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Risks of Converting Natural Gas Pipelines to CO2 Service

Photo of Paul Blackburn giving a presentation on Keystone Pipeline System.

By Paul Blackburn

News March 24, 2022

Tagged Carbon Pipelines, CCS, CO2 Pipelines

By Paul Blackburn, Bold Alliance


The carbon pipeline projects that are grabbing the most media attention involve the construction of new pipelines across several Midwest states. However, we are also hearing about the possibility of converting existing oil and natural gas pipelines to ship carbon dioxide (CO2) as well. Communities and landowners should be aware of these conversion pipeline proposals because the risks of living next door to a CO2 pipeline are very different that an oil or gas pipeline.

As landowners and citizens begin to understand the risks around carbon pipelines, we are working hard to publish information that citizens can use as they make decisions about their own land and tribal and local governments can use as they consider zoning, emergency response planning, and other measures to protect their communities.

Although federal law regulates all aspects of the conversion of a natural gas pipeline to CO2 service, this does not mean that there is nothing state and county governments can do to protect citizens and their properties around pipeline laws and zoning.

In particular, county commissions should consider land use and zoning controls, emergency planning and other means to ensure that carbon pipelines do not threaten the land and water or the lives and health of citizens.

Because carbon pipelines are new, state and federal laws are catching up to where industry wants to go, and how fast they want to build, to take advantage of available tax credits (e.g. 45Q credits which started in 2008 and were then expanded in 2018) which make these pipelines commercially feasible but also a risky proposition since these tax credits can also be removed by Congress at any time.

We caution all county and state governments to not take the industry only at their word. Experts and citizens on all sides of this issue should be listened to since it is always those that live in the community that will be there long after any project is built.

Converting a Gas or Oil Pipeline to a CO2 Pipeline

At present, there are few if any pipelines that ship CO2 as a gas, but it is entirely possible that a natural gas or oil pipeline could be converted to a CO2 gas pipeline. For safety reasons, pipelines that ship CO2 as a gas cannot operate at pressures above 1,070 psi, which as discussed below, is well within the pressure range of many existing natural gas and oil pipelines. So, even if an existing natural gas or oil pipeline is not strong enough to ship supercritical fluid CO2, then it likely could be used to ship CO2 gas.

Currently, the Federal Energy Regulatory Commission (FERC) can decide if a natural gas pipeline may be withdrawn from use for shipping natural gas, but once FERC grants a withdrawal from service, its jurisdiction ends, because it has no jurisdiction over carbon pipelines. In contrast, no federal agency regulates whether an oil pipeline may be withdrawn from service.

In addition, the U.S. Pipeline and Hazardous Materials Safety Administration (PHMSA) regulates the safety of natural gas, oil and supercritical fluid CO2 pipelines, but does not regulate the safety of a pipeline when CO2 (carbon) is pumped through it as a gas. Congress directed that PHMSA regulate CO2 gas pipelines, but PHMSA has failed to issue safety standards for these pipelines. Since PHMSA has jurisdiction over the safety of CO2 gas pipelines, but has failed to implement this jurisdiction, it is likely that state and local governments could not step into this gap to regulate CO2 gas pipeline safety.

Therefore, if a natural gas or oil pipeline is converted to ship CO2 gas, it might not be subject to any federal or state pipeline safety standards.

Engineering and Safety Concerns

DNV GL, an international standard setting organization, produced two recent general reports on behalf of the oil & gas industry, which identified the following concerns with repurposing natural gas pipelines for use in transporting CO2:

  • Insufficient pipe strength: Liquid CO2 pipelines must operate above the “critical point” pressure of 1,070 psig, because if the pressure falls below this point the CO2 will change phase to a gas, which creates a pressure spike and may lead to a rupture. Many natural gas pipelines are not capable of operating at such high pressures.
  • Insufficient pipe steel toughness: If a liquid CO2 pipeline is not made from sufficiently tough steel, it will be susceptible to “running ductile fractures” (RDF). A RDF may happen nearly instantly following an initial pipeline rupture, as some of the CO2 will convert from a liquid to a gas inside the pipeline and tear the pipe open next to the rupture site, but then more liquid CO2 will convert to a gas and more pipe will be torn open, and this explosive process can continue for an indeterminate distance along the pipe at more than 100 meters per second. Existing natural gas pipelines may not have sufficiently tough steel to stop running ductile fractures.
  • Incompatibility of CO2 with non-metallic pipeline components: Liquid CO2 is an excellent solvent, to the point that it may dissolve non-metallic pipeline components, such as seals, gaskets, valves and lubricants. Existing natural gas pipelines may include components that may be dissolved by CO2 and result in leaks, ruptures, and damage to pipeline equipment.
  • Risk to adjacent communities: Whereas the hazard zone for oil and gas pipelines is known, little is known about the hazard zone for CO2 pipelines, for which the zone will likely be much larger. When an oil pipeline ruptures, the primary risk is of an oil spill into water, because the water will disperse the oil and cause substantial environmental harm. The potential spread of oil on water is well understood and companies are generally required to model this spread as part of their oil spill response plans. Oil pipeline ruptures rarely put human life directly and immediately at risk (the Olympic gasoline pipeline rupture being a notable exception). The hazard zone for natural gas pipeline ruptures is based on the fact that they typically explode on rupture, and the force of the explosion and subsequent fires can kill and injure people and properties. Again, the hazard zone for natural gas pipelines can be estimated using readily available computer models and is rarely more than 1,500 feet, and then only for the very largest natural gas pipelines.In contrast, CO2 pipelines are dangerous because the very large volume of CO2 they may release can asphyxiate and intoxicate people and animals, and dangerous CO2 levels may spread more than a mile from the rupture site. For example, the Feb 22, 2020, CO2 pipeline rupture near Satartia, MS, was a mile away from the town yet caused some individuals in it to pass out and many to become disoriented (first responders described victims acting like “zombies”). Intoxication is dangerous because it could lead to life-threatening accidents. Although computer models exist to predict the size of the danger zone for CO2 pipelines, these models are still being improved and to our knowledge neither federal and state regulators nor the pipeline industry have developed a methodology for estimating the danger zone given pipeline size and length, weather, and topography. Since CO2 pipelines may have a much larger hazard area than other types of pipelines and could cause mass-casualty events, it may not be appropriate to convert an existing natural gas pipelines that passes near sensitive locations, such as hospitals, senior facilities, schools, etc.
  • Insufficient maintenance records and inspection history: Since CO2 pipelines usually require stronger steel and operate under greater pressure, it is vital that the weaknesses of used pipelines be well understood before conversion to CO2 service. A full understanding of a natural gas pipeline’s wear and tear is possible only if its owner has kept adequate maintenance records and inspection data. Not all natural gas pipeline owner keep adequate records and data.
  • Need for large-scale repairs and modifications: As part of a conversion process, a natural gas pipeline may need to be repaired and/or be modified to ensure safe operation. For example, it may need “crack arrestors” that can stop RDF to be installed along the pipeline, replacement of parts not compatible with liquid CO2, and/or repair of weakened pipe segments and other components. Such modifications and repairs may be expensive and/or time consuming, yet a failure to undertake such work without great care could result in a catastrophic rupture.

Conversion of an existing natural gas or oil pipelines to CO2 gas service would likely face a number of technical and safety challenges, but we should not forget the people who would live near a converted pipeline as they may be kept in the dark about the new risks they face.

The Energy Industry Has Concerns

In its three-volume treatise on carbon capture and sequestration (CCS), the National Petroleum Council discusses the potential for repurposing natural gas pipelines and finds that this is “not a practical option.” (National Petroleum Council), Meeting the Dual Challenge, A Roadmap to At-Scale Deployment of CCUS (Dec 2019; updated Mar 2021). In chapter 6 on pages 6-10 to 6-11 this report states:

Is Repurposing Natural Gas Pipelines an Option?

“The use of an existing natural gas pipeline is not a practical option for CO2 transport for large flow rates of 1 BSCF/D (19 Mtpa) or more over long distances of hundreds of miles and more. Existing natural gas pipelines have a maximum pressure rating of 1,480 psig, which are defined by the American National Standards Institute (ANSI) as Class 600 pipelines. A pipeline built for CO2 service is designed for 2,200 psig, which is an ANSI Class 900 pipeline.There are a few examples of an existing pipeline that was converted to CO2 service for lower flow rates and/or shorter distances (less than 100 miles). For longer distances, however, the lower rating of an existing gas pipeline requires many more pump stations along the route compared with a pipeline built for CO2 service.

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The life-cycle analysis showed that a repurposed pipeline was, at best, equal in cost to a new pipeline and would more likely cost more than a new pipeline that is designed for CO 2 transport. The likelihood of identifying a viable existing pipeline for a long transport route is low.Even if one was located, the large number of pump stations required would not be operationally practical for a long-distance pipeline.

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To answer the question about whether repurposing a natural gas pipeline for use with CO 2 is an option, the answer is that it depends on several factors. If the goal is to transport large volumes of CO 2 100 miles or more, then the lower pressure rating of existing natural gas pipelines makes it impractical to repurpose them for use with CO2. However, natural gas pipelines could be repurposed if the diameters are large enough and throughput volumes are optimized for a tighter operating range. Each pipeline’s potential should be studied based on the project-specific conditions being evaluated and verified that the conversion of the line from natural gas service to CO 2 services complies with PHMSA-Part 195 regulations.

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For this reason, it is not anticipated that repurposing existing natural gas pipelines would significantly help develop an expanded CO2 pipeline network in the United States. There may be some short sections of pipeline, or pipeline laterals, that could use a repurposed natural gas line, but project-specific engineering would be required to evaluate if this would be technically and economically viable.”

This reasoning helps explain why extensive new carbon pipeline sequestration systems, such as those proposed by Summit and Navigator, are comprised entirely of new pipelines. Even if existing pipelines traveled between CO2 emitters and carbon sequestration sites, which few do, using relatively low pressure existing natural gas and oil pipelines to ship CO2 as a gas for long distances at high volumes is likely not economical. This being said, the National Petroleum Council found that conversions of existing pipelines may be possible in particular circumstances. For example, an existing pipeline might be used to transport CO2 gas relatively short distances from an individual emitter to a regional CO2 collection hub where the CO2 gas would be further compressed for long distance transportation in a new high-pressure pipeline. Also, conversion might be practical to transport CO2 gas from an emitter to an enhanced oil recovery project that seeks to wring more oil out of an old oil field. Given the many existing natural gas and oil pipelines in oil producing states with large legacy fields, such as Texas, Louisiana, and Oklahoma, conversion of some of these old pipelines for use in enhanced oil recovery is possible. As oil and natural gas fields are depleted and/or dependence on oil and natural gas decline, we should expect that owners of vintage pipelines will seek new commercial purposes for their stranded assets, including transportation of CO2 gas.

Federal Pipeline Conversion Guidance

PHMSA Advisory Bulletin ADB-2014-04 contains general guidance for the repurposing of a pipeline to ship a different product, for example the conversion of a natural gas pipeline to oil service. However, this document does not have the force of federal law and does not specifically address the unique risks posed by CO2 pipelines. Instead, it mostly reminds operators of existing federal pipeline safety regulations and says that operators are “strongly encouraged” to submit a comprehensive written conversion plan. It states that operators “should be prepared” to demonstrate how they adopted their operations and maintenance programs, integrity management plans, emergency plans, control room management, operator qualification training, emergency responder training, public awareness, spill response, maps and records, and integrity management programs and plans, but does not itself require such actions. This “advisory” bulletin does not itself contain any new safety standards nor does it specifically address the unique challenges of conversion to CO2 gas service.

But, here’s the rub. Since PHMSA has no safety standards applicable to CO2 gas pipelines, the PHMSA Advisory Bulletin’s recommendations on how to comply with existing federal safety regulations is legally meaningless, because after conversion none of the existing PHMSA safety standards would apply. The owner of an existing natural gas or oil pipeline could convert it to CO2 gas service and ignore ADB-2014-04.


The primary reasons why the owner of an existing natural gas or oil pipeline might convert it to CO2 gas service is to take advantage of the generous federal CCS tax credits (e.g. 45Q) or to provide CO2 to an enhanced oil recovery project. It might be able to save a bundle of money by converting an existing pipeline instead of building a brand new one, and thereby extend the pipeline’s commercial life. We shouldn’t let this urge to save money put our lives and communities at risk. Before any pipelines are converted to ship CO2 gas, PHMSA must issue comprehensive federal safety standards applicable to these pipelines, which standards must address their unique safety risks. Otherwise, these converted pipelines could operate without any federal or state safety standards and oversight. This regulatory gap creates an unacceptable safety risk that no community should accept.

Should you be approached by a company that seeks to convert an existing natural gas or oil pipeline to CO2 gas, let us know and also contact PHMSA and ask it to comply with its Congressional mandate to issue federal standards to ensure that the CO2 gas pipelines operate safely. Any conversion to transport CO2 gas should be put on hold at least until PHMSA issues federal safety regulations specifically applicable to CO2 gas pipelines.


  • Meeting the Dual Challenge: A Roadmap to At-Scale Deployment of Carbon Capture, Use, and Storage, EEIA
  • Fracture Control Strategy for the Conversion of Oil and Gas Pipelines to Transport CO2, Caraballo et al., 5th Pipeline Technology Conference (2010)
  • Capturing Carbon Dioxide: the Feasibility of Re-Using Existing Pipeline Infrastructure to Transport Anthropogenic CO2, Seevam et al., Proceedings of the 8th International Pipeline Conference (2010)
  • A systematic review of key challenges of CO2 transport via pipelines, Onyebuchi et al., Renewable and Sustainable Energy Reviews, Vol. 81, Part 2, pp. 2563-2583 (2018)
  • Safely Re-Using Infrastructure for Co2 Transport and Storage, DNV GL (2019)
2010 Fracture Control Strategy for Conversion of O&G Pipelines to CO2
2010-01 The_Feasibility_of_Re-Using Existing PIpelines for CO2

2018-01 Kolios et al_A systematic review of key challenges of CO2 transport via pipelines

2019-09 DNV Safely re-using infrastructure for CO2 transport and storage
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