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Design for Reliability – Applied to development of subsea process systems
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Productions and Quality Engineering.
2010 (English)MasteroppgaveStudent thesis
Abstract [en]

New products arrive on the market every day. Whether it is a computer, a cellular phone or a car, the consumers are attacked by commercials enticing them to try “the newest invention”. Getting a customer to buy a product may be a challenge, but trying to keep him or her satisfied can be far more difficult. The regular western consumer is often well aware of what he or she demands of a product. Depending on the product, a safe failure can be accepted with a swift repair. What is not accepted is for a cellular phone to fail three times in seven months. Every product has an expected reliability. If the product cannot answer to this reliability, the manufacturer will be forced to repair products, answer to warranty claims and possibly suffer a large economic loss.

Some industries demand very high reliability of the systems they use, especially as the systems are expensive and failures could cause extreme harm. A country’s authorities have regulations for most industries and especially strict regulations for “high risk” industries. An example of a “high risk” industry is the petroleum industry. A normal requirement for new subsea process systems in this industry is an availability of 97%. To achieve such a high number, the reliability must be high as well. When a new Subsea Compression System (SCS) is built for Norwegian oil and gas production, the laws and regulations of the Norwegian authorities must be followed. These concern the maintainability and reliability of the system, as well as the safety of the system, the environment and the employees of the operator.

Reliability is an increasingly popular subject to consider for manufacturers and authorities around the world. A problem is that there are many different thoughts on how reliability can be achieved. To ensure a common understanding between authorities, manufacturer and client, several standards concerning reliability have been developed. These are often specific to an industry and one example is ISO 14224; Petroleum and natural gas industries – Collection and exchange of reliability and maintenance data for equipment.

With a large number of specified reliability standards, one should think that considering the product reliability throughout the product life cycle was normal. This is not necessarily the case. In the early parts of the product life cycle, before the physical development commences, many still believe that reliability activities are a waste of time, resources and money. What they do not consider is the fact that alterations are easier to perform before a product is manufactured than after.

A product life cycle is usually split into phases. For reliability activities in the product life cycle, Murthy et al. (2008) suggests eight phases. The first three occur during the predevelopment, the two following take place during production, while the last three are part of the post-development. The events taking place in these phases and the main tasks of a reliability engineer are well described, and it is thus a good option for Design for Reliability.

Reliability engineering has existed as an engineering discipline for several decades now. Especially the nuclear and the aerospace industries have studied and developed methods for  reliability. The methods can help detect and evaluate possible hazards and failure modes experienced by the system or product during its operational life. Some of the methods study how and why the hazards may occur, while other studies how a failure affects the overall system. Through probability estimates, the reliability of a system is found. Examples of such methods are HAZID, FMEA and FTA.

Even though we have methods for reliability straight in front of our nose, many are unaware of why they should be used. A system will never be 100% reliable, because of all the factors contributing to a reduced reliability. In all eight life cycle phases such factors can be found. Whether the manufacturer is in the car industry or the petroleum industry, many of the factors will be the same. One important issue is uncertainty, especially of the epistemic type. This is the uncertainty which we cannot know is there. It is hard to say whether the communication is good enough or if the inputs to the reliability methods are acceptable. Another factor is the human being who is unpredictable and thus unreliable. He or she partakes in every step of the product development and is thus probable to contribute to the decreased reliability. However, we cannot let the fear for such factors leading to less reliable products keep us from developing something new. By being aware of them, we can use the factors to employ reliability methods and thus increase the possibility that the methods are used correctly.

In using several methods to study the same product or system, we are more likely to get a full picture of the hazards, failures and overall product reliability. One type of analysis including several methods is the RAM analysis. This studies availability and maintainability together with reliability. The three disciplines are highly connected and equally important for the product performance. Although the RAM analysis is a very efficient tool, it cannot stand alone. It is necessary to use other methods prior to it to obtain the input, as well as some methods afterwards which can make use of the outputs.

Placing a reliability method at a random time during the design and development phases is not considered good utilization of the method. It must be used when the necessary information is available and the output can be of use. To combine and place the methods correctly, a methodology has been developed. This is described at a level meant for entirely new products, whether they are standard products or one-of-a-kind. The methodology is very general, but for industries where the reliability is very important, they should be specified. The specification can be according to the industry, but it would be even better according to organisation. A specified example has been prepared for a subsea organisation. The purpose of both the general and the specified methodology is to use them as a basis in the development of reliability programmes.

Reliability programmes are established specifically for one product development project, often for one phase at the time. It states why a method is chosen, when it should be used and the responsibilities where the product reliability is concerned. It should be based on the project risk, the project tasks and the available time and resources. Using a reliability methodology to choose the methods and their combination will simplify the programme development and ensure its quality.

For manufacturers who do not understand why reliability should be included in the design process, or how this can be done, a website is useful. The internet is highly accessible, easy to use and not time consuming. If a website for Design for Reliability first is developed, it can be used as an educational tool by and for reliability engineers. It can also help in the development of more specific methodologies and reliability programmes.

Reliability methods, methodologies and programmes will train a manufacturing organisation in thinking differently when they develop new systems and products. The outcome of the development will be products which are reliable, safe and functioning as they are supposed to. This will again lead to more satisfied customers. No customer will accept that reliability activities were left out of the product development when they stand with a failed product in their hands.

Place, publisher, year, edition, pages
URN: urn:nbn:no:ntnu:diva-12821OAI: diva2:426662
Available from: 2011-06-24 Created: 2011-06-24 Last updated: 2011-11-02Bibliographically approved

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