Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

111

TOOL OF RISK MANAGEMENT: FAILURE MODE AND EFFECTS ANALYSIS AND FAILURE MODES, EFFECTS AND CRITICALITY ANALYSIS Katarína RIPLOVÁ University of Žilina, Faculty of Management Science and Informatics, Slovak Republic e-mail: [email protected] Abstract Keywords: Failure mode and effects analysis, Failure modes, effects and criticality analysis, criticality analysis, risk priority numbers, risk management. 1

INTODUCTION Risk Management is a process of identifying hazards associated with a product, estimating and evaluating the associated risks, controlling these risks, and monitoring the effectiveness of the control. The process includes Risk Analysis, Risk Evaluation, and Risk Control. Risk Management uses a Failure mode and effects analysis (FMECA) and Failure modes, effects and criticality analysis (FMCEA) as a tool when evaluating and controlling risks. Failure mode and effects analysis (FMEA) is a method (first developed for systems engineering) that examines potential failures in products or processes. It may be used to evaluate risk management priorities for mitigating known threatvulnerabilities. 2

FAILURE MODE AND EFFECTS ANALYSIS FMEA process was originally developed by the US military in 1949 to classify failures "according to their impact on mission success and personnel/equipment safety". FMEA has since been used on the 1960s Apollo space missions. In the 1980s it was used by Ford to reduce risks after one model of car, the Pinto, suffered a fault in several vehicles causing the fuel tank to rupture and it to subsequently burst into flames after crashes.

112

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

Calculate Risk Priority Number Values (O x S x D)

Start FMEA

BELLOW CUTOFF

Identify Team Members and FMEA Descriptions

Review against Acceptable RPN Ratings

Identify Manufacturing Operation Process Flow

Identify Potential Failure Modes for Each Key Step/function in the Manufacturing Opertation Process Identify Potential Failure Mode Causes and Effects

Identify Occurance (O), Severity (S) and Detection (D) Ratings

Complete for All Steps/ Function?

ABOVE CUTOFF

Define Planned Controls and Implement Corrective Action as Needed Recalculate RPN Based on Implemented Actions if Required

Route FMEA for Approvals and File. Periodic Review und Update

NO YES

Figure 1 FMEA flowchart [3] FMEA Analysis is very important for dynamic positioning systems. FMEA is often applied through the use of a FMEA table combined with a rating chart to allow designers to assign values to the: - Severity of potential failures

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

113

- Likelihood of a potential failure occurring - The chance of detection within the process FMEA is a prevention tool used to assess, manage, and reduce risk associated with failure or potential failure of products, processes, services, and other systems. This approach is summarized in the flowchart in Figure 1. FMEA can be used as an assessment tool to identify potential risk. Cause-andeffect model is shown in Figure 2. The model illustrates the FMEA risk assessment concept. Causes

Effects Failure mode

Figure 2 Cause and effect model [3] FMEA is most commonly applied but not limited to design (Design FMEA) and manufacturing processes (Process FMEA). Both Design and Process FMEAs address three issues for each potential failure mode: the severity of the effect of the failure downstream, the probability of occurrence of the failure, and the likelihood of prevention or detection of the failure by design or process controls. Rankings based on ordinary scales from one to ten are used. Design FMEA (DFMEA) identifies potential failures of a design before they occur. DFMEA then goes on to establish the potential effects of the failures, their cause, how often and when they might occur and their potential seriousness. Design FMEA addresses the design intent and assumes that the design will be manufactured or assembled accordingly. The Design FMEA does not rely on process controls to overcome potential design weaknesses but takes into consideration technical and physical limitations of manufacturing and assembly processes. Process FMEAs (PFMEA) are based on manufacturing or assembly processes used to make the product. Process flow diagrams and risk assessments form the basis for the Process FMEA. Process flow diagrams illustrate the flows of the manufacturing and assembly processes, the inspection points. Risk assessment is used to determine high risk parts of the process. The Process FMEA assumes that the product as designed will meet the design intent. PFMEA is a systemized group of activities intended to: - Reognize and evaluate the potential failure of a product/process and its effect - Identify actions which could eliminate or reduce the occurrence, or improve detectability, document the process - Track changes to process-incorporated to avoid potential failures

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

114

FMEA and RCA Failure Mode and Effect Analysis uses the opposite approach of Root Cause Analysis. Ways FMEA and RCA differ: - FMEA is proactive and RCA is reactive

3

FMEA occurs during development and RCA occurs after-the-fact FMEA prevents errors and RCA satisfies patients or requirements FMEA helps processes to work and RCA changes processes that do not work FMEA encourages good outcomes and RCA changes bad outcomes

RISK MANAGEMENT AND FAILURE MODES, EFFECTS AND CRITICALITY ANALYSIS If we want to find one definition of risk management it is difficult, because there are many of them. Risk Management is the process of measuring, or assessing, risk and developing strategies to manage it. Strategies include transferring the risk to another party, avoiding the risk, reducing the negative effect of the risk, and accepting some or all of the consequences of a particular risk. Traditional risk management focuses on risks stemming from physical or legal causes (e.g. natural disasters or fires, accidents, death, and lawsuits). 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 are Risk Priority Numbers and Criticality Analysist. 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 [12]: RPN = Severity x Occurrence x Detection (1) 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 FMEA. There are two types of Criticality Analysis: quantitative and qualitative. To use the quantitative criticality analysis method, the analysis team have to define the reliability/unreliability for each item, at a given operating time, to identify the portion of the item’s unreliability that can be attributed to each potential failure mode, to 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:

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

115

Mode Criticality = IU x MR x P (2) Where: IU .....Item Unreliability MR ...Mode Ratio of Unreliability P........Probability of Loss The result of the Criticality Analysis will leads itself to the development of a Criticality Matrix. The failure mode criticality number for each specific failure mode (Cm) is calculated as follows: Cm = β – α - λP – t (3) Where: Cm .... Failure mode criticality number β .......Conditional probablity of failure effect, α .......Failure mode ratio, λP ......Partfailure rate per million hours, t ........Duration of the relevant mission phase (operation). The criticality number of each assembly (or system) is calculated per each severity category. This criticality number is the sum of the specific failure mode criticality numbers related to the particular severity category: m

Cr =∑ (β – α - λP – t)i (4) i=1

Where m......Number of failure modes at the particular severity category. Β – e . g (β – 1 ) (5) The resulting FMECA analysis will enable a criticality matrix to be constructed, figure 3. The criticality matrix displays the distribution of all the failure mode criticality numbers according to the severity category and referring to the criticality scale. The scale is divided into five levels [6]: - level A: frequent. The high probability is defined as a probability which is equal or bigger than 0.2 of the overall system probability of failure during the defined mission period, - level B: reasonable probable. The reasonable (moderate) probability is defined as probability which is more than 0.1 but less than 0.2 of the overall system probability of failure during the defined mission period, - level C: occasional probability. The occasional probability is defined as a probability, which is more than 0.01 but less than 0.1 of the overall system probability of failure during the defined mission period,

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

116

- level D: remote probability. The remote probability is defined as a probability, which is more than 0.001 but less than 0.01 of the overall system probability of failure during the defined mission period, - level E: extremely unlikely probability. The extremely unlikely probability is defined as probability which is less than 0.001 of the overall system probability of failure during the defined mission period. INCREASED CRITICALY

Probability of number Increasing level of Probability)

Criticaly number Cr

high A B

C

D

E

low IV

III

II

I

Severity classification (Increasing level of Probability)

Figure 3 Criticality matrix [6] A severity classification category assigned to each failure mode depending upon its effects of an equipment and/or system operation. The severity classification are listed below [6]: - category I : catastrophic, failure which may cause death or weapon system loss (i.e. aircraft, tank, missile, ship, etc.) - category II: critical, a failure which may cause severe injury, major property damage, or major system damage which will result in a mission loss. - category III: marginal, a failure which may cause minor injury, minor property damage, and minor system damage which will result in a delay or loss of availability or mission degradation.

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

117

- category IV: minor, a failure not serious enough to cause injury, property damage, or system damage, but which will result in unscheduled maintenance or repair. Criticality is a relative measure of the consequences of a failure mode and its frequency of occurrence. FMECA can be a starting point for many other types of analyses, figure 5, including: - System Safety Analysis - Production Planning - Test Planning and Validation - Repair Level Analysis - Logistics Support Analysis - Maintenance Planning Analysis

System Safety Analysis Maintenance Planning Analysis

Test Planning

FMECA

Pruduction Planning

Logistics Support Analysis

Repair Level Analysis

Figure 4 Starting point FMEA 4

CONCLUSION FMEA is applied for a prospective and a retrospective risk analysis. risk analysis, analyses are made constantly of the current schedule, personnel, and resource situation in order to detect and prevent possible problems at an early stage. The Purpose of an FMEA/FMCEA

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

118

FMEAs help focus on and understand the impact of potential process or product risks. FMEA is a systematic way to recognize and evaluate the potential failures of a product or process. It provides a formal mental discipline for eliminating or reducing the risks of product failure. It also serves as a living document, providing a method of organizing and tracking concerns and changes through product development. The best time to start the FMEA is before a failure is designed into a product or manufacturing process. FMEAs help reduce crises during product development and launch and thus reduce costs, since early, up-front changes tend to cost less than late, downstream ones. The corrective action review and evaluation can avoid creating new concerns, and the cost impact of changes can be evaluated during development. FMEAs can also be used to develop new equipment or to evaluate the operations of existing equipment and systems. FMEA is an interactive process of continuous improvement that involves team effort. Functional areas involved include design, materials, manufacturing, assembly, packaging, shipping, service, recycling, quality, reliability, vendors, and customers. The purpose of the FMCEA is to rank each failure mode as identified in the FMEA, according to each failure mode's severity classification and its probability of occurrence. When to use FMEA The FMEA is based on a qualitative approach, where the FMECA takes a Quantitative approach and is an extension of the FMEA, assign a criticality and probability of occurrence for each given failure mode. An FMEA is a tool to: - Identify the relative risks designed into a product or process. - Initiate action to reduce those risks with the highest potential impact. - Track the results of the action plan in terms of risk reduction. - Use it when designing products or processes, to identify and avoid failureprone designs. - Use it when investigating why existing systems have failed, to help identify possible causes and remedies. - Use it when investigating possible solutions, to help to - select one with an acceptable risk for the known benefit of implementing it. - Use it when planning actions, in order to identify risks in the plan and hence identify countermeasures. The 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

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

119

and corrective action information that can be used as a resource in future troubleshooting efforts and as a training tool for new engineers. Advantages and Disadvantages of FMEA FMEA is useful mostly as a survey method to identify major failure modes in a system. It is not able to discover complex failure modes involving multiple failures or subsystems, or to discover expected failure intervals of particular failure modes. For these, a different method called fault tree analysis is used. Its structured analysis evaluates processes before implementation. Time and resources for FMEA are allocated during development, when changes are easier and less expensive to make. Benefits of FMEA An FMEA provides benefits to both the manufacturer and the customer. Some of these benefits include: - Assists in determining the best possible design and development options to provide high reliability and manufacturability potential. - Assists in considering the possible failure modes and their effect on the reliability and manufacturability of the product. - Provides a well-documented record of improvements from corrective actions implemented. - Provides information useful in developing test programs and in-line monitoring criteria. - Provides historical information useful in analyzing potential product failures during the manufacturing process. - Provide new ideas for improvements in similar designs or processes.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8]

DELLAMANO, H.: Reliability Services in the Design Phase http://www.opsalacarte.com/Pages/reliability/reliability_des_fmeca.htm http://www.ihi.org/ihi/workspace/tools/fmea/ LEE, s.: Using FMEA to Develop Alternatives to Batch Testinghtt http://www.devicelink.com/mddi/archive/04/01/018.html http://www.medialabinc.net/keyword-etails.asp?keyword=fmea&courseid=1451 http://www.mech.utah.edu http://www.mtain.com/relia/relfmeca.htm http://www.national.com/quality/fmea.html

http://www.relex.com/resources/fmea.asp

Journal of Information, Control and Management Systems, Vol. 5, (2007), No.1

[9] [10] [11] [12] [13]

120

http://www.simpletech.cn/support/fmea.html SMEJKAL, V., RAIS, K.: Řízení rizik. Grada. Praha, 2003. ISBN 80-247-0198-7 http://www.tzi.de/~uniform/gdpa/methods/m-fmea.htm http://www.weibull.com/basics/fmea.htm http://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis#Applications