Chemistry related damage of components in thermal power plant

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Chemistry related damage of components in thermal power plant

  1. 1. CHEMISTRY RELATED DAMAGE OF COMPONENTS IN THERMAL POWER PLANT SHIVAJI CHOUDHURY
  2. 2. Chemical Transport and Corrosion Characteristics of a Drum Boiler Cycle –
  3. 3. TURBINE  Corrosion fatigue  Galvanic corrosion  Erosion  Stress corrosion cracking  Deposition  Crevice corrosion  pitting
  4. 4. Steam turbine
  5. 5. Mollier diagram with regions of chemical and corrosion effects (turbine). LP inlet
  6. 6. Mollier Diagram with LP Turbine Steam Expansion Line and Behavior of Chemical Impurities in Relation to Condensation and Corrosion
  7. 7. Heater drain and feedwater piping  Mechanism -Flow accelerated corrosion (FCA) of carbon steel.  Chemistry influence- attack by reducing feedwater conditions and high velocities, excessive hydrazine with zero oxygen ,low pH.
  8. 8. Condensate and feedwater systems  Mechanism – carbon steel and copper alloy corrosion and product transport.  Chemistry influence- low pH, acid constitutes, excess carbon dioxide and oxygen present in condensate ,alternating oxidizing and reducing conditions, excess hydrzine solubilizing magnetite.
  9. 9. Copper alloy condenser and heater tubes  Mechanism ammonia attack / condensate corrosion.  Chemistry influence- simultaneous excess ammonia ,oxygen ,and CO2,in steam synergistically oxidizing and solubbilizing copper.
  10. 10. Feedwater heater tubes  Mechanism – stress corrosion cracking Cu/Ni, monel, stainless steel.  Chemistry influence- excessive corrodents in steam synergistic with tensile stress ,corrodent concentration in crevices dry-wet transition.
  11. 11. Condenser and heater tubes  Mechanism – admiralty brass stress corrosion cracking.  Chemistry influence- excessive ammonia /chloride present in steam synergistic with residual stress at tubesheets and in u bends.
  12. 12. Feedwater heater tubes  Mechanism – copper/nickel exfoliation.  Chemistry influence- excessive oxygen on shutdown combined with thermal cycling and thermal stresses.
  13. 13. Chemical Transport Characteristics of A Drum Boiler Cycle During Normal Operation
  14. 14. Chemical Transport and Corrosion Characteristics of a Drum Boiler Cycle – Effects of startup
  15. 15. BOILER TUBES,DRUM & HEADER  Hydrogen damage  Acid phosphate corrosion  Caustic gouging  Corrosion fatigue  Scale or deposit  Induced overheating  pitting
  16. 16. Supercritical boiler
  17. 17. SUPERHEATER TUBES  Corrosion fatigue  Overheating  Pitting  Stress corrosion cracking
  18. 18. ECONIMIZER TUBES  Corrosion fatigue  Pitting  Hydrogen damage  Flow accelerated corrosion
  19. 19. REHEATER TUBES  Corrosion fatigue  Pitting  Exfoliation
  20. 20. Recommendations to Reduce Deposition  Deposition in turbines is mainly due to carry-over of impurities from the boiler.  The amount of carry-over can be reduced by lowering the feedwater purity limits, improved boiler level control, operation at lower pressures, and elimination of organic feedwater treatment chemicals which could cause foaming.
  21. 21. Exfoliation  Exfoliation of deposits from superheater and reheater tubing can cause significant damage to turbine blade surfaces and contributes to iron and copper transport to the turbine.
  22. 22. Optimization of cycle chemistry  Optimization of cycle chemistry is the easiest method for reducing impurity transport and deposition.  The optimal cycle chemistry will result in reduced corrosion and minimized impurity transport.  This is especially important if copper alloys are present in the system because the optimal pH for copper alloys and ferrous materials are not the same and the incorrect pH can result in high levels of iron or copper transport.
  23. 23. Stress Corrosion Cracking (SCC)
  24. 24. Boiler Water treatment  The primary purposes of boiler water treatment are to ensure that  (i) the steam has minimum impurities to protect the turbine  (ii) that the treatment can neutralize any contaminant ingress to prevent concentration and resultant boiler tube failures.  There are current five choices for boiler water treatment for drum cycles:  • Equilibrium phosphate treatment (EPT)  • Phosphate treatment (PT)  • All-volatile treatment (AVT)  • Caustic treatment (CT)  • Oxygenated treatment (OT)
  25. 25. THANKING YOU

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