Coal & Thermal Power Generation
Coal-fired and thermal power generation continues to rank among the most demanding industrial environments for structural metallic materials. Across ultra-supercritical (USC) boilers, circulating fluidized bed (CFB) combustion systems, heat recovery steam generators (HRSGs), and gas turbine combined-cycle hot sections, plant components operate under extreme combinations of elevated temperature, high steam pressure, oxidizing and sulfidizing atmospheres, molten ash deposits, and cyclic mechanical loading that challenge the limits of conventional engineering alloys. The global transition toward higher thermal efficiency — driven by carbon reduction commitments and energy security priorities — has progressively pushed operating steam temperatures and pressures to new levels, creating a sustained demand for advanced heat-resistant materials throughout the power plant.
Modern USC plants operate at steam temperatures above 600 °C and pressures exceeding 30 MPa, while next-generation advanced ultra-supercritical (A-USC) programs now target 700 °C steam — a threshold that marks the practical performance boundary between austenitic stainless steels and nickel-based superalloys as the primary structural material class. Fushun Special Steel has developed a focused production portfolio of heat-resistant stainless steels and high-temperature nickel-based alloys that addresses the full temperature and performance spectrum of this sector, supplying boiler OEMs, EPC contractors, turbine manufacturers, and emission control system fabricators across Asia, the Middle East, and Europe.
High-Temperature Degradation Mechanisms
Degradation of structural materials in coal and thermal power plant service proceeds through several concurrent mechanisms, each requiring specific alloy chemistry countermeasures. High-temperature oxidation progressively depletes chromium from alloy surfaces, consuming the protective oxide scale that separates the base metal from the combustion atmosphere. Under thermal cycling — a daily operational reality for load-following plants — mechanical mismatch between the oxide scale and the substrate metal causes progressive scale spallation, exposing fresh alloy and dramatically accelerating the effective metal-loss rate. Elevated chromium content combined with rare earth or aluminum microadditions are the primary alloy chemistry strategies for improving scale adhesion and reducing steady-state growth rate.
Sulfidation, driven by the combustion of sulfur-bearing coals, attacks alloy grain boundaries through the formation of low-melting iron and nickel sulfides, producing a catastrophic acceleration in corrosion rate relative to pure oxidation. Hot corrosion — initiated by alkali iron trisulfate and vanadium-pentoxide-rich fly ash deposits on superheater tube surfaces — involves a molten-salt dissolution mechanism distinct from gas-phase sulfidation and requires independent compositional strategies to resist. It is particularly aggressive in plants co-firing waste or biomass fuels with high alkali content. Creep deformation governs the long-term structural integrity and dimensional stability of all pressure-containing components and defines the permissible design stress at each operating temperature; an alloy's oxidation performance is irrelevant if its creep rupture life does not meet the plant's scheduled maintenance interval. These interacting demands make material selection for thermal power plant components a multi-objective optimization problem that Fushun Special Steel's production portfolio is specifically configured to address.
Production Platform & Melting Capabilities
Fushun Special Steel operates a vertically integrated melt shop and downstream processing facility for specialty alloys. Process routes are selected and individually qualified for each alloy grade based on the purity, microstructural homogeneity, and mechanical property requirements mandated by relevant power generation standards and customer procurement documents.
Electric Arc Furnace + AOD Refining
Electric Arc Furnace primary melting followed by Argon Oxygen Decarburization enables large-scale production of heat-resistant stainless steels. AOD delivers precise carbon control to ultra-low levels, deep desulfurization, and consistent alloy additions — the essential foundation for repeatable chemistry across full production heats of 310S, 321, 347H, and related grades.
Vacuum Induction Melting
Vacuum Induction Melting is the mandatory primary process for all nickel-based superalloy production. Melting entirely under vacuum prevents oxidation of reactive elements — aluminum, titanium, and niobium — enabling precise chemistry targeting and substantially reducing oxide and nitride inclusion content. VIM electrodes are the starting material for all subsequent remelting operations.
Vacuum Arc Remelting
Vacuum Arc Remelting of VIM-cast electrodes refines ingot solidification structure, eliminates macro-segregation, and reduces micro-shrinkage porosity through controlled directional solidification in vacuum. VAR is required for critical rotating components — turbine discs, compressor impellers, and high-integrity fastener stock — where through-thickness property consistency is mandatory for fatigue-life qualification.
Electroslag Remelting
Electroslag Remelting produces dense, clean ingots with refined grain structure and excellent surface quality through controlled solidification in a resistively heated liquid slag pool. ESR is applied to heat-resistant stainless steels and selected nickel alloys requiring maximum non-metallic inclusion cleanliness, superior forgeability, and high surface yield for premium pressure-containing applications.
Downstream processing encompasses hot-rolled plate, sheet, and coil; seamless tube and pipe by hot piercing and rolling; bar and rod; and open-die forgings in a broad range of dimensions. All product forms are tested and certified to applicable international standards including ASTM, ASME, EN, and GB/T. Third-party inspection by authorized agencies and ASME-authorized inspectors is accommodated as standard for all power generation project orders.
Heat-Resistant Stainless Steels for Thermal Power
Austenitic heat-resistant stainless steels provide cost-effective high-temperature performance for the majority of thermal power plant components operating below approximately 650–700 °C. All grades listed below are standard production items, available in plate, seamless tube, bar, and forging forms, with chemistry and mechanical properties certified to ASTM and equivalent international standards.
Type 310S is the benchmark heat-resistant austenitic grade, with 25% chromium and 20% nickel delivering outstanding oxidation and sulfidation resistance up to 1100 °C in continuous service. Its fully austenitic microstructure provides good creep ductility and broad weldability with matching consumables. In thermal power plants it is specified for radiant boiler baffles, furnace liners, hot gas ducting, and ash-handling components where sustained high-temperature exposure is the primary design constraint and the cost of nickel-based alloys is not warranted by the stress level or service environment.
Titanium-stabilized Type 321 resists sensitization and intergranular corrosion in the 450–850 °C range where chromium carbide precipitation attacks unstabilized grades following welding or long-term exposure. In power plants it is applied to steam exhaust manifolds, connecting pipework, expansion joints, and heat exchanger shells that cannot receive post-weld heat treatment. Its fabricability, weldability, and moderate cost make it one of the most widely inventoried austenitic grades for general-purpose structural service in power generation systems.
Type 347H is the high-carbon, niobium-stabilized austenitic grade selected specifically for maximum creep rupture strength in elevated-temperature pressure service. Niobium stabilization provides both sensitization immunity and a refined carbide distribution that improves creep performance relative to 321H. It is the primary stainless steel specification for superheater and reheater tubing, steam outlet headers, and high-pressure steam pipelines in subcritical and supercritical boilers operating up to 650 °C, where ASME Code allowable stresses at temperature govern material selection.
253MA achieves outstanding cyclic oxidation resistance through rare earth element additions — primarily cerium — that dramatically improve adhesion and self-healing kinetics of the surface chromia scale. Under thermal cycling conditions where standard 310S suffers progressive scale spallation and accelerated metal loss, 253MA maintains a stable, adherent oxide layer, providing superior performance at substantially lower material cost than nickel-based alternatives. It is the preferred grade for ash-handling ducting, biomass and waste co-firing combustion zones, and high-cycling furnace components associated with power generation facilities.
Type 309S bridges the performance gap between standard 300-series grades and the higher-alloyed 310S, offering improved oxidation resistance combined with adequate resistance to the acid chloride environments of emission control systems. In coal-fired power plants it is applied to flue gas desulfurization absorber shells and liners, transition ducting, intermediate-temperature combustion chamber walls, and refractory-backed structural members in the hot gas path. Its lower nickel content relative to 310S provides a competitive cost advantage for large fabricated assemblies.
Type 316H is the elevated-carbon variant of Type 316, where the molybdenum addition provides pitting and crevice corrosion resistance in chloride-bearing steam condensate and cooling water environments, and the higher carbon content enhances creep rupture strength at temperature. In coal-fired power stations it is used for pressure vessel shells, steam turbine casings, valve bodies, and heat exchanger tube sheets operating to approximately 600 °C where chloride-laden condensates are a persistent concern. ASME Section VIII Code allowable stresses for 316H at temperature support pressure design, and certification to SA-240 and SA-479 is issued as standard.
High-Temperature Nickel-Based Alloys
Where austenitic stainless steels approach their creep strength and oxidation resistance limits — typically above 650 °C, or in particularly aggressive corrosive environments — nickel-based superalloys provide the critical additional performance margin required for advanced power generation service. Produced via the VIM–VAR or VIM–ESR double-vacuum route, these alloys satisfy the stringent cleanliness, segregation control, and microstructural consistency requirements of power generation and aerospace procurement standards.
Inconel 625 derives its strength entirely from solid-solution hardening by molybdenum and niobium, with no reliance on precipitation hardening, resulting in exceptional fabricability and weldability that are unaffected by welding thermal cycles — a critical advantage for large, complex fabrications. Its outstanding resistance to oxidizing and reducing acids, pitting, crevice corrosion, and chloride stress-corrosion cracking makes it the primary material for FGD absorbers, wet scrubber linings, HRSG tubing in biomass co-firing plants, and seawater-cooled condenser components. Weld overlay cladding with Inconel 625 filler is extensively used to economically protect carbon steel vessels in aggressive acid and flue gas environments throughout the power plant.
Inconel 718 is the world's most widely produced nickel superalloy, combining exceptional tensile and fatigue strength up to 700 °C with good oxidation resistance and superior weldability relative to other age-hardened nickel alloys. Strengthening is governed by the γ'' (Ni₃Nb) precipitate phase, controlled through precise niobium content and heat treatment cycle selection. In power generation it is specified for steam turbine discs, compressor impellers, high-temperature fasteners, and structural retaining rings. VIM–VAR double-vacuum melting ensures the inclusion cleanliness and ingot grain homogeneity required for rotating component fatigue-life certification to power generation standards.
Inconel 601's aluminum addition promotes a dual alumina-chromia surface scale that provides oxidation resistance approaching that of aluminum-forming FeCrAl alloys while retaining the ductility and weldability of a conventional nickel-chromium alloy. This makes it uniquely suited to radiant tubes in process heaters adjacent to power generation facilities, combustion chamber liners, burner nozzle assemblies, thermocouple protection sheaths, and industrial furnace basket components operating up to 1200 °C. Resistance to carburizing and nitriding atmospheres is an additional advantage in the complex combustion gas chemistry of CFB and gasification-based power systems.
Incoloy 800H is a controlled-chemistry iron-nickel-chromium alloy specified with carbon 0.05–0.10%, constrained Al and Ti additions, and a minimum annealed grain size of ASTM No. 5 — parameters that together optimize creep rupture life without compromising oxidation resistance. Listed in ASME Code Sections I and VIII for pressure service to 900 °C, it is widely used in superheater and reheater tubing, HRSG tube banks, heat exchanger shells, and high-temperature expansion bellows. Its iron base relative to pure-nickel alloys provides significant material cost efficiency within this temperature envelope, making it a broadly specified grade for A-USC transition projects.
Incoloy 800HT refines the 800H specification by tightening the combined Al+Ti minimum to ≥ 0.85%, increasing the strengthening precipitate volume fraction to improve creep rupture life at the upper limit of the alloy's service temperature. It is the preferred specification for the most thermally stressed boiler pressure parts — main steam outlet headers, final superheater elements, and high-pressure reheater connections — in advanced supercritical designs where incremental improvement in allowable creep stress reduces required wall thickness, improves thermal fatigue resistance, and extends maintenance intervals. Certification to ASME SB-409, SB-407, and SB-408 is provided as standard.
Hastelloy X combines molybdenum and tungsten solid-solution strengthening with one of the broadest environmental resistance profiles among wrought nickel alloys, sustaining structural integrity to 1200 °C under both oxidizing and mildly reducing combustion gas compositions. In gas turbine combined-cycle power plants it is specified for combustion transition liners, flame tube segments, heat exchanger cores downstream of turbine exhaust, and afterburner structural elements. Its long-term resistance to sigma-phase embrittlement during extended high-temperature service, validated through decades of industrial service data, supports its selection for components requiring continuous hot-section service life exceeding typical major inspection intervals.
Key Application Areas in Power Plants
Boiler Pressure Parts & Steam Circuits
Superheater and reheater tubing, steam outlet headers, main steam and hot reheat piping, and high-pressure manifolds are the most thermally demanding pressure-retaining components in coal-fired plants. Material selection must simultaneously satisfy creep rupture strength, oxidation resistance, steam-side oxide growth control, and weldability requirements within ASME Code allowable stress limits. Primary grade selections are 347H for superheater duty to 650 °C, for high-temperature baffles and hot gas enclosures, and Incoloy 800H or Incoloy 800HT for the most thermally loaded components at the top of the steam temperature envelope.
Steam Turbines & Rotating Machinery
Turbine discs, last-stage blades, fasteners, compressor impellers, and structural retaining rings demand high fatigue strength, creep resistance, and dimensional stability under sustained centrifugal loading at operating temperature. Precipitation-hardened nickel alloys produced via VIM–VAR double-vacuum melting are the established material standard for high-integrity rotating components. Inconel 718 is the primary alloy for steam turbine disc and high-temperature fastener applications, while Hastelloy X is applied to stationary combustion zone and transition duct structures in gas turbine combined-cycle configurations.
Flue Gas Desulfurization & Emission Control
FGD absorber vessels, reaction tank internals, agitator shafts, mist eliminators, and wet chimney liners operate in corrosive mixtures of sulfuric and hydrochloric acid condensates combined with chloride slurries that rapidly attack standard stainless steels through pitting and stress-corrosion cracking. Inconel 625 — as solid plate or as weld overlay cladding on carbon steel substrates — is the established industry solution for the most severely corrosive FGD zones. 309S and 316H serve intermediate zones where reduced acid concentration permits a cost-effective stainless solution.
Heat Exchangers & Heat Recovery Systems
Economizers, air preheaters, HRSGs, and condensers are subject to high-temperature flue gas on the process side and steam, cooling water, or process fluids on the utility side, requiring grade selection tailored to the specific temperature and chemistry at each circuit location. 321 and 316H serve the moderate-temperature and lower-corrosivity envelope, while Inconel 625 and Inconel 601 are specified where the combined demands of high flue gas temperature and aggressive chemistry exceed the performance limit of austenitic stainless steels.
Standards, Testing & Traceability
All heat-resistant stainless steel and nickel alloy products for power generation service are manufactured, tested, and certified to internationally recognized standards. Stainless steel plate is produced to ASTM A240; seamless tube to ASTM A213, A269, and A312; bar and rod to ASTM A276 and A479; forgings to ASTM A182. Nickel alloy products are certified to applicable ASTM B-series specifications: B409 and B407 for Incoloy 800H/HT plate and tube; B443 and B446 for Inconel 625 plate and bar; B637 for Inconel 718 bar and forging; and equivalent EN 10095, EN 10216-5, and EN 10272 standards for European market deliveries. PED (Pressure Equipment Directive) compliance documentation is available on request for EU-destined orders.
Our quality management system operates under ISO 9001 certification. Third-party inspection by authorized agencies and ASME-authorized inspectors is accommodated as standard for all power generation project orders. Non-destructive testing capabilities include ultrasonic testing (UT), eddy current testing (ET), radiographic testing (RT), dye penetrant inspection (PT), and magnetic particle inspection (MT), all performed by qualified personnel under written inspection and test plans. Full material test reports (MTRs) documenting heat chemistry, lot mechanical properties, NDT records, and dimensional inspection results are issued with every shipment, providing complete end-to-end material traceability from melt heat number to finished product delivery.
