On-site assembly of large container equipment

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In the early 1960s, except for a few petrochemical vessel equipment that were overlong, overweight, and wide, general pressure vessels, storage tanks, and various reaction volumes were assembled and welded in the manufacturing plant. After completing the entire workload of the equipment, they were then transported to the site for installation, operation, and use. Since the 1970s, with the continuous development of science and technology, the production scale of the petroleum, chemical and fertilizer industries has continued to expand, accelerating towards large-scale and specialization. The manufacturers of these petrochemical equipment have also continued to move towards large-scale and specialization. In addition, the nuclear power plant The development of a single petrochemical container equipment and nuclear power plant equipment has made the weight, length, and diameter of a single petrochemical container equipment and nuclear power plant equipment exceed the limits of train transportation and factory assembly and welding. This raises a new topic for us, which is the problem of on-site assembly and welding, especially for factories. It is more important. By transferring the workload in the factory to the construction site, the problem of equipment overrun can be overcome. 1. Conditions for on-site assembly and welding of container equipment. On-site assembly and welding of large-scale container equipment is very important for manufacturers. It is an important factor in developing large-scale products, improving the factory's technical level, and increasing economic benefits. The investment in on-site assembly and welding is large, and the product cost increases accordingly. It is not worthwhile for the factory to invest a lot of financial resources in one-time on-site assembly and welding. However, in the long run, the costs of transportation, assembly and welding, lifting, loading and unloading of large petrochemical containers, application for large transportation railway trucks, etc. are much higher than the costs of on-site assembly and welding, so on-site assembly and welding of large petrochemical container equipment is more feasible. The following introduces the minimum production conditions required for on-site assembly and welding.: There must be enough space ； Must have simple lifting equipment and poles ； Senior assemblers and welders are required ； Must have a complete mobile detector ； Simple heat treatment and hydrostatic testing methods must be available. Only with the above five items can on-site assembly and welding of large petrochemical containers be realized. 2. Manufacturing procedures in the factory For overweight, long and wide products, in addition to going to the construction site for assembly and welding, a considerable amount of work must also be done in the factory to minimize the workload on the construction site. The in-factory manufacturing part can be roughly divided into two situations:: Products with an equipment diameter of no more than 4,000 mm and extremely long lengths cannot be transported by railway. They must be manufactured into two or three sections in the factory, and the ring seams must be assembled and welded on site to complete the remaining workload. ； Products whose diameter exceeds the limit and weight also exceeds the limit can only be manufactured into a single-section barrel or a single-section rolled half piece in the factory, and then transported to the construction site for assembly and welding. The following is an introduction to the manufacturing of semi-finished products in the factory. First, the incoming materials are re-inspected, including chemical composition, mechanical properties, and ultrasonic flaw detection. After passing the inspection, enter the manufacturing plant workshop and mark the blanking line (including the blanking line and processing line for the initial processing of raw materials, and the processing allowance and gas cutting gap must be considered). At the same time, attention should be paid to reasonable arrangements to improve material utilization. After processing the bevel, it is hot-rolled, cold-rolled, and pressed into half pieces. The barrel is assembled in the factory or the half pieces are transported to the construction site for assembly and welding. For materials of different materials and thicknesses, process procedures such as preheating before welding, hydrogen elimination after welding, and stress-relieving heat treatment after the overall welding are required during assembly and welding. During heat treatment, attention should be paid to coordinating factory and on-site heat treatments. Some materials require more than three heat treatments, which require strict compliance with process disciplines. 3 On-site assembly and welding On-site assembly and welding mainly assembles and welds the cylinder sections and mutual halves manufactured in the factory into a whole, completes the rest of the workload, and then installs and operates the equipment. The welding method used is mainly manual welding. Different thicknesses and different types of materials need to be preheated before welding. Different preheating temperatures require different preheating methods.: Some use gas, some use electric heaters, some use power frequency, etc. Non-destructive inspection is carried out after welding, and heat treatment is carried out after passing the test. Heat treatment is a key issue in on-site assembly welding. Because the product will generate residual stress after welding, it will cause deformation of the product equipment and increase the risk of brittle deformation. The combination of residual stress and residual oxygen in the weld will cause the hardening of the heat-affected zone, resulting in cold cracks and delayed cracks. Therefore, welding residual stress should be eliminated as much as possible. Heat treatment can eliminate residual stress, and materials of different materials and thicknesses have clear specifications for heat treatment. 4 Several methods of on-site heat treatment 4.1 Internal combustion heat treatment of the container The so-called internal combustion method is to use the container product itself as a combustion chamber, with an insulation layer on the outer surface, so that the gas or liquid can be burned directly in the equipment to achieve the heat treatment effect. This method is especially suitable for large spherical storage tanks. The outer surface of the spherical container is equipped with an insulation layer of about 150mm, and the combustion nozzle is inserted into the container from the lower manhole of the spherical container for combustion to eliminate welding stress. When using this method, special attention must be paid to ignition, control of combustion flow, and careful selection of heat treatment processes to prevent uneven combustion and achieve the overall effect of eliminating welding stress. 4.2 Resistance wire heating and heat treatment: The resistance wire is energized to generate current, and the resistance wire is evenly discharged within the equipment using a bracket. The workpiece is heat treated using the thermal radiation method. It can also be used for external local heat treatment. The advantages of this method are good insulation layer, tight sealing, easy temperature control, uniform heating, and high accuracy. ； The disadvantage is that there must be an insulation layer. If the insulation is not good, it will be difficult to control the heating and insulation time. 4.3 The heat treatment of local electric heaters uses belt-type electric heating, which is directly covered on the circumferential or longitudinal seams of the local equipment to be heated. This method is easy to control the temperature, has uniform heat treatment, and is easy to carry and transport. This method is generally used during assembly at the construction site. 4.4 Using this method for power frequency induction heat treatment requires the use of a large number of copper cables and large transformers. This method is difficult to operate and install and is uneconomical. This method is rarely used on construction sites. 4.5 Quick assembly simple annealing furnace heat treatment uses a simple assembly type annealing furnace to eliminate stress on the longitudinal and circumferential welds or the entire equipment product on site. This method is economical, easy to operate, and can be used repeatedly. For heat treatment of equipment with different diameters, the distance between the nozzles is adjusted to ensure uniform combustion. 5 Conclusion This article briefly introduces the problem of on-site assembly of large container equipment. Neither the manufacturing method nor the heat treatment method is omnipotent and has limitations. Whether to perform on-site assembly should be decided based on specific conditions.