Reliability Assessment: A Guide to Aligning Expectations, Practices, and Performance. Daniel Daley
ignore on-going maintenance (say regular oil changes), it is possible to again begin changing oil. But that will not reverse the wear or other deterioration from the period of inadequate maintenance.
If expectant mothers choose to smoke and drink and use drugs during the period they are pregnant, it is possible that their unborn children will be affected. The problems inherent at birth will stay with their children their entire lives. Similarly, if a system is designed without adequate attention to reliability, the inherent reliability of the system will suffer. It is possible that configuration will be inadequate or robustness of components will not meet expectations for the entire life of the system.
Extending the comparison between the human condition and physical systems, we might compare the issue of naivety or naïve expectations.
If you are an old movie buff and enjoy old detective movies, you seldom see Phillip Marlowe without a cigarette hanging from his lips or Sherlock Holmes without his pipe smoking. In fact, if you go back more than forty years, there is lots of evidence that there was little or no stigma associated with smoking. There were no studies linking smoking to cancer, heart disease, or problems with unborn children. In the last twenty-five years, there has been a tremendous amount of information available for consumers telling them about the ill effects of smoking. A person would have had to live under a rock to avoid being exposed to information about the negative consequences of smoking.
Because of that, if a person is a heavy smoker and gets cancer or develops heart problems, you can say, “What did you expect? You have been bombarded with information telling you what to expect.” I recall seeing the warning label on a package of local cigarettes during a visit to Ireland. Being very simple and direct, it stated, “Smokers die younger.” That is what they should expect. Anything better is luck.
Unfortunately, physical systems do not have warning labels saying, “Inadequate maintenance practices lead to early failures.” Maybe they should.
The inherent reliability of a system is determined during design, procurement, and construction. Many design processes are focused entirely on the functionality and integrity of a system. Meanwhile, the design processes ignore reliability, availability, and maintainability — the three characteristics people typically roll into the commonly accepted concept of reliability.
For pumping and piping systems, the designers will determine the size of the pipe and the head and capacity of the pump to achieve the desired functionality. They will see that the appropriate pipe schedule or thickness is selected to ensure system integrity. They will even determine that the metallurgy is compatible with the properties of the liquid being handled to avoid corrosion.
On the other hand, design processes frequently do not analyze the MTBF (Mean Time Between Failures) of pumps in similar services. Therefore, designers often have difficulty determining if a spare pump should be installed or if a more robust pump should be selected — for reasons of reliability. Designers seldom analyze the required maintenance program and inspection programs, or the resulting lifecycle cost, to ensure that the installed system provides the most cost-effective system for the long haul. More typically, redundancy is the result of a design standard — in other words, they are either used or not used in specific applications independent of reliability. In turn, reliability is determined first by costs and then by standards intended to address other issues, like functionality.
Operating procedures are typically developed during construction. They are based on how the design engineers expect the system to function. The design engineers have seldom if ever been operators; they are interested only in keeping the system performing whatever function it was designed to perform. The characteristics that develop over time as a result of how a device functions as part of a complete system are not known to designers. Therefore, these characteristics are never addressed in the operating procedures. As a result, systems are never operated in a way that maximizes reliability by eliminating harmful practices by operators.
As with the initial design, few of the individuals involved with preparing modifications understand how to take reliability issues into account when making changes. As a result, changes intended to increase capacity may have a negative impact on production because they decrease reliability and availability.
Finally, as systems age, there is frequently a poorly quantified deterioration of reliability that is the result of scattered degradation of a variety of components. Without some conscious effort to thwart this deterioration, performance is viewed as the impact of “getting old.” If the reliability of a system is properly managed, performance can actually improve with age rather than deteriorate.
As suggested at the beginning of this chapter, without conscious efforts to manage reliability, you are depending on the “kindness of strangers” for your reliability. In many cases, the stranger is nature itself. Unfortunately, nature has a desire to introduce randomness and return all things to their natural state. It is naïve to expect anything else.
Assessing What You Have a Right to Expect
One who asks a question is a fool for five minutes;one who does not ask a question remainsa fool forever.
Chinese proverb
This chapter provides an introduction to the rest of the book. I hope the first two chapters whetted your interest in understanding the elements that affect reliability. More specifically, I hope you have begun to ask yourself the question, “What do I have a right to expect?” If so, the chapters were successful. If not, I hope that your curiosity will lead you at least a little further into this book.
Generally speaking, individuals who are responsible for managing complex equipment and systems cannot afford to be in a position where they do not know the answer to that question. If they do not know the answer:
•They do not understand the extent of the lost opportunity.
•They do not know how difficult or how easy it might be to capture that opportunity.
As a starting point for this chapter, I would like to create a term that is much easier to use than “What Do You Have a Right to Expect?” For the sake of simplicity, I will use the term Wide-Hart (WDYHARTE) as a shorthand notation for the comprehensive assessment of your reliability opportunity.
One of the unfortunate characteristics of reliability is that there are so many elements that determine the reliability of a system over its entire lifecycle. Dropping your guard with respect to any one of these elements can lead to poor reliability. It is not acceptable to be good for 90% of the elements and ignore the last 10%.
Consider, for example, the owners of a high-end car like a Mercedes-Benz or a BMW. They have purchased a product with good inherent reliability. Let’s assume that the owners drive their cars in a sensible caring manner and they perform all the required preventive maintenance using the highest quality materials. The owners have done everything they should up to the point that the engine needs an overhaul. Rather than purchasing a “crate” engine that was assembled with the same care and sensitivity as the original car, they allow a local mechanic (who normally handles only oil changes) to perform the overhaul in a non-certified corner garage. After the “backyard mechanic” overhaul, the car is never again the same. The reliability suffers until the owners decide to replace the car.
In this example, it could have been a poor mechanic, overaggressive operation, or poor inherent reliability in the original product, but only one lapse can result in poor reliability. It is possible to recover from some of these situations by correcting the deterioration they caused or by eliminating the defects they introduced into the