Welded steel pipe refers to a steel pipe with a seam formed by bending a steel strip or plate into a circular, square, or other shape, then welding it. The raw material used for welded steel pipe is steel plate or strip.
1. Based on the intended use, welded steel pipe can be categorized into general-purpose and high-temperature and high-pressure applications. The latter often uses special alloy steels, requiring consideration and resolution of shrinkage cracks in the weld seam during welding and ensuring that the mechanical properties of the heat-affected zone (HAZ) do not change significantly due to the welding process.
2. Based on the wall thickness of the steel pipe, high-frequency welding can be used for steel pipes made from relatively thin materials, such as steel strips. Some thin-walled steel pipes can be welded using shielding gas. Manual arc welding can be used for steel pipes with a wall thickness exceeding 2mm.
3. Based on the diameter of the steel pipe, there are two types: small-diameter pipes that can only be welded on one side, and those that require technicians to drill into the pipe to weld on both sides. Single-sided welding requires the welder to be able to weld both sides of the pipe and form the pipe. The welder must pass the steel ball test to ensure that the cross-sectional area capacity and weld profile meet design requirements.
4. For all steel pipes made of high-strength alloy steel, including those with heat, pressure, wear, and low-temperature resistance, the welding process must prioritize preventing the formation of martensitic structures and cracks caused by high-temperature welding. Generally, welding rods must be carefully selected and baked as required before being issued to the welder. Both sides of the weld must be cleaned and degreased before welding, dewatered, rusted, and free of debris. The weld heat input must be kept as low as possible, and oscillation during welding must be minimized. The final weld should be arranged to anneal the heat-affected zone as much as possible. After welding, the pipe should be cooled slowly and covered with asbestos cloth.

First, Preparation of the Steel Pipe Before Welding
1. Determine Welding Materials: Select appropriate steel pipes and welding materials based on actual needs to ensure weld quality.
2. Prepare Tools: Obtain the appropriate welding equipment and tools, and perform proper maintenance and inspection. 3. Pre-treating the Steel Pipe: The steel pipe surface must be cleaned, degreased, and polished before welding to ensure weld strength.

Second, Safety Measures During Steel Pipe Welding
1. Personal Safety: Wear protective equipment such as a welding helmet, goggles, gloves, and protective clothing.
2. Welding Site Preparation: Ensure that there are no flammable or explosive materials around the steel pipe welding area to avoid fire or explosion accidents.
3. Current Control: Adjust the current level according to the material and external environment to ensure weld quality.

Third, Quality Inspection of Steel Pipes After Welding
1. Visual Inspection: Check the weld penetration and fusion seam quality to ensure weld quality.
2. Sound Inspection: Use a tool to tap the welded area of the steel pipe to listen for the sound and determine the size and quality of the weld pool.
3. Current Density Inspection: Use a special instrument to check the current density to ensure the quality of the welded steel pipe.

Summary: Before welding steel pipes, it is important to carefully select welding materials and conduct preparatory work. During welding, pay attention to personal safety, control the current, and operate with caution. After welding, appearance inspection, sound inspection, and current density inspection can be carried out to ensure the quality of the steel pipe.