Equipment Availability – Concept & Issues
Author: Jogeswara Rao Kavala
In many industrial situations, performance analyses often lead to queries about the Equipment Availability.
This document mainly gives the concepts of the same and discusses about the calculations and issues in calculations.
The Availability & MTTR, MTBR
The Availability of an Equipment is known by different names such as
– Equipment Availability
– Operational Availability etc.
Common formula used for the Equipment Availability computation is
This is expressed in percentage and calculated using the following methods
A (Available Hrs) = Mission period in Hrs – Maintenance Hours
B (Breakdown Hours) = Downtime in jobs recorded through M2 Notifications
Mission Period in Hrs = 720, when you are querying the report for a period of 30 days
Maintenance Hours is Downtime in Jobs recorded through preventive jobs.
(usually through M3 Notifications)
MTBR = Mean Time Between Repairs (Hrs)
(Also known as Mean Time Between Failures – MTBF)
MTTR = Mean Time To Repair (Hrs)
MTTR and MTBR
The above figure shows details of M2 Notifications (Breakdowns) in a month.
The Yellow lines indicate the details of 4 Breakdowns in the month.
The Brown line indicates the details of immediate previous breakdown.
MTTR = Sum of Downtimes (Hrs) / No. of Breakdowns
= (1.35 + 0.17 + 0.18 + 0.83) / 4
= 0.6325 Hrs
MTBR = Sum of Intervals between two
Breakdowns in sequence / No. of Breakdowns
(Here the Brown line details are
used to calculate the interval before the fist yellow-line.)
This comes to 153.45 Hrs.
Here the Availability = [ 153.45 / (153.45 + 0.6325) * 100 ] = 99.6 %
We know that MCJB and MCJC are the PMIS Tcodes to see the MTTR, MTBR values of an Equipment or a Functional Location respectively.
There will be no issues when availability figures are calculated through Z-Reports for equipments as individual objects.
But issues arise at Hierarchical cases like few explained below:
The ‘Crane’ situation:
End-users create Breakdown notifications simultaneously with several time overlaps on many equipments under a single Industrial Crane (F/L) during breakdown stoppage. They do not create any notification on Crane proper (F/L).
But expectations will be there that because of hierarchical representation in the system, database should be able to give the Availability figures at Crane Level.
Please see this article posted several months after the present one: Hierarchical Equipment Availability Calculations (on Functional Locations)
‘Functional Agencies’ Situation:
In the maintenance function of large manufacturing/process industries, maintenance agencies are sectionalised such as Mechanical, Electrical, Hydraulics, Instrumentation etc. Here these agencies record their Breakdowns / Preventive maintenance activities on their respective equipments independently.
The cases where proper structuring is not done with a focus to capture the availability figures on key assets, involving all the data entered by these agencies,the availability computations on top hierarchy equipments looks very difficult.
Please refer to this document for some situations like above: Hierarchical Equipment Availability Calculations (on Functional Locations)