Equipment Availability - Concept & Issues
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Author: Jogeswara Rao Kavala
The Availability & MTTR, MTBR
In the maintenance function, often things end-up with questions about the Availability of Machines for Production, for a specified mission (time period)
This parameter is known by different names such as
- Equipment Availability
- Operational Availability etc.
Usually the Equipment Availability value is computed with a base formula:
This is expressed in percentage and calculated using the following methods
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Method1
Where
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
(30*24).
Maintenance Hours is Downtime in Jobs recorded through preventive jobs.
(usually through M3 Notifications)
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Method 2
where
MTBR = Mean Time Between Repairs (Hrs)
(Also known as Mean Time Between Failures - MTBF)
MTTR = Mean Time To Repair (Hrs)
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MTTR and MTBR
Example Data:
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.
‘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.
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