The paper investigates aspects of the development of corrosion processes under conditions of moisture condensation in the gas phase in the presence of carbon dioxide, which lead to the formation of local damage. The authors developed and tested a methodology for conducting steels corrosion testing The causes of the formation and the corrosive effect of moisture condensation on steel under conditions of carbon dioxide corrosion at gas production facilities are analyzed. It was found that at elevated temperatures, when the temperature difference is higher, more moisture condenses on the surface of the steel, which leads to an increase in the rate of both general and local corrosion by 2–3 times, compared to room temperature. The increased localization of corrosion processes under conditions of moisture condensation and the presence of CO2 makes the depth index of steel corrosion much higher than the general corrosion rate. When assessing the corrosiveness of environments with condensation of the aqueous phase, the rate of corrosion associated with the depth of the observed corrosion damage should be taken into account. According to the test results, it was determined that samples from the weld compared with the sample from the main body of the pipe differ in the degree of localization of corrosion in conditions of moisture condensation.
The use of various intrusive and non-intrusive methods of corrosion monitoring makes it possible to assess the corrosion situation and the effectiveness of the applied corrosion protection agents in conditions of internal corrosion at gas production facilities due to the presence of aggressive gases. The analysis of the application of ultrasonic testing methods as part of corrosion monitoring of internal corrosion at gas production facilities in the presence of corrosive components is carried out. Ultrasonic thickness measurement is widely used as a non-intrusive method for monitoring internal corrosion and detecting corrosion defects in promising gas fields. Many gas fields (Bovanenkovskoye oil and gas condensate field, Urengoy oil and gas field and others) revealed corrosion defects due to cases of internal corrosion due to the presence of increased amounts of carbon dioxide in the produced hydrocarbons. Under conditions of corrosion in the presence of carbon dioxide, ultrasonic methods for measuring the thickness of a metal have certain limitations associated with the unpredictable local nature of carbon dioxide corrosion, which should be considered when used in gas facilities. The main method for measuring thickness under operational conditions is ultrasonic thickness measurement, which is used in conjunction with radiographic monitoring. Using these two main non-intrusive methods, corrosion monitoring monitors the thinning of the metal, the size and depth of local defects and the dynamics of their change over time. Based on the results of measuring the residual wall thickness of the pipe and equipment, the possibility of their further work is determined, and recommendations are made on extending the safe life of gas facilities. The authors analyzed the literature data on new options and technical solutions for the use of ultrasonic methods in the measurement of the thickness of a metal surface.
Products of several going and promising onshore and offshore hydrocarbon extraction sites both in Russia and foreign countries are known due to elevated level of corrosive СО2. The article analyzes present procedures aimed at rating corrosive hazard of extracted fluids, selection and implementation of measures for protection of equipment and pipelines against of inner corrosion. Onshore and offshore facilities work within specific environment, which affects arrangement of corrosion protection and corrosion monitoring systems. Presence of СО2 in the extracted products together with other factors stimulate intensive growth of corrosion, and require attentive and reasonable attitude to choose engineering solutions providing safe and reliable operation of production facilities.
Products of several currently operated production facilities (Bovanenkovskoye, Urengoyskoye oil and gas condensate fields, etc.) contain an increased amount of corrosive CO2. Effect of CO2 on the corrosion of steel infrastructure facilities is determined by the conditions of its use. Carbon dioxide has a potentially wide range of applications at oil and gas facilities for solving technological problems (during production, transportation, storage, etc.). Each of the aggregate states of CO2 (gas, liquid and supercritical) is used and affects the corrosion state of oil and gas facilities. Article analyzes the results of simulation tests and evaluates the corrosion effect of CO2 on typical steels (carbon, low-alloy and alloyed) used at field facilities. The main factors influencing the intensity of carbonic acid corrosion processes in the main conditions of hydrocarbon production with CO2, storage and its use for various technological purposes are revealed. Development of carbon dioxide corrosion is accompanied and characterized by the localization of corrosion and the formation of defects (pitting, pits, etc.). Even alloyed steels are not always resistant in the presence of moisture and increased partial pressures of CO2, especially in the presence of additional factors of corrosive influence (temperature, aggressive impurities in gas, etc.).
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