I. Overview of Longitudinal Submerged Arc Welded (LSAW) Steel Pipes
Longitudinal submerged arc welded (LSAW) steel pipes are high-strength carbon steel pipes manufactured using a longitudinal welding process from steel plates.
Compared to other welding methods, LSAW steel pipes can produce large-diameter, high-strength, and thick-walled pipes, widely used in oil, natural gas, and chemical liquid transportation pipelines.
Main Features:
- Reliable welding process: Uses longitudinal submerged arc welding, resulting in strong welds and ensuring overall pipe strength.
- High-strength materials: Meets steel grades X42–X70, suitable for high-pressure and critical engineering pipeline requirements.
- Controllable large diameter: Common diameter range DN100–DN1000, wall thickness can be customized according to pressure conditions.
- Strict quality control: The pipe body and welds undergo UT/RT non-destructive testing, hydrostatic testing, and dimensional correction to ensure safety.
- Wide applicability: Can be used in onshore and offshore oil pipelines, long-distance pipelines, industrial pipelines, and municipal water supply and drainage systems.
Application Advantages:
- Provides high pressure bearing capacity and corrosion resistance.
- Suitable for long-distance transportation, improving engineering efficiency.
- Can be combined with anti-corrosion coatings (3PE, epoxy, hot-dip galvanizing) to extend pipe life.
II. Longitudinal Submerged Arc Welded (LSAW) Steel Pipe Steel Grade Comparison Table
| Standard | Steel Grade Classification | Common Grades | PSL Level | Application / Description |
|---|---|---|---|---|
| API 5L | Yes | X42, X46, X52, X56, X60, X65, X70, X80 | PSL1 / PSL2 | Used for transportation of oil, natural gas, and chemical fluids; higher grades are suitable for high-pressure, offshore, or long-distance pipeline systems |
| GB/T 9711.1 (China Standard) | Yes | X42, X46, X52, X56, X60, X65, X70 | PSL1 / PSL2 | Oil and gas transmission pipelines; higher grades are selected for critical projects; PSL2 requires stricter control on weld quality and impact testing |
| ASTM A53 / ASTM A106 | No | Classified by material grade, such as Grade A / B, Gr.B | — | Used for boiler tubes and low-pressure service; classified by material and strength level, not by X42–X70 pipeline grades |
| EN 10208-2 (European Pipeline Standard) | Yes | L245, L290, L320, L360, L415, L450, L485, L555 | — | Oil and gas transmission pipelines; European grades correspond to API X42–X70, expressed by minimum yield strength in MPa |
| EN 10217 / EN 10219 (Industrial Welded Pipes) | No | S235, S275, S355 | — | Industrial piping and structural applications; classified by yield strength, not by pipeline steel grades |
| GB/T 8163 / GB/T 3087 (China Industrial / Structural Pipes) | No | 20#, 35#, Q235B, Q345B | — | Carbon steel seamless or welded pipes; selected by material type and strength level, not designated as X42–X70 pipeline grades |
III. Application Fields of Longitudinal Submerged Arc Welded (LSAW) Steel Pipes
- Oil and Gas Transportation
- Long-distance pipelines: High-pressure natural gas and oil pipelines across countries and provinces.
- Subsea pipelines: Buried in deep sea, resisting high pressure and corrosion from seawater.
- Large Building Structures
- Landmark buildings: Steel structure supports for airports and stadiums (e.g., large-span beams).
- Offshore engineering: Piles for drilling platforms, support structures for offshore wind power.
- Bridges and Pile Foundations
- Bridge pier support: Steel pipe piles as foundations for bridges.
- Bridge structures: Load-bearing components of large bridges such as suspension bridges.
- Urban Lifelines
- Large-diameter water supply: Water diversion projects in urban main roads (e.g., South-to-North Water Transfer Project).
- Heating systems: High-pressure steam main pipelines for central heating.
IV. Selection Guide for Longitudinal Submerged Arc Welded (LSAW) Steel Pipes
1. First, determine: Is LSAW suitable for your project?
LSAW steel pipes are typically used in the following situations:
- Large diameters (generally ≥ DN400 / ≥ 16″)
- Medium-high or high-pressure transportation
- Long-distance pipelines or critical engineering projects
- High requirements for weld quality and dimensional stability
- For small diameters, low pressure, and general structural applications, ERW or seamless pipes are often more economical.
2. Selecting Steel Grade Based on Operating Conditions
A higher steel grade isn’t always better; the most reasonable choice is the one that is “just sufficient.”
- Low-pressure / Ordinary onshore pipelines: X42 / X46
- Medium-pressure transmission, general long-distance pipelines: X52 / X56
- High-pressure long-distance transmission, important main pipelines: X60 / X65
- Offshore pipelines / High-safety-grade projects: X65 / X70 (PSL2)
Selection Principles:
- Higher pressure → Higher steel grade
- More complex operating conditions (low temperature, offshore) → Higher steel grade and PSL level
3. PSL1 or PSL2? Many customers choose incorrectly.
PSL1
- Standard engineering projects
- Relatively basic testing requirements
- Lower cost
PSL2
- High-pressure, long-distance, offshore, or critical pipeline sections
- Mandatory non-destructive testing and impact testing of welds
- Higher safety level
- If the project documents mention “oil and gas pipeline / critical engineering / offshore,” you can generally choose PSL2 directly.
4. How are the outer diameter and wall thickness determined?
Outer Diameter (OD)
- Determined by the design flow rate and transport capacity.
- Common LSAW range: 16″–60″ (406–1524 mm)
Wall Thickness (WT)
- Determined by three factors:
- Design pressure
- Steel grade (higher steel grade allows for relatively thinner walls)
- Corrosion allowance (especially for buried or offshore applications)
Common practice in actual engineering projects:
- An additional 1.5–3.0 mm is added to the calculated wall thickness as a corrosion allowance.
5. The operating environment determines the corrosion protection scheme:
- Ordinary onshore environment: Epoxy paint on the outer wall / Anti-corrosion coating on the inner wall
- Buried pipelines: 3PE / 3PP
- Offshore or highly corrosive environments: Reinforced 3PE / FBE + inner coating
- Temporary or bare pipe projects: Bare pipe
6. Typical Selection Combination Examples
- Onshore natural gas long-distance pipeline: API 5L X60 PSL2 + 3PE
- Offshore oil pipeline: API 5L X65 / X70 PSL2 + enhanced corrosion protection
- General crude oil transmission pipeline: API 5L X52 PSL1 + external corrosion protection
