The National Transmission System (NTS) has approximately 300 locations where large diameter gas transmission pipes pass through reinforced concrete walls (e.g. into valve pits). Currently a variety of seals are used to prevent water, soil and pipe surround materials from passing through the interface between the wall and pipe. Many of these seals are known to be failing (e.g. allowing seepage and grit etc. to enter the space between the pipe and surrounding concrete) typically due to the breakdown of the seal materials and /or settlement of the pipe.

Where such failures are occurring there is the risk that the protective coating to the pipeline is being damaged and corrosion taking place. With evidence of seal failure and potential pipeline damage, current practice involves major works to cut out significant volumes of reinforced concrete around the pipeline to expose the seal, enabling inspection and repair. This is then followed by reconstruction of the reinforced concrete wall and replacement of the transition seal. Significantly more concrete must be removed than would ordinarily be necessary to allow for inspection and repair of the seal. Important areas of the existing reinforcing material need to be exposed to enable effective reinstatement of the concrete wall. The reconstruction process is complex, high risk, time consuming and inevitably creates difficulties in achieving good seals to the older concrete and to the new transition seal.

This process is currently undertaken on approximately 10 occasions annually and is likely to increase due to increasing age of the asset. In the event of future seal failure / further pipe settlement, the entire process would need to be repeated with the risks of progressive weakening of the reinforced concrete wall.

Benefits

Application of knowledge gained during the feasibility study, concept design and field trial of a removable composite gas transition seal unit that is fit for purpose.