Mean Time to Repair

Expectation of the time to restoration.

Source: ISO 20815:2008, Petroleum, petrochemical and natural gas industries – Production assurance and reliability management. Global Standards

expected time to achieve the repair of a failed item

Note 1 to entry: This term MTTR is used in ISO 14224[15] and ISO 20815[16] where the fault detection time is not

really considered: ISO 14224[15] deals with detected faults (in fact, the actual time spent to detect the fault is never

known and cannot be collected); ISO 20815[16] deals mainly with immediately revealed failure where t he t ime

spent to detect the faults is close to 0 (i.e. negligible). As the fault detection time is very important for the purpose

of this Technical Report there is a need to clearly distinguish between the two following times (cf. Figure 5):

1) the time elapsing from the actual occurrence of the failure of an item to its detection (cf. 3.1.35, MFDT);

2) the time elapsing from the detection of the failure of an item to the restoration of its function (cf. 3.1.33, MRT).

Note 2 to entry: The acronym MTTR is defined as the mean time to restore in the IEC 60500–191[14] or in the

IEC 61508[2]. This is not the same as in ISO 14224[15] or ISO 20815[16]. Therefore, in order to avoid any mixed-up,

the acronym MTTRes is used in this Technical Report instead of MTTR (cf. 3.1.32).

FIG.5

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

Glossary