T. Dudziak

Steam oxidation of TP347HFG, super 304H and HR3C – analysis of significance of steam flowrate and specimen surface finish

Abstract This paper delivers an analysis of the steam oxidation of the austenitic steels used for the super heater and re-heater tubing. It compares the behaviour of TP347HFG, Super 304H and HR3C at 650 and 700°C with three different steam flowrates: 4, 16· 40 mm/s. Steam oxidation tests were performed in closed loop system for 1000 h. The differences in the steam oxidation behaviour of these materials are considered in terms of the alloy compositions (especially chromium content), the steam flowrate and the material surface finish.

Effect of Steam Flow Rate and Sample Orientation on Steam Oxidation of Ferritic and Austenitic Steels at 650 and 700 C

Steam oxidation of heat exchanger tubing is of growing interest as increasing the efficiencies of conventional pulverised fuel fired power plants requires higher steam temperatures and pressures. These new, more severe steam conditions result in faster steam oxidation reactions, which can significantly reduce the lifetime of boiler components. This paper reports some results from an investigation into the impact of steam flow rates and sample orientation on the steam oxidation of surface ground superheater tube materials. The results show that an increased steam flow rate not only causes faster oxidation rates but also a change in oxide scale morphology. In case of T23, it triggers formation of micro-layered inner oxide, whereas for T92 it promotes the formation of an outer haematite layer. For austenitic steels, the faster steam flow increases the formation of initially protective oxide scales, but also accelerates the growth of oxide nodules with prolonged exposure times.

Characterisation of oxide scales developed on high temperature resistant alloys in pure steam environments

Abstract Steam oxidation of heat exchanger tubes and pipe work is of growing interest as research into the improvement of power plant efficiencies shows the need for much higher steam temperatures and pressures. This paper reports on the characterisation of the oxide scales grown during the steam oxidation of four alloys (T23, T92, TP347HFG and Inconel 740) in atmospheric pressure steam at four temperatures (600, 650, 700 and 750°C) for periods of 250, 500 and 1000 h. Three methods have been employed in analysing these scales: reflected light optical microscopy, scanning electron microscopy with energy dispersive X-ray analysis and X-ray diffraction. The thickness, composition, morphology and spalling behaviour of the oxides differed with alloy composition, exposure times/temperatures and sample shapes. The ferritic steels exhibited the most severe oxidation, with the scales formed on these typically being triple-layered: an inner layer of Fe – Cr spinel, central layer of magnetite and outermost layer of haematite. However, the amount of haematite formed changed with the exposure time/temperature, alloy and sample orientation. In comparison TP347HFG and Inconel 740 showed significantly slower oxidation, with generally thin oxide scales (<5 µm) developing even at the highest exposure temperatures, though TP347HFG started to form some nodular growths after 1000 h exposure at the two higher temperatures.

Impact specimen geometry on T23 and TP347HFG steels behaviour during steam oxidation at harsh conditions

Ferritic T23 steel and austenitic TP347HFG steel have been studied with an emphasis on understanding the impact of specimen geometry on their steam oxidation behaviour. The selected materials were tested over a wide range of temperatures from 600 to 750°C. The tests were carried out in 100% steam conditions for 1000 hours. The tests indicated that the ‘curved-shaped’ specimens show slower mass gain, scale ticking and void nucleation rates than ‘bridge-shaped’ specimens (with flat and convex surfaces combined). Furthermore, a bridge TP347HFG sample showed the formation of lower amount of flaky oxide at 750°C.

Steam Oxidation of Fe‐Based Materials

Coal‐fired power units are important player in energy production worldwide; howev‐ er, during combustion, solid fossil fuels produce large amount of CO2 and contribute to climate change, to inverse this process, higher efficiency of power plants can be achieved through out higher steam parameters (higher T, higher p). This chapter is related to steam oxidation at high temperatures where important aspects of degradation are discussed. Steam oxidation in close‐loop system using deionised water was used to perform research at high temperatures. Analyses were performed at temperatures in the range of 600–750°C for 2000 h. Different steels were included during analysis, such as T22, T23, T91, T92, E1250, 316L, 347HFG, Super 304, 309S, 310S, and HR3C. Kinetic data, metal loss data, and microscopic investigations were performed in order to evaluate corrosion degradation of ferritic and austenitic steels.

Long exposure test in air, conducted on super-lattice coatings at 850°C for 4,000 hours

Purpose – The purpose of this study is to investigate the high-temperature behavior of newly developed high-impulse power magnetron sputtering system (HIPIMS) coatings and compare them to the standard TiAlCr system deposited on to a Ti–Al intermetallic alloy. The corrosion test was performed in air for 4,000 hours at 850°C. Design/methodology/approach – In this study, air oxidation test was performed at high temperature. Design and methodology is described in detail in the methodology section in the submitted manuscript. The test was carried out by discontinuous exposure of the three different systems produced by different deposition technique. The exposed samples were investigated using scanning electron microscope coupled with energy dispersive X-ray spectroscopy. The exposed samples were investigated from the surface and cross-sections. Findings – The performed study shows that HIPIMS coatings had a much better oxidation resistance at a high temperature than that offered by the standard physical vapor ...

Steam oxidation behaviour of plasma nitrided Fe-based alloys

Purpose – It is well known that alloys, based on iron, were exposed to steam oxidation environment producing thick and non-protective oxide scale. More expensive stainless steels contain more Cr and are able to form more protective scales. The purpose of this research was to show ability to employ nitride coating on different alloys (T23, T91, E1250, 347HFG and HR3C) in order to enhance steam oxidation resistance. Design/methodology/approach – The alloys were exposed to steam oxidation rig. Before the test, furnace was purged by nitrogen in order to remove moisture and oxygen. Di-ionised water was pumped from the reservoir using a peristaltic pump into the furnace. System was kept in the closed circle. To reduce solubility of oxygen, di-ionised water was constantly purged by nitrogen. The total exposure time was 2,000 h at 650°C under 1 bar pressure. Findings – Due to the research, it was found that plasma nitriding process is detrimental for the protection of high-temperature structured materials; the hi...