Fabric Expansion Joint

Industrial Applications

Since their introduction, expansion joints have been used to solve an increasing range of flexible sealing challenges. However, the major application is in power generation. As materials have been developed and the technology of expansion joint design have been improved, they have been used successfully in a much wider variety of industrial applications, including:

• Cement
• Chemical
• Heating and ventilation
• Marine and offshore
• Metal Foundries
• Petrochemical
• Power generation
- Co-generation
- Fossil Fuel
- Gas Turbine
- Nuclear

• Pulp and paper
• Steel and aluminium
• Waste incineration

Advantage of Fabric Expansion Joints

Expansion joints provide flexibility in ductwork and are used to allow for 4 main situations:

1. Expansion or contraction of the duct due to temperature changes
2. Isolation of components to minimize the effects of vibration or noise
3. Movement of components during process operations
4. Installation or removal of large components, and erection tolerances

The benefits of fabric expansion joints include:

• Large movements in a short length – this requires fewer expansion joints, reducing the overall number of units and providing additional economies

• Ability to absorb simultaneous movements easily in more than one plane – this allows the duct designer to accommodate composite movements in fewer (and simpler) expansion joints

• Very low forces required to move the expansion joint – the low spring rate enables their use to isolate stresses on large, relatively lightweight, equipment. A particular example is a gas turbine exhaust, where it is crucial to minimize the forces from the duct expansion on the turbine frame

• Corrosion resistant materials of construction – modern technology materials enable the use in aggressive chemical conditions

• Noise and vibration resistance – fabric expansion joints provide a high degree of noise isolation and vibration damping Ease of installation and maintenance

• Minimal replacement cost – the fabric of the expansion joint assembly can be replaced simply and economically

• Design freedom – fabric expansion joints can be tailored to suit the duct application, with taper, transition, or irregular shape, so allowing the designer the maximum variety of options

• Thermal breaks – self-insulating properties of the fabric allow simple hot-to-cold transition

Construction

There are 2 basic forms of construction, dependent upon the number of layers in the expansion joint:

1. Single layer construction

They are suitable solutions for low temperature and low saturated environments. It is made of silicone, PTFE, etc. elastomer reinforced fabrics. Flange reinforcement is given to the edges of the compensator fabric to ensure flange sealing, in addition, PTFE gaskets are recommended for environments with aggressive chemicals. In this way, a good sealing is prevented from damaging the compensator of the connecting elements.

2. Multi-layer construction

In multi-layer compensators, it is aimed to achieve working performance suitable for ambient conditions by combining fabrics with different properties.

The usage purposes of compensator fabric layers from outer layer to inner layer is roughly follows as ;

1. Outer Layer: Protects the compensator against external factors (UV, acid, water, dirt, etc.). The elastomer coated fabric to be used in this layer protects the sealing layer in a lower layer against impacts and contributes to the sealing according to the type of elastomer. If 100% gas tight Laminated PTFE Glass fiber fabric is used in this layer, the use of the lower sealing layer is not required.

2. Sealing Layer: Provides fluid sealing and ensures safe operation of compensator layers and line.

3. Heat Insulation Layer: It protects the layers on it from the high temperature of the fluid and at the same time ensures that the outer surface temperature of the compensator cloth is reduced to suitable temperatures for worker safety.

4. Strength Layer: This layer provides resistance against;
a. Sudden pressure changes (pulsation)
b. Vibrations (vibrations)
c. Line movements (extension, compression, lateral shear, torsion, bending)
thus, increases the service life of the compensator.

Clamping Configurations

There are 3 types of clamping configurations, each of which may employ either of the above constructions:
1) Belt type expansion joint configuration
2) Flanged expansion joint configuration
3) Combination type expansion joint configuration

Ambient conditions

Ambient temperature
An expansion joint should not be in an area of poor air circulation, or subject to high temperature radiation. Fabric expansion joints working at elevated temperatures (above 250°C) depend upon a temperature gradient across the joint. This gradient is the difference between the high internal temperature (hot face) and colder external temperature (cold face) of the joint. High ambient temperatures in the vicinity of the joint will reduce this temperature gradient reducing the rate at which heat can be radiated from the external surface of the joint. This in turn will lead to failure of the primary seal (i.e. PTFE membrane) and hence the joint. Therefore, it is important to ensure that adequate provision is made to keep local ambient temperatures within manufacturer’s recommendations, and external lagging or insulating of joints is generally not allowed. Where cold external ambient conditions prevail, due consideration should be given to the possibility of condensation forming inside fabric expansion joints. Counter measures such as internal or external insulation may be considered appropriate.

Environment
Fabric expansion joints are very often situated in arduous industrial locations such as power generation plants, chemical works, cement plants etc. In such locations, they may be subjected to higher than normal levels of pollutants, some of which may contain aggressive agents, with possible attack to the elastomer outer cover of the joint. If the type and concentration of such pollutants is known at the design stage, it is possible to design a joint which will resist such attack by selection of an appropriate outer cover, resistant to specific agents.

Location
Whether a joint is located internally within a building or outside and exposed to the elements may also have a bearing on the selection of the type of outer cover. Internally located joints may not necessarily require waterproof outer covers.

Bolting guidelines for bolted expansion joints

Bolt loading guide (valid for MoS2-lubricated bolting) used to achieve flue gas tightness (TI-002) or nekal tightness (TI-003).

Guidelines for the dimensioning of clamp bars

Dust loading and velocity

The content of dust in the medium may require a specific design of the expansion joint section and the inner sleeves. In general, the following must be avoided:

• Abrasion caused by dust particles
• Sedimentation and compression of dust in the flexible element

Due to the large variety of applications and associated complexities, please refer to Metrik for specific engineering advice

Finite Element Analysis

Finite Element Analysis is a computerised method for predicting how a real world structure or assembly will react to forces, heat, vibration, mechanical stress etc. in terms of whether it will break, wear out, or work as it was intended. It is called “analysis” but in the product design cycle it is the method used to predict what will happen when the product is used.

The finite element method works by breaking a real object into many elements, and the behavior of each element is examined in the conditions in which it will operate, by a set of mathematical equations. The computer program then adds up all the individual behaviors to predict the behavior of the complete object.

The Finite Element Method is used to predict the behavior of expansion joints with respect to the physical phenomena of:
• Heat transfer • Mechanical stress • Vibration

The method is used widely to verify the design of expansion joints and their structures used in gas turbine exhaust systems.

Leakage

Fabric expansion joints are designed to be as leak tight as is reasonably practical. Although under laboratory conditions it is a relatively simple matter to demonstrate zero leakage, or nekal tightness, high temperature multiple layer expansion joints should not be considered leak tight (or zero leakage) in service without first verifying site performance with extensive testing under operating conditions.

Through the careful selection and design of single layer elastomeric expansion joints, with their inherent resilience, it is much easier to ensure zero leakage systems, provided adequate attention is paid to the quality and design of adjacent metalwork.

The vast majority of expansion joints (both single and multiple layer) can be considered leak tight through the body of the expansion joint, provided suitable materials have been specified. However, special attention should be drawn to the general metalwork condition and design, clamping areas and their surface finishes, fixing systems such as bolts or clamps and the flange reinforcements of expansion joints. It is these areas where there is the greatest potential for system losses.

Where practical, new metalwork supplied with the expansion joint integrally installed (an expansion joint “cartridge” system) and supplied direct from the manufacturers’ facilities will almost always ensure a much lower rate of leakage than field splices and installation of the expansion joint to metalwork at site.

Under laboratory conditions it is possible to demonstrate flue-gas tight3 and nekal tight(4) systems, using appropriate test methods (5).

To ensure nekal tightness in service, these types of test must be carried out after installation on site.

(3) Test specification RAL TI-002 Rev. 1- 06/98 Flue-Gas Tight Fabric Expansion Joints refers to leak tight as “…no bubbles may appear in the bellows area…” and that”… the occurrence of a limited number of foam bubbles in the clamping area and joint area of the bellows is however permitted…”.

(4) Test specification RAL TI-003 Rev. 1- 06/98 Nekal Tight Fabric Expansion Joints refers to nekal tight as no bubbles may appear in the bellows area …” and that”…this refers to both the bellows area and to the clamping area…”.

(5) Test methods similar to DECHEMA Information Bulletin ZfP 1, annex 2 Item 2.2 “Bubble method with foaming liquid”.

Moisture content, condensation and washing

Moisture within a flue duct system can have a severe, detrimental effect on the life of fabric expansion joints and therefore, should be considered carefully. At operating temperatures above the dew point of the fluid, the moisture content will appear only when the system cools down. However, this moisture often appears as aggressive condensate and is an important factor if there are frequent thermal cycles. At operating temperatures below the dew point, the media may contain a high degree of moisture, which can be very corrosive and damaging to the expansion joint.

Where cold ambient conditions prevail, due consideration should be given to the use of fabric expansion joints as they may give rise to condensation problems. Condensation can occur when a joint is located in a relatively low temperature duct system. The joint will provide an internal cold face on which condensation can form if the cold face falls below dew point, giving rise to the formation of condensate which will attack the joint from the inside causing premature failure. This can be countered by providing external insulation (note; internal insulation should be avoided). Joints should be externally insulated only on applications where the internal duct temperature is below the maximum temperature capabilities of the constituent joint materials.

Further consideration may be given to the use of alternative materials which are less effected by acidic condensate.

Where duct or gas turbine washing is required, provision should be made for a suitable drain adjacent to the expansion joint, in order to prevent the accumulation of moisture in the expansion joint material. Where possible, the expansion joint should not be the lowest point of the system.

Movement

Fabric expansion joints are designed to absorb movements and misalignments in ducts and pipelines. The active length of the expansion joint is that part which allows movement. It absorbs vibration and thermal movements of the ductwork, and may or may not be the same as the flexible length, which is that part of the expansion joint between the clamping areas:



Movements are normally induced by thermal expansion of the duct plate or pipe, but other types of movements are also possible, such as wind, snow load, duct misalignment, vibration, settling and earthquake.
Fabric expansion joints allow 5 different movements:



Vibration and Movement Cycles
Movement caused by vibration should not be confused with movement due to thermal cycling, which is slow and relatively infrequent. Fibrous materials are poor in conditions of high frequency and amplitude. Consequently, vibrations must be considered separately from thermal movements, to ensure correct material selection and provide suitable design recommendations.

Noise

In-duct noise breakout may be an important design consideration under certain circumstances and can be reduced by acoustic treatment of the duct. Fabric expansion joints may be the primary source of noise breakout in a duct system, and an internal acoustic bolster may be incorporated into the design to reduce such noise. The bolster would normally be manufactured from insulation material encased in a temperature resistant woven fabric or wire mesh (or both) and located between the joint and the internal flow sleeve. The design of the internal flow sleeve(s) can also play an important part in the acoustic performance of a joint.

Pressure - pulsation and flutter

The operating pressure in a system is a crucial factor affecting the design of fabric expansion joints. The very flexible nature of the materials brings several design issues which must be addressed. Although maximum operating pressures in duct systems are low by comparison with pipeline systems, wide variations of pressure, such as a change from positive to negative, or short-term peak pressures can occur. Such variations should be reflected in the design pressure specified, and the measure of gas tightness expected by the customer. Care in the choice and construction of materials must allow for:

• Containment of the stated design pressure under all conditions of movement and temperature, without over-stressing any of the expansion joint element
• Changes from positive to negative pressure which could entrap materials under compression, or cause them to be in contact with sharp or hot parts of a duct
• High positive pressure and compression allowing materials to abrade on bolt heads of clamp flanges
• Changes in pressure causing significant air spaces between layers of composite joint materials, which could allow circulation of hot gas
• Pressure surges occurring as a result of system operation

Pulsation
Pressure pulsation in a duct or pipeline can be detrimental to a fabric expansion joint, particularly those manufactured from plies of woven glass-cloth or ceramics. Rapid variation in pressure causes fatigue of the fibers and can lead to premature failure of the expansion joint. Caution is required when designing expansion joints for combustion engine exhaust systems to ensure that the joint is not fitted too close to the engine. A sufficient distance is required to allow the pressure fluctuations to subside.

Flutter
Flutter can be induced by fans, particularly where the system is unbalanced, and the materials used for expansion joints adjoining fans must be selected with this in mind. To overcome flutter of the joint materials, which could lead to premature failure, the materials must be of sufficient thickness and density to damp out the oscillations. Reinforced elastomeric materials are commonly specified for expansion joints fitted to the fan inlet or outlet.

Flutter in expansion joint seals can be induced by high gas velocity but is usually eliminated by careful design of a suitable flow liner attached to the duct or joint frame. The inclusion of a bolster can help to minimize flutter.

Temperature

Operating temperature
The operating temperature is the normal temperature of the media within the flue duct system under operation. Normally indicated in degrees C as design or maximum operating temperature.

Thermal cycles
The definition of a thermal cycle is when the temperature in a flue duct system moves from ambient to full operating temperature and then returns to ambient. The number of thermal cycles is often used when calculating the life expectancy of steel frames for gas turbine exhaust systems or when considering the number of times moisture could appear in the system on cool down.

Excursion temperature
Occasionally, flue duct systems will have an upset condition or excursion. This is a situation when, for a short period of time, the temperature in the system increases above normal operating temperature. The expansion joint designer must consider this upset condition for duration and temperature when making material selection.

External insulation
External insulation should not cover a fabric expansion joint, except when it is part of the joint design to avoid condensation below dew point. The termination of duct insulation is critical to the airflow over the outer cover and in general should be chamfered back at an angle of not less than 45°. For extremely hot applications, the insulation termination must be carefully designed to minimize stress in metal frames and overheating in the clamping area.

Bolsters

This is part of an expansion joint assembly incorporating bulk materials, often in the form of an encased pillow, which can be used to fill the cavity between the flexible element and the internal sleeve.

The primary reasons for their inclusion in an expansion joint design are:

• To provide additional thermal protection for the expansion joint, using bulk insulation materials with good thermal properties.
• To prevent the ingress of solid particles into the cavity of the expansion joint. In systems where the media may have a heavy dust content there are two main challenges. Firstly, the potential for abrasive particles causing damage and premature failure to the flexible element. Secondly, particles may accumulate in the cavity, becoming compacted and preventing compressive movements in the system.
• To improve the acoustic performance of the expansion joint system using bulk materials with good acoustic attenuation or absorption properties.
• To provide support to the flexible element and minimize the effects of pulsations or “flutter” by preventing the onward transmission of these variations to the flexible element.


İzolasyon Yastığı Konstrüksiyonları

A. Flanged Type
This construction maintains the position of the insulation bolster and provides the highest level of heat resistance. In this system, the flanges of the bolster are bolted between the compensator cloth and the metal flanges. Thus, the bolster acts together with the expansion joint, protecting the critical layers of expansion joint against the corrosive effects such as heat and abrasive dust.



B. Pinned Type
In this system, the isolation pad is fixed with the help of metal parts isolation pins so that it can move with the compensator cloth. Fixing can be done inside the channel edges or on the baffle plates.



C. Block Type
Block type insulation pads, which offer the most practical manufacturing and assembly possibilities, are placed between the compensator cloth and the flow sleeve.

Internal Flow Sleeve

Design of internal flow sleeves (also known as flow liners) is strongly associated with the expansion joint frame design, and the liner is often formed by part of the duct itself. Many variations are possible, but a range of common types is defined below.

The shape of an internal flow sleeve is an important design aspect, to ensure that the movement is not restricted. The main function is to exclude high velocity gases or particles, so preventing the erosion of seal or bolster materials. Other important considerations are:

• The thickness of material in relation to the possibility of erosion,
• The length of each section of flow sleeve, bearing in mind expansion and deformation due to temperature,
• Requirements for duct washing, and the need to protect seals and bolsters
• Flow sleeves are normally stitch-welded to the frame

Internal flow sleeves must be designed so that they will not entrap dust or condensation. Please consult Metrik for specific advice.

Particle Barrier

Particle Barrier is used in systems with very high solid particle content to minimize the entry of particles carried in the environment into the expansion joint frame
In this way, it is aimed that the compensator works for a long time.

Please consult us for details.

• 

Particle Discharge Pipe

Particle Discharge Pipe is used for automatic or manual evacuation of particles filled into the compensator cavity in systems with very high solid particle content.
In this way, it is aimed that the compensator works for a long time.

Please consult us for details.

FanFlex

Fanflex compensators dampen thermal expansion, vibrations and misalignments in piping and duct systems in low temperature regions.

• Single or multi-layer structure
• Absorbs movement in many axes simultaneously
• Use in dry and wet environments
• Metal ring support for high pressure (+/-) protection
• Optional metal flange or clamp production
• Operating temperature range: -50 °C / +300 °C
• Operating pressure range: -0,25 bar / +0,25 bar

ChemFlex

ChemFlex expansion joints dampen thermal expansion, vibrations and misalignments in pipe and duct systems containing aggressive chemicals.

• Single layer structure
• Absorbs movement in many axes simultaneously
• Suitable for use in dry and wet environments
• High resistance to acids
• Optional metal flange or clamp production
• Operating temperature range: -35 °C / +425°C
• Working pressure range: -0.35 bar / +0.35 bar

MultiFlex

MultiFlex compensators absorb thermal expansion and misalignment in piping and duct systems in dry and medium temperature regions.

• Multi-layered structure
• Absorbs movement in many axes simultaneously
• Suitable for use in dry environments
• Low acid resistance
• Optional steel frame can be manufactured
• Operating temperature range: -50 °C / +575 °C
• Working pressure range: -0.25 bar / +0.25 bar

UltraFlex

UltraFlex compensators absorb thermal expansion and misalignment in piping and duct systems in dry and medium temperature regions.

• Multi-layered structure
• Absorbs movement in many axes simultaneously
• Suitable for use in dry environments
• Low acid resistance
• Optional steel frame can be manufactured
• Operating temperature range: -50 °C / +800 °C
• Working pressure range: -0.30 bar / +0.30 bar

ArmiFlex

ArmiFlex compensators safely absorb thermal expansion and slippage of piping and duct systems in dry, high temperature and high flow areas. It has a high elongation capacity thanks to its special curved structure.

• Multi-layered structure
• Absorbs movement in many axes simultaneously
• Suitable for use in dry environments
• Specially designed for high elongation movement
• High acid resistance
• Operating temperature range: -50 °C / +850 °C
• Working pressure range: -0.35 bar / +0.40 bar