failure mode and effect analysis ( fmea) power boiler
DESCRIPTION
Failure Mode and Effect Analysis ( FMEA) Power Boiler. Agenda. Introduction to FMEA. 1. Introduction to Power Boiler Causes of failures in boiler system. 2. 3. Case Study boiler pressure part. F ailure M ode and E ffects A nalysis (FMEA). DEFINITION. - PowerPoint PPT PresentationTRANSCRIPT
Failure Mode and Effect Analysis (FMEA) Power
Boiler
Agenda
1
2
3
Introduction to FMEA
Introduction to Power BoilerCauses of failures in boiler
systemCase Study boiler pressure part
Failure Mode and Effects Analysis
(FMEA)
3
• Potential Failure Mode – สภาพหรอืรูปแบบความเสยีหายของผลิตภัณฑ์ กระบวนการผลิต หรอืแมแ้ต่การบรกิาร ท่ียงัไมเ่กิดขึ้น แต่คาดวา่จะเกิดขึ้นได้ในอนาคต
• Potential Cause –สาเหตท่ีุเป็นไปได้ ท่ีก่อใหเ้กิดสภาพหรอืรูปแบบความเสยีหายกับอุปกรณ์
• Effect – ผลลัพธท่ี์เกิดขึ้นเน่ืองจากความเสยีหาย และสง่ผลโดยตรงต่อ ผลิตภัณฑ์ กระบวนการผลิต และ การบรกิารในท่ีสดุ
• Analysis – การวเิคราะหอ์ยา่งเป็นระบบ ได้แก่ การวเิคราะหก์ารออกแบบ กระบวนการ การทำางานของผลิตภัณฑ์ และรวมไปถึงการวเิคราะหข์อ้มูลท่ีเก่ียวขอ้งด้วย
DEFINITION
4
• Severity(SEV) – ค่าความรุนแรงของ Effect ในเชงิปรมิาณ
• Current Control – การควบคมุหรอืการตรวจจบัความเสยีหายท่ีดำาเนินการอยูใ่นปัจจุบนั
• Detection (DET) – ค่าความสามารถในการตรวจจบัความเสยีหายท่ีเกิดขึ้นในเชงิปรมิาณ
• Recommended Action - วธิกีารสำาหรบัป้องกันหรอืลดความเสีย่งในการเกิด Potential Cause
DEFINITION
5
• Risk Priority Number (RPN) – ค่าท่ีแสดงถึงความเสีย่งของแต่ละ Potential Cause
RPN = SEV x OCC x DET
DEFINITION
6
• ค้นหาอุปกรณ์วกิฤต• รวบรวมขอ้มูลต่างๆของอุปกรณ์ เชน่ หน้าท่ีการทำางาน
ประวติัความเสยีหาย ประวติัการบำารุงรกัษา• วเิคราะหห์า Failure Mode ท่ีเป็นไปได้ เชน่ Leakage,
Crack, Explosion, Deformation, Electrical Short เป็นต้น
• วเิคราะหห์า Effect ของแต่ละ Failure Mode เชน่ การบาดเจบ็, หยุดการเดินเครื่อง, ประสทิธภิาพลดลง เป็นต้น
• กำาหนด Severity (SEV) ของ Effect• วเิคราะหห์า Potential Cause ของแต่ละ Failure
Mode
FMEA PROCESS
7
• กำาหนด Occurrence (OCC) ของแต่ละ Potential Cause
• ระบุ Current Control ของแต่ละ Potential Cause• กำาหนดค่าความสามารถในการ Detection (DET)• คำานวณหาค่า Risk Priority Number (RPN) ของ
แต่ละ Failure Mode• หาวธิกีารสำาหรบัป้องกันหรอืลดความเสีย่งในการเกิด
Failure Mode ท่ีมค่ีา RPN มากกวา่ Criteria ท่ีกำาหนด
FMEA PROCESS
8
FMEA PROCESS
RecommendedActions
PotentialCause(s)SeverityPotentialFailureEffects
PotentialFailureModesFunctionEquipment
RPNDetectionPredictiveMethodsOccurence
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? Ho
w 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
คือ การกระทำา หรอื วธิกีารใดๆ ท่ีชว่ยลดค่า Risk Priority Number ของ Potential Cause ซึ่งสามารถทำาได้โดยการลด Severity, Occurrence, Detection อยา่งใดอยา่งหน่ึง หรอื ทัง้ 3 อยา่งพรอ้มกัน
RECOMMENDED ACTION
16
Boiler pressure part
Component Potential 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 pointECO. FAC tube leak 5 parameter model
Evap/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 flow
SH/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 susceptHdr
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 Plant Hoz. 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 partFACThermal FatigueErosionGraphitization
Conclusions
