Search Results for nickel-chromium coating

The U.S. Department of Energy (DOE) and the Ohio Coal Development Office (OCDO) are sponsoring the “Boiler Materials for Ultrasupercritical Coal Power Plants” program. This program is aimed at identifying, evaluating, and qualifying the materials needed for the construction of critical components for coal-fired boilers capable of operating at much higher efficiencies than the current generation of supercritical plants. Operation at ultrasupercritical (USC) conditions (steam temperatures up to 760°C (1400°F)) will necessitate the use of new advanced ferritic materials, austenitic stainless steels and nickel-based alloys. As well as possessing the required mechanical properties and fireside corrosion resistance, these materials must also exhibit acceptable steamside oxidation resistance. As part of the DOE/OCDO program, steamside oxidation testing is being performed at the Babcock & Wilcox Research Center. More than thirty ferritic, austenitic and nickel-based materials have been exposed for up to 4,000 hours in flowing steam at temperatures between 650°C (1202°F) and 800°C (1472°F). In addition to wrought materials, steamside oxidation tests have been conducted on weld metals, coated materials and materials given special surface treatments. Exposed specimens were evaluated to determine oxidation kinetics and oxide morphology. High chromium ferritic, austenitic and nickel-based alloys displayed very good oxidation behavior over the entire temperature range due to the formation of a dense chromium oxide. With increasing steam temperature, low chromium ferritic materials experienced breakaway oxidation, and low chromium austenitic materials experienced significant oxide exfoliation. Special surface treatments that were applied to these materials appeared to have a beneficial effect on their oxidation behavior.

Steam turbine is one of the critical equipments in coal-fired power plants, steel P91 is a common material of its control valves. CoCr-based hardfacing on valve seats can resist long time exposure to water vapor with high temperature, thermal fatigue and solid particles erosion under high pressure. However, these hardfacing can crack and disbond during operation, which generates high risks for turbine systems and power plants. This article discussed the failure reasons of CoCr-based hardfacing, and introduced a method and practical experience of on-site repairing steam turbine valve seats with laser cladding NiCr coating.

The INCONEL filler metals 72 and 72M have been utilized significantly for weld overlay protection of superheaters and reheaters, offering enhanced corrosion and erosion resistance in this service. Laboratory data conducted under simulated low-NOx combustion conditions, field exposure experience, and laboratory analysis (microstructure, chemical composition, overlay thickness measurements, micro-hardness) of field-exposed samples indicate that these overlay materials are also attractive options as protective overlays for water wall tubes in low-NOx boilers. Data and field observations will be compared for INCONEL filler metals 72, 72M, 625 and 622.

Coal ash corrosion testing was conducted on six solution-treated nickel-based alloy plates (Alloy 617, Alloy 263, Alloy 740, Alloy 141, HR6W [45Ni-23Cr-7W], and HR35 [50Ni-30Cr-4W-Ti]) intended for advanced-USC boilers, along with conventional ferritic and austenitic stainless tubes for comparison. Tests used synthetic coal ash (Na 2 SO 4 , K 2 SO 4 , Fe 2 O 3 ) with varying SO 2 concentrations (0.02-1.00 vol%). Results showed maximum metal loss at 700°C, with higher SO 2 levels causing increased corrosion. Materials with higher chromium content demonstrated better corrosion resistance, suggesting chromium content is a crucial factor in material selection for these applications.

Trials have been performed to study the enhancement of the high temperature strength of alloy 617 by utilizing the solid solution strengthening effects of tungsten additions in the amounts of 3.30 weight % and 5.61 weight %. It could be successfully demonstrated that with the 5.61 wt.% tungsten addition, the resultant mechanical high temperature properties in the range of 700 to 750 °C were far superior to standard alloy 617. Also with regard to the oxidation resistance behavior, tungsten alloyed alloy 617 exhibited superior behavior to tungsten free standard alloy 617. Only in the hot corrosion simulated tests, the tungsten containing alloys showed increasing disadvantage with increased tungsten content. However in the real world under actual service conditions, this is of lesser relevance because the gas turbine components are and could be protected by TBC (thermal barrier coatings) and/or MCrAlY coatings. This paper describes the results of these developments. Very recent data generated on the aging response indicates drastic loss in impact values on the tungsten modified alloys after aging at 3000 hours and 5000 hours at 700°C and 750°C.

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.

Materials are the key to develop advanced ultra-supercritical (A-USC) steam generators. Operating at temperature up to 760°C and sustained pressure up to 4500 psi. Pressure vessel and piping materials may fail due to creep, oxidation, and erosion. Valves are particularly subjected to loss of function and leakage due to impermeant of the sealing surfaces. New materials, less susceptible to the above damage modes are needed for A-USC technology. Two Ni-based superalloys have been identified as prime candidates for valves based materials. Hardfacing is applied to sealing surfaces to protect them from wear and to reduce friction. Stellite 6 (Cobalt-based alloy) is the benchmark hardfacing owing to its anti-galling properties. However, the latest results tend to indicate that it is not suitable for high pressure application above 700°C. An alternative hardfacing will be required for A-USC. New Ni- and Co- based alloys are being developed for applications where extreme wear is combined with high temperatures and corrosive media. Their chemistry accounts for the excellent dry-running properties of these alloys and makes them very suitable for use in adhesive (metal-to- metal) wear. These new alloys have better wear, erosion, and corrosion resistance than Stellite 6 in the temperature range 800°C ~ 1000°C. As such, they have the potential to operate in A-USC. Velan recently developed an instrumented high temperature tribometer in collaboration with Polytechnique Montreal to characterize new alloys including static and dynamic coefficients of friction up to 800°C. We present herein the methodology that has been devolved to explore the effects of elevated temperature on the tribological behavior of those advanced material systems, with the goal of capturing the basis for the specification, design, fabrication, operation, and maintenance of valves for A-USC steam power plants.

Preface for the 2010 Advances in Materials Technology for Fossil Power Plants conference.

Oxyfuel combustion efforts to burn fossil fuels with oxygen, for easier post-combustion CO 2 capture, include schemes to use flue gas to drive turbines for power generation. The environment examined here is 10% CO 2 and 0.2% O 2 , with the balance being steam, with temperatures ranging from 630 to 821 °C. The relatively high C and O 2 activities of this environment, as compared to pure steam, may lead to changes in oxidation behavior and mechanical properties. Oxidation coupons of Ni- and Co-base superalloys, in both bare metal and TBC coated conditions, were exposed to this environment for up to 1000 hours. The results of these exposures, in terms of mass gain and scale morphology, are presented.

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.

Preface for the 2007 Advances in Materials Technology for Fossil Power Plants conference.

Extended storage of spent nuclear fuel (SNF) in intermediate dry cask storage systems (DCSS) due to lack of permanent repositories is one of the key issues for sustainability of the current domestic Light Water Reactor (LWR) fleet. The stainless steel canisters used for storage in DCSS are potentially susceptible to chloride-induced stress corrosion cracking (CISCC) due to a combination of tensile stresses, susceptible microstructure, and a corrosive chloride salt environment. This research assesses the viability of the cold-spray process as a solution to CISCC in DCSS when sprayed with miniature tooling within a characteristic confinement in two different capacities: cleaning and coating. In general, the cold-spray process uses pressurized and preheated inert gas to propel powders at supersonic velocities, while remaining solid-state. Cold-spray cleaning is an economical, non-deposition process that leverages the mechanical force of the propelled powders to remove corrosive buildup on the canister, whereas the cold spray coating process uses augmented parameters to deposit a coating for CISCC repair and mitigation purposes. Moreover, both processes have the potential to induce a surface compressive residual stress that is known to impede the initiation of CISCC. Surface morphology, deposition analysis, and microstructural developments in the near-surface region were examined. Additionally, cyclic corrosion testing (CCT) was conducted to elucidate the influence of cold-spray cleaning and coating on corrosion performance.

The pursuit of reduced emissions and increased efficiency in ultra-critical steam plants has led to the investigation of systems operating at temperatures up to 720°C and pressures up to 300 bars, necessitating the use of nickel-based alloys. This study focuses on control valves manufactured from Alloy 617, designed for steam temperatures of 725°C, examining specific challenges in their design and manufacture, including machining and welding processes. Initial operational experiences with the valve at 725°C are presented, along with ongoing tribological investigations of nickel-based alloys at 725°C, as standard material pairings with optimized wear behavior are unsuitable at such elevated temperatures. These investigations aim to develop material pairings that can maintain good wear behavior under these extreme conditions.

One of the pathways for achieving the goal of utilizing the available large quantities of indigenous coal, at the same time reducing emissions, is by increasing the efficiency of power plants by utilizing much higher steam conditions. The US Ultra-Supercritical Steam (USC) Project funded by US Department of Energy (DOE) and the Ohio Coal Development Office (OCDO) promises to increase the efficiency of pulverized coal-fired power plants by as much as nine percentage points, with an associated reduction of CO 2 emissions by about 22% compared to current subcritical steam power plants, by increasing the operating temperature and pressure to 760°C (1400°F) and 35 MPa (5000 psi), respectively. Preliminary analysis has shown such a plant to be economically viable. The current project primarily focuses on developing the materials technology needed to achieve these conditions in the boiler. The scope of the materials evaluation includes mechanical properties, steam-side oxidation and fireside corrosion studies, weldability and fabricability evaluations, and review of applicable design codes and standards. These evaluations are nearly completed, and have provided the confidence that currently-available materials can meet the challenge. While this paper deals with boiler materials, parallel work on turbine materials is also in progress. These results are not presented here in the interest of brevity.

Cast nickel-based superalloys used as structural materials for gas turbine parts need to withstand high temperatures and dynamic mechanical loads. When in contact with ambient air, the formation of protective oxide scales causes a depletion of γ’-precipitates in the surface-near region and leaves a weakened microstructure. This environmentally based degradation of the material might be accelerated under cyclic thermal exposure. In this paper, the cyclic oxidation behavior of two cast nickel-based superalloys and one single crystalline variant are investigated: C1023, CM-247 LC and M-247 SX. Exposure tests were carried out under both isothermal and cyclic conditions in air at 850 °C, 950 °C and 1050 °C for times up to 120 h to investigate the impact of thermal cycling. The differences in oxidation mechanisms are analyzed phenomenologically via light and electron microscopy and brought in correlation with the oxidation kinetics, determined based on net mass change and depletion zone growth. An assessment of the impact of precipitation loss on local mechanical strength is attempted via nano-indentation method. The found relations can be transferred onto an acceleration of crack growth under creep-fatigue and thermo-mechanical fatigue conditions.

Most effective method to increase the boiler efficiency and decrease emissions is to increase the steam temperature of modern coal-fired power plants. The increase in the steam temperature of the AUSC power plants will require higher grade heat-resistant materials to support the long-term safety and service reliability of power plants. The corrosion resistance of alloys is one of the most important factors for the application in AUSC power plants.

Six types of solution treated Ni-based alloy plates having a thickness of 25mm, namely Alloy 617, Alloy 263, Alloy 740, Alloy 141, HR6W (45Ni-23Cr-7W) and HR35 (50Ni-30Cr-4W-Ti) for advanced-USC boilers, were subjected to corrosion testing. In addition, three types of conventional ferritic and five types of conventional austenitic stainless tubes were also tested to compare their corrosion properties. Hot corrosion tests were conducted in order to assess the effects of temperature, material composition and coal ash composition on hot corrosion. The maximum average metal loss and the maximum corrosion rate were observed under 700°C test conditions. Cr content in the materials played an important role in the corrosion rate, with higher Cr content materials tending to show lower rates. However, Ni-based alloy materials showed slightly greater corrosion rates than those of stainless steels having equivalent Cr content in the over-700°C test condition. It was considered that rich Ni in the alloys easily reacted with sulfur, thus forming corrosion products having low melting points, such that corrosion was accelerated. The concentration of Fe 2 O 3 and NiO in the synthetic coal ash was also observed to affect the corrosion rate.

Preface for the 2004 Advances in Materials Technology for Fossil Power Plants conference.

Abradability, erosion and steam oxidation tests were conducted on commercial and experimental abradable coatings in order to evaluate their suitability for applications in steam turbines. Steam oxidation tests were carried out on free-standing top coat samples as well as coating systems consisting of a bond and an abradable top coat. Mapping of the abradability performance under widely varied seal strip incursion conditions was carried out for a candidate abradable coating that showed good steam oxidation performance in combination with good erosion resistance. The abradability tests were carried out on a specially designed test rig at elevated temperatures. The steam oxidation analysis combined with the abradability mapping results provide a potentially improved seal coating system that can be integrated into existing steam turbine designs for various seal locations. Such design integration is easily achieved and can be applied to steam turbine components that are sprayed in dedicated coating shops or even at the site of final turbine assembly.

The recently developed 12%Cr steel VM12-SHC is characterized by very good creep properties at temperatures up to 620°C. This new material development exhibits an excellent oxidation resistance in steam atmospheres at the typical application temperature but also at temperatures up to 650°C. In comparison to the existing 9% Cr grades T/P91 and T/P92, VM12-SHC steel opens due to its excellent oxidation behavior, new possibilities for its application as a heat exchanger boiler component. It was found that outside its application temperature range VM12-SHC also shows, as all 9-12%Cr steels, the appearance of the so called Z-phase. This effect was investigated to understand its influence on creep properties of this class of ferritic/martensitic steels aiming at controlling the microstructure stabilities for future grade developments. Creep testing has been carried out in the temperature range between 525°C and 700°C. Selected crept specimens have been investigated using light optical microscopy, SEM with EDX and TEM. In this study, the oxidation behavior of a number of typical martensitic 9-12%Cr steels was compared with the newly developed 12% Cr steel VM12-SHC. The compositions and morphologies of oxide scales formed after 5000 h exposure steels in simulated steam environments as function of temperature were characterized by light optical metallography and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX).