Overview

Pipelines play a vital role in CCS, providing a reliable means of transporting CO₂ from emission sources to their intended storage sites. But as CCS projects increase, a significantly greater number of both onshore and offshore pipelines is going to be needed to meet future CO₂ transportation demands and this will require both innovative technologies and specialist pipeline expertise. 

This article explores the technical challenges and design considerations involved in CO₂ pipelines, the steps involved in converting oil and gas pipes for CO₂, the use of alternative materials, and how digital twin technology can benefit pipeline integrity management.

Advantages of Pipelines for CO₂ Transportation

Pipelines are the most common method for transporting captured CO₂ thanks to their ability to handle large volumes safely and efficiently. Unlike trucks, rail or ships, pipelines offer better capacity and continuous flow as well as lower operational costs and reduced risk of accidents. 

Pipelines are a mature and well understood technology that can be widely deployed both onshore and offshore, making them extremely versatile for CCS projects. Additionally, pipelines benefit from economies of scale, robust monitoring and leak detection systems, and minimal environmental impact. They can be adapted and scaled up to meet increasing demand and future growth positioning them as a critical component for CO₂ transportation as CCS projects expand.

Current pipeline infrastructure

Currently, there are over 5,000 miles of onshore and offshore CO₂ pipelines in the US, compared to 260,000 miles of hazardous liquid pipelines, and 3 million miles of natural gas pipelines.

Onshore pipelines are primarily used to transport CO₂ from capture facilities, such as power plants or industrial sites, to onshore buffer storage locations. These pipelines are crucial for the initial stage of CO₂ transport, ensuring that the captured CO₂ is safely and efficiently moved to a storage site where it can be temporarily held before further transportation.

Offshore pipelines extend the transportation network by carrying CO₂ from the onshore buffer storage locations to offshore injection points. These injection points are typically located in geological formations beneath the seabed, such as depleted oil and gas fields or saline aquifers, where the CO₂ can be securely stored. Offshore pipelines are engineered to withstand the harsh marine environment and the high pressures required for deep-sea injection.

Together, onshore and offshore pipelines form an integrated CO₂ transportation network that facilitates the movement of CO₂ from its point of capture to its final storage location. This network is essential for large-scale CCS projects, however, it has been estimated that achieving economy-wide net-zero emissions by 2050 will require an additional 30,000 to 90,000 miles of CO₂ pipelines. The development of new pipeline infrastructure and the adoption of innovative technologies will be critical in expanding pipeline networks to meet future needs.

Pipeline Challenges and Considerations

Use of existing or new pipelines for CCS transportation of CO₂, however, presents several key challenges and important issues to be aware of:

• Fracture Control.  CO₂ pipelines must be designed to prevent running ductile fractures, which can propagate rapidly and cause significant damage. This requires careful selection of materials and design standards.

• Corrosion and Material Selection.  The presence of impurities in CO₂ like water, hydrogen sulphide, and oxygen can lead to corrosion. Selecting materials that can withstand these impurities is crucial.  Protective coatings and cathodic protection systems are often used to prevent external corrosion.

• Flow Assurance and Operational Issues.  CO₂ can exist in gas, liquid, or supercritical states, and its phase behaviour can change with temperature and pressure variations. Ensuring stable flow and avoiding phase transitions that could cause blockages, e.g. hydrates, or pressure drops is a key challenge.  Managing temperature and pressure to prevent hydrate formation is essential.

• Impurity Control.  Impurities in the CO₂ can affect the density, viscosity, and other properties of CO₂, complicating the design and operation of the pipeline.  Before transportation, CO₂ often needs to be purified to remove impurities, which adds complexity and cost to the process.

• Safety and Environmental Considerations.  Implementing reliable leak detection systems is critical to ensure the safety of CO₂ pipelines. This includes both monitoring technology and emergency response plans. Designing pipelines to minimize environmental disruption during construction and operation is also a significant consideration.

• Repurposing Existing Pipelines.  Existing pipelines may need to be repurposed for CO₂ transport. This involves assessing their compatibility with CO₂, including pressure ratings and material suitability.  Necessary upgrades and modifications to existing infrastructure can be costly and technically challenging.

Converting a Carbon Steel Oil and Gas Pipeline to Transport CO₂

As there are many miles of existing pipelines, the conversion of existing pipelines to transport CO₂ is an attractive and viable option but there are some important considerations to ensure safety and efficiency:

1. Material Compatibility: Assessing the pipeline material to ensure it can handle CO₂ is an essential first step. Carbon steel is generally suitable, but it should be checked for resistance to CO₂-induced corrosion.

2. Pressure and Temperature Adjustments: CO₂ is typically transported in a supercritical state, which requires the pipeline to handle higher pressures and temperatures. This may require reinforcing the pipeline or adjusting operating conditions.

3. Fracture Control: Implementing a fracture control strategy will help prevent and manage potential fractures. This will also involve evaluating the pipeline’s toughness and implementing measures to control crack propagation.

4. Coatings and Linings: Appling protective coatings or linings to the interior of the pipeline will prevent corrosion and ensure long-term durability.

5. Compression and Pumping Stations: Installing or upgrading compression and pumping stations to handle the supercritical CO₂ will ensure it remains in the desired state throughout transportation.

6. Safety and Monitoring Systems: Enhancing safety and monitoring systems to detect leaks is key to ensuring the integrity of the pipeline. This can include installing sensors and implementing regular inspection protocols.

By following these steps, an existing oil and gas pipeline can be effectively converted to transport CO₂, supporting carbon capture and storage efforts.

Benefits of Composite Materials for Pipelines

The production of steel is a carbon-intensive process, significantly contributing to global greenhouse gas emissions.  To improve sustainability, one promising alternative is the use of composite pipe. Composite materials are highly resistant to corrosion, are lightweight and flexible, and have improved flow capacity. This means that pipelines made from composite materials require less maintenance than steel pipelines and have a longer service life.

Another advantage of composite pipes is their ability to be pulled through existing steel pipelines. Repurposing aging steel pipelines to transport different materials can reduce the need for new rights of way and associated permits, thereby reducing environmental impact and cost.

Installation of composite pipes is also more efficient. They can be installed four times faster than steel pipes, require only one-third of the labor, and have significantly lower operating costs. The continuous structure of composite pipes allows for longer sections of pipe to be produced, resulting in fewer joints and welds, which further enhances their reliability and reduces potential leak points.

The use of composite pipe in pipeline construction is expected to continue to grow as technological advancements make these materials even more reliable and cost-effective. 

High-Density Polyethylene (HDPE) for pipeline use

High-Density Polyethylene (HDPE) is a thermo-plastic material that is gaining recognition for its potential in CO₂ pipeline applications. It offers excellent resistance to corrosion, flexibility and durability making it beneficial for transporting CO₂, especially in environments where corrosion is a concern. However, unlike carbon steel, HDPE is only suitable for lower-pressure applications. 

Compression fit liner pipe is well suited for protecting CO₂ pipelines, ensuring complete protection from the severe corrosion associated with CO₂ gathering.  Using HDPE as a liner leverages the best properties of both materials, making it a practical solution for CO₂ transport including for applications where corrosion and pressure are concerns.

The use of HDPE for CO₂ pipelines offers numerous advantages, including superior corrosion resistance, flexibility, cost-effective installation and maintenance, and environmental benefits such as a lower carbon footprint and recyclability. As technological advancements continue to enhance the material’s properties, HDPE is likely to play an increasingly important role in the future of CO₂ transport.

Digital Twin Technology in CO₂ Pipelines

With the rapid development of AI, digital pipeline and digital twin technology have become invaluable tools for pipeline safety monitoring, integrity, maintenance determination, and fatigue assessments.

Digital twin technology leverages physical models and sensors to gather pipeline data, and uses an algorithm to predict the life cycle of the pipeline. The advantages of digital twin for CO₂ pipelines include:

• Real-Time Monitoring:  Digital twins create a virtual replica of the physical pipeline, allowing operators to monitor conditions in real-time and make informed decisions.

• Simulation and Testing:  Operators can use digital twins to simulate different scenarios, such as pressure changes or potential failures, to test responses and improve pipeline design and operation.

• Predictive Analytics:  By integrating data from sensors and historical records, digital twins can predict future performance and maintenance needs, enhancing reliability and reducing costs.

• Enhanced Safety:  Digital twins help identify potential risks and develop strategies to mitigate them, ensuring the safe transport of CO₂.

Expert Assessment for Successful Repurposing Pipelines

By expanding CO₂ pipeline networks, we can make significant strides toward achieving global net-zero emissions and mitigating the impacts of climate change. However, we need to invest in innovative strategies and technologies to develop the infrastructure.

Successfully converting carbon steel oil and gas pipelines to transport CO₂ requires in-depth knowledge of flow assurance, material selection, pipeline design, pipeline integrity and digital twin technology. Proper assessment of existing pipelines is crucial to determine their suitability for CO₂ transportation.

 2H offers comprehensive analysis services with unparalleled expertise in assessing pipeline suitability, conducting integrity assessments, and designing pipelines.  Our extensive experience, deep domain knowledge, and advanced analytical capabilities enable us to deliver assessments that maximise value for our clients, ensuring the successful repurposing of pipelines for their CCS initiatives.