Abstract:
Reliability, Availability and Maintainability (RAM) are used to increase and/or maintain
operational availability in both industries where failures result in catastrophic damage and
scrap output. Even if increasing/maintaining high availability avoids/reduces failure
effects by executing maintenance before a failure occurs, maintenance may not be cost-effective in businesses where the consequence of failure is scrap output. The study's goal
was to incorporate RAM into maintenance cost analysis in order to avoid those
uneconomical expenditures in the case of the Amhara Pipe Factory (APF). RAM was
combined with maintenance cost analysis in two stages: (1) optimizing unavailability and
cost; and (2) maintaining optimal availability by enhancing reliability and/or
maintainability based on the importance measure's value. These were done, once the
time between failures (TBF), time to repair (TTR) and scrap in each failure of each
component as well as associated costs were collected. Statistically, distributions were
fitted by selecting best using Anderson Darling (A-D) goodness of fit test and correlation
coefficient. The parameters‟ values were determined by maximum likelihood estimation
(MLE) and least square estimation (LSE) methods in Minitab software. The optimization
was carried out in MATLAB software using the non-dominated sorting genetic
algorithm-II (NSGA-II), which outperforms other tools in terms of convergence to true
optimal and diversified solutions for both objectives.
NSGA-II programming provided fifty Pareto optimal solutions among them availability
56.96% was chosen based on sensitivity index value. The maintenance was planned
based on the optimal availability obtained or availability requirement, with the least
available component being considered first because the components have a series
functional link to the line's intended operation. By reducing and avoiding most work in
process scrap as well as unnecessary maintenances, the maintenance plan devised can
save birr of 1,354,662 in two years. The study showed how RAM integrated to
maintenance cost.
The implementation model developed helps how other companies integrate RAM into
maintenance cost and the factory use it, using Bayesian Inference estimation, in addition
to MLE and LSE to prepare preventive maintenance plan.
Key words: RAM, NDSG_II, independent and identical distribution, maintenance cost.