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Vishwadeep Khatri

FMECA (Failure Mode, Effects and Criticality Analysis)

Failure Mode, Effects and Criticality Analysis (FMECA)

 

Failure Mode, Effects and Criticality Analysis (FMECA) is an extension of FMEA. The additional element is the criticality analysis that is used to determine the probability of failure modes along with the severity of their consequences. This brings the focus of remedial actions on the modes which have a high combined score of probability and severity . FMECA is usually preferred over FMEA for space and military applications. 

 

An application-oriented question on the topic along with responses can be seen below. The best answer was provided by Prashanth Datta on 8th February 2019.

 

Applause for all the respondents- Prashanth Datta, Vastupal Vashisth and Shivkumar Samant

 

Also review the answer provided by Mr Venugopal R, Benchmark Six Sigma's in-house expert.

Question

Q. 133  How is FMECA different from FMEA? When is FMECA supposed to be carried out? What is the value FMECA brings if a company is already using FMEA? 

 

This question is open till 5 PM Indian Standard Time on Friday, 8th February 2019. If your answer is selected as the best answer, your name will be permanently displayed in the World's best business excellence dictionary in the making - https://www.benchmarksixsigma.com/forum/business-excellence-dictionary-glossary/

 

Please remember, your answer will not be visible immediately on responding. It will be made visible at about 5 PM IST on 8th February 2019, Friday to all 53000+ members. It is okay to research various online sources to learn and formulate your answer but when you submit your answer, make sure that it does not have content that is copied from elsewhere. Plagiarized answers will not be approved. (and therefore will not be displayed) 

 

All Questions so far can be seen here - https://www.benchmarksixsigma.com/forum/lean-six-sigma-business-excellence-questions/

 

All rewards are mentioned here - https://www.benchmarksixsigma.com/forum/excellence-rewards/

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5 answers to this question

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With increasing demands from Customers for high Quality and Reliable Products or Service, it is posing additional challenges for the Vendors (or Service Providers) to accomplish this through more scientific approach and reliable modeling, especially at the early phase of design or planning to ensure the outcome maps to Customer requirement by the time the final deliverables are ready.  

Failure Modes and Effects Analysis (FMEA) is  a tool for evaluating possible reliability issues at the early stages of process cycle where it is simpler to acquire actions to overcome these matters, thereby improving consistency through design.

In this method, we recognize probable failure mode, evaluate its effect on the process or product and categorize actions to diminish the failures at early stages to ensure the final deliverables maps to the Customer requirements. With this approach we move from what is “find failure and fix-it” approach to “anticipate failure and prevent it”

From a Six Sigma perspective, be it identifying critical X’s or selecting effective solution to implement for identified root causes, FMEA is the Process Map based approach which provides us with the required scientific approach

In crux, FMEA uses 3 components that are applied on the identified risks i.e. it takes into account

a.      Severity – What will be the severity of the anticipated failure?

b.      Occurrence [O] – How frequently we expect this failure to occur?

c.      Detection [D] – Do we have the required controls to detect the failure?

The combination of this three results in what is called as a Risk Priority Number [RPN]. RPN = SXOXD.

Identified failures with higher RPN numbers are focused for corrective actions. Most of the times, the key controllable levers within the RPN formulae are Occurrence and Detection as Severity remains same once the issue occurs.

What is FMECA and When FMECA helps?

Let us look at a scenario as below

·        Failure item a – Severity = 8; Occurrence = 10; Detection = 2. RPN = 160

·        Failure item b – Severity = 10; Occurrence = 8; Detection = 2. RPN = 160

·        Failure item c – Severity = 8; Occurrence = 2; Detection = 10. RPN = 160

·        Failure item d - Severity = 10; Occurrence = 2; Detection = 8. RPN = 160

In this case, the RPN is same across and it needs a further deep dive. While in this simple example, we can take a SWAG by looking at Occurrence and Detection numbers and then mapping to Severity and assign priority, in real world problems, especially on design of Scientific / Military or Space equipment’s, the values can be too close to differentiate or go with a SWAG approach.

We use what is called as FMECA (Failure Mode, Effects and Criticality Analysis) methodology to handle such tricky scenarios.

 

While FMEA is an approach that identifies all possible ways that equipment can fail, and analyzes the effect that those failures can have on the system as a whole, FMECA goes a step beyond by assessing the risk associated with each failure mode, and then prioritizing corrective action that should be taken.

In FMECA, each failure mode is assigned a severity level and FMECA approach will not only identify but also investigate potential failure modes and their causes. i.e. a root cause of the reason for failure and corrective actions are evaluated for each identified failure.

A key thing to note here is, for FMECA to occur, we need to first have FMEA in place. A criticality analysis on FMEA results in FMECA.

FMECA is calculated in two ways.

Quantitative:

·        Mode Criticality = Item Unreliability x Mode Ratio of Unreliability x Probability of Loss

·        Item Criticality = SUM of Mode Criticalities.

Qualitative:

·        Compare failure modes using a Criticality Matrix, in a graphical form which keeps severity on the horizontal axis and occurrence on the vertical axis.

FMEA vs. FMECA

a.      FMEA is the first step required to generate FMECA. While FMEA focuses on failures, FMECA goes a step further to analyze the root cause for each failure

b.      FMEA focuses on problem prevention while FMECA focuses on detection and control for each identified failure mode

c.      FMEA can have multiple analysis levels while FMECA is focused at each failure level i.e. each failure is treated individually.

d.      FMEA has no criticality analysis while FMECA looks at criticality of the potential failure and the areas of the design that need the most attention.

e.      FMEA is focused on product design and process. It genrates new ideas for improvements in like designs or processes. FMECA Identifies system and its operator safety concerns. Provide new ideas for system and machinery improvements.

f.       FMEA is fairly less time consuming activity compared to FMECA. FMECA is more time consuming.

g.      FMEA requires knowledge about process, product, service and customer requirements. FMECA goes a step ahead to have additional inputs around system, machinery etc., as each failure root cause needs to be evaluated i.e. FMECA is more knowledge based activity.

 

Finally, Choosing FMECA over FMEA purely depends on the company deliverables. If the design involves delivery of critical product or service pertaining to Space, Medical or Military designs where we need to get into criticality evaluation of each potential failure, we need to go for FMECA. Please take note time should be at your side as these evaluations are time consuming.

FMEA can be a good starting point and usage of FMECA needs to be evaluated basis business case.

 

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                      Benchmark Six Sigma Expert View by Venugopal R

 

The damage or extent of damage due to a failure may be often saved or reduced if the failure is detected sufficiently early. Very common example is that if the smoke detector gives an alarm, then there is a high possibility that a fire that is about to spread could be attended and put out. It gives certain comfort when we are assured that we have adequate detection ability for certain potential failures.

 

Historical data and experience that a particular type of failure has a very low frequency of occurrence is another information that could influence our comfort levels with respect to a potential failure. We do have better quantifiable methods available today to express the ‘capabilities’ of processes, if we have to.

 

Even if the failure occurs the extent of consequential damage it could cause is yet another factor that decides the extent to which we may breathe easy.

 

We recognize that the above 3 factors have been considered in the FMEA methodology in the form of Detection, Occurrence and Severity. Thus, the worst can happen if a failure capable of causing damage of high severity, occurs frequently and catches us by surprise. Even if any one of these factors are addressed favorably, we can prevent / save damages.

 

With many knowledgeable members in this forum, the FMEA method, which is essentially a cross functional activity would not require any further detailing here.

 

While FMECA is widely defined as an extension of FMEA and the criticality calculation is also defined by MIL1629A way back, it is still possible to raise questions on clarity and uniform understanding of the method. I am not getting into the details of the calculations for the ‘qualitative and quantitative’ methods to evaluate criticality that decides prioritizing the corrective actions for risk mitigation, which most of the forum members would have been exposed to.

 

However, the emphasis on Criticality analysis is to improve the design and system reliability. Whereas the RPN number in FMEA gives a practical approach for prioritization, considering the detection capabilities as well.

 

It is my belief that we would all be in agreement that FMECA is a step up from FMEA that drives us to keep improving design robustness, preventive controls and mistake proofing as much as possible and make it a continuous effort.

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FMEA is a very effective risk analysis method and stands for Failure Modes Effects and Analysis and is a live document. FMEA is of following types:

  • Design FMEA
  • Process FMEA
  • System FMEA
  • Service Delivery FMEA

This methodology is designed to identify the potential failure modes of a product  or process before the problems occur or to assess the risk. FMEA can be conducted in design phase as well as existing products or services and can be updated at any point of time of analysis and that is why it is live document. The FMEA team determines the potential failure modes and then their potential effect of failure and potential cause of failure and identify single failure point which is crucial by giving rank to each failure with the help of RPN ( Risk Priority Number) RPN is calculated by multiplying of severity, occurrence and detection. 

 

On the other hand FMECA is FMEA with Criticality Analysis, and is of two types:

  • Quantitative 
  • Qualitative 

To use FMECA, team must define

  • the reliability/unreliability for each item at a given operating time
  • identify the item's unreliability which is contributing to each potential failure mode
  • Rate of probability of loss or severity
  • calculate criticality for each failure mode by multiplying Item unreliability, Mode ration of unreliability  and Probability of loss. 
  • Compare failure mode via a criticality matrix

FMECA is supposed to be used in following conditions:

  • to improve design of products or processes for 
    • Upping the reliability
    • Better Quality
    • Enhanced Safety
  • to improve customer satisfaction
    • for cost saving
    • by decreasing development and design cost
    • by decreasing warranty cost
    • by reducing waste NVA
  • to contribute to development of control plans, testing requirement, reliability growth analysis

FMECA adds some value to the company if that company is already using FMEA. We can see that FMEA provides only qualitative information and is used in industries as " what if" method. but in this case we are not able to identify that how critical that product or process is? FMECA fulfill this as it provides quantitative information. FMECA is extension of FMEA and provides a level of criticality to the failure modes, which can be carried out in two phases, first do FMEA and then do Criticality Analysis.

 

FMEA identifies the failure mode of a product or a process and their effects while CA ranks those failure modes in order of importance, according to severity and failure rate. FMECA does nothing but adds reliability to the failure modes. it is more suitable for hazardous control. By doing FMECA,  Designer gets helps to identify the criticality of potential failure and the areas of the design that need the most attention.With the help of Criticality Matrix, we can compare each failure mode to all other failure modes with severity.

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FMECA includes performing Criticality analysis after standard FMEA.

FMEA is typically a table-top exercise where possible causes for failure are identified. Estimates of rankings are assigned to severity, occurrence and detection – before and after the corrective action plan. FMECA goes one step forward – to determine criticality of the effect, and therefore a preventive action plan.

FMECA can be performed at any stage of system design: (i) during the early development stages; (ii) updates throughout the development; (iii) near the end of the design process.

FMECA facilitates determination of how a system can be modified to improve overall reliability and to avoid failures. Once FMECA has identified possible failures, we can explore ways to prevent the failure or to lessen their criticality. This is a step forward to FMEA.

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The chosen best answer is that of Prashanth. He has detailed FMEA, FMECA and the situations under which spending more time and effort on doing FMECA becomes viable.

 

Worth reading is Vastupal's answer, too. Good explanation!

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