Dynamic Components

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Product group 3 encompasses all those components which are dynamically stressed, i.e., subject to alternating load directions. These dynamic restraints are fitted to protect piping and other plant components against unforeseen displacement resulting from shocks. Normal operational thermal expansion must not be thereby obstructed. Shocks can be caused by internal or external stimuli, such as water hammer or earthquake.

Additional conceptional applications are the support of planned thermal expansion through guides and the securing of points of zero movement. With vertical riser pipes, the formation of "flexible" fixed points is a frequent requirement.

For optimum coverage of the various applications, specialized products are correspondingly required. Where up-to-date pipe support concepts are concerned, LISEGA's rigid struts, energy absorbers and shock absorbers (snubbers) form indispensable elements for the control of dynamic loads.

Shock absorbers (Snubbers) Type 30, 31

Shock absorbers are usually employed to protect thermal systems against sudden shocks. LISEGA shock absorbers do not restrict gradual thermal expansion. When subjected to sudden movements which exceed designated velocity limits, the shock absorber "locks up" momentarily and forms a rigid connection.

Shock absorbers type 30

Series produced standard design. Available from stock or from running production.

Shock absorbers type 31

Type 31 shock absorbers are specially designed to deal with large loads. They are mainly used in nuclear power stations to protect steam generators and large pumps. Due to the restricted space in such areas, their dimensions are generally designed to suit the given conditions.

Installation extensions type 33

Type 33 extensions are used to bridge larger installation lengths, thus avoiding structural adjustments on site.

Weld-on brackets type 35

This unit is used as a connection for shock absorbers type 30 and 31, energy absorbers type 32 and rigid struts type 39 (also for types 16, 20, 27), and forms the structural attachment.

LISEGA hydraulic shock absorbers, with their well-tried and tested design principle, have proven themselves in safe, long-term and maintenance-free operation.

non-corroding materials
special sealing systems
vibration-proof guiding systems
pressurized self-contained hydraulics
full dynamic response
proven maintenance-free operation longer than 20 years
comprehensive range of accessories
approval through independent authorities

The design load covers a spectrum of 0.675 - 1,124 kip. The standard range encompasses type 30 and stretches to 224 kip. Furthermore, type 31 is custom-built to specific requirements.

LISEGA maintains a continuous series production of shock absorbers. At least 4,000 items are supplied annually, predominantly to nuclear installations. Most of these are used to replace obsolete designs in order to reduce maintenance costs.

Energy absorber (E-bar) type 32

In cases of minimal movement, energy absorbers can be used as an alternative to shock absorbers. A minor dynamic displacement, harmless for the system, is permitted through an adjustable free stroke. If the free stroke previously set is exceeded, movement is restricted by limit stops. Undesirable stress peaks are avoided through conversion of kinetic energy to deforming energy via expansion of the housing.

These components are thereby particularly suitable as pipe whip restraints. The amount of energy to be absorbed can be predetermined at the design stage.

Due to the absence of wear components no recurrent testing is required. The particular advantages are as follows:

adjustable free stroke
no maintenance
overload limits
gradual stress reduction
no recurrent testing

A special calculation program is available should any verification be needed for the piping when installing these components.

Rigid struts type 39

Rigid struts form a rigid connection in axial direction between piping and structure. As the rigid strut has articulated connecting points, limited movement of the pipe within the angular movement of the struts is permitted with no resistance.

LISEGA rigid struts are distinguished by their simple design and economical application:

adjustable length via left-hand and righthand threads
no welding
safe locking of connecting parts via fine threading
favorable performance/weight ratios
suitability proven by independent authorities

Force distribution in a dynamic pipe clamp

Dynamic pipe clamps type 36, 37

In the sphere of dynamic supports, the design of pipe clamps is often not carried out with sufficient care. In spite of impeccable main support units (shock absorbers, rigid struts and energy absorbers), the functioning of the whole construction can be adversely affected by faulty pipe clamps.

To prevent twisting, LISEGA recommends on principle the use of shear lugs with dynamic pipe clamps.This way, defined and verifiable behavior is ensured.

Dynamic pipe clamps type 36

Dynamic pipe clamps type 37

Special clamp for angular arrangement

Dynamic axial pipe clamp with shock absorbers

Pipe whip restraints

One speciality in the area of dynamic pipe supports is the pipe whip restraint. Alongside the energy absorber type 32, which provides the optimum solution to this problem, a U-bolt design for specially large loads has proven to be highly successful.

Pipe whip restraints are exclusively used in the nuclear industry. They dampen and absorb the kinetic energy of bursting pipes in emergency cases. For this purpose, the elongation capacity of the encompassing U-bolts is used, as they are designed to absorb the expected dynamic loads.

Pipe whip restraints have safety-related significance and are subject to the highest demands in quality, design and manufacture. As a large scale supplier to the latest generation of nuclear plants, LISEGA has successfully proven its qualification to supply this specific design.

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