Types of Maintenance Management
There are three main types of maintenance management that may be applied to the maintenance of machines, including tower cranes: breakdown maintenance, preventive maintenance, and predictive maintenance. Not all of these are appropriate for the effective maintenance of tower cranes, as explained below.
Breakdown Maintenance
Breakdown or “run-to-failure” maintenance management has a simple and straightforward logic. “If it ain’t broke, don’t fix it” is often seen as a way of limiting expenditure on maintenance and keeping costs low. The problem with this approach for tower cranes is that any failure could present an immediate and unacceptable risk. Additionally, repair costs may well be very high when the machine does break down, often at the most inconvenient moment, with considerable downtime whilst repairs are carried out.
Planned Preventive Maintenance
All planned preventive maintenance systems are time-driven. In other words, maintenance tasks are carried out at intervals that are based on actual hours of operation or on an interval of time that equates to an average number of operating hours. The maintenance interval is based on the experience of breakdowns or the mean time to failure (MTTF) as illustrated in Figure 1. The MTTF or bathtub curve indicates that a newly installed machine has a higher probability of breakdown due to installation problems in the first few weeks of operation. Following this initial period, the probability of failure is relatively low for an extended period until wear and deterioration mean that the probability of breakdown/failure increases sharply with elapsed time.
