CMRP Exam Tutorial
3D-MDS Academy [www.3d-mds-academy.com]
This document is supplementary to CMRP Exam tutorial
series. It is intended to provide additional calculation
examples for maintenance and reliability key performance
indicators (KPI).
Daniel Amevor, P. Eng., CMRP.
8/11/2018
EXAMPLE: A piece of equipment (centrifugal pump) was installed to transfer fluid from a lower tank to
an upper tank at plant site. The pump ran continuously for 2000 hours and failed the impeller. The
maintenance crew took 20 hours to fix it and return it to service. It ran for 100 hours and failed again
due to seal leakage. The seal kit repair work took 10 hours and put back to service. The pump has run for
additional 3000 hours without failure. Calculate the pump availability, MTTR, MTBF and failure rate?
This narration is illustrated in the diagram below.
down
uptime
2000hrs
down
100hr
s
20hrs
uptime
3000hrs
10hrs
Pump Failure Data:
Total uptime = 2000+100+3000= 5100Hrs
Total Downtime = 20 + 10 = 30Hrs
Total number of down events = 2
Total available time = 5130Hrs
I.e. 2000+20+100+10+3000=5130Hrs
a) Pump availability =
Total Uptime
Total Available Time
=
Uptime
=
Uptime + Downtime
Availability = 99.4%
b) MTTR =
Total Repair Time
=
Total number of repairs
Total Downtime
Total number of repairs
=
30
2
MTTR = 15Hrs
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= 15
5100
5100 + 30
= 0.994
c) MTBF =
Total Uptime
=
5100
= 2550
2
Total number of repairs
MTBF = 2550Hrs
d) Failure rate ( λ) =
1
MTBF
=
1
=
0.000392
2550
Failure rate (λ) = 0.000392 failures per hour
Availability:
Availability by definition is a measure of the likelihood that a system will be ready to operate (system is
up) when it is called on to operate. Reasons the system would not be ready to operate (system is down)
include the possibility that a failure has occurred and the corrective action has not been completed and
the possibility that the system is not operable because preventive maintenance actions are necessary.
What is MTBF and MTTR?
MTBF, or Mean Time Between Failures, is a metric that concerns the average time elapsed between a
failure and the next time it occurs. Whereas the MTTR, or Mean Time To Repair, is the average time it
takes to carry out a repair after the occurrence of the failure.
Check the ways to calculate MTBF and MTTR:
MTBF - total time of correct operation in a period divided by number of failures
For example: MTBF = 2550Hrs
This index reveals that a failure in the system occurs every 2550 hours, leaving it unavailable and
generating losses to the company. The opportunity to spot this index allows you to plan strategies to
increase this time.
MTTR - total hours of downtime divided by number of failures
For example: MTTR = 15Hr above, this is the average time of each downtime. Therefore, the company
knows that every 2550 hours, the pump will be unavailable for 15 hours. Being aware of our limitations
is the first step to eliminate them.
CMRP Exam Tutorial by 3D-MDS Academy [www.3d-mds-academy.com]