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Mean Time To Repair(MTTR)

Reliability Engineering
mechanicalelectricalinstrumentation

Definition

The average time required to repair a failed item and restore it to operational status, measured from the point of failure detection to the point of verified restoration. MTTR includes fault diagnosis, logistics (obtaining parts and tools), physical repair, testing, and recommissioning. It does not include administrative delays or waiting time unless specifically defined as Mean Time To Restore.

Context

MTTR directly impacts availability and is a key input to spare parts strategy, maintenance planning, and turnaround scheduling. In Reliatic, MTTR is tracked per equipment type and per failure mode, enabling identification of maintainability problems. High MTTR items are candidates for design modifications, pre-staged spare parts, or maintenance procedure improvements.

Formula

MTTR = Total Repair Time / Number of Repairs

Examples

  1. A compressor valve replacement has an MTTR of 8 hours (2 hours diagnosis, 1 hour parts retrieval, 3 hours repair, 2 hours testing and restart).
  2. Analysis reveals that 60% of MTTR for instrument failures is spent on diagnosis, leading to investment in improved diagnostic tools and fault-finding procedures.

Applicable Standards

  • IEC 60300-3-1
  • EN 13306
  • ISO 14224:2016

Related Terms

Mean Time Between Failures(MTBF)

The average time between consecutive failures of a repairable system or component, calculated as the total operating time divided by the number of failures during that period. MTBF is the primary reliability metric for repairable systems and represents the expected time of continuous operation between failure events. Higher MTBF indicates better reliability.

Availability

The proportion of time that an item is in a state to perform its required function under given conditions, assuming that the required external resources are provided. Availability combines reliability (how often it fails) and maintainability (how quickly it can be restored). Inherent availability considers only corrective maintenance; operational availability includes all downtime including preventive maintenance and logistics.

Maintainability

The probability that a failed item can be restored to operational condition within a specified period of time when maintenance is performed under stated conditions using prescribed procedures and resources. Maintainability is a design characteristic that reflects how easy, fast, and cost-effective it is to diagnose, access, repair, and verify the restoration of a failed item.

Reliability

The probability that an item will perform its required function under stated conditions for a specified period of time. Reliability is a quantitative measure expressed as a probability (0 to 1) or percentage. It is a function of the failure rate and time: for constant failure rate systems, R(t) = e^(-lambda*t). Higher reliability means lower probability of failure over the same period.

Where this appears in Reliatic

This concept is used in the Reliability Analytics module.