31 May 2023

Boiler Metallurgy | Super Critical Boiler Metallurgy

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Boiler Metallurgy

Requirements of Materials

The following major properties of materials is of interest in the choice of materials for Boiler and Pressure Vessel applications:

  • Strength at room temperature and elevated/ service temperature
  • Corrosion/ Oxidation resistance
  • Stability of structure over a service period normally about 30 years
  • Ease of fabrication including welding


Effect of Common Alloying Elements

Carbon: This is the main element which provides strength. For considerations of weldability the carbon content is restricted to 0.25% in IBR and in many of the European codes.

American Code (ASME B&PV) allows carbon up to 0.35%.

The purchase specifications of BHEL restricts the carbon to a maximum value of 0.30%.

Carbon has a major bearing on the high temperature strength also, for example a minimum of 0.04% of carbon is required as per ASME B&PV code to ensure the high temperature creep properties of austenitic SS grades.

Chromium: This is the major alloying element conferring the oxidation /corrosion resistance to the steel. This element also provides resistance to corrosion in sulphur rich flue gases.

Molybdenum: The main alloy element which confers creep resistance for the steel. 100,000 hrs rupture strength is used in these presentations for the purpose of various comparisons.


Material Selection

  • Materials for Main Feed Water Piping    : SA 106- C (Carbon Steel)
  • Material for Economizer Tubing  : SA 210- C (Carbon Steel)
  • Material for Water wall Tubing  : SA 213- T 22 (2.25 Cr–1.0 Mo)
  • Materials for Super heater and Re-heater Tubing : SA 213- T 91 (9Cr-Mo-V)
  • Materials for Super heater and Re-heater Steam Piping  : SA 335- P 91 (9Cr-1Mo-V)


High Temperature Material Composition

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