High Temperature oxidation behavior of materials for Super critical fossiel fuel Power plant edited.docx (original) (raw)
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High-Temperature Degradation and Protection of Ferritic and Austenitic Steels in Steam Generators
Journal of Materials Engineering and Performance, 1998
The useful life of superheaters and reheaters of power stations which use heavy fuel oil is shortened and their continuous service is inhibited by corrosion (fireside) and creep-type problems. The increase of corrosion attack on boilers is caused by the presence of fuel ash deposits containing mainly vanadium, sodium, and sulfur which form low-melting-point compounds. The tubes are exposed to the action of high stresses and high temperatures, producing the so-called "creep damage." In this work, two kinds of results are reported: lab and field studies using a 2.25Cr-1Mo steel. The laboratory work was in turn divided into two parts. In the first, the steel was exposed to the action of natural ash deposits in oxidant atmospheres at 600 °C for 24 h. In the second part, tensile specimens were creep tested in Na 2 SO 4 , V 2 O 5 , and their mixture over a temperature range of 580 to 620 °C. In the field work, components of a power station were coated with different types of nickel-and iron-base coatings containing chromium, Fe-Cr, and Fe-Si using the powder flame spraying technique. After testing, the coated tubes were analyzed using electron microscopy. The results showed that all the coating systems had good corrosion resistance, especially those containing silicon or chromium.
2016
Reduction in CO2 emissions from coal-fired power plants is one of the major challenges in order to decrease global warming effect. In energy sector, the aim to reduce CO2 emission can be achieved by increasing the operating temperature (and pressure) of water steam system, which results in an increase in overall coal fired power plant efficiency. Currently the main components of coal fired power plants are made from the materials designed years ago; to meet harsh eco criteria such materials are not suitable for harsh conditions of modern coal-fired power plant. Subcritical power stations are main contributor in CO2 emission globally, with high CO2 emission and low efficiency ~ 37 %. The next-gen coal-fired power plants have potential to reach 55% efficiency, taking into account, that 1% increase in absolute efficiency results in as much as 3% reduction in CO2 emissions, 55 % of CO2 lower emission achieved. Modern, advanced coal fired power stations operating under Ultra Super Critic...
Materials Research-ibero-american Journal of Materials, 2004
In recent years a new group of ferritic-martensitic chromium steels for the use in fossil power stations has been developed with chromium contents between 9 and 12%. Typical representatives of these steels are P91, E911 and Nf616, which are nowadays widely used in the more advanced power plants. In the development phase the focus was on the mechanical properties of these steels but when taking them to practical operation conditions it turned out that much of the lifetime of the materials and components is determined by their oxidation properties. Oxidation resistance is first of all a function of alloy composition. For the steels of this group it is chromium, silicon, manganese and molybdenum that decide their oxidation performance and since the contents especially of the four elements can be significantly different for the different steels there can be clear differences in oxidation behaviour. One of the most important issues from this point of view is how the concentrations of these elements change in the metal subsurface zone during operation/oxidation since if their level drops below a critical level oxidation resistance of the steels will be lost. In the work to be reported the influence of alloy composition and metal subsurface zone concentration as a function of oxidation time up to 10000 h was investigated in dry air and air up to 10% water vapour at 650 °C. The investigations comprised several of the advanced commercial 9% Cr steels including P91, E911, Nf616 and six laboratory melts of Nf616 with different amounts of silicon. As the results of the investigations show humidity, which is omnipresent in combustion environments, can dramatically accelerate oxidation. Silicon as an alloying element reduces the detrimental effect of water vapour significantly while molybdenum has a negative effect. The effects of the key alloying elements in these steels was quantified for conditions with and without water vapour in the environment including the role of mechanical load and recommendations were developed on how to guarantee the optimum oxidation resistance of these steels.
Corrosion Science, 2004
The oxidation behavior of a number of selected ferritic steels in a simulated steam environment at temperatures between 550 and 650°C was studied. In the prevailing test gas, some of the studied 9-12% Cr steels tended to exhibit an anomalous temperature dependence of the oxidation behavior. This means, that the oxidation rates do not steadily increase with increasing temperature. At higher temperatures, some of the studied steels tend to form a very thin and protective oxide scale whereas at lower temperature rapidly growing, less-protective oxides are being developed. The anomalous temperature dependence is related to differences in chromium distribution in the inner part of the oxide scale. The effect is observed for steels with intermediate-Cr contents ($10-12%) whereas steels with either lower or higher Cr contents exhibit an increasing oxidation rate with increasing temperature.
Paper on High Temperature Corrosion and Its Control in Coal Fired Boilers
2018
Recent research and development on high temperature corrosion problems, with the techniques available to control this problem, is reviewed and discussed in this paper. Boiler is an essential element of power generation plants. With increasing fuel and energy costs, maintaining the reliability and consistent performance of a boiler while minimizing energy costs is challenging for any industrial plant. Since boiler systems are constructed primarily of carbon steel, the potential for corrosion is high which can result in a forced shutdown of the boiler and the industrial process. The fireside corrosion in coal fired utility boilers is one of the main problems. Superheaters and reheaters suffer from steam oxidation on their inner surfaces and hot corrosion on the fireside. Fireside corrosion cannot be eliminated completely but it can be controlled. There are several techniques to control the high temperature corrosion problems in boilers which are Fuel blending, use of additives, replacing tubes with more corrosion resistant materials, thermal spray coating, thicker tube walls, adjustment of firing rate, amount of excess air, air temperature and amount of recirculating flue gas can be very effective in controlling the amount and composition of ash deposit, and effective boiler design and construction can also help in controlling ash deposition etc.
Protective coatings for high-temperature steam oxidation in coal-fired power plants
Surface and Coatings Technology, 2019
The corrosion resistance of protective coatings on stainless steels against high-temperature steam oxidation has been studied. The coatings are made through the thermal diffusion process and consist of aluminides with a 2-3 layer structure or with more complex architectures when the aluminide layers are covered by thin oxide-based (e.g. Al 2 O 3 , SnO 2 , ZrO 2) or BN layers. The oxidation behaviour of these coatings compared to bare materials (e.g. 310SS and 800H) was studied at 800 o C for 3000 hours. In this work, along with determination of mass change of the samples vs. time (kinetic of oxidation), extensive structural analysis and surface hardness determination have been carried out. The developed multi-layered coating architectures demonstrated promising high-temperature steam oxidation performance with no breakaway degradation issues. Their performance is defined by the inertness of the aluminium intermetallides with a total thickness of protective coatings of greater than 100 µm, which are formed through the thermal diffusion process, with high diffusion-related bonding between the layers and with the substrate, and by the formation of the aluminium oxide films occurred due to the surface oxidation. The additional layer from the selected oxides or BN applied on the top of the aluminized structure can provide additional corrosion protection; however, it is important to maintain a high level of bonding between this layer and the intermetallide structure. The thermal diffusion technology and obtained coating systems are applicable for the protection of products with different sizes and shapes, including long tubing required in industry.
Studies on High-Temperature Corrosion resistance of low carbon Steel in Actual boiler environment
IOP Conference Series: Materials Science and Engineering, 2019
In coal based power generated plants, hot corrosion and erosion are identified as serious problems, resulting in deterioration of boiler tube. In this present study, the High-Temperature Corrosion behavior of bare SA 210 Gr. A1 steel and Friction stir processed Cr3C2-25(NiCr) inserted Gr. A1 steel samples were compared under cyclic condition of 1500 hours in actual both environments. The kinetics of hot corrosion was measured on the base of weight-change after each cycle. The tool rotation speed for three processed samples were recorded as 1600rpm, 2000rpm, 2400 rpm respectively with transverse speed of 30 mm/min processed by three number of passes. Microstructure evolution of base and FSPed was done by electron back scatter diffraction (EBSD). X-ray diffraction (XRD)and scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS) were performed on the exposed sample to analyze the corrosion products. The base steel sample suffered extreme erosion-corrosion in ...
Japanese experience with steam oxidation of advanced heat-resistant steel tubes in power boilers
Materials at High Temperatures, 2005
Japanese experience of steam oxidation behavior of advanced heat-resistant steel tubes in power boilers is discussed. Severe scale separation, cracking, and exfoliation were observed in T91 pendant reheater tubing in a Japanese utility boiler after around 40,000 hours of operation. Separation occurred at the interface between the inner and outer layers of scale. A highpressure steam oxidation test rig in which the steam conditions could be controlled in a similar manner to that of an actual boiler was developed and T91 steel samples were tested up to 10,269 hours. The scale separation behavior of T91 was reproduced in the steam oxidation test. The growth rate of T91 was lower than that for conventional 9Cr-1Mo steel reported by EPRI. The scale separation was related to void formation at the interface between the inner and outer layers of scale, as well as the transformation of magnetite into hematite in the outer layer. Field exposure testing was carried out for T23 and T122 for 80,000 hours, and the properties of steam oxidation scale were obtained.
High-temperature oxidation of pure Fe and the ferritic steel 2.25Cr1Mo
Materials Research-ibero-american Journal of Materials, 2005
The global pressure for recycling and ecological energy production increases steadily in combination with the demand of cost-effective application of materials. However, some severe corrosion problems, associated with the high internal/intergranular corrosion rates in boiler components need to be avoid. Some commercial boiler materials contain a Cr content of 0.55 (wt. (%)) - 2.25 (wt. (%)). This Cr concentration in the alloys is not sufficient for the formation of a complete dense Cr2O3 scale. Hence, high oxidation kinetics may result. In this study, pure Fe and the steel 2.25Cr1Mo were oxidized in laboratory air at 550 °C using a thermobalance system. The surface as well as the cross section of oxidized specimens were analysed using scanning electron microscopy in order to quantify several factors (e.g. surface finishing, cold working and grain size) on the overall oxidation kinetics. For alloys with low Cr content, a decreasing in the grain size leads to an acceleration of the oxidation rate by facilitating the oxygen diffusion along alloy grain boundaries leading to an inward oxide layer formation. The study of effects of surface finish and cold working yielded results revealing that the oxidation process is complex and comparison of results from different laboratories is difficult and should be done.