In the oil and gas industry, equipment and metal structures are used under complex conditions of mechanical immersion and attack of corrosive media, which causes frequent failures and creates emergency situations, especially in presence of mixtures containing hydrogen sulfide. Lately, oil and gas deposits containing hydrogen sulfide are being developed in Western Siberia. The major causes of loss of performance of steel piping systems in presence of hydrogen sulfide are general corrosion and corrosion cracking caused by hydrogen sulfide. Failure due to hydrogen embrittlement and corrosion cracking induced by hydrogen sulfide generally occurs suddenly with serious consequences, e.g., disruption of the technological process, production loss, forced unscheduled repair, development of emergency situations, environmental pollution, etc.The intensity of the corrosion process depends a great deal on the presence in the media of corrosive agents, especially hydrogen sulfide and oxygen. Stratal water extracted along with oil contains dissolved impurities like hydrogen sulfide, carbon dioxide, gaseous hydrocarbons, and atmospheric oxygen. Carbon dioxide, hydrogen sulfide, and oxygen produce the most active stimulating effect on corrosion of metals.We conducted experimental and theoretical studies of the effect of H.,S and O., on the mechanism of carbon dioxide corrosion that occurs due to presence of CO., in the corrosive media.Carbon A schematic drawing of the experimental arrangement is shown in Fig. 1. In addition to the autoclave, a dissolution loop (Fig. 2) was also used to study the effect of 0 2 on CO 2 corrosion of samples of pipes serially produced from steels 10 and 20. The dimensions of the test samples are 40 x 10 x 5 mm for the autoclaving arrangement; O 59 x 2 mm and length 70 mm for the arrangement with a dissolution loop. The experiments were performed in closed systems with no contact with air.Corrosion studies were carried out in a wide mixture temperature range (30-250~ and at a constant CO 2 pressure (1.5 MPa). The partial pressure of hydrogen sulfide PH2S and oxygen PO2 varied discretely within 0--1.5 MPa. Sample preparation, control of solution temperature and CO.,, H.,S, and O 2 pressure, and measurements of the required parameters were carried out by standard procedures. The corrosion products were studied by X-ray diffraction and local X-ray spectral microanalysis.The effect of H2S and 02 content on the corrosion rate in a wide temperature variation range is shown in Fig. 3 and the effect of mutual effect of H2S and temperature on the corrosion resistance of carbon steel, in Fig. 4.It is evident from Fig. 3a that the corrosion rate v c rises with rise of the partial pressure of H-,S in the mixture in the temperature range 20-80~However, only at PH2S = 0.5 MPa does the corrosion rate exceed by 1.5-2 times the rates typical for media containing only CO 2. Further rise of PH2S from 0.5 to 1.5 MPa leads to slowing down of corrosion causing an opposite effect, especially in the temperature range I0(O250...

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The effect of rare-earth (REE) and alkali-earth (AEE) elements and, zirconium on the corrosion resistance of welded joints has been studied insufficiently and, consequently, the problem still requires urgent examination.In this work, in order to determine the optimum content of the microadditions of REE and AEE, investigations were carried out into the corrosion resistance and corrosion sulphide cracking of deposited metal.In the experiments, REE were represented by cerium and ytrium, and AEE by barium and calcium. These microadditions result in high corrosion-mechanical properties of metal, are easily obtained, are relatively cheap under the condition of efficient alloying, and are produced by the metallurgical industry.For comparison, zirconium was used in addition to REE and AEE. Modifying additions were in the form of powders and their chemical compositions and grain size corresponded to GOST and TU standards, described in ref. 1-4. TableThe specimens for experiments were produced from 17G1S steel and were welded with electrodes whose coating contained variable amounts of microadditions. To ensure constant chemical composition of deposited metal, the content of ferroalloys in coating experimental electrodes was corrected in relation to the modifying microadditions, added to the composition of the coating. This resulted in almost the same degree of deoxidation of deposited metal (Table).The coating of ANO-26 electrodes [5] was the main coating deposited on the rod of Sv-08A electrodes with a diameter of 4 mm, the coefficient of the mass of the coating K mc = 45%. The electrodes were produced using a potassium-sodium water glass with a density of 1.55 g/cm 3 , modulus 2.76.The first batch of welded specimens with a size of 60 x 10 x 2 mm were tested for the corrosion rate, the second batch (standard dimensions) were tested for corrosion sulphide cracking. Electrode Ets EB EI ES EK ANO-26 Microaddition, content in coatinj

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