Points to note in straight seam steel pipe welding technology and diameter expansion technology

The welding current in the swing welding of straight seam steel pipe is slightly larger than that in the traditional welding method; secondly, the elongation of the tungsten electrode in the swing welding of straight seam steel pipe is determined according to the thickness of the pipe wall, usually 4-5mm; the argon gas flow rate is slightly larger than that of the traditional welding method, about 8-10l/min; finally, the swing amplitude in the swing welding of straight seam steel pipe is 2mm from the blunt edge of the bevel on both sides of the fusion; the left and right hands cooperate flexibly, the swing is uniform, and the wire feeding is uniform. The swing welding technology of straight seam steel pipe is generally used for the welding of thick-walled straight seam steel pipe. The technical parameters of the swing welding of straight seam steel pipe are slightly different from those of the traditional linear welding method. First, the porcelain nozzle end of the argon arc welding is slightly thicker than that of the traditional linear welding method. Secondly, the gap between the welds is also different. Taking the φ89×5 00Cr19Ni10 weld as an example, the gap of the traditional linear welding method is 0~3mm, while that of the swing method is 4mm, and the welding specifications are also different.

The expansion of straight seam welded pipe is a pressure processing process that uses hydraulic or mechanical methods to apply force from the inner wall of the steel pipe to expand the steel pipe radially outward. The mechanical method is simpler and more efficient than the hydraulic method. It is adopted in the expansion process of several large-diameter straight seam welded pipe pipelines in the world. The process is: mechanical expansion uses the fan-shaped blocks at the end of the expander to expand radially so that the pipe blank can be plastically deformed in sections along the length direction in a step-by-step manner. It is divided into 5 stages.

1. Initial rounding stage. The fan-shaped blocks are opened until all the fan-shaped blocks contact the inner wall of the steel pipe. At this time, the radius of each point in the inner round pipe of the steel pipe within the step range is almost the same, and the steel pipe is initially rounded.

2. Nominal inner diameter stage. The fan-shaped blocks start to reduce the movement speed from the front position until they reach the required position, which is the required inner circumference position of the finished pipe.

3. Springback compensation stage. The fan-shaped block starts to further reduce the speed at the position of stage 2 until it reaches the required position, which is the inner circumferential position of the steel pipe before rebounding required by the process design.

4. Pressure-maintaining and stable stage. The fan-shaped block remains stationary at the inner circumferential position of the steel pipe before rebounding for some time. This is the pressure-maintaining and stable stage required by the equipment and the diameter expansion process.

5. Unloading and returning stage. The fan-shaped block begins to shrink rapidly from the inner circumferential position of the steel pipe before rebounding until it reaches the initial diameter expansion position. This is the minimum shrinkage diameter of the fan-shaped block required by the diameter expansion process.

What are the advantages of using straight seam welded pipe pipelines to transport fluids?

1. Low infrastructure costs. Compared with railway transportation, infrastructure costs can be saved by one-third, while the transportation volume is twice that of railways.

2. Simple construction and fast construction speed. It is generally laid underground, reliable, and adaptable to various terrains.

3. The transportation and operating costs are low and can be highly automated. Compared with other transportation methods, straight seam welded pipe pipeline transportation is cheap, and its freight is only one-tenth of that of railways and about one-half of that of waterways.

At present, the proportion of oil and gas transported by straight seam welded pipes in the world is increasing, accounting for about 75%-95% of the total oil and gas. At present, the range of transport varieties is gradually expanding, not only oil and gas, various chemical raw materials and products, but also solid substances are being transported by straight seam welded pipes. The development direction of straight seam welded pipe pipeline transportation is towards large diameter and high pressure.

What are the characteristics of welded pipes compared with seamless steel pipes?

1. The production process is simple.

2. Less equipment, simple structure, lightweight, easy to achieve continuous, automated, and mechanized production.

3. Low product cost.

4. It is suitable for a wide range of varieties and specifications, with a diameter of 6-3100mm and a wall thickness of 0.3-35mm.

Forming and welding are the basic processes of welded pipe production, and the production methods of welded pipes are classified according to the characteristics of these two processes. The welding method can be divided into four types: furnace welding, electric welding, gas welding, and gas-electric welding.

Furnace welding is divided into lap welding and butt welding according to the form of welds. And the forming method of butt welding is divided into two types: drawing and rolling. There are two types of equipment used for drawing: chain furnace welding machine and continuous furnace welding machine. Rolling forming uses a continuous roller machine. Electric welding is divided into contact welding, induction welding, and arc welding. Among them, contact welding is divided into resistance welding and flash welding, arc welding is divided into open arc welding, submerged arc welding, and shielded arc welding, submerged arc welding is divided into straight seam and spiral seam, gas welding is divided into acetylene welding and water gas welding. The equipment for water gas welding is divided into a roller welding machine and a forging welding machine. Gas electric welding is hydrogen atom welding.