1. Limiting Factors for Steam Parameters
Presented by,
Nithin Seenivasan,
FH Aachen, Jülich, 15th December, 2011

2. Contents of the Presentation
Introduction
Main Steam Parameters
Various Limiting Factors for Steam Parameters
Corrosion
Material Limitations
High Steam Velocity Limitations
Impure Feedwater
Fuel Heating Value Limitations
References

3. What is Steam?!
Technical term for water vapor, the gaseous phase of water, which is formed when water boils.

4. What is Steam?! Source: Alliance Knowledge, 2011 Source: Petaflop Blog
Water
Steam
Steam + Water Droplets
Source: Alliance Knowledge, 2011
Source: Petaflop Blog
Heat
Water Vapor
Water Droplets + Vapor
Condensation
Condensation

5. What is Steam?!
Technical term for water vapor, the gaseous phase of water, which is formed when water boils.
Dry Steam is INVISIBLE

6. Main Steam Parameters Pressure Temperature 40 Mpa (400 Bar)
Mass Flow of Steam
40 Mpa (400 Bar)
900 °C (1173 K)
600 Kg/s
Example of an Exploded Chemical plant in Nevada, USA
Source: Exponent Consultants

7. Limiting Factors of Steam Parameters
Oxidation Corrosion
Fuel Ash Corrosion
Carburization
Hydrogen Damage
Creep
Fatigue
Erosion
Increased Losses
Water Hammer
Impure Feed Water
Fuel Heating Values
Corrosion
Material Properties

8. Limiting Factors of Steam Parameters

9. Corrosion
Source: Checkthishouse Inc

10. Oxidation Corrosion
Oxidation rates of metals increases with Temperature
Typical Value for tubes mm / Year
Parts built below Oxidation Limit
A high magnification optical microscope view of a cross-section through a failed Aluminum Tube reveals that a localized area of the coating on the ID surface has been replaced by oxide scale (arrow)
Source: Metallurgical Technologies Inc.

11. Hydrogen Damage Caused by Excessive Deposition and low pH of feedwater
Increases at higher Temperature and Pressure
Hydrogen ions from water are adsorbed into Metal Matrix causing Hydrogen Embrittlement
Brittle failure in a pipe due to hydrogen damage
Source: Babcock and Wilcox –
Boiler Tube Analysis

12. Fuel Ash Corrosion
Wastage of tubing caused by chemical reactions with the fuel ash
Chlorides, Sulfur corrode Oxidation resistant surfaces
Ash forms a corrosive liquid layer on surface
Fuel Ash Corrosion of OD of a Superheater. Very thick scale was observed on the OD, with a significant amount of chlorine detected in the deposit
Source: Maintenanceworld.com

13. Carburization
Occurs due to incomplete combustion, giving rise to CO and un-burnt fuel in Flue Gas
Chromium from surface of steel reacts with C to form Chromium Carbides
Causes severe Embrittlement and reduced Corrosion resistance
Excessive temperature in combination with high carbon activity in the Furnace caused changes in microstructure of the tube, which resulted in severe embrittlement and premature failure.
Source: Lifechem

14. Limiting Factors due to Material Properties
Source: Infograph

15. Creep
Creep is the tendency of a solid material to deform permanently under the influence of stresses for a prolonged period of time
Stresses may be lower than Yield Strength
Creep always increases with Temperature
Even if no other failure occurs in the tube metal, creep will definitely occur
Plastic Paper Clip
Metal Paper Clip

16. Fatigue
Fatigue is the progressive and localized structural damage (crack propagation) that occurs when a material is subjected to cyclic loading
In Steam generation, stresses due to Temperature differences in Startup and Shutdown cause fatigue. (larger the temperature, larger the chance of fatigue failure)
Versailles train crash!
Fatigue failure in a Train axle
Source: Wikipedia

17. Increased Losses
High-pressure steam leaks from piping, components, and pressure reducing valves
High-pressure radiation loss for steam piping and components
High Pressure Steam Leak being repaired by a technician
Source: Super Shakti Sealing Services

18. Erosion
Erosion is a function of Ash content in Fuel, Ash Composition and Gas velocity
Coupled with Stresses, can result failure
Source: INSA Lyon
Source: Pair O Docs LLC

19. Melting!
Source: Hackaday.com

20. Limiting Factor due to High Steam Velocity
Source: CWLP, Illinois

21. Steam Hammer
Steam hammer is a pressure surge or wave resulting when Steam in motion is forced to stop or change direction suddenly.
Can cause noise, vibration or Pipe Collapse
Due to high Fluid Velocities resulting from high pressure
Steam Expansion joints destroyed due to a Steam Hammer (magnitude up to tune of 5000 Psi = MPa)
Source: Wikipedia

22. Limiting Factors due to Impure Feedwater
Source: Water Rhapsody

23. Effects of Impure Feedwater
Scaling (Deposition of impurities on boiler walls)
Hinders Heat Transfer and Steam Production
Higher Temperature and Pressure increases rate of scaling
Internal deposits resulting from poor boiler water treatment. These deposits, besides hindering heat transfer, allowed boiler water salts to concentrate, causing corrosion.
Source: Steam – The Babcock &
Wilcox Company

24. Effects of Impure Feedwater- Scaling
Power Output- 450 MW
Boiler- Natural Circulation Boiler
Steam Production- 378 kilograms per second
Feedwater Hardness – 1 ppm (minerals and oxides)
Deposits in Boiler - 11,340 Kg per year!!
Source: Steam – The Babcock & Wilcox Company

25. Effects of Impure Feedwater
Corrosion
Oxygen Pitting Corrosion (DO – Dissolved Oxygen)
Acid Corrosion
An Economiser showing the effects of Pitting corrosion, caused due to Feedwater impurities. The tube was damaged by oxygen pitting and poor feed water chemistry.
Source: Power Corrosion (Consultants) LTD

26. Limiting Factor due to Fuel Heating Values
Source: Texas Tribune

27. Heating value of Fuels Used for Steam Generation
Source: Steam – The Babcock & Wilcox Company

28. More Fuels Compared
Source: BioMass Energy Center

29. Conclusion
A huge number of Limiting Factors exist for Steam Parameters
All the Limiting Factors have to be taken into consideration while designing a plant
Careful maintenance has to be done to avoid preventable breakdowns due to a few Limiting Factors

30. Book References
Steam/its generation and use, Edition 41 by The Babcock & Wilcox Company
Standard Handbook of Powerplant Engineering, 2nd Edition by Thomas C. Eliott, Kao Chen and Robert C. Swanekamp

31. Internet References
ftp://ftp.eia.doe.gov/features/steamgen.pdf
(Hydrogen Embrittlement)

32. Thank you!