Radius PLUS has commenced a development project of its own to develop live access electrofusion access saddles for deployment of stopper systems to PE mains, specifically the smaller diameter type needed for its RTP stopper deployment. Such systems will be available for mains 63mm to 450mm when fully completed, including imperial 3” to 8” sizes. It is proposed that the NIA project run concurrently with that development to accelerate the development through offline deployment testing, review and definition of engineering standards for medium pressure RTP stoppers, preparation of codes of practice/engineering policy documents that all lead to ability to undertaken field trial deployment safely within the network. Three field trial deployments have been included within the scope of the RSL cost elements, the value can clearly be adjusted if further field trial deployments were preferred for the purpose of statistical or practical confidence of the technique in the network.
Benefits
The successful operational deployment of unsupported bag flow stopping systems on medium pressure gas distribution mains 90mm to 450mm PE (with future scope to go down to 63mm) enabling withdrawal of policy approval for use of squeeze off techniques in this size range specifically relating to medium pressure PE mains.
Learnings
Outcomes
A draft standard has been produced which sets the requirements for a new generation of inflatable stoppers with increased lifetime and improvements in (reductions of) fugitive emissions from their use. This will be taken to the Technical Standards Forum for review and possible publication.
A draft standard has been produced which sets the requirement that electrofusion saddles should be designed and approved in conjunction with specific live launch tools to polyethylene pipes. The combined products should have a stated capability and the manufacturer of the saddle should warrant the installed asset lifetime that results. This will be taken to the Technical Standards Forum for review and possible publication.
As a result of field trials, Electrofusion saddles for PE mains 180mm/8” have now been developed, demonstrated and approved to the requirements of GIS/PL2 Part 4 and GIS/PL3. Also, approved to the requirements of Part 4 + Annex A1 in the ‘I-State’ with an RTP stopper system
An RTP stopper system has been assessed for compatibility with saddles and for gas application. This has been approved to the requirements of GIS/E5 proposed standard matching the above size ranges with a let by rate at pressures to 2 bar of less than 0.02 SCMH at the primary seal position. Additionally, having capability for use to 2 bar, to 40 Celsius, for up to 1 week, up to 3 times at the same position
Risks arising from the use of the squeeze off technique are perhaps greater than originally expected following research and testing through this project. In addition to incidents arising from transfer of loads to surrounding infrastructure, it is known that the pipe can fail at the position of a squeeze tool during use. The risk of this occurring has increased with the prevalent technique of slip lining used for mains replacement. Polyethylene pipes are relatively soft and when pulled or pushed through old metallic pipes they suffer longitudinal scratches and scoring. If the scratch ends up in the wrong place, the position of maximum strain deformation in a squeeze off tool, under conditions of moderate to low temperatures, the potential exists to create a localized partial or through wall pipe fracture due to the pressure of the squeeze off tool.
In relation to the risk profile, it is recommended the continued use of squeeze off on any asset should involve investigation of controlled rate compression and release tools to mitigate against early onset of wear out failure modes. Testing should assess actual lifetime of the asset, not the minimum acceptable lifetime which is the premise of current standards.
Lessons Learnt
Field trial sites and respective site manager engagement resulted in greater success in securing filed trial locations. The field trials should be identified and built into work programs to ensure increased effectiveness of execution. Operational staff need to remain informed through that stage of the project otherwise these sites can be lost – lengthening the project.
