I. Technical evolution and core classification of ERW steel pipe
The development of ERW steel pipe as the “blood vessels” of modern industry began in the 19th century with the demands of oil extraction and mechanical engineering. As technology evolved, these tubes gradually formed two major branches: seamless pipes and welded pipes.
Among them, welded steel pipe has been widely used in oil, gas, construction and other fields due to its advantages of high production efficiency, low cost and flexible specifications.
The core of the production of welded steel pipe is to process steel plate or steel strip into pipe through forming and welding process.
According to the difference of process, it is mainly divided into spiral welded pipe, straight-seam submerged arc welded pipe (LSAW) and straight-seam high-frequency resistance welded steel pipe (ERW steel pipe).
Among them, ERW steel pipe pipes have become the fastest growing segment in recent years due to their unique high-frequency welding technology.
II. Advantages of high-frequency resistance ERW steel pipe process
High-frequency resistance welded steel pipe adopts the principle of electromagnetic induction, through the skin effect and neighborhood effect of high-frequency current, the edge of the billet is rapidly heated to a molten state, and then seamlessly welded through the extrusion roller. Compared with the traditional arc welding, this technology has three major advantages:
(1) High welding efficiency: high-frequency current can complete the weld fusion within a few seconds, and the production speed can reach more than 80 meters/minute.
(2) Small heat-affected zone: rapid heating to reduce metal oxidation, weld strength up to more than 95% of the base material.
(3) Strong material adaptability: it can process carbon steel, stainless steel and other materials to meet the diversified needs of oil pipelines, building structures and so on.
In the U.S. market, for example, ERW steel pipe has accounted for more than 60% of the welded steel pipe for oil pipelines, and its high-precision wall thickness control (error ± 0.1mm) and automated production line (automation rate of more than 90%) is highly favored.
III. Core production process of ERW steel pipe
The production process of high-frequency resistance welded steel pipe is highly standardized, mainly including the following links:
(1) Raw material pretreatment: hot rolled coil is used to ensure that the surface of the steel strip is free of oxidized layer and burr through the processes of leveling and trimming.
(2) Roll forming: the use of pre-bending machine and forming rollers will be curled into a billet, precision control of ± 0.3mm, to avoid subsequent welding misalignment.
(3) High-frequency welding: High-frequency current is applied through induction coil or contact electrode, and the pressure welding is completed with extrusion rollers. Key parameters include current frequency (200-450kHz), welding temperature (1350-1380℃).
(4) Quality inspection: ultrasonic flaw detection and X-ray detection of weld defects are used to ensure that the fusion rate is ≥90%.
(5) Post-processing and Packaging: Sizing and straightening, surface galvanizing or spraying, and finally verifying the reliability of the finished product through eddy current testing and hydrostatic testing.
IV. ERW steel pipe specification sheet
| Model | Outer Diameter (mm) | Wall Thickness (mm) | Length (m) | Steel Grade | Applicable Standard | Application Field |
|---|---|---|---|---|---|---|
| ERW-1 | 21.3 | 1.5 - 3.0 | 6 - 12 | Q195/Q215 | GB/T 3091 | Construction, Decoration |
| ERW-2 | 33.4 | 2.0 - 4.0 | 6 - 12 | Q235 | GB/T 3091 | Low-pressure Fluid Conveyance |
| ERW-3 | 48.3 | 2.5 - 5.0 | 6 - 12 | Q345 | GB/T 3091 | Mechanical Manufacturing |
| ERW-4 | 60.3 | 3.0 - 6.0 | 6 - 12 | L245 | GB/T 9711 | Oil and Gas Conveyance |
| ERW-5 | 88.9 | 3.5 - 8.0 | 6 - 12 | L290 | GB/T 9711 | Oil and Gas Conveyance |
| ERW-6 | 114.3 | 4.0 - 10.0 | 6 - 12 | L360 | GB/T 9711 | Oil and Gas Conveyance |
| ERW-7 | 168.3 | 5.0 - 12.0 | 6 - 12 | L415 | GB/T 9711 | Oil and Gas Conveyance |
| ERW-8 | 219.1 | 6.0 - 16.0 | 6 - 12 | L450 | GB/T 9711 | Oil and Gas Conveyance |
| ERW-9 | 323.9 | 8.0 - 20.0 | 6 - 12 | L485 | GB/T 9711 | Oil and Gas Conveyance |
| ERW-10 | 406.4 | 10.0 - 25.0 | 6 - 12 | L555 | GB/T 9711 | Oil and Gas Conveyance |
V. Quality control system of ERW LSAW steel pipe
In order to meet the international standards such as API 5L, ASTM A53, etc., high frequency resistance welded steel pipe needs to implement strict quality control:
(1) Raw material inspection: the chemical composition and mechanical properties of steel coils are tested in full batch, for example, the carbon content needs to be controlled at 0.17%-0.23%.
(2) Process monitoring: real-time monitoring of welding current, extrusion pressure and billet temperature to prevent low-temperature unfused or over-burning defects.
(3) Non-destructive testing: Combining ultrasonic (detecting longitudinal cracks) and magnetic particle flaw detection (detecting surface defects), the sampling rate is not less than 10%.
Taking China SY/T6423.2 standard as an example, ERW steel pipe weld needs to pass flattening test (flattening to 1/3 of the original diameter without cracking) and flaring test (flaring rate of more than 15%).
VI. Application Scenario and Market Prospect
By virtue of its performance and economy, ERW steel pipe replaces seamless steel pipe in many fields:
(1) Energy transportation: used in long-distance pipelines for oil and natural gas, and can withstand up to X80 grade steel (yield strength of 555MPa).
(2) Building structure: as a building frame and support parts, accounting for 35% of the global welded steel pipe market.
(3) Machinery manufacturing: for automotive drive shafts, hydraulic cylinder barrels and other precision parts.
According to industry forecasts, in 2025 the global welded steel pipe market size will exceed 200 billion U.S. dollars, of which the compound annual growth rate of ERW category reached 6.2%, becoming the core direction of technological upgrading.
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