R&D

SEALING CONCEPTS

In high-pressure technology both static seals such as flange gaskets and dynamic seals for longitudinal and rotational movement in valves are used. The choice of the static seal depends on the design specification, the chemical and physical loads, the installation conditions, the allowable leakage rate and the environment. The chemical and physical loads such as pressure, temperature, media or external loads determine the basic material used and the gasket basic concept of removable seals. Basic sealing concepts distinguish between self-energized and non-self-energized gaskets. Non-self-energized gaskets need an external force to establish and maintain the sealing contact during the operation, while for self-energized gaskets the sealing contact pressure increases with the media pressure and almost no external force is required. Due to increased temperature and media interaction, mainly metallic gaskets are used at BHDT GmbH.

The perfect gasket that could be used in almost all static (flanged) assemblies has the following characteristics:

  • Self-energized: It is self-energized – smaller bolts can be used because no pretension for the generation of sealing contact pressure is necessary
  • Optimal diameter: The fluid seal diameter is nearly equal to the pipe diameter (for flange gaskets) - smaller flanges and screws can be used, because the axial force resulting from sealing diameter cross sectional area and internal pressure is smaller
  • Insensitivity: It is insensitive to geometric tolerances – manufacturing and assembly costs are kept low
  • Corrosion resistance: The used material has great corrosion resistance
  • High static strength: The used material has high static strength – much elastic energy is stored in the gasket why the required seal contact pressure remains high enough despite external forces or the partial loss of the bolt tensioning
  • High static strength: The used material has high creep resistance over a wide temperature range – time-dependent creep and setting effects at elevated temperature are minimized which would lead to an increase in the leakage rate
  • High static strength: The thermal properties of all materials in the assembly are very similar – cyclic thermally induced forces may not result in large-scale plastic seal deformation that leads to the loss of sealing contact pressure
  • Economical: The seal is producible in a very economical way

There are numerous requirements for a sealing system to provide a tight connection for a variety of loads caused by temperature, medium and internal pressure and external mechanical loads. These requirements cannot be realized economically with just one material and one gasket geometry. For this reason, the most suitable sealing concept must be determined and selected for each single application.

BHDT Gmbh provides tailor-made sealing concepts for special applications. Currently a self-energized gasket for a deep-water application is developed, which is equally suitable for large internal and external pressure.

Sealing Technology

The figure shows the stress distribution in the contact area of a seal.