Tinsley Viaduct is a multi-level bridge structure allowing the M1 and A631 to span the Sheffield and Tinsley canal and the River Don. It provides a vital link to the north of England and is deemed to be a strategic national infrastructure asset.  In addition to facilitating traffic flows, it also houses a number of utility pipelines and other services.

Access to the structure for effecting reactive and planned maintenance activities is strictly controlled and all work has to be pre authorised and then completed within very tight project timescales, including out of “normal hours” working.

The utility pipe-lines, including two 24” diameter water mains which form part of the Sheffield and Rotherham distribution network, are within the southern abutment of the viaduct.

Yorkshire Water was aware of leakage on this section of the network and instructed Planned Maintenance Pennine (PMP Ltd) to undertake an asset condition survey and report the findings.   The survey undertaken by PMP’s confined space survey team identified that one of four 24” flow control/isolation valves required replacing and a section of complex cross connections were heavily corroded.

Following the survey, Yorkshire Water instructed PMP to formulate an outage plan to facilitate the repair of the cross connections, rather than facing a serious reactive challenge at a later date. The tee section to be changed was located within a valve chamber and the access cover had been constructed after the pipework had been installed.  The size of the access was such that it was totally impractical to remove the corroded tee without removing a section from the top of the chamber.  This wasn’t considered to be a viable option as it would cause major disruption to local traffic and the cost of reinstatement would be prohibitive.

The chamber lid was 600mm square and the tee to be removed from the chamber contained 3 flanges measuring 800mm on the outside edge. PMP offered a solution that required the off-site manufacture of a bespoke tee in which the centre flange could be separated from the tee body. This allowed all components to fit through the existing access arrangement.

An AMEX-10 seal was then used in the reassembly of the tee section and flanges when inside the chamber. The provisional cost savings were estimated at £80k, which was influenced by the fact that no reinstatement or traffic management required as PMP adopted an innovative and flexible engineering approach to a complex issue. In-house workshop capacity enables PMP to undertake bespoke engineering projects and to manufacture constituent components for complex jobs such as this.