PLANT MAINTENANCE
CONDITION MONITORING
- ALL OR NOTHING? If you can predict the failure of a machine early enough you have an opportunity to do something about it, so as to minimise downtime and disruption to production. Often a simple remedial action such as re-greasing at the right time can prevent not only failure but also any permanent damage. Unfortunately neither past experience nor MTBF (Mean Time Between Failure) can predict the failure of any particular machine. Some machines will fail much earlier and some much later than expected. The only approach to achieving such machine specific details is to utilise Condition Monitoring. However Condition Monitoring is only part of the solution since once you have identified a faulty machine and gained some insight into its
seriousness the next and crucial step is to do something about it and this is usually referred to as Condition Based Maintenance (CBM). It is CBM that gives the benefits but these can only be gained by implementing CM with its associated costs (see Table 1). A wide range of Condition Monitoring techniques are available, each of which has its own strengths and weaknesses and it is fair to say that no single technology can provide information on all machine faults. Even within one area of CM technology the range of instrumentation available can be bewildering. Therefore, for the newcomer wishing to get started on CM it can be a daunting prospect and two commonly encountered approaches are as follows:
TABLE 1 CBM Benefits :
CM Costs :
Increase Machine Life & Availability
Purchase New Equipment
Reduce Secondary Damage
Learn New Skills
Reduce Unplanned Stoppages
On-going Implementation
Focus Maintenance Effort Improve Product Quality
Picture curtesy of Elyo Systems Ltd
When we purchase a machine we accept that it will not last forever. The problem isn’t that it will eventually fail but the consequences of it failing unexpectedly. In fact a machine is more likely to fail just when you need it
Some companies approach the task in a proactive and systematic way whereby each machine is analysed in terms of possible failure modes, likelihood and consequences. The capabilities of appropriate CM techniques are then matched to each of the failure modes and a cost benefit analysis for each can then be performed. In an ideal world every company would follow such a procedure but in the real world few have the luxury of financial and manpower resources to pursue it. As a result, some companies leave CM on the back burner from one year to the next.
At the other extreme some companies get bounced into CM in response to an unexpected and serious machine failure which has had a major adverse impact on production/operations. This often results in a panic to get CM implemented so that “It never happens again”. Needless to say hasty decisions made by newcomers to CM, often with blank cheque books, are a recipe for later regrets. In the absence of knowledge and under extreme pressure human nature is to buy the most expensive as it must be the best!
11 EMS Mar/Apr 2008 www.engineeringmaintenance.info