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Under Pressure Operations on Dense Phase CO2 Pipelines: Issues for the Operator

[+] Author Affiliations
Julian Barnett

National Grid, Solihull, West Midlands, UK

Richard Wilkinson, Alan Kirkham

National Grid, Warwick, UK

Keith Armstrong

DNV GL, Brampton, Cumbria, UK

Paper No. IPC2014-33309, pp. V004T08A008; 17 pages
doi:10.1115/IPC2014-33309
From:
  • 2014 10th International Pipeline Conference
  • Volume 4: Production Pipelines and Flowlines; Project Management; Facilities Integrity Management; Operations and Maintenance; Pipelining in Northern and Offshore Environments; Strain-Based Design; Standards and Regulations
  • Calgary, Alberta, Canada, September 29–October 3, 2014
  • Conference Sponsors: Pipeline Division
  • ISBN: 978-0-7918-4613-1
  • Copyright © 2014 by ASME

abstract

National Grid, in the United Kingdom (UK), has extensive experience in the management and execution of under pressure operations on its natural gas pipelines. These under pressure operations include welding, ‘hot tap’ and ‘stopple’ operations, and the installation of sleeve repairs.

National Grid Carbon is pursuing plans to develop a pipeline network in the Humber and North Yorkshire areas of the UK to transport dense phase Carbon Dioxide (CO2) from major industrial emitters in the area to saline aquifers off the Yorkshire coast. One of the issues that needed to be resolved is the requirement to modify and/or repair dense phase CO2 pipeline system.

Existing under pressure experience and procedures for natural gas systems have been proven to be applicable for gaseous phase CO2 pipelines; however, dense phase CO2 pipeline systems require further consideration due to their higher pressures and different phase behaviour. Consequently, there is a need to develop procedures and define requirements for dense phase CO2 pipelines. This development required an experimental programme of under pressure welding trials using a flow loop to simulate real dense phase CO2 pipeline operating conditions.

This paper describes the experiments which involved:

• Heat decay trials which demonstrated that the practical limitation for under pressure welding on dense phase CO2 systems will be maintaining a sufficient level of heat to achieve the cooling time from 250 °C to 150 °C (T250–150) above the generally accepted 40 second limit.

• A successful welding qualification trial with a welded full encirclement split sleeve arrangement.

The work found that for the same pipe wall thickness, flow velocity and pressure, dense phase CO2 has the fastest cooling time when compared with gaseous phase CO2 and natural gas.

The major practical conclusion of the study is that for dense phase CO2 pipelines with a wall thickness of 19.0 mm or above, safe and practical under pressure welding is possible in accordance with the existing National Grid specification (i.e. T/SP/P/9) up to a flow velocity of around 0.9 m/s.

The paper also outlines the work conducted into the use of the Manual Phased Array (MPA) inspection technique on under pressure welding applications.

Finally, the paper identifies and considers the additional development work needed to ensure that a comprehensive suite of under pressure operations and procedures are available for the pipeline operator.

Copyright © 2014 by ASME

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