I. Analysis of the Production Process for Submerged Arc Welded Steel Pipes
The production of submerged arc welding steel pipes begins with precision forming processes. Depending on different product requirements, the following three technical routes are primarily used:
i. JCOE Continuous Forming Process (Specifically for Medium to Thick-Walled Steel Pipes)
(1) Application Scenarios:
This process is specifically designed for producing submerged arc welding steel pipes with thicker walls.
(2) Process Details:
J-Stage: Using an 8,000–12,000-ton hydraulic press, one-third of the steel plate width is pressed into a 135° arc shape.
C-stage: The remaining steel plate is bent in stages to ensure the curvature radius error is ≤1.2%D (steel pipe diameter).
O-stage closure: The mold is squeezed to complete the closure of the round pipe, with ellipticity strictly controlled within 0.5%D.
(3) Comparison notes:
Compared to ERW LSAW pipes, submerged arc welded steel pipes have higher forming precision and are more suitable for high-pressure conditions.
ii. UOE High-Efficiency Forming (Specialized for Large-Diameter Pipes)
(1) Application Scenarios:
Primarily used for the production of large-diameter submerged arc welding steel pipes with a diameter of Φ≥508mm.
(2) Process Details:
U-shaped pressing: A 3,000-ton hydraulic press pre-bends a 120° section, with a forming speed stabilized at 1.2m/min.
O-type Sealing: Geometric sealing is achieved using a three-roll expanding machine, with outer diameter tolerance controlled within ±0.15%D.
(3) Comparison Notes:
ERW steel pipe are typically used for thin-walled tubes, while submerged arc welded steel pipes are more suitable for thick-walled, large-diameter applications.
iii. Spiral Continuous Forming (Low-Cost Mass Production)
(1) Application Scenarios:
Suitable for mass production of submerged arc welded steel pipes, particularly for low-cost requirements.
(2) Process Details:
Precise control of strip feeding using an electric contact pressure gauge, with weld seam gap accuracy of ±0.1mm.
Wide range of producible pipe diameters (Φ219–3620mm), with material utilization improved by 15% compared to spiral welded pipes.
(3) Comparison Notes:
Submerged arc welded steel pipes outperform traditional spiral welded pipes in terms of strength and pressure resistance, making them suitable for more demanding industrial environments.
II. Analysis of Quality Control and Testing Technology for Submerged Arc Welding Steel Pipes
i. Quality Requirements for Submerged Arc Welded Steel Pipes
Submerged arc welded steel pipes are widely used in the petroleum, natural gas, and construction industries, and their quality directly affects engineering safety. Compared with ERW carbon steel pipes, submerged arc welded steel pipes are more suitable for high-pressure, large-diameter environments. Therefore, strict quality control is of utmost importance.
ii. Common Inspection Methods
(1) Ultrasonic Testing (UT) — Precise Detection of Internal Defects
Function: Utilizes high-frequency sound waves to detect internal defects such as cracks and pores in steel pipes.
Advantages: Fast inspection speed, suitable for automated production lines.
Application: Submerged arc welded steel pipes, welded stainless steel pipes, and other high-end pipe materials.
(2) X-ray Testing (RT) — Ensuring Weld Quality
Function: Uses X-ray imaging to inspect welds and assess welding quality.
Advantages: Can detect small defects such as incomplete fusion and slag inclusions.
Industry Applications: Commonly used for high-pressure pipeline inspection in accordance with API 5L standards.
(3) Hydrostatic Testing — Verifying Pressure Resistance
Function: Injecting water into the steel pipe and applying pressure to test its pressure resistance.
Standard Requirements: Typically conducted in accordance with ASTM A252 standards to ensure no leaks.
Importance: Preventing pipeline rupture under high-pressure conditions.
iii. Industry Key Standards
API 5L: Special standard for oil and gas pipelines, applicable to submerged arc welded steel pipes.
GB/T 9711: Chinese national standard covering quality requirements for welded steel pipes.
ASTM A252: Standard for steel pipes used in construction, applicable to structural pipes such as pile foundation pipes.
iv. How to Ensure the Quality of Submerged Arc Welded Steel Pipes?
Select qualified suppliers: Prioritize manufacturers with UT and RT testing capabilities.
Strictly enforce standards: Acceptance testing should be conducted in accordance with API 5L or GB/T 9711.
Conduct regular spot checks: Even with automated production, manual reinspection of critical batches is still required.
v. Submerged Arc Welded Steel Pipes vs. Other Welded Pipes
Compared to ERW carbon steel pipes: Submerged arc welded steel pipes are more suitable for high-pressure and thick-walled applications.
Compared to welded stainless steel pipes: Submerged arc welded steel pipes are more cost-effective but have slightly lower corrosion resistance.
III. Post-treatment and strengthening process
(1) Mechanical flaring
Tapered flare head eliminates 0.6-1.2% residual stress, yield strength uniformity increased by 20%.
Three-roll micro-tension sizing unit compresses OD tolerance to ±0.1%D.
(2) Pressure verification system
Hydrostatic test according to API 5L standard pressure (1.5 times the working pressure), holding time ≥ 10 seconds.
Fiber optic sensor monitors the local deformation amount and the threshold value is set at 0.2%.
(3) End finishing
CNC chamfering machine processing pipe end bevel, angle tolerance ± 0.5 °.
Fluorescent magnetic particle detection of pipe end cracks, detection rate 100%.
IV. Quality control system
| Control Dimension | Technical Specifications | Testing Method |
|---|---|---|
| Material Composition | Carbon Equivalent ≤ 0.42% | Spectrometer |
| Weld Strength | Tensile Strength ≥ 485 MPa | Universal Testing Machine |
| Dimensional Accuracy | Wall Thickness Tolerance ± 0.2 mm | Laser Thickness Gauge |
| Corrosion Resistance | Salt Spray Test ≥ 2500 hours | ISO 9227 Standard |
V. Industrial application scenarios
(1) Energy transportation
X80 steel grade straight seam pipe (Φ1219mm×40mm) is used for the West-East Natural Gas Pipeline Project.
The Gulf of Mexico submarine pipeline uses double anti-corrosion coated spiral pipe.
(2) Construction
Ultra-high-rise building support structure (ASTM A500 Gr.C, square cross-section)
Cross-sea bridge pile foundation pipe (wall thickness 50mm, impact toughness ≥ 100J)
(3) Specialty areas
Nuclear power plant cooling system (316L stainless steel, Φ610mm × 25mm)
Hydrogen energy storage and transportation pipeline (hydrogen embrittlement resistant steel grade, bearing pressure 70MPa)
