How robotic total station technology found its niche on a landmark gas project.
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On the coast of West Wales, strategically located for shipping from the Arabian Gulf, a landmark project is underway which could provide 20% of the UK's gas demand after completion in 2007/08.
The terminal is a state of the art facility and has been designed to process 7.8 million tonnes per annum of LNG. When cooled to -160°C, natural gas becomes liquefied and 600 cubic metres can be condensed to approximately 1 cubic metre of LNG. The LNG will arrive by tanker at Milford Haven's newly refurbished jetty and be discharged into five insulated tanks onshore. It is then sent to vapourisers for re-gasification by warming the cold liquid until it reverts to a gas.
Undertaking the tank's construction is Taylor Woodrow Construction (TWC) operating as a subcontractor to Chicago Bridge and Iron (CBI). Each tank has a capacity of 155,000 cubic metres, a concrete wall 27.5m high and 0.7m thick and an interior diameter of 94m. Easily able to house an A380 Airbus, these tanks will be some of the largest structures of their type ever to be slipformed.
In early 2005 Taylor Woodrow established their construction site at the South Hook LNG Terminal and began work. Conventional survey methods using EDMs and levels were used to construct the tank bases whilst vertical lasers were used to monitor the construction of the first Tank.
As slipforming began on this first Tank, a Technical Representative from KOREC was on site demonstrating a Trimble S6 Robotic Total Station to CBI. The TWC survey team attended the demonstration and although impressed, felt that at that time they had an insufficient volume of suitable work to justify the hire or purchase of a robotic instrument.
However as the first tank was slipformed, several points emerged. John Rainnie, Project Quality Manager for Taylor Woodrow Construction explained, " The vertical lasers that we were using to monitor the slipform were not sufficient on their own and although the conventional survey equipment we used to supplement them produced useful information, the process was slow. As work on the remaining tanks progressed, lines of sight would be restricted by both the tanks and follow on work (materials and equipment) needed to finish them. On top of this, we were also bidding to construct the process areas and buildings to control the receipt and distribution of gas. This work was spread over a large area although the individual structures would be much smaller than an LNG tank. Reflecting on our experiences with the first tank and the potential of new work bringing an increased demand for surveying, we decided to revisit using a robotic instrument."
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