No 2 (2019)

Carbon dioxide corrosion is one of the most common reasons for the failure of oil-production equipment. This issue is very urgent for the Russian Federation where the carbon dioxide content is high in the oilfield medium of the most production fields. The paper deals with the obtaining of information on the basic issues of development of tube steels resistant to the carbon dioxide corrosion: the type and the level of alloying of steels reducing carbon dioxide corrosion lower than 0.2 mm per year; the influence of high content of corrosive H₂S and Cl^- components in the carbon dioxide medium on the mechanism and kinetics of corrosion failure. To get this information, the authors carried out pilot tests maximally proximal to operating conditions. Oil-well tubing was tested on seven working wells with intermittent monitoring of pipe condition. The authors carried out field tests of oil-and-gas tubing on testing field of Priobskoye production field consisting of operating oil-pipeline, parallel with which a bypass line made of pipes of experimental steels was mounted. The production fields and wells where the oilfield media have high CO₂ content and the intensive carbon dioxide corrosion is manifested were used for the tests. In most cases, they are the production fields where the carbon dioxide medium is additionally saturated with the corrosive H₂S and Сl^- components. The authors divided steels under the study in two groups: steels with high chromium content (≈4.6 %) forming the passivating film when in operation and low-alloyed tube steels (Cr≤0.6 %). The tests show that: - high-chromium 15H5MFBCh steel is resistant to carbon dioxide corrosion even in carbon dioxide media with high H₂S and Cl^- content; - the high chlorine content in oilfield media intensifies corrosion failure and promotes the transition to more aggressive forms of local corrosion in low-alloyed tube steels; - according to the increase of resistance to carbon dioxide corrosion, the steels under the study can be arranged in the following sequence: 09G2Sà13HFAà08HMFAà15H5MFBCh.

The author considered the issues of working capacity improvement of multi-element cutting tools (in terms of such operational characteristics as, for example, the intensity of breakdowns of cutting element and its support plates, etc.) by changing the regulation of status parameters of a surface layer of their parts. The weakness and low reliability of cutters prove the necessity in the elements with the defined properties within the cutting tools structure. The shape of the cutting element supporting surface influences the specified properties of cutting tool parts. The author considered the shape of a profile of cutting element supporting surface in the form of two irregularities located at a distance of waviness step (in the form of oil pockets). The profile shape is considered as a stress concentrator. According to the decrease in the concentrator durability period, the study determined which parameters influence the durability. Cutting element reacts to the cutting force load and transmits it to other parts of a cutting tool through its base and fastening nodes. The author calculated the surface status complex which includes the achievement of life duration with the dominating influence of height and step roughness and waviness parameters. The calculation is carried out in the base and fastening nodes of a cutting element. In the base nodes, normal stresses dominate on the surface; in the fastening nodes, tangential stresses prevail. It is shown that normal and tangential stresses are equal. The author determined the complex value dependent and independent of the surface treatment conditions (process value and calculated-engineering value respectively). The study indicates how the complex behaves under the loading (breaking-in) of a contact joint as well as how its change influences the working capacity of the multi-element cutter. Block (multi-element) cutters differ from the modular and one-piece cutting tools both by the presence of a large number of elements (30 and more) and by the high contact stresses resulting from their operational conditions. High cutting forces, vibrations (amplitude and vibration frequency of the technological system), wear of elements, low toughness and high suppleness of contact joints are the peculiarities of operational conditions.

To guarantee operational characteristics in the process of manufacturing parts for aeronautical equipment and rocket production, it is necessary to satisfy strict technological requirements. The production of a surface with minimum roughness is one of such requirement which is worthy of separate attention as this factor directly influences the fatigue strength and the resource. The objects of the study are the titanium alloys which are characterized by low cutting performance and proved to have valuable structural properties. The paper describes the mechanism for the formation of irregularities of parts depending on the properties of treated material, types of processing, equipment parameters, tools, processing modes, and other design and technology factors. The paper presents the results of the study of the influence of ultrasonic superfinishing technological process modes on the value of roughness of a treated surface of titanium alloy parts. The authors carried out the research when finishing titanium alloys using the ceramic-based bars of green silicon carbide and the ultrasonic head. In the research process, the authors calculated the bearing surface area to define the forms of the lobes of irregularity top sides at various bearing area values. For this purpose, the authors determined the corner radius R and the angle b which is formed by the profile sides. To obtain the relation between the relative bearing area and relative approach of bearing area curves, the least square method was used. The research allowed concluding that the applying of ultrasonic oscillations to the processing area with the simultaneous oscillation mechanism transmission to the hones in the process of superfinishing caused the decrease in roughness by 15-25 % in comparison with usual superfinishing.

The authors carried out the experimental study of the influence of ultrasonic dressing of grinding wheels on the energy-force indicators of the grinding process. The study showed the degree of ultrasonic dressing influence on the cylindrical plunge grinding indicators in the automatic cycle of processing. The authors identified that ultrasonic dressing of grinding wheels with a dressing tool executing vibrations with the frequency of 22 kHz and the amplitude of 10…15 µm allows decreasing the supporting face of a grinding wheel texture 4-5 times through the increase of the abrasive grains quantity with the relatively sharp micro-edges and microcracks. It is shown, that the distinctive features of formation of the grinding wheel working surface texture during ultrasonic dressing ensure the reduction of cutting perpendicular force about by 30 % during the whole period of grinding wheel life as well as allows increasing the wheel life 1.5…2 times. It is noted that during the ultrasonic dressing, the abrasive grains break due to the repetitive impact loading creating numerous cutting edges and microcracks at the less dressing depth than after traditional dressing. In the result of interference of sinusoidal trajectories of diamond points of a dressing tool, on a grinding wheel, a certain cammed texture forms, what decreases the wheel bearing surface. The existence of two texture components explains the higher cutting power of a grinding tool compared to the traditional dressing.