API 5L PSL1 Grade X65 Double-Sided Submerged Arc Welding (DSAW) Steel Pipe
Basic Overview
API 5L PSL1 Grade X65 DSAW (Double-Sided Submerged Arc Welding) steel pipe is a high-strength carbon steel line pipe manufactured to the American Petroleum Institute specification for pipeline transportation systems. The "X65" designation indicates a minimum yield strength of 65,000 psi (448 MPa) , representing a significant strength upgrade over X60 (60 ksi) and X52 (52 ksi) .
X65 is a premium high-strength grade offering approximately 8% higher yield strength than X60 (448 MPa vs. 414 MPa) and 25% higher than X52 (448 MPa vs. 359 MPa). It is commonly specified for demanding high-pressure transmission pipelines, offshore installations, and arctic service where lower grades would require excessive wall thickness .
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 high-pressure oil and gas transmission, offshore pipelines, 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) |
| X65 | Grade designation: "X" indicates pipeline grade, "65" represents minimum yield strength in ksi (65,000 psi / 448 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 | X65 (L450 in ISO notation) |
| Minimum Yield Strength | 448-450 MPa (65,000-65,300 psi) |
| Minimum Tensile Strength | 531-535 MPa (77,000-77,600 psi) |
| Elongation | Per API 5L formula (varies by wall thickness) |
| 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 (DSAW/LSAW) | 406 mm to 1829 mm (16" to 72") OD – typical for DSAW; up to 84" available |
| 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) |
| Coating Options | Black paint, varnish, anti-rust oil, FBE, 3LPE, coal tar epoxy, CWC |
Chemical Composition (API 5L PSL1 Grade X65 Welded Pipe)
Based on API 5L PSL1 requirements for welded pipe :
| Element | Maximum % | Notes |
|---|---|---|
| Carbon (C) | 0.26% | Low carbon for good weldability |
| Manganese (Mn) | 1.45% | Provides strength; higher than lower grades |
| Phosphorus (P) | 0.030% | Controlled for weldability |
| Sulfur (S) | 0.030% | Controlled for toughness |
| Silicon (Si) | Not specified for PSL1 | Typically ≤ 0.45% |
| Chromium (Cr) | 0.50% max | Residual element |
| Nickel (Ni) | 0.50% max | Residual element |
| Molybdenum (Mo) | 0.15% max | Residual element |
| Copper (Cu) | 0.50% max | Residual element |
| Vanadium (V) + Niobium (Nb) + Titanium (Ti) | ≤ 0.15% | Micro-alloying for grain refinement |
Note: For each reduction of 0.01% below the specified maximum carbon content, an increase of 0.05% above the specified maximum manganese is permitted, up to a maximum of 1.75% . PSL1 has no requirement for maximum yield strength, carbon equivalent, or mandatory impact testing .
Mechanical Properties (API 5L PSL1 Grade X65)
| Property | Requirement |
|---|---|
| Yield Strength (min) | 448-450 MPa (65,000-65,300 psi) |
| Yield Strength (max) | Not specified for PSL1 |
| Tensile Strength (min) | 531-535 MPa (77,000-77,600 psi) |
| Tensile Strength (max) | Not specified for PSL1 |
| Weld Tensile Strength (min) | ≥ 535 MPa (77,600 psi) |
| Elongation | Per API 5L formula (varies by wall thickness) |
| Charpy Impact | Not required for PSL1 – only PSL2 requires mandatory impact testing |
| Yield-to-Tensile Ratio | Not specified for PSL1 |
X65 vs. Adjacent Grades Comparison
| Grade | Yield Strength (min) | Tensile Strength (min) | Relative Strength vs. X65 | Typical Application |
|---|---|---|---|---|
| X52 | 359 MPa (52 ksi) | 455-460 MPa (66 ksi) | -20% | General transmission |
| X56 | 386-390 MPa (56 ksi) | 490 MPa (71 ksi) | -13% | Higher-pressure transmission |
| X60 | 414-415 MPa (60 ksi) | 517-520 MPa (75 ksi) | -7% | High-pressure transmission |
| X65 | 448-450 MPa (65 ksi) | 531-535 MPa (77 ksi) | Baseline | High-pressure, offshore, demanding applications |
| X70 | 483-485 MPa (70 ksi) | 565-570 MPa (82 ksi) | +8% | Long-distance high-pressure |
| X80 | 552-555 MPa (80 ksi) | 621-625 MPa (90 ksi) | +23% | Ultra-high-pressure trunk lines |
*X65 offers approximately 8% higher yield strength than X60 and 25% higher than X52, making it a premium choice for high-pressure transmission lines where lower grades would require excessive wall thickness .*
Dimensional Specifications
| Parameter | Range / Tolerance |
|---|---|
| Outside Diameter | 406 mm to 1829 mm (16" to 72") – typical DSAW range; up to 84" available |
| Wall Thickness | 6.0 mm to 50 mm (up to 75 mm for special applications) |
| Diameter Tolerance (Pipe Body) | ±0.75% of specified OD |
| Diameter Tolerance (Pipe Ends, D ≤ 168.3mm) | -0.4 mm to +1.6 mm |
| Diameter Tolerance (Pipe Ends, 168.3mm < D ≤ 610mm) | ±0.005D, max ±1.6 mm |
| Diameter Tolerance (Pipe Ends, 610mm < D ≤ 1422mm) | ±1.6 mm |
| Wall Thickness Tolerance (t ≤ 5mm) | ±0.5 mm |
| Wall Thickness Tolerance (5mm < t < 15mm) | ±0.1t |
| Wall Thickness Tolerance (t ≥ 15mm) | ±1.5 mm |
| 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 X65 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" | 1829 | 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 X65 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 (when 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 X65
| Feature | PSL1 X65 | PSL2 X65 | 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 |
| Manganese (Mn) max | 1.45% | 1.65% | Higher for strength |
| Yield Strength | 450 MPa min only | 450-600 MPa range | PSL2 specifies maximum to prevent over-strength materials |
| Tensile Strength | 535 MPa min only | 535-760 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 |
| Traceability | Batch level | Pipe-by-pipe full traceability | PSL2 offers complete quality documentation |
| Typical Use | General service, water lines, non-critical | Critical service, sour service, low temperature |
Common Applications
| Application | Description |
|---|---|
| High-Pressure Gas Transmission | Long-distance natural gas pipelines requiring high operating pressures |
| Offshore and Subsea Pipelines | Subsea pipelines requiring high strength-to-weight ratio |
| Crude Oil Trunk Lines | Main transmission lines for crude oil transport |
| Onshore Gathering Networks | Regional trunk systems connecting production areas to processing |
| Station and Header Piping | Compressor stations, pump stations, metering facilities |
| Water Transmission | Large-diameter, high-pressure water mains |
| Industrial Process Piping | Refineries, chemical plants, power generation |
| Arctic/Cold Climate Pipelines | Low-temperature environments (with PSL2 and impact testing) |
Key Advantages
| Advantage | Description |
|---|---|
| High Strength | 65,000 psi yield – 8% higher than X60, 25% higher than X52 |
| Cost-Effective | PSL1 is more economical than PSL2 – suitable for general service 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 |
| JCOE/UOE Forming | Precise dimensional accuracy through advanced forming methods |
| Proven Performance | Widely used in high-pressure gas transmission, offshore pipelines, and demanding applications |
International Approximations
| Standard | Equivalent Grade | Notes |
|---|---|---|
| ISO 3183 | L450 | International standard equivalent |
| GB/T 9711 | L450 | Chinese equivalent |
| DNV OS-F101 | Grade 450 | Offshore standard (similar strength level) |
| EN 10208-2 | L450MB | European equivalent |
Coating Options
API 5L PSL1 X65 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 |
| CWC (Concrete Weight Coating) | Offshore/subsea pipelines | Negative buoyancy and mechanical 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
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. X65 vs. Lower/Higher Grades
X52: General transmission (52 ksi yield)
X56: Higher-pressure transmission (56 ksi yield)
X60: High-pressure transmission (60 ksi yield)
X65: High-pressure, offshore, demanding applications (65 ksi yield)
X70/X80: Higher pressure, long-distance, ultra-high-pressure trunk lines
3. DSAW Size Limitations
DSAW manufacturing for X65 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
Upgrading to PSL2 (which mandates impact testing)
5. Temperature Limitations
Maximum recommended service temperature: 350°C (662°F)
No guaranteed low-temperature toughness under PSL1 – not suitable for sub-zero applications without evaluation
6. Third-Party Inspection
Available inspection services include SGS, BV, Lloyds
7. Mill Test Certificate
Typically provided as EN 10204 Type 3.1B with full test results
Third-party inspection available upon request
8. 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
For sour service applications with PSL2, low hydrogen practices required
Summary
API 5L PSL1 Grade X65 Double-Sided Submerged Arc Welded (DSAW/LSAW) steel pipe is a premium high-strength line pipe for demanding oil and gas transmission applications. With minimum yield strength of 65,000 psi (448 MPa) – approximately 8% higher than X60 and 25% higher than X52 – and tensile strength of 77,000 psi (531 MPa), this material is the preferred choice for high-pressure transmission pipelines, offshore applications, and demanding service conditions where X60 would require excessive wall thickness .
Key features:
Material standard: API 5L PSL1 X65 – high-strength grade for general service
Yield strength: 448 MPa (65,000 psi) minimum – 8% higher than X60
Tensile strength: 531 MPa (77,000 psi) minimum
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 high-pressure large-diameter line pipe
Common applications include:
High-pressure gas transmission pipelines
Offshore and subsea pipelines
Crude oil trunk lines
Station and header piping
Water transmission mains
Industrial process piping
When ordering, specify: API 5L PSL1 Grade X65, 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 X65 instead . For most high-pressure transmission applications, X65 PSL1 offers an excellent balance of strength and economy.
