TP Compact Flanges for wind turbine tower flanges

Wind turbine towers are normally erected by assembling several cylindrical or conical shaped elements on top of each other. These elements are built by fabricators in lengths which are practical to transport and to handle, including lifting at site, see figure.

The most practical way of assembling these elements is by joining using bolted connections. A number of different designs have been developed, built and installed over the years, but still the industry is experiencing challenges with the existing tower flanged connections.

The main challenges are related to;

  • Structural strength

  • Fatigue resistance

  • Loosening of nuts during operation

There have been several collapses of wind turbine towers where the cause of the failure has been from poorly bolted joint design. The industry also has a challenge with the new and bigger wind turbines requiring higher capacity connectors to transfer to loads to the foundation.

TP-Products has developed a wind turbine tower flange design based on the principles used in compact flanges for piping applications with extreme dynamic loads. The new flange designs meet the design and functional requirements of the wind industry, including the offshore applications with the additional environmental loads from waves and current.

Compared with the traditional compact flanges, these flanges are characterized by the bolts being internal to the connecting tubulars or conical shells.

TP Compact Flanges for floating load bearing structures

Based on the same design as used for the tower splices, TP-Products has developed a bolted flange connection for tubular connections in floating structures, typically used to support wind turbine towers. The high face to face contact stress between the flange faces proved a pressure tight metal to metal seal. For connections located under water, an additional sealing element can be included on the flange face to give a sealing function even for accidental loads of the order giving some flange separation.

TP Compact Flanges for floating load bearing structures

Higher test pressure can be used, but this does not provide any better confirmation of the seal functionality for internal pressure. Using too high pressure will push the seal off the seat and create a leakage. A condition which has no relevance to the actual use. A reverse integrity test pressure higher than 150bar should not be applied, except in the case of testing to verify external pressure capacity.

It is only in the case of using the TPC Clamp Connector subsea that a higher external pressure than 150bar needs to be applied. The actual external pressure capacity is depending on seal ring material strength and the seal ring.