API 5L PSL2 X46 ERW Steel Pipe
Basic Overview
API 5L PSL2 Grade X46 ERW (Electric Resistance Welded) steel pipe is a medium-strength line pipe that offers enhanced quality requirements over PSL1. The "X46" designation indicates a minimum yield strength of 46,000 psi (317 MPa) , positioning it between X42 and X52 in the API 5L grade ladder . PSL2 adds stricter chemical controls, mandatory impact testing, maximum strength limits, and full traceability.
The designation breaks down as follows:
API 5L: American Petroleum Institute specification for line pipe
PSL2: Product Specification Level 2 (enhanced quality with mandatory testing)
X46: Grade indicating minimum yield strength of 46 ksi (317 MPa)
ERW: Electric Resistance Welded – pipe formed from steel coil and welded longitudinally without filler metal
Key Specifications
| Parameter | Specification |
|---|---|
| Standard | API 5L (aligned with ISO 3183) |
| Product Specification Level | PSL2 |
| Grade | X46 (L320 in ISO notation) |
| Minimum Yield Strength | 317-320 MPa (46,000-46,400 psi) |
| Maximum Yield Strength | 524-525 MPa (76,000-76,100 psi) – PSL2 specifies both min and max |
| Minimum Tensile Strength | 434-435 MPa (63,000-63,100 psi) |
| Maximum Tensile Strength | 758-760 MPa (110,000-110,200 psi) |
| Yield-to-Tensile Ratio (max) | 0.93 |
| Manufacturing Type | ERW (Electric Resistance Welded) / HFW |
| Size Range (ERW) | 21.3 mm to 660 mm (1/2" to 26") OD; typical ERW up to 24" |
| Wall Thickness | 1.5 mm to 22.2 mm; Schedule 10 to 160, STD, XS |
| Length | 5 m to 14 m; SRL, DRL; 5.8 m, 6 m, 11.8 m, 12 m standard |
| End Finishes | Plain ends, beveled ends, threaded ends |
| Coatings | 3LPE, FBE, coal tar epoxy, black painting, varnish |
Chemical Composition (PSL2 Welded Pipe)
| Element | Maximum % | PSL1 Comparison |
|---|---|---|
| Carbon (C) | 0.22% | 0.26% (tighter control) |
| Manganese (Mn) | 1.40% | 1.40% (similar) |
| Silicon (Si) | 0.40-0.45% | Not specified for PSL1 |
| Phosphorus (P) | 0.025% | 0.030% (stricter) |
| Sulfur (S) | 0.015% | 0.030% (50% reduction) |
*Note: PSL2 also requires carbon equivalent (CE) calculation and control. The total content of micro-alloying elements (Nb+V+Ti) does not exceed 0.15% .*
Mechanical Properties
| Property | PSL2 Requirement | PSL1 Comparison |
|---|---|---|
| Yield Strength (min) | 317-320 MPa (46,400 psi) | Same minimum |
| Yield Strength (max) | 524-525 MPa (76,000-76,100 psi) | Not specified |
| Tensile Strength (min) | 434-435 MPa (63,000-63,100 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 | Same formula |
| Charpy Impact (CVN) | Mandatory at specified temperature | Not required |
Dimensional Tolerances (API 5L)
| Parameter | Size Range | Tolerance |
|---|---|---|
| Pipe Body OD | 219.1～457 mm | ±0.75% |
| Pipe Body OD | 508～610 mm | ±0.75% |
| Pipe Ends (219.1-273.1 mm) | - | +1.6 mm / -0.4 mm |
| Pipe Ends (274-320 mm) | - | +2.4 mm / -0.8 mm |
| Pipe Ends (323.9-457 mm) | - | +2.4 mm / -0.8 mm |
| Wall Thickness (508-610 mm) | - | +19.5% / -8% |
| Wall Thickness (219.1-457 mm) | - | +15% / -12.5% |
ERW Manufacturing Process
ERW steel pipe is a straight seam electric resistance welded pipe produced through a continuous process :
Uncoiling – Steel coil is uncoiled and leveled
Edge Preparation – Strip edges are milled for proper welding
Forming – Steel strip is cold-formed into cylindrical shape
Electric Induction Welding – High-frequency welding joins edges without filler metal
Heat Treatment – Medium frequency heat treatment normalizes the weld zone
Sizing – Pipe passes through sizing rolls to achieve final dimensions
NDT – 100% non-destructive testing (ultrasonic or eddy current) of weld seam
Hydrostatic Testing – Each pipe individually tested for pressure integrity
End Finishing – Ends prepared (plain or beveled)
Grade Comparison: X46 vs. Adjacent Grades
| Grade | Yield Strength (min) | Yield Strength (max) | Relative Strength vs. X46 | Typical Application |
|---|---|---|---|---|
| X42 | 290 MPa (42 ksi) | 496 MPa (72 ksi) | -9% | Medium-pressure transmission |
| X46 | 317 MPa (46 ksi) | 524 MPa (76 ksi) | Baseline | Higher-pressure transmission |
| X52 | 359 MPa (52 ksi) | 531 MPa (77 ksi) | +13% | General transmission |
*X46 offers approximately 10% higher yield strength than X42 and serves as a cost-effective intermediate option when X42 is under-strength but X52 would be over-specified .*
Testing 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 |
| Flattening Test | Required for ERW pipe | Checks ductility |
| Bend Test | Required | Verifies weld integrity |
| Hydrostatic Test | Each pipe | Pressure integrity verification |
| NDT (Ultrasonic/Eddy Current) | 100% of weld seam | Mandatory for PSL2 |
| Hardness Testing | For sour service | Hardness mapping required when specified |
PSL1 vs. PSL2 Comparison for X46
| Feature | PSL1 X46 | PSL2 X46 | Significance |
|---|---|---|---|
| Carbon (C) max | 0.26% | 0.22% | Better weldability, lower HAZ hardness |
| Sulfur (S) max | 0.030% | 0.015% | 50% reduction – critical for toughness |
| Phosphorus (P) max | 0.030% | 0.025% | Improved toughness and weldability |
| Yield Strength | 317 MPa min only | 317-524 MPa range | Prevents over-strength materials |
| Tensile Strength | 435 MPa min only | 434-758 MPa range | Ensures consistent mechanical properties |
| Yield-to-Tensile Ratio | Not specified | ≤ 0.93 | Ensures adequate ductility |
| Charpy Impact Testing | Not required | Mandatory | Guarantees low-temperature toughness |
| NDT Requirements | Standard | More stringent | Better defect detection |
| Traceability | Batch level | Pipe-by-pipe full traceability | Complete quality documentation |
Common Applications
| Application | Description |
|---|---|
| Oil and Gas Transmission | Medium-pressure pipelines for crude oil and natural gas |
| Natural Gas Gathering Lines | Connecting wells to processing facilities; Class II/III onshore gas transmission |
| Water Transmission Mains | Large-diameter municipal and industrial water pipelines |
| Sour Service | H₂S environments (with supplementary requirements) |
| Low-Temperature Service | Applications requiring guaranteed impact toughness |
| Industrial Process Piping | Refineries, chemical plants, power engineering |
| Pipeline Station and Terminal Piping | Compressor stations, pump stations, metering facilities |
| Offshore Pipelines | Subsea applications with enhanced toughness requirements |
Real-World Project Example
A 2018 project in Asia specified API 5L X46 PSL2 ERW/LSAW/HSAW line pipe for pre-coated pipeline systems . The tender included:
150mm NB (168.3mm OD) and 200mm NB (219.1mm OD) diameters
6.4mm wall thickness
3LPE coated
Hydrostatic test pressures: 184.5 kg/cm² and 142 kg/cm² respectively
Beveled ends for field welding
This demonstrates commercial availability and real-world application of X46 PSL2 pipes .
Key Advantages
| Advantage | Description |
|---|---|
| Guaranteed Toughness | Mandatory Charpy impact testing ensures low-temperature performance |
| Stricter Chemistry | 50% lower sulfur content improves weldability and HIC resistance |
| Controlled Strength | Maximum yield strength (524 MPa) prevents over-strength materials |
| Full Traceability | Pipe-by-pipe traceability for complete quality documentation |
| Enhanced NDT | More stringent non-destructive testing requirements |
| Cost-Effective Intermediate Grade | ERW process provides economical production for sizes up to 24" |
| Micro-Alloyed | Fine grain structure with acicular ferrite and bainite for excellent impact toughness |
Important Considerations
1. Size Limitations
ERW manufacturing for X46 is typically available up to 24-26 inches (610 mm) OD
Larger diameters require LSAW or SSAW manufacturing
2. PSL1 vs. PSL2 Selection
PSL2: Required for low-temperature service, sour service (H₂S environments), regulated pipelines (FERC, DOT), and critical applications
PSL1: Suitable for general service, water lines, non-critical applications where low-temperature toughness is not required
3. Impact Testing Temperature
Standard Charpy impact testing can be specified at various temperatures (0°C, -20°C, etc.)
For colder applications, impact testing at lower temperatures ensures performance
4. Equivalent Grades
ISO 3183: L320
GB/T 9711: L320
EN 10208-2: L320MB
5. Coating Options
3LPE (3-layer polyethylene): Most common for buried pipelines
FBE (Fusion Bonded Epoxy): Corrosion protection
Coal Tar Epoxy: Heavy-duty protection
Black (bare): Standard mill finish
Varnish/Anti-rust oil: Temporary protection during transport
6. Mill Test Certificate
Typically provided as EN 10204 Type 3.1 with full test results
Third-party inspection (SGS, BV, Lloyds, TUV, ABS) available upon request
7. Microstructure Characteristics
X46 steel pipe features a structure composed of acicular ferrite and bainite
This provides high resistance to dynamic tearing and low ductile-brittle transition temperature
Summary
API 5L PSL2 Grade X46 ERW steel pipe is a medium-strength line pipe that combines the X46 strength grade (317 MPa minimum yield) with the enhanced PSL2 quality requirements. With stricter chemical controls (S ≤ 0.015%, P ≤ 0.025%), mandatory Charpy impact testing, maximum strength limits (≤ 524 MPa yield), yield-to-tensile ratio control (≤ 0.93), and full pipe-by-pipe traceability, PSL2 X46 is the preferred choice for medium-pressure transmission applications requiring guaranteed low-temperature toughness or sour service capability .
Key features:
Available in PSL2 quality level with enhanced testing requirements
Manufactured by ERW process – sizes from 1/2" to 24" OD
Mandatory Charpy impact testing ensures low-temperature performance
50% lower sulfur content (0.015% vs. 0.030%) improves toughness and HIC resistance
Maximum yield strength (524 MPa) prevents over-strength materials
Micro-alloyed with fine grain structure for excellent impact properties
Full traceability from steelmaking to finished pipe
Common applications include:
Medium-pressure oil and gas transmission pipelines
Natural gas gathering and distribution networks
Low-temperature service requiring guaranteed impact toughness
Regulated pipelines under FERC, DOT, or other authorities
Sour service applications (with supplementary requirements)
Offshore and subsea pipelines
When ordering, specify: API 5L PSL2 Grade X46 ERW steel pipe, Size (OD x WT), Length, End Finish (plain/beveled), Heat Treatment Condition (N/Q/M if required), Coating Requirements (3LPE/FBE/bare), and any supplementary requirements (impact test temperature, sour service). Mill Test Certificate to EN 10204 Type 3.1 is standard .
