The "SPb SEC" Association has developed a standard of the organization (STO) "Refractories. Method for Determining Hydration Resistance." The standard covers powders and articles based on magnesium oxide. The hydration resistance of powders is evaluated in terms of the change in the mass or in the grain composition of a sample after treating it with steam under pressure; the hydration resistance of articles is estimated from the change in their appearance.Refractories based on periclase (magnesium oxide) and bearing calcium oxide can undergo hydration in a warm humid atmosphere. In this case the powder grains break, the material is pulverized, and the articles crack. Various methods exist for determining the hydration resistance of refractories. The most frequently used methods are (1) treatment of the tested material with steam at normal or elevated pressure and a temperature corresponding to the steam pressure and (2) holding in a climatic chamber at a temperature below 100°C at a high moisture content. The second method is closer to natural conditions under which such articles are stored, especially in a humid tropical climate, but the test takes a long time. In Great Britain and in the USA the methods for determining the hydration resistance of refractories have been standardized. The main items of the standards are presented in Table 1.In Russia, where periclase and periclase-containing refractories are produced in considerable volumes, such standards are absent. In this connection it seems appropriate to evaluate the hydration resistance of domestic and imported refractories used in the RF. It has been decided that a method for determining hydration resistance should be developed and standardized.The "St. Petersburg Scientific-and-Engineering Center" Association of Producers and Consumers of Refractories ("SPb SEC" Association) has developed a standard of the organization (STO) "Refractories. Method for Determining Hydration Resistance." The STO has been created with allowance for the experience of foreign standardization and for the results of an experimental study. The method consists in treating the studied samples and refractory specimens with steam under specified conditions and subsequent evaluation or visual estimation of the changes that have occurred.The choice of the method for preparing samples of granular materials (powders) was preceded by an analysis of standards for periclase powders (GOST 24862, GOST 10369, etc.) [1,2]. It was established that the majority of such powders consist of fractions finer than 4 mm. Accordingly, a representative sample for the test is prepared by milling the powder for passage through sieve No. 4 and screening the undersize through screen No. 0.1. It should be noted that producers in Great Britain and in the USA use periclase powders with coarser grain composition and thus test samples with larger grains (see Table 1).The material can be partially hydrated during storage, milling, and screening. In order to ensure the same initial state the samples are baked at ...