GOAL Highlights Seawater Mixed Grout

The use of seawater mixed grout connections in offshore jacket foundations reduces costs, as well as the environmental footprint, according to a research project led by innogy and funded by the Carbon Trust Offshore Wind Accelerator program.

innogy, SPR/Iberdrola, SSE, EnBW, Ørsted, Statkraft and ORE Catapult investigated Grouted OPC (Ordinary Portland Cement) Connections with Annuli of Large Dimension (GOAL) in pre-piled and lightweight jacket foundations.

Seawater mixed neat grout cement connections using OPC have a long track record in offshore oil & gas as a cost-effective, reliable subsea connection type, Project Director Daniel Bartminn said, emphasizing that this technology has been transferred to offshore wind with approximately 100 jackets of this type installed so far.

“We have particularly emphasised the verification of the use of seawater mixed OPC as it significantly reduces the environmental footprint for these structures. In contrast high strength grouts require freshwater, which offshore adds significant to the cost,” Bartminn said.

“Particular offshore wind jacket structures are requiring project specific certification, where applications exceeded the limits of existing standards. So there is an urgent need to fill the gap in the underlying test data and designs to establish and verify the use of OPC for large annuli offshore wind applications, because it brings clear cost advantages compared to the use of high strength grouts or grout mortar mixes. Especially because OPC is easier to install, with contractors having decades of experience with this material. Additional savings could arise from de-risking and avoidance of repair works, as well as ease of certification.”

This type of grouted connection has been used for existing offshore wind farms, such as Thornton Bank in Belgium, Ormonde in the UK and Alpha Ventus in Germany.

Carried out at KIT Karlsruhe, the tests are the largest consistent tests series for large annuli in full and half scale adding extensive knowledge to further improve existing ISO guidelines, innogy said.

The dataset will be analyzed in the upcoming month and summarized in a study report, expected to be published during the second quarter of 2018.