Full-Scale Testing on CRA Mechanically Lined Pipes (MLP) for Submarine Pipeline
The specification of Corrosion-Resistant Alloy (CRA) materials for subsea pipelines is indeed crucial, particularly when dealing with environments where carbon steel may not be a viable option due to technical, operational, or economic constraints. Corrosion, exacerbated by high temperatures and elevated partial pressures of carbon dioxide, remains a significant challenge across industries worldwide. The presence of hydrogen sulfide further complicates the selection of suitable CRA materials.
Among the various types of CRA subsea pipes, three are commonly used: solid CRA pipes, CRA-clad (metallurgically bonded) pipes, and CRA Mechanically Lined Pipes (MLP). Of these, CRA-MLPs are often considered the most cost-effective option. CRA-MLPs have been employed in the oil and gas industry for over four decades, providing a reliable solution for transporting corrosive hydrocarbons. When considering overall lifecycle costs, CRA-MLPs frequently present a more economical choice compared to CRA-clad and solid CRA pipes.
Advantages of CRA-MLPs Compared to CRA-Clad Pipes:
- Improved Fit-Up: The tailor-made ends of CRA-MLPs result in superior installability and reliability during pipeline construction.
- Wider Choice of CRA Materials: CRA-MLPs offer a broader selection of CRA materials, unlike clad plates, which are limited by heat treatment requirements. The carbon steel component in MLPs is also optimally heat-treated.
- Better Diameter to Wall Thickness Ratios: CRA-MLPs accommodate a wider range of diameter-to-wall thickness ratios compared to CRA-clad pipes, which are formed through JCO/UOE processes.
- Reduced CO2 Emissions: The production of CRA-MLPs generates nearly 50% less CO2 emissions compared to similar CRA-clad pipes, and the materials are easily recyclable.
- Shorter Lead Times: CRA-MLPs typically have shorter lead times than CRA-clad or solid CRA pipes.
- Significant Cost Savings: CRA-MLPs can provide potential cost savings of approximately 40-50% compared to solid CRA pipes.
Full-Scale Testing by Cladtek
Cladtek, recognized as the world’s largest CRA weld overlay cladding company and a leading global supplier of CRA Mechanically Lined Pipe (MLP), has conducted extensive testing on CRA-MLPs to ensure their performance under real-world conditions. In one notable test, a 273.1 mm outside diameter CRA-MLP with a 3 mm liner underwent full-scale fatigue resonance testing at the TWI facility.
The testing was designed to replicate the stresses experienced by the triple point, a critical area in MLPs, throughout the pipe’s lifecycle. Periodic inspections during the testing process were carried out to monitor for any potential cracking of the liner before it could reach the backing steel.
This testing underscores the robustness and reliability of CRA-MLPs in demanding subsea environments, highlighting their suitability as a cost-effective and environmentally friendly alternative to CRA-clad and solid CRA pipes.
