Over the past few years PMP have assisted United Utilities and framework partners during the series of TA Outages.

Initially PMP were called in to carry out long distance confined space Aqueduct surveys, sometimes penetrating over 4km under the mountains of the lake district.

As a result of the detailed condition reports of both structural and mechanical assets, PMP were asked to offer bespoke engineering solutions to some of the Victorian assets including the Lever Plug valves and the Canoe Overflows.

When constructed in 1810, the aqueduct was provided with tubular overflows, nicknamed “canoe overflows” because of their elongated shape, positioned at stream locations to prevent the aqueduct surcharging along the 96 mile length – basically the overflows relieve the aqueduct of excess water by allowing water to overflow into the beck below.

Originally the overflows were made entirely from cast iron and stood 1.25m high but, due to increasing demand, needed extending to 1.6m high to allow a higher volume of water to flow. To achieve this increased flow the canoes had been extended in height using mild steel ‘canoe’ shaped sections which were fixed on top of the original cast iron structures.

As a result of mild steel being used, the extensions had corroded over the years and were becoming unreliable with an increasing risk that the overflow could fail, reducing the aqueduct capacity.

PMP were tasked with the challenge of removing the mild steel extensions, and in some cases cast iron extensions, and providing new, noncorroding extensions. The contract called for 12 overflows to be modified in just a single 4 week outage; and, of course, the solution had to be Regulation 31 approved.

Various materials were researched, including polyethylene and polypropylene, before settling upon 316 stainless steel. Once this decision had been made, and prior to the aqueduct outage, each replacement canoe extension was individually manufactured to the specific dimensions obtained during our previous surveys – all 12 overflows were unique.

The new stainless steel sections were electrically isolated from the original cast iron structures to avoid the risk of galvanic corrosion.

Installation was completed at all 12 remote, rural sites during the tight 4 week outage, all completed on time, with no incidents, with the aqueduct back in service on programme and with no leakage reported.