Damage mechanism in boiler (thermal power plant)

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Damage mechanism in boiler (thermal power plant)

  1. 1. DAMAGE MECHANISM IN BOILER (THERMAL POWER PLANT) SHIVAJI CHOUDHURY
  2. 2. DAMAGE MECHANISM <ul><li>Corrosion fatigue </li></ul><ul><li>Thermal mechanical fatigue </li></ul><ul><li>Creep fatigue </li></ul><ul><li>Flow induced vibration fatigue </li></ul><ul><li>Flow accelerated corrosion </li></ul><ul><li>Acid phosphate corrosion, caustic gouging, hydrogen damage </li></ul><ul><li>internal pitting </li></ul><ul><li>Thermal fatigue </li></ul><ul><li>Acid dew point corrosion </li></ul><ul><li>Stress corrosion cracking </li></ul><ul><li>Short term heating </li></ul><ul><li>Long term overheating /creep </li></ul><ul><li>Low temperature creep cracking </li></ul><ul><li>Fly ash erosion </li></ul><ul><li>Fire side erosion </li></ul><ul><li>Soot blower erosion </li></ul><ul><li>Chemical cleaning damage </li></ul><ul><li>Coal particle erosion </li></ul>
  3. 3. CORROSION FATIGUE <ul><li>Where damage occurs. </li></ul><ul><li>Water touched components especially the economiser </li></ul><ul><li>Steam touched tubing containing condensate during operation transients </li></ul><ul><li>welded connection ,bends and attachments with high thermally induced force and bending movements. </li></ul><ul><li>Locations </li></ul><ul><li>Tube to header welds </li></ul><ul><li>Scallop bar attachments </li></ul><ul><li>U bend to drain line weld </li></ul><ul><li>Riser and down comer tube </li></ul>
  4. 4. THERMAL MECHANICAL FATIGUE <ul><li>Where damage occurs </li></ul><ul><li>All boiler section most likely at weld connections and attachments occasionally at bends. </li></ul><ul><li>Locations with significant thickness transitions. </li></ul><ul><li>Locations </li></ul><ul><li>Tube to header welds </li></ul><ul><li>Tube bends near header attachments </li></ul><ul><li>Lower slope region near ash hopper. </li></ul>
  5. 5. CREEP FATIGUE <ul><li>Where damage occurs </li></ul><ul><li>Components in creep regime notably SH and RH </li></ul><ul><li>Location with welded connections bends, attachments and header boreholes. </li></ul><ul><li>Locations </li></ul><ul><li>Tube to header connections. </li></ul><ul><li>SH header boreholes. </li></ul>
  6. 6. FLOW INDUCED VIBRATION FATIGUE <ul><li>Where damage occurs </li></ul><ul><li>All sections ,most notably SH and RH </li></ul><ul><li>Welded connection ,bends and attachments. </li></ul><ul><li>Locations </li></ul><ul><li>Vertical screen tubes and horizontal at near pass tubes. </li></ul>
  7. 7. FLOW ACCELERATED CORROSION <ul><li>Where damage occurs </li></ul><ul><li>High pressure portions of feed water system. </li></ul><ul><li>Water touched components in temperature (280 – 300 deg c). </li></ul><ul><li>Locations </li></ul><ul><li>Economizer inlet header stub tubes nearest the feed water inlet. </li></ul>
  8. 8. ACID PHOSPHATE CORROSION,CAUSTIC GOUGING,HYDROGEN DAMAGE <ul><li>Where damage occurs </li></ul><ul><li>Location where/fluid flow adjacent to the tube wall is disrupted </li></ul><ul><li>Location where stable steam films are likely to form </li></ul><ul><li>Locations </li></ul><ul><li>Down stream of welds </li></ul><ul><li>Location with internal deposits </li></ul><ul><li>Location with high heat transfer or high steam quality. </li></ul><ul><li>Horizontal tubes </li></ul>
  9. 9. INTERNAL PITTING <ul><li>Where damage occurs </li></ul><ul><li>Oxygen pitting prevalent in economiser , possible at wet surfaces, especially non drainable horizontal surfaces. </li></ul><ul><li>Pitting caused by improper chemical cleaning . </li></ul><ul><li>Location where condensate forms and remains as liquid during shutdown periods </li></ul><ul><li>Locations </li></ul><ul><li>Bottom of pendent loops </li></ul><ul><li>Low point in sagging horizontal tubing. </li></ul>
  10. 10. GRAPHITIZATION <ul><li>Where damage occurs </li></ul><ul><li>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) </li></ul><ul><li>Locations </li></ul><ul><li>Low temperature portions of the SH and RH. </li></ul><ul><li>Near weld heat affected zones. </li></ul>
  11. 11. THERMAL FATIGUE <ul><li>Where damage occurs </li></ul><ul><li>Where there is slag buildup high heat fluxes or flame impingement. </li></ul><ul><li>Where cyclic thermal stress is sufficient high. </li></ul><ul><li>Locations </li></ul><ul><li>Fireside ,waterwall and membraness </li></ul><ul><li>Header to stub tube attachment weld of economizer inlet. </li></ul>
  12. 12. ACID DEW POINT CORROSION <ul><li>Where damage occurs </li></ul><ul><li>Gas touched surfaces where the metal temperature are below the acid dew point. </li></ul><ul><li>Locations </li></ul><ul><li>Tubes, casings, ducts, stacks etc </li></ul>
  13. 13. STRESS CORROSION CRACKING <ul><li>Where damage occurs </li></ul><ul><li>Location with highest potential for concentration of contaminations as well as high stress. </li></ul><ul><li>Locations </li></ul><ul><li>Condensate collection points (concentration of contamination ) </li></ul><ul><li>Welds, bends, attachments ,supports (high stress location) </li></ul>
  14. 14. STRESS CORROSION CRACKING
  15. 15. SHORT TERM HEATING <ul><li>Where damage occurs </li></ul><ul><li>Locations overheating is likely. </li></ul><ul><li>Locations where partial or complete blockage of flow through tube likely. </li></ul><ul><li>Locations </li></ul><ul><li>Down stream of bends where blockage by oxide, condensate debris can occur. </li></ul><ul><li>Above orifice in lower water walls, where blockage results from feedwater corrosion products. </li></ul><ul><li>Bottom bends in SH blocks. </li></ul>
  16. 16. LONG TERM OVERHEATING /CREEP <ul><li>Where damage occurs </li></ul><ul><li>Steam cooled tubing where overheating is likely. </li></ul><ul><li>Near material change </li></ul><ul><li>Where there is a variation is gas touched length among tubes of the same material. </li></ul><ul><li>Locations </li></ul><ul><li>Final leg of tubing just before outlet header. </li></ul><ul><li>Lowest tube in a horizontal platen of leading tube in a pendant section. </li></ul>
  17. 17. LOW TEMPERATURE CREEP CRACKING <ul><li>Where damage occurs </li></ul><ul><li>High stress locations with residual stress from fabrication </li></ul><ul><li>Locations </li></ul><ul><li>Weld connection and header bore holes </li></ul>
  18. 18. FLY ASH EROSION <ul><li>Where damage occurs </li></ul><ul><li>Where non uniform high gas flows develop locally location. </li></ul><ul><li>Locations </li></ul><ul><li>Back pass in the water wall. </li></ul><ul><li>Inlet section of RH tubes. </li></ul>
  19. 19. FIRE SIDE CORROSION <ul><li>Where damage occurs </li></ul><ul><li>Water wall tubes generally at crown of the tube facing the flames </li></ul><ul><li>SH/RH tubing </li></ul><ul><li>Where metal temperature 600 deg C. </li></ul><ul><li>Locations </li></ul><ul><li>Leading sides of tubes, pendent platens </li></ul><ul><li>Tubes out of alignment </li></ul><ul><li>Spacer and uncooled hangers </li></ul><ul><li>Tubes with longer gas touched length. </li></ul>
  20. 20. SOOT BLOWER EROSION <ul><li>Where damage occurs </li></ul><ul><li>Water wall tubes </li></ul><ul><li>SH/RH tubes </li></ul><ul><li>Locations </li></ul><ul><li>Circulation Patterns wall blowers </li></ul><ul><li>SH/RH tubing in the direction path retractable blower. </li></ul>
  21. 21. CHEMICAL CLEANING DAMAGE <ul><li>Where damage occurs </li></ul><ul><li>Inside surface of fluid touched tubes </li></ul><ul><li>Locations </li></ul><ul><li>SH/RH tubes </li></ul><ul><li>Water wall. </li></ul>
  22. 22. COAL PARTICLE EROSION <ul><li>Where damage occurs </li></ul><ul><li>Fire side water wall tubes </li></ul><ul><li>Locations </li></ul><ul><li>Replaceable wear liners near the end the burners. </li></ul><ul><li>Refractories covering water wall tubes. </li></ul>
  23. 23. THANKING YOU

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