Rapid evaluation of metal properties for high-temperature high-chromium turbine and steam line components

Abstract

Metal of a stopper valve made of steel 1Kh11MFBL, a bent pipe of considerable diameter made of steel 1Kh12V2MF (ÉI-756) and a pipe billet of steel 10Kh9MFBSh (DI-82) are used to consider application of a new procedure, according to which by combined analysis of stress-rupture strength data for a small number of cylindrical and notched specimens it is possible to evaluate metal stress-rupture strength and the relative reserve of thickness for possible initial defects in high-temperature components of cylindrical shape.Complexly alloyed high-chromium steels are used currently in order to manufacture the main components of boilers, turbines and steam lines that operate with a steam temperature of 565°C or more. In our country assimilation of these materials had a considerable history that was interrupted for almost twenty years. Now in view of the construction of power generating units with high steam parameters it is necessary to set up again production of steam lines with steels of this class. Therefore it is important to compare their operating reliability, i.e., mechanical properties under creep conditions on the basis of relatively short-term laboratory studies that do not require a considerable number of specimens. It is necessary to develop special rapid methods for this purpose.It is assumed that the most important property on which the high-temperature operating life of a component depends is metal stress-rupture strength. In addition, it is important to know the reserve of wall thickness for the size of initial defects, permitted by the technical conditions on supply, that compensate their probable presence and provide a life not less than the standard period. It is well known that typical initial defects in pipes are sinks due to scale and longitudinal score marks, and in the bodies of cast components they are blow holes, rat tails, large non-metallic inclusions, etc. In view of this the aim of the article is description of the results of using procedures for evaluating the level of metal stressrupture strength and the reserve of wall thickness for possible initial defects in high-temperature components of cylindrical shape from the results of stress-rupture tests for a relatively small number of cylindrical specimens with an annular notch.The test materials were metal of the cast body of a stopper valve for a high-pressure turbine K-300-240 LMZ made of steel 1Kh11MFBL (cutting was done after 140,000 h of operation); metal from a bent branch pipe 219/187 mm in diameter made of steel 1Kh12V2MF (ÉI-756) operated in a steam line of a live steam unit of 300 MW for 170,000 h, and also (due to a lack of metal from a steam line pipe) metal from a pipe billet 105 mm in diameter of steel 10Kh9MFBSh (DI-82) supplied by JSC "NPO TsNIITMASh."The chemical composition of the metal of these components is given in Table 1, and the mechanical properties of their specimens are given in Table 2.With respect to chemical composition the metal of all of the components answered the standards of the corresponding technical speci...