MATERIAL CHALLENGES FOR ADVANCED STEAM PLANTS Dr. M. Shekhar Kumar Materials Technology Division Central Power Research Institute Bangalore

Challenges  Challenge faced by the power generation industry to meet increasing demand through increased efficiency and reduction of operation and maintenance costs and also meeting environmental and safety regulations  Need for development of advanced materials  Material changes over the years have resulted in operation at 170 bar and 540 C –efficiency of 35%  Need to step up steam parameters

Drawbacks on the boiler side  Fireside corrosion of water walls and superheater  Creep, Crack and Rupture  Steam side oxidation  Fracture toughness  Thermal Fatigue  Acid corrosion on the exhaust side

Drawbacks on the Turbine side  Strength, ductility and toughness  Wear and erosion  Creep, Crack and Rupture  High cycle fatigue  Scaling  Embrittlement  Lack of mechanical property data

Material Options  Super Alloys  Ferritic Steels  Stainless Steels  Coatings  Composites  Intermetallics

Material Considerations Strength to resist deformation and rupture at design conditions Fatigue strength and damping capacity when cycling stresses are involved Ability to resist stress concentrations Resistance to oxidation, corrosion and erosion Ability to resist damaging metallurgical changes during operation Ease of fabrication, field construction and maintenance Good physical properties to minimise thermal stresses Cost

LOW ALLOY STEEL Low Alloy Steel2 ¼ Cr-1Mo 4~5Cr-Mo High Strength Low Alloy Steelos 2 ¼ Cr-1Mo-V-Nb-(Ti) 4~5Cr-Mo-V-Nb-(Ti) Solution Strenmgthening - 2 Mo - -Mo-(W) Precipitate Strengthening -V-Nb, -V-Nb Ti, Others High Strength 9-12 Cr Steels With improved Weldability Low C, V  0.3%, Nb  0.1 % 9-12 Cr Steels9 Cr 12 Cr

Austenitic Steel 18 Cr-8 Ni Type 304 Solution Strengthening Type 316 (Mo) Precipitate Strengthening Cr-Carbide, Cr-Nitride StabilisingType 321 (Tic) Type347(NbC) Improved 18Cr-8Ni Steels Optimization of 300 Series Stainless Steels Under StabilizingType A-1 (TiC, NbC) Alloy Design for Elevated Temperature Application 15 Cr-15 NiType CuMoHigh Strength Austenitic Steels 25Cr-20NiType 310Highperformance Cr Austenitic Steels 21 Cr-32NiType 800H

Candidate Boiler Materials Component31.0 Mpa (4500psi): 565/565/565ºC 31.0 Mpa(4500psi): 565/565/565ºC 34.5 Mpa (500 psi) 565/565/565ºC Furnace wall1Cr-1/2 Mo(T12) 1 ¼ Cr- 1/2 Mo(T11) !Cr-1/2 Mo(T12) or 1 ¼ Cr –1/2 Mo(T11) For Lower wall; Super 9 Cr Same as phase 1 Finishing Super heater Non Coorrosive Corrosive Super 9 Cr(T91) HCM12 304SS HR3C Chromised 347 SS Tempalloy A-1 347SS HR3c Chromised 347SS NF Cu-Mo Esshete 1250 NF709 CR30A Inconel Cu Mo Chromised or Extruded with Incone l 671 or 310 SS Finishing Reheater Same as above Shot blasted 347H Headers and Steam Pipes 2 ¼ Cr- 1 Mo(P22)316 H Super9 Cr (P91) 9 Cr-2Mo(HCM9M 12 Cr-Mo-V(Ht(0 9Cr-Mo-W(NF616) 316H

TURBINE PARTS STEAM TEMPERATURE 565 C or LOWER 595 C 620 C or HIGHER SP,VHP,HP,VHP+H P,IP ROTOR Cr-Mo-V STEEL12% Cr STEELAUSTENTIC SUPER ALLOY INNER CYLINDERCr – Mo STEEL9 % Cr STEEL316 AUSTENTIC STEEL BLADEHEAT RESISTANT SUPER ALLOY STEAM VALVECr- Mo STEEL or 9% Cr STEEL 316 AUSTENTIC STEEL ( FORGING ) NOZZLE BOXCr – Mo STEEL or 9% Cr STEEL 316 AUSTENTIC STEEL ( CASTING or FORGING ) INLET STEAM PIPE Cr – Mo STEEL316 AUSTENTIC STEEL ( FORGING ) OUTER CYLINDER Cr – Mo STEEL ( CASTING ) LP ROTORNi – Cr – Mo – V STEEL FOR 595 C or HIGHER, IMPROVED MATERIAL or ADVANCED MATERIAL FREE FROM EMBRITTLEMENT MATERIALS FOR STEAM TURBINES

Conclusions  Advances in materials development need focus  Potential use of ceramics, ceramic matrix composites and ceramic/metal joining technologies  Protective coatings  Emphasis on materials for efficiencies greater than 55%  Allied services