Maintenance free bolted joints with IHF fasteners

IHF Stretchbolt and IHF Roundnut

  • Stress-optimized design, no washers required
  • Substitution of common bolts and nuts

Maintenance free bolted joint

  • Proven by more than 3,000 measurements on wind turbines over 18 months

Approved by theGerman institute for technical approvals (DIBt)

Substituting common HV connections

Compared to conventional HV connection (one hexagon bolt, one hexagon nut, and two washers) the IHF Stretch-System reduces the connection to two core elements: IHF Stretchbolt und IHF Roundnut.

  • IHF Stretchbolt: Stress-optimized bolt, the washer is integrated in the head of the bolt
  • IHF Roundnut: Stress-optimized nut, large contact area
  • IHF Stretch-System: IHF fasteners are applied with ITH bolt tensioning cylinders.

IHF fasteners are generally used in steel construction, especially on flanges.
Available standard dimensions are: M36 to M64 (1 3/8'' to 2 1/2'')

HV-connection with torque method

On conventional HV-connections the standard pre tensioning force is applied by torquing the nut with a hydraulic wrench. It is not uncommon to have very different friction coefficients from bolt to bolt with the torquing process. This in turn can lead to big fluctuations in pre tensioning forces. Therefore it is possible that the pre tensioning force on some of the connections is below the minimum pre tensioning force required. With dynamic loads a bigger stress intensity factor appears which can lead to bolt failures.

Innovative IHF Stretch-System

By using the IHF Stretch-System a higher repeatability of the pre tensioning force on the bolt is guaranteed. This improved connection allows

  • longer maintenance intervals and therefore reduces maintenance costs. The more compact tensioning tool (bolt tensioning cylinder) makes it possible to reduce
  • reduction of the distance from the center of the bolt to the casing inner wall. Thus the flange diameter of the ring can be reduced which leads to a considerable cost reduction

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