Fabric Expansion Joints

fabric-textile-expansion-joints-iran Fabric Expansion Joints

Fabric Expansion Joints

These are often used in ducts which carry hot gases at low pressures. The major design parameters are the temperatures and flow rates of the gases and the amount and abrasiveness of solids suspended in the gases. Layers of different fabrics, insulation, and metal foils can be combined to accommodate the temperatures and pressures in the system. The fabric belt may need to be replaced periodically.

EGP has been awarded to be a LBH License Partner to provide a wide range of Textile Fabrics used for many range of applications. Fabric expansion joints are used for absorbing movements between joining connections in gas conveying ducts and pipe-lines. The movements can be caused by thermal expansion of the ducting system, wind conditions or vibrations from other system components or machines. In addition, fabric expansion joints can serve as seals and compensate for installation misalignments. The implementation of fabric expansion joints provides a number of advantages, which are technically and economically important.
They are:

  1. Extremely flexible
  2. Absorbing large movements
  3. Absorbing different movements simultaneously
  4. Only requiring a limited building length
  5. Lightweight
  6. Easy to handle, store, install, repair, replace
  7. Not transmitting noise or vibrations
  8. Reducing the necessary strength of fix-points and supports
  9. Not corroding
  10. Dimensionally stable
  11. Cost effective

Fabric expansion joints are widely used for a large number of industrial applications, such as: Power Plants, Boiler Systems, Flue Gas Desulphurization Systems (FGD), Nitrogen Oxide Reduction Systems (DeNox), Gas Turbines, Nuclear Power Plants, Incinerator Plants, Cement Industry, Filter Systems, Ventilators and Ventilation Systems, Dust Suction Systems, _ Offshore Installations, Shipbuilding, Chemical Industry, Paper Industry, Limeworks, Steelworks, Industrial Furnaces, Painting-& Drying Systems.

Selection Criteria
Expansion joints are one of the most important and at the same time relatively vulnerable components in duct systems and pipe lines. It is therefore of vital importance, in order to avoid costly shutdowns of systems and technical problems in general, that each individual expansion joint is designed exactly in accordance with the operational conditions present. The most important factors of which several are interdependent are described in the following.

Installation Place
In case the expansion joint is for a new plant or system, it has to be taken into consideration, even on the project stage which solution concerning expansion joints that is technically and economically to be preferred. First of all, the mounting place for each expansion joint should be evaluated. For mounting places, which are e.g. not easy to access for installation, it could be considered to choose a complete expansion joint unit, including all steel parts and ready for bolting into the duct work. In other cases, it could be preferred to order only the fabric expansion joint, in either a “closed” version, or as an “open” version including a joining kit for joining of the expansion joint on site. Additionally, it could be chosen that some of the steel parts, e.g. the backing flanges, are to be delivered along with the expansion joint, and it should be decided whether it would be an advantage to make the bolt holes on site or have the expansion joint delivered with the bolt holes already drilled. In any case, the optimal type and profile of the expansion joint has to be determined, and the dimensions and type of duct flanges etc. must be designed accordingly.

The composition of the layers of an expansion joint is highly dependent on the medium, which is to be conveyed. It is therefore of the utmost importance that the contents of the gas is known. The influences on the fabric layers could be acids, solvents, dust, solid matter and many others. If there are abrasive particles or solid matter in the gas stream, an inner metal sleeve should always be installed, and preferably in combination with an insulation bolster, if there is a risk of particles or dust accumulating between the inner sleeve and the expansion joint. When the medium is flue gas, an analysis of the gas is normally required in order to make the proper choice of expansion joint type. Especially when conveying highly aggressive or otherwise dangerous gases, gas tightness of the expansion joint can be a requirement. In general, LBH expansion joints can be described as being gastight. However, it is not possible to guarantee that the clamping area of an expansion joint is totally gastight. Nevertheless, the majority of special requirements can be complied with, either by choice of fabrics, by suggesting an LBH elastomeric expansion joint, by using various sealants or by supplying a clamping arrangement, where bolt holes in the clamping area can be dispensed with.

The properties of the fabrics used for manufacturing an expansion joint naturally also have to be suitable for the temperature of the medium. The basic selection criteria are operating, design and peak temperature, together with the ambient temperature and the duration of the peak temperature. For protection of the individual layers and the expansion joint, the standard means are one or more insulation layers, respectively insulation bolster. For some applications, external insulation of the expansion joint can be an advantage, in order to prevent the temperature of an aggressive medium from continuously dropping below the dew point and thereby condensation, with the danger of causing an acid attack of the expansion joint materials and corrosion of the metal parts. However, it is important to note that expansion joints may only be covered with external insulation in the low-/medium temperature range, and only after approval from LBH.

The pressure of the medium is another important factor, which determines the optimal type of expansion joint. The LBH range of expansion joints includes profiles for overpressure as well as for vacuum applications. The design criteria are operating, design and peak pressure, together with information regarding the possibility of pulsations occurring in the gas stream. Damage to the expansion joint due to pulsations can be avoided by a special composition of the fabric layers, by metal support rings, or by choosing a suitable inner sleeve. An inner sleeve is always recommendable, but can be dispensed with under certain conditions in connection with a relatively low gas velocity.

The profile, and in particular the building length of an expansion joint is highly dependent on the movements of the duct or pipe line, which are to be absorbed by the expansion joint. The possible movements of non-metallic expansion joints, except for vibrations, are illustrated below (left to right): axial compression (-) / axial extension (+), lateral offset, angular offset, and torsion. The need for a relatively large length, due to excessive movements, can sometimes be reduced by installing the expansion joint in a “pre-set” position. Please note that non-metallic expansion joints are not self-supporting, why the function requires correctly dimensioned fix points and supports in the ductwork.

External Influences
External ,damaging, influences could be: acid attack appearing from polluted ambient air condensation on the outer layer of the expansion joint, attack caused by solvents, e.g. used to wash the ductwork, radiant heat from other system components, or atmospheric influences such as the ambient temperature, acid rain, salt water, sand storms, and so others. As long as the possible influences are known in advance, the necessary measures can be taken. Some solutions could be a resistant outer layer, insulation layers and various shields.

Fabric Types LN: Suitable for Medias of air, without contents of chemicals. MN: Suitable for flue gas with light acid attack. RN: Suitable for Medias of flue gas with heavy acid attack. HD: Suitable for extreme conditions concerning medium, pressure and temperatures. GTX: Suitable for gas turbine applications.