Failure Mode and Effect Analysis (FMEA) Power

Boiler

Agenda

1

2

3

Introduction to FMEA

Introduction to Power BoilerCauses of failures in boiler

system

Case Study boiler pressure part

Failure Mode and Effects Analysis

(FMEA)

3

• Potential Failure Mode – สภาพหรื�อรืปแบบความเส�ยหายของผลิ�ตภ�ณฑ์� กรืะบวนการืผลิ�ต หรื�อแม!แต"การืบรื�การื ที่�$ย�งไม"เก�ดข'(น แต"คาดว"าจะเก�ดข'(นได!ในอนาคต

• Potential Cause –สาเหต+ที่�$เป,นไปได! ที่�$ก"อให!เก�ดสภาพหรื�อรืปแบบความเส�ยหายก�บอ+ปกรืณ�

• Effect – ผลิลิ�พธ์�ที่�$เก�ดข'(นเน�$องจากความเส�ยหาย แลิะส"งผลิโดยตรืงต"อ ผลิ�ตภ�ณฑ์� กรืะบวนการืผลิ�ต แลิะ การืบรื�การืในที่�$ส+ด

• Analysis – การืว�เครืาะห�อย"างเป,นรืะบบ ได!แก" การืว�เครืาะห�การืออกแบบ กรืะบวนการื การืที่/างานของผลิ�ตภ�ณฑ์� แลิะรืวมไปถึ'งการืว�เครืาะห�ข!อมลิที่�$เก�$ยวข!องด!วย

DEFINITION

4

• Severity(SEV) – ค"าความรื+นแรืงของ Effect ในเชิ�งปรื�มาณ

• Current Control – การืควบค+มหรื�อการืตรืวจจ�บความเส�ยหายที่�$ด/าเน�นการือย"ในป2จจ+บ�น

• Detection (DET) – ค"าความสามารืถึในการืตรืวจจ�บความเส�ยหายที่�$เก�ดข'(นในเชิ�งปรื�มาณ

• Recommended Action - ว�ธ์�การืส/าหรื�บป3องก�นหรื�อลิดความเส�$ยงในการืเก�ด Potential Cause

DEFINITION

5

• Risk Priority Number (RPN) – ค"าที่�$แสดงถึ'งความเส�$ยงของแต"ลิะ Potential Cause

RPN = SEV x OCC x DET

DEFINITION

6

• ค!นหาอ+ปกรืณ�ว�กฤต• รืวบรืวมข!อมลิต"างๆของอ+ปกรืณ� เชิ"น หน!าที่�$การืที่/างาน

ปรืะว�ต�ความเส�ยหาย ปรืะว�ต�การืบ/ารื+งรื�กษา• ว�เครืาะห�หา Failure Mode ที่�$เป,นไปได! เชิ"น Leakage,

Crack, Explosion, Deformation, Electrical Short เป,นต!น

• ว�เครืาะห�หา Effect ของแต"ลิะ Failure Mode เชิ"น การืบาดเจ7บ, หย+ดการืเด�นเครื�$อง, ปรืะส�ที่ธ์�ภาพลิดลิง เป,นต!น

• ก/าหนด Severity (SEV) ของ Effect• ว�เครืาะห�หา Potential Cause ของแต"ลิะ Failure

Mode

FMEA PROCESS

7

• ก/าหนด Occurrence (OCC) ของแต"ลิะ Potential Cause

• รืะบ+ Current Control ของแต"ลิะ Potential Cause• ก/าหนดค"าความสามารืถึในการื Detection (DET)• ค/านวณหาค"า Risk Priority Number (RPN) ของ

แต"ลิะ Failure Mode• หาว�ธ์�การืส/าหรื�บป3องก�นหรื�อลิดความเส�$ยงในการืเก�ด

Failure Mode ที่�$ม�ค"า RPN มากกว"า Criteria ที่�$ก/าหนด

FMEA PROCESS

8

FMEA PROCESS

RecommendedActions

RecommendedActions

PotentialCause(s)

PotentialCause(s)

SeveritySeverityPotential

FailureEffects

PotentialFailureEffects

PotentialFailureModes

PotentialFailureModes

FunctionFunctionEquipmentEquipment

RPNRPNDetectionDetectionPredictive

MethodsPredictive

MethodsOccurenceOccurence

9

FMEA PROCESS

Component

Potential

Failure Mode

Potential

Failure Effects

SEV

Potential

Causes

OCC

Current Control

s

DET

RPN

Recommended

Actions

What is the Inpu

t? What can go wrong with the

Input?

What is the Effect

on the

Outputs?

How

bad? What

are the Causes

?

How Often?

How can this be

found?

How

Well?

What can be

done?

10

SEVERITY

11

Effect Severity of Effect Ranking

Hazardous – W/O

Warning

Very high severity ranking – Affects operator, plant or maintenance personnel, safety and or affects non-compliance with government regulations, without warning.

10

Hazardous – With

Warning

High severity ranking – Affects operator, plant or maintenance personnel, safety and/or affects non-compliance with government regulations with warning.

9

Very High

Downtime of more than 8 hours or the production of defective parts for more than 4 hours.

8

High Downtime of between 4 and 8 hours or the production of defective parts for between 2 & 4 hours.

7

Moderate

Downtime of between 1 and 4 hours or the production of defective parts for between 1 and 2 hours.

6

SEVERITY

12

Effect

Severity of Effect Ranking

Low Downtime of between 30 minutes and 1 hour or the production of defective parts for up to 1 hour.

5

Very Low

Downtime of between 10 and 30 minutes but no production of defective parts.

4

Minor Downtime of up to 10 minutes but no production of defective parts

3

Very Minor

Process parameter variability not within specification limits. Adjustment or other process controls need to be taken during production. No downtime and no production of defective parts.

2

None Process parameter variability within specification limits. Adjustment or other process controls can be taken or during normal maintenance

1

OCCURENCE

13

Probabilityof

Failure

Criteria: No. of

failures within Hrs of

operation.

Criteria: The reliability based

on the users required time.

Ranking

Failure Occurs every Hour

1 in 1 R(t) <1 %: MTBF is about 10% of the User’s required time.

10

Failure occurs every shift

1 in 8 R(t) = 5%: MTBF is about 30% of User’s required time

9

Failure occurs every day

1 in 24 R(t) = 20%: MTBF is about 60% of the User’s required time.

8

Failure occurs every week

1 in 80 R(t) = 37%: MTBF is equal to the User’s required time.

7

Failure occurs every month

1 in 350 R(t) = 60%: MTBF is 2 times greater than the User’s required time.

6

OCCURENCE

14

Probability

of Failure

Criteria: No. of

failures within Hrs of

operation.

Criteria: The reliability based

on the users required time.

Ranking

Failure occurs every 3 months

1 in 1000 R(t) = 78%: MTBF is 4 times greater than the User’s required time.

5

Failure occurs every 6 months

1 in 2500 R(t) = 85%: MTBF is 6 times greater than the User’s required time

4

Failure occurs every year

1 in 5000 R(t) = 90%: MTBF is 10 times greater than the User’s required time.

3

Failure occurs every 2 years

1 in 10,000

R(t) = 95%: MTBF is 20 times greater than the User’s required time.

2

Failure occurs

> 5 years

1 in 25,000

R(t) = 98%: MTBF is 50 times greater than the User’s required time.

1

DETECTION

15

Detection

Criteria Ranking

Very Low

Design or Machinery Controls cannot detect a potential cause and subsequent failure, or there are no design or machinery controls.

10

Low Design or Machinery controls do not prevent the failure from occurring. Machinery controls will isolate the cause and subsequent failure mode after the failure has occurred.

7

Medium

Design controls may detect a potential cause and subsequent failure mode. Machinery controls will provide an indicator of imminent failure.

5

High Design controls may detect a potential cause and subsequent failure mode. Machinery controls will prevent an imminent failure and isolate the cause.

3

Very High

Design controls almost certainly detect a potential cause and subsequent failure mode, machinery controls not required.

1

ค�อ การืกรืะที่/า หรื�อ ว�ธ์�การืใดๆ ที่�$ชิ"วยลิดค"า Risk Priority Number ของ Potential Cause ซึ่'$งสามารืถึที่/าได!โดยการืลิด Severity, Occurrence, Detection อย"างใดอย"างหน'$ง หรื�อ ที่�(ง 3 อย"างพรื!อมก�น

RECOMMENDED ACTION

16

Boiler pressure part

ComponentPotential Failure

Mode

Potential Effect(s) of

FailureSev

Potential Cause(s)/ Mechanism(s) of

FailureOcc

tube          

Preheater Fire side corrosion Tube leak,gas side p. drop, low eff. acid dew point

ECO. FAC tube leak 5 parameter modelEvap/Wall FAC tube leak 5 parameter model

  Underdeposit Corrosion tube leak high heat flux, low flow, high debris water

  Short Term Overheat tube burst low water flowSH/RH tube Graphitization Tube burst mis mat'l, high temp.

  High Temp. Corrosion tube burst   mat'L, corrosive media.,temp.

  Long Term Overheat tube burst   low flow, inside oxide thk., high heat flux

  Type IV Crack tube burst   service condition, weld mat'l

  Dissimilar Weld tube burst   shaffer diagram.Pipe        

MSP Weld Defect pipe leak   poor joint fitup & weld control

RH Weld Defect, Type IV Crack pipe leak   poor joint fitup & weld control

Bypass Thermal Fatigue pipe leak   poor design, operation high cycle,mat'L suscept

Hdr         ECO T Way FAC leak   5 parameter model

Final SH Crack dissimiilar weld leak    

Introduction to Power Boiler &Causes of failures in boiler system

Combine Cycle Power Plant

Thermal Power PlantHoz. flow

Ver. flow

Sub. Cri Pressure

Sup. Cri Pressure18

Causes of failures in boiler systemCorrosion Crack Degradation- Water Side - Weld Defect - Graphitization FAC Lack of

Fusion - Creep

Under deposit

Undercut Weld Creep -> IV Crack

- Fire Side Base Metal Creep High Temp. - Spherodisation Low temp. Erosion SCCReference Nalco Guide

Weld Defect

DISCONTINUITY POSSIBLE CAUSES

Excessive Convexity Slow travel speed  that allows weld metal to build up Welding currents too low

Insufficient Throat A combination of Travel speed to fast and current too highImproper placement of weld beads when multiple pass welding

Undercut 

Amperage too high Arc length too long increasing the force of the arc so that it cuts into cornersImproper weld technique causing the corners to be left unfilled or cut intoGroove joint not completely filled and overlapped

Insufficient Leg Size Using the wrong electrode angle causing the weld to be deposited to heavily on one sideUsing the wrong angle on multiple pas welds Causing the welds to overlap incorrectly

Poor Penetration Amperage too low Travel speeds too fast Using too large an electrode for the root of the jointImproper electrode angle at the root of the jointImproper weave techniqueUsing the wrong electrode for the desired joint penetration: (using E-6013 instead of E-6010)

Poor Fusion Amperage too low Travel speeds too fast Improper electrode angle at the sides of the jointImproper weave technique that does not allow enough time at the sides of the jointUsing the wrong electrode for the application

Overlap Amperage too low and /or travel speed too slowElectrode too large with low currents

Porosity Dirty base metal  painted or galvanized surfaces Arc length too long especially with E-7018 ElectrodesMoisture in low hydrogen electrodesWind or fans strong enough to break down the shielding gas

Slag Inclusions Improper manipulation of the electrode especially with E-6013Improper cleaning and slag removal between multiple pass welds

Cracks Using the wrong Electrode for the applicationUsing Excessively high amperage on some metals

Excessive Spatter Amperage too highElectrode angle too extremeArc length too long

Boiler tube Failure

Case Study boiler pressure part

FACThermal FatigueErosionGraphitization

Conclusions