Internal-corrosion inhibitors for pipelines carrying deaerated heating water

Abstract

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 ...

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

“…These data have been confirmed at VTI under industrial conditions in Rostov-on-Don [6]. These experiments showed that the major antiscaling phosphonates (IOMS, OEDP, PAF-13A) also inhibit corrosion in deaerated water, but to a lesser extent than OEDP-Zn.…”