Your SlideShare is downloading. ×
  • Like
Corrosion
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Now you can save presentations on your phone or tablet

Available for both IPhone and Android

Text the download link to your phone

Standard text messaging rates apply
Published

 

Published in Engineering , Technology , Business
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads

Views

Total Views
97
On SlideShare
0
From Embeds
0
Number of Embeds
0

Actions

Shares
Downloads
5
Comments
0
Likes
0

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 1. Corrosion
  • 2. Type of Corrosion • Uniform • Galvanic • Pitting and Crevice Corrosion • Stress Corrosion Cracking • Erosion • Microbiologically Induced Corrosion
  • 3. Uniform Corrosion • Can be a good or a bad thing • Corrosion occurs evenly over the surface • Oxide layers can be very tough – Magnetite • Fe3O4
  • 4. Effect of pH • Magnetite (for example) – Low pH no oxides form – High pH porous Fe(OH)3.xH2O forms – pH 10-12 ideal range for carbon steel • Different metals require different conditions for uniform corrosion • pH is controlled to control uniform corrosion
  • 5. Galvanic Corrosion • Chemical reactions • Electrons removed from one reactant travel through an external circuit • On material tends to disappear
  • 6. Galvanic Cell ANODECATHODE -e -e -e (Fe)(Cu) Fe ++ ions Corrosion Product ELECTROLYTE (H2O + NaCl) H2 Bubbles 2e- + 2H+ H2 (bubbles) Fe++ + 2 OH - Fe (OH)2 (corrosion product) Fe Fe++ + 2e- In the Electrolyte: At the Cathode: Reactions At the Anode: H2O OH- + H+
  • 7. Cathodic Protection • Each metal has a different potential to donate electrons • Anode always corrodes • To protect a metal – Select a metal that more easily donates electrons – Build a cell with metal to be protected as cathode
  • 8. Factors Affecting Galvanic Corrosion • Oxygen concentration of the electrolyte • Temperature • Conductivity of the electrolyte • Cathode/anode surface area
  • 9. Pitting and Crevice Corrosion Scale Region where pit will form Metal Electrolyte (H2 O plus dissolved oxygen)
  • 10. Stress Corrosion Cracking • Three conditions required for most common kind – Metal under tensile stress – Dissolved Oxygen – Chloride Ion • Brittle cracks form at the sites of stress • Failure can be fast • Failure can occur at stress loads far below yield strength
  • 11. Erosion Corrosion • Flow removes protective layer • New protective layer forms using up metal • Promoted by – High flow – Turbulent conditions – Particulates in fluid • Concern with feeders in HTS
  • 12. Example of Erosion Corrosion
  • 13. Microbiologically Induced Corrosion • Bacteria in water – Can be in presence of oxygen or not – Bacteria form a nodule • Similar to pitting corrosion.
  • 14. General Corrosion Control • Eliminate oxygen • Eliminate chloride ion • Maintain pH levels • Prevent stagnation • Chlorinate
  • 15. HTS pH Control inner zone outer zone TEMP. ( °C ) 225 240 255 270 285 300 0 2 4 6 8 10 pH 9.3 pH 10.2 pH 9.7 342SOLUBILITYOFFeO(µgFe/kgHO) PNGS BNGS-A Reactor Inlet Header PNGS BNGS-A Reactor Outlet Header
  • 16. pH Control • Add LiOH for low pH • Ion exchange columns for high pH • Lithium tends to collect in the pressurizer – pH goes up if water goes to main system – Called lithium hide out – Possible pH excursions during cool down
  • 17. Dissolved Oxygen HTS • Oxygen is corrosive – More so in hot water • Attacks zirconium, iron, their protective oxide coatings • Continuous source through radiolysis of D2O • Controlled by adding excess D2 or H2 • Explosion Hazard
  • 18. Conductivity HTS • Used for troubleshooting • Not controlled
  • 19. pH Secondary Side • pH controlled by adding chemicals – Ammonia (from decomposed hydrazine) – Morpholine • Chemicals must be volatile
  • 20. Dissolved O2 Secondary Side • O2 is corrosive particularly if Cl- is present • Three levels of removal – Air extraction – Deaerator – Hydrazine addition • Environmental hazard – chemicals discharged in boiler blow off
  • 21. Conductivity Secondary Side • Conductivity of boiler water shows the presence of bad boiler things • Specifically cation conductivity is measured – Measures the conductivity of anions Cl-, SO4 -, HCO3 - – IX is used to replace cations with H+ – Conductivity sensitive to the anions
  • 22. Moderator Normal • Stainless steel system • Requires neutral pH and low conductivity • Deuterated IX columns remove all impurities • Conductivity monitored • pH is used for troubleshooting
  • 23. Moderator Over Poisoned • pH 4-6 to prevent gadolinium nitrate precipitation • pH is monitored
  • 24. Moderator Chemistry Control • Proper use of IX’s • Prevent air in-leakage
  • 25. Sludge and Scale Boiler Tube HT Fluid Scale Flakes Boiler Water Deposits/Sludge Pile Corrosion occurs here Boiler Tubesheet or Tube Support Plate
  • 26. For You to Do • Read the section on corrosion pp. 19-37 • Answer questions p. 38