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Stationary oxygen concentration in a closed heat-supply system, which is filled and replenished with nondeaerated water at a temperature of 20 ° C, has been calculated. The calculation takes into account the system surfaceto-volume ratio and the relative added makeup water volume fraction. In the case of a system using corrosion inhibitors, the stable oxygen concentration at a preset makeup rate falls within 400-800 µ g/dm 3 . Experiments performed in a special setup for polarization measurements showed that, at an oxygen concentration of 600 µ g/dm 3 , a decrease in the general internal corrosion rate can be achieved using IOMS-1 and PAF-13A inhibitors at a concentration of 4 − 5 mg/dm 3 , or a zinc complex of oxyethylidenediphosphonic acid at 25 mg/dm 3 .

Measures to reduce the rate of internal corrosion of piping in heating networks are described, including: raising the mains water pH, reducing the oxygen content in feed and mains water to established norms, introducing direct monitoring of the oxygen content in heating systems, using corrosion inhibitors, and installing corrosion indicators. A test stand is constructed for determining the antiscaling efficiency of various complexones. Based on the test results, a method for antiscaling treatment of mains water and the water in circulating cooling systems is developed and introduced in a number of installations.Protection of heating systems from internal corrosion. At present there are more than 250,000 km of two-line heating mains in Russia and the rate of damage to heating system pipes has risen over the last twenty years to 70 incidents per 100 km per year. According to data at VTI, on the average 20% of the damage is related to internal corrosion, which is local in character and shows up in the form of pits that develop into fissures.For a long time the problems of internal corrosion in heating pipes were not studied. Work at the VTI over the last 17 years shows that the main factors influencing internal corrosion of steel piping under the conditions of a heating system are the pH of the water and the concentration of oxygen, sulfates, and chlorides in the water. Their significance and combined effect determine the aggressiveness of the mains water toward the metal. Nomograms developed at VTI (only for a standard oxygen content of 20 ìg/dm 3 in the system water) can be used to distinguish water as corrosion aggressive or corrosion safe in heating systems [1,2].In 1992 -1993 VTI evaluated the vulnerability to internal corrosion and the parameters of the water-chemical regime of the heating networks of 147 heat supply systems. In terms of their operational data averaged over a 5 year period, these systems were subdivided into three groups: with mains water pH below 8.30, 8.30 -9.25, and above 9.25. Table 1 summarizes the susceptibility to damage owing to internal corrosion caused by the pH of mains water. Table 1 shows that for mains water pH exceeding 9.25, there is a sharp reduction (by roughly a factor of 7) in the damage to heating systems by internal corrosion. At the same time, the rate of accumulation of iron in the mains water, which characterizes the rate of corrosion, decreases significantly. This is related to reduced corrosion with pitting in steel. On going from mains water with a pH below 8.30 to mains water with pH = 8.30 -9.25, there is no great change in the damage to the piping. The reduction in the rate of accumulation of iron observed in this case may be associated

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The effect of internal-corrosion inhibitors on heating-system pipelines is investigated. Tests were conducted on a testing device for polarization measurements under conditions corresponding to the Rostov Heat-Supply System. The concentration of OEDP-zinc, which provides a high degree of protection from general corrosion, is determined. The reagent has been successfully incorporated into the Rostov No. 2 TPP.According to [1], more than 220,000 km of water-heating grids, which operate primarily during the winter, are in service throughout Russia. More than 90% of the heating lines reside in this type of layout.The damage sustained by the heating runs differs in different regions of Russia, and fluctuates from 0.2 to 1.5 damages per 1 km of run per year. Corrosion failures of the pipe metal are the causes of nearly all damages. They are, in large part, governed by external corrosion; considerable attention is therefore being devoted to its elimination. At the same time, internal corrosion, according to data derived by the JSC "RAO EÉS Rossii," had increased by 28% during the 2002/03 heating season., i.e., more than one-fourth of all damages sustained by the pipelines in the heating systems [2].It can be stated that today means of solving problems of the external corrosion of pipelines are already in the planning stage. They consist in the creation of a dependable external insulation, for example, foam polyurethane insulation and a system to monitor its disturbance. Broad implementation of quality pipeline insulation, which has begun in many cities of Russia, will, in the future, lead to a reduction in external corrosion, and, correspondingly, to a significant increase in the percentage of internal corrosion in the overall damage sustained by the heating systems. Expansion of the search for means of solving this problem is therefore urgent.For closed heat-supply systems, an increase in the pH of the heating water to 9.5 -10.0 is a highly effective means of controlling internal corrosion. A water-chemical regime with high-pH heating water, which has been introduced to heating systems maintained by the Mos nergo, has made it possible to prevent the formation of corrosion pitting on the internal surface of pipes, and also suppress the development of the pitting that already exists; this has been substantiated by an appreciable reduction in damages sustained by the pipelines of the heating systems [3]. The rate of uniform corrosion of steel, from which, in addition to corrosion-indicator readings, a reduction in iron content in the heating water is judged, is also diminished at a pH of 9.5 -10.0 [4].According to [5], an increase in the pH of the heating water to more than 9.0 is acceptable for open heat-supply systems; use of corrosion inhibitors is therefore an effective means of protecting against internal corrosion.We investigated the anti-corrosion effectiveness of sodium phosphate, sodium silicate, and a zinc disulfate complex of 1-oxy-1.1-ethylidene diphosphonate (OEDP-zinc), which have an allowable concentration ...