API 5L PSL2 Grade X70 Double-Sided Submerged Arc Welding (DSAW) Steel Pipe
Basic Overview
API 5L PSL2 Grade X70 DSAW (Double-Sided Submerged Arc Welding) steel pipe is a premium high-strength, micro-alloyed line pipe manufactured to the American Petroleum Institute specification for critical pipeline transportation systems. The "X70" designation indicates a minimum yield strength of 70,000 psi (483 MPa) , representing the premium tier of high-strength pipeline materials .
PSL2 (Product Specification Level 2) is the enhanced quality level with significantly stricter requirements than PSL1, including tighter chemistry controls, mandatory impact testing, maximum strength limits, yield-to-tensile ratio control, and full traceability . For X70, PSL2 is the standard choice for critical applications such as long-distance high-pressure gas transmission, offshore pipelines, arctic service, and sour service environments .
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 demanding pipeline applications .
Name Explanation
| Part | Meaning |
|---|---|
| API | American Petroleum Institute |
| 5L | Specification for line pipe used in pipeline transportation systems |
| PSL2 | Product Specification Level 2 – enhanced quality level with stricter requirements (mandatory impact testing, tighter chemistry, max strength limits) |
| X70 | Grade designation: "X" indicates pipeline grade, "70" represents minimum yield strength in ksi (70,000 psi / 483 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 | PSL2 – enhanced quality level |
| Grade | X70 (L485 in ISO notation) |
| Minimum Yield Strength | 483-485 MPa (70,000-70,300 psi) |
| Maximum Yield Strength | 620-635 MPa (90,000-92,100 psi) – PSL2 specifies both min and max |
| Minimum Tensile Strength | 565-570 MPa (82,000-82,700 psi) |
| Maximum Tensile Strength | 758-760 MPa (110,000-110,200 psi) |
| Yield-to-Tensile Ratio (max) | 0.93 – ensures adequate ductility |
| 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) |
| Delivery Condition | X70M (Thermomechanical rolled/TMCP) – most common; X70Q (Quenched and tempered) available |
Chemical Composition (PSL2 Requirements)
Chemical Composition for PSL2 X70 (Welded Pipe)
| Element | Maximum % | PSL1 Comparison |
|---|---|---|
| Carbon (C) | 0.12-0.24% | PSL1 X70: 0.26% – significantly tighter control |
| Silicon (Si) | 0.45% | Not specified for PSL1 |
| Manganese (Mn) | 1.65-1.85% | PSL1 X70: 1.65% – similar range |
| Phosphorus (P) | 0.025% | PSL1: 0.030% – stricter |
| Sulfur (S) | 0.015% | PSL1: 0.030% – 50% reduction |
| Vanadium (V) | As agreed | Micro-alloying for grain refinement |
| Niobium (Nb) | As agreed | Micro-alloying for strength |
| Titanium (Ti) | As agreed | Micro-alloying for grain refinement |
| Carbon Equivalent (CEIIW) | 0.43% max | Required and controlled for weldability |
| Carbon Equivalent (CEpcm) | 0.25% max | Required and controlled |
*Note: The total content of micro-alloying elements (Nb+V+Ti) does not exceed 0.15% . PSL2 requires carbon equivalent (CE) calculation and control to ensure good field weldability .*
Mechanical Properties
| Property | PSL2 Requirement | PSL1 Comparison |
|---|---|---|
| Yield Strength (min) | 483-485 MPa (70,000-70,300 psi) | Same minimum |
| Yield Strength (max) | 620-635 MPa (90,000-92,100 psi) | Not specified |
| Tensile Strength (min) | 565-570 MPa (82,000-82,700 psi) | Same minimum |
| Tensile Strength (max) | 758-760 MPa (110,000-110,200 psi) | Not specified |
| Yield-to-Tensile Ratio | 0.93 max | Not specified |
| Elongation | Per API 5L formula (varies by wall thickness) | Same formula |
| Charpy Impact (CVN) | Mandatory – 27J-101J at specified temperature (typically 0°C to -20°C) | Not required |
| Hardness (max) | 250 HV10 (sour service: 248 HV10) | Not specified |
X70 vs. Adjacent Grades Comparison (PSL2)
| Grade | Yield Strength (min) | Yield Strength (max) | Tensile Strength (min) | Typical Application |
|---|---|---|---|---|
| X52 | 359 MPa (52 ksi) | 531 MPa (77 ksi) | 455 MPa (66 ksi) | General transmission |
| X60 | 414 MPa (60 ksi) | 565 MPa (82 ksi) | 517 MPa (75 ksi) | High-pressure transmission |
| X65 | 448 MPa (65 ksi) | 600 MPa (87 ksi) | 531 MPa (77 ksi) | High-pressure, offshore |
| X70 | 483 MPa (70 ksi) | 620-635 MPa (90-92 ksi) | 565 MPa (82 ksi) | Long-distance high-pressure, offshore, arctic |
| X80 | 552 MPa (80 ksi) | 690-705 MPa (100-102 ksi) | 621 MPa (90 ksi) | Ultra-high-pressure trunk lines |
X70 offers approximately 8% higher yield strength than X65, 17% higher than X60, and 35% higher than X52 .
Delivery Conditions (Heat Treatment Suffixes)
PSL2 X70 DSAW pipes are supplied with suffixes indicating heat treatment condition :
| Suffix | Condition | Typical Application |
|---|---|---|
| X70N | Normalized | General transmission, improved grain structure |
| X70Q | Quenched and tempered | Maximum strength uniformity |
| X70M | Thermomechanical rolled (TMCP) | Most common – enhanced toughness and weldability |
| X70QS | Quenched and tempered + Sour service | H₂S environments with NACE compliance |
| X70MS | Thermomechanical rolled + Sour service | H₂S environments with enhanced toughness |
Note: Suffix "S" indicates Sour Service application per NACE MR0175 .
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 X70 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 |
Source: Based on industry manufacturer data .
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 PSL2 X70 requirements (fully killed, fine grain steel)
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
Finishing – End processing, beveling, coating, and marking according to specifications
Testing & Inspection Requirements (PSL2)
| Test Type | Requirement | Notes |
|---|---|---|
| Chemical Analysis | Per heat lot | Tighter PSL2 limits |
| Tensile Test | Per lot | Verifies both min and max limits |
| Yield-to-Tensile Ratio | ≤ 0.93 | Mandatory verification |
| Charpy Impact Test (CVN) | Mandatory | Required for all PSL2 grades; typically 27J-101J at 0°C or -20°C |
| Flattening Test | Required | Checks ductility and weld integrity |
| Bend Test | Required | Verifies weld integrity |
| Hydrostatic Test | Each pipe | Pressure integrity verification |
| Ultrasonic Inspection (UT) | 100% of weld seam | Mandatory for PSL2 |
| X-ray Inspection (RT) | When specified | For critical applications; 100% available upon request |
| Hardness Testing | For sour service | Hardness mapping required; ≤250 HV10 (≤248 HV10 for sour) |
| HIC/SSC Testing | For sour service | Per NACE MR0175/ISO 15156 |
| DWTT (Drop Weight Tear Test) | For critical applications | Fracture toughness verification |
| Dimensional Inspection | 100% | Per standard tolerances |
| Mill Test Certificate | EN 10204 Type 3.1B | Provided with full test results |
PSL1 vs. PSL2 Comparison for X70
| Feature | PSL1 X70 | PSL2 X70 | Significance |
|---|---|---|---|
| Carbon (C) max | 0.26% | 0.12-0.24% | 54% reduction – better weldability, lower HAZ hardness |
| Sulfur (S) max | 0.030% | 0.015% | 50% reduction – critical for toughness and HIC resistance |
| Phosphorus (P) max | 0.030% | 0.025% | Improved toughness and weldability |
| Manganese (Mn) max | 1.65% | 1.65-1.85% | Higher for strength optimization |
| Yield Strength | 483 MPa min only | 483-635 MPa range | Prevents over-strength materials |
| Tensile Strength | 565 MPa min only | 565-760 MPa range | Ensures consistent mechanical properties |
| Yield-to-Tensile Ratio | Not specified | ≤ 0.93 | Ensures adequate ductility |
| Charpy Impact Testing | Not required | Mandatory (27J-101J at 0°C or -20°C) | Guarantees low-temperature toughness |
| Carbon Equivalent (CE) | Not required | Calculated and controlled | Ensures good field weldability |
| NDT Requirements | Standard | 100% UT mandatory for PSL2 | Better defect detection |
| Traceability | Batch level | Pipe-by-pipe full traceability | Complete quality documentation |
| Hardness Control | Not specified | ≤250 HV10 (sour: ≤248 HV10) | Essential for sour service applications |
| Typical Use | General service, water lines, non-critical | Critical service, sour service, low temperature, offshore, arctic |
Common Applications
| Application | Description |
|---|---|
| Long-Distance High-Pressure Gas Transmission | Major trunk lines requiring high operating pressures |
| Offshore and Subsea Pipelines | Subsea pipelines requiring high strength-to-weight ratio |
| Arctic and Cold Climate Pipelines | Low-temperature environments requiring guaranteed impact toughness |
| 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 |
| Sour Service | H₂S environments (with X70MS/X70QS grades) |
| High-Pressure Water Transmission | Large-diameter, high-pressure water mains |
| Pipeline Station Piping | High-pressure applications in pipeline terminals |
Key Advantages of PSL2 X70 DSAW Pipe
| Advantage | Description |
|---|---|
| Highest Strength in Standard Pipeline Grades | 70,000 psi yield – 8% higher than X65, 17% higher than X60, 35% higher than X52 |
| Guaranteed Low-Temperature Toughness | Mandatory Charpy impact testing (27J-101J at 0°C to -20°C) ensures reliable performance in cold climates |
| Stricter Chemistry Controls | 50% lower sulfur content (0.015% vs. 0.030%) improves weldability and HIC resistance |
| Controlled Strength Range | Maximum yield strength (635 MPa) prevents over-strength materials that can cause welding issues |
| Full Traceability | Pipe-by-pipe traceability for complete quality documentation |
| 100% Ultrasonic Inspection | Mandatory NDT ensures weld seam integrity |
| Micro-alloyed with TMCP | Ultra-low carbon acicular ferrite structure with high-density dislocations provides excellent fracture toughness |
| Sour Service Capability | Available with NACE MR0175/ISO 15156 compliance (X70MS/X70QS grades) |
| 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 |
Coating Options
API 5L PSL2 X70 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 |
| 3LPP (3-layer polypropylene) | Offshore pipelines | High temperature resistance (up to 140°C) |
| 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 |
|---|---|---|
| ISO 3183 | L485ME or X70ME | Harmonized with API 5L; "E" indicates suitable for offshore/arctic |
| GB/T 9711 | L485 | Chinese equivalent |
| DNV OS-F101 | Grade 485 | Offshore standard |
| EN 10208-2 | L485MB | European equivalent |
Important Considerations
1. PSL2 is the Standard for Critical X70 Applications
PSL2 is required for low-temperature service (especially below 0°C), sour service (H₂S environments), regulated pipelines (FERC, DOT), offshore applications, arctic service, and critical infrastructure
PSL1 is rarely specified for X70 in critical applications
2. Impact Testing Temperature
Standard Charpy impact testing is at 0°C with 27J minimum for PSL2
For arctic applications, impact testing at -20°C or -45°C can be specified with higher energy requirements (up to 101J)
3. Sour Service Capability
PSL2 X70 with additional requirements can be used for sour service (H₂S environments):
X70MS/X70QS grades specifically designed for sour service
Hardness testing (≤ 248 HV10)
HIC and SSC testing per NACE TM0284 and NACE TM0177
Sulfur content may be further limited to ≤ 0.002%
4. Delivery Conditions
PSL2 X70 DSAW pipes are typically supplied in the following conditions :
X70M – Thermomechanical rolled (TMCP) – most common for enhanced toughness and weldability
X70Q – Quenched and tempered – for maximum strength uniformity
X70N – Normalized – for improved grain structure
5. DSAW Size Limitations
DSAW manufacturing for X70 is typically available from 16" to 72" OD
Smaller diameters (under 16") are typically produced by ERW or seamless methods
6. Weldability
Low carbon content (≤0.12-0.24%) ensures good weldability
Suitable for all standard welding methods (SMAW, GTAW, GMAW, SAW)
Preheat may be required for thicker sections (typically 100-150°C)
For sour service applications, low hydrogen practices are required
Qualified welding procedures with impact-tested filler metals essential
7. NDT Requirements
100% ultrasonic inspection (UT) of weld seam is mandatory for PSL2
X-ray inspection (RT) is available upon request, especially for critical applications
For sour service, additional NDT may be required
8. Third-Party Inspection
Available inspection services include SGS, BV, Lloyds, DNV, TÜV
9. Mill Test Certificate
Typically provided as EN 10204 Type 3.1B with full test results
Third-party inspection available upon request
10. Regulatory Compliance
PSL2 is required for pipelines regulated by:
FERC (Federal Energy Regulatory Commission)
DOT (Department of Transportation)
FEMSA (Federal Environmental, Management and Safety Agency)
PED (Pressure Equipment Directive) for Europe
Summary
API 5L PSL2 Grade X70 Double-Sided Submerged Arc Welded (DSAW/LSAW) steel pipe is the premium high-strength line pipe specification for the most demanding pipeline applications. With minimum yield strength of 70,000 psi (483 MPa) – approximately 8% higher than X65, 17% higher than X60, and 35% higher than X52 – and guaranteed Charpy impact toughness, this material is the preferred choice for long-distance high-pressure gas transmission, offshore pipelines, arctic service, and sour service environments .
Key features:
Material standard: API 5L PSL2 X70 – premium high-strength grade for critical service
Yield strength: 483 MPa (70,000 psi) minimum – 8% higher than X65, 17% higher than X60
Tensile strength: 565 MPa (82,000 psi) minimum
PSL2 quality level: Mandatory impact testing, 50% lower sulfur (0.015% vs. 0.030%), maximum strength limits (≤635 MPa), yield-to-tensile ratio ≤0.93, and full traceability
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 is mandatory
Excellent weldability with low carbon content (≤0.12-0.24%)
Sour service capable with NACE MR0175/ISO 15156 compliance (X70MS/X70QS grades)
TMCP delivery (X70M) provides enhanced toughness and weldability
Common applications include:
Long-distance high-pressure gas transmission pipelines
Offshore and subsea pipelines
Arctic and cold climate pipelines
Sour service applications (with X70MS/X70QS grades)
Crude oil trunk lines
Station and header piping
High-pressure water transmission mains
When ordering, specify: API 5L PSL2 Grade X70M (or X70Q), DSAW/LSAW (Double-Sided/Longitudinal Submerged Arc Welded), Size (OD x WT), Length, End Finish (plain/beveled), Coating Requirements, Impact Test Temperature (e.g., 0°C, -20°C, -45°C), and Mill Test Certificate to EN 10204 Type 3.1B .
For sour service applications, specify X70MS or X70QS with NACE MR0175/ISO 15156 compliance . For the most demanding projects, consider specifying DNV Type Approval, EN 10204 3.2 certification, and third-party surveillance to ensure full compliance with international standards.
