API 5L PSL2 Grade X65 Double-Sided Submerged Arc Welding (DSAW) Steel Pipe

✅ Basic Overview

API 5L PSL2 Grade X65 DSAW (Double-Sided Submerged Arc Welding) steel pipe is a high-strength, low-alloy line pipe manufactured to the American Petroleum Institute specification for critical pipeline transportation systems. The "X65" designation indicates a minimum yield strength of 65,000 psi (448 MPa) , representing a significant strength upgrade over lower grades .

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 X65, PSL2 is the standard choice for critical applications such as 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

🔧 Key Specifications

🔬 Chemical Composition (PSL2 Requirements)

Chemical Composition for PSL2 X65 (Welded Pipe)

*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

📊 X65 vs. Adjacent Grades Comparison (PSL2)

X65 offers approximately 8% higher yield strength than X60 and 25% higher than X52 .

📏 Delivery Conditions (Heat Treatment Suffixes)

PSL2 X65 DSAW pipes are supplied with suffixes indicating heat treatment condition :

Note: Suffix "S" indicates Sour Service application per NACE MR0175.

📏 Dimensional Specifications

Typical Size Availability (API 5L Grade X65 DSAW):

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

Process Steps

Plate Selection – Steel plates meeting API 5L PSL2 X65 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)

📊 PSL1 vs. PSL2 Comparison for X65

🌊 Real-World Application Example

A notable real-world application of API 5L PSL2 X65 DSAW pipe was the deepwater pipeline project offshore Mexico undertaken by Tata Steel . The project specifications included:

Total length: More than 140 km (87 miles)

Pipe size: 457 mm OD x 28.6 mm WT (approx. 18" OD x 1.125" WT)

Standard: API 5L PSL2 X65MO (with "MO" indicating offshore/sour service)

Water depth: Greater than 3,000 ft (914 m) – setting a new deepwater record

Manufacturing: Double Submerged Arc Welded (DSAW) from Hartlepool mill, UK

Repair rate: 0.25% (exceptionally low for small diameter, thick wall deepwater pipe)

Key features: Upgraded welding equipment with closed loop digital weld control, laser profiling system for 3,600-point profile monitoring, and enhanced "O" press control for optimal pipe shape critical for deepwater collapse resistance

This project demonstrates the stringent quality requirements for X65 PSL2 DSAW pipe in offshore applications, including:

High hydrostatic test pressure with extended hold times

Strict impact test acceptance criteria (low-temperature toughness)

High-quality requirements for both base metal and finished pipe

100% non-destructive testing of weld seam

🏭 Common Applications

✅ Key Advantages of PSL2 X65 DSAW Pipe

🛡️ Coating Options

API 5L PSL2 X65 DSAW pipe can be supplied with various coatings for corrosion 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

📋 Important Considerations

1. PSL2 is the Standard for Critical X65 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 suitable for general service, water lines, non-critical applications where low-temperature toughness is not required

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 X65 with additional requirements can be used for sour service (H₂S environments):

X65MS/X65QS 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 X65 DSAW pipes are typically supplied in the following conditions:

X65M – Thermomechanical rolled (TMCP) – most common for enhanced toughness and weldability

X65Q – Quenched and tempered – for maximum strength uniformity

X65N – Normalized – for improved grain structure

5. 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

6. Weldability

Low carbon content (≤0.12-0.18%) 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 X65 Double-Sided Submerged Arc Welded (DSAW/LSAW) steel pipe is a premium high-strength line pipe specification for demanding pipeline applications. With minimum yield strength of 65,000 psi (448 MPa) – approximately 8% higher than X60 and 25% higher than X52 – and guaranteed Charpy impact toughness, this material is the preferred choice for high-pressure gas transmission, offshore pipelines, arctic service, and sour service environments .

Key features:

Material standard: API 5L PSL2 X65 – premium high-strength grade for critical service

Yield strength: 448 MPa (65,000 psi) minimum – 8% higher than X60, 25% higher than X52

Tensile strength: 531 MPa (77,000 psi) minimum

PSL2 quality level: Mandatory impact testing, 50-67% lower sulfur (0.010-0.015% vs. 0.030%), maximum strength limits (≤600 MPa), yield-to-tensile ratio ≤0.93, and full traceability

DSAW manufacturing produces pipes from 16" to 72" OD with wall thickness up to 60 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 ultra-low carbon content (≤0.12-0.18%)

Sour service capable with NACE MR0175/ISO 15156 compliance (X65MS/X65QS grades)

TMCP delivery (X65M) provides enhanced toughness and weldability

Proven deepwater performance – successfully deployed in pipelines exceeding 3,000 ft water depth

Common applications include:

High-pressure gas transmission pipelines

Offshore and subsea pipelines

Arctic and cold climate pipelines

Sour service applications (with X65MS/X65QS grades)

Crude oil trunk lines

Station and header piping

High-pressure water transmission mains

When ordering, specify: API 5L PSL2 Grade X65M (or X65Q), 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 X65MS or X65QS 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.