Pipes / tanks
Video probe surveys
Inspectahire Instrument Company
The largest single-skin LPG tanks in the world are located at the Sullom Voe oil terminal in the Shetland Islands. Each tank has a capacity of 22,000 tonnes, measures 48m in diameter and was erected in the 1970s.
The tanks were constructed on concrete ring foundations, which had been subject to the exposed maritime climate as well as the cyclical loading that occurred as the tank was operated.
LPG was stored at -48°C. While a base heating system was in place to stop the ground from freezing, this was known to have failed in part on one of the tanks, and ice was present.
After a life extension was given to the terminal in 2000, a management review by the operators of the terminal had determined that an inspection of the concrete structure and the tank foundation would be a worthwhile exercise. Inspectahire had had initial involvement with the base heating system, and was also tasked with the client’s Consulting Engineer to undertake this inspection.
The key to a successful project is the level of planning that takes place prior to implementation – in this instance, Inspectahire was asked to undertake a survey of the concrete ring and foundation to ascertain whether an ice lens was forming under the tank, to determine the general condition of the concrete. Given that this was an operational tank, and no previous inspection had taken place there were various considerable challenges.
A key aim was to maintained the structural integrity of the foundation. There was no access, so investigations would be intrusive and involve coring into and through the concrete. Although not a particularly complex civil engineering task, carrying out concrete investigations in such an environment meant great care and planning had to be undertake so as to ensure the safety of both the asset and those performing the task.
Given the small diameter of the conduits and their length, Inspectahire considered utilising various fibre optic and CCTV equipment. The small size of these instruments meant that systems rated as intrinsically safe or explosion proof were not available. In the majority of the conduits, cables were still in place, so it was determined that video endoscopes would provide the best means of viewing.
The removal and reinstatement of heating cables has meant utilising a number of pieces of inspection equipment and tooling. The primary tooling was custom-made as this type of challenge has not been widely faced.
The on-site team utilised skills in rigging and lifting, drilling, on-site machining, jetting and retrievals to clear through the conduits – all while working in a zoned area in Europe’s largest oil terminal.