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SPOTLIGHT


T


he design principles of the Barrier to protect London from flooding was based on a unique idea by the consulting engineers for the project,


Rendel, Palmer and Tritton (now Highpoint Rendel) on behalf of the clients, the Greater London Council. The principle of the design was based on a “gas tap” fixing, discovered by chance, with the “inventor” presenting a paper to the Institute of Corrosion conference in 1994. Chief Engineer, Martin Earlam explained that


to completely span the width of the Thames at the point that the Barrier was to be erected, it needed six rising sector gates, which would be maintained in the river bed to enable marine navigation to continue at all times that the gate was not in use. Four of these gates were over 60 metres in span, allowing the larger vessels to navigate through the gate openings (with difficulty), including such large vessels as the Ark Royal Aircraft Carrier. There were also four falling radial gates to complete the protection across the Thames and these were over 30 metres in width. This made the total width of the river protected by all of these gates to be over 500 metres at the position of the Barrier. The coating system to protect these large


steel gates (GLC requested at least a 25 year life to first major maintenance) meant that the


coating protection had to be exceptional in terms of resistance to the immersed conditions in the Thames water, which in the 70s was polluted and very corrosive. It also had to be exceptional in resisting impact damage from floating debris together with grit and silt surge abrasion. So both the chemical and physical properties of the applied coating had to be extremely tough and protective. The coating consultants, the late Keith Julyan


Day, Derek Bayliss and David Deacon, now part of the UK’s Steel Protection Consultancy, had to come up with a coating that would protect all of the steel gates, both the immersed and exposed structures for as long as possible in the varied, immersed or exposed aggressive conditions. The selection and evaluation of the coatings


programme covered a five year period and included a range of coating systems. These were subjected to a series of stringent tests, including half tide immersion in the river on deliberately damaged panels on a jetty at Woolwich, as well as numerous laboratory accelerated tests to identify the good and bad properties of the 35 coating systems examined at the time. The coating systems put forward by 17


different paint suppliers varied in type from five coat systems to single coat applications. After the completion and evaluation of all of


Photo by DAVID ILIFF. License: CC-BY-SA 3.0


APRIL-JUNE 2013 PCE 17


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