ดาวน์โหลด All Proceeding - AS Nida

The next step was the statistical analysis of reliability data
(time to failure) of the critical components and the assessment of the
probability density functions (pdf) of time to failure distributions.
4.4 Failure Data Analysis
Reliability Parameters Estimation – Failure and
maintenance data of the plant was collected from the maintenance log
book. The related data were used to obtain failure and repair rates of the
major components associated with the paper production unit of the
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plant. In this study, Weibull distribution has been used to represent
equipment failure time. The shape parameter (β) and scale parameter
(η) of the Weibull distribution have been computed using least square
curve fitting technique. At this stage the statistical software was used in
order to conduct the statistical analysis, and the Kolmogorov-Smirnov
(K-S Test) goodness of fit test was used in order to ensure a good pdf
fitting to the data. Table 7 shows a sample of some results.
Table 7 Reliability Parameters Estimation & Goodness of Fit Test
Component
Parameters
β η
Correlation
Coefficient
K-S Test (α = 0.05, n = 21)
max d dα
Test Results
1. Motor 1.42682 62.6639 0.972 0.2177 0.287 Accept
2. Belt 1.37027 23.5603 0.918 0.1902 0.287 Accept
3. Shaft & Shaft sleeve 1.12241 26.0567 0.984 0.1518 0.287 Accept
4. Pump bearings 5.26308 10.2572 0.963 0.1971 0.287 Accept
5. Motor bearings 1.20565 56.2784 0.969 0.2282 0.287 Accept
6. Packing 5.49178 3.86463 0.970 0.1958 0.287 Accept
7. Flange 1.42214 15.9930 0.988 0.1630 0.287 Accept
8. Impeller 1.30804 111.277 0.982 0.1847 0.287 Accept
9. Body 1.18374 113.604 0.978 0.1905 0.287 Accept
10. Pulley 1.01427 82.1241 0.972 0.2019 0.287 Accept
11. Pump base 1.01035 137.051 0.987 0.1864 0.287 Accept
Since a distribution closed to the data so it can be a
parameter β (Shape parameter) and η (Scale parameter) used to
analysis and selection of maintenance tasks.
4.5 Maintenance Task Analysis and Selection
Once failure mode and reliability parameters have been
identified, the next step is to analyze and provide the applicability of
maintenance task by using these principles:
1. Task selection for β ~ 1 (almost Exponential), PM was
selected to machines with a constant failure rate. The Optimal
inspection interval for component parts and interval is called the failurefinding
interval (FFI) which is the mean time to fail (MTTF or η)
applies as a guideline such as motors have the MTTF is 62.6639 weeks,
thus the FFI for motor at 60 weeks or 15 months. Table 8 provides the
expected availability obtained from different FFIs.
Table 8 Failure Finding Interval (FFI)
Component
Parameters
β η
FFI
(months)
1. Motor 1.42682 62.6639 15
2. Belt 1.37027 23.5603 5
3. Shaft & Shaft sleeve 1.12241 26.0567 6
4. Pump bearings 5.26308 10.2572 -
5. Motor bearings 1.20565 56.2784 14
6. Packing 5.49178 3.86463 -
7. Flange 1.42214 15.9930 3
8. Impeller 1.30804 111.277 27
9. Body 1.18374 113.604 28
10. Pulley 1.01427 82.1241 20
11. Pump base 1.01035 137.051 34
2. Task selection for > 1, PdM was selected to machines with a
increasing failure rate. Determination of maintenance intervals in this
section is to determine the best times at which replacements should
occur to minimize total downtime per unit time. The total downtime per