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Fully automatic pipeline welding technology and process control: Full-position automatic welding of pipelines refers to the process in which, with the pipeline held in a relatively fixed position, a welding cart moves the welding torch along tracks around the pipe wall, thereby enabling automatic welding. Generally, a full-position automatic welding device consists of a welding trolley, traveling tracks, an automatic control system, and other components. The purpose of developing all-position automatic welding equipment is to improve welding quality and labor productivity, as well as to reduce the workload on workers. Welding trolley: The welding trolley is the driving mechanism that enables the automatic welding process. It is mounted on welding tracks and moves the welding torch in a circular motion along the pipe wall; it is one of the key components for achieving automatic welding at pipe ends. The welding trolley should feature an attractive design, small size, light weight, and ease of operation. Its core components are the walking mechanism, the wire feeding mechanism, and the welding torch swinging adjustment mechanism. The traveling mechanism consists of a motor and a gear transmission system. To enable the traveling motor to carry out the position and speed commands issued by the computer control unit, the motor must be equipped with a speed feedback mechanism, ensuring accurate positioning at various locations along the pipe seam as well as good speed tracking capabilities. The wire feeding mechanism must ensure an accurate and stable wire feeding speed, have a low moment of inertia and good dynamic performance, as well as sufficient driving torque. The welding torch swing adjustment mechanism should have the capabilities to allow the welding torch to swing left and right relative to the weld seam, to pause at the left and right ends, to enable control of its orientation in all directions, and to adjust the angle of the welding torch. All the aforementioned components of the welding trolley are under programmable automatic control via a computer; once the program is activated, the various parts of the welding trolley operate in coordination according to the logical sequence specified by the program. Manual intervention can also be applied to the welding process when necessary; in such cases, the program can automatically adjust the welding parameters based on the extent of the intervention and carry out the welding. Welding track: The track is a specialized mechanism mounted on the pipe to allow the welding cart to move and be positioned; its structure directly affects the stability and precision of the welding cart’s movement, which in turn influences the quality of the weld. The track should meet the following requirements: it should be easy to install and remove, as well as easy to position ； Well-structured and lightweight ； It has a certain strength and hardness, as well as wear and corrosion resistance. Tracks are divided into flexible tracks and rigid tracks. A rigid track refers to one whose structural stiffness is high and it does not deform easily, whereas a flexible track is the opposite of a rigid track. The two types of tracks each have their own characteristics. Rigid tracks offer accurate positioning and minimal deformation after installation, which ensures smooth movement of the welding trolley; radial adjustment of the welding torch is required less during welding. However, they are heavy and not easy to install or remove. Flexible tracks are easy to install and remove, weigh less, and have lower precision compared to rigid tracks. Wire feeding method: The smoothness of wire feeding has a direct impact on the welding quality. The wire feeding method can be simply divided into two types: pull feeding and push feeding. During wire drawing, the welding torch is positioned close to the wire feeder; as a result, the wire experiences less resistance after leaving the wire feeder during welding, which ensures a smooth wire feeding process. However, both the wire feeder and the wire spool must be installed on the welding trolley, which increases the weight of the trolley and makes it more difficult to assemble and disassemble manually. Moreover, this increased weight can cause the welding trolley to move unevenly. The use of small disc electrodes with a diameter of 0.8 mm or 1.0 mm (with a weight of about 5 kg) reduces the weight and load of the welding trolley, making the welding process easier to control; however, it has a certain impact on welding efficiency. When the wire-feeding method is used, the wire-feeding mechanism is installed outside the welding trolley, which reduces the size and weight of the trolley. This allows for the use of high-power wire feeders and large-diameter wire rods with a diameter of 1.2 mm (weighing about 20 kg), thereby improving welding efficiency. However, since the wire feeder is located far away from the welding torch when pushing the wire, a wire feeding hose is required to connect the two. As the wire is continuously pushed toward the tip of the welding torch, it encounters significant frictional resistance. Moreover, the degree of bending of the wire feeding hose during welding affects the smoothness of wire feeding; in severe cases, this can lead to problems with wire feeding. Therefore, these factors must be taken into full consideration when using wire pushing techniques. Selection of welding processes: Currently, in addition to manual welding, the submerged arc automatic welding process and gas shielded welding process are commonly used for pipeline welding. Submerged arc automatic welding features good weld shape, high welding efficiency, and low welding costs. For pipeline construction, it can be used for the welding of two pipes together, referred to as \"two-to-one welding\"; in this method, the welding torch remains fixed in one position while the pipes rotate. Obviously, it is impossible to rotate the pipes during long-distance pipeline welding; therefore, the “two-to-one” method can only be used for the prefabrication of pipes. If submerged arc welding is used for the full-position automatic welding of pipes, then the welding apparatus must be equipped with mechanisms for feeding, supporting, and recovering the flux, which makes the structure of the welding apparatus more complex. This leads to difficulties in operation and disassembly, and it also increases the load on the traveling cart, affecting its stability during movement. Submerged arc welding typically uses thick welding wires and high currents. When applied to all-position automatic welding, it may suffer from welding defects such as droplet sagging and flow due to the high deposition rate, which affects the shape and quality of the weld; therefore, it is quite difficult to use submerged arc welding for all-position automatic welding of pipes. The welding process uses flux-cored wire with gas protection; if multiple passes are required for formation, removing slag from the weld surface after each pass is time-consuming and labor-intensive ； If forced forming is used, a forming copper slider that moves together with the welding torch must be employed, along with circulating cooling water, which can **improve welding efficiency; however, this not only makes the structure of the welding device more complex but also increases its weight. Due to the high cost of flux-cored wires, as well as the need to secure a supply of shielding gas, the welding cost is high. Using self-shielded welding wire alone saves on shielding gas, but it presents the problem of difficult slag removal. The welding process uses solid wire along with gas protection; in the case of multiple passes for shaping, the welding process can be simply divided into three stages: root pass, fill pass, and cap pass. It is possible to proceed to the next stage without cleaning the weld surface, but the welding speed is relatively slower compared to forced forming. The shielding gas is generally pure carbon dioxide, or a mixture of carbon dioxide and argon, or carbon dioxide and oxygen. A mixture of carbon dioxide and argon can help to stabilize the arc during welding and reduce spatter, but in field operations it is difficult to find sources of argon and it is relatively expensive. From an economic perspective, when welding oil pipelines, it is best to use pure carbon dioxide as the shielding gas. When constructing in areas with suitable conditions, it is ideal to use carbon dioxide and argon as shielding gases. Control methods: During the welding process, the traveling speed of the welding trolley, the wire feeding speed, and the left-right vibration frequency of the welding torch are the three main parameters; the up-and-down adjustment of the welding torch can be ignored. Use a perpendicular line to divide the circumference of the pipe into two semicircles, left and right, and then divide these two semicircles equally in a clockwise and counterclockwise direction to determine the welding joints. Through numerous tests, ideal welding parameters can be obtained at each node of the weld. However, the data from actual welding and testing will not be exactly the same; during welding, the parameters such as wire feeding speed and vibration frequency can be adjusted according to the actual conditions. However, the adjustment of these parameters is interrelated; even if the wire feeding speed is set correctly, the vibration frequency and the welding vehicle speed may not be appropriate. It takes some time of experimentation to adjust all these parameters to work together properly. If another control method is used, the situation is quite different. The wire feeding speed, the movement speed of the welding vehicle, and the vibration frequency of the welding torch are taken as the three dependent variables and placed in a spatial coordinate system; time is used as the independent variable, while the welding current and voltage serve as the boundary conditions. Finally, the relationship among the wire feeding speed, the movement speed of the welding vehicle, and the vibration frequency of the welding torch is determined, which corresponds to the spatial coordinate equation. During actual welding, each adjustment involves modifying all three parameters simultaneously to ensure the accuracy of the adjustment process. Faced with the increasingly fierce international market competition, to secure a position in the pipeline welding industry it is necessary to improve construction equipment and technical capabilities. Therefore, researching full-position automatic pipeline welding devices holds great practical significance for enhancing the level of pipeline construction in our country. Source: China Petroleum Pipeline Network, January 21, 2008