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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The Manager of Reliability and Maintenance (to whom Joe reported) started with, “Joe is a very conscientious employee. He takes his job seriously and works a lot of long hours.”
After another few moments of silence, the Plant Manager began, “I guess I have two observations. The first has to do with the information in this file. From my viewpoint, it is too late to bring these things up at this time. If they were as critical as Joe contends, he should have brought them up earlier.”
The good-hearted but naïve Operations Manager responded, “I think he did bring them up, but no one listened.”
His face reddening, the Plant Manager responded, ignoring the Operations Manager and speaking directly to the Assistant Plant Manager (to whom the Operations Manager reported), “You miss my point entirely. It is his job to get our attention. He needs to get our attention when there is a problem. He needs to be more persistent. That is his job.”
By this time, the room was completely silent. No one but the Plant Manager spoke. “I said there were two things. The second is the defeatist attitude I heard. What I heard in the tone of what he said, if not the words, was that he was giving up on this machine. We just cannot afford that kind of attitude.”
The meeting was over. Ignoring the others in his office, the Plant Manager looked down on his desk and began working on something else. One by one, the other members of the audience got up and left the office.
Some months later Joe was given his annual appraisal. Although there was nothing specific, his supervisor mentioned that he was not viewed as a “team player.” Several months later, Joe parted and joined another company.
Joe’s new employer thought he walked on water. Joe’s old company continued to suffer along with frequent failures of the recycle compressor and poor reliability in general.
Although this story is only fictional, it is a compilation of a variety of real-life experiences. It is intended to impart several messages to the reader:
1.Each of the papers Joe extracted from his folder represents one of the elements that contribute to the overall reliability of any system or piece of equipment.
2.The composite reliability or “what you have a right to expect” is a combination of all the items mentioned.
3.Unless the impact of each choice is clearly quantified, it is impossible to have an accurate understanding of reasonable expectations. Most people like to recall only the good things.
4.People can become defensive when their decisions are shown to be faulty.
5.It may be better to have a third party perform the analysis than sacrifice an employee by asking him to perform the evaluation and deliver the bad news.
Let’s discuss the elements that should be included in a WDYHARTE (What do you have a right to expect?) analysis. As our fictional reliability engineer explained, each and every point in the life of a system affords us with opportunities to make choices that will affect reliability. In some cases, the individuals involved are aware they are making choices that affect reliability. In other cases, they are not aware. Sometimes they make sound choices that positively affect the reliability, but sometimes they make choices that compromise the reliability. They then often rationalize that current savings are more important to the business than the added costs — stemming from poor reliability — that will be experienced much later (or by someone else).
Let’s go back and review the elements one by one that determine “what you have a right to expect.” Expectations for performance are often not based on any comprehensive analysis or assessment. Instead, they are based on a “gut feel” or “hoping for the best.” Expectations without the information needed to provide an informed opinion are misinformed and ultimately lead to disappointment. When expectations are aligned with reality, people and businesses are more likely to get what they expect and expect what they get.
Inherent reliability is probably the single most important characteristic of any system or piece of equipment in terms of determining overall reliability performance. The inherent reliability of a system or device is determined by its configuration and component selection. For instance, if a plant has redundant feed pumps or recycle compressors, that fact will profoundly affect the inherent reliability. Also, if the components were chosen based on lifecycle cost rather than just first cost, the inherent reliability will be enhanced. In performing this analysis, the lifecycle cost includes first cost, all forms of maintenance costs, the costs associated with unreliability (e.g., lost profit associated with unplanned outages), and costs associated with unavailability (e.g., lost profit associated with necessary planned outages).
The inherent reliability is a measure of the overall “robustness” of a system or piece of equipment. It provides an upper limit to the reliability and availability that can be achieved. In other words, no matter how much inspection or maintenance you perform, you will never exceed the inherent reliability. If you operate, maintain, and inspect a device as well as possible, you will be able to harvest all of the inherent reliability. On the other hand, if there are gaps in your operating, maintenance, or inspection practices, you will harvest only some portion of the inherent reliability.
If you wish to improve the inherent reliability of an existing system or device, you will need to change the current configuration or component choices and you will need to do so in a manner that improves reliability rather than detracts from it.
Because most systems and devices spend their lives with much the same inherent reliability as was decided by the original design, it is critical that the initial design take reliability and availability requirements into consideration. Adding a redundant component is both difficult and expensive after the original system has been built. In the case of a plant, piping has to be run a great distance to a spot where space is available. This awkward configuration is also confusing for operators. Although redundancy in printed electronic circuits is less expensive than in large physical systems, the difficulty of changing the software that controls the circuits and takes advantage of redundancy is complicated; it is difficult to ensure that new defects have not been introduced.
It is best to apply one or more of the design techniques that fall under the heading of Design-For-Reliability to ensure that long-term reliability requirements are addressed concurrently with the physical design of any system. One example of a DFR technique is RBD or the Reliability Block Diagram technique. Using this technique, each of the elements of a system is represented by a block and connected to other elements in a manner that closely represents the manner in which they interact in the actual system. Characteristics are assigned to each block; they cause it to act mathematically in the same manner as the actual component.
If the actual component has poor reliability, it will fail frequently. If it has poor availability, it will have characteristics that cause it to be down for maintenance a large portion of the time. For manually constructed RBDs, there are techniques that allow the composite reliability to be calculated by hand. It is also possible to construct RBDs in software that simulates the actual performance of real systems. These programs simulate the planned and unplanned outages of components СКАЧАТЬ