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How the Thames Barrier gate system works


protective coating applicators to ensure that the high quality standards originally set for the Thames Barrier are transferred to the next generation of coating applicators. The Queen officially opened the Barrier in


1984, but some of the gates had been installed since 1979 and they were first used in 1982. This meant that the first of the gates had been in position and exposed for over 30 years at the 25th anniversary. The coating condition on the gates has been


examined at regular five year intervals, since 1982 by David Deacon, with intermittent spot inspections on each of the individual gates to ensure that the coating system was performing satisfactorily and as projected. The official 25th anniversary of the gates was “celebrated” in May 2009, and leading up to that event a major full inspection of all of the gates was implemented by Martin Earlam of the Environment Agency to establish that the structural, mechanical and corrosion protection properties had been successful and when major maintenance would need to be commenced. The detailed coating inspection was carried out by SPC and the inspection team included Halcrows, Atkins and the contractor was Volker Stevin. This major inspection programme covered


a two year period, and every area of the coating was examined and tested. This testing programme was carried out by William Deacon, Director of SPC, and at the completion it was projected that the coating not only was satisfactory, but would last a further 15 years before major maintenance need be considered. This was a significant result and clearly Martin Earlam was delighted at the outcome and findings of the inspection team.


REPAIRS REQUIRED In the 1990s it was clear that there had been a number of areas of minor mechanical damage, and patch repairs had to be carried out to the gate structure. This was of concern to the Environment Agency, since some of the patch repairs were on the falling radial gates, which were exposed to the environment and were visible. The coating system was a black coating over the high build protective coating (a light cream), and the Environment Agency wanted a patch repair system that would be suitable for both the falling and rising sector gates. So, with tide and timings being critical it was important to have a patch coating that would be able to be immersed within an extremely short period of time (20 minutes) into the Thames River water, and continue curing and protecting patches after immersion. Eleven manufacturers put forward coating


systems which they thought could be considered, and these were all tested by SPC on behalf of the Environment Agency on an area of gate arm close to the river level with boat access. After preparation and application, the various systems


were subjected to immersion within 30 minutes and were then examined to see the effect after days and weeks to ascertain the coating condition. After this detailed practical testing programme had been carried out, one material in particular supplied by Corrocoat under the trade name of Zip Coat E was selected as the most appropriate coating to meet these conditions and requirements. Since that time, the Zip Coat E has been used successfully on numerous patched areas across the ten gates.


EXCEPTIONAL INCIDENT One exceptional incident in the barrier’s history occurred in 1997, and is known as the “Sandkite incident”. A gravel barge impacted on the pier and sunk on the submerged flat face of the Foxtrot rising sector gate in the Thames. The salvage company had to discharge the complete contents of the gravel barge, and so all of the gravel contents were left on the upper flat surface of the gate on the river bed when the barge was salvaged and removed. The salvage company then tried to remove


the large deposits of gravel with high pressure water jetting pipes, and this salvage exercise and incident damaged a number of areas on the flat face of the Foxtrot gate. The repair process was disputed by


the insurance company, and after detailed independent surveys by SPC consultants it was agreed that the entire face of the Foxtrot gate would need to be repaired and recoated. The operation of this repair process involved the use of a vacuum high pressure water jetting unit (rather than wet/dry abrasive blasting). The unit


APRIL-JUNE 2013 PCE 21


SPOTLIGHT


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