Effects of Thermal Barrier Coating and Cooling System on a Heat-Resisting Stainless Steel Ring Performance in a Gas Turb
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TECHNICAL ARTICLE—PEER-REVIEWED
Effects of Thermal Barrier Coating and Cooling System on a Heat-Resisting Stainless Steel Ring Performance in a Gas Turbine Burner Aliakbar Fallah Sheykhlari . Saeed Khani Moghanaki . Safarali Khatir . Meisam Khodabakhshi
Submitted: 27 May 2020 Ó ASM International 2020
Abstract Burners are the heating source of a gas turbine which are working at high temperatures and under high thermo-mechanical stresses. These components are always threatened by cracking and hot corrosion damages due to high-temperature working environment. In this study, the effects of employing thermal barrier coating and modified cooling system on the temperature distribution and the cracking phenomenon in a burner ring of a power plant gas turbine are investigated. Microstructural examinations on a ring without thermal barrier coating demonstrate that nitrogen uptake by the ring at high temperature leads to the formation of some undesirable phases. These phases, hot corrosion, and high thermal loads lead to cracking of the ring during turbine operation. Results show that both modification of cooling system and applying thermal barrier coating reduce ring temperature, but the latter has significant effect on reducing ring temperature and cracking phenomenon. Keywords Burner ring Gas turbine Heat-resistant stainless steel Thermal barrier coating
A. Fallah Sheykhlari S. Khani Moghanaki (&) S. Khatir Chemistry and Materials Research Center (CMRC), Metallurgy Department, Niroo Research Institute (NRI), Tehran, Iran e-mail: [email protected] M. Khodabakhshi MAPNA Turbine Engineering and Manufacturing Company (TUGA), Fardis, Karaj 15875-5643, Iran
Introduction Superior high-temperature properties of heat-resistant stainless steel extend its applications to various industries such as power plants [1]. One of the important applications of the heat-resistant steel is as an insert ring in gas turbine burner. The insert ring is used to conduct and shape the flame into the combustion chamber. These rings are positioned above the flame tube by 12 bolts [2]. The microstructure of the ring is usually stabilized by Nb, and the microstructure includes inter-dendritic NbC in the austenitic matrix [3]. Niobium is known as a strong carbide former (NbC) which prevents the formation of grain boundary M23C6 and concomitant inter-granular chromium depletion [4, 5]. Although Nb addition has a favorable role as mentioned above, this element also results in austenite instability due to the formation of intermetallics when exposure to high temperature [6]. The formation of an intermetallic phase known as r-phase not only reduces corrosion resistance of a stainless steel by absorbing chromium and molybdenum of austenitic matrix, but also reduces the mechanical properties [7–9]. Some precipitates such as Laves phase of the type Fe2Nb and M6C are usually formed after heat treatment below 850 °C [10–14]. Ayer et al. [11] observed a nitride termed Z-phase, chromium niobium carbide or carbo-nitride (CrNb(C,N)), in a stabilized and n
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