Introduction to maintenance engineering
Preface:
The Metal Age, which started around 3000 BC, saw the appearance of metal tools and the
evolution of civilizations in different regions of the world. This led to the development of tools
for warfare and farming, and the building of roads, boats, houses, and so on. The Industrial
Revolution created new mechanical devices and machines. This, in turn, led to the development
of the electrical, hydraulic, and other devices and equipment that are used nowadays in nearly
all sectors – farming, processing, mining, manufacturing, transport, communication, and so
on, all with specific needs for maintenance. The construction of infrastructures (such as
electricity, water, gas and sewage networks, dams, roads, railways, bridges, etc.) resulted in
new maintenance challenges in order to keep them operational.
The reason why engineered objects (be they products, plants, or infrastructures) need
maintenance is that every object is unreliable, in the sense that it degrades with age and/or
usage and ultimately fails when it is no longer capable of discharging its function. Maintenance
actions compensate for the inherent unreliability of an object and may be grouped broadly into
two categories: (i) preventive maintenance (PM) to control the degradation process and
(ii) corrective maintenance (CM) to restore a failed object to the operational state.
Maintenance actions were mainly of the corrective type until the middle of the last century –
the adage being, “don’t touch if it ain’t broke.” Also, preventive actions were viewed as money
wasted. Maintenance was done by trained technicians who were very good at fixing failures
(often fondly referred to as “grease‐pit monkeys” in the popular literature). Maintenance was an
afterthought in the design of new objects and was simply viewed as an unavoidable cost to be
incurred after these objects were built and put into operation.
There was a dramatic change after the Second World War. Reliability evolved as a new
discipline, and the theory of reliability dealt with various aspects, such as (i) the science of
degradation, (ii) the use of statistical methods to assess reliability, and (iii) mathematical
models to predict item failures and the importance of preventive maintenance. Investing in
preventive maintenance lowers the cost of corrective maintenance but results in additional
costs. Operational Research (the application of scientific methods to solve industrial problems)
focused on models to decide on the optimal level of preventive maintenance to achieve a
proper trade‐off between the costs of corrective and preventive maintenance.