Enough works in which positive action of the vibration fluctuations imposed both in the course of welding of a design and after it is specified are known. In the article features of influence of low-frequency vibration fluctuations in the course of a welding cycle on properties of welded connections from steel A 516-55 are considered. The conducted pilot studies of influence of vibration influence of a welding bathtub in the course of welding on structure and physico-mechanical properties of metal of welded connections have allowed to prove positive action of this technology which leads to increase in durability and fatigue endurance of welded connections. This fact will allow to expand using of technology of vibration processing in the course of welding for production of the welded equipment of various type.
The aim of the study described in this paper is to assess the effect of forces acting on the tube sheet during friction welding on the stress-strain state of the tube sheet.For this, we calculated the stresses and displacements arising in the tube sheet during friction welding. The calculations were carried out in the ANSYS (finite element analysis software package). To carry out the calculations, solid-state models of tube sheets with diameters of 400, 600, 800, 1000, 1200, 1400 mm and thicknesses of 30, 40, 50, 60, 70 mm were created. The diameter of the holes for the heat exchange tubes was chosen equal to 25 mm, the holes are placed on the vertices of an equilateral triangle with a step equal to 32 mm. Then, based on geometric models, grids of 8-node finite elements were created. The calculation model takes into account the symmetry of the geometric model and the character of loading relative to the YZ and XZ planes. The material used was steel with a Poisson's ratio of 0.3 and an elastic modulus of 2,11·105 MPa.As a result of the calculations, it was found that as a result of the action of force factors during friction welding, significant stresses and deformations arise in the tube sheet. The greatest values of deflection and stresses occur in the central sector of the tube sheet in the area of application of force. In this case, the zone of maximum stresses is significantly localized: they are concentrated around the central hole, and movements smoothly increase from the periphery to the center of the tube sheet.The value of this study is that it allowed to determine the need to use special equipment that increases the local stiffness of the tube sheet sector subjected to friction welding.
The paper shows the possibility of using the technology of vibration treatment in the process of welding of high-temperature chromium steel of martensitic class P91 applied to the product to increase the technological strength of welded joints and the effect of this technology on mechanical properties before and after thermal treatment. Application of vibration action on welding bath and weld seam in process of manufacturing of welded structure may allow to reduce inhomogeneity of weld metal structure in liquid phase, as well as increase its microchemical inhomogeneity within crystallites during crystallization, reduce grain size due to more efficient heat removal and increase of number of crystallization centers. On the example of manufacturing the turbine support housing of the gas turbine drive, it is shown that it is necessary to replace part of the heat treatment operations with other more energy - efficient and less labor-intensive operations. Results of studies of influence of vibration treatment of welded joint on tendency of welded joint metal to form cold cracks, strength, hardness and impact toughness are given. Based on the obtained results, diagrams of average values of parameters are constructed and conclusions are drawn on the possibility of using the technology of vibration treatment of the turbine casing in the process of welding in order to reduce the number of heat treatment operations during its manufacture.
In this work, one of the main methods of strengthening the hole in the apparatus is considered - strengthening with overhead rings, the advantages and disadvantages of using reinforcing rings are indicated. An analysis of the main methods of strengthening the openings of pressure vessels and devices shows that the difficulties in designing and installing the reinforcing rings are in the technology of assembly, detection of weld defects and detection of the local location of this defect. The work shows the possibilities of using locally rib-reinforced nozzle assemblies, which in some cases can serve as an alternative to reinforcing rings, and are also more technological in manufacture, repair and control. Calculations show that the use of two stiffening ribs oriented along the generatrix of the shell to strengthen the hole allows reducing stresses in the area of welding of the nozzle to the body of the apparatus under static load. Practical experiments carried out at the same time showed that in conditions of dynamic loading, it is categorically not recommended to use the strengthening of the nozzle with local stiffening ribs oriented along the generatrix of the shell.
In order to increase corrosion resistance, different types of insulation of the inner surface of pipes are used, but corrosion in this case often occurs on the inner surface of pipes in the zone of annular welded joints, where there is no insulation. There is no doubt that protection of the internal weld joint is an urgent task, the purpose of which is to increase the reliability of pipeline transport systems. There is a problem of insulation of the area of welded joints of pipes. In areas of welded joints of pipelines, effective corrosion protection shall be provided. A variety of methods have been used to protect internal coated welded joints from corrosion. Protective bushings are the most common method of protection of welded joints of field pipelines with internal coating.
Liquefied natural gas (LNG) is of great importance in the energy segment of the economy. Natural gas, has a higher calorific value, better fuel efficiency and is more environmentally friendly, thereby gaining more importance compared to oil and coal. Not only does LNG offer greater flexibility in supply, it also has cost advantages for transportation starting from a distance of 2,000 km (at sea) and 4,000 km (on land) respectively. Consequently, the LNG market will grow in the coming decades compared to two other fossil sources - oil and coal. To use natural gas, it is necessary to create safe and economically profitable transportation routes from natural gas deposits to end users. One possibility is to transport gas in a liquefied state, at low temperatures. To ensure safe and reliable storage of liquefied gas at minus 163 ° C, good physical and mechanical properties of the base material and weld (corresponding tank system) are required. To meet these high requirements, appropriate welding methods and welding materials are selected. The paper presents an analysis of activities on the development of new welding materials and improvement of welding technologies for the construction of LNG tanks.
Introduction. Repair of pipelines under pressure of pumped media by means of welding is relevant to reduce the complexity of work. However, it may reduce the safety of work. To solve this issue, the authors consider applying the technological processes of machine welding with controlled drop transfer.Aim. To determine the main parameters of technological processes of machine welding with controlled drop transfer, affecting the safety of welding.Materials and methods. The authors developed a theoretical model for calculating the working thickness of a pipeline wall under pressure which they used for calculating the strength during welding. The dependence of the pipeline wall thickness at the edge of the penetrated hole on the internal pressure was also used in the calculations.Results. It was found that machine welding with controlled transfer of metal drops allows the wall penetration depth to be regulated by changing the welding variables. This significantly increases the safety of welding on pipelines under pressure of pumped media, compared to other types of welding. The developed welding processes ensure the safety of welding operations by means of a smooth and accurate control of the wall penetration depth. This is achieved by the correct selection of the background and peak current, control of the drop transfer process by arc voltage, control of the amount of weld metal and the heating temperature of welded structures.Conclusion. Recently, a number of repair technologies have been developed to improve the quality of welds in the construction and repair of trunk pipelines. The highly significant results of research on the development of machine welding technology with controlled drop transfer allow this technology to be recommended as an effective way to improve the safety of welding operations on pipelines under pressure of pumped media.
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