API 5L PSL1 Grade B Double-Sided Submerged Arc Welding (DSAW) Steel Pipe
Basic Overview
API 5L PSL1 Grade B DSAW (Double-Sided Submerged Arc Welding) steel pipe is a standard carbon steel line pipe manufactured to the American Petroleum Institute specification for pipeline transportation systems . The "Grade B" designation indicates a minimum yield strength of 35,000 psi (241 MPa) , and it is the most commonly used grade for general pipeline service where the enhanced requirements of PSL2 are not necessary .
The DSAW manufacturing process-also known as LSAW (Longitudinal Submerged Arc Welding)-is a high-integrity welding method where both inside and outside welds are applied, forming a single high-quality weld nugget. This process is specifically designed for large-diameter, thick-wall pipes used in oil and gas transmission, water mains, and structural applications .
Name Explanation
| Part | Meaning |
|---|---|
| API | American Petroleum Institute |
| 5L | Specification for line pipe used in pipeline transportation systems |
| PSL1 | Product Specification Level 1 – standard quality level with basic requirements (no mandatory impact testing) |
| Grade B | Carbon steel grade with minimum yield strength of 35,000 psi (241 MPa) |
| DSAW | Double-Sided Submerged Arc Welding – both inside and outside welds are applied; the welding arc is submerged in granular flux during welding |
| Also Known As | LSAW (Longitudinal Submerged Arc Welding) – when the weld seam runs longitudinally along the pipe |
Key Specifications
| Attribute | Description |
|---|---|
| Standard | API 5L (46th Edition, aligned with ISO 3183) |
| Product Specification Level | PSL1 – standard quality level |
| Grade | B (L245 in ISO notation) |
| Minimum Yield Strength | 241 MPa (35,000 psi) |
| Minimum Tensile Strength | 414 MPa (60,000 psi) |
| Manufacturing Process | DSAW (Double-Sided Submerged Arc Welding) / LSAW (Longitudinal Submerged Arc Welding) |
| Forming Methods | JCOE (progressive J-C-O forming) or UOE (U-ing, O-ing, Expanding) |
| Size Range | 406 mm to 1820 mm (16" to 72") OD – typical for DSAW |
| Wall Thickness | 6.0 mm to 50 mm (up to 75 mm for special applications) |
| Length | 6 m to 12 m standard; up to 18 m available |
| End Finishes | Plain ends, beveled ends (30° bevel angle), threaded |
| Coating Options | Black paint, varnish, anti-rust oil, FBE, 3LPE, coal tar epoxy |
Chemical Composition (API 5L PSL1 Grade B Welded Pipe)
| Element | Maximum % | Notes |
|---|---|---|
| Carbon (C) | 0.26% | Low carbon for good weldability |
| Manganese (Mn) | 1.20% | Provides strength |
| Phosphorus (P) | 0.030% | Controlled for weldability |
| Sulfur (S) | 0.030% | Controlled for toughness |
Note: PSL1 has no requirement for maximum yield strength, carbon equivalent, or mandatory impact testing .
Mechanical Properties (API 5L PSL1 Grade B)
| Property | Requirement |
|---|---|
| Yield Strength (min) | 241 MPa (35,000 psi) |
| Yield Strength (max) | Not specified for PSL1 |
| Tensile Strength (min) | 414 MPa (60,000 psi) |
| Tensile Strength (max) | Not specified for PSL1 |
| Elongation | Per API 5L formula (varies by wall thickness) |
| Charpy Impact | Not required for PSL1 – only PSL2 requires mandatory impact testing |
Dimensional Specifications
| Parameter | Range / Tolerance |
|---|---|
| Outside Diameter | 406 mm to 1820 mm (16" to 72") – typical DSAW range |
| Wall Thickness | 6.0 mm to 50 mm (up to 75 mm for special applications) |
| Diameter Tolerance | ±0.75% of specified OD (typical) |
| Wall Thickness Tolerance | +15% / -12.5% of nominal (typical) |
| Length | 6 m to 12 m standard; up to 18 m available |
| Out-of-Roundness | ≤ 1% of specified OD |
Typical Size Availability (API 5L Grade B DSAW):
| OD (inch) | OD (mm) | Wall Thickness Range (mm) |
|---|---|---|
| 16" | 406 | 6.0 - 14.0 |
| 20" | 508 | 6.0 - 16.0 |
| 24" | 610 | 6.0 - 18.0 |
| 30" | 762 | 7.0 - 21.0 |
| 36" | 914 | 8.0 - 24.0 |
| 40" | 1016 | 8.0 - 26.0 |
| 48" | 1219 | 9.0 - 28.0 |
| 56" | 1422 | 10.0 - 29.0 |
| 60" | 1524 | 10.0 - 29.0 |
| 64" | 1626 | 10.0 - 30.0 |
| 72" | 1820 | 10.0 - 30.0 |
DSAW/LSAW Manufacturing Process
Double-Sided Submerged Arc Welding (DSAW), also known as Longitudinal Submerged Arc Welding (LSAW), is a high-efficiency process used primarily for large-diameter steel pipes .
Process Description
Welding arc is submerged in granular flux during welding, protecting the weld from atmospheric contamination
Both inside and outside welds are required, usually accomplished in separate processes
The separate welds consume a portion of the other, resulting in a single high-quality weld nugget
Forming Methods
| Method | Description | Typical Diameters |
|---|---|---|
| JCOE | Progressive J-C-O forming steps (J-shape → C-shape → O-shape), expanded after welding | 406-1626 mm (16"-64") |
| UOE | Plate pressed into U-shape, then O-shape, expanded after welding | 508-1118 mm (20"-44") |
Process Steps
Plate Selection – Steel plates meeting API 5L PSL1 Grade B requirements
Edge Preparation – Edges are beveled to create a V-shaped groove
Forming – Steel plates are formed into cylindrical shapes using JCOE or UOE presses
Tack Welding – Formed plates are tack-welded to maintain shape
Double Submerged Arc Welding – Pipe seam welded on both interior and exterior surfaces
Cold Expansion – Pipe may be expanded up to 1.5% to achieve final OD dimension
Ultrasonic Inspection – Seam inspected by continuous ultrasonic automatic flaw detection
Hydrostatic Pressure Test – Each pipe undergoes hydrostatic pressure testing (if specified)
Finishing – End processing, beveling, coating, and marking according to specifications
Testing & Inspection Requirements (PSL1)
| Test Type | Requirement | Notes |
|---|---|---|
| Chemical Analysis | Per heat lot | Verifies composition limits per API 5L PSL1 |
| Tensile Test | Per lot | Verifies yield and tensile strength |
| Flattening Test | Required | Checks ductility and weld integrity |
| Bend Test | Required | Verifies weld integrity |
| Charpy Impact Test | Not required for PSL1 | Only PSL2 requires mandatory impact testing |
| Hydrostatic Test | Each pipe (when specified) | Pressure integrity verification |
| Ultrasonic Inspection | 100% of weld seam | Standard practice for DSAW |
| X-ray Inspection | For "T" joints | Where strip butt welds intersect spiral seams |
| Dimensional Inspection | 100% | Per standard tolerances |
| Mill Test Certificate | EN 10204 Type 3.1B | Provided with full test results |
PSL1 vs. PSL2 Comparison for Grade B
| Feature | PSL1 Grade B | PSL2 Grade B | Significance |
|---|---|---|---|
| Carbon (C) max | 0.26% | 0.22% | PSL2 has tighter control for better weldability |
| Sulfur (S) max | 0.030% | 0.015% | PSL2 has 50% reduction – critical for toughness |
| Phosphorus (P) max | 0.030% | 0.025% | PSL2 has stricter limits |
| Yield Strength | 241 MPa min only | 241-448 MPa range | PSL2 specifies maximum to prevent over-strength materials |
| Tensile Strength | 414 MPa min only | 414-758 MPa range | PSL2 specifies maximum for consistency |
| Yield-to-Tensile Ratio | Not specified | ≤ 0.93 | PSL2 ensures adequate ductility |
| Impact Testing | Not required | Mandatory | PSL2 guarantees low-temperature toughness |
| Carbon Equivalent | Not required | Calculated and controlled | PSL2 ensures good field weldability |
| NDT Requirements | Standard | More stringent | PSL2 provides better defect detection |
| Typical Use | General service, water lines, non-critical | Critical service, sour service, low temperature |
Common Applications
| Application | Description |
|---|---|
| Oil and Gas Transmission | Onshore and offshore pipelines for crude oil, natural gas, and refined products |
| Water Transmission Mains | Large-diameter municipal and industrial water pipelines |
| Natural Gas Distribution | Low to medium-pressure gas networks |
| Gathering and Flow Lines | Upstream oil and gas operations |
| Structural Applications | Piling, bridge supports, construction |
| Industrial Process Piping | Refineries, chemical plants, power generation |
Key Advantages
| Advantage | Description |
|---|---|
| Cost-Effective | PSL1 is more economical than PSL2 – suitable for general service applications |
| Good Strength | 35,000 psi yield – standard baseline for pipeline applications |
| Excellent Weldability | Low carbon content ensures good field weldability |
| Large Diameter Capability | DSAW produces pipes from 16" to 72" OD – ideal for large-diameter applications |
| High Weld Integrity | Double-sided welding creates a single high-quality weld nugget with 100% UT inspection |
| Wide Availability | Commonly stocked by manufacturers globally |
| Dual Certification | Often dual-certified with ASTM A53 Grade B for general piping applications |
| JCOE/UOE Forming | Precise dimensional accuracy through advanced forming methods |
Coating Options
API 5L PSL1 Grade B DSAW pipe can be supplied with various coatings for corrosion protection :
| Coating Type | Best For | Key Features |
|---|---|---|
| 3LPE (3-layer polyethylene) | Buried pipelines | Most common; excellent corrosion protection, high impact resistance |
| FBE (Fusion Bonded Epoxy) | Oil & gas pipelines | Strong adhesion, chemical resistance |
| Coal Tar Epoxy | Marine environments | Heavy-duty protection |
| Varnish / Anti-rust oil | Temporary protection | Short-term corrosion protection during transport |
| Bitumen Coating | Buried service | Cost-effective protection |
| Black Oil Coating | Standard mill finish | Temporary protection |
End Finishes
Available end treatments include :
Plain ends (PE) – standard for most applications
Beveled ends (BE) – for field welding (30° bevel angle)
Threaded ends – for mechanical connections
International Approximations
| Standard | Equivalent Grade | Notes |
|---|---|---|
| ASTM A53 | Grade B | Similar yield strength |
| ASTM A106 | Grade B | Similar chemistry (seamless) |
| EN 10217-1 | P235TR1 / P235TR2 | Similar strength |
| GB/T 9711 | L245 | Chinese equivalent |
| ISO 3183 | L245 | International standard equivalent |
| JIS G3454 | STPG410 | Japanese equivalent |
Important Considerations
1. PSL1 vs. PSL2 Selection
PSL1: Suitable for general service, water lines, non-critical applications where low-temperature toughness is not required
PSL2: Required for low-temperature service (below 0°C), sour service (H₂S environments), regulated pipelines (FERC, DOT), and critical applications
2. PSL1 Grade B is the "Workhorse" Grade
Grade B PSL1 is the most commonly specified grade for general pipeline service, offering the best balance of strength, weldability, and cost .
3. DSAW Size Limitations
DSAW manufacturing for Grade B is typically available from 16" to 72" OD
Smaller diameters (under 16") are typically produced by ERW or seamless methods
4. Impact Testing
PSL1 does not require Charpy impact testing by the standard . If low-temperature service is anticipated, consider specifying impact testing as a supplementary requirement or upgrading to PSL2.
5. Third-Party Inspection
Available inspection services include SGS, BV, Lloyds
6. Mill Test Certificate
Typically provided as EN 10204 Type 3.1B with full test results
Third-party inspection available upon request
7. Weldability
Low carbon content (≤0.26%) ensures excellent weldability
Suitable for all standard welding methods (SMAW, GTAW, GMAW, SAW)
No post-weld heat treatment required for most thicknesses
Summary
API 5L PSL1 Grade B Double-Sided Submerged Arc Welded (DSAW/LSAW) steel pipe is the standard workhorse for large-diameter line pipe applications. With minimum yield strength of 35,000 psi (241 MPa) and tensile strength of 60,000 psi (414 MPa), this material offers a reliable balance of strength, weldability, and cost-effectiveness for general pipeline service .
Key features:
Material standard: API 5L PSL1 Grade B – most common grade for general pipeline service
Yield strength: 241 MPa (35,000 psi) minimum – baseline for API 5L grades
PSL1 quality level: No mandatory impact testing; standard requirements for general service
DSAW manufacturing produces pipes from 16" to 72" OD with wall thickness up to 50 mm
Double-sided welding creates a single high-quality weld nugget
JCOE or UOE forming methods ensure precise dimensional accuracy
100% ultrasonic inspection of weld seam ensures quality
Excellent weldability with low carbon content (≤0.26%)
Cost-effective – most economical choice for large-diameter line pipe
Dual certification available with ASTM A53 Grade B
Common applications include:
Oil and gas transmission pipelines
Water transmission mains
Natural gas distribution networks
Gathering and flow lines
Structural applications (piling, bridge supports)
Industrial process piping
When ordering, specify: API 5L PSL1 Grade B, DSAW/LSAW (Double-Sided/Longitudinal Submerged Arc Welded), Size (OD x WT), Length, End Finish (plain/beveled), Coating Requirements, and Mill Test Certificate to EN 10204 Type 3.1B .
For applications requiring guaranteed low-temperature toughness, tighter chemistry controls, or sour service capability, specify API 5L PSL2 Grade B instead .
