Selection and calculation criteria of fabric expansion joints
The dimensions and conditions of using fabric expansion joints in different types of plants and equipment are completely individual, as well as equipment itself and customers wishes. Fabric expansion joints are most commonly made in accordance with the specifications and customers’ requirements; they are literally made to measure.
A fabric compensator usually consists of several layers. These are gas-tight foils, as well as fabrics and impregnating layers which withstand against temperature and mechanical stress. The materials do not contain asbestos.
Generally, the layers are unconnected. However, they can be fastened together (glued or stitched) -in places of connection along the edges- for better safety during transportation.
Not only size and shape, but also materials’ components and order of layers should be selected on a case-by-case basis.
Accurate basic data from customer, designer or constructor, who know better the equipment characteristics, is the main factor for an optimal construction project of the expansion joint.
In case of replacing the expansion joints you should take into account the experience of working with them and answer the following questions:
- initial material components
- possible causes for the damage
- operational modes of the equipment: constant stress or daily switching on/off
- possible problems with steel parts at the connection points of fabric expansion joints with metal pipes
- other factors which are unaccounted in designing or newly arisen ones
Below are the BASIC criteria for quick and optimal project solution, which should be taken into account to design expansion joints:
- Mounting location: inside buildings, outside, if the mounting location is come-at-able, as well as the place of future maintenance and condition monitoring
- Operating (fluid) medium: it is the main parameter in choosing the material components.
The dew point data (occurrence of condensate) as well as the chemical influence data (the chemical formula of the operating medium) make easy the design solution.
- Solids content in medium: significantly affects both the materials composition of the joint (type of coating, its thickness) and its design, for example, in steel parts, deflectors. The following indicators of solid particles in the operating medium are most important: their quantity (mg / nm3), grain size and flow direction (up, down).
- Temperatures: as well as the operating medium data affect the composition of layers and materials.
Accurate data on operative temperature, ambient temperature, expansion joint’s surface temperature and places of its attachment to metal parts, possible emergency temperatures permit to develop the expansion joint project “made to measure" without unfunctional surplus.
- Pressure: similarly, as temperature data, it is necessary to have the most accurate data on pressure values: overpressure, rarefaction (normal, maximum), pressure fluctuations, single pressure hammer and test pressure value.
- Deformations: determination of the types of deformations - axial, shear, angular, their combinations and frequency. All this affects the structural dimensions of expansion joints, as well as required mounting dimensions.
- Operating medium speeds: affect not only the composition of the layers and materials of the expansion joint itself, but also the construction and materials of metal parts. In any case, at speeds above 10 m/s we recommend using a pilot insert to protect soft parts, which will reduce pressure losses and will prevent unwanted turbulence.
