Equipment Availability – Concept & Issues
Equipment Availability – Concept & Issues
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Author: Jogeswara Rao Kavala
The Objective:
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
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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.
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)
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HIelo jogeswara Rao garu,
Nice and simple to understandable doc. Please provide notification raising/process in details.
Regards,
Subrahmanyam B
Thank you Subrahmanyam garu for compliments.
Document has basic assumption that readers are aware of Notification process.
Regards
Jogeswara Rao K
Great post Sir,
few clarifications .
What is breakdown ? Equipment totally out of order or not performing as per designed parameters ? . How you resolve this conflict ? . Operation always creates M2 notification saying that when you repair the equipment, anyway there is a downtime . Unfortunately MTTR is based on M2 Notifications . But what if , we want to capture downtime from some approval stage in notification , till notification is completed? and calculate for all these notifs ?
In system language Breakdown can simply be dfined as the Notification event where Breakdown checkbox is ticked. So as long as this checkbox is there there need not be a confusion about the Breakdown Notification even if it is M2 type. Coming back to practicality it is the management which should define a Breakdown. It can be a function of parameters such as A,B, C indicators and the downtime of a repair. Example Guidelines: Category A equipment if undergoes any unplanned repair it should be a Breakdown irrespective of repair duration. Likewise an unplanned repair for 30 minutes or more on a B category equipment should be a breakdown and so on..
So it is important to rememebr that MTR, MTBR are based on Breakdown tick, not on type of notification, if I am correct.
See this thread What are the prerequisite for getting MTTR / MTBR data.
If anything is left out you may start a discussion.
KJogeswaraRao
Hello Jogeswara
Thank you for this valuable document. If I may ask, when does a Breakdown ceases to be a breakdown so that it becomes a repair?
Regards
Gibson
Hello Gibson,
In my experience it always a function of process category and defined by company managements. Example, a Process industry will have a different definition for Breakdown when compared to a Discrete manufacturing industry because of the impact on production will be different in these 2 cases. Few companies might not relate it to Production at all, They might define in a way I wrote above. This is to control the effectiveness of maintenance function. So global definitions can not be valid because of several geographical, cultural reasons. My view