Expansion joint

The compensator is a flexible element to compensate for movements in the pipelines, in particular for thermal length variations, vibrations, wall penetrations or subsidence. The compensation takes place mechanically via an elastic bellows. Depending on the media, pressure, temperature and life requirements of the compensator is made ​​of different materials. In the power plant area metal and fabric expansion joints are the most common, but there are also applications where expansion joints made ​​of rubber, PTFE or other plastics are used.

• 3.1 Axial
• 3.2 Angular
• 3.3 lateral

• 4.1 fabric expansion
• 4.2 metal compensator 4.2.1 Expansion joint
• 4.2.2 Angular expansion
• 4.2.3 Lateral
• 4.2.4 Universal expansion

History

• Historical Brochures

Brochure back from 1930

In 1920 Emil joke man reported the first so-called metal hose compensator for a patent (German Reich Patent No. 367 185 dated 29 July 1920). On the technical side, it was in this forerunner of today compensators to a large-sized pressure-tight metal hose, with defined limited mobility.

In the 1930s, the metal tube principle was replaced as the central functional element through the metal bellows. This design principle - metal bellows with fittings - is still the constructive basis of modern metal expansion joints.

Structure of the compensator

Each compensator is composed of a single-or multi-layer elastic bellows and a pipe connection. In metal expansion bellows and connecting usually form a unit, while expansion joints always consist of a combination of metal frame or tension bands and Gewebebalg. The tissue is clamped in the frame or directly to the pipe. Fixation is achieved either by clamping bands (only for round cables possible ), fittings or special terminals.

Expansion joint

The bellows of the expansion joint can consist of metal, a composite of technical fabrics, plastics or rubber. Always is both a single layer and a multilayer structure in which the layers of different design criteria (eg, leaks, corrosion protection, etc. ) follow possible. The elasticity of the bellows is concluded by a mostly undulating defined material compression.

Duct connection

The connection of the compensator to the channel either via a flange or directly, in each case by screwing or welding.

Baffle

For gaseous media flow conduit tubes or baffles optionally be used to minimize efficiency losses due to flow deflection and damage to the compensator. Turbulent eddies due to the enlargement of the flow cross section in the region of the compensator can lead to both deposition of particles in the flow compensator as well as to damage from abrasion. For the design of a compensator with baffle, it is essential that the maximum movements and the flow direction are defined.

Insulation

In hot gas lines compensators are additionally externally or internally insulated. Failure to do so due to high temperature differences ( between the outside and inside of the channel or sudden Kaltlufteinströmung by emergency stop) the risk that material stresses lead to the failure of the compensator.

Cover

To protect against external influences ( chemical interactions, temperature effects, for example by heat radiation of other components, weather), expansion joints can be provided with a cover. The insulation which is formed by the cover, but must be taken into account.

Special construction of metal expansion joints ( many layers and multiwalled )

In modern Kompensatorenbau the metal bellows are often made ​​in the so-called multi- layer design. At this time, the simultaneous increase of flexibility and stability, combines several thin layers of metal as a wall of the bladder. A distinction is made between two types of construction, the multi-layered and multi-walled bellows assembly. The multi-layered structure consists of a pressure-tight welded along the outer and inner cylinder made of stainless steel. Therebetween is an open helical cylinder forming a plurality of inner layers, depending on the design. In the multi-walled structure there are a plurality of longitudinally welded cylinders that are plugged into each other. Each cylinder forms a pressure-tight and self-contained " wall ".

The main advantages of multi-walled bellows:

Divided bending beam

• Control of high and highest pressures
• Great movement recording
• Small dimensions
• Low adjusting
• Optimal compensation in the smallest space
• Early leak detection ( in case of damage ) over standard check hole
• Full to bursting
• Opportunity for permanent leak monitoring in critical media
• Economic use of high quality, corrosion resistant materials such as Inconel, Incoloy, Hastelloy, titanium and tantalum
• Insulation against structure-borne noise up to 20 dB

This construction brings not only technical and economical advantages.

Thus, different materials can be used for the bellows assembly. Such as high-alloy stainless steels for Materials with medium internal and / or external tube and niederlegierte stainless steels for liners.

Types of compensation

A distinction is made in the design of joints between axial, lateral and angular movements. For rectangular joints not only the motion, but also in addition, the spatial direction of movement is important. Depending on the movement form of different restoring forces. Restoring forces are spring forces, the return force of the compensator in its initial position. Rise especially in metal expansion joints, the restoring forces with increasing deformation sharply.

Axial

In the axial compensation, the thermal expansion of a straight line segment between two fixed points is received by a expansion joint. The distance between the two fixed points determined to be compensated line length and thus the axial movement executed by the compensator.

For the axial compensation following basic rules apply:

• The planar or spatial piping system is currently divided by fixed points in individual sections that they can be compensated for in each case by a single expansion joint.
• The fixed points are designed so that they can withstand the pressure and spring forces the axial compensator, the frictional forces of the guide bearings and the flow forces.
• Long pipelines are to be secured between the fixed points by pilot bearing against buckling.
• The expansion joint should be installed in the immediate vicinity of a fixed point and a guide bearing.
• Inadmissibly large fixed-point loads can be avoided by pressure force balanced axial expansion joints.

Angular

In the angular compensation of thermal expansions are at least two required for a complete compensation even three angular expansion. Angular expansion joints offer a variety of combinations in so-called two - or three- joint systems.

The planar three- joint systems come with one-sided angular movable joints, while the spatial three-hinged systems to accommodate thermal expansion in three axes need at least two sides angularly movable Kardankompensatoren.

For the angular compensation following basic rules apply: There are always at least two angular expansion joints required.

• The angular compensation is always associated with multiple flow deflection by 90 °.
• Since angular expansion joints absorb than the hinged compensators released from the bellows pressure forces themselves, the anchor points for pipes will be charged only by their displacement forces and moments, as well as the friction forces of the cable guides and the flow forces.
• The angular compensation is particularly suitable for pipe runs spatially complicated.

Lateral

The lateral compensation is also connected to a deflection of the flow by 90 degrees within the planar or three-dimensional piping system. Most existing rectangular deflections for the installation of lateral expansion can be used in the system.

The movement of a lateral expansion is always composed of the desired lateral movement and a slight, unavoidable axial movement of the compensator along itself. The simple lateral expansion for lateral movement in one plane only allow in comparison to the axial expansion joints a much greater expansion capability. Universally movable Lateral also allow the simultaneous recording of two line routes stretching in different directions.

For the lateral compensation following basic rules apply:

• According to their movement Lateral always be perpendicular to the compensating pipe. That is, lateral compensation is always associated with flow deflection.
• Discharge of the fixed points of pressure forces as angular expansion.

The unavoidable, small axial movement of lateral expansion is included in the "total compensation" of an additional Gelenkkompensator. Often, however, it can balance the pipeline by elastic bending. In this case, the line guides provide enough clearance. Lateral allow an angular motion around the bolts or joint axes. This can be exploited to accommodate cable slack between the pipe supports. Lateral and angular expansion joints are often combined in the three joint systems.

Materials and designs

The choice of a suitable compensator based on the principle of cost-effective functional performance. In an economic analysis not only the cost of the expansion joints, but also the necessary fixed points, pipe fittings and manholes must be observed. In addition, especially the maintenance and repair costs into economic considerations must be taken into account. Repair and replacement of expansion joints exceed the investment costs usually many times: the cost of the plant shutdown to safety arrangements and scaffolding to sometimes hard to reach places come in case of damage, in addition to new investment may be added.

Fabric expansion

Soft cloth or fabric expansion joints are made ​​from technical fabrics and elastomers management and channel members. They are used for the compensation of offset and the mechanical noise and vibration reduction. The soft material is either mounted on a steel frame or - connected to the pipe using straps - at low load. Depending on the purpose fabric expansion joints are manufactured in single layer or multi-layer design. Different functions, for example, can through the multi-layer structure Insulation, tightness, pressure surge behavior, etc. are combined according to specific requirements. Compared to metal expansion joints Fabric expansion joints to draw (also called restoring forces ) through a low weight and low reaction forces. Therefore, fabric expansion joints are particularly suitable for large dimensions at low operating pressures and gases (air, exhaust, smoke). For the interpretation, there is no standardization, but a collection of technical information of the Quality Association for Fabric Expansion Joints in RAL Association, which describe the state of the art.

Metal compensator

Metal expansion joints are preferably used when the pipeline systems are pressurized, with high temperatures or if aggressive media must be conducted. They consist of one or more metal bellows and connecting parts at both ends. Depending on the application and to be compensated movements they additionally have joint anchorages. Corresponding to the three basic types of movement, a distinction is axial, angular and lateral. Apart from low-alloy stainless steels and nickel - base alloys or pure metals are used as materials for the Kompensatorherstellung. For example, in areas of application in the chemical industry or in the field of sea water or Subsea Hastelloy, Inconel, Incoloy or titanium and Tatal are often used materials. In the field of steel production bricked compensators come from high-alloy stainless steels are used, which have a temperature resistance of over 1000 ° C. Round stainless steel expansion joints are limited in their diameter due to the technical production possibilities. Rectangular metal expansion joints can be manufactured in any size and are only limited in size by the transport.

Expansion joint

The expansion joint is used to move recording in the axial direction. Standard connection parts of the axial compensator are welded ends, fixed and loose flanges. Frequently Axial equipped on the inside of the metal bellows with a draft tube. This reduces the flow resistance and to prevent damage that may be caused by direct contact with the flowing medium. Axial expansion joints that can accommodate large movements, often consist of two metal bellows and an inner or outer guide tube which protects against buckling by internal pressure. For small diameters protection tubes serve to exclude mechanical damage during installation and operation. Axial expansion joints are suitable for internal and external pressure.

If the metal bellows of Axial außendruckbeaufschlagt, then allow the expansion joints under internal pressure in a pipeline very large axial movements. Since external pressure there is no danger of buckling, very long metal bellows or bellows combinations of a very large movement recording can be used here.

Angular expansion

The angular compensator absorbs bends or angular movements. As the simple expansion joint, it is composed of a metal bellows and the mutual connection parts. In addition, however, it has a

• Articulated anchoring this connection parts for angular movements in one plane or
• A gimbal anchorage for all-round angular movements

Consequently, the anchor determines the type of movement recording.

Lateral

The lateral expansion joint, absorbs the transverse or lateral movements. It consists of

• One or two metal bellows with intermediate tube
• The mutual connection parts, and an articulated anchoring this connection parts for lateral movement in a plane or on all sides for lateral movements.

Normally, the anchor consists of spherical mounted circular anchors. At high axial compressive forces flat anchors are used with bolts or cross joints. The size of the lateral movement increases with the bending angle of the two metal bellows and with the length of the intermediate tube.

Universal expansion

The universal expansion can not take combined only axial but also angular and lateral movements. It consists of two metal bellows with the intermediate tube and the mutual connection parts. As a special form of the universal expansion joint axial compensator for stability reasons, has only a low compressive strength and also pollutes the subsequent Leitungsauflager with the resulting from the internal pressure axial compressive force. It is most often used when large axial and lateral movements are offset at low pressure.

In contrast to the floating axial and Universal expansion hinged compensators pollute the subsequent Leitungsauflager not with the axial thrust due to internal pressure, since it is absorbed by the anchoring joint.

Rubber expansion joint

The expansion joint consists of vulcanized synthetic rubber sheets, which can be selected depending on the medium and the desired resistance. For the pressure and temperature resistance properties different base layers such as nylon cord, aramid and steel cord are available. Rubber expansion joints are characterized by high flexibility in the axial, lateral and angular direction, and a high expansion absorption at extremely short dimensions from. In addition to the expansion absorption, they also have an excellent sound and vibration- reducing effect.

Arch structures ( 'natural' compensation)

Arch structures, usual U-bends and Z- bends, suitable only for natural compensation of thermally induced changes in length. These structures are also referred to as sheet Lyrabogen, but no special components but they are made of pipe members. For rigid pipes four 90 ° bends and a Z- bend two 90 ° bends are required, are inserted between each of shorter pieces of pipe for a U-bend. For flexible pipes, the pipes may alternatively be bent itself accordingly, the minimum permitted bending radii must not be exceeded during installation and operation. The use of sheets, the angle of which differs significantly from 90 °, is avoided, as in such designs, very large forces can act in adverse directions. The great advantage of arch structures is that they consist of the same material as the rest of the pipeline. This means that no restrictions of the operating parameters by the compensation elements arise. With metallic piping also the possibility of electrochemical corrosion at material interfaces is turned off in the already heavily loaded compensation elements. The disadvantage is the large space requirement for the sheets. When Z -arm also is added an offset of the pipeline, which is to be considered in the planning, but for example in district heating house connections may well be advantageous.

Linsenkompensator

A Linsenkompensator comprises at least two S-shaped half-shells, which are welded at the periphery. The wall thickness is compared to a Wellrohrkompensator significantly stronger. The Linsenkompensator is widely used in heat exchangers to compensate for the change in length between the shell side and tube side.

Langmuffenkompensator

Langmuffenkompensatoren (also Stopfbuchsenkompensator or Dehnungsstopfbuchse ) consists of two telescopically displaceable tubes, which are sealed by means of a sliding seal. The change in length corresponding to the insertion depth of the pipes.

Failure of expansion joints

Kompensatorversagen can be attributed to diverse causes. The most common causes of damage are:

• Shipping damage, improper storage and handling
• Improper installation or inadequate protection during assembly or operation
• Inadequate anchoring, guiding and supporting
• Failure of the suspension
• Corrosion: Due to the increase of the channel cross-section that can occur due to the temperature gradient between the outside and inside of the compensator in gaseous media for dew point and thus the accumulation of condensate. This can damage or destroy the compensator and must therefore be minimized or controlled by baffles removed.
• System pressure
• Illegal deflections of the bellows
• Torsion
• Balgabtrag

Many risks for Kompensatorversagen can be minimized through proper design of the compensator. Most Kompensatorenhersteller have a broad knowledge and experience can suggest, in coordination with the operating parameters suitable compensation solutions. Damage that is not due to the design, can be minimized by proper handling and storage according to the manufacturer, compliance with safety regulations and inspection and regular maintenance.

After installation, check:

• Whether the expansion joint has been damaged during installation,
• Whether the compensator is in the correct position,
• Whether the flow direction is correct according to the specifications.