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Concrete spotlight: Let the gas flow

The new liquefied natural gas terminal in Milford Haven, Wales, has called for large scale concrete work to upgrade a 1km-long jetty.

As part of the construction programme of the new liquefied natural gas (LNG) Terminal at South Hook in Milford Haven, Wales principal jetty contractor, a joint venture (JV) between Belgian company Besix and Kier Construction, engaged subcontractor Freyssinet to carry out large scale concrete repair and cathodic protection works.

The focus of the work involved upgrading the existing 30-yearold, 1km jetty serving the facility to provide for a further 30-year service life.

According to Freyssinet, the jetty concrete repair and cathodic protection elements of the project is one of the biggest repairs contracts of its type undertaken within the UK.

The existing 1km-long jetty comprised 125 separate support structures. The jetty head was a further 1km in length and, in addition to the repair and cathodic protection works, was subject to various alterations to provide facilities to berth four vessels.

The old structure had suffered from chloride contamination. This meant that there was corrosion of reinforcement and that without cathodic protection any concrete repair carried out would fail in the short-term.

The South Hook terminal is central to securing future energy supplies in the UK. It is one of the largest hydrocarbon projects of its kind in Europe

Freyssinet carried out hydrodemolition of the defective concrete, along with the sprayed concrete reinstatement and the installation of the cathodic protection system.

These works were applied to the reinforced concrete pile caps and pre-stressed concrete piles as well as to the new and old steel piles to achieve the necessary design life of the jetty upgrade.

Firstly, the subcontractor carried out a detailed survey to assess the extent of damage and determine the scope of repairs. The concrete repairs themselves were then carried out using a hydro-demolition technique and with reinstatement of concrete to the repair zones by means of dry-spray concrete.

Cathodic protection to the reinforcement within the concrete was achieved using a titanium mesh anode fixed to the surface of the concrete, with a cementitious overlay of dry-spray concrete. A transformer rectifier was installed to convert the AC power to DC before being applied to the anode. The technique reverses the polarity of the reinforcing steel, halting any ongoing corrosion and preventing any new corrosion cells from forming.

The Freyssinet team encompassed the skills from various divisions of the Freyssinet Group including Freyssinet in the UK, Freyssinet France and CCSL. Sprayed concrete personnel were provided by Freyssinet France, cathodic protection design by CCSL and installation works by Freyssinet.

Following a five-year construction and repair programme for Qatar Petroleum, Exxon Mobil and Total, the project at the LNG plant is now drawing to a close. The facility has been constructed to receive LNG from Qatar and resolve the issue of dwindling gas supplies in the North Sea.

The South Hook terminal is central to securing future energy supplies in the UK, allowing importation and re-gasification of LNG, and is one of the largest hydrocarbon projects of its kind in Europe.

The LNG terminal’s upgraded jetty allows docking of large tankers along with five LNG storage tanks and a re-gasification plant from where gas will be delivered into the UK transmission system.

Milford Haven offers perfect anchorage conditions in deep waters, which are easily accessible by the large capacity double-hulled LNG tankers, each carrying up to 265,000m³ of liquid gas.

  • Construction work taking place on the jetty

    Concrete spotlight: Let the gas flow

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