How to Have Highly Reliable Systems

There are only two ways to get high system reliability: meeting outstanding task quality performance standards so excellence is done everywhere; by building parallel arrangements where the failure of one has no impact on system performance. Both are done in a PWW EAM System-of-Reliability

Equipment can be configured in series or in parallel arrangements. A series arrangement is when one item or task connects sequentially to the next. It takes only one item to fail in a series arrangement and the whole system will fail. Exceptionally reliable individual equipment is needed to experience a high reliability system with a series arrangement.

Parallel arrangements are when each item is arranged as a companion, one duplicates another. In this circumstance, exceptionally reliable systems can be formed even if individual equipment has poor reliability.

A system is formed when equipment is combined to do a duty. For example, when a pump, coupling, and electric motor are connected they form a series system used to move liquid through pipes from one point to another.

How Plant Wellness Way Enterprise Asset Management is used to design and build an EAM System for Operational Excellence

Figure 1. Sample Reliability Block Diagrams, Reliability Equations and Reliability Calculations for both a Series System and Parallel System.

Series System Reliability

The standard EAM strategy is to first use preventative and predictive maintenance to reduce breakdown occurrences. Then proactive maintenance is used to improve reliability by keeping plant and equipment healthy. This process to high reliability is often called “the journey”. With this approach the journey can take 5 or more years before substantial gains in availability and lower maintenance costs are achieved.

Plant Wellness Way EAM creates an EAM strategy that captures the full plant and equipment availability possible. It simplifies and speeds up designing and constructing an EAM system which is focused on making the greatest operating profit. As a result, low maintenance costs and high equipment availability are automatic and natural outcomes of the way your business and people work.

Parallel System Reliability

The other way to combine equipment is as a parallel system arrangement. An example of this is when two filter stations operate in parallel. 

This can be configured to work in one of two ways. One is the duty circuit taking the full service, and the other is the standby doing no work, but ready to come online when the duty goes offline. This set up is known as a duty and standby configuration, or a standby redundancy. The other arrangement is where both circuits operate together and share the service load. If one circuit goes offline the remaining circuit can handle the full duty. This operating philosophy is called a fully active arrangement.

As shown in Table 2, Figure 1, when two components of 0.6 reliability operate in parallel in a fully active arrangement the system reliability is 0.84. When six separate systems of 0.6 reliability are paralleled, the system reliability is 0.996. By putting equipment in parallel you create a more reliable system because when one item fails the other item continues delivering the duty.

When you use equipment there are only two ways to get a highly reliable system. If it is a series system, then every piece of equipment in the arrangement must exceptionally reliable. The other way is to duplicate the system and have a complete second system in parallel ready to replace the first system when it fails.