Connection methods of welded steel pipe

A welded steel pipe is a metal pipe produced by rolling steel plates and welding them into a specific diameter on a mold. Widely used in industries such as construction, machinery manufacturing, and bridge engineering, welded steel pipes offer high production efficiency and are robust and pressure-resistant, especially in larger sizes. They can be categorized into carbon steel pipes and stainless steel pipes. Here's an overview of the connection methods of welded steel pipe.

Connection Methods of Welded Steel Pipe

(1) Threaded Connection

A threaded connection involves joining pipes, or pipes to valves, using internal and external threads. This method is commonly used for connecting threaded equipment and accessories, especially in situations where disassembly is frequent and fire hazards are present.

- Galvanized Welded Steel Pipes: Typically used for low-pressure fluid transport with a nominal diameter below 150mm and working pressure below 1.6MPa.

- Water Supply Pipes: Working pressure does not exceed 1.6MPa, and the maximum nominal diameter is 150mm.

- Hot Water Pipes: Working pressure does not exceed 0.2MPa, and the maximum nominal diameter is 50mm.

- Thin-Walled Stainless Steel Welded Pipes: Suitable for connecting pipe sections from DN65 to DN100.

When connecting threaded pipes, appropriate packing should be placed between the external thread of the pipe and the internal thread of the pipe opening or valve. The packing serves to seal, protect the pipe opening, and facilitate disassembly. Features of threaded connections include ease of installation, disassembly, adjustment, simple construction, and low pressure resistance. The main installation procedures include pipe cutting, threading, assembling pipe fittings, and straightening pipe sections.

(2) Flange Connection

Flange connections are often used for temporary drainage and irrigation pipelines, pump station pipe-fitting combinations, welded steel pipes, valves, and accessories. Flanges can be made from various materials such as cast iron, steel, plastic, non-ferrous metals, glass, and fiberglass.

Flanges are selected based on the nature, pressure, and temperature of the medium. The nominal pressure must meet design requirements. When connecting pipe sections using flanges, the standard method must be selected according to design requirements and working pressure. Flange connections feature easy disassembly, high strength, good sealing performance, and the ability to withstand high pressures. When installing, ensure the two flanges are parallel, the sealing surface is undamaged and clean, and the gasket is chosen based on design requirements.

(3) Welding

Welding is a common method for connecting welded steel pipes. It involves heating the steel pipe interface and welding rod, then connecting and fixing the weldments together. This method provides firm welding, good sealing, durability, and low cost, and does not require frequent maintenance.

Common welding methods for steel pipes include gas welding, arc welding (automatic spot welding, manual electric welding), resistance welding, manual arc welding, manual argon arc welding, submerged arc automatic welding, and contact welding. For instance, ERW (Electric Resistance Welding) pipe is a type of resistance welding that uses the resistance heat generated by current passing through the weldment to locally heat and pressurize it, resulting in high productivity, minimal deformation, and easy automation.

(4) Groove Clamp Connection

The grooved clamp connection is a modern method with many advantages. It uses clamps and grooves to compress the pipe through bolt tightening, achieving a sealed connection. Components typically include clamps, slots, seals, and flanges. Clamps are usually made of gray cast iron, ductile iron, or stainless steel, while clamping grooves and sealing plates are often round or square, and flanges withstand the pressure in the welded pipe.

Advantages of grooved clamp connections include fast installation, simple operation, reliable sealing, and suitability for large-diameter, high-pressure, high-temperature, and corrosion-resistant pipeline systems. They also tolerate installation errors well, save costs by not requiring precision machining, and are easy to repair and replace. However, they may not be suitable for high-pressure, high-temperature, or highly corrosive environments, and sealing performance can be an issue. Therefore, selection should be based on specific engineering needs and environmental conditions.