Key steps and main equipment for processing large-diameter straight seam steel pipes

As the demand for energy infrastructure expands—especially with major national projects like the West-East Gas Transmission Project—the role of domestically produced large-diameter straight seam submerged arc welded (LSAW) steel pipes has become increasingly prominent. These pipes are crucial for high-pressure oil and gas transport, and their quality directly impacts pipeline safety and performance. Below are the core processing steps and main equipment involved in manufacturing high-precision LSAW steel pipes.

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1. Precision Edge Preparation

Steel Plate Milling Machine: Precisely mills both edges of the steel plate, ensuring parallelism and required curvature for accurate pipe forming. This step prepares the plate for a tight and seamless weld later in the process.

Steel Plate Pre-Bending Machine: Pre-bends the plate edges after milling to form the correct welding groove and prevent excessive straight edges after forming, which helps maintain roundness.

2. Pipe Forming

Fully Automatic Pipe Forming Machine: Bends and forms the processed steel plate into a pipe shape in one continuous operation, ensuring forming consistency.

3. Pre-Welding and Seam Formation

Pipe Pre-Welding Machine: Tack welds the formed pipe to stabilize its shape before final welding.

4. Internal Welding

Internal Welding Machine + Welding Trolley: Performs automatic submerged arc welding (SAW) inside the pipe using a double-wire system, guided by a welding trolley that ensures precise movement along the track.

5. External Welding

External Welding Machine + Welding Trolley: Completes the external SAW welding in coordination with the forming and internal welding process.

6. Pipe Sizing and Straightening

Pipe Finishing Machine: Applies uniform pressure section by section to correct any deformation and achieve specified roundness.

Gantry-Type Mobile Straightening Machine: Ensures longitudinal straightness of the finished pipe body.

7. End Beveling

Pipe Chamfering Machine: Bevels and flattens pipe ends according to specified groove angles and blunt edges, preparing the pipe for joint welding in the field.

8. Stress Elimination and Dimensional Correction

Pipe Expansion Machine: Enhances dimensional accuracy and eliminates residual stresses from forming and welding.

9. Hydrostatic Testing

3000T Hydrostatic Tester: Performs pressure testing to verify weld tightness and pipe strength under operating conditions.

10. Non-Destructive Testing

Line Wave Ultrasonic Testing Equipment: Conducts 100% NDT of all weld seams, detecting longitudinal, transverse, and heat-affected zone (HAZ) defects.

Key Points for Rebar Thread Processing in Steel Pipe Reinforcement:

Thread Shape Accuracy: Threads must match the sleeve’s design in terms of pitch and shape. Gauge inspection is mandatory.

Lubrication During Threading: Use water-soluble cutting lubricants. Add 15%-20% sodium nitrite if ambient temperature is below 0℃. Do not use engine oil or operate dry.

Appearance Inspection: Thread heads must be visually checked one by one, with each operator marking their own work.

Quality Sampling: Perform random checks on 10% of each thread size, with at least 10 samples. If any are unqualified, recheck the full batch and reprocess as needed.

Post-Processing Protection: Qualified threads should be protected with caps and sorted according to specification for easy access and further use.