damage mechanism in boiler (thermal power plant)

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By: anwarhas05 (14 month(s) ago)

Would appreciate if I could have a softcopy of this presentation for my reading/reference. Thank you.

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DAMAGE MECHANISM IN BOILER (THERMAL POWER PLANT):

1 DAMAGE MECHANISM IN BOILER (THERMAL POWER PLANT) SHIVAJI CHOUDHURY

DAMAGE MECHANISM:

2 DAMAGE MECHANISM Corrosion fatigue Thermal mechanical fatigue Creep fatigue Flow induced vibration fatigue Flow accelerated corrosion Acid phosphate corrosion, caustic gouging, hydrogen damage internal pitting Thermal fatigue Acid dew point corrosion Stress corrosion cracking Short term heating Long term overheating /creep Low temperature creep cracking Fly ash erosion Fire side erosion Soot blower erosion Chemical cleaning damage Coal particle erosion

CORROSION FATIGUE:

3 CORROSION FATIGUE Where damage occurs. Water touched components especially the economiser Steam touched tubing containing condensate during operation transients welded connection ,bends and attachments with high thermally induced force and bending movements. Locations Tube to header welds Scallop bar attachments U bend to drain line weld Riser and down comer tube

THERMAL MECHANICAL FATIGUE:

4 THERMAL MECHANICAL FATIGUE Where damage occurs All boiler section most likely at weld connections and attachments occasionally at bends. Locations with significant thickness transitions. Locations Tube to header welds Tube bends near header attachments Lower slope region near ash hopper.

CREEP FATIGUE:

5 CREEP FATIGUE Where damage occurs Components in creep regime notably SH and RH Location with welded connections bends, attachments and header boreholes. Locations Tube to header connections. SH header boreholes.

FLOW INDUCED VIBRATION FATIGUE:

6 FLOW INDUCED VIBRATION FATIGUE Where damage occurs All sections ,most notably SH and RH Welded connection ,bends and attachments. Locations Vertical screen tubes and horizontal at near pass tubes.

FLOW ACCELERATED CORROSION:

7 FLOW ACCELERATED CORROSION Where damage occurs High pressure portions of feed water system. Water touched components in temperature (280 – 300 deg c). Locations Economizer inlet header stub tubes nearest the feed water inlet.

ACID PHOSPHATE CORROSION,CAUSTIC GOUGING,HYDROGEN DAMAGE:

8 ACID PHOSPHATE CORROSION,CAUSTIC GOUGING,HYDROGEN DAMAGE Where damage occurs Location where/fluid flow adjacent to the tube wall is disrupted Location where stable steam films are likely to form Locations Down stream of welds Location with internal deposits Location with high heat transfer or high steam quality. Horizontal tubes

INTERNAL PITTING:

9 INTERNAL PITTING Where damage occurs Oxygen pitting prevalent in economiser , possible at wet surfaces, especially non drainable horizontal surfaces. Pitting caused by improper chemical cleaning . Location where condensate forms and remains as liquid during shutdown periods Locations Bottom of pendent loops Low point in sagging horizontal tubing.

GRAPHITIZATION:

10 GRAPHITIZATION Where damage occurs Graphitization of carbon and carbon molybdenum steels in form of microstructure degradation that Occurs after prolong exposure to temperature above (450 to 700 deg C) Locations Low temperature portions of the SH and RH. Near weld heat affected zones.

THERMAL FATIGUE:

11 THERMAL FATIGUE Where damage occurs Where there is slag buildup high heat fluxes or flame impingement. Where cyclic thermal stress is sufficient high. Locations Fireside ,waterwall and membraness Header to stub tube attachment weld of economizer inlet.

ACID DEW POINT CORROSION:

12 ACID DEW POINT CORROSION Where damage occurs Gas touched surfaces where the metal temperature are below the acid dew point. Locations Tubes, casings, ducts, stacks etc

STRESS CORROSION CRACKING:

13 STRESS CORROSION CRACKING Where damage occurs Location with highest potential for concentration of contaminations as well as high stress. Locations Condensate collection points (concentration of contamination ) Welds, bends, attachments ,supports (high stress location)

STRESS CORROSION CRACKING:

14 STRESS CORROSION CRACKING

SHORT TERM HEATING:

15 SHORT TERM HEATING Where damage occurs Locations overheating is likely. Locations where partial or complete blockage of flow through tube likely. Locations Down stream of bends where blockage by oxide, condensate debris can occur. Above orifice in lower water walls, where blockage results from feedwater corrosion products. Bottom bends in SH blocks.

LONG TERM OVERHEATING /CREEP:

16 LONG TERM OVERHEATING /CREEP Where damage occurs Steam cooled tubing where overheating is likely. Near material change Where there is a variation is gas touched length among tubes of the same material. Locations Final leg of tubing just before outlet header. Lowest tube in a horizontal platen of leading tube in a pendant section.

LOW TEMPERATURE CREEP CRACKING:

17 LOW TEMPERATURE CREEP CRACKING Where damage occurs High stress locations with residual stress from fabrication Locations Weld connection and header bore holes

FLY ASH EROSION:

18 FLY ASH EROSION Where damage occurs Where non uniform high gas flows develop locally location. Locations Back pass in the water wall. Inlet section of RH tubes.

FIRE SIDE CORROSION:

19 FIRE SIDE CORROSION Where damage occurs Water wall tubes generally at crown of the tube facing the flames SH/RH tubing Where metal temperature 600 deg C. Locations Leading sides of tubes, pendent platens Tubes out of alignment Spacer and uncooled hangers Tubes with longer gas touched length.

SOOT BLOWER EROSION:

20 SOOT BLOWER EROSION Where damage occurs Water wall tubes SH/RH tubes Locations Circulation Patterns wall blowers SH/RH tubing in the direction path retractable blower.

CHEMICAL CLEANING DAMAGE:

21 CHEMICAL CLEANING DAMAGE Where damage occurs Inside surface of fluid touched tubes Locations SH/RH tubes Water wall.

COAL PARTICLE EROSION:

22 COAL PARTICLE EROSION Where damage occurs Fire side water wall tubes Locations Replaceable wear liners near the end the burners. Refractories covering water wall tubes.

THANKING YOU :

23 THANKING YOU