The protective concrete outer tank for liquified natural gas (LNG) storage at a processing facility in Angola is engineered to withstand a complex range of potential impacts including the extreme pressure and temperature of the liquid inside.

Protection in the event of leakage, earthquake and other impacts

Angola LNG is one of the world’s most modern LNG processing facilities. It has an annual production capacity of more than 5.2 million tonnes of LNG, as well as associated gases and condensate. Supplied with gas produced during oil field operations, it helps eliminate gas flaring in the country, reducing emissions and establishing a source of clean energy.

To store the liquified gases prior to export, four tanks were required – two for LNG storage and the others for liquified petroleum gases propane and butane. The outer tanks, constructed from post-tensioned concrete, provide protection in the event of crack or failure of the internal steel containers. They also need to withstand a variety of impacts including earthquake, blasts and fire. A further challenge in the project was the situation of the tanks. Two are on reclaimed land and two are on soft soil.

Royal HaskoningDHV provided geotechnical design and structural engineering for the tanks as well as supervision of the soil investigation, excavation works and tank construction.

Parametric tools simulate conditions over lifetime of the structures

As is usual in this type of project, there were tight time pressures. For speed and accuracy in the design calculations, the team developed 3D parametric-style tools to simulate the conditions that will occur during the lifetime of the structures, taking into account crack formation and temperature loading. To stabilise the tanks, piled foundations to depths of up to 40 m were sunk.

“Our strength results from our software and our experience,” explains Sander Meijers, Lead Engineer at the Advanced Technology and Research Centre. “In post-tensioning the concrete, there is a delicate balance to be struck between accommodating the pressure of the liquid while avoiding over-compression which introduces cracks. We have a proven track record in successfully managing these challenges.”

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