152 UDС 620.195 RESEARCH OF THE INFLUENCE OF SAMPLE WITNESS CHARACTERISTICS ON THE EFFICIENCY OF CORROSION MONITORING ИССЛЕДОВАНИЕ ВЛИЯНИЯ ХАРАКТЕРИСТИК ОБРАЗЦОВСВИДЕТЕЛЕЙ НА ЭФФЕКТИВНОСТЬ КОРРОЗИОННОГО МОНИТОРИНГА A.P. Efremenko, A.Y. Spasсhenko, I.F. Sadretdinov, K.V. Aleksandrova, FSBEI НРЕ “Ufa State Petroleum Technological University”, Ufa, the Russian Federation LLС “R&D Center Salavatnefteorgsyntez”, Salavat, the Russian Federation Ефременко А.П., Спащенко А.Ю., Садретдинов И.Ф., Александрова К.В., ФГБОУ ВПО «Уфимский государственный нефтяной технический университет», г. Уфа, Российская Федерация ООО «Научно-технический центр Салаватнефтеоргсинтез», г. Салават, Российская Федерация email: [email protected] Abstract. In this paper the advantages of corrosion monitoring are described using gravimetric witnesses samples for oil production and refining companies, the necessity and effectiveness of their use are founded, the additional capabilities of the method are shown, especially control of deposits on the internal surfaces of equipment and their effect on the corrosion rate. The paper presents data on the coupons geometric form, it is noted that witnesses samples of rectangular shape are the most widespread. This article also presents information about the modernization of coupon holders for existing CDU VDU - 4 of JSC "Gazprom neftekhim Salavat", the advantages of suggested design are described, data of corrosion monitoring on © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 153 the unit since December, 2013 are provided. Noted, that to hold a valid comparison of different coupons characteristics in an industrial environment is not possible, due to the lack of coupon holders substitutability on different corrosion control sites of unit. In this regard, comparative tests of coupons were conducted in the laboratory, coupons selected for the tests were rectangular, disk-shaped and rectangular with a weld, and the basis for coupon selection is shown. Lab installation was prepared for tests which scheme is given. All samples were made from the same material - BSt3sp by GOST 380 – 2005. Tests were carried out in 50% of mass water solution of lemon acid, duration of each series of tests were 3, 6 and 9 hours. By the tests results the mass loss of samples was defined and mass and deep indicator of corrosion rate was calculated. On the basis of obtained data, diagrams of corrosion rates dependence on the sample witness type and tests time were made. The received results showed that coupons with an additional source of residual internal stresses in the form of weld are exposed to more serious corrosive attack (show greater tendency to corrosion) in comparison with rectangular and disk-shaped coupons. The explanation of revealed regularity is given in the article using data on macro and micro electrochemical heterogeneity of welded connections and the doctrine about electrochemical potentials. Thus, using samples witnesses that have additional source of internal stresses such a weld, for corrosion monitoring make it as close as possible to the actual conditions. Аннотация. В работе описаны преимущества коррозионного мониторинга с использованием гравиметрических образцов-свидетелей на предприятиях необходимость нефтедобычи и и эффективность нефтепереработки, их обоснована применения, показаны дополнительные возможности метода, в частности контроль отложений на внутренних поверхностях оборудования и их влияния на скорость коррозии. Приведены данные по геометрической форме купонов, отмечено, что наибольшее распространение получили образцы-свидетели прямоугольной формы. © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 154 В статье также представлены сведения о проведенной модернизации купонодержателей для действующей установки ЭЛОУ-АВТ-4 ОАО «Газпром нефтехим Салават», описаны достоинства предложенной конструкции, приведены данные коррозионного мониторинга установки с декабря 2013 г. Отмечено, что провести корректное сравнение купонов различных характеристик в промышленных условиях не представляется возможным, ввиду отсутствия взаимозаменяемости купонодержателей для различных узлов контроля коррозии установки. В связи с этим были проведены сравнительные испытания купонов в лабораторных условиях, для этого выбраны купоны прямоугольной и дискообразной формы, а также купон прямоугольной формы со сварным швом, приведено обоснование выбора данных купонов. Для испытаний была подготовлена лабораторная установка, представлена схема установки. Все образцы были изготовлены из одинакового материала – ВСт3сп ГОСТ 380 – 2005. Испытания проводились в 50% масс. водном растворе лимонной кислоты, продолжительность каждой серии испытаний составила 3, 6 и 9 часов. По результатам испытаний была определена потеря массы образцов и рассчитаны массовый и глубинный показатель скорости коррозии. На основе полученных данных были построены графики зависимости скоростей коррозии от типа образца-свидетеля и от времени испытаний. Полученные результаты показали, что купоны прямоугольной формы с дополнительным источником остаточных внутренних напряжений в виде сварного шва, в сравнении с прямоугольным и дискообразным купонами, подвергаются более значительному коррозионному воздействию (проявляют большую склонность к коррозии). В статье приведено объяснение выявленной закономерности с привлечением данных о макрои микроэлектрохимической неоднородности сварных соединений и учения об электрохимических потенциалах. Таким образом, наличие у образцовсвидетелей остаточных внутренних напряжений в виде сварного шва © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 155 делает коррозионный мониторинг с его использованием максимально приближенным к реальным условиям. Key words: corrosion monitoring, witness sample, corrosion coupon, corrosion inhibitor, corrosion rate, galvanic couple, internal stress. Ключевые слова: коррозионный мониторинг, образец-свидетель, купон коррозии, ингибитор коррозии, скорость коррозии, гальваническая пара, внутреннее напряжение. In order to detect and prevent the destruction of corrosion hazardous areas of refineries equipment, as well as for the selection and effective use of corrosion inhibitors it is necessary to conduct corrosion monitoring. The most widely used and quite effective method of corrosion monitoring is the application of gravimetric corrosion witness samples (corrosion coupons) [1]. Witness samples can be both a source of information about the condition of the equipment at the moment, and a base for implementation of measures to prevent accidents. With their help, possible both a quantitative measurement of the corrosion rate, and the visual determination of the corrosion type. Also, corrosion coupons may be used to determine the probable replacement of existing equipment material by one that is more resistant to these conditions [2]. Now coupons of different types and forms are available. Their number includes samples of rectangular and disk-shaped form, in the form of half rings, the rings which surface has a certain roughness, and samples with additional residual internal stress. Rectangular samples are the most widely used. They have the largest surface area among all given above at identical conditions of assembling, do not require sophisticated equipment for installation in the pipeline, and have no noticeable effect on the hydrodynamics of the flow [3]. © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 156 Another advantage of the corrosion witness samples is their ability to detect the presence of corrosion deposits on the equipment walls. Corrosion inhibitors typically work by forming a protective film on the surface of the equipment. In the presence of depositions inhibitor’s film cannot fully cover the metal surface and the protective effect of inhibiting decreases, consequently, under the layer of depositions corrosion continues, which usually has ulcerative nature. Since corrosion coupons may be exhibited for a long time on their surface deposits similar to deposits on the walls of equipment are accumulated, whereby it is possible to study the influence of deposits on the corrosion rate [4,5]. On CDU VDU - 4 of JSC "Gazprom neftekhim Salavat" was decided to upgrade the witness samples holders, in such a way that three discoid coupon were installed on each coupon holder. It is important that the coupons were isolated from the stem and adjacent witness samples by the teflon bushings (Figure 1). The advantages of this design are the simplicity, reliability, ability to install additional coupons only by changing the width of teflon bushings without changing the design of coupon holder. Figure 1. Witness samples holders for CDU VDU – 4 © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 157 One more advantage of disk-shaped coupons is when exhibiting rectangular samples it is impossible to tell with an accuracy, under what corner to movement of a stream samples are and what is the way of their flow over by stream. In case of disk-shaped coupons, the smooth flow over of samples with a stream is provided, thanks to their form. If we compare the surface area of the samples, that, when mounting through the same nozzle, rectangular coupons may be produced with greater surface area than the disk-shaped. The question arises how the surface area and shape of coupons affects on the efficiency and accuracy of corrosion monitoring results. Due to small pipeline diameter of the one of witness samples installation sites (1PA) of the CDU VDU – 4 retained rectangular samples. Table 1 shows the corrosion monitoring CDU VDU – 4 with witness samples. First pumparound Average corrosion rate, mm/year Brand of coupons steel. Corrosion pattern (visual inspection) Average weight loss, g. Brand of coupons steel. Corrosion pattern (visual inspection) Average corrosion rate, mm/year Average weight loss, g. Average corrosion rate, mm/year End of exposure Date Beginning of exposure Gasoline from the K-210 Witness samples fitting position Gasoline from the K-220 Average weight loss, g. Table 1. Results of corrosion monitoring CDU VDU – 4 Brand of coupons steel. Corrosion pattern (visual inspection) After upgrading of coupon holders conducted Ltd. “R&D center Salavatnefteorgsyntez” 7.11. 9.12. St.20, St.20, Obstipation at the coupons 0.0139 0.009 0.0061 0.004 2013 2013 uniform uniform installation site St.3, ulcerative, a 9.12. 10.01. St.3, St.3, large amount 0.0788 0.054 0.0174 0.012 0.2425 0.259 2013 2013 ulcerative uniform of black deposits on the coupons St.3, uniform 10.01. 11.02. St.3, St.3, 0.0250 0.016 0.0256 0.017 0.0620 0.064 black deposits 2014 2014 uniform uniform on the coupons 11.02. 12.03. St.3, St.3, 0.0256 0.018 0.0237 0.017 0.0196 0.022 St.3, uniform 2014 2014 uniform uniform The obtained data do not allow fully evaluating the applicability and effectiveness of using rectangular and disc-shaped witness samples, because coupon holders for various corrosion control installation sites are not © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 158 interchangeable, so it was decided to conduct a comparative analysis of various samples of witnesses in a laboratory experiment to ensure the same test conditions. As objects of research chose the witness samples differing in shape, surface area and the presence of residual internal stresses (Figure 2). Selection of the submitted coupon samples caused by the following: rectangular witness sample (sample R) is the most common, easy to manufacture; discoid coupon (sample D) when mounted in a pipeline provides minimal flow resistance thanks to constant positioning from all angles during exposure; coupon with additional source of internal stresses such a weld (sample RS) is selected for the reason that the main way of pipelines and equipment connection is welded connection which change structure of the main metal in the heat affected zone, reducing resistance to corrosion therefore existence of a welded seam does these samples the most approximate to real conditions. All samples were made from the same material - BSt3sp by GOST 380 – 2005. Tests were carried out in 50% of mass water solution of lemon acid. Figure 2. Corrosion witness samples a – witness sample rectangular (R); b – witness sample disk-shaped (D); c – witness sample rectangular shape with residual internal stress (RS). The measurement results and the surface area of the samples are presented in Table 2. © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 159 Table 2. Parameters of witness samples Sample № Sample shape D1 D2 D3 R1 R2 R3 RS1 RS2 RS3 disk disk disk rectangle rectangle rectangle rectangle rectangle rectangle The surface area of the sample, m2 0.0019987 0.0019991 0.0019941 0.0037421 0.0036883 0.0036804 0.0036255 0.003655 0.0036546 Sample weight before the test, g 22.6829 22.7474 22.452 44.3604 44.3134 43.4432 41.9859 42.6725 41.8801 For the tests, lab installation presented in Figure 3 was prepared. Figure 3. Laboratory installation 1 – circulation pump; 2 – feed vessel; 3 – cylinder; 4 – witness sample Feed vessel 2 was filled with corrosive media - 50% of mass water solution of lemon acid, circulation pump 1 pumps corrosive media from the feed vessel 2 through the cylinder 3, where the witness samples 4 were installed. Depending on the frequency of the pump motor rotation 1 in cylinder 3 appropriate flow regime was established, with the aim of creating the experiment conditions closest to reality. The experiments were performed in the following order [6]: 1) The sample surface smoothed to a surface roughness Ra no more than 1.6 microns in accordance with GOST 2789-73, then polished on felt circle GOI paste and degreased with acetone. Degree of degreasing controlled by full © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 160 wetting of the surface of the sample with distilled water. After degreasing, the following operations were carried out with samples with tweezers. 2) For surface activation, the sample before test plunged for 1 min. into water solution of 15% of mass hydrochloric acid then it was carefully washed out flowing water and then the distilled water. The samples were then dried with filter paper and kept in a desiccator with a desiccant dryer for 12 hours and were weighed on analytical scales with a margin error no more than 0,0001 g. 3) The prepared witness samples were located in the device. Test time was counted from the moment of placing the sample in corrosive environment; test duration was 3; 6; 9 hours. Speed of the corrosion environment stream was 0,5 m/s according to GOST 9.905-82. 4) Immediately after test samples were subjected to visual inspection: the presence of corrosion products and color is detected, and after removal of corrosion products - the nature (type) of corrosion. 5) To determine the mass loss of samples their surface was cleared in sequence: a) friable corrosion products were removed with a spatula, brush and one of the solvents: gasoline, kerosene or mineral spirits. In the presence of a dense film from corrosion products their removal was carried out by the solutions which aren't interacting with the main metal; b) samples were washed with flowing water and then with distilled water, dried with filter paper, degreased with acetone and packaged in filter paper, kept in a desiccator with a desiccant dryer for 12 hours and weighed on an analytical scales. To recalculate the values of mass loss witness samples in value of the corrosion rate used two indicators: the mass and depth. Corrosion rate, expressed in terms of mass index Km (g/m2h), determined by the formula (1): © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 161 where m1 – mass of the sample before the test, g; m2 – mass of the sample after the test, g; S – the sample surface area, m2; – exposure time, hour. Since the change in weight of the sample is directly proportional to the penetration depth of corrosion in general corrosion rate is recalculated mass in the deep index ПFe (mm / year), which describes the thinning of the sample per unit time and determined according to the formula (2): where 8760 – number of hours per year; 7,87 – iron density, g/sm3. Results and discussion The results of the mass and depth corrosion rate indicators obtained after exposure witness samples in a corrosive environment for 3, 6 and 9 hours are shown in Tables 3, 4, 5, respectively. Table 3. Measurement results of the corrosion rate after 3 hours test Sample Sample mass loss, g Mass index of the corrosion rate Кm, g/m2·h Deep index of the corrosion rate, ПFe mm/year D1 0.0111 1.851238839 2.060591134 D2 0.0068 1.133842749 1.26206639 D3 0.0118 1.972487034 2.195551006 R1 0.017 1.514316858 1.68556743 R2 0.0142 1.283345973 1.428476585 R3 0.0202 1.829495339 2.036388713 RS1 0.0229 2.105483573 2.343587814 RS2 0.0213 1.942519133 2.162194105 RS3 0.0226 2.061324192 2.294434552 © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 162 The data in Table 3 show that sample RS-1 was subjected to corrosion at the greatest rate, and sample D-2 was subjected to corrosion at the least rate; samples RS-1-3 average were more sensitive to corrosion. Table 4. Measurement results of the corrosion rate after 6 hours test Sample Sample mass loss, g Mass index of the corrosion rate Кm, g/m2·h Deep index of the corrosion rate, ПFe mm/year D1 0.0146 1.217481398 1.355163539 D2 0.0158 1.320563353 1.469902792 D3 0.0112 0.933752853 1.039348791 R1 0.0276 1.229268979 1.368284149 R2 0.0297 1.342090683 1.493864597 R3 0.0321 1.453633673 1.618021725 RS1 0.0311 1.418130166 1.578503208 RS2 0.0314 1.43198185 1.593921348 RS3 0.0323 1.484871602 1.652792279 From the received results in table 4 it follows that the sample of RS-3 was subjected to corrosion at the greatest rate, and sample D-2 was subjected to corrosion at the least rate. Also as well as after three-hour endurance of samples in the corrosion media, samples RS-1-3 average were more sensitive to corrosion. Table 5. Measurement results of the corrosion rate after 9 hours test Sample Sample mass loss, g Mass index of the corrosion rate Кm, g/m2·h Deep index of the corrosion rate, ПFe mm/year D1 0.0179 0.995110367 1.107645084 D2 0.0152 0.844824009 0.940363192 D3 0.0222 1.236983394 1.37687097 R1 0.0331 0.982821333 1.093966313 R2 0.0351 1.05740478 1.176984228 R3 0.0384 1.159284176 1.290384927 RS1 0.0478 1.464950724 1.630618595 RS2 0.0382 1.16125557 1.292579262 RS3 0.0429 1.304289201 1.451788234 © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 163 Analysis of data in Table 5 showed that the sample RS-1 was subjected to corrosion at the greatest rate, and sample D-2 was subjected to corrosion at the least rate; samples RS-1-3, as in previous experiments showed a higher sensitivity to corrosion. On the basis of data in tables 3-5 diagrams of corrosion rates dependence on the sample witness type and tests time were made (Figures 4,5). Figure 4. Dependence of mass index of corrosion rate on the witness sample type and tests time Figure 5. Dependence of deep index of corrosion rate on the witness sample type and tests time © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 164 From the figures 4 and 5 it follows that RS samples in comparison with D and R samples show greater tendency to corrosion. It is known that the corrosion destructions mechanism of welded joints essentially doesn't differ from the destructions mechanism of the base metal. However welded joints represents difficult, non-uniform, thermodynamic unstable system which heterogeneity is caused by distinction of a chemical composition, structures of separate zones, connection geometry, residual stresses and plastic deformations in connection with uneven heating and cooling when welding [7,8]. Therefore, the welded joints are characterized by increased macro and micro electrochemical heterogeneity in comparison with the base metal. Welded connections can be considered as a combination of a multi electrode element with macro electrodes, such as seam, overheat zone, recrystallization zone, main metal. Summary corrosive effect in each zone of the welded joint is determined by corrosion losses due to: a) work of macro corrosion elements and b) self-dissolution of each zone, i.e. the corrosion caused by work of micro corrosion couples and dissolution on the homogeneous mechanism and the corresponding zone. Depending on the degree of inhomogeneity of the weld (in structure, chemical composition, etc.) and corrosive conditions will prevail one or other corrosion mechanism [9]. Macro galvanic corrosion cells, weld - the main metal, for various established electrochemical potentials can be divided into three groups [10]: 1) potentials of the base metal and weld almost identical, in this case macro galvanic couple doesn't function, and corrosion of various zones is defined by self-dissolution; 2) potential of the weld metal more negative than the base metal therefore weld corrodes more intensively as a result of anode dissolution; 3) potential of the weld metal is more positive than the base metal, wherein the base metal collapses more strongly. © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 165 Thus, existence of additional source of internal stresses inside the RS sample, such as weld, makes monitoring with its use as close as possible to the actual conditions. Conclusion As a result of carried out tests it is founded that shape of witness samples doesn’t influence essentially on the effectiveness of corrosion monitoring. However, rectangular coupons with additional residual internal stresses in the form of weld are exposed to corrosion at greater rate in comparison with rectangular and disk-shaped coupons made from entire metal. Use of such samples with the weld will provide more effective corrosion monitoring of the welded technological equipment primarily exposed to corrosion. References 1 Bradford S.A. Corrosion control. Edmonton: CASTI, 2001. 485 p. [in English]. 2 ASM Metals Handbook. Volume 13 Corrosion. L.J. Korb, D.L. Olson. Houston: ASM International, 1987. 3455 p. [in English]. 3 Burlov V.V., Altsyibeeva A.I., Parputs I.V. Corrosion protection of refinery equipment. Petersburg: HIMIZDAT, 2005. 248 p.[in Russian]. 4 Sukhotin A. Corrosion and protection of chemical equipment. Volume 9 Refining and Petrochemical Industry. Moscow: Himiya, 1974. 576 p. [in Russian]. 5 Ahmad Z. Principles of corrosion engineering and corrosion control. Amsterdam: Elsevier Science & Technology Books, 2006. 660 p.[in English]. 6 GOST 9.506-87. Corrosion inhibitors of metals in water-petroleum media. Methods of protective ability evaluation. Moscow: Standards publisher, 1988. 17 p. [in Russian]. 7 Vinokyrov V., Grigoriants A. Theory of welding strains and stresses. Moscow: Engineering, 1984. 280 p. [in Russian]. © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 166 8 Zemzin V., Shron R. Heat treatment and welds properties. Petersburg: Engineering, 1987. 369 p. [in Russian]. 9 Logan G. Corrosion of metals under stress. Moscow: Metallurgy, 1970. 340 p. [in Russian]. 10 Breinshtein M., Zaimovsky M. Mechanical properties of metals. Moscow: Metallurgy, 1979. 496 p. [in Russian]. Список используемых источников 1 Bradford S.A. Corrosion control – Edmonton: CASTI, 2001. 485 p. 2 ASM Metals Handbook. Volume 13 Corrosion / L.J. Korb, D.L. Olson. Houston: ASM International, 1987. 3455 p. 3 Бурлов В.В. Альцыбеева А.И., Парпуц И.В. Защита от коррозии оборудования НПЗ. СПБ.: ХИМИЗДАТ, 2005. 248 с. 4 Коррозия и защита химической аппаратуры / под ред. А. М. Сухотина, А.В. Шрейдера, Ю.И. Арчакова. М.: Химия, 1974. Т. 9 Нефтеперерабатывающая и нефтехимическая промышленность. 576 с. 5 Ahmad Z. Principles of corrosion engineering and corrosion control - Amsterdam: Elsevier Science & Technology Books, 2006. 660 p. 6 ГОСТ 9.506-87. Ингибиторы коррозии металлов в водно-нефтяных средах. Методы определения защитной способности. Введ. 1988-01-07. М.: Изд-во стандартов, 1988. 17 с. 7 Винокуров В.А., Григорьянц А.Г. Теория сварочных деформаций и напряжений. М.: Машиностроение, 1984. 280 с. 8 Земзин В. Н., Шрон Р. 3. Термическая обработка и свойства сварных соединений. Л.: Машиностроение, 1987. 369 с. 9 Логан Г.Л. Коррозия металлов под напряжением. М.: Металлургия, 1970. 340 с. 10 Бернштейн М.Л., Займовский М.А. Механические свойства металлов 2-е изд. М.: Металлургия, 1979. 496 с. © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru 167 About the authors Сведения об авторах A.P. Efremenko, Master Student of MTP 21-12-02 Group of the Chair «Oil and Gas Technology» FSBEI НРЕ USPTU, Ufa, the Russian Federation Ефременко А.П., магистрант группы МТП 21-12-02, кафедра «Технология нефти и газа» ФГБОУ ВПО УГНТУ, г. Уфа, Российская Федерация A.Y. Spaschenko, Candidate of Engineering Sciences, Head of Refining Process Laboratory LLС “R&D Center Salavatnefteorgsyntez”, Salavat, the Russian Federation Спащенко А.Ю., канд. техн. наук, начальник лаборатории процессов нефтепереработки ООО «Научно-технический центр Салаватнефтеоргсинтез», г. Салават, Российская Федерация I.F. Sadretdinov, Candidate of Chemical Sciences, Head of Problem Research Laboratory LLС “R&D Center Salavatnefteorgsyntez”, Salavat, the Russian Federation Садретдинов проблемных И.Ф., канд. исследований хим. ООО наук, начальник лаборатории «Научно-технический центр Салаватнефтеоргсинтез», г. Салават, Российская Федерация e-mail: [email protected] K.V. Aleksandrova, Candidate of Engineering Sciences, Leading Specialist of Refining Process Laboratory LLС “R&D Center Salavatnefteorgsyntez”, Salavat, the Russian Federation Александрова К.В., канд. техн. наук, ведущий специалист лаборатории процессов нефтепереработки ООО «Научно-технический центр Салаватнефтеоргсинтез», г. Салават, Российская Федерация © Electronic scientific journal "Oil and Gas Business". 2014. №3 http://www.ogbus.ru
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