hazard is the source of harm. Components that are
used to transport, store, or process a hazardous material can be a source of hazard. Human error and external
events may also create a hazard.
hazard and operability study
HAZOP study
A HAZOP study is a form of failure modes and effects analysis (FMEA). HAZOP studies, which were originally
developed for the process industry, use systematic techniques to identify hazards and operability issues throughout
an entire facility. It is particularly useful in identifying unforeseen hazards designed into facilities due to lack of
information, or introduced into existing facilities due to changes in process conditions or operating procedures.
— to systematically review every part of the facility or process to discover how deviations from the intention of the
design can occur;
— to decide whether these deviations can lead to hazards or operability issues;
— to assess effectiveness of safeguards.
Activities performed to verify that materials, fabrication, erection, examinations, testing, repairs, etc., conform to
applicable code, engineering, and/or owner’s written procedure requirements. It includes the planning,
implementation, and evaluation of the results of inspection activities. The external, internal, or on-stream assessment
(or any combination of the three) of the condition of pressure equipment.
integrity operating window
Established limits for process variables that can affect the integrity of the equipment if the process operation deviates
from the established limits for a predetermined amount of time.
management of change
A documented management system for review and approval of changes in process, equipment or piping systems
prior to implementation of the change.
Limitation of any negative consequence or reduction in probability of a particular event.
process unit
A group of systems arranged in a specific fashion to produce a product or service. Examples of processes include
power generation, acid production, fuel oil production, and ethylene production.

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