API 5L Gr B Longitudinal Submerged Arc Welding (LSAW) Pipe
Basic Overview
A standard specification for longitudinally submerged-arc welded steel line pipe under the API 5L specification. Grade B is the most common baseline grade for oil and gas transmission, offering a reliable balance of strength, weldability, and cost-effectiveness for medium-pressure pipeline applications .
Name Explanation
| Part | Meaning |
|---|---|
| API | American Petroleum Institute |
| 5L | Specification for line pipe |
| Gr B | Grade B – the standard carbon steel grade with minimum yield strength 35,000 psi (241 MPa) |
| Longitudinal Submerged Arc Welding (LSAW) | Manufacturing process – steel plates are formed and welded along a single straight longitudinal seam using submerged arc welding with filler metal added |
Key Features of API 5L Gr B LSAW Pipe
| Feature | Description |
|---|---|
| Material Type | Carbon steel (non-alloyed) with controlled chemistry for weldability |
| Manufacturing | LSAW (Longitudinal Submerged Arc Welding) – plates formed by UOE, JCOE, or RBE processes, then welded with submerged arc |
| Product Spec Levels | PSL1 or PSL2 (PSL2 offers tighter chemistry control and mandatory impact testing) |
| Yield Strength | 241 MPa (35,000 psi) minimum |
| Tensile Strength | 414 MPa (60,000 psi) minimum |
| Elongation | 21-27% minimum |
| Key Advantage | Most widely available grade – excellent balance of properties for general service |
| Typical Diameters | 323.9 mm to 1820 mm (12" to 72") |
| Typical Wall Thickness | 5.0 mm to 50 mm (up to 75 mm available from some manufacturers) |
| Length | 6 m to 12 m standard; up to 18 m available |
Chemical Composition (API 5L Gr B)
| Element | PSL1 (max %) | PSL2 (max %) | Notes |
|---|---|---|---|
| Carbon (C) | 0.28 | 0.24 | PSL2 has tighter control for weldability |
| Manganese (Mn) | 1.20 | 1.20 | |
| Phosphorus (P) | 0.030 | 0.025 | Stricter in PSL2 |
| Sulfur (S) | 0.030 | 0.015 | Significantly tighter in PSL2 |
*Sources: *
Mechanical Properties Comparison
| Grade / PSL Level | Yield Strength (MPa) min | Tensile Strength (MPa) min | Elongation % |
|---|---|---|---|
| API 5L Gr B PSL1 | 241 | 414 | 21-27 |
| API 5L Gr B PSL2 | 245 | 415 | 22 min |
| Seamless Pipe Equivalent | 245 | 415 | - |
PSL1 vs. PSL2 for Grade B LSAW Pipe
| Aspect | PSL1 | PSL2 |
|---|---|---|
| Chemistry | Standard limits (C ≤ 0.28%, S ≤ 0.030%) | Tighter controls (C ≤ 0.24%, S ≤ 0.015%) |
| Strength | Min only specified | Min and Max specified (prevents over-strength) |
| Impact Testing | Not required | Mandatory at specified temperature |
| Carbon Equivalent | Not required | Calculated and controlled |
| NDT Requirements | Standard | More stringent |
| Typical Use | General service, low-pressure lines | Critical service, sour service, low temperature |
| CVN Energy at 0°C | - | 27 J minimum average (PSL2 requirement) |
LSAW Manufacturing Process
Forming Methods
| Method | Description | Typical Diameters |
|---|---|---|
| UOE / UOE | Plate pressed into U-shape, then O-shape, expanded after welding | 508-1118 mm (20"-44") |
| JCOE / JCOE | Progressive J-C-O forming steps, expanded after welding | 406-1626 mm (16"-64") |
| RBE / RBE | Roll bending process | Various |
Process Steps
Plate Preparation: Hot-rolled steel plates undergo incoming inspection, edge milling for precise bevels, and online ultrasonic testing to detect laminations
Forming: Progressive hydraulic pressing (JCO or UOE) creates uniform roundness
Pre-Welding: Tack welding secures seam temporarily
Submerged Arc Welding: Multi-wire SAW applies internal and external seams for full penetration under flux
Mechanical Expanding: Pipe expanded to precise dimensions (for UOE/JCOE processes)
NDT & Testing: Ultrasonic testing, radiographic examination, hydrostatic testing
Finishing: End beveling (ANSI B16.25), coating application
Size Availability
| Parameter | Range | Notes |
|---|---|---|
| Outside Diameter | 323.9 mm to 1820 mm (12" to 72") | Up to 1626 mm (64") common; larger available on request |
| Wall Thickness | 5.0 mm to 50 mm | Up to 75 mm available from some manufacturers |
| Length | 6 m to 12 m standard | Up to 18 m available |
| End Finish | Plain ends, beveled ends per ANSI B16.25 | Beveled for welding standard |
Testing & Inspection Requirements
API 5L Gr B LSAW pipes typically undergo :
| Test Type | Purpose |
|---|---|
| Chemical Analysis | Verify composition meets API 5L limits |
| Tensile Test | Confirm yield and tensile strength |
| Flattening Test | Check ductility |
| Bend Test | Verify weld integrity |
| Impact Test (Charpy V-notch) | Required for PSL2 at specified temperature |
| Hydrostatic Test | Proof of leak-tightness |
| Radiographic Examination (X-ray) | Detect weld defects |
| Ultrasonic Examination | Detect internal defects |
| Exterior Size Inspection | Verify dimensions |
Mill Test Certificate: EN 10204 / 3.1B typically provided
Coating & Protection Options
API 5L Gr B LSAW pipe is commonly supplied with :
| Coating Type | Application |
|---|---|
| Black (bare) | Standard mill finish, indoor use |
| Varnish / Anti-rust oil | Temporary protection during transit |
| Black painting | Basic corrosion protection |
| 3LPE (3-layer polyethylene) | Buried pipelines, harsh environments |
| FBE (Fusion Bonded Epoxy) | Corrosion protection |
| Coal Tar Epoxy | Heavy-duty protection |
| Bitumen coating | Buried service |
| Concrete Weight Coating (CWC) | Offshore pipelines (negative buoyancy) |
Comparison Table: LSAW vs. Other Manufacturing Methods
| Aspect | LSAW (Longitudinal) | SSAW (Spiral) | ERW |
|---|---|---|---|
| Weld Seam | Single straight seam | Continuous spiral seam | Single straight seam (no filler metal) |
| Diameter Range | 16" to 72"+ | Very large diameters | Typically ≤ 24" |
| Wall Thickness | Up to 75 mm | Medium | Limited |
| Typical Application | High-pressure transmission, offshore, critical service | Low-medium pressure, cost-driven | Small to medium diameter lines |
| Inspection | Easier to examine straight seam | More complex NDT | Standard |
| Design Preference | Preferred for high-consequence areas | Allowed in less critical sections | Smaller distribution lines |
*Sources: *
Common Applications
API 5L Gr B LSAW pipe is widely used in :
| Industry | Applications |
|---|---|
| Oil & Gas | Medium-pressure transmission pipelines, gathering lines, flow lines |
| Water Transmission | Large-diameter water mains, irrigation systems, desalination conduits |
| Infrastructure | Structural piling, bridge foundations, tunnel linings |
| Petrochemical | Low to medium pressure process lines, industrial conveyance |
| Mining | Slurry pipelines, tailings transport |
| Power Generation | Cooling water lines, steam services (within temperature limits) |
Advantages of LSAW Manufacturing for Grade B
| Advantage | Description |
|---|---|
| Large Diameter Capability | Can produce pipes from 16" to 72"+ diameter – much larger than seamless or ERW capabilities |
| Thick Walls | Suitable for applications requiring substantial wall thickness (up to 75 mm) |
| High Structural Integrity | Single longitudinal seam provides superior strength and pressure resistance, with full-penetration welding ensuring minimal defect risks |
| Excellent Dimensional Accuracy | Tight tolerances on OD, ovality, and straightness reduce installation issues |
| Enhanced Toughness | PSL2 options with Charpy V-notch testing for low-temperature service |
| Quality Assurance | Automated welding with recorded parameters; full NDT traceability |
| Cost-Effective for Long Runs | Fewer seams than SSAW for long pipelines; efficient production |
PSL2 Supplementary Requirements
For critical applications, PSL2 Grade B LSAW pipe offers :
| Requirement | Specification |
|---|---|
| CVN Impact Testing | 27 J minimum average at specified temperature (typically 0°C) |
| Maximum Yield Strength | Prevents over-strength materials (ensures consistent field behavior) |
| HIC/SSC Resistance | Available for sour service applications (NACE MR0175/ISO 15156) |
| DWTT (Drop Weight Tear Test) | For fracture toughness verification when specified |
| Carbon Equivalent Control | Ensures good field weldability |
International Equivalents
| Standard | Equivalent Grade | Notes |
|---|---|---|
| ISO 3183 | L245 | Harmonized with API 5L |
| GB/T 9711 | L245 | Chinese equivalent |
| ASTM A53 | Gr.B | Similar strength level |
| EN 10217 | P235GH / P265 | Approximate equivalents |
Important Selection Notes
1. Grade B vs. Higher Grades
Grade B is suitable for medium-pressure applications up to approximately 100 bar depending on wall thickness
For higher pressures, consider X42 (42 ksi yield) or higher grades (X52, X60, X65, X70)
Grade B offers the best balance of cost and availability for general service
2. PSL1 vs. PSL2 Selection
PSL1: Sufficient for most general service, non-critical applications
PSL2: Recommended for:
Low-temperature service (requires impact testing)
Sour service (H₂S environments)
Critical high-pressure lines
Projects with specific toughness requirements
3. Manufacturing Process Selection
LSAW is preferred for:
Large diameters (≥16")
High-pressure transmission lines
Offshore and critical service
When straight seam is specified for easier NDT
4. Testing & Certification
Standard certification: EN 10204 3.1 (manufacturer's independent testing)
For critical projects: EN 10204 3.2 (third-party witnessed testing)
Ensure Mill Test Certificate includes: chemical composition, mechanical properties, NDT results, hydrostatic test results
5. Application Fit
Water supply lines: Grade B PSL1 is common and economical
Natural gas gathering: Grade B PSL2 with impact testing for safety
Industrial process piping: Verify temperature limits (typically -20°C to 120°C)
Final Takeaway: API 5L Gr B LSAW Pipe is the standard, most widely used large-diameter welded line pipe for oil, gas, water, and industrial applications requiring a reliable balance of strength, weldability, and cost-effectiveness. With minimum yield strength of 35,000 psi (241 MPa) , it serves as the baseline grade for medium-pressure transmission systems where higher-strength grades (X42-X70) are not required. The LSAW manufacturing process enables production of pipes from 12" to 72" diameter with wall thicknesses up to 75 mm, making it the preferred choice for large-diameter pipeline systems. For critical service requiring enhanced toughness or sour service resistance, specify PSL2 with Charpy V-notch impact testing and tighter chemistry controls .
