Studies on Principally A-Type Deflections Appeared in Steam Turbine Rotors during Heat Indication Test

Abstract

In previous studies of other authors, it has been shown that the so-called A-type deflection (as classified by Kaplan) observed in steam-turbine rotors during the heat-indication test (H. YOSHIDA, et ib., Vol. 47 (1961), 591-599) is caused by non-uniformity in heat aborbability of the rotor surface and the heat absorbability is a function of the degree of roughness of the machined surface. Also it has been shown that non-uniformity in the heat absorbability is a result of non-uniformity in heat-treatment of the material, which can be shown by hardness testing.
In the present investigation, by using an apparatus designed by the anthor, measurements of the heat-absorbability of a Cr-Mo-V steel, a Ni-Mo-V steel and a plain carbon steel tempered under various conditions were carried out to establish a quantitative relationship between the heat-absorbability and the tempering conditions.
The results obtained are as follows:
(1) In the same steel, the heat absorbability has a linear relationship to the hardness of the machined surface: Hard surface shows a low absorbability.
(2) Relation between the heat absorbability and the hardness depends on the kind of steel, and it is found that the carbon steel is the most sensitive to non-uniformity in the heat absorbability, while Cr-Mo-V steel and Ni-Mo-V steel are less sensitive.
(3) The heat absorbability at between room temperature and 380°C depends mainly on the surface roughness, while at above 380°C oxide layers make a large effect on the absorbability.