Thames Water Issue: Failing manhole covers Solution: Wrekin Unite™
Result: Supplied in excess of
100,000 units to Thames Water
without one recorded failure
over a 17 year period.
Prior to 2004 Thames Water observed two specific trends regarding their ongoing Manhole cover replacement program. Firstly that the requirement to replace was accelerating but of greater concern was the number of instances that called for recently replaced covers to be replaced for a second time and even a third.
An in-depth study showed that whilst Kitemarked units to BS EN 124 were being used there was a growing problem with life expectancy of these units. In 2002 Wrekin approached Thames Water suggesting this was a specific problem and offering a product solution in the form of their Unite Manhole Cover.
The Unite concept came about as a consequence of designing a unit that was “fit for purpose” as opposed to simply compliant to a standard or a price requirement. The failing covers that Thames were observing were all displaying modes of failure caused by wear as a consequence of inadequate design and inappropriate material usage. Frankly often there was quite simply insufficient material as castings were produced to a price. The cost of replacement and of course the often required Traffic Management in the Thames area served to amplify the problem.
Unite is an engineered solution which is totally compliant with BS EN 124, but there the similarity ends. The compliance to BS EN 124 and subsequent Kitemarking of the Unite is a given however the fitness for purpose element is where Unite excels. Failure mechanisms were studied in depth and designed out of the Unite. This was achieved by using latest FEA analysis of existing designs and subsequent FEA analysis of the subsequent solution. Areas that were addressed were cover stiffness and frame rigidity as well as bedding mortar friendly frame designs. The material commonly accepted as being the best possible for Manhole cover production is Ductile SG Iron.
This material does safely deflect however the offending designs utilised this property to the extreme resulting in large deflections which caused very significant wear. The Unite eliminates all but the minutest wear which in itself improves longevity dramatically. Wrekin engineering staff worked with Thames Water Engineers to hone the design and understand the whole life cost benefits. The benefits were so dramatic that Thames awarded Wrekin a 5 year contract which has been continually renewed since 2004.
Wrekin have now supplied in excess of 100,000 units to Thames Water without one recorded failure over a 17 year period. Thames has continued to monitor the situation over the period and is delighted with the longevity being achieved. The monitored installations are on some of the capitals busiest and most demanding routes. The “real life” experience with Thames has enabled Wrekin to become the first manufacturer of BS EN 124 D400 products to be able to offer warranties of 5 years regardless of location in the carriageway. Such is the sophistication of the Thames specification suite that they have been able to develop a “cost per year ownership model” which demonstrates that the Unite is by far and away the best performing D400 Manhole Cover available.