AN UNSTABLE concrete foundation pad is threatening to rupture a liquid gas tank and ignite a massive explosion near one of Europe's largest oil terminals in Shetland.
Engineers from inspection specialist Inspectahire are on site at Sullom Voe oil refinery trying to stabilise the 50m diameter 20,000t Liquid Petroleum Gas (LPG) tank.
The tank keeps the LPG at a continuous - 46infinityC temperature. It sits on a 2m thick concrete foundation which has to be continuously heated to prevent the ground below from freezing and causing cracking in the structure.
However, thermal conduits which carry copper heating elements within the slab have failed. These run in two circuits but only 45% are still working. According to BP engineer Mike Killeen the elements have now frozen solid within the slab.
Engineers are now rushing to replace the conduits before the foundation slab cracks.
Killeen warned that if this happened there was a risk that the huge tank could lose stability and rupture in extremely high winds.
The resulting spillage would cause a massive fireball as the LPG boiled and ignited.
Previous attempts by BP engineers to remove the failed element by injecting antifreeze have already failed. The latest plan is to drill the copper elements and steel conduits out of the slab.
Inspectahire managing director Cailean Forrester said: 'Engineers from drilling specialist Hamdeen, BP and ourselves have had to develop a specially designed rig to drill a small diameter horizontal bore through the slab.'
Sullom Voe terminal was built between 1978 and 1981 and handles around 500,000 barrels of oil per day. There are 16 crude oil storage tanks, each with a capacity of 80,000t within the blast zone of four 20,000t LPG tanks. Four 25MW gas turbines used to power the terminal are also within the zone.
Draining the carbon steel tanks is not practical it is claimed as there is nowhere else to store the LPG. Operations in the terminal are continuing as normal.