Search Results for corrosion resistance

A combined pilot-scale combustion test and long-term laboratory study investigated the impact of oxy-firing on corrosion in coal-fired boilers. Four coals were burned under both air and oxy-firing conditions with identical heat input, with oxy-firing using flue gas recirculation unlike air-firing. Despite higher SO 2 and HCl concentrations in oxy-firing, laboratory tests showed no increase in corrosion rates compared to air-firing. This is attributed to several factors: (1) Reduced diffusion: High CO 2 in oxy-firing densified the gas phase, leading to slower diffusion of corrosive species within the deposit. (2) Lower initial sulfate: Oxy-fired deposits initially contained less sulfate, a key hot corrosion culprit, due to the presence of carbonate. (3) Reduced basicity: CO 2 and HCl reduced the basicity of sulfate melts, leading to decreased dissolution of metal oxides and mitigating hot corrosion. (4) Limited carbonate/chloride formation: The formation of less corrosive carbonate and chloride solutes was restricted by low O 2 and SO 3 near the metal surface. These findings suggest that oxy-firing may not pose a greater corrosion risk than air-firing for boiler materials.

The U.S. Department of Energy (DOE) and the Ohio Coal Development Office (OCDO) are co-sponsoring a multi-year project managed by Energy Industries of Ohio (EIO) to evaluate materials for ultra-supercritical (USC) coal-fired boilers. USC technology improves cycle efficiency and reduces CO 2 and pollutant emissions. With turbine throttle steam conditions reaching 732°C (1350°F) at 35 MPa (5000 psi), current boiler materials, which operate below 600°C (1112°F), lack the necessary high-temperature strength and corrosion resistance. This study focuses on the fireside corrosion resistance of candidate materials through field testing. Evaluated materials include ferritic steels (SAVE12, P92, HCM12A), austenitic stainless steels (Super304H, 347HFG, HR3C), and high-nickel alloys (Haynes 230, CCA617, Inconel 740, HR6W), along with protective coatings (weld overlays, diffusion coatings, laser claddings). Prior laboratory tests assessed corrosion under synthesized coal-ash and flue gas conditions for three North American coal types (Eastern bituminous, Midwestern high-sulfur bituminous, and Western sub-bituminous), with temperatures ranging from 455°C (850°F) to 870°C (1600°F). Promising materials were installed on retractable corrosion probes in three utility boilers burning different coal types. The probes maintained metal temperatures between 650°C (1200°F) and 870°C (1600°F). This paper presents new fireside corrosion probe results after approximately one year of exposure for Midwestern and Western coal types.

Ni-38Cr-3.8Al has high hardness and high corrosion resistance with good hot workability, and therefore, it has been applied on various applications. However, in order to expand further application, it is important to understand the high temperature properties. Then, this study focused on the high temperature properties such as thermal phase stability, hardness, tensile property, creep property and hot corrosion resistance. As the result of studies, we found that the thermal phase stability of (γ/α-Cr) lamellar structure and the high temperature properties were strongly influenced by the temperature. Although the high temperature properties, except for creep property, of Ni-38Cr-3.8Al were superior to those of conventional Ni-based superalloys, the properties were dramatically degraded beyond 973 K. This is because the lamellar structure begins to collapse around 973 K due to the thermal stability of the lamellar structure. The hot corrosion resistance of Ni-38Cr-3.8Al was superior to that of conventional Ni-based superalloys, however, the advantage disappeared around 1073 K. These results indicate that Ni-38Cr-3.8Al is capable as a heat resistant material which is required the hot corrosion resistance rather than a heat resistant material with high strength at high temperature.

The “Coal Ash Corrosion Resistant Materials Testing Program” by The Babcock & Wilcox Company (B&W), the U.S. Department of Energy (DOE), and the Ohio Coal Development Office (OCDO) at Reliant Energy's Niles plant provides full-scale in-situ testing of advanced boiler superheater materials to address fireside corrosion, a key issue for improving efficiency in new coal-fired plants and service life in existing ones. In 1998, B&W developed a system with three identical sections containing multiple segments of twelve different materials from contributors like Oak Ridge National Laboratory (ORNL), cooled by reheat steam and installed in 1999 above the furnace entrance in the Niles Plant 110 MWe Unit #1 firing high-sulfur Ohio coal to test materials at advanced supercritical steam temperatures (1100°F+) in corrosive conditions. The first section was evaluated after 29 months in 2001, the second in 2003, and the final section is expected for removal in 2005. This paper outlines the program, test system, and materials, and it presents the evaluation results for the first two sections.

This presentation compares the corrosion resistance of uncoated Haynes 230 and SS316HS substrates to the same substrates coated with a Fe-based amorphous alloy. The substrates were exposed to highly corrosive media, FLiNaK, for 120 hours at 700 °C. The findings indicate that the thermal spray amorphous alloy coating provided superior corrosion resistance within the coatings while protecting the substrates against the aggressive environment. As a result, the new amorphous metal coating improved the substrate's lifespan by providing better protection against high-temperature corrosion, paving the way for a more efficient and cost-effective future in various industrial applications.

Inconel Filler Metal 72 (FM 72) and Incoclad 671/800H co-extruded tubing have been successfully used for over 20 years to protect boiler tubing from high-temperature degradation. A newer alloy, FM 72M, offers superior weldability and the lowest corrosion rate in simulated low NOx environments. Both FM 72 and 72M show promise in addressing challenges like circumferential cracking and corrosion fatigue in waterwall tubing overlays. Additionally, 72M’s superior wear resistance makes it ideal for replacing erosion shields in superheater and reheater tubing. Beyond improved protection, these alloys exhibit increased hardness and thermal conductivity over time, leading to reduced temperature difference across the tube wall and consequently, enhanced boiler efficiency and lower maintenance costs. This paper discusses the historical selection of optimal alloys for waterwall and upper boiler tubing overlays, analyzes past failure mechanisms, and highlights the key properties of successful choices like FM 72 and 72M.

Structural alloy corrosion is a major concern for the design and operation of supercritical carbon dioxide (sCO 2 ) power cycles. Looking towards the future of sCO 2 system development, the ability to measure real-time alloy corrosion would be invaluable to informing operation and maintenance of these systems. Sandia has recently explored methods available for in-situ alloy corrosion monitoring. Electrical resistance (ER) was chosen for initial tests due the operational simplicity and commercial availability. A series of long duration (>1000 hours) experiments have recently been completed at a range of temperatures (400-700°C) using ER probes made from four important structural alloys (C1010 Carbon Steel, 410ss, 304L, 316L) being considered for sCO 2 systems. Results from these tests are presented, including correlations between the probe measured corrosion rate to that for witness coupons of the same alloys.

Coal burning power companies are currently considering FeAlCr weld overlay claddings for corrosion protection of waterwall boiler tubes located in their furnaces. Previous studies have shown that these FeAlCr coatings exhibit excellent high-temperature corrosion resistance in several types of low NOx environments. In the present study, the susceptibility of FeAlCr weld overlay claddings to hydrogen cracking was evaluated using a gas-tungsten arc welding (GTAW) process. Microsegregation of alloying elements was determined for the FeAlCr welds and compared to a currently used Ni-based superalloy. Long-term gaseous corrosion testing of select weld overlays was conducted along with the Ni-based superalloy in a gaseous oxidizing/sulfidizing corrosion environment at 500°C. The sample weight gains were used along with analysis of the corrosion scale morphologies to determine the corrosion resistance of the coatings. It was found that although there were slight differences in the corrosion behavior of the selected FeAlCr weld coatings, all FeAlCr based alloys exhibited superior corrosion resistance to the Ni-based superalloy during exposures up to 2000 hours.

A consortium which includes Energy Industries of Ohio, the Electric Power Research Institute, Inc., and four major US boiler manufacturers (the Babcock & Wilcox Company, Riley Power, Foster Wheeler, and Alstom Power) is conducting a 5-year materials development program to advance the technology in coal-fired power generation. As part of this development effort, new high temperature, corrosion resistant alloys must be evaluated and qualified for dependable operation in a corrosive coal-fired environment to produce steam for Ultra Supercritical (USC) cycle operation up to 760°C (1400°F) and 35 MPa (5000 psi.) To evaluate the fireside corrosion resistance of candidate materials for USC power generation, two superheater test loops comprised of seven different advanced alloys were designed and fabricated by the Babcock and Wilcox Company (B&W) in Barberton, Ohio. These loops were installed at the Reliant Energy power plant located in Niles, OH, and testing of these loops was initiated in December, 2003. Following a minimum of 18 months of testing, the loops will be removed for metallurgical examination and assessment by B&W. This paper describes some of the considerations in designing, fabricating, and installing the two USC test loops, as well as the methodology for monitoring their performance during operation.

Alloy 33 is a weld overlay material that has generated a lot of interest in the fossil boiler industry. The high chromium content of Alloy 33 has been shown to provide excellent corrosion protection in both waterwall and superheater/reheater tube applications. For waterwall applications, the corrosion resistance has been demonstrated in both laboratory and field tests conducted over the last 5 years. In addition to corrosion resistance, the Alloy 33 has also shown that it is also resistant to cracking (although no material is 100% immune). In the superheater/reheater, the use of spiral clad weld overlay tubes is able to provide resistance to excellent coal ash corrosion. Laboratory and field tests have shown Alloy 33 to have among the best corrosion resistance of all materials studied. The application of Alloy 33 is also easier than other more highly alloyed materials (such as FM-72) and is less expensive. As a result of these favorable experiences, Alloy 33 is now being used commercially to weld overlay both waterwall and superheater/reheater tubes on fossil boilers.

Super Duplex stainless steels (SDSS) are alloys based on the Fe-Cr-Ni-N system. The chemical composition is tailored to achieve a balanced microstructure of 50% ferrite and 50% austenite. Hyper Duplex Stainless Steels (HDSS) are also duplex materials distinguished by their remarkable yield strength (≥700 MPa) and corrosion resistance (PREN>48). They have been developed as an alternative to the well-established SDSS when superior mechanical and corrosion performance is required. This enhanced performance is attributed to alloying additions, primarily Cr, Mo, and N. In this study, a comparison is conducted between filler metals of SDSS and HDSS for the root welding of SDSS plates. The gas tungsten arc welding (GTAW) process was used to carry out root welding passes and Gas Metal Arc Welding (GMAW) for filling passes on SDSS substrates arranged in a V groove to simulate a repair scenario. The heat input was controlled in both processes, keeping it below 2.0 kJ/mm in the GTAW and 1.2 kJ/mm in the GMAW. GTAW with constant current was used and the parameters achieved producing full penetration welds with SDSS and HDSS. In this case, Nitrogen was used as backing gas to avoid oxidation of the root. Thus, a special GMAW-Pulsed version was applied to achieve good wettability and defect-free joints. ASTM G48 tests were performed to evaluate the corrosion resistance through Critical Pitting Testing (CPT) analysis on the root pass, microstructural analysis via optical microscopy, and impact toughness. Consequently, a comprehensive examination of the welded joints outlines manufacturing conditions, limitations, and the applications of SDSS and HDSS filler metals.

Recently, a γ’ precipitation strengthened Ni-base superalloy, USC141, was developed for 700°C class A-USC boiler tubes as well as turbine blades. In boiler tube application, the creep rupture strength of USC141 was much higher than that of Alloy617, and the 105 hours’ creep rupture strength of USC141 was estimated to be about 180MPa at 700°C. This is because fine γ’ particles precipitate in austenite grains and some kinds of intermetallic compounds and carbides precipitate along austenite grain boundaries during creep tests. Good coal ash corrosion resistance is also required for tubes at around 700°C. It is known that coal ash corrosion resistance depends on the contents of Cr and Mo in Ni-base superalloys. Therefore the effect of Cr and Mo contents in USC141 on coal ash corrosion resistance, tensile properties, and creep rupture strengths were investigated. As a result, the modified USC141 containing not less than 23% Cr and not more than 7% Mo showed better hot corrosion resistance than the original USC141. This modified alloy also showed almost the same mechanical properties as the original one. Furthermore the trial production of the modified USC141 tubes is now in progress.

A new 18Cr-9Ni-Nb-V-W-N-low C austenitic boiler tube (XA704) has been developed. Conventional high-strength austenitic stainless steel boiler tubes usually have high susceptibility to intergranular corrosion because of their high carbon content, and require special care for heated sections such as weld joints. Generally, when the carbon content decreases, the intergranular corrosion resistance improves, while the creep strength reduces. However, the creep strength of the developed steel is very high despite lower carbon content in comparison to conventional austenitic boiler tubes. The high temperature strength and the intergranular corrosion resistance of the steel are superior to those of conventional 18Cr steels such as TP347H. This excellent creep strength of XA704 is mainly due to precipitation strengthening by CrVN, and solid solution strengthening by tungsten and nitrogen. Matching welding consumables for the developed steel have also been developed. Thus, newly developed XA704 is a promising material for superheater and reheater tubes for the “600°C generation” of USC boilers. XA704 has already been used in six power plants in Japan. Currently, the steel is being standardized in the ASME Code.

The Advanced Ultrasupercritical (A-USC) power plants are aimed to operate at steam inlet temperatures greater than 700°C; consequently, a complete materials overhaul is needed for the next-generation power plants. HAYNES 282, a gamma-prime strengthened alloy, is among the leading candidates because of its unique combination of properties, superior creep and LCF strength, fabricability and thermal stability. It is currently being evaluated in wrought and cast forms for A-USC turbine rotors, casings, boiler tubings, header, and valves. The candidate materials for A-USC applications not only require oxidation resistance for steam cycles but fireside corrosion resistance to coal ash is also of an extreme importance. In order to study the effect of both environments on the performance of 282 alloy, the alloy was exposed for extended periods in various oxidizing environments, such as air, air plus water vapor (10%), and 17bar steam up to 900°C. The fireside corrosion resistance of 282 alloy was evaluated at 700°C in synthetic coal ash and at 843°C in alkali salt deposits in a controlled gaseous environment.

Utilities worldwide are facing increased demand for additional electricity, reduced plant emissions and greater efficiency. Part of the solution is achieved by increasing boiler temperature, pressure and coal ash corrosion resistance of the materials of boiler construction. In this paper, a new nickel-base tube alloy, INCONEL alloy 740, meeting this challenge is characterized with emphasis on mechanical properties, coal ash and steam corrosion resistance as well as weldability. Microstructural stability as a function of temperature and time is addressed as well as some of the early methodology employed to arrive at the current chemical composition. Brief mention is made of certain current and future alloy characterization efforts and potential environmental benefits to be expected should the boiler technology utilizing INCONEL alloy 740 be adopted.

An attempt is being made to develop novel Ni-Mo-W-Cr-Al-X alloys with ICME approach with critical experimental/simulations and processing/microstructural characterization/property evaluation and performance testing has been adopted. In this work, based on thermodynamic modeling five alloy compositions with varying Mo/W and two alloys with high tungsten modified with the addition of Al or Ti were selected and prepared. The newly developed alloys were evaluated for their response to thermal aging in the temperature range of 700 to 850 °C and corrosion in the KCl-NaCl-MgCl 2 salt under suitable conditions. Thermally aged and post-corrosion test samples were characterized to ascertain phase transformations, microstructural changes and corrosion mechanisms. Al/Ti modified alloys showed significant change in hardness after 400 hours aging at 750°C, which was found to be due to the presence of fine γ’/γ” precipitates along with plate-shaped W/Mo-rich particles. These alloys show comparable molten salt corrosion resistance as commercial alloys at 750°C for 200-hour exposures. The good corrosion behavior of these alloys may be attributed to the formation of a protective multicomponent Al-or Ti-enriched oxide as well as the unique microstructure.

The article gives a brief overview of the newly developed austenitic material “Power Austenite”. The microstructure of the Power Austenite is characterized by grain boundary strengthening with boron stabilized M23(C,B)6 and secondary Nb(C,N) in combination with sigma phase and Nb(C,N) as the major grain strengthening precipitates. The material shows a significant creep strength at 700 °C (1292 °F) and 650 °C (1202 °F) as well as fireside corrosion resistance which makes it a possible candidate for 700 °C (1292 °F) power plants.

This study examines the corrosion resistance of additively manufactured 316L stainless steel (SS) for nuclear applications across three environments: pressurized water reactor primary water (PWR PW), hot concentrated nitric acid, and seawater. Wire-feed laser additive manufacturing (WLAM) specimens showed oxidation behavior similar to wrought 316L SS in PWR PW, though stress corrosion cracking (SCC) susceptibility varied with heat treatment. In nitric acid testing, laser powder bed fusion (L-PBF) specimens demonstrated superior corrosion resistance compared to conventional SS, primarily due to improved intergranular corrosion resistance resulting from cleaner feedstock powder and rapid solidification rates that minimized grain boundary segregation. Laser metal deposition (LMD) repair studies in seawater environments successfully produced dense, crack-free repairs with good metallurgical bonding that matched the substrate’s mechanical properties while maintaining corrosion resistance. These results emphasize the importance of corrosion testing for additively manufactured components and understanding how their unique microstructures affect performance.

The Department of Energy and Ohio Coal Development Office jointly sponsored research to evaluate materials for advanced ultrasupercritical (A-USC) coal power plants, testing both monolithic tube materials and weld overlay combinations under real operating conditions. Testing was conducted in the highly corrosive, high-sulfur coal environment of Reliant Energy's Niles Plant Unit 1 boiler in Ohio. After 12 months of exposure, researchers evaluated six monolithic tube materials and twelve weld overlay/tube combinations for their high-temperature strength, creep resistance, and corrosion resistance in both steam-side and fire-side environments. Among the monolithic materials, Inconel 740 demonstrated superior corrosion resistance with the lowest wastage rate, while EN72 emerged as the most effective weld overlay material across various substrates, offering consistent protection against corrosion.

The power generation industry worldwide aims to develop coal-fired boilers operating at much higher efficiencies than current supercritical plants. This increased efficiency is expected through ultrasupercritical steam conditions, requiring new materials for critical components. To limit the use of expensive alloying materials, it is necessary to maximize the strength and corrosion capabilities across the material spectrum from ferritic to austenitic and nickel-based alloys. Sandvik Materials Technology has developed an austenitic alloy, Sanicro 25, with excellent high-temperature strength and corrosion resistance using an economical alloy composition. The alloy is designed for use within 700°C (1300°F)/300 bar (4500 psi) steam conditions and is a leading candidate material for such high-temperature applications. This paper introduces Sanicro 25, its development status, and properties.