Correlation Between Sodium Sulfate Mass Transfer and Low-Temperature Hot Corrosion (original) (raw)
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High Temperature Corrosion in Gas Turbines: Thermodynamic Modelling and Experimental Results
The introduction of new materials as well as the improvements in fuel quality have raised a need for re-evaluation of the hot corrosion risk in industrial gas turbines. In this study, the risk of hot corrosion was determined using thermodynamic modelling for different impuritycontents and combustion parameters. Based on these results, the parameters for the corrosion tests have been selected to investigate the response of the different materials under corrosive conditions.
Prediction of Low Temperature Hot Corrosion Rate in Film Cooled Coal Fired Gas Turbines
Heat Transfer, Volume 2, 2003
The concept of coal based gas turbine power plants has drawn considerable interest in recent years. Coal or syngas based power plants like IGCC have shown significant potential for meeting the ever-increasing power demands as well as stricter environmental regulations. The trouble free operational life of such power plants is limited by a major factor namely hot corrosion of the turbine components. Hitherto, the mechanism of hot corrosion has been investigated in a simpler context, which is not directly applicable to gas turbines in the presence of film cooling techniques. The present paper is an attempt to model hot corrosion in the presence of film cooling relevant to gas turbines, using a simple resistance model and the inherent analogy between heat and mass transfer. This paper considers film cooling air temperatures in the range of 450°C to 550°C, and a free stream gas temperature of 1425°C, with 0.5% sulfur in the fuel. For lower cooling air temperatures (less than 500°C), film cooling air suppresses corrosion, whereas for higher cooling air temperature corrosion rate is more in the presence of film cooling. With film cooling, there is a sharp peak in corrosion rate close to the cooling hole (within 10 slot widths). Due to the possibility that the base superalloy may be exposed in this region, designers should consider the high corrosion rate seriously. However, the present model is limited in its prediction because of its simplicity. Further improvement of the model is essential for optimization purposes. NOMENCLATURE Cp Specific heat at constant pressure D Binary mass diffusion coefficient of SO 2
Laboratory and field corrosion behavior of coatings for turbine blades
Surface and Coatings Technology, 1997
The present work reports the results of a comparative evaluation of three commercial coatings for turbine blades: (i) low activity pack cementation aluminide; (ii) high activity pack cementation Pt modified aluminide: and (iiij slurry deposited Si modified aluminide. For a laboratory corrosion test, bare substrate (Udimet 520) and coated samples were subjected to two different salts baths, 25% NaCl-75% Na$04 and 100% NalSOA, at 750°C in an inert atmosphere (Ar) and a gas mixture of S03-SO&. For a rainbow teht, nine coated blades were mounted in a gas turbine for 10 000 h. The test results showed that for the N&l-Na2S0, bath the damage mode of bare samples was Type I hot corrosion, while for the 100% Na2S04 bath thedamage was Type II; this effect was independent of the tebt atmosphere. Coated samples showed an incipient corrosion for the same test,. In accordance with the damage intensity, the coatings were rated (from Worst to best) as: Al-Pt, Al, Al-Si. The rainbow test showed the same tendency; however, the corrosion damage was less intensive in all cases. 0 1997 Elsevier Science S.A.
Hot corrosion in gas turbine components
Engineering Failure Analysis, 2002
The macroscopic and microscopic characteristics as well as the proposed mechanisms of Type I (high-temperature) and Type II (low-temperature) hot corrosion are reviewed. Two case histories of gas turbine blade failures are presented. Dierent practical approaches to minimize hot corrosion are described. #
Hot corrosion of ceramic engine materials
1988
1 A number of c o m m e r c i a l l y a v a i l a b l e Sic and Si3N4 m a t e r i a l s were exposed t o 1000 O C i n a h i g h v e l o c i t y , p r e s s u r i z e d b u r n e r r i g as a s i m u l a t i o n o f a t u r b i n e e n g i n e environment. Sodium i m p u r i t i e s added t o t h e b u r n e r f l a m e r e s u l t e d i n m o l t e n Na2S04 d e p o s i t i o n , a t t a c k o f t h e S I C and Si3N4, and f o r m a t i o n o f subs t a n t i a l Na20*x(Si02) c o r r o s i o n p r o d u c t . Room t e m p e r a t u r e s t r e n g t h o f t h e Sic, and g r a i n boundary d i s s o l u t i o n and p i t t i n g i n Si3N4. C o r r o s i o n regimes f i e d i n r i g t e s t s of S i 0 2 coupons. i n v e s t i g a t e d as a s o l u t i o n t o t h e c o r r o s i o n problem f o r Sic and Si3N4. c o r r o s i o n o c c u r r e d t o c o r d i e r i t e (Mg2AlqSi5018>, b u t some c r a c k i n g o f t h e subs t r a t e o c c u r r e d . e m a t e r i a l s decreased. T h i s was a r e s u l t of t h e f o r m a t i o n o f c o r r o s i o n p i t s i n e Ln I d LL1 for such Si-based ceramics have been p r e d i c t e d u s i n g thermodynamics and v e r i -P r o t e c t i v e m u l l i t e c o a t i n g s a r e b e i n g L i m i t e d
Journal of Engineering Physics and Thermophysics
A computational-experimental approach to analysis of long-time processes of mass transfer of aluminum in metallic MCrAlY coatings of gas-turbine blades and to prediction of their service life is proposed. The approach is based on the mathematical model describing the oxidation and diffusion processes in the coating and in the alloy of a blade, the parameters of which are identified by the data of short-time experiments. The results of theoretical and experimental determination of the aluminum-concentration distributions in the coating and in the basic alloy of a gas-turbine blade and the results of prediction of the service life of the coating are presented. It is shown that this approach allows one to perform analysis of long-time processes of mass-transfer in metallic coatings of gas-turbine blades and predict their service life with a high degree of accuracy.
Corrosion Issues for Ceramics in Gas Turbines
The requirements for hot-gas-path materials in gas turbine engines are demanding. These materials must maintain high strength and creep resistance in a particularly aggressive environment. A typical gas turbine environment involves high temperatures, rapid gas flow rates, high pressures,and a complexmixture of aggressive gases. .1 illustrates the requirements for components of an aircrat_engine and critical issues . Currently, heat engines are constructed of metal alloys, which meet these requirements within strict temperature limits. In order to extend these temperature limits, ceramic materials have been considered as potential engine materials, due to their high melting points and stability at high temperatures. These materials include oxides, carbides, borides, and nitrides. Interest in using these materials in engines appears to have begun in the 1940s with BeO-based porcelains [2]. During the 1950s, the efforts shifted to cermetso These were carbide-based materials intended to exploit the best properties of metals and ceramics. During the 1960s and 1970s, the silicon-based ceramics silicon carbide (SIC) and silicon nitride (Si3N4) were extensively developed. Although the desirable high-temperature properties of SiC and Si3N4 had long been known, consolidation of powders into component-sized bodies required the development of a series of specialized processing routes [3]. For SiC, the major consolidation routes are reaction bonding, hot-pressing, and sintering. The use of boron and carbon as additives which enable sintering was a particularly noteworthy advance [4]. For Si3N4 the major consolidation routes are reaction bonding and hot pressing [5]. Reaction-bonding involves nitridation of silicon powder. Hot pressing involves addition of various refractory oxides, such as magnesia (MgO), alumina (AI203),
Effect of Nano-coating on Molten Salts for Turbine Blades
2020
The purpose of this study is to optimize hot corroded pack coated Ni-based superalloy K417G using grey relational analysis. Optimization of the pack cementation parameters was performed using quality characteristics of diffusion coatings for pack cementation process, i.e., salt activator, Nanopowders master alloy powder, and wt.% Y2O3. Analysis of variance (ANOVA) was used for observing the most influencing pack cementation parameters on the quality characteristics, i.e., Na2So4-6% wt. V2O5 (kp1), 100 wt% NaSO4 (kp2), and 75 wt. % NaSO4-25 wt % NaCl (kp3). The optimal process parameters were calculated using a grey relation grade and a confirmation test was performed. Based on the analysis of variance results, the wt.% Y2O3 is the most significant controllable diffusion coating factor for the hot corroded pack coated K417G at optimum setting conditions (A2, B3, C3) i.e., activator (NaCl), master alloy (94Cr-6Al), and wt.%Y2O3 (4%). according to the quality characteristics. Grey rela...
Hot Corrosion Behaviour of HVOF Sprayed Stellite-6 Coatings on Gas Turbine Alloys
The coal burned natural gas in contact with gas turbine can contain impurities of sodium, sulfur, vanadium, silicon and possibly lead and phosphorous, induce accelerated hot corrosion during long term operation. Coatings are frequently applied on gas turbine components in order to restrict surface degradation and to obtain accurate lifetime expectancies. High velocity oxy-fuel thermal spraying has been used to deposit Stellite-6 alloy coatings on turbine alloys. Hot corrosion behavior of the coatings were investigated for 50 cycles of 1 h heating at 800°C followed by 20 min cooling in presence of Na 2 SO 4 ? 50 % V 2 O 5 measuring weight gain (or loss). X-ray diffraction and SEM/ EDAX techniques were used to characterize the oxide scale formed. The superior performance of Stellite-6 coating can be attributed to continuous and protective thin oxide scale of CoO, Cr 2 O 3 and SiO 2 formed on the surface. The coating region beneath this thin oxide scale was partially oxidized. Uncoated SuperCo-605 and MDN-121 showed less weight gain than Stellite-6 coated samples, but they showed spalling or sputtering during cyclic oxidation. Stellite-6 coating was dense and pore free even after 50 cycles, indicating that it can resist the hot corrosion cycle.
METAL 2021 Conference Proeedings, 2021
The paper focuses on the evaluation of the ability of selected heat sprayed coatings to protect the surface of the component in an environment simulating the environment of a geothermal turbine. The subject of testing were coatings based on hardmetals, applied by HVOF technology (WC-CoCr, Cr3C2-NiCr) and Fe and Ni based alloys, applied by HVOF (NiCr, FeCrAlY) and TWAS (FeCrAlNiC, FeCr, NiCr) technologies. It has been shown that although HVOF coatings provide higher protective properties in terms of both corrosion and resistance to mechanical influences, it is also possible to apply the protective coating with TWAS technology if mobile spraying is required. From the materials tested, the Fe-based Metco 8294 can be recommended as a most promising, providing high wear resistance and sufficient corrosion resistance in aggressive environment.