Currently, Dr. Ntokozo Mthembu (Advisor to the ODI Board) is doing an online course in Introduction to Maintenance Engineering offered by Lulea University of Technology, Sweden, through the FutureLearn educational online channel. The course leader is Professor Uday Kumar.
To read Dr. Mthembu’s series of articles, click on the following links:
Part 1: The Kumar’s Why, What, When, How, Who and Where Concepts of Engineering Maintenance
Part 2: The Kumar’s How, Who, and Where concepts of engineering maintenance
Part 3: Kumar’s concept of Reliability in maintenance engineering
In part 4 he writes:
“There is a fascinating relationship between failure and reliability. Maybe ‘fascinating’ is not an appropriate word, but I will leave that to the English linguists and pundits. Be that as it may, my opinion remains unfased by the slither of doubt in my mind, which I abhor of course.
Blake’s contraries
Failure and reliability are twins with opposing objectives. Their relationship reminds me of what Chelsea Babalo Malunga taught me when she was doing her major in English, Blake’s Contraries. Blake is none other than the famous English poet William Blake. Without going to his philosophy of contraries which is not the subject of this article, some of them that I find interesting are
(i) the Marriage of Heaven and Hell,
(ii) Innocence and Experience,
(iii) Attraction and Repulsion,
(iv) reason and energy, and lastly for me
(v) love and hate.
I must pause here because this is not Blake’s poetry lecture, but the takeaway from Blake’s view of his contraries, is that he believed the interrelation between the synthesis and antithesis are necessary to human existence.
Prof Uday Kumar’s maintenance contraries
Now, taking a great leap from Blake’s romanticism (spiritual and political freedom) to Prof Kumar’s treatise on maintenance engineering, one is tempted to view failure and reliability from Blake’s prism and realise that they too are contraries that are ‘necessary for human existence’. Failure and reliability are our modern contraries that ‘attempt to achieve human perfection or systems equilibrium’ within the contrary forces of the entropy of the system. Driving my car from Jozi to eKapa without a hitch signal that it is reliable. Most of us are drivers and can attest to the occurrence of this while navigating the roads. The contrary is true that it is unreliable. However, without the existence of these two contraries, how would I know whether a system is reliable or not? This is the burning question, “to be OR not to be” – a ’la a famous soliloquy from William Shakespeare’s play Hamlet, which, incidentally is a Blakean!
Kumar begins his short lecture by defining the relationships between failure and reliability, failure and fault, and what is the failure mode.
- Failure is the termination of the ability of an item to perform a required function. A system failure occurs due to the failure of one or more of its components.
- A fault is the state of an item characterized by its inability to perform its required function.
- A failure mode is a description of a fault, sometimes referred to as a fault mode.
Murphy’s Law
Then comes Murphy, not Eddie, but the infamous Murphy’s Law.
If a piece of equipment can fail, it will fail
(Anything that can go wrong, will go wrong)
Failure will usually occur at the most inconvenient time. An example of Murphy’s law would be stumbling upon a pothole. As you attempt to avoid it, simultaneously the car driving in the opposite direction appears. You pass each other at the point or epicentre of the pothole! Interesting indeed. Examples of Murphy’s Law in action in replete when driving along our roads, trips, leisure of any form of driving, and its practical effects are as ubiquitous as the air we breathe. Our saving grace is that we are always oblivious to its invisible hand and its machinations.
Technically, a strong and symbiotic relationship between Reliability and Failure exists. Kumar describes reliability as the probability of no failure over a specified time interval under specified conditions.
What is failure then?
It comprises three components, namely
(i) fracture,
(ii) loss of function, and
(iii) loss of function when we want the function.
In other words, failure can be defined as the termination of the ability of an item to perform a required function.
Failure causes
The failure cause is useful information in the prevention of failures or their re-occurrence. Failure causes may be classified (in relation to the life cycle of the object), as indicated below:
- Design failure: Due to inadequate design;
- Weakness failure: Due to weakness (inherent or induced) in the system so that the system cannot stand the stress it encounters in its normal environment;
- Manufacturing failure: Due to non‐conformity during manufacturing;
- Aging failure: Due to the effects of age and/or usage;
- Misuse failure: Due to misuse of the system (operating in environments for which it was not designed);
- Mishandling failure: Due to incorrect handling and/or lack of care and maintenance.
Exercise:
Assuming you are learning about Key 9 of the 20 Keys system,
- Can you identify the types of failures you have encountered in your key equipment and machines?
- Once identified, which one of the Keys can you use to minimise the equipment failures?
- How can you measure their effectiveness to monitor their health before failure kicks in?
Kumar says that every item is unreliable in the sense that its failure is inevitable whether sooner or later, even with the best design, construction, maintenance, and operation. Failure causes are useful information in the prevention of failures or their recurrences.
Different Types of Failures
- Evident
- Hidden
Failure Classification
- Intermittent failures
- Extended failures
- Potential failures
- Gradual failure / Degraded failure
- Sudden failure
- Functional failure
- Gradual failure
- Sudden failure /Catastrophic
- Potential failures
To be continued“
Professor Uday Kumar. Professor and Head of Subject, Head of Division
Luleå University of Technology | Research subject: Operation and Maintenance | Division: Operation, Maintenance, and Acoustics| Department of Civil, Environmental and Natural Resources Engineering.