Carbon Dioxide Pipeline Transportation – Our Contribution for Carbon Neutrality

Corrosion control and material selection are essential for the safe and reliable operation of CO₂ transmission pipelines. Pure dry CO₂ does not corrode carbon steel, but impurities and moisture can greatly increase corrosion rates. Even trace amounts of water can condense in cooler sections during pressure drops or shutdowns, forming an aqueous phase. When CO₂ dissolves in this water, the pH decreases and carbonic acid forms, causing uniform wall thinning or pitting. Contaminants such as oxygen (O₂), sulfur dioxide (SO₂), nitrogen oxides (NO_X), and hydrogen sulfide (H₂S) further change the condensed phase chemistry, creating aggressive environments that promote localized corrosion or sulfide stress cracking. However, removing or reducing some of these impurities can be either impractical or prohibitively costly, depending on the source gas composition and process configuration.

Effective mitigation depends on proper material selection and strict control of fluid quality. Pipeline steels must be specified according to operating pressure, temperature, impurity concentration, and dehydration efficiency. Internal coatings and corrosion inhibitors can provide additional protection, but cannot replace adequate dehydration and impurity management. Material choice must also account for fracture toughness, weldability, and low temperature behavior since decompression can cause rapid cooling. Steels should meet corrosion resistance and toughness requirements, including suitable ductile to brittle transition temperatures and Charpy impact energy levels. Achieving long-term integrity requires an integrated understanding of fluid chemistry, thermodynamics, and metallurgy to ensure safe and durable CO₂ transport.

Fracture control is a critical aspect of CO₂ pipeline design and safety management because of the unique thermodynamic behavior of CO₂ and the severe consequences of rupture. Unlike natural gas, CO₂ is usually transported in the dense phase or supercritical state, where decompression behavior is very different. During depressurization, CO₂ experiences rapid phase change and expansion, which strongly influences crack propagation speed and the ability of the pipeline to arrest a running fracture.

Fracture control strategies must account for material toughness, operating pressure, and the decompression characteristics of CO₂ mixtures that may include nitrogen, oxygen, hydrogen sulfide, or methane. These impurities affect decompression wave speed and can shift the fracture arrest boundary, making natural gas design models unreliable for CO₂ service. Effective control requires a combined understanding of thermodynamics, fracture mechanics, and material performance to ensure that, in the event of a release, any fracture remains contained and does not propagate through the pipeline system.

Hydraulic analysis is critical to the design and operation of CO₂ transmission pipelines, ensuring safe and efficient transport under changing thermodynamic and flow conditions. CO₂ is commonly transported in the dense phase or supercritical region, where its behavior differs from natural gas. Near the critical point, pressure and temperature relationships are highly nonlinear, so accurate thermophysical modeling is required to predict pressure drop, density, and velocity. Small temperature changes can cause large density variations, creating gaseous or two-phase flow that affects frictional losses and stability. Reliable analysis depends on equations of state that accurately describe CO₂ mixtures containing impurities such as nitrogen, oxygen, methane, and hydrogen sulfide.

Design and operation rely on steady and transient hydraulic modeling to determine pressure profiles, compressor or pump spacing, and flow assurance parameters under normal and upset conditions. Steady analysis evaluates frictional, elevation, and thermal pressure losses, while transient analysis captures rapid changes during start-up, shutdown, or depressurization. Maintaining the fluid within its phase envelope is essential to prevent vaporization or condensation, and managing transients helps avoid surges, flow reversals, and control instability. Overall, hydraulic analysis combines thermodynamics, fluid dynamics, and safety engineering to ensure reliable performance and prevent issues such as solid CO₂ or hydrate formation and excessive pressure fluctuations.

Risk and safety management are fundamental in the design, construction, and operation of CO₂ transmission pipelines to prevent incidents, limit consequences, and protect people and the environment. CO₂ introduces particular challenges compared with natural gas because of its asphyxiant properties, high density, and rapid phase changes during release. A leak or rupture can cause gas to collect in low areas and displace oxygen, creating serious suffocation hazards. An effective safety framework must combine preventive and mitigative measures through systematic hazard identification and quantitative risk assessment. 

Typical failure mechanisms such as corrosion, third-party interference, material flaws, and overpressure are assessed for likelihood and consequence to define safe setback distances and emergency planning zones. These assessments inform risk-based design decisions on materials, wall thickness, valve spacing, and isolation strategies to reduce release volumes and enable fast containment. Ultimately, effective risk and safety management rely on the integration of sound engineering design, inspection programs, monitoring technologies, and human performance to ensure reliable and secure CO₂ transport under all conditions.

In-line inspection of CO₂ pipelines is both essential and achievable, though it involves specific challenges arising from the physical and thermodynamic properties of the transported fluid. At ROSEN, we have developed and implemented advanced inspection technologies designed for these conditions, building a proven record in CO₂ pipeline integrity assessment. Effective fracture toughness testing also depends on detailed knowledge of the material population, which enables more targeted sampling and ensures that testing focuses on the most representative pipe groups.

CO₂ systems may experience time-dependent degradation mechanisms that can develop even within short operating periods. Continuous monitoring is therefore necessary to confirm the effectiveness of control measures. High-resolution metal loss and crack detection tools, including Magnetic Flux Leakage (MFL) and Electromagnetic Acoustic Transducer (EMAT) technologies, are vital for early detection and precise sizing of metal loss and crack-like features. Combined, these inspection and monitoring methods deliver a comprehensive framework for maintaining the integrity, safety, and reliability of CO₂ transmission pipelines throughout their service life.