Steam Turbine Materials for High Temperatures

The Process of Regenerative Heat Treatment of the Valve Chamber of the Steam Turbine

Journal of KONES ◽

10.2478/kones-2019-0079 ◽

2019 ◽

Vol 26 (3) ◽

pp. 243-248

Author(s):

Agata Wieczorska

Keyword(s):

Steam Turbine ◽

High Temperatures ◽

Elevated Temperatures ◽

Cast Steel ◽

Degradation Process ◽

Steam Turbines ◽

Regenerative Heat ◽

Plastic Properties ◽

Term Operation ◽

Dynamic Damage

Abstract Steel castings are often used in the construction of valve chambers of steam turbines. Stringent requirements are set due to the continuous operation of the material at elevated temperatures, in the order of 300°C to 600°C. The material of the valve chamber must be resistant to fatigue-creep changes as well as corrosion. This material must be also resistant to dynamic damage which occures when the turbine is starting and stopping. Dynamic damage is induced by a short-lasting but intense accumulation of localized stresses. The castings of the valve chambers of the steam turbine are usually made from the “three-component” type CrMoV-cast steel. Mentioned castings of the valve chamber are continuously subjected to high temperatures, either constant and periodically variable stresses. Due to this, the degradation process of material of the castings is taking place. It is caused by physicochemical processes such as: creep, relaxation, thermal fatigue, corrosion, erosion and changes in material properties, e.g. displacement of the critical point of brittleness. Finally, first cracks and deformations can be observed in the material during the operation. The art presents the process of revitalization technology of the steam turbine valve chamber which was subjected to long-term operation at high temperatures. The revitalization process is aimed at improving the plastic properties of the material and, as the result, extending its service life. The research presented in the article show that impact strength of the chamber material after revitalization is very high. Also the strength properties of the valve chamber, after revitalization, are high and in line with the requirements. The study show that the revitalization of the valve chamber was carried out correctly and restored the material to plastic deformation.

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Paper 16: Shaft Wear Due to the Formation of Carbonaceous Deposits in the Oil Baffles of Steam-Turbine Bearings

Proceedings of the Institution of Mechanical Engineers Conference Proceedings ◽

10.1243/pime_conf_1965_180_337_02 ◽

1965 ◽

Vol 180 (11) ◽

pp. 253-264 ◽

Cited By ~ 1

Author(s):

E. M. Evans ◽

Miss A. Hughes ◽

S. G. Rushton

Keyword(s):

Steam Turbine ◽

High Temperatures ◽

Rotor Shaft ◽

Carbonaceous Deposits ◽

Mechanism Of Failure ◽

Type Of Failure

Several cases have occurred in which heavy wear of rotor shafts has been caused by the build-up of carbonaceous deposits in the oil baffles of steam-turbine bearings. Thois problem appears to have been confined to those designs of steam turbine in which the oil baffles operated at unusually high temperatures. A bearing rig has been constructed to reproduce as closely as possible the practical conditions at which the shaft failures occurred. Heat was applied externally so that the oil baffle temperature was 280°C and the rotor shaft temperature was 260°C. The type of failure which had occurred in service was reproduced in this rig, but could not proceed to the catastrophic extent encountered in practice owing to lack of power in the rig. A mechanism of failure is proposed, together with some suggestions for avoiding failure. These suggestions include restricting baffle temperatures and redesigning the baffles to reduce the tendency to form carbonaceous deposits.

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In situ REM imaging of surface processes on ceramic bulk crystals from 300 to 1670 K in a conventional TEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087616 ◽

1991 ◽

Vol 49 ◽

pp. 660-661

Author(s):

Z. L. Wang ◽

J. Bentley

Keyword(s):

High Temperatures ◽

Image Resolution ◽

Atomic Processes ◽

Crystal Surfaces ◽

Beam Radiation ◽

Surface Areas ◽

Transmission Electron ◽

Reflection Electron Microscopy ◽

Gas Reactions

Studying the behavior of surfaces at high temperatures is of great importance for understanding the properties of ceramics and associated surface-gas reactions. Atomic processes occurring on bulk crystal surfaces at high temperatures can be recorded by reflection electron microscopy (REM) in a conventional transmission electron microscope (TEM) with relatively high resolution, because REM is especially sensitive to atomic-height steps.Improved REM image resolution with a FEG: Cleaved surfaces of a-alumina (012) exhibit atomic flatness with steps of height about 5 Å, determined by reference to a screw (or near screw) dislocation with a presumed Burgers vector of b = (1/3)<012> (see Fig. 1). Steps of heights less than about 0.8 Å can be clearly resolved only with a field emission gun (FEG) (Fig. 2). The small steps are formed by the surface oscillating between the closely packed O and Al stacking layers. The bands of dark contrast (Fig. 2b) are the result of beam radiation damage to surface areas initially terminated with O ions.

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