Mechanically Lined Pipe (MLP) in Subsea Applications: Technology, Benefits, and Future Outlook

MLP is gaining increasing traction in subsea pipeline systems due to its effective balance of strength, corrosion resistance, and cost-efficiency. In this post, we'll explore what MLP is, its relevance in deepwater offshore environments, advantages over traditional pipe technologies, technical considerations during installation, real-world applications, and its potential role in energy transition projects.

Table of Contents

• Understanding Mechanically Lined Pipe (MLP)
  • Definition and Structure
  • Comparison with CRA Clad and Weld Overlay Pipe
• The Role of MLP in Subsea Oil & Gas Applications
  • Corrosion Challenges in Subsea Environments
• Installation Methods and Technical Considerations
  • S‑Lay, J‑Lay, Reel‑Lay Techniques
  • Qualification, Testing, and Fatigue Performance
• Advantages of MLP for Operators and EPCs
  • Cost and Material Savings
  • Performance and Safety Benefits
• Future Outlook for MLP in the Energy Transition
  • Emerging Standards and R&D
  • Potential Beyond Oil & Gas (Hydrogen, CCS)
• Conclusion – Key Takeaways
• References

Understanding Mechanically Lined Pipe (MLP)

Definition and Structure

Mechanically Lined Pipe (MLP) is a composite pipeline solution featuring a carbon steel outer carrier pipe for structural integrity and a corrosion‑resistant alloy (CRA) inner liner. The liner is mechanically bonded—typically via hydroforming or expansion—to the host pipe, ensuring tight contact and performance under harsh conditions.

Comparison with CRA Clad and Weld Overlay Pipe

MLPs offer similar corrosion protection to CRA-clad pipes but achieve this with a lower material cost and optimized design. According to testing, MLPs can match CRA-clad corrosion resistance, even though the bonding is mechanical rather than metallurgical (ASME Digital Collection). Compared to weld overlay, MLPs are lighter, faster to produce, and more economical over long lengths while still delivering effective corrosion protection.

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The Role of MLP in Subsea Oil & Gas Applications

Corrosion Challenges in Subsea Environments

Subsea pipelines face aggressive environments involving seawater, CO₂, H₂S, and elevated pressures. CRA liners in MLP protect against internal corrosion and help preserve pipeline integrity over decades. This makes MLP particularly suited for transporting corrosive fluids in subsea flowlines and risers.

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Installation Methods and Technical Considerations

S-Lay, J-Lay, Reel-Lay Techniques

MLP pipes are compatible with major pipelaying methods including S-lay, J-lay, and reel-lay (proclad.com). In the case of MLPs, ensuring the liner-carrier integrity during reel-lay spooling and unspooling is critical; tight manufacturing tolerances and strong bonding prevent debonding and fatigue issues (proclad.com).

Qualification, Testing, and Fatigue Performance

Full-scale testing confirms MLPs meet or exceed fatigue requirements for subsea service. Studies show MLPs satisfy DNV class D fatigue curves even after reel-lay qualification, with effective non-destructive inspections revealing minimal issue rates (proclad.com). Design features like the “triple point” are optimized to reduce stress accumulation at liner transitions (ASME Digital Collection).

Advantages of MLP for Operators and EPCs

Cost and Material Savings

MLPs can offer up to 40% cost savings compared to solid CRA pipes thanks to the cost-effective use of a carbon steel outer pipe with a thinner CRA liner. High-volume manufacturers like Proclad can produce up to 24 km per month, reducing lead times and streamlining supply chains.

Performance and Safety Benefits

With 100% residual bonding, MLPs display robust mechanical integrity and fatigue resistance (proclad.com). Tight manufacturing tolerances—such as precise ID, ovality, and triple point realm control—ensure installation safety and performance in high-stress subsea environments (Stainless Steel World).

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Future Outlook for MLP in the Energy Transition

Emerging Standards and R&D

MLP production adheres to API 5LC, 5LD, and DNV-ST-F101 standards (proclad.com). Ongoing studies are evaluating collapse pressure models and fatigue behavior to further refine design standards (ScienceDirect).

Potential Beyond Oil & Gas (Hydrogen, CCS)

MLPs are also being considered for CCUS and hydrogen applications due to their corrosion resistance and flexible material configurations (proclad.com).

Conclusion – Key Takeaways

• MLP balances structural strength and corrosion resistance cost-effectively.
• Suitable and proven in subsea oil & gas, with reel-lay compatibility and DNV-approved specs.
• Substantial cost savings, high production throughput, and reliable fatigue performance.
• High-quality manufacturing and tight tolerances ensure installation reliability.
• Versatile across offshore energy sectors, with promising applications in CCS and hydrogen transport.

References

1. Proclad. “Guide to Mechanically Lined Pipe.” October 23, 2024. (proclad.com)
2. Proclad. Mechanically Lined Pipe (MLP). (proclad.com)
3. ASME Digital Collection. “Full-Scale Testing on Corrosion Resistant Alloy‑…” June 9, 2024. (ASME Digital Collection)
4. OnePetro OTC Brasil. “Mechanically Lined Pipe MLP with Improved Fatigue…” 2019. (OnePetro)
5. ScienceDirect. Reda, A. (2024). CRA Clad Pipes vs. MLP Selection. (ScienceDirect)
6. ScienceDirect. Yuan, L. (2022). On the buckling of MLP under onshore/offshore. (ScienceDirect)
7. ScienceDirect. Yuan, L. (2023). Collapse pressure prediction of MLP. (ScienceDirect)
8. ASME. “Full‑Scale Testing of Corrosion Resistant Alloy…” (tripoint fatigue). (ASME Digital Collection)

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