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AMMJ Mill Downtime Tracking 35
THE MILL DOWNTIME TRACKING DATABASE OVERVIEW
The MDTDB is an MS Access database which was set up in 1999 for the recording and reporting of mill downtime
incidents to facilitate the control of outages in the mill. The author has taken custody of it and has kept it up dated
since 2003.
The type of information entered in the MDTDB include the shift, the crew working the shift, productive unit which would
be either one of the six mills, equipment causing the productive unit to go down, the time and date of the downtime
event. The time and date are straight from the PI-Process Monitoring System and the duration is automatically
calculated when outage start and end times are entered into the MDTDB.
There is a field to describe the problem and the problem is stated using the 5 Whys Methodology [1] . The answer to
the 5th Why is usually stated in the ‘Suspect Cause’ field. Actions done to return the equipment back to service are
also stated in the ‘Action(s) Taken’ field.
Figure 1 is the screen shot showing the features of the form for recording of the mills downtime incidents.
To ensure accuracy of problem description a downtime record is sourced from and verified from three sources: Mill
Electrical Shift Reports, Mill Operations Logs and Personnel Interviews.
COMBINED MILL AVAILABILITY
The Combined Mill Availability is determined from the data extracted
from the MDTDB. This is the reliability requirement of this project.
Table 1 summarizes this combined availability since 2003.
The challenge of this project is about identifying solutions and
implementing the solutions to improve and sustain this combined
Mill Availability.
UNDERSTANDING AVAILABILITY
So what is Availability? Since availability is determined by reliability and maintainability and to grasp the concept of
availability an upfront definition of reliability and maintainability is deemed most appropriate.
There are four elements to the definition of reliability. Reliability is (1) a probability that a system/component will
perform a (2) specific function over a (3) specific time interval under (4) specific set conditions. It is usually expressed
in terms of the mean life (MTBF).
Maintainability is the ease with which maintenance is done to prevent failure, or during breakdown, return a system/
component to service. Maintainability is often determined at the design stage and is also dictated by the availability
of spares. Maintainability is expressed in terms of the mean time to repair (MTTR).
Reliability and Maintainability interact to form Availability. Availability is the probability that a system/component will
be in operating condition at any point in a given time interval under specific operating conditions and with specific
support condition. This interrelationship between reliability, maintainability and availability can be simply expressed
as in (1).
MTBF
Availability = --------------------- (1)
MTBF + MTTR
Therefore Availability can be simply stated as the measure of the Mill’s Uptime. High reliability combined with short
maintenance duration gives high availability and vice versa.
SAG1 MILL DOWNTIME ANALYSIS
The data from the MDTDB was exported out in MS Excel
spreadsheet format and analyzed using MS Excel. In
particular the Pivot Tables from MS Excel were used to a
great extent in carrying out these analyses.
A. Top 10 by Cumulative Breakdown Hours and
the Equivalent in Cost of Production Loss
The graph in Figure 2 is a comparison between the cumulative
hours and the equivalent in cost of loss production in the 18
months from July 2006 to December 2007.
The equipment contributing to SAG1 Mill’s downtimes
are ranked from the highest to the lowest by number of
cumulative hours.
The Top 10 equipment contributing to SAG1 Mill’s downtimes
are listed in Table 2.
Year Achieved Availability Target Availability
2003 88.08 % 94.60 %
2004 88.02 % 94.60 %
2005 94.67 % 93.70 %
2006 95.01 % 95.00 %
2007 94.64 % 95.00 %
TABLE 1 COMBINED MILL AVAILABILITY SINCE 2003
Equipment Cumulative Hours Equivalent Revenue
Loss (USD)
0231ML01 135.22 $ 10,135,145.00
0231CV01 51.95 $ 3,893,808.00
IPC/TARA 44.97 $ 3,370,636.00
0231SC10 24.35 $ 1,825,106.00
Unknown 18.48 $ 1,385,131.00
Flotations 8.70 $ 652,091.00
0231FE02 6.27 $ 469,955.00
0342UPS02 6.08 $ 455,714.00
0231ML01B 5.67 $ 424,984.00
0231CV03 5.62 $ 421,236.00
TABLE 2 SAG1 MILL TOP 10 EQUIPMENT BY
DOWNTIME DURATION
Vol 24 No 1