Corrosion Processes on Steel Under Conditions of Moisture Condensation and in the Presence of Carbon Dioxide
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MATERIALS SCIENCE. CORROSION PROTECTION CORROSION PROCESSES ON STEEL UNDER CONDITIONS OF MOISTURE CONDENSATION AND IN THE PRESENCE OF CARBON DIOXIDE R. K. Vagapov, K. A. Ibatullin, and D. N. Zapevalov
UDC 620.197.3
Development of corrosion processes under conditions of moisture condensation in the gas phase in the presence of carbon dioxide that lead to formation of local damage are studied. These conditions for creation of a condensation film of water on steel arise on objects for gas production and processing where there are differences in temperature and pressure. It is confirmed that at elevated temperature when the temperature gradient is greater a more significant amount of moisture condenses on a steel surface that leads to an increase in the rate of both overall and local corrosion by a factor of two to three compared to room temperature. The overall corrosion rate is low (up to 0.1 mm/year) and local corrosion with respect to depth index is from 0.9 to 1.8 mm/year. Condensation processes and associated corrosion in aqueous-alcoholic and aqueous-glycolic media in the presence of CO2 depend on the amount of water in these solutions i.e., corrosion does not develop with low concentrations of water. Keywords: corrosion processes, moisture condensation, corrosion rate, local corrosion, carbon dioxide, local corrosion defects.
Provision of operational reliability and safety for objects in the recovery of hydrocarbons are connected with studying corrosion processes in order to select effective means of corrosion protection. Corrosion conditions are presence of moisture and corrosion-active acid gases dissolved within it, for example hydrogen sulfide (H2S) and carbon dioxide (CO2). During hydrocarbon recovery and processing the main sources of aqueous phases are seam water and/or condensed water vapor. Possible areas for corrosion formation within a gas pipeline system [1]: lower part of a pipe (with moisture accumulation), six-hour corrosion or bottom-of-line corrosion (BOL); upper part of a pipe (with moisture condensation, twelve-hour corrosion, or top-of-line corrosion (TOL); areas of moisture accumulation (slots, gaps, stagnant areas, drop in height, etc.). During TOL corrosion there is localization of corrosion processes with formation of pitting and spots. These corrosion processes occur under moisture condensation conditions, only typical for gas objects, but not for oil objects. Conditions for the onset of occurrence of the TOL corrosion process are a high moisture content in the seam gas recovered; thermobaric conditions for separation of water from a gas medium and its condensation on the inner surfaces of the upper part of a pipe. Conditions for moisture condensation in a gas phase and occurrence of corrosion are implemented also on gas processing objects, i.e., with drops in temperature and pressure in the presence of corrosion-active gases OOO Scientific Research Institute of Natural Gases and Gas Technology, Gazprom VNIIGAZ, Russia; e-mail: [email protected].
Translated from Khimichesko
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