FAILURE MODES EFFECT ANALYSIS/FAILURE MODES EFFECT CRITICALITY ANALYSIS

FMEA and FMECA

An Overview of Basic Concepts and Directory of Other Resources

Failure Mode and Effects Analysis (FMEA) and Failure Modes, Effects and Criticality Analysis (FMECA) are methodologies designed to identify potential failure modes for a product or process, to assess the risk associated with those failure modes, to rank the issues in terms of importance and to identify and carry out corrective actions to address the most serious concerns.

Although the purpose, terminology and other details can vary according to type (e.g. Process FMEA, Design FMEA, etc.), the basic methodology is similar for all. This document presents a brief general overview of FMEA / FMECA analysis techniques and requirements.

FMEA / FMECA Overview
In general, Failure Modes, Effects and Criticality Analysis (FMEA / FMECA) requires the identification of the following basic information:

• Item(s)
• Function(s)
• Failure(s)
• Effect(s) of Failure
• Cause(s) of Failure
• Current Control(s)
• Recommended Action(s)
• Plus other relevant details

Most analyses of this type also include some method to assess the risk associated with the issues identified during the analysis and to prioritize corrective actions. Two common methods include:

• Risk Priority Numbers (RPNs)
• Criticality Analysis (FMEA with Criticality Analysis = FMECA)

Published Standards and Guidelines
There are a number of published guidelines and standards for the requirements and recommended reporting format of failure mode and effects analyses. Some of the main published standards for this type of analysis include SAE J1739, AIAG FMEA-3 and MIL-STD-1629A. In addition, many industries and companies have developed their own procedures to meet the specific requirements of their products/processes. Figure 1 shows a sample Process FMEA in the Automotive Industry Action Group (AIAG) FMEA-3 format. Click to enlarge the image.

Figure 1 [Enlarge]

Basic Analysis Procedure for FMEA or FMECA
The basic steps for performing an Failure Mode and Effects Analysis (FMEA) or Failure Modes, Effects and Criticality Analysis (FMECA) include:

• Assemble the team.
• Establish the ground rules.
• Gather and review relevant information.
• Identify the item(s) or process(es) to be analyzed.
• Identify the function(s), failure(s), effect(s), cause(s) and control(s) for each item or process to be analyzed.
• Evaluate the risk associated with the issues identified by the analysis.
• Prioritize and assign corrective actions.
• Perform corrective actions and re-evaluate risk.
• Distribute, review and update the analysis, as appropriate.

Risk Evaluation Methods
A typical failure modes and effects analysis incorporates some method to evaluate the risk associated with the potential problems identified through the analysis. The two most common methods, Risk Priority Numbers and Criticality Analysis, are described next.

Risk Priority Numbers
To use the Risk Priority Number (RPN) method to assess risk, the analysis team must:

• Rate the severity of each effect of failure.
• Rate the likelihood of occurrence for each cause of failure.
• Rate the likelihood of prior detection for each cause of failure (i.e. the likelihood of detecting the problem before it reaches the end user or customer).
• Calculate the RPN by obtaining the product of the three ratings:

RPN = Severity x Occurrence x Detection

The RPN can then be used to compare issues within the analysis and to prioritize problems for corrective action. This risk assessment method is commonly associated with Failure Mode and Effects Analysis (FMEA).

Criticality Analysis
The MIL-STD-1629A document describes two types of criticality analysis: quantitative and qualitative. To use the quantitative criticality analysis method, the analysis team must:

• Define the reliability/unreliability for each item and use it to estimate the expected number of failures at a given operating time.
• Identify the portion of the item’s unreliability that can be attributed to each potential failure mode.
• Rate the probability of loss (or severity) that will result from each failure mode that may occur.
• Calculate the criticality for each potential failure mode by obtaining the product of the three factors:

Mode Criticality = Expected Failures x Mode Ratio of Unreliability x Probability of Loss

• Calculate the criticality for each item by obtaining the sum of the criticalities for each failure mode that has been identified for the item.

Item Criticality = SUM of Mode Criticalities

To use the qualitative criticality analysis method to evaluate risk and prioritize corrective actions, the analysis team must:

• Rate the severity of the potential effects of failure.
• Rate the likelihood of occurrence for each potential failure mode.
• Compare failure modes via a Criticality Matrix, which identifies severity on the horizontal axis and occurrence on the vertical axis.

These risk assessment methods are commonly associated with Failure Modes, Effects and Criticality Analysis (FMECA).

Applications and Benefits
The Failure Modes, Effects and Criticality Analysis (FMEA / FMECA) procedure is a tool that has been adapted in many different ways for many different purposes. It can contribute to improved designs for products and processes, resulting in higher reliability, better quality, increased safety, enhanced customer satisfaction and reduced costs. The tool can also be used to establish and optimize maintenance plans for repairable systems and/or contribute to control plans and other quality assurance procedures. It provides a knowledge base of failure mode and corrective action information that can be used as a resource in future troubleshooting efforts and as a training tool for new engineers. In addition, an FMEA or FMECA is often required to comply with safety and quality requirements, such as ISO 9001, QS 9000, ISO/TS 16949, Six Sigma, FDA Good Manufacturing Practices (GMPs), Process Safety Management Act (PSM), etc.

You can use something as simple as a paper form or an Excel spreadsheet to record your FMEA / FMECA analyses. However, if you want to establish consistency among your organization's FMEAs, build a "knowledge base" of lessons learned from past FMEAs, generate other types of reports for FMEA data (e.g. Top 10 Failure Modes by RPN, Actions by Due Date, etc.) and/or track the progress and completion of recommended actions, you may want to use a software tool, such as ReliaSoft's Xfmea, to facilitate analysis, data management and reporting for your failure modes and effects analyses. More information on applications and benefits...

References
The following resources provide additional information on FMEA / FMECA.

Web Resources

• SAE International: The Society for Automotive Engineers provides the ability to purchase the J1739 and ARP5580 standards, as well as the AIR4845 document.
• AIAG: The Automotive Industry Action Group provides the ability to purchase the AIAG FMEA Third Edition (FMEA-3) guidelines.
• IEC: The International Electrotechnical Commission provides the ability to purchase the IEC 60812 standard.
• Reliability-Related Military Handbooks and Standards on weibull.com: This site provides access to U.S. Department of Defense standards and handbooks in PDF format, including the MIL-STD-1629A standard for Failure Modes, Effects and Criticality Analysis (FMECA) analysis.
• FMEA Info Center: This site provides information on books, publications, standards, software, consultants and other resources related to Failure Mode and Effects Analysis (FMEA). It also provides an on-line discussion list.
• NASA STI Special Bibliography for FMEA: NASA's Scientific and Technical Information (STI) program provides a "sampler bibliography" that contains abstracts for documents related to Failure Mode and Effects Analysis ( FMEA) and Failure Modes, Effects and Criticality Analysis (FMECA) in the NASA STI Database.

Printed Resources

• Automotive Industry Action Group (AIAG), Potential Failure Mode and Effects Analysis (FMEA Third Edition or Fourth Edition), July, 2001 or June, 2008.
• Automotive Industry Action Group (AIAG), Advanced Product Quality Planning and Control Plan (APQP First Edition or Second Edition), June, 1994 or July 2008.
• International Electrotechnical Commission (IEC), Analysis Techniques for System Reliability: Procedure for Failure Mode and Effects Analysis (FMEA), July 1985.
• Kececioglu, Dimitri, Reliability Engineering Handbook Volume 2. Prentice-Hall Inc., Englewood Cliffs, New Jersey, 1991. Pages 473-506.
• McDermott, Robin E., Raymond J. Mikulak and Michael R. Beauregard, The Basics of FMEA. Productivity Inc., United States, 1996.
• Stamatis, D.H., Failure Mode and Effect Analysis: FMEA from Theory to Execution. American Society for Quality (ASQ), Milwaukee, Wisconsin, 1995.
• Society of Automotive Engineers (SAE), Aerospace Recommended Practice ARP5580: Recommended Failure Modes and Effects Analysis (FMEA) Practices for Non-Automobile Applications, June 2000.
• Society of Automotive Engineers (SAE), Surface Vehicle Recommended Practice J1739: (R) Potential Failure Mode and Effects Analysis in Design (Design FMEA), Potential Failure Mode and Effects Analysis in Manufacturing and Assembly Processes (Process FMEA), and Potential Failure Mode and Effects Analysis for Machinery (Machinery FMEA), June 2000.
• U.S. Department of Defense, MIL-STD-1629A: Procedures for Performing a Failure Mode Effects and Criticality Analysis, Cancelled in November, 1984.