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CHEMICAL PROBLEMS 2023 no. 4 (21) ISSN 2221-8688
379
UDC. 620.194
CORROSION OF CARBON STEEL IN THE WATER BASINS OF SHEMKIR AND YENIKEND HYDROELECTRIC POWER PLANTS
H.M. Tahirli1, S.C. Verdiev1, S.A. Mammadova1, D.B. Tagiyev1, T.I. Shirinov2, M.N. Adigozalova1, A.S. Huseynova1
1Acad. M.Nagiyev Institute of Catalysis and Inorganic Chemistry Ministry of Science and Education of the Republic of Azerbaijan 113, H.Javid Ave. AZ1143 Baku, Azerbaijan e-mail: [email protected] 2Azerbaijan Technical University 25, H.Javid Ave., AZ 1073, Baku, Azerbaijan e-mail: [email protected]
Received 12.08.2023 Accepted 08.10.2023
Absrtact: Using gravimetric and electrochemical research methods, the corrosion-electrochemical behavior of carbon steel grade St3 in Kura river water has been. Gravimetric measurements were carried out under operating conditions of the Shemkir and Yenikend hydroelectric power stations for one year. Along with this, the ionic and bacteriological composition, as well as some physicochemical parameters of these waters were established. It revealed that St3 in the Kura water corrodes at a rate of (0.04^0.05) g/m2'hour, which is characteristic of steel corrosion in fresh waters. In the atmosphere of hydraulic structures, steel corrodes at rather a low rate, i.e. (5^6)10~3g/m2 hour. As a result of biochemical analysis, sulfate-reducing bacteria (SRB) were discovered in these waters, which are a dangerous organism that releases the corrosive substance of H2S. By taking the anodic and cathodic polarization curves, a quasi-stationary steel corrosion rate was established to be 0.06g/m2 h.
Keywords: corrosion, hydraulic structures, carbon steel, polarization curves, SRB, gravimetric measurements.
DOI: 10.32737/2221-8688-2023-4-379-387
Introduction
Waterworks (WW) play an important role in the economy of many countries, especially in those which are rich in water resources. These structures provide industry, agriculture and other sectors of the national economy with cheap electricity, drinking water, etc. These structures play a special role in the extraction of oil and gas in difficult conditions from the depths of the sea. The main material used in the construction of hydraulic structures is carbon steel, as well as aluminum, copper and their various alloys.
As is known, all steels, except for stainless steel, are thermodynamically unstable in electrolytes, which include river and sea waters, and corrode at a fairly high rate.
Particularly high speeds are observed in marine environments, where the concentration of corrosive ions is higher than in river waters. The corrosion behavior of steel structures and equipment in oceanic conditions has been discussed quite widely in the world [1.2] as well as in our scientific publications [3]. However, similar publications on the corrosion resistance of steels in fresh waters have been discussed sporadically [4-6]. Scientific research into the corrosion of steels in river waters in our Republic began quite recently - in 2015 at some hydroelectric power stations, namely the Mingachevir and Varvar hydroelectric power stations, as well as the Upper Shirvan Canal, which were built on the Kura River. A similar
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CHEMICAL PROBLEMS 2023 no. 4 (21)
study has been carried out at the Bakhramtapa water junction. The results of these studies have been published in [5-6]. But there were and still are other hydroelectric stations in the Republic with fairly high energy indicators. The Shemkir and Yenikend hydroelectric power stations were put into operation in the period of 1987-2000 are among similar structures. These hydroelectric stations are located in the upper pool of the Kura Reservoir and corrosion monitoring has never been carried out there, i.e. the corrosion state of equipment that was
systematically exposed to the corrosive and erosive effects of water, not counting cavitation destruction of the metal, has not been checked
[7].
The purpose of this work is to study the corrosion state of above-water and underwater structures by analyzing the corrosion rate of steel in the waters of the above mentioned hydroelectric power stations, using gravimetric and electrochemical measurement methods, as well as physical and chemical analysis of water.
Experimental part
The corrosion rate of steel based on the loss of sample mass was examined under natural conditions, i.e. rectangular steel samples cut from the same steel sheet of St-3 grade with an area S = (80x25x3mm) 46 cm2 and secured to a steel frame using a nylon line. The samples were first subjected to mechanical cleaning from corrosion and carbon deposits, then mechanically polished to a shine, and degreased with acetone or ethyl alcohol. After this operation, the steel frames were lowered into water to a depth of 3-4 meters using a reinforced steel rope. The similar operations were carried out for the samples prepared for testing under atmospheric conditions. In this case, the frame with the samples was hung 10-12 meters above the water surface. Taking into account that as a result of corrosion, the mechanical properties of steels can deteriorate, steel rods with a length of 600 mm and a diameter of (8^10) mm were also prepared. In a similar manner, they were also secured to a steel frame and lowered into the water. Samples immersed in water from the beginning often, i.e. in 1, 3, 7, 10, 20, 30 days and then every month were removed from the
water, cleaned from corrosion products using a known method, dried with filter paper from moisture, degreased and were brought to the laboratory in a special container to determine the corrosion rate. Samples for atmospheric corrosion tests were removed once a month and treated as above and placed in a container. After a month, the steel rods for mechanical testing were removed from the water, dried and prepared for tensile testing using an Italianmade Matest-24048 device.
Considering that the corrosion of metals strongly depends on the ionic content of electrolytes, the samples of water taken from the place where the steel samples were located had been subjected to physical and chemical analyzes and determined their ionic and, if possible, biochemical composition was established as well. These data are given in Table. 1. It ought to be noted that each time before removing steel samples, water samples were taken from the pool and its pH and temperature was immediately established on site. The corrosion rate of the samples was established using the well-known formula [8-9].
^ m-L—
where K - is the corrosion rate,
mi, m2 - mass of the sample before testing and after testing, respectively S-geometric area of the sample, T- is the test time.
It has to be kept in mind that these copper, brass, aluminum, etc. The corrosion experiments were carried out within one year. In resistance of these metals was tested in all hydroelectric power plants, in addition to laboratory conditions under hydrodynamic steel, other metals and alloys are used, such as movement of water. For this purpose,
cylindrical samples with an area S = 11 cm2 were made from the above mentioned metals and they were attached to an asynchronous motor and rotated at a speed of 1270 rpm in river water. The corrosion rate of these metals was also determined by mass loss. Electrochemical studies were carried out using a
Dutch-made potenciostat iVIUM-Stat. This device was used to record cathode and anodic curves on steel samples in river waters. Using these curves, it is possible to determine the rate of metal corrosion in current units [9]. In some cases, the composition of corrosion products was determined using the RFA method.
Results and discussion
As noted above, the Shemkir hydroelectric power station has been in operation for 26 years, and the Yenikend hydroelectric power station for approximately 23 years [10]. During this time, the corrosion state of the underwater and surface metal structures of these stations was not systematically studied. The study of the corrosion state of hydraulic structures is also
useful due to the fact that, based on the data obtained, it is possible to predict the service life of these structures.
Table 1 shows the chemical composition, as well as some physical and chemical data of the Kura water taken from the basin of the mentioned above mentioned hydroelectric power stations.
Table 1. Ionic, physicochemical and bacteriological indicators of water taken from the Shemkir and
Yenikend hydroelectric power stations
№ Name of indicator Unit Shemkir/Yenikend result Quality requirements
QOST 2874-82
1 pH 8.16 6.0-9.0
2 Electrical conductivity /¿S/sm 465/436
3 Carbonate mq/L 0/3,60
4 Bicarbonate mq/L 144/150
5 calcium (Ca2+) mq/L 51.7/51,3 250
6 Magnesium (Mg ) mq/L 10.7/12,4 50
7 Ammonium (NH4+) mq/L 0.13/<0,1
8 Chloride (CI) mq/L 16/17 <350
9 Nitrite (NO2-) mq/L 0.097/0.11
10 Nitrate (NO3-) mq/L 4.3/4 <45
11 Sulfate (SO42-) mq/L 94/92 <500
12 Phosphorus phosphat mq/L <0.4/1.06
13 Total coliform bacteria KYV/100 ml CFU/100 ml 1.94 <3( KYV/100 ml)
14 E.Coli KYV/100 ml CFU/100 ml 3
15 Clostridium perfingens KYV/100 ml CFU/100 ml 147/7200
As can be seen from the Table, the concentration of corrosive ions such as CI-, SO42", HCIO3- is much lower than in ordinary drinking water. These data for both
hydroelectric power stations can be said the same, but the bacteriological composition is different. In our opinion, such a difference in running water is a random. On the other hand,
the distance between these stations is only 17 km and sulfate-reducing bacteria SRB, which, feeding on SO42- ions, release H2S, and this substance is a very corrosive component for many metals and alloys. Over this short period, the concentration of SO42- ions cannot change much so that the quantity, or rather the volumetric concentration, of SRP differs so significantly from each other. Of course, these bacteria (SRB) exist in the Kura Reservoir, as our previous reports indicate this [5]. But for now, it is impossible to accurately establish their population in flowing fresh waters and the
dependence of reproduction on various natural factors, since this requires systematic biochemical research for quite a long time.
The results of corrosion experiments are shown in Fig. 1. As can be seen from the Figure, at first the steel naturally corrodes at a high speed, and then after 1.5-2 months the speed stabilizes and corrodes at a constant speed equal to 0.03q/m2-hour. Under atmospheric conditions, the dependence of the corrosion rate on time is approximately linear, but at the end of the experiment it stabilizes at a rate equal to (5^6)10"3q/m2-hour.
Fig. 1. Dependence of the corrosion rate of St3 on time in the waters of the Shemkir (o) and Yenikend (A) hydroelectric power stations and in the atmospheres of the indicated hydroelectric
power stations
Fig. 2 shows the results of a tensile test of steel rods after they were corroded in the Kura water. As can be seen from the Figure, during the test
the steel lost its mechanical properties by approximately 17%.
Fig. 2. Dependence of the tensile strength of the steel bar on the time of corrosion testing in the
water of the Shemkir hydroelectric station.
During corrosion tests at the Yenikend hydroelectric power station, black corrosion products were revealed on some samples. Typically, the corrosion products of low-alloy steels are brown in color and consist of various oxides and oxohydroxides of iron. Analysis of these corrosion products by X-ray phase analysis (RFA) showed that among the corrosion products, in addition to oxygen compounds, there is also iron sulfide FeS. These data are shown in Fig. 3.
As is known [1.2], waterworks operating in marine conditions are subjected to the corrosive effects of not only aggressive ions and oxygen dissolved in sea water, but also the
action of SRB. The hydrogen sulfide released by these bacteria vigorously interacts with the main component of steel, iron, and intensively destroys these structures in the absence of the necessary protection. As is seen from Tables 1 and 2, the amount of SRB in the Shemkir reservoir is 147 pieces per 100 ml of water, and in the Yenikend reservoir 7200 pieces per 100 ml of water. Perhaps, for this reason, we discovered FeS in corrosion products. It should be immediately noted that in our subsequent tests FeS was not observed and only oxygen compounds of iron were present in the corrosion products.
Fig. 3. X-ray diffraction pattern of St3 corrosion products formed on steel in the water of the
Yenikend hydroelectric station
In hydraulic structures of any hydroelectric power station, in addition to steel, other metals and alloys are used, such as copper, brass, aluminum and its alloys. Information about the corrosion resistance of these materials in the waters under study is also of no small interest. With that end in view, cylindrical samples were made from these materials and
subjected to corrosion testing under hydrodynamic conditions for 10 days in a laboratory setup, which we noted in the methodological part of this message. Cylindrical samples were made of aluminum alloy D16, brass grade L68 and copper M3. The obtained data are shown in Fig. 4.
Fig. 4. Dependences of the corrosion rate of St3 (1), aluminum alloy D16 (2), brass L68 (3) and copper M3 (4) on time in the waters of the Shemkir hydroelectric power stations
For comparison, the Fig. 4 shows similar data for St3. Steel in river water first corrodes at a high rate (~1.6 g/m2-hour), and then gradually decreases and stabilizes. Alloy D16 (cr.2) in comparison corrodes with steel at a low speed and after ~10 hours stabilizes and continues to dissolve at a lower speed (3-4)10-2 q/m2-hour. Brass and copper corrode at a still low rate (3-4)10-2 q/m2-hour. It is possible that with a longer test, the data presented may be even
lower.
Along with corrosion tests, in order to study the corrosivity of the environment, in line with accepted practice, research also studies the electrochemical characteristics of steel in the given environment. Fig.5 shows the cathode and anodic polarization curve of St 3 in the Kura water, taken from the Yenikend hydroelectric station.
Corrosion rate analysis
E
o $
L/2
1 /y /
-1 0
-0 6 -0 6 -04
Potential
-0 2 V
Fig. 5. Cathode (1) and anodic (2) polarization curve of St3 in the water of the Yenikend
hydroelectric station
*a correction has been made to the computer version of the slope of the polarization curve
As can be seen from the Fig. 5, the open reduction of molecular oxygen occurs according circuit potential of steel is E = -0.680v. In the to the reaction negative region from this potential, as usual, the
02+2H20+4e —► 40H" And after the potential E = -0.98 v, hydrogen is released according to the reaction
2H20+2e H2+20H"
More positive than E = -0.680v, the similar way, is equal to icorr~6T0-6A/cm2. The anodic process of steel dissolution occurs. The corrosion rate measured by mass loss (negative intersection of the slope of the Tafel sections mass measurement indicator) Km (q/M2-r) is near the stationary potential corresponds to the related to the current corrosion rate indicator corrosion rate in current units. The corrosion (A/cm2) by the following dependence [9]: rate of steel in the Kur a water, measured in a
i-A
Km" d
71-2.68-10
where
K-m - negative indicator of corrosion rate, g/m2-hour i - Corrosion rate in current units, A/cm2 n - Number of electrons participating in the anodic process A - Atomic mass of the metal
The corrosion rate calculated using this equation measurements, is the actual corrosion rate in is K"m=6.3T0"2 g/m2-hour. This corrosion rate river water [6]. value, being slightly different from gravimetric
References
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3. Negreev V.F., Khanlarova A.G., Gadzhieva R.G. Corrosion protection of offshore oil field structures. Moscow: "Nedra" Publ., 1964, 311 p.
4. Krasnoyarskoy V.V., Frenkel G.Ya., Nosov R.P. Corrosion protection of metals. Moscow: "Metallurgy" Publ., 1969, 301 p.
5. Tahirly H.M., Verdiev S.Ch., Bakhshalieva K.F., Taghiev D.B. Corrosion of carbon Streel St-3 under exploitation of hydrotechnical unilities buildings on the Kura and Araz rivers. National Academy of
Sciences of Azerbaijan Reports. 2017, no.1, pp. 59-65.
6. Verdiev S.Ch., Agallarova T.A., Tagirli G.M., Velieva S.M., Shirinov T.I., Jafarova S.Z. Corrosion behavior of some metals and alloys in fresh natural waters. Chemical problems. 2017, no. 1, pp. 98-105.
7. Bellendir L.E., Vlasov D.Yu., Durchaeva V.N., Tsarovtseva I.M. The role of the biofactor in the corrosion of metal and reinforced concrete structures of hydraulic structures. Aviation materials and technologies. 2015, no. S1, pp. 61-66. (In Russian).
8. Keshe G. Corrosion of metals. Physicochemical principles and current problems. Moscow: "Metallurgy" Publ., 1984, 399 p.
9. Zhuk N.P. Course on Theory of Corrosion and Protection of Metals. Moscow: "Metallurgy" Publ., 1976, 472 p.
10. Ahmadzadeh A.C., Hashimov A.C. Management. Baku. 2016, p. 632. Encyclopedia Meloration and Water
§9MKÍR УЭ YENÍK9ND SES-L9RÍNÍN SU H0VZ9L9RÍND9 KARBONLU POLADIN
KORROZiYASI
1H.M. Tahirli, 1S.C. Verdiyev, 1S.А. Mammadova, 1D.B. Tagiyev, 2T.i. Çirinov, 1M.N. Adigözalova, 1A.S. Huseynova
1 Azarbaycan Respublikasi Elm va Tahsil Nazirliyi akad.M.Nagiyev adina Kataliz va Qeyri-üzvi Kimya institutu AZ 114S, Baki, H.Cavid pr, 11S 2Azarbaycan Texniki Universiteti AZ 107S, Baki, H.Cavidpr.,25
Xülasa: Kür çayi sularinda qravimetrik va elektrokimyavi metodlarin kömayi ila karbonlu St3 poladinin korroziya elektrokimyavi xassalari tadqiq olunaraq öyranilmi§dir. Qravimetrik ôlçmalar bir müddat §amkir va Yenikand SES-larin istismari §araitinda aparilmi§dir. Bununla yana§i sularin ion va bakterioloji tarkibi, hamçinin bazi fiziki-kimyavi parametrlari öyranilmi§dir. Malum olmuçdur ki, St3 polad Kür çayi sularinda bu tip poladlarin §irin sular ûçûn xarakterik olan •saat süratla korroziya maruz qalir. Qeyd olunan sularda biokimyavi analiz naticasinda H2S ifraz edarak poladlarin korroziya davamliligi ûçûn tahlüka yaradan sulfat reduksiyaedici bakteriyalar (SRB) açkar edilmi§dir. Çay suyunda katod va anod ayrilari çakmakla poladin 0.06 q/m^saat barabar olan kvazistasionar korroziya sürati müayyan edilmiçdir. Alinan malumatlara asasan, hidrotexniki qurgularin metal konstruksiyalarinin xidmat müddatini proqnozlaçdirmaq mümkündür, bela ki, metal ilkin qalinliginin 30% itirdikda, о özünün konstruksiya qabiliyyatini da itirir.
Açar sözlar: korroziya, hidrotexniki qurgular, karbonlu poladlar, polyarlaçma ayrilari, sulfat reduksiyaedici bakteriyalar, qravimetrik ö^ülar.
КОРРОЗИЯ УГЛЕРОДИСТОЙ СТАЛИ В ВОДНЫХ БАССЕЙНАХ ШЕМКИРСКОЙ И
ЕНИКЕНДСКОЙ ГЭС
1Г.М. Тагирли, ХС.Ч. Вердиев, ХС.А. Мамедова, ХД.Б. Тагиев, 2Т.И. Ширинов,
1М.Н. Адыгезалова, 1А.С. Гусейнова
1 Институт Катализа и Неорганической Химии им.акад.М. Нагиева Министерства науки и образования Азербайджана AZ1143, пр. Г.Джавида 113, Баку 2Азербайджанский Технический Университет AZ1073, пр. Г.Джавида 25, Бaку
Аннотация: Гидроэлектростанции (ГЭС) подвергаются разрушению в результате коррозии, эрозии, кавитации и нередко биокоррозии, особенно в морских условиях. В результате длительных (1 год) испытаний, проводимых на Шемкирском и Еникендском ГЭС, было установлено, что углеродистая сталь марки Ст3 подвергается коррозионному разрушению квазистационарно со скоростью (0.04—0.05) г/м2-час. Во время проведения коррозионных опытов нами были обнаружены в обоих гидротехнических сооружениях сульфат редуцирующие бактерии (СРБ), которые выделяют с точки
зрения коррозии очень опасное вещество Н28. В атмосферных условиях (в атмосфере ГЭС) сталь корродирует примерно на порядок с низкой скоростью, т.е. (5^6)10 "3г/м2-час. Кроме коррозионных испытаний нами был установлен ионный состав, а также некоторые физико-химические показатели Куринской речной воды. На основе полученных данных можно прогнозировать срок службы металлических сооружений этих гидротехнических сооружений, исходя из того, что металл при потере первичной толщины на 30% теряет свои конструкционные способности.
Ключевые слова: коррозия, гидротехнические сооружения, углеродистая сталь, поляризационные кривые, СРБ, гравиметрические измерения.
