Reducing the rate of corrosion and scale formation in heating mains and circulating cooling systems

Abstract

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

Creation and study of formulations as inhibitors of metal corrosion and scaling for stabilization water treatment in water utilization systems (a review)

“…For example, the efficiency of ZnHEDP was studied using corrosion indicators, and for comparison, that of known inhibitors: IOMS-1, HEDP itself, PAPh-13A (NTP aqueous solution, methyliminodiphosphonic acid (MIDP), and polyaminopolymethylphosphonates), as corrosion inhibitors for internal pipe surfaces in a hot water supply system [9]. These OPs were found to inhibit corrosion in deaerated water, but their efficiency is much lower than that of ZnHEDP.…”