Longitudinal Welded (LSAW) Steel Pipes

Manufacturing Methods

1. Roll-Based LSAW (Longitudinal Submerged Arc Welded):

   • Process: Steel coils are unrolled and formed into a cylindrical shape by folding across the width. The longitudinal seam is welded using submerged arc welding, creating a continuous pipe until the coil is fully utilized.

   • Advantages: Efficient for producing pipes with standard diameters and thicknesses, ideal for high-volume production.

   • Applications: Pipelines for oil, gas, and water, as well as structural components.

2. Plate-Based DSAW (Double-Sided Submerged Arc Welded):

   • Process: Individual steel plates are rolled into a cylindrical shape tailored to project specifications. The longitudinal seam is welded on both interior and exterior surfaces using submerged arc welding, often with V-shaped grooves for precision. Multiple pipe sections are joined with circular seams for longer lengths.

   • Advantages: Offers flexibility for large diameters and thick-walled pipes, suitable for custom dimensions.

   • Applications: Offshore pipelines, piling, and heavy-duty structural applications requiring specific sizes.

Metal Grades Comparison

The following grades are commonly used for LSAW steel pipes. This standardized comparison enables buyers to select the appropriate grade based on strength, toughness, and environmental requirements.

API 5L

• Type: Carbon and alloy steel.

• Standard: API 5L (ANSI/API specification).

• Yield Strength: Varies by grade; A25 (172 MPa), A (207 MPa), B (241 MPa), X42 (290 MPa), X46 (317 MPa), X52 (359 MPa), X56 (386 MPa), X60 (414 MPa), X65 (448 MPa), X70 (483 MPa), X80 (552 MPa).

• Equivalents: Comparable to ASTM A106, ASTM A53 for certain grades.

• Wall Thickness: 6.2 mm (5.75 mm), 8.2 mm (7.75 mm), 10.2 mm (9.75 mm), 12.2 mm (11.75 mm), 25 mm, 36 mm, 40 mm.

• Applications: Oil and gas pipelines, high-pressure fluid transport, and structural applications requiring superior strength.

• Key Features: Available in PSL1 (standard quality) and PSL2 (higher quality with stricter chemical, mechanical, and testing requirements, including Charpy impact testing). Provides excellent toughness and corrosion resistance for extreme conditions.

• Comparison: Offers the highest strength range (up to 552 MPa), making it superior for critical applications like high-pressure pipelines compared to Q235B, Q345B, Q355D, and S355J2H.

Q235B

• Type: Carbon structural steel.

• Standard: GB/T9711-2020.

• Yield Strength: Approximately 235 MPa (may vary with thickness).

• Equivalents: European S235JR (DIN EN), American ASTM A36.

• Wall Thickness: 5.0 mm to 40 mm.

• Applications: General structural applications, such as buildings, bridges, and non-critical infrastructure.

• Key Features: Cost-effective with good weldability and moderate strength, suitable for low-stress environments.

• Comparison: Lower strength than API 5L, Q345B, Q355D, and S355J2H, making it less suitable for high-pressure or heavy-load applications but ideal for budget-conscious projects.

Q345B

• Type: Low-alloy steel.

• Standard: GB/T700, GB/T1591.

• Yield Strength: Approximately 345 MPa.

• Equivalents: European S355JR or S355J2 (EN 10025-2), American ASTM A572 Grade 50.

• Wall Thickness: 5.0 mm to 40 mm.

• Applications: Bridges, ships, vehicles, and construction projects requiring moderate to high strength.

• Key Features: Offers a balance of strength, weldability, and machinability, suitable for structural applications with moderate stress.

• Comparison: Stronger than Q235B but less robust than API 5L high grades (e.g., X70, X80) and slightly less tough than Q355D or S355J2H. Versatile for general construction.

Q355D

• Type: Low-alloy high-strength steel.

• Standard: GB/T1591-2018.

• Yield Strength: Approximately 355 MPa.

• Equivalents: European S355J2 (EN 10025-2).

• Wall Thickness: 5.0 mm to 40 mm.

• Applications: Heavy machinery, bridges, and construction requiring high strength and toughness.

• Key Features: Improved toughness and weldability compared to Q345B, ideal for demanding structural applications.

• Comparison: Comparable to S355J2H in strength and toughness, stronger than Q235B and Q345B, but less suited for extreme pipeline applications compared to API 5L high grades.

S355J2H

• Type: Non-alloy structural steel.

• Standard: EN 10210-1, EN 10219-1.

• Yield Strength: Minimum 355 MPa.

• Equivalents: Comparable to Q355D, ASTM A500 Grade C for hollow sections.

• Wall Thickness: 5.0 mm to 40 mm.

• Applications: Construction, structural tubing, and pipelines, particularly in low-temperature environments.

• Key Features: High strength with excellent impact resistance at low temperatures, designed for hollow sections and structural applications.

• Comparison: Similar to Q355D in strength, stronger than Q235B and Q345B, but less suitable for high-pressure pipelines compared to API 5L high grades. Excels in low-temperature applications.

Types of Steel for LSAW Pipes

The following steel types are used in LSAW pipe production, each tailored for specific conditions and applications, with comparisons to the highlighted grades (API 5L, Q235B, Q345B, Q355D, S355J2H).

• Carbon & Alloy Steel

  • SA53 / A53 Grade B: Welded steel pipes for general use, with yield strength (~241 MPa) similar to Q235B but lower than Q345B, Q355D, S355J2H, and API 5L high grades. Less robust for high-pressure applications compared to API 5L.

  • API 5L Grades: B, X42, X46, X52, X56, X60, X65, X70, X80 (PSL1 and PSL2). Offers the highest strength range among the grades, making it superior for oil and gas pipelines compared to Q235B, Q345B, Q355D, and S355J2H.

• Low-Temperature Carbon Steel

  • A333 / A333M: Grades 1, 3, 4, 6, 7, 8, 9, 10, 11, designed for low-temperature applications. Provides better low-temperature performance than Q235B, Q345B, and API 5L standard grades, comparable to S355J2H for cold environments.

  • A334 / A334M: Similar to A333, tailored for low-temperature environments, offering superior impact resistance at low temperatures compared to Q235B and Q345B, and similar to S355J2H.

• Stainless Steel

  • ASTM A312 & A409: Grades 304, 304H, 304L, 309, 310, 316, 316L, 317L, 321, 347, designed for corrosion resistance. Unlike API 5L, Q235B, Q345B, Q355D, and S355J2H, these prioritize corrosion resistance over high strength, making them suitable for chemical or marine environments.

  • ASTM B673: Includes UNS N08925, N08354, N08926 for specialized applications, offering superior corrosion resistance compared to all highlighted grades but lower strength than API 5L high grades or Q355D/S355J2H.

• Duplex / Super Duplex Steel

  • ASTM A790: Grades UNS S31803, S32205, S31500, S32550, S31200, S31260, S32304, S39274, S32750, S32760, S32900, S32950, S39277, S32520, S32906, S32003, offering high strength (comparable to or higher than Q355D/S355J2H) and excellent corrosion resistance, surpassing Q235B, Q345B, and most API 5L grades in corrosive environments but not as cost-effective for general use.

• Nickel Alloy

  • ASTM B514, B517, B619, B705, B725, B775, B464: Includes UNS N06600, N06603, N06025, N06045, N06625, N06219, N08825, N02200, N02201, N04400, N08020, designed for high-temperature and corrosive environments. Superior corrosion and heat resistance compared to API 5L, Q235B, Q345B, Q355D, and S355J2H, but typically lower strength and higher cost, limiting use to specialized applications.

Pipe Standards

• ASME B36.10: Standardizes dimensions of welded and seamless wrought steel pipes for high/low temperatures and pressures.

  • Pipes NPS 12 (DN 300) and smaller: Outside diameter (O.D.) larger than nominal size.

  • Pipes NPS 14 (DN 350) and larger: O.D. matches nominal size.

• ASME B36.19: Standardizes dimensions of welded and seamless wrought stainless steel pipes, with specific schedules (e.g., 10S, 40S, 80S) differing from B36.10.

• ASME B16.25: Covers preparation of butt weld connections between pipes.

• ASME B16.49: Specifies marking details for pipes.

• API 5L: Covers seamless and welded steel pipes for oil and gas pipelines.

  • Levels: PSL1 (standard quality) and PSL2 (higher quality with stricter chemical, mechanical, and testing requirements, including Charpy impact testing).

  • Grades: A25, A, B, X42 to X80 (yield strength in thousands of psi).

LSAW Pipe Specifications

• Materials: Carbon steel, alloy steel, mild steel (e.g., SA53/A53 Grade B, API 5L up to X80 PSL2).

• Outer Diameter: 406 mm (16″) to 1829 mm (72″).

• Wall Thickness: 5.0 mm to 40 mm.

• Length: Single random (5–7 m), double random (11–13 m), or custom lengths.

• End Types:

  • Plain Ends (PE): Used for smaller diameters with slip-on flanges or socket weld fittings.

  • Threaded Ends (TE): Used for small-diameter systems with threaded flanges/fittings.

  • Beveled Ends (BE): Applied to all diameters for butt welding, typically at 30° (+5°/-0°) with a root face of 1.6 mm (±0.8 mm).

• Finish: Mill finish (no coating).

• Testing: Chemical analysis, mechanical tests (tensile, yield, elongation), technical tests (flattening, bending, hardness, Charpy impact, etc.).

• Test Certificates: As per EN 10204 3.1B.

Standard Specifications

• ASME B36.10, B36.19: Standardization of dimensions for welded and seamless steel and stainless steel pipes.

• ASME B16.25: Butt weld connection preparation.

• ASME B16.49: Marking details.

• API 5L: For oil and gas pipelines, including sour service (Annex H) and offshore applications (Annex J).

• ASTM A53: For black, hot-dipped, zinc-coated pipes.

• EN 10219: For cold-formed welded structural hollow sections.

Steel Grades for LSAW Pipes

• EN 10219: S235, S275, S355J2H, S420, S460.

• ASTM A53: Gr. A, Gr. B, Gr. C, Gr. D.

• API 5L: A, B, X42, X46, X52, X56, X60, X65, X70, X80.

Measurements of LSAW Pipes for Piling

• HSN Code: 7305.1100.00

• Examples:

  • Steel Grade: API 5L X65/S460, LSAW Weld:

    • 1420 mm OD x 25.8 mm Th x 12 m

    • 1220 mm OD x 25.8 mm Th x 12 m

    • 1016 mm OD x 20 mm Th x 12 m

  • Steel Grade: API 5L X52/EN 10219/S355J2H:

    • 610 mm OD x 16 mm Th x 12 m (2.763 MT/piece)

  • Steel Grade: API 5L X65/S460:

    • 48″ OD x 25.8 mm Th x 12 m (9111.85 kg)

    • 36″ OD x 25 mm Th x 12 m (6580.18 kg)

  • Steel Grade: API 5L X52/S420, LSAW Weld:

    • 1800 mm OD x 40 mm Th x 31.5 m

    • 1500 mm OD x 30 mm Th x 31.5 m

    • 1066 mm OD x 24.6 mm Th x 34 m

    • 914 mm OD x 20 mm Th x 34 m

Applications

LSAW pipes are highly versatile and used in various industries:

• Liquid Transportation: Water supply and drainage systems.

• Gas Transportation: Natural gas, steam, and liquefied petroleum gas.

• Structural Use: Piling pipes, bridges, docks, roads, and building structures.

• Offshore and Marine: Pipelines connecting subsea wells to onshore processing equipment, mooring posts, fenders, and jetties.

• Petrochemical and Industrial: High-pressure pipelines for hydrocarbons and chemical transport.

Conclusion

Longitudinal Welded (LSAW) Steel Pipes provide a robust, flexible, and cost-effective solution for large diameter and thick-walled piping requirements. The standardized comparison of steel grades—API 5L, Q235B, Q345B, Q355D, and S355J2H—alongside other steel types (carbon, low-temperature, stainless, duplex, and nickel alloy) empowers buyers to choose the optimal grade based on strength, corrosion resistance, and environmental suitability. Compliance with international standards such as API 5L, ASME, ASTM, and EN ensures exceptional performance in critical applications, including oil and gas pipelines, piling, and marine construction.