Offshore wind design

Bolted flange TP-MP gasket seal – providing advanced low-cost protection

An o-ring type rubber gasket seal that provides an instant permanent seal and full environmental protection when built into the steel of a TP’s lower flange is being developed by LICenergy UK with industrial seal partner, Trelleborg, as an ultra-low-steel, low-cost, bolted flange TP-to-MP connection system. With no grouted skirt involved, a series of advanced manpower access and corrosion protection options are also included that add no extra stress to primary steel.

( Text content written by Twenty6 for Luke Fussell, LIC Energy )

Client challenge

Bolted TP-to-MP connections are popular in the offshore wind energy industry for their low use of expensive secondary steel. Theoretically, no grout skirt is needed, saving tons of steel at a stroke.

However, keeping the elements at bay is still a challenge. Traditional grouted connections that run from below low to above high sea level are protected from the marine environment by grout and steel.

This is not the case with bolted connections. One option is to add a short, non-structural grouted skirt. However, this negates the steel savings and still requires expensive offshore grouting operations. A more radical solution is needed.

Our response

Advanced gasket seal

During a comprehensive 2016 North Sea concept design study, LICenergy UK began developing an innovative o-ring-type seal with wide potential offshore applications.

Because of their position – in the primary load path and splash zone – bolted flange joints designed to last for many years in the offshore environment need protection from corrosive sea water.

The extremely robust and low-cost gasket solution we are taking forward in partnership with global seal manufacturer, Trelleborg, comprises a rubber seal seated outside the bolted ring in a flange. This is designed to provide an immediate and long-term seal and can dramatically cut the cost of installation by completely removing the need for grouting operations.

Access and corrosion protection systems

Conventional grouted connections are strong structural welding points for boating landings and corrosion protection systems. Our lean-steel alternatives avoid welding secondary to MP primary steel, with potential stress and pile hammering damage.

As a further corrosion protection alternative, we are also co-developing with strategic partners an advanced TS(Z) A (Thermally Sprayed (Zinc or) Aluminium process to replace the use of anodes.


The o-ring-type rubber gasket seal is being designed to: –

  • Provide a long-term seal solution
  • Reduce secondary steel use dramatically
  • Reduce installation time
  • Provide complete protection in the marine environment
  • Minimise the potential for pile hammering damage to welded attachments
  • Avoid grouting operations in difficult offshore conditions
  • Minimise the presence of people in a demanding H and S environment

Note on concept design study methodology

Our concept design review considered a wide variety of options used across the industry, including: –

  • Manufacturing cost estimates for primary steel and secondary steel attachments
  • Installation costs: – Installation vessel size Number and size (weight) of offshore lifts; Installation time (grout curing)
  • Weather window needs – down time
  • Corrosion protection
  • Cable routing – external J-tubes v internal routing
  • Sealing requirements
  • O and M
  • Health and Safety – from transport and installation to eventual decommissioning