Post-Tensioning – LNG Tanks Trinidad & Tobago

LNG tanksClient
Atlantic LNG

Consultant
Ove Arup & Cleveland Bridge

Contractor
Whessoe & Carrillion

Post-tensioning Specialist
Freyssinet Ltd

Contract Duration
Over 5 years

Work Completed
2003

Contract Value
£2.5m

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Following the successful completion of post-tensioning to two 130,000cum LNG tanks for the Atlantic LNG Project at Point Fortin in Trinidad and Tobago, Freyssinet was awarded the sub-contract for the supply and installation of the post-tensioning system to the third tank of 160,000 com capacity on the same site.

The first two tanks 74.4m internal diameter and 30.18m high with a wall thickness of 450mm and post tensioned by 176 No. 15K15 vertical U tendons and 164 No. 15K15 circumferential tendons per tank.

Construction commenced in December of 1997 with the post tensioning of the closure completed in 1999.

Freyssinet worked closely in the UK with the tank main contractor, Whessoe and the consulting engineer, Ove Arup, to design the post-tensioning systems required, ensuring cryogenic requirements for LNG construction were adhered to and recognising the aggressive and corrosive nature of the nearby Caribbean, the site being constructed on reclaimed land. A feature of the construction specification was the testing requirements to achieve those corrosion standards and the implementation of the new grouting specification being introduced at that time in the UK through TR47. Corrosion trials were established on site to determine levels of protection to be applied to the strand and grout trials, both vertical and horizontal were carried out to ensure adequacy of the grouting operations.

Tanks 1 & 2 were constructed for LNG train 1 at Point Fortin and with the expansion of the facility a further tank was required with LNG trains 2 & 3. This third tank was of 160,000cum capacity, 34m high and 89m diameter with a wall thickness of 500mm. Freyssinet was once again chosen as the post-tensioning subcontractor, this time with Carillion Caribbean carrying out the civils works for the tanks for the main contractor Chicago Bridge & Engineering. Tank 3 construction commenced in January 2001. Freyssinet was responsible for the post-tensioning design and worked in conjunction with Chicago Bridge engineers in the USA to develop a system that required 100 No. 19K15 circumferential tendons with no vertical post tensioning. The information gained from trials on tanks 1 and 2 were again used on tank 3 with proven corrosion prevention techniques and grouting procedures used.

Freyssinet has substantial experience of prestressing LNG tanks throughout the world, with post-tensioning anchorage systems used in this type of construction being specifically designed and tested to comply with the stringent requirements of LNG specifications, particularly the need for high performance at low temperatures.

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