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LiFE
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LiFE is a way to save money and reduce risk. LiFE stands for Linear Failure-rate Estimation. LiFE models the failure rate - z(t) - of systems and components in such a way that the failure rate varies linearly with time. This is in contrast to the more common Exponential model, where the failure rate is constant, and the Weibull model, in which the failure rate varies non-linearly with time. As explained below, LiFE offers several advantages over Exponential and Weibull models, especially for risk calculations and for planned maintenance.
LiFE saves money and reduces risk for its members by offering more accurate and more convenient models of component failure rates. The advantages of these features are:
These advantages are explained in detail below.
The Exponential distribution is unrealistic for the majority of mechanical components because it does not reflect the fact that most items wear out. I.e. their failure rate is not constant, but increases with time. The Weibull distribution does model wear-out correctly, but the majority of Weibull models are non-linear and are thus more difficult to use. Very few Weibull models are available.
The LiFE models lie between the Exponential and Weibull models. They correctly model the variation of failure rate with time, but do so in a linear fashion, which makes them very easy to use. Risk, reliability, and availability calculations made with LiFE models are thus more accurate than those made on the basis of Exponential models and generally as accurate as those made with Weibull, though far more convenient. Accurate predictions are especially important in risk calculations. Currently, many risk calculations are forced to use pessimistic values of constant failure rates - leading to over-pessimistic risk assessments - and the beneficial effects of equipment overhaul or replacement cannot be taken into account. LiFE overcomes all of these problems.
It is often said that constant failure rates are the only such data which can be simply added to produce an overall failure rate for a system. This is not true. Linear models, such as LiFE, can also be added; non-linear models such as Weibull cannot. The major consequence of this is that using Weibull models requires expensive and slow stochastic simulation programs. LiFE does not. Using templates and macros, LiFE models for systems may be constructed on an ordinary spreadsheet.
Failure rate data for mechanical and process equipment is generally very poor: most published data offers constant failure rates, with little or no information on wear-out. LiFE offers much more accurate models of an item's reliability performance and can help to reveal the reasons for failure.
The Exponential distribution cannot be used to plan for the replacement of equipment before it wears out. The Weibull can, but only if the necessary data has been collected. With LiFE, it is possible to plan for replacement using the models available to the Consortium - which include data from a wide variety of plants and operating conditions.
The process and manufacturing industries are very competitive and every effort must be made to reduce down-time incurred by failures or planned maintenance. LiFE allows plant and equipment performance to be both monitored and predicted. In monitoring, weak or under-performing equipment can be quickly identified. In prediction, the effects of, say, increasing times between preventive maintenance shutdowns can be seen and optimum maintenance strategies developed.
The LiFE Consortium is a non-profit organisation owned and administered by its members. ility Engineering, which derived the original LiFE models, manages data collection, analysis, distribution of the models, and production of the necessary software on behalf of the Consortium. There are three levels of participation in the Consortium: Members; Associates; and Users.
Members contribute data to the project, pay a membership fee to cover the costs of data analysis, and receive all the LiFE models and appropriate software in return. Each Member has a vote in the Consortium management.
Associates do not contribute data to the project, pay a higher membership fee than Members, but receive the same benefits as Members. Associates also have a vote.
Users do not contribute data to the project. They pay a small membership fee for which they receive all the LiFE models. However, Users must pay for their software and have no vote in the Consortium.
LiFE depends upon Members contributing data from their plant operations to the project. Such data is naturally sensitive and is not something that would be revealed to a competitor - who may be a participant in the Consortium. To overcome this problem, ility Engineering is the sole custodian of data contributed to the project. Since "raw" data is never revealed, no one, other than the staff of ility Engineering, can know who contributed what data to a LiFE model.
Prospective participants must apply to the LiFE consortium for membership. (See the address below.) The Consortium will then request certain information from the applicant. Once this has been received and a draft confidentiality agreement signed, the Consortium votes on whether to accept the applicant. Once a successful applicant has paid the appropriate fee, the new participant receives all the benefits appropriate to their level of membership.
Applications should be sent to:
The LiFE Consortium, c/o ility Engineering, Näsilinnankatu 30-B32, 33200 Tampere, FINLAND
In addition to the models, LiFE currently offers a set of models and macros for constructing Reliability Block Diagrams (RBD) on an Excel spreadsheet. A similar facility for Availability Block Diagrams (ABD) is under development.
Members $5,000 per year. Associates $8,000 per year. Associates pay more than Members because the latter are required to provide data to the project and this incurs in-house costs which do not apply to Associates. Users $2,000 per year. Note that Users must pay separately for any LiFE software.
Information in this brochure applies from 1 June 2001. The LiFE Consortium reserves the right to review and alter the terms of participation every six months. Prospective applicants should check with the consortium for current membership details.
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LiFE
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