Unavailability

Oil & Gas Drilling Glossary - IADCLexicon.org

Glossary

Browse the IADC Lexicon alphabetically or by category. Get comprehensive definitions of drilling industry terms.

Need help using the IADC Lexicon? The FAQ section will answer most of your questions, and you can also submit questions directly.

Become a Lexicon Contributor. Simply fill out the form, then submit new terms for approval and/or edit existing terms.

3.1.12

instantaneous unavailability

point unavailability

U(t)

〈measure〉 probability for an item not to be in a state to perform as required at a given instant

Note 1 to entry: The unavailability is the complementary of the availability: U(t)=1− A(t )

Note 2 to entry: The unavailability is called “Probability of Failure on Demand” (PFD) by the standards related to

the functional safety of safety related/instrumented systems (e.g. IEC 61508[2]).

Note 3 to entry: Note 3 to entry: When dealing with safety U(t) is generally small compared to 1 and this property

is used to develop approximated formulae (see Clause 7).

Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards

Comments are closed.