Docstoc

Modified Failure Mode and Effects Analysis

Document Sample
Modified Failure Mode and Effects Analysis Powered By Docstoc
					<div class="KonaBody">
        <!--INFOLINKS_ON-->
        <p>The marine industry is recognising the need for powerful
techniques that can be used toperform risk analysis of marine systems.
One technique that has been applied in both nationalandinternational
marine regulations and operations is Failure Mode and Effects
Analysis(FMEA). This risk analysis tool assumes that a failure mode
occurs in asystem/component through some failure mechanism.</p>
<p>The effect of this failure is then evaluated.A risk ranking is
produced in order to prioritise the attention for each of thefailuremodes
identified. The traditional method utilises the Risk Priority Number
(RPN)rankingsystem. This method determines the RPN by finding the
multiplication of factor scores. The threefactors considered are
probability of failure, severity anddetectability.Traditional FMEA has
been criticised to have several weaknesses.</p>
<p>Theseweaknesses are addressed in this Chapter. A new approach, which
utilisesthe fuzzy rulesbase and grey relation theory, is presented.
Keywords: Failure mode andeffects analysis, fuzzy set, grey theory, risk
ranking. <br><br>FMEA is intended to provide information for making risk
management decisions. Detailedprocedures on how to carry out an FMEA and
its various application in the differentindustries have been documented
in (Stamatis (1995)). Over the years severalvariations of the traditional
FMEA have been developed. Russomano and Price discussed the use
ofknowledge base system for the automation of the FMEA process (Russomano
et al. (1992),Price et al. (1992, 1995)).</p>
<p>The use of a causal reasoning model for FMEA isdocumented in (Bell et
al. (1992)). An improved FMEA methodology, which uses a single matrix to
model theentire system and a set of indices derived from probabilistic
combination to reflect theimportance of an event relating to the
indenture under consideration and to the entire system,was presented by
Kara- Zaitri (Kara-Zaitri et al. (1991, 1992)).</p>
      <!--INFOLINKS_OFF-->

                <div style="width:300px;float:right;margin:12px 0px 12px
12px">
          <script type="text/javascript">
          <!--
            AB_pos         = "intext";
            AB_lang        = "en";
            AB_cat_channel = "0016438529, ";
            AB_path        = "http://d21j60o022fwiu.cloudfront.net/";
            document.write(unescape("%3Cscript
src='http://d21j60o022fwiu.cloudfront.net/gads/controller3.js'
type='text/javascript'%3E%3C/script%3E"));
          //-->
          </script>
          <script type="text/javascript">
            google_ad_channel = "7940249670, " + AB_cat_channel +
AB_unit_channel;
            google_language = "en";
            google_ad_region = 'test';
          </script>
          <script type='text/javascript'
src='http://pagead2.googlesyndication.com/pagead/show_ads.js'></script>
        </div>
                             <!--INFOLINKS_ON-->
<p>A similar approach wasmade to model the entire ystem using a fuzzy
cognitive map (Pelaez and Bowles (1996)).Many FMEAs have a quantitative
objective, that is, to predict the likelihood of certaintypes of system
failures. This requires good information on the statistical distribution
ofcomponent failures. It also requires knowledge of dependency
relationships amongcomponents under normal operations and under external
perturbations. <br><br>FMEA can also be used as part of a qualitative
analysis (or a semi-quantitative analysis). Itattempts to identify
critical components whose failure will lead to accident, injury,
and/orproperty loss. The goal is to make systems safer or more reliable
by: 1. Evaluating theeffects ofcomponent failures on system performance.
2. Identifying those components thatare critical to safety. 3. Developing
system enhancements or administrative changes toimprove safety and/or
system reliability.</p>
<p>The major safety-related objectives of FMEA include:1. Analysis of the
system to determine effects of component failures on systemperformance
and safety. 2. Identification of components that are critical to
safety(identifying where component failure would compromise system
operation, resulting ininjuries, property damage, or other losses). 3.
Redesigning the system to improve "passive"reliability and safety. 4.
Improving maintenance routines to reduce the likelihood ofcomponent
failures. <br><br>FMEA is used to assist analysts to perform hazard
analyses and it is regarded as a supplementrather than a replacement for
hazard analyses. Safety analysts can use FMEA toverify that all safety
critical hardware has been addressed in the hazard analyses. The FMEAfor
hardware systems is an important technique for evaluating the design
anddocumenting the review process.</p>
<p>All credible failure modes and their resultant effects at the
componentandsystem levels are identified and documented. Items that meet
defined criteria areidentified as critical items and are placed on the
Critical Item List (CIL). Each entry of theCIL is then evaluated to see
if design changes can be implemented so that the item can bedeletedfrom
the CIL. Items that cannot be deleted from the CIL must be accepted by
theprogramme/project, based on the rationale for acceptance of the
risk.</p>
<p>The analysis follows awell-defined sequence of steps that encompass:
(1) failure mode, (2) failure effects,(3)causes, (4) detectability, (5)
corrective or preventive actions, and (6) rationale for acceptance.
Thegeneral process of FMECA and criticality analysis has been described
in Chapter 3. </p>
<p>In an FMEA, Risk Priority Number (RPN) can also be used to model each
failure mode in orderto rank all the failure modes. Such a process can be
divided into several steps as seen inFigure 7.1.</p>
<p>These steps are briefly explained as follows: 1. Develop a good
understanding of what the system is supposed to do when it is operating
properly. 2. Divide the system into sub-systems and/or assemblies in
order to "localise" the search for components. 3. Use Piping and
nstrument Diagrams (P&amp;ID), Process Flow Diagrams (PFD), schematics
and flow charts toidentify components and relations among components.</p>
<p>4. Develop a complete component listfor each assembly. 5. Identify
operational and environmental stresses that can affect thesystem.
Consider how these stresses might affect the performance of
individualcomponents.6. Determine failure modes of each component and the
effects of failuremodes on assemblies, sub-systems, and the entire
system. <br><br><br><br></p>        <!--INFOLINKS_OFF-->
        </div>

http://www.articlesbase.com/computers-articles/modified-failure-mode-and-
effects-analysis-5087011.html

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:7
posted:8/4/2011
language:English
pages:3
mr doen mr doen mr http://bineh.com
About just a nice girl