Corrosion Science and Engineering in Action in Climate Change Technology

Carbon capture and storage is a technology that could be crucial in our attempts to slow the effects of climate change. The methodology is relatively simple:

• Carbon dioxide (CO₂) is captured from power plants and industrial sources before it is released into the atmosphere.
• Captured CO₂ is then transported and stored underground in geological formations, such as depleted oil and gas reservoirs, deep saline aquifers, and coal seams that can no longer be mined.

This process can significantly reduce CO₂ emissions released into the atmosphere from power generation and heavy industry.

However, the long-term storage of CO₂ in underground reservoirs poses many technical challenges. One of these is corrosion management of the pipelines used to transport CO_2.to carbon capture and storage (CCS) facilities.

Why corrosion management is crucial in carbon capture and transportation

Pipelines are often made of materials that are vulnerable to corrosion, and, if left under-managed, this can lead to various problems. For example, corrosion can cause equipment to leak or fail, potentially releasing the captured carbon dioxide into the environment.

Effective corrosion management helps to ensure the safe and reliable operation of the system, while also protecting the environment. By proactively managing corrosion, the efficiency and longevity of the system can be maintained, reducing the costs and potential risks associated with equipment failure – including the risks to the environment and human health.

Therefore, corrosion management should be considered as a crucial aspect of carbon capture and transportation systems.

What causes corrosion in CCS facilities and transportation?

Corrosion in CO₂ pipelines is somewhat different from the conventional CO₂ corrosion that occurs during the transportation of oil and gas. In these systems water mixed with oil is unavoidable – it’s in the ground with the oil. CO₂ is also usually present in large quantities because oil and gas fields tend to contain CO₂. During transportation, the CO₂ dissolves in the water and acidifies it. This can lead to corrosion of the metallic material from which the pipeline is made.

With CCS on the other hand, we are normally transporting CO₂ in its dense phase – either as a liquid or as a ‘supercritical’ fluid which is not quite a liquid and not quite a gas (a fluid with a mixture of the two properties). From a corrosion perspective, if we could ensure that we only have pure dense-phase CO₂ in the pipeline (with no water or other impurities present), there would be no corrosion.

The corrosion problem exists because of the way in which the CO₂ is produced before being delivered to the pipeline or other transportation system. For example, CO₂ generated by the burning of a fossil fuel in a power station is captured in a solvent and later released from the solvent in a secondary step and pumped into the pipeline. Impurities are created during this process. Sulphur oxides, nitrogen oxides, carbon monoxide, hydrogen sulphide, and water can all be present. It’s the water that can initiate the corrosion problem.

How does corrosion occur in CCS transportation?

When water condenses in the pipeline, other impurities will dissolve in the water, as well as the CO₂.

“The presence of other impurities can increase the likelihood of corrosive phases forming, either by reducing the water solubility or via chemical reactions between different impurities,” explains Gareth Hinds of the National Physical Laboratory (NPL). “Acid dropout is the most significant concern for pipeline operators, whereby highly corrosive aqueous phases, such as nitric and sulphuric acid, can form as a result of reactions between water, NOx, SOx, O₂ and H₂S impurities.”

Corrosion Management Strategies in CCS Facilities

In oil and gas installations and transportation, corrosion is quite predictable. It can be managed with inhibitors, coatings and cathodic protection. It is not so straightforward in CCS facilities and pipelines.

In dense-phase CO₂, the concern is the impurities. It is difficult to predict where these will condense, nor do we know what reactions will happen between the impurities.

In short, it is crucial to consider corrosion as a priority in both the design and operation of CCS pipelines. Any leak can lead to many issues, including potential loss of life where ground level CO₂ concentration rises above 100,000 ppm.

Corrosion management in CCS transportation is largely concerned with specifying impurity limits at the inlet to the pipeline – and maintaining these for the life of the pipeline. Therefore, the industry must focus on ensuring impurities are kept within limits that don’t propagate bulk phase reactions and form aqueous phases.

The future of corrosion management in CCS facilities

As long ago as 2014, the Materials Performance magazine published an article discussing the pipeline corrosion issues related to carbon capture, transportation, and storage. It explored a range of potential advances in corrosion management in CCS, including:

• Using sealants made from inorganic materials
• Continuing research into the compatibility of non-metallic materials (polymers, ceramics, and plastics) in dense phase CO₂ containing impurities
• Evaluation and testing of suitable corrosion inhibitors

There has been much work into all such considerations, but the work is not yet concluded. Indeed, corrosion is such a complex subject that research and discovery is likely to have no end. Writing in Corrosion Management Magazine, Gareth Hinds notes some of the corrosion management issues that the CCS industry faces:

“Assessment of the risk of water and acid dropout in CO₂ pipelines due to the presence of multiple impurities is a complex process, which requires an understanding of the thermodynamics of fluid composition, the impact of operating temperature and pressure variations (including potential upset conditions) and interactions between impurities. The requirements for ship transport are typically more stringent than those for pipelines, with lowest temperatures representing the worst-case scenario.

Published corrosion rate data in the open literature should be treated with caution due to challenges in control of test parameters and the high degree of uncertainty around the correlation between laboratory test data and real-world application. Combined with the relative lack of service experience in transport of CO₂ captured from a range of industrial sources, this often leads to a degree of over-conservatism in materials selection.

For CO₂ specifications, thresholds in relation to acid drop out are set based on limited available data (often not lower than 25°C) and are therefore likely not conservative enough. The development of reliable standard test methods that are more representative of service conditions will go a long way towards addressing these issues.”

The bottom line – It’s a question of delivering sustainability

There is no simple answer to managing corrosion in CCS facilities and pipelines more effectively. There are no internationally agreed specifications for CO₂ composition during pipeline transport, despite general industry guidance on impurity limits. Currently, the responsibility lies with the pipeline operator.

The Institute of Corrosion is at the forefront of this conversation on the international stage. We understand that the corrosion industry – engineering and academia – has a great opportunity and responsibility to deliver the knowledge and solutions required to create a more sustainable planet.

The Institute of Corrosion, partnering with the North of England Institute of Mining and Mechanical Engineers, is hosting a not-to-be-missed conference on Integrity Engineering for a Sustainable Future. Delegates will have the opportunity to learn more about the advances being made in corrosion management across the energy industry, as well as networking with some of the most prominent experts involved in the corrosion conversation.

To learn more about how the Institute of Corrosion is helping to combat climate change, and how you can get involved, please email the Institute of Corrosion.