Introduction

There a number of unknowns and uncertainties associated with the conveyance of bulk quantities of dense phase or supercritical CO₂ in pipelines. Work is currently being undertaken to develop better understanding of the hazards of and standards for the conveyance of liquid, dense phase and supercritical CO₂ in pipelines.

In line with the principle that those who create the risks need to understand, manage and control them, the operators of carbon capture, storage (CCS) and sequestration projects need to understand the hazards, and the mechanisms, consequences and probabilities of pipeline failures in conveying CO₂ in pipelines in order to ensure safe design, commissioning and operation.

This note seeks to draw attention to:

• Current knowledge and guidance on the hazards from CO₂
• Current UK legislation
• Possible legislative changes
• Existing pipeline design codes and standards
• Ongoing initiatives and research; and
• Good practice

in the design of pipeline systems for transporting bulk quantities of CO₂ in the UK.

HSE will continue to monitor the development of relevant codes and standards and the outcomes of any relevant research (e.g. on modelling dense phase / supercritical CO₂ releases and the dispersion of CO₂ from pipelines) in future and will update this guidance as and when appropriate.

It will also draw attention to any proposals for changes to the regulatory regime and / or the land use planning arrangements in force in Great Britain.

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Background

The Government’s energy strategy, set out in the 2007 Energy White Paper, aims to provide the UK with secure energy supplies and contribute to the global climate change effort. Fossil fuels are expected to continue to play a vital role in providing the UK with secure, reliable electricity for the foreseeable future.

Around a third of UK carbon dioxide (CO₂) emissions result from electricity generation. As part of a long term strategy for reducing emissions from the power generation sector, the Government is keen for the UK to play a leading role in the development and demonstration of carbon capture and storage (CCS) technologies; currently the only option available for making significant cuts in global emissions from fossil fuel power stations.

CCS technologies seek to capture the CO₂ that would otherwise be emitted from large combustion plants (primarily fossil fuel power stations) and permanently store it in geological structures deep underground. CCS is an integrated process involving:

• The capture of CO₂ from power plants and other industrial sources
• Its compression to a form in which it is suitable for transportation
• Transporting it (usually via pipelines) to a storage site; and
• Its permanent storage in geological sites such as deep saline formations or depleted oil and gas fields.

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UK Government initiatives

The processes involved in CCS are not new, but have yet to be demonstrated together at scale. As a first step towards demonstrating the viability of the full chain of CCS technologies on a commercial scale coal fired power plant, the Government launched the UK CCS Demonstration Competition in November 2007; paving the way for the development of a CCS industry.

• Further information on the competition and the next steps on carbon capture

On 30 June 2008, the Government published a consultation document 'Towards Carbon Capture and Storage' which seeks views on several aspects of the regulation of CCS. Specifically, it consults on several aspects of the regulation of CCS and invites views on the principle of 'carbon capture readiness’ for combustion plants and the regulation of carbon dioxide storage.

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Industry initiatives

Recognising the novel issues and that current industry standards do not adequately address the risks associated with the transmission of CO₂ in pipelines other initiatives are currently being undertaken by industry stakeholders working in partnership and with government agencies. For example, the Det Norske Veritas (DNV) initiated Joint Industrial Project on pipeline transmission of CO₂ which aims:

• To review and integrate current knowledge and interpret results from available research and development and technical studies; and
• To develop comprehensive best practice guidelines for the transmission of CO₂ in onshore and submarine pipelines

so as to ensure compliance with current conventions, regulations and directives.

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Possible legislative changes

As part of the wider cross-Government approach to understanding the risks from CCS, HSE is working with other Government departments in key areas such as:

• Determining whether certain physical states of CO₂ (e.g. high pressure / supercritical phase) together with consideration of the quantities involved merit classification as 'dangerous fluids’ for the purpose of the Pipelines Safety Regulations 1996 (PSR) and/or 'dangerous substances’ for the purpose of the Control of Major Accident Hazards Regulations 1999 (as amended) (COMAH);
• Proposing and progressing any necessary legislative changes;
• Identifying technical and other issues which need to be progressed;
• Considering land use planning arrangements, in the context of proposals for changes to the arrangements in Great Britain recommended by the Buncefield Major Incident Investigation Board; and
• Identifying research needs.

In the interim and for the purposes of the UK CCS Demonstration Competition, pre-bidders / project developers have been required to give a health and safety compliance demonstration as if CO₂ was classified as a 'dangerous substance’ or a 'dangerous fluid’ under COMAH and PSR and (for offshore installations) as if all relevant offshore regulations applied, in order to satisfy the requirements of the Health and Safety at Work etc Act 1974. In addition, the successful competitor must provide technical information to HSE throughout the project, to inform the development of appropriate health and safety standards.

HSE will be working closely with BERR throughout the UK CCS Demonstration Competition.

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Conveying CO₂ in pipelines

Many of the proposals for CO₂ storage and sequestration schemes are likely to involve its conveyance by pipeline; either through the modification of existing pipeline infrastructure or the construction of major new pipeline systems.

Whilst future schemes may include proposals for conveying CO₂ as a gas, for economic and technical reasons it is more likely to be handled at high pressures as a dense phase or supercritical fluid.

Current UK experience of CO₂ pipelines is limited, and only some pipeline design codes include it as a relevant fluid within their scope of application. Moreover, current pipeline codes did not anticipate the bulk transportation of CO₂ in the quantities likely to be seen in CCS projects.

Oil and gas companies, particularly in the USA, have some experience of using high pressure injection of CO₂ in oilfields to 'push’ oil towards producing wells (Enhanced Oil Recovery); but the extent of this experience is very limited when compared to hydrocarbon pipelines.

Because there are currently no suitable guidelines or standards it has been suggested that industry treat CO₂ pipelines as though they are conveying natural gas. However the hazards are very different, and in doing so, the designers and developers of CCS and sequestration projects need to keep in mind that whereas natural gas is a flammable, potentially explosive substance, CO₂ is both toxic and an asxphyxiant.

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Health hazards from CO₂

At room temperature and ambient pressure, CO₂ is a colourless, odourless gas that supports neither combustion nor life. It is not just an asphyxiant but also has toxicological effects and has been recognised as an occupational health hazard for more than a hundred years.

Dense phase and supercritical CO₂ give rise to additional hazards particularly when the pressure suddenly falls or is lost completely.

• Further information on the cryogenic, traumatic and toxicological effects

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Hazards to pipelines

CO₂ presents a number of hazards to pipelines which designers and operators will need to consider carefully:

• Corrosion- CO₂ is an acid gas which reacts with water to form carbonic acid and this is familiar to corrosion engineers as "sweet gas corrosion". This means that water content of CO₂ transported through carbon steel pipelines needs to be considered and pipeline materials selected accordingly. Other constituents may be present in the transported CO₂ depending on its origin and these also need to be considered. These might include oxygen, methane, carbon monoxide, NOx and SOx. Compatibility of all pipeline system materials e.g. elastomeric seals in valves with these contaminants needs to be considered.
• When loss of containment (LOC) occurs, there are a number of highly complex interactions between the pipeline, the surrounding environment and the decompressing fluid. These are complex enough for natural gas, but with CO₂ they are further complicated by the potential for phase changes of the fluid which are dependent on the level of impurities, the temperature and pressure along with the geometry of the orifice through which the gas is decompressing. This all adds complexity to the modelling of the release that cannot be easily incorporated into existing outflow models, which makes modelling of the gas dispersion or gas concentration extremely difficult. The behaviour of the pipeline and its ability to arrest a fracture is also very difficult to model. When the pressure of CO₂ is reduced, there is a change in temperature. Where a large drop in pressure occurs, the temperature change is likely to be significant, and this could lead to material embrittlement and the risk of brittle fracture. All components, both metallic and non metallic, need to be capable of tolerating temperature deviations without impairment. The toughness of steel to prevent fracture propagation following loss of containment is therefore a key consideration.
• The likelihood of loss of containment events occurring also needs to be determined to enable realistic understanding of risk to be developed, and again, given limited experience of transporting CO₂ in pipelines, there is a paucity of information on this.

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Current guidance and standards

(A) Reducing risk As Low As Reasonably Practicable (ALARP)

Application of good practice at the design stage is essential to demonstrating reduction of (ALARP). In judging compliance and as a minimum, HSE expects duty holders to apply relevant good practice.

Depending on the level of risk and complexity involved, it is possible the adoption of good practice alone may not be sufficient to comply with the law. For example, in high hazard situations, where the circumstances are not fully within the scope of the good practice, additional measures may be required to reduce risks ALARP. Furthermore, where the potential consequences are high, HSE will take a precautionary approach by giving more weight to the use of sound engineering and operational practice than to arguments about the probability of failure.

• Further guidance on assessing compliance with the law in individual cases and the use of good practice
• Policy and guidance on Reducing Risks as Low as Reasonably Practicable in Design

(B) Pipelines Safety Regulations 1996 (PSR)

Regulation 5 requires that the design of a pipeline, or any modification to it, takes account of the operating regime of the pipeline and the conditions under which the fluid is to be conveyed as well as the environment to which the pipeline will be subjected. In particular with regard to the re-use of existing pipelines, any proposal to change the fluid conveyed will require a re-assessment of the original pipeline design to ensure that the pipeline is capable of conveying the fluid safely.

European Standards implemented in the UK as British Normative Standards (BS EN series) and supported by published documents (such as the British Standards PD series) provide a sound basis for the design of pipelines. Other national or international codes e.g. a relevant standard or code of practice of a national standards body or equivalent body of any member state of the European Union are likely to be acceptable provided the proposed standard, code of practice, technical specification or procedure provides equivalent levels of safety.

(C) European Standards

Standards relevant to the transport of fluids in pipelines include:

• PD 8010: 2004 Parts 1 - Steel pipelines on land and 2 - Subsea pipelines
• BS EN 14161: 2003 - Petroleum and Natural Gas Industries. Pipeline Transportation Systems
• Institute of Petroleum Pipeline Code IP6
• DNV OS-F101 - Submarine Pipeline Systems (2007)

Codes IP6, BS EN 14161, BS PD 8010 and DNV OS-F101 are all applicable to pipelines transporting CO₂; the last three categorising it as a non- flammable, non-toxic fluid which is gaseous at ambient temperature and pressure. IP6 also treats CO₂ as a gas.

However none of these standards address CO₂ transported in its dense or supercritical phases. This is not oversight by the standards organisations but rather a reflection of the fact that to date, CO₂ has not been transported in these phases and hence there has been no driver to address the issues associated with such activities.

Although IP6 is still in existence and contains useful guidance on operational issues, it is not widely used for new pipelines. BS 8010 has been withdrawn and has been replaced by BS PD 8010: 2004 Parts 1 and 2. European Standard BS EN 14161: 2003 – Petroleum and Natural Gas Industries, Pipeline Transportation Systems has also been introduced although the HSE recommends that any pipelines designed to BS EN 14161 should be supported by good industry practice as presented in BS PD 8010: 2004 Parts 1 and 2. DNV OS-F101 is specifically an offshore standard, limited to submarine pipeline systems.

(D) US Pipeline Codes

The US Federal Code of Regulations, Title 49, Volume 3, Part 195 – Transportation of Hazardous Liquids by Pipeline and the associated ASME standards B31.4 and B31.8 are the main American codes which address the transportation of liquids and gases by pipeline respectively.

The US Federal Code only applies to pipelines transporting CO₂ in the supercritical phase and is therefore only relevant to proposals to use pipelines to convey supercritical CO₂. There does not appear to be any equivalent code which addresses the transport of gaseous or liquid CO₂.

ASME Standard B31.4 does not specifically exclude pipelines transporting CO₂, but does not include CO₂ within the list of fluids to which it is intended to apply. ASME Standard B31.8 specifically excludes pipelines carrying CO₂ (in any phase).

HSE considers there may be technical benefit to applying the US Federal Code to proposals for conveying supercritical CO₂ but little or no benefit to applying the ASME standards either in part or their entirety.

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Interim recommendations for the design of CO₂ Pipelines

The designers of CCS and sequestration projects involving the transport of CO₂ in pipelines need to understand the hazards and the mechanisms, consequences and probabilities of pipeline failures. HSE intends to consult on an amendment to the Pipelines Safety Regulations which would deem pipelines carrying bulk quantities of CO₂ at high pressure as Major Accident Hazard Pipelines.

Pending further guidance:

1. So as to better understand the risks, the designers and developers of all CCS and sequestration projects are encouraged to become actively involved in relevant ongoing research and other joint industry initiatives / projects to develop best practice guidelines for the transmission of CO₂ in onshore and submarine pipelines.
2. Developers of proposals under the UK CCS Demonstration Project are required to give a health and safety demonstration as if CO₂ will be classified as a 'dangerous fluid’ under PSR and (for offshore installations) as if all relevant offshore regulations applied, in order to satisfy the requirements of the Health and Safety at Work etc Act 1974.
3. The developers of proposals for other CCS and sequestration projects should take into account the possible change to the PSR described above.

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Hazardous Installations Directorate
Specialised Industries Division
Gas & Pipelines Unit
12 August 2008