I. Introduction to double-sided submerged arc welded pipes
Double side submerged arc welded pipe belongs to cost-effective industrial pipes, which are manufactured by using steel coil as base material, through spiral forming process and double side submerged arc welding technology.
i. Spiral Welded Steel Pipe Production Process
（1）Raw Material Processing
The production of spiral welded steel pipes begins with raw material processing.
Narrow steel strips are continuously fed into the forming unit.
This ensures that the steel strips are flat and clean, suitable for subsequent processing.
（2）Spiral Forming
During the forming process, the steel strips pass through a three-dimensional roll forming system.
The equipment bends them into a stable and precise spiral angle.
This step ensures that the pipe’s diameter and roundness meet the required specifications.
（3）Welding System
During the welding stage, both internal and external submerged arc welding are performed simultaneously.
This process achieves full-penetration welds across the entire cross-section.
This method is typically used in the production of double-sided submerged arc welded pipes.
It effectively enhances weld strength and product reliability.
（4）Product Types
The spiral welded steel pipe process is commonly used for manufacturing carbon steel welded pipes.
It is also widely applied in the production of various large-diameter welded steel pipes.
These products play a crucial role in oil and natural gas transportation and structural engineering.
（5）Quality Control
After production, rigorous quality inspections are conducted.
Online ultrasonic testing is used to promptly identify weld defects.
Additionally, X-ray imaging is employed to comprehensively inspect the welds and base material.
This ensures that every steel pipe shipped from the factory meets international standards.
ii. Advantages of Double-Sided Submerged Arc Welded Pipes
(1) High Welding Quality
Using a double-sided submerged arc welding process on both the inner and outer surfaces, the weld seam achieves full-penetration fusion across the entire cross-section, ensuring stable and reliable welding quality.
(2) High Strength and Pressure Resistance
The weld strength exceeds that of the base material, providing robust pressure resistance for the entire pipe body, making it suitable for high-pressure transmission pipelines.
(3) Wide Range of Diameters
Capable of producing large-diameter thick-walled steel pipes with a wide range of diameters to meet diverse engineering requirements.
(4) High dimensional accuracy
The combination of spiral forming and double-sided welding ensures good roundness of the steel pipe and minimal dimensional tolerances.
(5) Strict inspection and high safety
Ultrasonic testing and X-ray testing are conducted during production to ensure defect-free products and enhance safety during use.
(6) Wide range of applications
Widely used in oil and gas transportation, structural pile foundations, offshore platform structures, and large-scale steel structure engineering projects.
iii. Application Scenarios:
| Application Field | Pressure Rating (MPa) | International Standard Reference |
|---|---|---|
| Municipal Water Supply System | 0.6-2.5 | AWWA C200/EN 10224 |
| Regional Heat Supply Network | 1.6-4.0 | ASTM A139/A53 |
| Marine Piling Engineering | - | API 5L/ISO 3183 |
| Oil and Gas Transmission Pipelines | 5.0-12.0 | API 5L X60-X80 |
II. Double-sided submerged arc welded pipe technology features
The following are the core technical advantages and process characteristics of double-sided submerged arc welded pipe, combined with international engineering standards and quality control system, applicable to oil and gas transportation, municipal infrastructure and industrial pipeline system selection reference:
i. Molding control and size adaptability
Stress optimization: Adopting spiral continuous molding technology, the steel plate realizes uniform plastic deformation in three-dimensional roll pressure, the residual stress is reduced by 40%-60%, and the surface has no mechanical scratches.
Specification coverage: Supporting diameter range DN300-DN3000, wall thickness 6-25mm, especially good at producing X80/X100 high steel grade thick-walled pipes (wall thickness ≥15mm) to meet the customized demand for large-diameter and high-pressure pipelines in API 5L standard.
Material Utilization: Narrow width steel strip can produce different pipe diameters by adjusting the spiral angle, reducing raw material loss rate by 18%-25%.
ii. Welding process and quality stability
Two-step welding method:
Pre-welding positioning: Initial fixation of weld is realized through high frequency pre-welding (100-150kHz), and the amount of misalignment is controlled at ≤1.5% wall thickness.
Double-sided submerged arc precision welding: internal and external weld channels are synchronized with Lincoln automatic welding machine, the melting depth reaches more than 90% of the plate thickness, and the impact toughness of the weld is ≥80J (-20℃ low-temperature environment).
Defect control: integrated ultrasonic and X-ray online inspection, weld porosity ≤ 0.5%, unfused defect detection rate of 100%, in line with ASME B31.8 oil and gas pipeline specifications.
iii. Mechanical Expansion and Stress Management
Dimensional accuracy: overall expansion rate of 3%-5%, ellipticity ≤ 0.8% (better than 1.5% required by API 5L), to ensure the matching accuracy of on-site ring welding.
Stress homogenization: The circumferential residual stress of the pipe is reduced to ≤100MPa after the expansion, which reduces the risk of Stress Corrosion Cracking (SCC), and is suitable for environments containing H₂S acidic media.
Construction compatibility: The geometric consistency of the expanded diameter increases the efficiency of on-site welding bevel preparation by 30% and reduces installation costs.
iv. Engineering Applications and Standards Compatibility
Double-sided submerged arc welded pipe has passed the following international certifications:
Oil and gas transportation: API 5L X70-X120 (PSL2), ISO 3183 Class III pipe
Municipal engineering: AWWA C200 (water transmission), EN 10224 (low pressure fluids)
Special scenarios: NACE MR0175 (resistance to hydrogen sulfide corrosion), ASTM A139 (heat pipe network)
III. Double-sided submerged arc welding pipe production process
| Process Step | Description | Key Parameters | Precautions |
|---|---|---|---|
| Raw Material Preparation | Select suitable steel plates or steel strips as raw materials | Steel material (e.g., Q235, Q345) Plate thickness and width |
Ensure the quality of raw materials meets the standard, free of defects |
| Plate Pre-treatment | Remove rust, oil, and other impurities from the surface of the steel | Cleaning method (e.g., sandblasting, chemical cleaning) Cleaning quality standard |
The surface should be free of residual impurities, clean and dry after pre-treatment |
| Plate Forming | Roll the steel plate or strip into a tubular shape | Forming angle Forming speed |
Ensure the formed pipe blank has no wrinkles or cracks |
| Welding | Welding is performed using double-sided submerged arc welding technology | Welding current Welding voltage Welding speed Welding protective gas |
Strictly control parameters during welding to ensure weld quality |
| Weld Inspection | Inspect the quality of the weld to ensure there are no defects | Non-destructive testing methods (e.g., X-ray testing, ultrasonic testing) Inspection standard |
Defects should be repaired promptly to ensure the weld quality meets the standard |
| Heat Treatment | Heat treatment is performed on the welded steel pipe to eliminate welding stress | Heat treatment temperature Insulation time Cooling method |
The performance of the steel pipe after heat treatment should meet the requirements |
| Finishing | Adjust the dimensions and perform surface treatment on the steel pipe | Dimensional accuracy requirements Surface treatment method (e.g., painting, galvanizing) |
Ensure the dimensions of the steel pipe meet the standard and the surface quality is good |
| Inspection | Comprehensive inspection of the finished steel pipe | Dimensional inspection Appearance inspection Performance inspection (e.g., tensile test, bending test) |
The inspection results should meet the relevant standards, and non-conforming products should be reworked |
| Packaging | Package the qualified steel pipes for transportation and storage | Packaging method Packaging material |
The packaging should be sturdy to prevent damage during transportation |
| Storage and Transportation | Store the packaged steel pipes in a suitable environment and arrange for transportation | Storage environment (e.g., dry, ventilated) Transportation method |
Prevent the steel pipes from being damaged during storage and transportation |
IV. Comparison of double-sided submerged arc welded pipe and straight seam welded pipe
| Characteristics | Double-sided Submerged Arc Welded Pipe | Straight Seam Welded Pipe |
|---|---|---|
| Production Process | Uses double-sided submerged arc welding technology, with simultaneous welding of internal and external seams, ensuring high welding quality | Uses single-sided submerged arc welding or high-frequency welding, typically with only one seam |
| Welding Quality | High-quality welds, uniform and strong, with low defect rates | Relatively lower welding quality, with potential for welding defects |
| Wall Thickness Range | Typically thicker, suitable for high-pressure, large-diameter pipelines | Relatively thinner, suitable for low-pressure, medium and small diameter pipelines |
| Outer Diameter Range | Large diameter (usually ≥219mm) | Medium and small diameter (usually ≤630mm) |
| Strength | High strength, suitable for high-pressure and heavy load applications | Relatively lower strength, suitable for general purposes |
| Corrosion Resistance | Can be improved by surface treatment (e.g., anti-corrosion coating) | Can be improved by surface treatment (e.g., anti-corrosion coating) |
| Production Efficiency | High production efficiency, suitable for mass production | Relatively lower production efficiency, suitable for medium and small batch production |
| Cost | Higher cost, especially for large-diameter and thick-walled pipes | Relatively lower cost, especially for medium and small diameter and thin-walled pipes |
| Application Fields | Widely used in oil and gas transmission, chemical industry, construction structures, etc. | Widely used in water, gas, air transmission, building decoration, etc. |
| Standards | GB/T 9711, API 5L, SY/T 5037, etc. | GB/T 3091, GB/T 13296, JIS G 3444, etc. |
| Weld Inspection | Typically uses non-destructive testing methods such as X-ray testing and ultrasonic testing | Typically uses non-destructive testing methods such as X-ray testing and ultrasonic testing |
| Surface Treatment | Can be painted, galvanized, coated with anti-corrosion coating, etc. | Can be painted, galvanized, coated with anti-corrosion coating, etc. |
| Dimensional Accuracy | High dimensional accuracy, suitable for applications requiring high precision | Relatively lower dimensional accuracy, suitable for general precision requirements |
| Fatigue Resistance | Good fatigue resistance, suitable for dynamic load environments | Relatively lower fatigue resistance, suitable for static load environments |
