Reliability Assessment: A Guide to Aligning Expectations, Practices, and Performance. Daniel Daley
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Название: Reliability Assessment: A Guide to Aligning Expectations, Practices, and Performance
Автор: Daniel Daley
Издательство: Ingram
Жанр: Здоровье
isbn: 9780831190613
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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 system. However, this approach is useful only in instances where the population is small and relatively few problems need corrective action. Individual owners can correct their own cars. But if a fleet manager allows an entire fleet to become run-down, it will be near impossible to flush out all of the defects.
Some situations involve hundreds or thousands of pieces of equipment. The likelihood of managing all the corrective actions needed to address all lapses is small. The only way to guarantee reliability is to prevent problems in the first place. This philosophy applies to each and every element that affects reliability. In maintenance, this philosophy is called Preventive Maintenance. There are other preventive approaches in each and every activity that affects reliability over the entire lifecycle of a system.
The following outline for a Wide-Hart assessment describes the elements that should be included in a comprehensive assessment of how you deal with all the choices and activities that affect reliability of your systems.
Outline for a Wide-Hart Assessment
Assess Cost of Unreliability
It is best to begin a reliability assessment with an evaluation of the overall cost of unreliability. In this context, I am using the term “cost of unreliability” to mean the overall cost resulting from all situations caused by reliability-related failures. This cost will include both the direct and indirect costs associated with all reliability issues that could have been prevented by adherence to good reliability practices.
These costs include the cost of repairing equipment after failure. They also include the lost value of the asset while it is unavailable to perform its intended function after a failure. In addition, they include the cost associated with off-spec product made while equipment was in the process of failing and the cost of energy consumed while shutting down and re-starting. If poor design practices have resulted in additional maintenance costs to support a system with inadequate inherent reliability, the cost of the added maintenance must be included. The cost of unreliability includes all costs resulting in any manner from poor reliability.
In fact, it makes best sense to evaluate the overall cost of unreliability twice:
•Once before performing a detailed assessment of each element that contributes to reliability.
•Once after performing the detailed assessment of each element affecting reliability
The first approach is a macro view from the outside-in of how much business is being lost because of lost production or cost being added. СКАЧАТЬ