4.3 Automatic welding Automatic welding can be applied to root welding and filling, and surface welding. (1) Automatic root welding The automatic root welding method adopts an automatic inner welder or an outer welder to perform double-sided forming on one side. a. Inner welder The automatic internal welder used in the “West-East Gas Pipeline†pipeline project is a pipe root welding special machine for Φ1016mm pipe diameter, which is the inner welder produced by NOREAST Company of the United Kingdom and the PIW3640 type internal welder of China National Petroleum Pipeline Bureau. The characteristic is that the applicable pipe diameter range is narrow, the equipment has a large investment at a time, but the welding efficiency is very high, and the root welding of the Φ1016mm steel pipe takes about 70 seconds. Since the welding is carried out in the steel pipe, the influence of the ambient wind speed during the welding process is relatively small, as shown in Fig. 1. b. Automatic external welding machine single-sided welding double-sided forming root welding The single-sided welding double-sided forming root welding equipment is mainly the CWS.02NRT automatic outer welding machine of PWT Company of Italy, and the STT power matching automatic outer welding machine of LINCOLN Company of the United States. The automatic welding machine single-side welding double-sided forming root welding equipment solves the problem of single-side welding double-sided forming root welding without backing liner. The thickness of root welding is 4.5mm, which is much higher than the welding thickness of the inner welding machine (1～ 1.2mm), the welding efficiency is high, and the root welding of Φ1016mm steel tube takes about 8 minutes. Due to the gas protection, the welding process is sensitive to the ambient wind speed, and windproof measures such as windproof sheds should be used during construction. (2) Automatic outer welder The PAW-2000 external welder produced by the Pipeline Bureau, as shown in Figure 2, is characterized by uniform weld penetration and a large groove width for welding, but usually requires a groove angle greater than 13° to avoid welding arc Figure 1 Pipeline automatic welder welding process Figure 2 PAW-2000 outer welder The edge of the groove is not fused to the edge of the base material. It has similar functions to the APW-II automatic outer welder produced by the Engineering Research Institute of China National Petroleum Corporation. [3] The automatic outer welder produced by NOREAST of the United Kingdom, the MOW-1 automatic outer welder produced by RMS of Canada and the M-300 automatic outer welder of the American CRC company are characterized by easy implementation of a small groove of 5-8°. The welding operation of the angle, the groove surface is well fused, but the weld penetration is not uniform, and the width of the groove that can be welded is usually not more than 10 mm, otherwise it is difficult to ensure the weld formation in the overhead welding portion. CWS.02NRT automatic outer welding machine produced by PWT Company of Italy, which is characterized by uniform welding penetration depth, large groove width which can be welded, and easy to realize welding operation of small groove angle of 5-8°, groove The surface is well fused. 5. Welding process 5.1 Welded joint groove form Pipe groove welding usually adopts the groove type of API standard 30°V groove, which is suitable for manual welding. However, for large-diameter, thick-walled steel pipes, such welded joints have a large amount of grooved metal filling, high labor intensity, and are not suitable for automatic welding, usually semi-automatic welding with 23°V groove, automatic welding Narrow gap compound groove type. 5.2 Preheating and interlayer temperature The purpose of preheating is to prevent cold cracks in the root by slowing the stress state of the base metal and reducing the cooling rate of the root bead. The preheating temperature range of pipeline welding construction should consider the strength of the base metal, the change law of the microstructure, the diameter of the pipe and the wall thickness, and the hydrogen content of the welding material. For multi-layer welding of thick-walled steel pipes, it is also necessary to control the temperature between the weld bead layers to control the cooling rate of the near-seam zone. The interlayer temperature is generally similar to the preheating temperature. Under the premise of avoiding overheating in the near seam area, the higher interlayer temperature can prevent the occurrence of cold cracks during multi-layer welding. 5.3 Welding line energy The determination of the welding line energy needs to take into account the composition of the base metal, the type of welding material, the metallurgical reaction of the coating (drug core, flux) and the protective effect of the protective gas, the preheating condition before welding, the temperature control of the interlayer, and the specification of the pipe. , wire (bar) diameter, embrittlement and softening tendency of heat affected zone, desired microstructure and mechanical properties, as well as welding position, welding pass, thickness of each weld layer, weld formation and transition form of droplets, etc. factor. 5.4 Post heat treatment and heat treatment Pipeline welding construction generally does not perform post-weld post-heat treatment and heat treatment. However, when pre-weld preheating and inter-layer temperature control are difficult to play a role in the construction of high-cold areas, it is necessary to take certain post-heating and heat treatment measures on the welded joints to ensure the microstructure and performance of the welded joints. 5.5 other In the pipeline welding construction process, the influence of external stress on the high-strength and large-wall steel pipes should be considered. At the same time, the influence of ambient temperature, ambient humidity and ambient wind speed on different welding methods should be considered, and necessary measures should be taken to ensure the welding quality. 6. Outlook The application status of domestic pipeline welding technology is introduced in the past. The gap between the welding materials, methods, processes and equipment and foreign technology is getting smaller and smaller, and the automatic welding technology has been basically popularized and applied. However, domestic welding materials are mostly satisfied with manual welding, automatic welding wire and semi-automatic welding materials are independently developed and produced, and a considerable part of them need to be imported. At the same time, the performance of domestic welding materials needs to be improved, and product serialization is insufficient. In terms of welding power supply, domestic Aotai and Era welding machines have been widely used, but they are not as widely used as Lincoln welding machines; automatic root welding power supplies for bottoming have not yet been produced in China. Recently, deep-melt electron beam welding and laser-assisted melting gas-shielded arc welding have made breakthroughs in pipeline applications. With the successful welding of domestic X80 pipeline steel in Suining pipeline, the more advanced pipeline steel X100 and X120 will soon be applied to domestic pipeline construction. The improvement of pipeline steel grade will inevitably increase the requirements of welding technology, especially the performance requirements of welding materials and welding equipment. Therefore, there is still much room for improvement in welding technology in China, and the demand for welding materials and equipment. It will increase further. Previous page We offer a complete range of flanges for use with OD tube and nominal bore pipe in carbon steel and stainless steel to tables D, E, F, and H. Specials can be manufactured to customers' special requirements. We offer different surface treatment, such as galvanized flanges. Galvanized Flange,Pipe Flanges,Electro Galvanized Flanges,Galvanized Plate Flanges Shandong Zhongnuo Heavy Industry Co.,Ltd. , https://www.zhongnuoflanges.com