Thick Wall Longitudinal Welded Steel Pipe

Zhongtian Thick Wall Longitudinal Welded Steel Pipe is used in key fields such as chemical engineering and marine engineering. We strictly adhere to the EEAT 2.0 standard, leveraging mature product quality, proven project experience, and comprehensive technical services to provide reliable pipe solutions to global customers.

Basic Definitions and Specifications

1. Product Definition

- Thick-walled pipes: Wall thickness ≥ 8 mm

- Extra-thick wall high-value-added pipes: Wall thickness ≥ 25 mm

- Diameter range: Outer diameter 219–2500 mm (mainstream specifications 610–1420 mm)

- Wall thickness range: 6–60 mm

- Standard single length: 12 meters, customizable 18 meters and above ultra-long pipes

2. Commonly Used Materials

- Carbon steel: Q235B, Q355B/C/D/E, suitable for general structures and conventional working conditions

- Pipeline steel: L245–L555, API 5L X42–X80, primarily for high-pressure oil and gas transportation

- Alloy steel: 16Mn, ASTM A106 Gr.B, suitable for high-temperature and high-pressure operating environments

3. Standards

- Domestic standards: GB/T 9711, GB/T 3091, SY/T 5037

- International Standards: API 5L, ASTM A53, EN 10217

Double-sided Submerged Arc Welding (LSAW): The Main Process for Large-Diameter Thick-Walled Pipes

1. Raw Material Selection: Medium-thick steel plates that have passed flaw detection are used, with a plate thickness of 6–60 mm.

2. Steel Plate Edge Milling: Welding bevels are machined on the edges of the plates to ensure weld penetration and welding quality.

3. Edge Pre-bending: Both sides of the steel plate are pre-bent to avoid cracking after forming.

4. Forming Process (Three Mainstream Methods)

- JCOE Forming: J-type, C-type, and O-type step-by-step stamping is completed sequentially, suitable for pipes with diameters of 406–1626 mm and wall thicknesses of 6–40 mm, offering high cost-effectiveness and stable quality.

- UOE Forming: First, U-shaped stamping, then O-shaped seam joining, and finally mechanical diameter expansion. This results in optimal dimensional roundness and precision, and is widely used in key projects such as high-voltage trunk lines, river crossings, and deep-sea operations. Representative specification: X80 steel grade, outer diameter 1422 mm × wall thickness 32.1 mm.

- RBE Roll Forming: Continuous roll forming is suitable for small and medium diameter pipes, accommodating both standard and thick-walled products, offering outstanding production efficiency.

5. Welding Operation: Multi-wire double-sided submerged arc welding (commonly four-wire welding) is used. Welding current is 800–1200A, voltage is 28–36V, and welding speed is 0.8–1.2 m/min. All welds undergo 100% ultrasonic (UT) + radiographic (RT) flaw detection to eliminate defects such as cracks and incomplete fusion.

6. Post-treatment

- Heat Treatment: Normalizing and tempering treatments eliminate residual stress in the pipe and improve overall toughness.

- Finishing: Straightening, cutting, chamfering, and full-dimensional verification.

- Hydrostatic Testing: Standard pressure test (10 MPa, 30 minutes) to ensure no leakage.

- Corrosion Protection: 3PE anti-corrosion, epoxy powder coating, hot-dip galvanizing, etc., suitable for buried and corrosive environments.

High-Frequency Resistance Welding (ERW): Auxiliary Production Process

This process is mainly used for producing small and medium diameter pipes, applicable to diameters of 20–610 mm and wall thicknesses of 1.2–12.7 mm. It offers high production efficiency, controllable costs, continuous and uniform welds, fewer defects, and excellent sealing performance.

Core Performance Advantages

1.High Strength and High Pressure Resistance

Thick Wall Longitudinal Welded Steel Pipe, relying on its thick-walled structure and high-quality raw materials, boasts a yield strength of no less than 235 MPa, with X80 steel grade reaching 555 MPa. It has a pressure range of 10–30 MPa, exhibiting excellent impact and deformation resistance, meeting the requirements of high-pressure and heavy-duty applications.

2.Stable and Reliable Weld Quality

Double-sided submerged arc welding achieves deep penetration, with a weld coefficient reaching 1.0; high-frequency resistance welding provides excellent sealing. Both processes are suitable for transporting flammable and explosive media.

3.High Dimensional Accuracy

Outer diameter deviation ≤ ±1% of pipe diameter, wall thickness deviation ≤ ±12.5% of wall thickness, ellipticity ≤ 0.5% of pipe diameter. Its roundness and straightness performance are superior to spiral welded pipes, resulting in greater adaptability for on-site installation.

4.Significant Overall Cost Advantage

For large-specification products with a diameter ≥325 mm, production efficiency is far higher than seamless steel pipes, reducing overall costs by 30%–50%. Compared to spiral welded pipes, it boasts higher axial strength, shorter weld seams, and lower defect risk, making it the preferred choice for long-distance transmission lines.

5.Wide Range of Operating Conditions

It can withstand environments ranging from -40℃ to 450℃, while possessing excellent fatigue and corrosion resistance, making it suitable for various harsh environments such as deep sea, permafrost, and chemical corrosion.

Main Application Areas

1. Oil and Gas Transportation: High-pressure trunk pipelines for oil and natural gas, urban high-pressure gas pipeline networks (mainstream use of X70 and X80 steel grades)

2. Power Energy: Power plant circulating water pipelines, desulfurization pipelines, pulverized coal conveying pipelines, thermal power boiler headers, hydropower station pressure steel pipes

3. Chemical Refining: High-temperature and high-pressure process pipelines, flammable and explosive medium conveying pipelines, sewage treatment pipelines

4. Building Steel Structures: Bridge load-bearing pile foundation pipes, large building columns, pile foundation steel casings, shield tunneling casings

5. Marine Engineering: Offshore platform jackets, submarine pipelines, port and wharf pile foundations

6. Municipal Engineering: High-pressure heating pipeline networks, large-scale water supply and drainage and water diversion projects, integrated pipe gallery structure pipelines

Real Case: Yangtze River Shield Tunneling Project

Zhongtian supplied X80 grade, Φ1422×32.1 mm UOE process double-sided submerged arc welded Thick Wall Longitudinal Welded Steel Pipe for the West-East Gas Pipeline key project—the Yangtze River Shield Tunneling Project. Located in a complex geological area, this project required pipes with high pressure resistance and a single-piece length of up to 18 meters (an ultra-long, extra-thick wall specification). All products underwent a full set of ultrasonic, radiographic, and hydrostatic tests, with a weld flaw detection pass rate of 99.8%. This project fully verified the stability and reliability of Zhongtian Pipes in long-distance, high-pressure, and cross-river major projects.

Quality Control and Testing Standards

1. Non-destructive Testing: 100% of welds underwent ultrasonic + radiographic testing, capable of detecting defects with an equivalent diameter of 2 mm, strictly controlling cracks, lack of fusion, and other issues.

2. Mechanical Property Testing: Tensile, low-temperature impact (-20℃ impact energy ≥34 Joules), bending, and flattening tests were conducted batch by batch.

3. Dimensional Inspection: Outer diameter, wall thickness, ovality, straightness, and bevel dimensions were inspected for each pipe.

4. Hydrostatic Testing: Pressure testing was conducted strictly according to industry standards; pipes were considered qualified if there was no leakage or plastic deformation.

FAQ

Q1: How to distinguish between Thick Wall Longitudinal Welded Steel Pipe and Thin-Wall Straight Seam Welded Pipe?

A: The industry uses wall thickness as the core classification criterion: Pipes with a wall thickness ≥ 8 mm are thick-walled welded pipes, with those ≥ 25 mm being extra-thick-walled welded pipes, mostly used in high-pressure and heavy-load conditions; pipes with a wall thickness < 8 mm are thin-walled welded pipes, generally used for low-pressure fluid transportation and ordinary structural construction, with relatively lower strength and pressure resistance.

Q2: Why is straight seam submerged arc welded pipe preferred over spiral welded pipe for high-voltage trunk line projects?

A: Straight seam submerged arc welded pipe has only one short weld seam, resulting in higher axial strength and more stable roundness and overall quality; while spiral welded pipe has a longer weld seam, leading to a higher probability of defects, and is only suitable for medium- and low-pressure conditions and ordinary structural projects. Therefore, straight seam submerged arc welded pipe is preferred for high-voltage long-distance trunk lines.

Q3: What authoritative qualifications does Zhongtian Thick Wall Longitudinal Welded Steel Pipe possess?

A: Our products strictly adhere to mainstream domestic and international standards such as API 5L, GB/T 9711, and ASTM A53, and also hold relevant certifications such as CE and ISO. As a legitimate supplier and manufacturer in China, our production facilities fully implement the EEAT 2.0 quality management system, and our products have complete qualifications, meeting the access requirements of various international engineering projects.