Workshop Prefabrication of Piping Systems
There are many hidden dangers in the construction process of the ship piping system, and the hidden dangers can only be checked when the equipment is used later. At this time, any rearrangement will consume a lot of manpower and material resources, and waste a lot of time. Therefore, according to the construction, step-by-step construction can reduce hidden dangers, and achieve twice the result with half the effort.
1.1 Cutting principles of piping systems
There are four standard lengths of straight pipes commonly used on ships, namely 6 m, 4 m, 3 m, and 2 m. The two ends of the planar curved pipe should not be of the same length; the long side is generally 2 to 4 meters, and the short side is 0.4 to 1 meter. Bending angles should be 15°, 30°, 45°, 60°, 90° and other special angles as much as possible. The bending radius is about 3 times the length of the outer diameter of the pipe. After the pipe is bent, it is necessary to check the roundness and bending, angle, corner, height of bending folds and length of the pipe section. Pipes for special media, such as liquid cargo pipes for transporting LPG, can be connected by shaped elbows with small bending radii. For piping systems that required branch pipes, the branch pipes should be opened at a distance of 150 mm from one end of the pipe as much as possible to facilitate grinding, cleaning and welding of the inner diameter of the branch pipes.
1.2 Cutting and assembly of piping systems
1) Marking of the cutting line
According to the corresponding drawings, each bending point and cutting point on the long straight pipe is marked with a horizontal line of a different color to facilitate the operation of the cutter and pipe bender, and the pipe section number and pipe number of the pipe section are marked on the pipe section with a special label for the pipe system material, tube grade, furnace batch number and other information.
2) Pipeline cutting and assembly processes Common pipe cutting machines include high-speed cutting machines, grinders, flame cutting machines, and sawing machines. After the pipe system is cut, the beveling machine is used to cooperate with the grinder to complete the beveling. For pipes with a wall thickness of less than 2mm, use an I bevel, and for pipes with a wall thickness greater than 2mm, use a V bevel. The bevel angle is 65°±5°. For pipes with a pipe diameter of less than 500 mm, the groove clearance at the bottom is 2 to 4 mm, and 3 to 4 spot welding points are fixed during assembly. For pipes with a pipe diameter not less than 500 mm, the bottom groove gap is 3.5 to 5 mm, and 4 to 8 spot welding points are fixed during assembly. When welding branch pipes on the main pipeline and the wall thickness of the branch pipe is less than 6 mm, no beveling is required; when the wall thickness is not less than 6 mm and the diameter of the main pipeline is not less than 2.5 times the diameter of the branch pipe, a bevel is made at the end of the branch pipe. When the diameter of the main pipeline is less than 2.5 times the diameter of the branch pipe, a bevel can be made partially at the left and right parts of the end of the branch pipe along the axis of the main pipeline, as shown in Figure 1. Figure 1 Beveling at the end of branch pipes
In the assembly process, the limit deviation of the inner diameter of the pipe center should be less than 2 mm. When the pipe is not completely centered, the deviation of the inner diameter of the nozzle can be adjusted by means of a hydraulic jack or a threaded jack, but no harmful stress can be caused. The adjustment method of the threaded jack is shown in Figure 2, that is, the cylindricity of the inner diameter of the tube is adjusted by tightening the screws on the tooling, thereby reducing the deviation of the inner diameter of the center of the tube.
1.3 Welding of piping systems
For special carbon steel pipes, full tungsten argon arc welding (GTAW) is generally used for one-sided welding and double-sided forming. In the welding process, both the welding gun mouth and the welded pipe need sufficient argon protection to prevent the pipe system from oxidation. Since carburization will occur in the welding process, special grinding wheels and stainless steel brushes must be used to remove carburization during the welding seam cleaning process to avoid damaging the pipe wall and welding seam. For ordinary carbon steel pipes, carbon dioxide gas shielded welding is used, the welding seam has low hydrogen content, good rust resistance, small cold crack tendency, good penetration ability, high welding current density, small deformation, and high production efficiency. In the welding process, when there is welding bending deformation of the weld seam, certain corrections can be made according to the deformation of the welding seam. For pipe fittings with small sizes and thinner walls, welding deformation is easy to occur for welding seams. The pipe fittings are prone to weld deformation. When welding, it is necessary to pay attention to the pipe end in real time, flexibly adjust the welding direction according to the actual situation, and keep the temperature of the weldment not too high to reduce the occurrence of deformation.
1.1 Cutting principles of piping systems
There are four standard lengths of straight pipes commonly used on ships, namely 6 m, 4 m, 3 m, and 2 m. The two ends of the planar curved pipe should not be of the same length; the long side is generally 2 to 4 meters, and the short side is 0.4 to 1 meter. Bending angles should be 15°, 30°, 45°, 60°, 90° and other special angles as much as possible. The bending radius is about 3 times the length of the outer diameter of the pipe. After the pipe is bent, it is necessary to check the roundness and bending, angle, corner, height of bending folds and length of the pipe section. Pipes for special media, such as liquid cargo pipes for transporting LPG, can be connected by shaped elbows with small bending radii. For piping systems that required branch pipes, the branch pipes should be opened at a distance of 150 mm from one end of the pipe as much as possible to facilitate grinding, cleaning and welding of the inner diameter of the branch pipes.
1.2 Cutting and assembly of piping systems
1) Marking of the cutting line
According to the corresponding drawings, each bending point and cutting point on the long straight pipe is marked with a horizontal line of a different color to facilitate the operation of the cutter and pipe bender, and the pipe section number and pipe number of the pipe section are marked on the pipe section with a special label for the pipe system material, tube grade, furnace batch number and other information.
2) Pipeline cutting and assembly processes Common pipe cutting machines include high-speed cutting machines, grinders, flame cutting machines, and sawing machines. After the pipe system is cut, the beveling machine is used to cooperate with the grinder to complete the beveling. For pipes with a wall thickness of less than 2mm, use an I bevel, and for pipes with a wall thickness greater than 2mm, use a V bevel. The bevel angle is 65°±5°. For pipes with a pipe diameter of less than 500 mm, the groove clearance at the bottom is 2 to 4 mm, and 3 to 4 spot welding points are fixed during assembly. For pipes with a pipe diameter not less than 500 mm, the bottom groove gap is 3.5 to 5 mm, and 4 to 8 spot welding points are fixed during assembly. When welding branch pipes on the main pipeline and the wall thickness of the branch pipe is less than 6 mm, no beveling is required; when the wall thickness is not less than 6 mm and the diameter of the main pipeline is not less than 2.5 times the diameter of the branch pipe, a bevel is made at the end of the branch pipe. When the diameter of the main pipeline is less than 2.5 times the diameter of the branch pipe, a bevel can be made partially at the left and right parts of the end of the branch pipe along the axis of the main pipeline, as shown in Figure 1. Figure 1 Beveling at the end of branch pipes
In the assembly process, the limit deviation of the inner diameter of the pipe center should be less than 2 mm. When the pipe is not completely centered, the deviation of the inner diameter of the nozzle can be adjusted by means of a hydraulic jack or a threaded jack, but no harmful stress can be caused. The adjustment method of the threaded jack is shown in Figure 2, that is, the cylindricity of the inner diameter of the tube is adjusted by tightening the screws on the tooling, thereby reducing the deviation of the inner diameter of the center of the tube.
1.3 Welding of piping systems
For special carbon steel pipes, full tungsten argon arc welding (GTAW) is generally used for one-sided welding and double-sided forming. In the welding process, both the welding gun mouth and the welded pipe need sufficient argon protection to prevent the pipe system from oxidation. Since carburization will occur in the welding process, special grinding wheels and stainless steel brushes must be used to remove carburization during the welding seam cleaning process to avoid damaging the pipe wall and welding seam. For ordinary carbon steel pipes, carbon dioxide gas shielded welding is used, the welding seam has low hydrogen content, good rust resistance, small cold crack tendency, good penetration ability, high welding current density, small deformation, and high production efficiency. In the welding process, when there is welding bending deformation of the weld seam, certain corrections can be made according to the deformation of the welding seam. For pipe fittings with small sizes and thinner walls, welding deformation is easy to occur for welding seams. The pipe fittings are prone to weld deformation. When welding, it is necessary to pay attention to the pipe end in real time, flexibly adjust the welding direction according to the actual situation, and keep the temperature of the weldment not too high to reduce the occurrence of deformation.
