Dismantling LNG holders

Paul Boughton

Decommissioning specialist Masterton, based in in Grangemouth, UK, has been awarded a £4m contract by international electricity and gas giant, National Grid.

The contractor is dismantling four liquefied natural gas (LNG) tanks and associated process plant at National Grid’s Heath Farm Lane storage facility at Partington, Manchester. This is the first LNG demolition project of its kind in Europe and will call upon a number of pioneering techniques.
Work commenced on the 195,000m² site with extensive testing and preparation required to ensure the site was fully purged of any residual risks. Masterton’s team of 12 used hot cutting techniques and demolition excavators with shears to remove low level pipe work and vessels from the vaporisation and liquefaction plant. It then turned its attention to the site’s four skyline- dominating LNG gas tanks.[Page Break]
The 45m high and 135m circumference double-skinned tanks had each been used to store over 21,000 tonnes of LNG at temperatures of minus 160 degrees. Very different in construction to traditional gas holders, these tall steel tank-within-a-tank structures were designed in the 1970s to safely store the highly volatile natural resource in its liquid state. With solid sides, the tanks have steeply sloping arched roofs supported by a series of arch beams and the roof alone weighs some 150 tonnes.
Masterton project manager Matt Harvey explains: “By liquefying the natural gas here at Partington, National Grid was able to store far larger quantities. The liquefaction process refrigerates the gas at extremely low temperatures and therefore the tanks were designed to effectively act as giant thermos flasks. They are double-skinned with perlite insulation between the inner and outer skin.[Page Break]
“Dismantling the steep roofs of the tanks was initially a concern; the safety of our men would have been compromised by working at such heights as the very heavy structure became unstable. However, using our extensive industrial demolition and structural engineering expertise, we designed a method that would use explosive charges to cut through the outer steel roof and ensure it dropped safely to the ground within the body of the gas holder whilst all our operatives were safely beyond the exclusion zone.”
Following rigorous testing, the 60 steel supporting roof beams of the first holder were exposed before being pre-weakened with sit cuts and 45 explosives charges were inserted. The first tank roof was successfully blasted at 12 noon on Thursday 4th October.
Masterton will continue with the demolition of the remaining three tanks and will also fell a 30m Solexol absorber column. The contract is due to be completed by the end of January 2013.

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