HS2 Cross Country Pipeline Diversion & PRS Rebuild


Rayden Engineering Limited (REL) were contracted by SGN to divert a section of the existing 600mm NB P074 Marsh Gibbon to Newton Longville High Pressure (HP) pipeline near Calvert, Buckinghamshire

Part of the existing pipeline needed to be rerouted to make way for the construction of the new High-Speed Rail Link (HS2). This diversion allowed the pipeline to be upgraded with new pipework and supporting infrastructure.

The general location of the works was to the southwest of the village of Steeple Claydon in the Aylesbury Vale District Council area. The new 2.8 miles (4.5km) pipeline diversion passed over semi-rural land, and therefore had limited impact on the local community.


SGN logo

Previously known as Scotia Gas Networks, SGN is a gas distribution company that delivers gas to over 5.9 million homes and businesses across Scotland and the South of England.

The company manages a network of underground gas pipelines covering more than 44,000 miles and has invested heavily in upgrading its network with new modern pipework.

HS2 Calvert 2.8 mile cross country pipeline diversion route shown in red


REL were employed in the role of Principal Contractor, under CDM 2015, to complete all required works.

Work included:

  • Construction of a new 600mm diameter cross-country gas pipeline diversion approx. 2.8 miles (4.5km) long.
  • Construction of new Pressure Reduction Station (PRS) & Above Ground Installation (AGI).
  • Intermediate Pressure (IP) and Medium Pressure (MP) modification works.
  • Removal of existing above ground equipment at the now redundant PRS Steeple Claydon site.


All new pipework was constructed in accordance with IGEM/TD/1 Edition 5 and other applicable SGN Specifications.

The following activities formed the key components of this project:

  1. All civil works required to construct the 2.5 mile pipeline diversion including working width preparation.
  2. All civil works needed for new PRS build including all excavation works, construction of bases for various new equipment i.e., skid units, buildings etc.
  3. Supply & erection of HERAS Fencing along complete perimeter route & for excavation, backfill & reinstatement.
  4. Excavation works completed to tie-in locations for P18 works.
  5. String, weld & laying of 600mm diameter pipeline.
  6. Completion of Auger Bores & micro-tunnel techniques for crossing locations.
  7. Hot-tap welding (P9) to install stopple arrangement in preparation for tie-in operations.
  1. Fabrication & installation of by-pass pipework at tie-in locations.
  2. Completion of under-pressure drilling operations through specialist contractor.
  3. Completion of tie-in operations including capping of redundant pipework.
  4. Installation of IP Outlet from Calvert PRS to tie in to adjacent 6″ Steel & 250mm PE mains.
  5. Installation of 180mm PE MP Gas Main approx. 1.5km in length.
  6. Installation of 125mm PE MP Gas Main approx. 1.7km in length, run in same corridor as HP pipeline.
  7. Decommissioning of redundant assets including  grouting of redundant pipework left in situ.

New PRS & AGI works included:

  • Decommissioning, removal, demolition & disinvestment of equipment & pipework at redundant PRS site.
  • Installation & commissioning of new pre-heat system, heat exchangers, filters, regulators & associated pipework for PRS site at new location Steeple Claydon.
  • All civil works required to construct new PRS including all excavation works, construction of bases for various new equipment i.e., AGI, skid units, buildings, E&I kiosk generator, transformer, & meter kiosk etc.
  • Additional ducting & pathways were also installed.
  • All prefabrication & welding works completed to SGN specifications.
  • 80% of pipework was prefabricated off-site at the REL HQ workshop & installed on-site to our agreed designs & programme.
  • Prefabrication & installation of all pipe supports for new pipework.
  • Installation of all new pipework & painting in accordance with NGN/P/A/10 & CW5 specifications.
  • Construction of new access roads & paths.
  • Supply & installation of new perimeter fencing for AGI.
  • Backfilling & reinstatement of whole site following completion of all phases of work.


REL approached this project as we do all others, by establishing a close working relationship with our client SGN. Through regular communication and meetings, we were able to develop an open, honest, and trustworthy environment that ensured the smooth running of the project and all associated works.

This meant that the project was delivered within programme specifications and without any major issues. All works were completed on time, in budget and in line with the approved design and RAMS.

REL fully satisfied their duties under CDM 2015 and provided full handover on completion in May 2019.

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