Failure Modes and Effects Analysis

Dr. M. Hodkiewicz

2Hodkiewicz – “FMEA”

Contents• Definitions and background• Design and Process FMEA• Terminology• The FMEA Process• Discussion• Future developments

Learning Outcomes• After this session you will be able to:

– Explain the role of FMEA/ FMECA in the AM life-cycle process

– Identify key components in the FMEA process– Conduct and report on a simple FMEA exercise– Appreciate challenges with FMEA implementation – Appreciate how FMEA can be updated by

integration into the routine maintenance environment

References (1 of 2)[1]Dailey, K.W., The FMEA Pocket Handbook. 2004: DW

Publishing company.[2]McDermott, R.E., R.J. Mikulak, and M.R. Beauregard,

The basics of FMEA. 1996: Productivity.[3]SAE J1739: Potential Failure Modes and Effects analysis

in Design and Potential Failure Effects in Manufacturing and Assembly Processes Reference Manual - Draft for review. 2005.

[4]MIL-STD-1629A: Procedure for performing a failure mode, effects and criticality analysis. 1980.

References (2of 2)[5]Tweeddale, M., Managing Risk and Reliability of Process

Plants. 2003: Gulf Publishing.[6]ISO 14224: Petroleum and natural gas industries -

Collection and exchange of reliability and maintenance data for equipment. 1999.

[7]IEC 60050-191: International Electrotechnical Vocabulary - Dependability and Quality of Service. 1990.

[8] MIL-STD-721C Definitions of terms for reliability and maintainability. 1995.

[9] Macaulay, D., The Way things work. 1988: RD Press.[10] What's wrong with your existing FMEAs, 24/7

Quality.com.

Software/Internet Resources• FMEA InfoCentre:

http://www.fmeainfocentre.com/• http://www.weibull.com/basics/fmea.htm• On-line paper: B. S. Dhillon, Failure modes

and effects analysis-Bibliography, Microelectronics

MH1 Add from Plant Maintenance web siteMelinda Hodkiewicz; 2006/07/16

Definitions and background

What is FMEA?• MIL-STD-1629A [4]: “The purpose of FMEA is to study the

results or effects of item failure on system operation and to classify each potential failure in terms of its severity”

• SAE J1739 [3]: “A FMEA can be described as a systemised group of activities intended to: (a) recognise and evaluate the potential failure of a product/process and its effect, (b) identify actions which could eliminate or reduce the chance of a potential failure occurring, and (c) document the process. It is complementary to the process of defining what a design or process must do to satisfy the customer”.

Informal definition• “FMEA is a non-quantitative analysis that aims to

identify the nature of the failures that can occur in a system, machine, or piece of equipment by examining the sub-systems or components in turn, considering for each the full range of possible failure types and the effect on the system of each type of failure.

• FMECA is an extension of FMEA that assigns a ranking to both the severity of the possible effects and their likelihood, enabling the risks to be ranked”[From 5]

Philosophy• FMEA is a ‘common sense’ procedure.• The aim is to provide a framework/process to assist

the thought process of a competent person engaged in identifying system or design problems.

• The process focuses on what we want the equipment to do not what it actually is. By identifying what functions need to be achieved, we can then identify situations when the equipment does not perform the required function, and focus attention on the related causes and effects.

An example FMEA report

For what activities is FMEA appropriate?

• New designs, new technology, or new process • Modifications to existing design or process • Use of existing design or process in a new

environment, location or application • Identify monitoring and inspection practices for

equipment• Identifying failure codes for the CMMS system• Part of the RCM process

Design and Process FMEA

Types of FMEA• FMEA can be applied to a physical

entity or to a functional entity.• For example,

– it can be applied to a particular equipment (design FMEA), or to

– A process function (process FMEA).

Example

2ND GAS EXPORT COMPRESSION TRAIN

DISCH. COOLER

DEHYD. PACK

LP STAGE COMPRESSION

HP SUCTION

LP DISCH.COOLER

HP STAGE COMPRESSION

ANTI-SURGE (LP) ANTI-SURGE (HP)

PCV 1(LP)

TO SUBSEA PIPELINE

LPSUCTION

LP SUCTION COOLER GAS

EXPORT HEADER

MGEARBOX

Design FMEA (DFMEA)• Identifies functional requirements of a design• Evaluates the initial design for manufacturing,

assembly, service and recycling requirements.

• Used by Design Team. The customer for the design team may be the end user, the design engineer of the higher level assemblies or the manufacturing process/assembly team.

Design FMEA in the AM context

• If you are the maintenance engineer in an oil and gas or similar facility, it is unlikely that you will be involved in a design FMEA process.

• However, if you are (1) troubleshooting equipment, (2) developing failure codes or (3) engaged in RCM, then information from the design FMEA conducted by the manufacturer may be helpful.

Process FMEA (PFMEA)• Identifies the process functions, process

requirements, potential product and process failures and the effects on the customer.

• Identifies process/operational variables on which to focus controls.

• Traditionally used by Manufacturing/ Assembly/ Process team. The customer can be a downstream team, a service operation, or even government regulations.

• In the AM arena, there is some overlap between HAZOP and Process FMEA for operational equipment

Machinery FMEA (MFMEA)• This is a new category in the draft SAE

J1739-2005 aimed at Plant Machinery and Tools.

• In AM, machinery FMEA may be applied to important maintenance support tools such as lathes, cranes, milling machines etc.

• There are similarities in approach between DFMEA, PFMEA and MFMEA.

RelationshipSYSTEM

MACHINERY

PROCESSDESIGN

Components, sub-systems, main systems

Manpower, Machine, Method,

Material, Measurement, Environment

Tools, Work stations, production

lines, operator training, processes,

gauges

Approaches to FMEA• A FMEA may be based on a • (a) hardware/physical, or (b) functional approach.• (a) The hardware approach lists individual hardware

items and analyses their possible failure modes.• (b) The functional approach recognises that every

item is designed to perform a number of functions that can be classified as outputs. The outputs are listed and their failure modes analysed.

• For complex systems, a combination of (a) and (b) may be required.

Maintenance• For Maintenance Personnel, FMEA is a direct

approach to the reduction of maintenance costs through the elimination of faults that give rise to the maintenance task.

• FMEA identifies the most critical problems first paving the way for improved maintenance techniques

• FMEA on installed equipment provides suggestions for redesign and ‘proactive maintenance’– (From: Hastings, 1998, Reliability and Maintenance Course

notes, QUT)

Terminology

Terms & definitions (1)• Failure: Termination of the ability of an item to

perform a required function [7]• Required function: Function, or combination of

functions, of an item which is considered necessary to provide a given service [7]

• Failure mode: The manner by which a failure is observed. Generally describes the way the failure occurs and its impact on equipment operation [4].

Terms & definitions (2)• Failure cause: • (1) Circumstance during design, manufacture or

use which have led to failure [7]. • (2) The physical or chemical processes, design

defects, quality defects, part misapplication, or other processes which are the basic reason for failure or which initiate the physical process by which deterioration proceeds [4].

• Failure mechanism: Physical, chemical or other process which has led to failure [7]

Terms & definitions (3)• Failure effect: The consequence a failure

mode has on the operation, function, or status of an item [4].

• Critical failure: Failure of an equipment unit which causes an immediate cessation of the ability to perform its required function [6]

• Non-critical failure: Failure of an equipment unit which does not cause an immediate cessation of the ability to perform its required function [6]

Terms & definitions (4)• Criticality: A relative measure of the

consequences of a failure mode and its frequency of occurrence [4]

• Severity: The consequence of a failure mode. Severity considers the worst potential consequence of a failure, determined by degree of injury, property damage, or system damage that could ultimately occur.

Terms & definitions (5)• Reliability [8]: The probability that an item will

perform its intended function(s) for a specified interval under stated conditions.

• Undetectable (Hidden) failure: A postulated failure mode in the FMEA for which there is no failure detection method by which the operator is made aware of the failure [4].

The FMEA Process

DEFINE SCOPE

DEFINE LEVEL OF ANALYSIS

IDENTIFY FUNCTIONS AND FAILURE MODES

IDENTIFY EFFECTS OF FAILURE & SEVERITY RATING

ASSIGN OCCURRENCE (FREQUENCY) RATING

IDENTIFY CONTROLS & ASSIGN DETECTION RATING

IDENTIFY CAUSES OF FAILURE

CALCULATE RISK PRIORITY NUMBER FOR EACH EFFECT

RANK FAILURE MODES FOR ACTION

RANK FAILURE MODES FOR ACTION & ANALYSIS

FMEA flowsheet

Steps in the FMEA process (from [3])

1. Define the SCOPE of the study (System boundary)

2. Decide on the LEVEL of analysis (System, sub-system, components)

3. For the selected system or sub-systems, IDENTIFY and list functions and the potential failure modes. Failure modes may be assessed at the hardware or functional level, or a combination of both.

Step 3 in the maintenance context

• IDENTIFY and list failure modes …– Information on what failed and when on a specific

piece of equipment or in a system should be available in the maintenance management system (CMMS)

– Depending on the organization of the system and the data quality processes then there may be a failure code indicating the cause of failure.

Continued …4. For the selected system or sub-system and for

each of the identified failure mode, identify the POTENTIAL EFFECT(s) on the machine, system or process and the relative importance (SEVERITY) of the effect(s).

Continued …4. continued.The effects could include:

– Injury to people– Damage to the environment– Damage to equipment– Loss of production– Reduced quality of production– Increased cost of operation

Continued …5. Assign an (OCCURRENCE) ranking to each failure

mode 6. For each failure mode for each element, identify

CONTROLS– The means of preventing the failure by design,

operating and maintenance practices, and management.

– The means of detecting the failure and responding effectively to it

– The means (if any) of limiting the impact of the failure, particularly by design changes.

Continued ..7. For each of the controls assign a DETECTION ranking8. Calculate the Risk Priority Number (RPN) for each

effect9. Prioritise the failure modes for action (RANKING)10. Take ACTION to eliminate or reduce the high risk

failure modes11. Calculate the resulting RPN as the failure modes are

reduced or eliminated.

DEFINE SCOPE

FMEA flowsheet

Selecting the team• Have you got representatives from all the

stakeholders?• Do you have a facilitator?• Are the team members familiar with the

subject but from diverse vantage points?

Setting up the meeting• Provide advance notice• Who will record meeting minutes?• Who will facilitate?• Establish ground rules• Provide and follow an agenda• Evaluate meetings• Who will you report the results to?• Allow no interruptions

Brainstorming rules [1]• Participants must be enthusiastic and give their

imagination free reign• The recorder must be given time to record ideas• The ideas must be concisely recorded and placed

in clear view of participants• Idea evaluation occurs after the session• Set a firm time limit• Clearly define the problem you want solved• The moderator must keep the group on subject and

moving• When time is up, the group rank the ideas

Selecting systems/sub-systems and components

• It is important to have an agreed taxonomy when breaking systems down into sub-systems and components.

• This may be agreed with by the team for a specific FMEA, or they may choose to use a taxonomy described in a Standard, for example: [6].

Deciding level for analysis [6]

Purge airCooling/ heating systemFilter/ CyclonePulsation damperFlange jointsOthers

ReservoirPump with motorFilterCoolerValvesPipingOil

ControlActuating deviceMonitoringValvesInternal Power supply

SupportCasingImpellerShaftRadial bearingThrust bearingSealsValvesPipingCylinder linerPiston Diaphragm

GearboxVariable driveBearingsSealsLubricationCoupling to driveCoupling to driven unit

Maintain-able item

Miscellaneous

LubricationControl & monitoring

Pump unitPower transmission

Subunit

Defining functions and failure modes

• Required function: Function, or combination of functions, of an item which is considered necessary to provide a given service [7].

• Be explicit so it is clear when a functional failure has occurred.

• Failure mode: The manner by which a failure is observed. Generally describes the way the failure occurs and its impact on equipment operation [4].

Defining functions and failures• Equipment: Diesel Engine Crankshaft• Function: To convert reciprocating force from

pistons and connecting rods into rotational force through the bearings and crankshaft to the drive coupling at a maximum rate of up to ‘x’ kW per cylinder at up to ‘y’ rpm continuously or ‘z’ kW per cylinder at ‘w’ rpm for up to ‘v’ hours in 12.

• Question: What are some possible functional failures?

Functional failure• Function: To convert reciprocating force from

pistons and connecting rods into rotational force through the bearings and crankshaft to the drive coupling

• Functional Failure: Unable to convert and transmit any force from the pistons

Failure mode (1 of 2)

• Failure Mode (1): Damaged crankshaft axial alignment bearing (ball race) due to lubrication failure

• Failure Effect (1): Crankshaft will float axially and foul on crankcase, misalignment of gear drives.

• Existing controls (1): Daily fuel dilution test, weekly oil screen, change oil and filters as required.

Failure mode (2 of 2)• Failure Mode (2): Damaged crankshaft axial

alignment bearing (ball race) due to bearing material failure

• Failure Effect (2): Same as (1). Crankshaft will float axially and foul on crankcase, misalignment of gear drives.

• Existing controls (2): Routine vibration monitoring. Replace bearing as required.

Examples of failure modes• For mechanical equipment

– Cracked, Loosened, Fractured, Leaking, Oxidised, Loss of structural support, Deformed, Slips, Disengages too fast, Failure to transmit torque.

• For electrical equipment– No signal, Intermittent signal, Inadequate

signal, Sticking, Drift,

Process Failure modes (from [4])

Structural deficiencySTD

UnknownUNKAbnormal instrument readingAIR

OtherOTHParameter deviationPDE

Minor in-service problemsSEROverheatingOHE

Plugged/chokedPLUOperation without demandOWD

Leakage in closed positionLCPAbnormal output - highAOH

Internal leakageINLAbnormal output – lowAOL

External leakage process mediumELPFail to function on demandFTF

External leakage lubricant, hydraulic fluidELUDelayed operationDOP

NoiseNOIFail to regulateFTR

VibrationVIBFail to open on demandFTO

Erratic outputEROFail to close on demandFTC

Low outputLOOSpurious stopSPS

High outputHIOFail to stop on demandSTP

BreakdownBRDFail to start on demandFTS

DefinitionFailure modeDefinitionFailure mode

Examples of design failure causes• Improper tolerances• Incorrect (stress or other) calculations• Wrong assumptions• Wrong material• Lower grade components• Lack of design standards• Incorrect algorithm• Insufficient lubrication capability• Excessive heat

Examples of failure causes in manufacturing & process

Poor FMEAS20Tools improperly prepared10

Stress connections19Equipment improperly set-up9.

Environment18Adjustment error8.

Failure to enforce controls17Mis-operation7.

Hardware failure16Processing incorrect work piece6.

Lack of safety15Wrong parts5.

Fatigue14Missing parts4.

Bad ‘recipe’13Set up errors3.

Improper equipment maintenance

12Processing errors2.

Poor control procedures11Skipped steps1.

Example of design failure mechanisms

• Yield• Fatigue• Material instability• Creep• Wear• Corrosion• Chemical oxidation

Examples of design controls• Prototype testing• Design reviews• Worst case stress analysis• FEA• Fault tree analysis

ACTIVITY• Workshop activity to identify functions

and failure modes• The aim of this activity is to see how the

functions are broken down and assessed at the different levels.

Bicycle for (Male) Commuter [from 3]

• List some design objectives (functions) of a regular commuter bicycle

• For two of the functions identify potential failure modes?

Bicycle example continued• Identify some of the sub-systems of the

bicycle• For one subsystem: Identify at least two

functions and failure modes.

DEFINE SCOPE

FMEA flowsheet

Recording the FMEA process

Severity (S)• A relative ranking, within the scope of the

individual FMEA. • A reduction in Severity can be achieved by

design change to system, sub-system or component, or a redesign of the process.

• The rank depends on the evaluation criteria. Examples of suitable tables are available in the literature. Some companies may have standard tables.

Severity Tables (from [1])

Occurrence (O)• This is the likelihood that a specific

cause/mechanism (listed in the previous column) will occur. Occurrence is usually based on ranking charts and is a relative rating within the scope of the FMEA.

Occurrence Tables (from [1])

Controls• (1) prevent to the extent possible the failure

mode or cause from occurring or reduce the rate of occurrence, or

• (2) detect the cause/ mechanism and lead to corrective action, or

• (3) detect the failure mode or cause should it occur.

Detection ranking (D)• A rank associated with the best type of

control listed in the previous column. Detection is a relative ranking within the scope of the FMEA.

Detection Tables (from [1])

Risk Priority number• RPN = (S) x (O) X (D)• Within the scope of the individual

FMEA, the resulting value (between 1 and 1000) can be used to rank order the concerns identified by the process. This allows the highest ranking items to be identified and addressed.

Action plans• Recommended action(s)• Corrective action should be addressed at high

severity, high RPN issues. The intent of the action is to reduce rankings in the order of preference: severity, occurrence and detection.

• Actions taken and resulting revised ratings• After a preventative/corrective action has been

identified, estimate and record the resulting S, O and D rankings. All revised rankings should be reviewed to see if further action is necessary.

Design FMEA actions• An increase in design validation/ verification

actions will result in reduction of ‘detection’ranking only

• Occurrence ranking can be effected by removing or controlling the causes or mechanisms through design revision

• Design revision can also affect severity ranking

DEFINE SCOPE

FMEA flowsheet

Discussion

Drawbacks (1 of 2)• 1. The ratings and RPN number are subjective• 2. The categorisation into failure mode and cause

does not allow for thinking in terms of causal chains, the’ 5 WHYS’ or other processes. For each mode you must have a failure cause. This cause may have a deeper cause. Sometimes the cause and the mode are the same.

• 3. It can be difficult to control brainstorming sessions

Drawbacks (2 of 2)• 4. Legal ramifications: if you have identified a failure

mode but you have not eliminated it, are you culpable of negligence?

• 5. Approach makes it difficult to allow for the interaction of two benign failure models.

• 6. FMEA often assumes that the part is ‘in tolerance’. To assume otherwise expands the scope of FMEA considerably. However in real life, out of spec parts are common.

Common problems with FMEA (from [10])

• Engineers often do not follow a recognised standard and company format

• Multiple descriptions of the exact same failure mode, cause or effect

• No recommendations or corrective action for high RPM items

• Inconsistent documents between parts of the study• No document control or revision control• Engineers don’t see a value in a FMEA, they find

them a pain to perform and labour intensive• Companies perform a FMEA study when it is too late.

Benefits of design FMEA (1 of 2)

• Aids in objective evaluation of design, including functional requirements and design alternatives

• Evaluating the initial design for manufacturing, assembly, service and recycling requirements

• Increasing the probability that potential failure modes and their effects on the system have been considered in the design/development process.

Benefits of design FMEA (2 of 2)

• Developing a ranked list of potential failure modes according to their effect on the customer (can be the assembly team), thus establishing a priority system for design improvements, development and validation testing/analysis.

• Providing an open-issue format for recommending and tracking risk reduction actions

• Providing future reference eg lessons learned, to aid in analysing field concerns, evaluating design changes and developing advanced designs

Benefits of Process FMEA• Identifies the process functions and requirements• Identifies potential product and process related failure

modes• Assesses the potential customer effects of the

failures • Identifies process variables on which to focus

process controls• Develops a ranked list of potential failure modes thus

establishing a priority system for preventative/corrective action considerations

• Documents the results of the analysis of the manufacturing, assembly or production process

Future developments

FMEA and Failure Analysis: Closing the Loop Between Theory

and Practice

Dr Joanna Sikorska, Imes Group LtdDr Melinda Hodkiewicz, UWA

Presented to Engineers Australia Conference, May 2006

Before and after events• FMEA identifies failure modes, causes and

effects based before they occur.• The Computerized Maintenance

Management system (CMMS) records events/failures as/after they occur.

• QUESTION: Is there benefit in a feedback loop from the CMMS to update the FMEA failure records and O, D, and S values?

What happens now?• FMEA process:

– Proactive but subjective analysis of hypothetical– Integrated into other methodologies– Large upfront costs– Results or benefits rarely substantiated– Static process– Non-inclusive– Completed reports collect dust– Data & process owned by engineering

What happens now?• Failure analysis process & storage in CMMS:

– Retrospective & selective view of reality – Hampered by bad/missing data– Evolved functionality– Dictated by accountants– Interfaces ruled by codes & structure– Poor integration with non-financial systems– Widely distributed, used & disliked– Data & process owned by ops/maintenance

What happens now?• FMEA & CMMS data rarely linked &/or integrated

• Why?– Different process owners – Non-uniform coding between FMEA & CMMS

systems– Reporting may be at different hierarchy levels– Hierarchies may be different– Tradition

Issues to overcome• Structural issues

– Consistency of coding & reporting– Adapt systems to users not administrators

• Data quality issues– Ensure data is fit for purpose– Real-time data verification– Up-skill data collectors

Issues to overcome• Organizational issues

– Implement cultural change– Include the disenfranchised– Increase frequency & quality of feedback– Improve status of data collectors

• Technical challenges are trivial by comparison

What is our vision?• Living FMEA• Live links between theoretical (FMEA) &

actual (CMMS)• Inclusive process, shared ownership for both

datasets• Managed, audited & utilized data processes• Live feeds into various business improvement

systems

How can we get there?• Living FMEA model • See Handout

Benefits• Aids prioritization & guides business response• Improves reliability analysis from:

– Reduced reliance on free text– More consistent failure classification

• Facilitates maintenance optimization• Uncovers disparity between theory & reality• Creates knowledge workers• Ensures a recorded, managed & auditable process

More benefits• Reviews & measures success of FMEA

process

• Maximizes return on FMEA investment

• Supplies future FMEAs with objective data

• Future studies become easier

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