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FMEA

Dr. Atti a Hussien Gom aaMaintenance Engin eer ing Cons ul tan t

2007 Engin eer ing serv ice - Am er ican Univers i ty in Cairo (AUC)

Failure Modes and Effects Analysis (FMEA)

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FMEA 2 Fai lure Mode Effect An alysis - Dr. Att ia Gom aa - 2007

For each Cri t ical co m po nent / i tem: Step 1: Func t ion Step 2: Func tion al Failures (full o r partial) Step 3: Failure m od es (failure rate date) definit io n Step 4: Failure Effect:

Local System Plan t Step 5: Fai lure Con sequence:

Cri t ical i ty parameters : HSE Cost Process

Severity level: Probabi l i ty level: Risk level:

Step 6: Crit ical failures (Top 5 failures)

Step 7: RCFA Step 8: Rem edy (best p ol icy se lect ion ) Step 9: Po l icy d escr ip t ion and prog ram Step 10: Pol icy plan and im plementat ion

Failure Modes and Effects Analysis (FMEA)

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A functional failure is the inability of an item to fulfill a functionto a standard of performance acceptable to the user

Functional failures can either be: Full loss of function or Partial loss of function

Example:

Function: To transfer water from tank 1 to tank 2 at 800 LPM

Functional failure: Unable to transfer any water at all Transfers less than 800 LPM

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Example : Function:

Keep system temperature between 50 C and 70 C,

Functional failures might be: Unable to raise temperature above ambient Unable to keep system temperature above 50 C Unable to keep system temperature below 70 C

Example:

Function:A hydraulic pump provides 3000 psi +/ - 200 psi.

Functional failures might be: Pump provides more than 3200 psi Pump provides less than 2800 psi

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Example

Function: The function of a hydraulic pump is to provide 3000 psi +/- 200 psi. Once the hydraulic pressure drops below 1000 psi a certain critical

component ceases function.

Functional failures: Pump provides more than 3200 psi Pump provides between 1000 psi and 2800 psi Pump provides less than 1000 psi

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Failure Modes:A failure mode is any event which causes a functional

failure

Two step Process: Identify failure modes which are likely to cause

functional failure Ascertain failure effects associated with each failure

mode

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Failure Modes: Bearing seizes Impeller comes loose Impeller jammed Coupling broken Motor burns out Inlet valve jammed Partially blocked suction line

Failure Modes:Hydraulic system failure mode High temperature

Low viscosity inadequate lubrication

Excessive thinning of lube film Low component life

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Discharge pressure low:--

--

- Knocking:--

--

Failure Modes: Reciprocating Compressor

Overheating:---

-

- It fails to attain speed:----

Excessive belt wear:--

--

- Oil in the discharge air:--

-- Pump bearing overload:

----

- Others----

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Discharge pressure low: Air leaks Leaking valves Restricted air intake Slipping belts Unloading mechanism not

operating properly Blown gaskets Worn compressor rings Defective gauge Compressor too small for

load

- Knocking: Loose motor pulley or compressor

flywheel Loose belts Lack of oil in crankcase Oil pump not functioning

Worn connecting rod bearings Worn piston pin bearing Worn main bearing Excessive crankshaft end play Excessive motor shaft end play Loose valve assemblies Loose piston Piston hitting the head, due to

foreign matter Piston hitting the head, due to

carbon deposits.


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Overheating: Poor ventilation Dirty cooling surfaces Incorrect flywheel rotation Defective valves Flywheel too close to wall Restricted air intake

- It fails to attain speed: Loose belts Low voltage Motor overload

- Excessive belt wear: Motor pulley or flywheel out of

alignment Belt too loose or too tight Belt slipping Flywheel wobble

- Oil in the discharge air: Worn piston rings Compressor air intake

restricted Restricted crankcase breather Excessive oil in compressor Wrong oil viscosity

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- Pump bearing overload: The wrong interference fit between the bearing and the shaft ( the shaft was out of

tolerance). Misalignment between the pump and its' driver.

Bent shafts. An unbalanced rotating element. Pushing the bearing too far up a tapered sleeve. Operating the pump off of its best efficiency point (B.E.P.). Shaft radial thermal expansion. Cavitation. Water hammer. Axial thrust. The bearing housing is out of round. A futile attempt to cool the bearings by cooling the bearing housing with a water hose or

some other similar system. Cooling the outside diameter of a bearing causes it to shrink,increasing the interference and causing additional stress.

Pulley driven designs. High vibration. The impeller is located too far away from the bearing. (common problem in many mixer/

agitator applications) A bad bearing was supplied counterfeit part

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Failure effects describe what happens when a failure mode occurs.

Examples of Failure Effects description

Loc al effect : Pump leaks hydraulic fluid

Next high er effect : Hydraulic system pressure drops

below 1000 psi / degraded controls

End effect : System stops

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Bra ins to rming :

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FMEA

100%

Item Function Failure

modeFailurecause

Failuremechanis

m

Failureeffects

Occ Det RPN Maintenance

task

Recomm-ended

intervalS A C

Severity

Is the part from the system or subsystem (assembly)

Is the main Task of the item

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FMEA


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

Is the manner by which a failure is observed and isdefined as non-fulfillment of one of the equipmentfunctions .

Example:

valve the failure mode is open,partially open,closed partially closed and wobble

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FMEA


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

For each failure mode there may be several failure

causes Select only potential failure to get root cause

By using why -why analysis you can get the root

cause for potential failure

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FMEA


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

For each failure cause there is one or several failuremechanisms examples of failure mechanism areFatigue ,corrosion and wear

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FMEA


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

Means what is happen when each failure mode occurs

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FMEA


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

Effect of failure is described in terms of the worst caseoutcome with respect to safety and environmental impacts,production availability and direct economic cost and all thatin numerical measure which are defined from ranking criteria

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modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

FMEA

Safety and Environment severity degree

Impact degree on Availability of production

Impact degree on C ost

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RANK SEVERITYLEVEL

DESCRIPTION

10 Catastrophic IA failure results in the major injury or death of personnel.

7 9 Critical IIA failure results in minor injury to personnel, personnelexposure to harmful chemicals or radiation, a fire or arelease of chemicals in to the environment.

4 6 Major III A failure results in a low level exposure to personnel, oractivates facility alarm system.

1 3 Minor IV

A failure results in minor system damage but does notcause injury to Personnel allow any kind of exposure tooperational or service personnel or allow any release of chemicals into environment.

FMEA

HSE severity ranking criteria

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modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

FMEA

The probability that a failure will occur during theexpected life of the system can be described in potentialoccurrence per unit time

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RANK DESCRIPTION

1An unlikely probability of occurrence during the item operating time interval.Unlikely is defined as a single failure mode (FM) probability < 0.001 of theoverall probability of failure during the item operating time interval.

2 3

A remote probability of occurrence during the item operating time interval (i.e.once every two months). Remote is defined as a single FM probability > 0.001but < 0.01 of the overall probability of failure during the item operating time

interval.

4 6

An occasional probability of occurrence during the item operating time interval(i.e. once a month).Occasional is defined as a single FM probability > 0.01 but < 0.10 of the overall

probability of failure during the item operating time interval.

7 9A moderate probability of occurrence during the item operating time interval(i.e. once every two weeks). Probable is defined as a single FM probability >0.10 but < 0.20 of the overall probability of failure during the item operatingtime interval.

10A high probability of occurrence during the item operating time interval (i.e.once a week). High probability is defined as a single FM probability > 0.20 of the overall probability of failure during the item operating interval.

FMEAOccurrence ranking criteria

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FMEA


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

This section provides a ranking based on anassessment of the probability that a failure of modewill be detected given the controls that are in place .

The probability of detection is ranked in reverse

order

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RANK DESCRIPTION

1 2 Very high probability that the defect will be detected. Verification and/orcontrols will almost certainly detect the existence of a deficiency or defect.

3 4High probability that the defect will be detected. Verification and/orcontrols have a good chance of detecting the existence of a deficiency ordefect.

5 7 Moderate probability that the defect will be detected. Verification and/orcontrols are likely to detect the existence of a deficiency or defect.

8-9 Low probability that the defect will be detected. Verification and/or

controls not likely to detect the existence of a deficiency or defect.

10Very low (or zero) probability that the defect will be detected. Verificationand/or controls will not or cannot detect the existence of a deficiency ordefect.

FMEADetection ranking criteria

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Occurrencex Severity

x Detection

RPN = O x S x D

Risk Pr io r i ty Num ber


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

FMEA

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32F il M d Eff A l i D A i G 2007


modeFailurecause

Failuremechanis

m

Failureeffects


task

Recomm-ended

intervalS A C

Severity

An appropriate maintenance action may hopefully be found by the decision logic in step 7

The identified maintenance action is performed at intervalsof fixed length.the length of the intervals is found in step 8

FMEA

014 fmea

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