Ability of an item to be in a state to perform a required function under given conditions at a given instant or over a given time interval, assuming that the required external resources are provided.
Source: DNVGL-RP-G108, Cyber security in the oil and gas industry based on IEC 62443, DNV GL, September 2017. Global Standards
Extent to which the system/structure/equipment is capable of retaining its functional integrity.
Source: ISO 16530-1:2017, Petroleum and natural gas industries – Well integrity – Part 1: Life cycle governance, First Edition, March 2017. Global Standards
The property of being accessible and usable upon demand.
Extended Definition: In cybersecurity, applies to assets such as information or information systems.
Adapted from: CNSSI 4009, NIST SP 800-53 Rev 4, 44 U.S.C., Sec 3542
Source: NICCS™ Portal Cybersecurity Lexicon, National Initiative for Cybersecurity Careers and Studies (https://niccs.us-cert.gov/glossary) as of 11 November 2015, Global Standards
Fraction of time that a system (e.g. safety instrumented system, atmospheric-relief system, or flare-relief system) is able to perform the designated function if required for use.
Source:API STD 521, Pressure-relieving and Depressuring Systems, Sixth Edition, January 2014. Global Standards
Property of being accessible and usable upon demand by an authorized entity.
Source: ISO/IEC 27000:2014, Information technology — Security techniques — Information security management systems — Overview and vocabulary, Third Edition, January 2014. Global Standards
Probability that a system will operate on demand.
Source: International Association of Drilling Contractors, Appendix 2 to Health, Safety and Environment Case Guidelines for Offshore Drilling Contractors, Issue 3.3.2, February 2010. IADC Guidelines
Ability of an item to be in a state to perform a required function under given conditions at a given instant of time or over a given time interval, assuming that the required external resources are provided.
NOTE: For a more detailed description and interpretation of availability, see Annex C.
Source: API STD 2000, Venting Atmospheric and Low-pressure Storage Tanks, Sixth Edition, November 2009. Global Standards
The ability, measured in terms of uptime percentage, of a system to perform its required function.
Source: OGP Report No. 415, Asset integrity – the key to managing major incident risks, International Association of Oil & Gas Producers, December 2008. Global Standards
Ability of an item to be in a state to perform a required function under given conditions at a given instant of time, or in average over a given time interval, assuming that the required external resources are provided.
Source: ISO 20815:2008, Petroleum, petrochemical and natural gas industries – Production assurance and reliability management. Global Standards
Probability that an asset, under the combined influence of its reliability, maintainability, and security, will be able to fulfill its required function over a stated period of time, or at a given point in time.
Source: ANSI/ISA–99.00.01–2007, Security for Industrial Automation and Control Systems, Part 1: Terminology, Concepts, and Models, 29 October 2007. National Standard
Note that the definition of availability given in IEC 60050-191:1990, 3.1.1, can be misleading because it can lead one to think that “availability” and “reliability” are the same concepts. This is not true because the meaning of “over a given time interval” is not at all the same for the concepts of “availability” and “reliability”. Even if the definitions of “availability” and “reliability” seem very close, these concepts are completely different, specifically: availability: item working at a given instant (no matter what has happened before); reliability: item working continuously over a whole period of time. “Availability” characterizes a function that can be interrupted without any problem and “reliability,” a function that cannot be interrupted over a whole period of time.
Source: API STD 689, Collection and Exchange of Reliability and Maintenance Data for Equipment, First Edition, July 2007. Global Standards