Gas Transmission Networks
NTS pipelines are constructed in accordance with IGEM/TD/1 Edition 5, and the current edition stipulates the
use of heavy wall pipe as protection against third party interference at road crossings. National Grid receives
two or three requests a year to divert or install thick wall pipe for a new high density road. For example,
planning revisions to the routing of the road scheme will lead to a road crossing a section of the pipeline
without reinforcement of heavy walled pipe. The gas transmission system will also be impacted by the planned high speed rail link (HS2) between London and the West Midlands and will involving a number of additional diversions or additional pipeline reinforcement operations.
The options for reinforcement are limited to a pipeline diversion and stoppling operation and the inherent
risks associated with type of operation and costs in terms of flow reduction and implications of buyback, give a strong case for further investigation into any alternative options. National Grid would like to evaluate the use of epoxy sleeves for providing the required level of protection against third party damage as an alternative to heavy wall pipe. An epoxy sleeve consists of two steel halfshells,
joined to encircle the damaged area, with the annular space filled with an epoxy grout. A significant
amount of research throughout the 1990s has meant that epoxy sleeves are now a common solution for
providing repairs to most types of damage including corrosion, gouges, dents, dent-gouge combinations,
cracking and girth weld defects. However the research to date has not been directed at assessing the
suitability of the technique for impact protection, both from a mechanical engineering and code compliance
perspective. The project will therefore look to address issues such as:
- Does the epoxy clamp arrangement reduce the SMYS (specified minimum yield stress) in the pipework system to an appropriate level to allow the crossing of a road/railway?
- Does the arrangement introduce excessive stresses on the pipe-work system either side of the
- Given that the shell length is restricted by the rolling capability of a mill, will a gap be an issue or
stress concentration factor? If so how does this need to be designed out or managed?
- Will this extra metalwork put an extra strain on the CP system, especially if it is a significant length of reinforcement? Do we need to manage the potential for corrosion between the shell and carrier pipework?
- What thickness of shell and what thickness of grout would be required?
If the epoxy sleeves can be proven a viable alternative to thick wall pipe, then reinforcement work could be
carried out with a significantly reduced safety risk associated with a diversion using stopple and bypass and
employees working downstream of the stopple fitting. The operation also leaves the stopple fitting on the
pipeline with an ongoing maintenance requirement and a long term risk of leakage. The project therefore will
deliver a specific novel arrangement of existing equipment.