MTBF and Condition Monitoring

In this final chapter of our investigation into The Destructive Force of Failure, we are going to look at the final two statistical tools that we identified. They are Mean Time between Failure, referred to as MTBF, and then Condition Monitoring.

Mean Time Between Failure – MTBF

Mean Time between Failure is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. The MTBF can be calculated as the arithmetic mean time between failures of a system. It will measure the average time that equipment is operating between breakdowns or stoppages. MTBF helps businesses understand the availability of their equipment and if they have a problem with reliability.

Not only do maintenance practices change but operating parameters change as well. Processes are run faster or slower to produce more or fewer products according to market demands. Product specifications change, which in turn change the process’s average running conditions. Changes in temperature, pressure, speed, flow, and viscosity can all affect machinery life in unknown or unquantifiable ways.

Mean Time between Failures – Formulae

The simple formulae used are as follows:

• Total working time minus the total downtime divided by the number of incidents

Using this simple example

• Total working time was 20 days
• Breakdowns 4 of 0.5 days each
• Total breakdown time = 2 days
• Calculation (20 – 2)/4 = 4.5 days
• Average running time between breakdowns = 4.5 days

Our job is to be prepared for this eventuality and then to try and increase the average running time and reduce the number of incidents through improved maintenance initiatives.

Condition Monitoring

Condition monitoring is the process of monitoring a parameter of condition in machinery, in order to identify a significant change that is indicative of a developing fault. It is a major component of predictive maintenance.

The use of condition monitoring allows maintenance to be scheduled, or other actions to be taken to prevent consequential damages and avoid its consequences. Condition monitoring has a unique benefit in that conditions that would shorten normal lifespan can be addressed before they develop into a major failure.

Monitoring Techniques and Methods

Condition monitoring techniques are normally used on rotating equipment, auxiliary systems, and other machinery (compressors, pumps, electric motors, internal combustion engines, presses), while periodic inspection using non-destructive testing (NDT) techniques and fit for service (FFS) evaluation are used for static plant equipment such as steam boilers, piping and heat exchangers.

The basic principle of condition monitoring is to select a physical measurement that indicates that deterioration is occurring and then to take readings at regular intervals.

Any upward trend can then be detected and taken as an indication that a problem exists.

Condition Monitoring

There are many different types of monitoring conditions and equipment available. This graphic demonstrates some of the more popular types of condition monitoring that can be used, subject to the industry and the type of machine involved.

• Vibration Analysis
• Pressure Monitoring
• Laser Alignment
• Performance Monitoring
• Thermography
• Lube and Oil Analysis
• Motor Current

Although this graphic shows a wide variety of monitoring options, it would be very unusual to use all of these on a single machine. An analysis of the types of incidents would need to be undertaken to identify the best option or options to implement.

Summary

Well, that brings us to the end of our journey in investigating The Destructive Force of Failure.

Thank you for journeying with me. Remember where our journey started.

‘Success is not final, Failure is not fatal, it is the courage to continue that counts

Winston Churchill

‘We learn from failure, not success’

Bram Stoker

Failure is a word no one wants to hear and yet fail so often can be the catalyst or starting point for something great to happen or be discovered. Let that be your story.

We cannot dig a hole and hide from failure. It has a unique way of finding where we are, so rather face up to it, accept it as part of life but also accept that we don’t have to live with it.

There are plenty of tools available that will help us to conquer failure and at least eliminate the “The Destructive Force” portion from the equation.

Watch out for our next eBook where we are going to be doing some ‘Smooth Running’ as we discuss Best Practices and Project Management.

For more information email us at info@strobe-al.co.za or visit www.strobe-al.co.za