Welsh Assembly Government – Demolition of redundant overhead pipe gantries – Former LG Plant
Connell Brothers were appointed MAIN contractors to dismantle / demolish the overhead pipes, together with tracks A1 and A3, at the former redundant LG site at Celtic Way, Newport South Wales.
The LG site had been purpose built in late nineties as a joint venture with the Welsh Assembly Government (WAG) and the Korean Government. Due to new technology, and the innovation of the flat screen television the purpose built plant was no longer required and therefore became redundant before it was commissioned.
The plant sat empty for several years awaiting new occupants, but unfortunately there were no takers, until the 3rd quarter of 2008 when interest was shown in one of the larger buildings. It was then decided that certain sections of the overhead pipes and gantries would be of no use to the new occupants and would therefore have to be removed.
The pipes ranged between 300 mm and 700 mm in diameter composed of mild and stainless steel with the stainless steel pipes being lagged with Fiberglas and a rubber membrane. The pipework totalled approximately 1.5 kilometres in length and weighed in excess of 120 tonnes.
The site consisted of 4 individual buildings linked together by the pipe gantries interconnecting each other. The gantries carried the pipes from the water desalination unit to each of the building.
The gantries were constructed from galvanised heavy duty RSJ’s, universal columns, channels and angle irons weighing approximately 850 tonnes.
The first task after the site set-up was to identify the exact split point in the gantry. The ground was also marked with different coloured paint to clearly identify the different live services beneath.
The gantries stopped approximately 150 mm from the building with the support legs and pipework passing through the flat roof and into the building. The buildings were constructed from a steel frame, the side walls formed by box profile polished aluminium type sheets and the roof formed by Kingspan type profile composite metal sheeting. The pipes passing through the roof, and the roof, were covered with this Dexian type rubber membrane.
Before any work started three of the flat roofs were covered with 8 ft x 4 ft x ¾” plywood sheets which were then covered with flame retardant sheeting to protect the roof in the unlikely event of any sparks landing on it during hot work.
Once the above was in place dismantling of the pipework entering the building commenced. Operatives working from a mobile elevating work platform and utilising a mobile crane first removed all of the rubber membrane and then the lagging material.
The pipes were then slung with nylon web slings attached to the mobile crane before being either unbolted or hot cut into suitable lengths before being lifted down and placed in a lay down area for processing.
Using a hydraulic excavator equipped with hydraulic shear attachment any non-reusable material was cut into 5 ft lengths before being removed from site for recycling.The pipes were segregated into their various sizes for recycling.
Due to the close proximity of the gantries to the buildings special care had to be taken so as not to damage the buildings. Whole sections of the gantry had to be removed intact as they could not be hot cut in-situ and lifted down.
Padding was attached to the ends of the steelwork to protect the cladding sheets on the building, and then the section of steel framework was slung with chains attached to the crane. The entire section was then unbolted by hand and carefully lifted out. This method was adopted with the other 3 end sections.
The main gantries were prepared by using a high reach excavator to cut out the cross bracing between the large columns, thus enabling the operative’s clear unobstructed access to enable them to work from the mobile access platforms.
The remaining sections of gantries were split into manageable sections by the operatives using hot cutting techniques and lifted down using the mobile crane. The vertical columns weighed in excess of 5.5 tonnes each. These were removed by operatives cutting through the bottom of the column utilising hot cutting techniques and the individual columns being lowered to ground level by the crane.
All operatives involved in this task had to wear RPE due to the steelwork being galvanized and therefore the potential of galvanic poisoning was ever present during any hot work.
The steel stumps of the columns together with all the concrete bases were then broken down to 150 mm below existing ground level and the whole area was graded and levelled to enable a new security fence to be erected around the site at a later date.
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