V3 - FMeCA

• Borth are carried out during the Design and Development Stage of a new product/service.

• But the methodologies have different/complementary objectives:

  • QFD => supports the design of a new product/service, consistently with the Voice of the Customer (VoC)

  • FMECA => aims at ensuring the reliability of a new product/process/system.

developing a reliable entity (product, system, component, process…).

• Reliability is the degree to which a generic entity performs specified functions, under specified conditions, for a specified period of time

• Quality => Satisfying needs

• Reliability => Satisfying those needs over time

• Methodology to identify and analyze:

  • All potential failure modes of the various parts of a system

  • The effects these failures may have on the system,

  • How to avoid the failures, and/or mitigate the effects of the failures on the system.

• Omdahl (1988) => FMECA is a technique used to identify, prioritize, and eliminate potential failures from the system, design or process before they reach customer

• Sematech (1992) => FMECA is a technique to “resolve potential problems in a system before they occur

• Initially, the FMECA was called FMEA (today synonym)

  • FMEA => Failure Modes and Effects Analysis

• The “C” remarks that failure modes are ranked based on their criticality

• FMECA => Failure Modes Effects andcriticality Analysis

• Should be initiated as early in the design process as possible

  • where we are able to have the greatest impact on the equipment reliability

  • A large part of the total costs are determined there

    • Lockin-costs are rouhgly 50% with the concept

    • From Pahse to Phase we have a *10 transmission of costs

• Is usually performed during the conceptual and initial-design phases of the system

  • …in order to assure that all potential failure modes have been considered and the proper provisions have been made to eliminate these failures.

• Assist in selecting design alternatives with high reliability and high safety potential during the early design phases.

• Ensure that all conceivable failure modes and their effects on operational success of the system have been considered.

• List potential failures and identify the severity of their effects.

• Develop early criteria for test planning and requirements for test equipment.

• Provide historical documentation for future reference to aid in analysis of field failures and consideration of design changes.

• Provide a basis for maintenance planning.

• Provide a basis for quantitative reliability and availability analyses.

  
  

  
  

• How can each part conceivably fail?

• What mechanisms (causes) might produce these modes of failure?

• What could the effects be if the failures did occur?

• Is the failure in the safe or unsafe direction?

• How is the failure detected?

• What inherent provisions are provided in the design to compensate for the failure?

  
  

• FMECA is carried out by a team of experts that includes individuals from different company functions and which collaborate from the beginning.

• This aspect has a positive effect, since it encourages the internal collaboration between several divisions, within the same company.

• Project Manager

• Design Engineer (hardware/software/systems)

• Test Engineer

• Reliability Engineer

• Quality Engineer

• Maintenance Engineer

• Field Service Engineer

• Manufacturing/Process Engineer

• Safety Engineer

• Bottom-up

• Top-Down

• It is used after the detailed-design phase.

• Each component on the lowest level of the WBS/BOM is analysed individually.

• The bottom–up approach is also called hardware approach.

• The analysis is complete since all components are considered.

• It is mainly used in an early-design phase, before the whole system structure is decided.

• The analysis is usually function oriented. It starts with the main system functions – and how these may fail.

• Functional failures with significant effects are usually prioritized.

• The analysis will not necessarily be complete.

• The top–down apprach may also be used on an existing system to focus on the most problematic parts.

• According to the top-down approach

  • The analysis should be carried out on an as high level in the system hierarchy as possible.

  • If unacceptable consequences are discovered on this level of resolution, then the particular element (subsystem, sub-subsystem, or component) should be divided into further detail to identify failure modes and failure causes on a lower level.

• The analysis should be carried out on an as high level in the system hierarchy as possible.

• If unacceptable consequences are discovered on this level of resolution, then the particular element (subsystem, sub-subsystem, or component) should be divided into further detail to identify failure modes and failure causes on a lower level.

• Starting from a low level (bottom-up approach) would provide a complete analysis, but at the same time be a waste of time and money!

• Design FMECA

• Process FMECA (P-FMECA)

• System FMECA

• is carried out to eliminate failures during equipment design, taking into account all types of failures during the whole life-span of the equipment.

• (P-FMECA)

• is focused on problems stemming from how the equipment is manufactured, maintained or operated.

• looks for potential problems and bottlenecks in larger processes, such as entire production lines.

• Main Steps are

  • 1) FMECA Prerequisites.

  • 2) System Structure Analysis.

  • 3) Failure Analysis and Preparation of FMECA Worksheets.

  • 4) Team Review.

  • 5) Corrective Actions

• Steps 3, 4 & 5 are executed iterative

• 1) FMECA Prerequisites.

• 2) System Structure Analysis.

• 3) Failure Analysis and Preparation of FMECA Worksheets.

• 4) Team Review.

• 5) Corrective Actions

• Define the system to be analyzed:

  • System boundaries (which parts should be included and which should not);

  • Main system missions and functions (including functional requirements);

  • Operational and environmental conditions to be considered

• Note => Interfaces that cross the design boundary should be included in the analysis

• Collect available information that describes the system to be analyzed

• Collect information about previous and similar designs from internal and external sources

• Collect available information that describes the system to be analyzed

  • drawings

  • specifications

  • component lists,

  • functional descriptions

• Collect information about previous and similar designs from internal and external sources

  • FRACAS (“Failure Reporting Analysis and Corrective Action System”, which is a methodology to keep track of all actual malfunctions of similar products/systems)

  • data

  • interviews with design personnel, operations and maintenance personnel, component suppliers

• Divide the system into manageable units – tipically functional elements

  • To what level of detail we should break down the system will depend on the objective of the analysis

• It is often desirable to illustrate the structure by a hierarchical tree diagram:

• A suitable FMECA worksheet for the analysis has to be decided

• In many cases the client (customer) will have requirements to the worksheet format

  • for example to fit into his/her maintenance management system.

• There is not a standard FMECA worksheet, but a sample covering the most relevant columns is given below:

• The FMECA analysis starts with the decomposition of the product into subsystems.

• Each subsystem is then decomposed into subcomponents.

• For each element the analyst must consider all the functions of the elements in all its operational modes and ask if “any failure of the element may result in any unacceptable system effect”.

  • If the answer is NO => no further analysis of that element is necessary.

  • If the answer is YES => the element must be examined further.

• Unique Reference

• Function

• Operational Mode

• Failure Mode

• Effect

• S

• Faolure Causes

• O

• Detection System

• D

• RPN

• Unique Reference

• unique reference to an element (subsystem or component) is given

• It may be a reference to an ID in a specific drawing, a so-called tag number, or the name of the element

• The functions of the element are listed.

• It is important to list all functions

• A checklist may be useful to secure that all functions are covered

• The various operational modes for the element are listed.

• Example of operational modes are:

  • idle

  • standby

  • running

• In applications where it is not relevant to distinguish between operational modes, this column may be omitted

• Failure Mode

• For each function and operational mode of an element the potential failure modes have to be identified and listed.

• Note that a failure mode should be defined as a non-fulfillment of the functional requirements of the functions specified in column 2.

• The effects each failure mode may have on other components in the same subsystem and on the subsystem as such (local effects) are listed

• The effects each failure mode may have on the whole system (global effects) are listed. The resulting operational status of the system after the failure may also be recorded, that is, whether the system is functioning or not, or is switched over to another operational mode.

• In some applications it may be beneficial to consider each category of effects separately, like: safety effects, environmental effects, production availability effects, economic effects, and so on.

  
  

• The Severity (S) of a failure mode is the worst potential (but realistic) effect of the failure considered on the system level (the global effects)

• The following severity classes for health and safety effects are sometimes adopted:

Failure causes

• The failure modes identified in column 4 are studied one-by-one.

• The failure mechanisms (e.g. corrosion, erosion, fatigue) that may produce or contribute to a failure mode are identified and listed.

• Other possible causes of the failure mode should also be listed.

• If may be beneficial to use a checklist to secure that all relevant causes are considered.

The Occurence (O)

• Refers to the frequency a combination of failure mode & failure cause (more in general, «item») is likely to be

• It is a natural number from 1 to 10 and it has negative connotation.

Detection System

• The various possibilities for detection of the identified failure modes (due to specific failure causes) are listed.

• Some failure modes are evident, other are hidden.

  • The failure mode «fail to start» of a pump with operational mode «standby» is an example of a hidden failure.

(un)detectability (D)

• indicator which ranks the likehood that a combination of failure cause & failure mode will be detected before the system reaches the end-user / customer.

• It is a natural number from 1 to 10 and it has negative connotation

• Failure mode => The way in which a system fails, or the way in which an equipment/machine failure occurs.

  • it focuses on the present

  • Each failure mode has one or more relevant causes.

  • It is better to avoid failures than to repair them.

  • Simpler designs are more effective in this respect than complex ones

• Failure cause => describes why a failure happened

  • it focuses on the past

• Failure effect => All about the consequences of the failure

  • it focuses on the future

• The review team studies the FMECA worksheets, the risk matrices and the RPN.

• The main objectives are:

  • To decide whether or not the system is acceptable

  • To identify feasible improvements of the system to reduce the risk.

• If improvements are decided, FMECA worksheets have to be revised and the RPN should be updated.

  • Problem solving tools like brainstorming, flow charts, Pareto charts and nominal group technique may be useful during the review process.

• reducing the likelihood of occurrence of the failure (O)

• reducing the effects of the failure (S)

• increasing the likelihood that the failure is detected before the system reaches the end-user (D)

• The risk related to the various failure modes is often presented by a

  • Risk Priority Number (RPN)

  • Risk / Cirticality Matrix

  • The two tools are complementary

    
    

• The RPN synthetically depicts the overall criticality of a generic combination of failure mode and failure cause.

• The RPN has no clear meaning since:

  • How the ranks O, S, and D are defined depend on the application and the FMECA standard that is used

  • The O, S, D, and the RPN can have different meanings for each FMECA

  • Sharing numbers between companies and groups is very difficult

• RPN= SOD

  • S = the rank of the severity of the failure mode,

  • O = the rank of the occurrence of the cause related to the failure mode,

  • D = the rank of the likehood the failure (when due to a specific cause) will be (un)detected before the system reaches the end-user/customer.

• based on the construction of the Pareto Chart. Here is an example:

• The risk associated to failure mode is a function of the frequency of the failure mode and the potential end effects (severity) of the failure mode.

• The risk may be illustrated in a so-called Risk Matrix

  • S = the rank of the severity of the failure mode,

  • O = the rank of the occurrence of the cause related to the failure mode,

• Possible actions to correct the failure and restore the function or prevent serious consequences may also be listed in the worksheet.

• Actions that are likely to reduce the frequency of the failure modes should also be recorded

• An additional column in the worksheet could possibly be dedicated for recording pertinent information not included in the other columns.

• The risk reduction related to a corrective action may be comparing the RPN for the initial and revised concept, respectively.

  
  

• Design changes to reduce the propensity to occur of failures (O)

• Engineered safety features (S)

• Safety devices (S)

• Warning devices (D)

• Procedures / Training.

• Design engineering (trough Desgin-FMECA)

  • The FMECA worksheets are used to identify and correct potential design related problems.

• Manufacturing (trhough Porcess FMECA)

  • The FMECA worksheets may be used as input to optimize production, acceptance testing, etc.

• Maintenance planning

  • The FMECA worksheets are used as an important input to maintenance planning – for example, as part of reliability centered maintenance (RCM). Maintenance related problems may be identified and corrected.

• FMECA is a very structured and reliable method for evaluating hardware and systems.

• The concept and application are easy to learn, even by a novice.

• The approach makes evaluating even complex systems easy to do.

  
  

• The FMECA process may be tedious, time-consuming (and expensive)

• The approach is not suitable for multiple failures

• Possible omission of failure modes/causes in the analysis (human errors).