Mean Time To Failure (MTTF)

แสดงความเห็นโดยpongsakorn monturatเขียนแล้วในSystem Reliability Analysis

MTTF or Mean Time To Failure is a reliability metric used to estimate the average time that a system, component, or device is expected to operate before experiencing a failure. MTTF is often expressed in terms of hours.

The benefits of studying MTTF in the field of reliability engineering are the following;

  • Reliability Assessment: MTTF can present how well a system or component performs over time before experiencing failure;
  • Maintenance Planning: MTTF helps in planning maintenance activities. It allows maintenance teams to schedule preventive maintenance and the inspection period.
  • System Design and Improvement: MTTF data is necessary data for analyzing the contribution factor to system failure. Understanding the MTTF can enhance the overall reliability of a system.

It’s important to note that MTTF applies to repairable systems, meaning they can be restored to operation after a failure.

There are other metrics of reliability engineering such as Mean Time To Restore (MTTR), and Mean Time Between Failure (MTBF).

  • MTTF focuses on the average time a system operates before failure in repairable systems, meaning they can be restored to operation after a failure.
  • MTTR measures the average time it takes to repair a system and bring it back into operation.
  • MTBF represents the average time between consecutive failures in non-repairable systems. MTBF is commonly used for non-repairable systems where failures result in permanent damage.

Calculation formula

Basic calculations of the MTTF and MTBF are similar. They are calculated as the total operating time divided by the number of failures.

Example-1

DCS system failure time as the following table.

Time to Fail (hours)Mode
Failure 12425Dangerous
Failure 23350Safe
Failure 34520Dangerous
Failure 41525Safe
Failure 53200Safe
Failure 64115Dangerous

A DCS system has measured dangerous failure data from the above table.

First dangerous failure = 2425 hours;

Second dangerous failure = 7870 hours (3350 + 4520);

Third dangerous failure = 8840 hours (1525 + 3200 + 4115)

The average of these three dangerous failure is (2425 + 7870 + 8840)/3 = 6,378 hours or it can be calculated by (2425 + 3350 + 4520 + 4525 + 1525 + 3200 + 4115)/3 = 6,378 hours.

MTTF of a system