Preventive Maintenance Approach

Preventive Maintenance Approach
Maintenance has changed over the past 30 years. This is due to a huge increase in the number and variety of physical assets that must be maintained, more complex designs, new maintenance techniques and changing views on maintenance organisation. Reliability-Centred Maintenance (RCM) has played a central role in the evolution of maintenance strategies.
In the past, preventive maintenance was considered the most advanced and effective maintenance technique available. A Preventive Maintenance (PM) program would assume a cause-and-effect relationship between scheduled maintenance and operating reliability. This assumption was based on the intuitive belief that because mechanical parts wear out, the reliability of

In simple terms: if the consequences of a failure do not have an adverse effect on safety; operations, environment or cost, then there is no need to carry out scheduled maintenance.
Reliability centered maintenance (RCM) is the maintenance approach used when following a process that assesses equipment condition and determines the maintenance requirements of any physical asset in its operating context. RCM emphasizes the use of Predictive maintenance (PdM) techniques in addition to traditional preventive measures.
“A reliability-centered maintenance program includes only those tasks which satisfy the criteria for both applicability and effectiveness. The applicability of a task is determined by the characteristics of the item, and its effectiveness is defined in terms of the consequences the task is designed to prevent.” (Source: Nowlan and Heap, 1978)
It provides a structured framework for analyzing the functions and potential failures for a physical asset, with a focus on preserving system functions, rather than preserving equipment. RCM is used to develop scheduled maintenance plans that will provide an acceptable level of operability, with an acceptable level of risk, in an efficient and cost-effective

Levels of criticality are assigned to the consequences of failure. Some functions are not critical and are left to "run to failure" while other functions must be preserved at all cost. Maintenance tasks are selected that address the dominant failure causes. This process can only address maintenance preventable failures, i.e. it cannot defend against unlikely events, non-predictable acts of nature, etc.

RCM Principles
The primary principles upon which RCM is based are the following:
• Function oriented: It seeks to preserve system or equipment function.

• Device group focused: It is concerned with maintaining the overall functionality of a group of devices rather than an individual device

• Reliability centered: It uses failure statistics in an actuarial manner to look at the relationship between operating age and the failures. RCM is not overly concerned with simple failure rate; it seeks to know the probability of failure at specific ages.

• Acknowledges design limitations: Its objective is to maintain the inherent reliability of the equipment design, recognizing that changes in reliability are the province of design rather than maintenance. Maintenance can only achieve and maintain the level provided for by