AYVAZ

RUBBER EXPANSION JOINTS

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Rubber expansion joint is a flexible connector fabricated of natural and/or synthetic elastomers and fabric, if necessary, internal metallic reinforcements designed to provide stress relief in piping systems due to thermal movements and mechanical vibration.

There are lots of material selection based on usage area of rubber expansion joints. Also rubber expansion joints have advantages and disadvantages between of the metal expansion joints. Rubber expansion joints can absorb large movement in very short distance. They provide all directional movement, such as axial, angular, lateral and torsional that may occur from external conditions. Also reduce wind, shock loading and seismic movements. 

APPLICATION AREAS

&#; Heating and cooling devices
&#; Materials handling technologies
&#; Water pipes
&#; Desalination plants
&#; Compressors
&#; Blowers and fans
&#; Cement industry
&#; Chemical industry
&#; Glass industy
&#; Wood-processing industry
&#; Pulp and paper industry
&#; Railed vehicles
&#; Refineries
&#; Shipbuilding
&#; Steel mills
&#; Sugar industry

ADVANTAGES

Spherical joints have a distinct advantage over metallic expansion joints for corrosive applications and installations requiring a high cycle life. The contour prevents sediment accumulation and creates less turbulence and pressure drop than spool joints. The seal bead eliminates any requirement for gaskets between mating flanges. Spheres may be installed on raised-face or flat-face flanges.

COMPARISON AGAINST METAL EXPANSION JOINTS

Temperature: Rubber joints with standard construction and materials have an upper range to 110°C. Can be offer special constructions up to 200°C. Metal expansion joints do offer a far greater range, from -250°C to +950°C. 

Pressure: Rubber joints depending on diameter, can have pressure capabilities up to 15 bar with a full vacuum rating. Metal joints can be designed for pressures up to 100 bar. 

Movements: Rubber and metal expansion joints have similar movement capabilities in the axial plane (compression and extension). However, rubber joints are certainly able to absorb greater lateral movements when compared to metal joints that have similar face to face lengths.

Spring Rates: Rubber and metal joints do have similar characteristics in the axial plane for the standard face to face dimensions. Metal joints are much stiffer when subjected to lateral motion and, typically have a  lower lateral movement capability. 

Acoustical Impedance: Although well designed (multi-ply) metal joints can lower the transmission of visible vibration, they will continue to transmit distracting and/or damaging noise. Rubber joints significantly reduce the undesirable transmission in piping systems. The elastomeric composition of the joint acts as a dampener that absorbs the greatest percentage of perceptible noise and vibration.

Abrasion/Erosion Resistance: Metal joints typically have a wall thickness anywhere between 0.15mm to 2mm. Rubber joints are much thicker, 12mm to over 25mm. The thin construction of metal joints makes them susceptible to erosive chemicals and abrasive liquids and slurries. Rubber joints are highly resistant to abrasion and erosion of all types and outperform metal joints in the applications where these conditions prevail.

Fatigue/Cycle Life: The fatigue life of a metal joint is affected by many factors such as temperature, pressure, movement, vibration and how the joint was initially designed. Typically, metal joints have a defined cycle or fatigue life that can be calculated through various formulas (EJMA). Metal joints frequently succumb to fatigue failure from excessive cycling/movement. Rubber joints on the other hand are constructed of resilient elastomers and the joint itself acts as a vibration dampener, not susceptible to fatigue/cycle failure.

Installation/Maintenance: Rubber joints do not require additional gasketing and, in many cases, are installed without the use of special handling equipment. Metal joints must be serviced occasionally to insure that the flange gasket is still intact and not deteriorated

MATERIAL SELECTION

Material selection of rubber expansion joints are very variable and depends on the pressure, temperature, fluid etc. parameters. The common materials are, EPDM, IIR, NBR, PTFE and combined with these materials depends of usage area. Also the inner tube and outer tube&#;s diameter can be different depends of design conditions. 

Table I: Maximum Temperature Ratings Reinforcing Fabric Tube or Cover Elastomer Pure Gum Rubber Neoprene Butyl Nitrile Hypalon® EPDM FKM Nylon 180 °F / 82 °C 225 °F / 107 °C 250 °F / 121 °C 210 °F / 99 °C 250 °F / 121 °C 250 °F / 121 °C 250 °F / 121 °C Polyester 180 °F / 82 °C 225 °F / 107 °C 250 °F / 121 °C 210 °F / 99 °C 250 °F / 121 °C 250 °F / 121 °C 250 °F / 121 °C Aramid 180 °F / 82 °C 225 °F / 107 °C 300 °F / 149 °C 210 °F / 99 °C 250 °F / 121 °C 300 °F / 149 °C 400 °F / 204 °C

 

Table II. List of Elastomers Used in Expansion Joints and Rubber Pipes MATERIAL
DESIGNATION RATING SCORE CODE ELASTOMER PHYSICAL AND CHEMICAL PROPERTIES COMPARISON ANSI/ASTM
D-77 ASTM-D-
D-77 7-Outstanding
6-Excellent
5-Very Good
4-Good
3-Fair to Good
2-Fair
1-Poor to Fair
0-Poor
X-Contact Mfg. ALKALI, CONC.
ANIMAL VEG. OIL
CHEMICAL
WATER OXYGENATED HYDRO.
LACQUERS
OIL & GASOLINE
ALKALI, DILUTE ACID DILUTE
ACID, CONC.
ALPHATIC HYDRO
AROMATIC HYDRO ELE. INSULATION
WATER ABSORP
RADIATION
SWELLING IN OIL REBOUND-COLD
COMP. SET
TENSILE STRENGTH
DIELECTRIC STR. ABRASION
IMPERMEABILITY
DYNAMIC
REBOUND-HOT HEAT
COLD
FLAME
TEAR OZONE
WEATHER
SUNLIGHT
OXIDATION COMMON NAME
CHEMICAL GROUP NAME CR BC BE NEOPRENE
CHLOROPENE 4 3 4 0 4 4 0 1 2 3 4 6 4 5 4 3 5 4 2 4 5 2 4 5 4 4 4 4 5 5 6 5 NR AA GUM RUBBER
POLYISOPRENE, SYNTHETIC 5 3 X X X 0 0 4 0 0 3 3 0 6 5 5 6 6 4 6 6 6 2 7 5 0 5 2 4 0 2 0 IR AA NATURAL RUBBER
POLYISOPRENE, SYNTHETIC 5 3 X X X 0 0 4 0 0 3 3 0 6 5 5 6 6 4 6 6 2 2 6 5 0 5 2 4 0 2 0 IIR AA BUTYL
ISOBUTENE-ISOPRENE 5 6 5 4 4 0 3 4 0 0 4 6 0 4 5 5 4 3 0 5 2 6 4 4 0 4 5 6 5 5 6 FKM HK FLUOROCARBON
ELASTOMER 5 6 6 0 4 6 1 0 6 6 6 5 6 5 5 3 5 5 6 2 4 5 5 5 2 6 2 7 7 7 7 7 EPR BA CA DA EPDM
ETHYLENE-PROPYLENE-
DIENE-TERPOLYMER 5 6 5 6 6 0 3 6 0 0 4 6 0 7 6 6 7 5 4 6 6 5 4 5 4 0 5 6 6 7 6 7 AFMU   PTFE/TFE/FEP
FLUORO-ETHYLENE-
POLYYMERS 7 7 7 7 7 7 7 7 7 7 7 7 7 3 7 X X X X X X X X 4 X X X 7 7 7 7 7 SI GE SILICONE 5 5 5 0 2 X 0 2 0 0 2 6 2 5 6 6 4 0 3 6 6 0 2 0 2 2 6 7 6 6 6 6

 

TYPES OF RUBBER EXPANSION JOINTS

ARCH TYPE:

A full face integral flange design is available in both Single Arch and Multiple Arch Types.

Single Narrow Arch Type: 

Construction is of fabric and rubber, reinforced with metal rings or wire. The full face flanges are integral with the body of the joint and drilled to conform to the bolt pattern of the companion metal flanges of the pipeline.

This type of rubber face flange is of sufficient thickness to forma tight seal against the metal flanges without the use of gaskets.

Multiple Narrow Arch Type: 

Joints with two or more arches may be manufactured to accommodate movements greater than those of which a Single Arch Type joint is capable.

 Multiple Arch joints of most manufacturers are composites of standard sized arches and are capable of movements of a single arch multiplied by the number of arches.

PTFE Lined

Spool Arch Type joints are available in many standard pipe sizes with Fluoroplastic liners of TFE and/or FEP. These liners are fabricated as an integral part of the expansion joint during manufacture and cover all wetted surfaces in the tube and flange areas. Fluoroplastic provides exceptional resistance to almost all chemicals within the temperature range of the expansion joint body construction. 

Non-metallic Reinforced Design

Constructed similar to the Spool &#;Arch&#; Type except the carcass does not contain wire or metal ring reinforcement. Pressure resistance is accomplished through the use of special external flanged retaining rings furnished with the joint.

Reducer Type

Reducing expansion joints are used to connect piping of unequal diameters. They may be manufactured as a concentric reducer with the axis of each end concentric with each other or as an eccentric reducer having the axis of each end offset from each other. Tapers in excess of 20 degrees are not desirable.

Sleeved Arch Type

This joint is similar to the &#;Arch&#;typeexcept that the capped sleeve ends have an I.D. dimension equal to the O.D. of the pipe. These joints are designed to slip over the straight ends of the open pipe and be held securely in place with clamps. This type of joint is recommended only for low to medium pressure and vacuum service because of the difficulty of obtaining adequate clamp

What is a rubber expansion joint?

A rubber expansion joint is a flexible connector to absorb noise, shock, vibration, physical and thermal energy. Made of natural or synthetic elastomers it may be internally reinforced with fabrics and metal for strength and pressure resistance whilst metal reinforcement may be used externally for movement control.

Why Use a Rubber Expansion Joint?

Rubber expansion joints offer flexibility allowing concurrent movements, isolation of vibration, reduction of noise, resistance to abrasion and chemical erosion within fluid systems.

Here are the key benefits of rubber expansion joints:

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Movement Absorption

Rubber joints can absorb greater movements when compared to similar length metal expansion joints. Equipment such as pumps, compressors and piping can move out of alignment due to wear and settling of their supporting structures. Rubber expansion joints can routinely manage the resulting lateral, torsional and angular movements whilst strategically located rubber expansion joints can mitigate thermal expansion and contraction movements. Metal joints typically have a lower lateral movement capability and the allowance for movement offered by rubber expansion joints has positive benefits in extending system life and maintenance intervals.

Vibration Reduction

Reducing vibration is important to prevent unbalanced forces building up to a level where they can damage a fluid system. Rubber pipe and expansion joints dampen these disturbances and provide resistance against shock stress from hydraulic surge and water hammer.

Sound Reduction

As systems age and wear, imbalances occur which cause unwanted noise. Rubber expansion joints dampen sound transmission with their rubber to steel interface. When compared to full metal joints, thick-walled rubber expansion joints offer a much higher reduction of sound transmission.

Corrosion, Abrasion and Erosion Resistance

Metal joints are typically thin wall elements, having a wall thickness anywhere between 0.15mm to 2mm. Rubber joints are thicker, from 12mm to over 25mm. Metal expansion joints are susceptible to chemical erosion and abrasion whereas rubber joints are resistant to abrasion and erosion.

A wide variety of natural, synthetic, and special purpose elastomers and fabrics are available to create high performance rubber expansion joints to meet challenging operating conditions. Special polymers resist chemicals, oil, sunlight, acid fumes, ozone and external coatings can be added for further protection.

Expansion joints may use PTFE (polytetrafluoroethylene) and FEP (fluoroethylene propylene) liners within the joint body. When fluoroplastics are used in rubber expansion joints this results in better thermal stability, low friction and resistance to corrosive fluids, chemicals, abrasion and erosion.

Fatigue Resistance

The ability to flex and absorb gives rubber expansion joints a distinct advantage over metal joints since natural and synthetic elastomers are not subject to fatigue breakdown, loss of ductility or electrolytic reaction. This results in a long-lasting expansion joint.

Ease of Installation

Rubber expansion joints are light in weight compared to metal expansion joints, making them easy to handle and install. The vulcanized rubber and fabric flanges of elastomeric expansion joints are integrated and therefore do not require additional gaskets which also eliminates the need for ongoing gasket maintenance checking. Additionally, elastomeric expansion joints can equalize the uneven surfaces of the pipe flange to provide a gas tight seal.

Industry Applications

Rubber expansion joints appear in all fluid systems. Rubber expansion joints relieve stress from movement, isolate vibration, reduce noise and compensate for misalignment in piping systems. Rubber expansion joints do not replace metal expansion joints in all applications but are recognized as the best choice for many applications involving high vibration and sound dampening.

Here are examples of applications that utilize rubber expansion joints:

 

• Air conditioning

• Paper and pulp

• Cement production

• Power generation

• Chemical production

• Pumps

• Compressors

• Refineries

• Desalination

• Sewage plants

• Fans

• Stormwater

• Glass production

• Transport

• Heating and ventilating

• Water pipes

• Metal production

• Wood processing

Construction Terms for Rubber Expansion Joints

Carcass

The body of the expansion joint consisting of fabric and / or interior metal reinforcement.

Cover

The natural or synthetic rubber exterior of the joint which protects the carcass from damage.

Fabric Reinforcement

A synthetic or natural fabric between the tube and cover that flexibly supports the expansion joint for movement or pressure.

Metal Reinforcement

Solid rings or wire embedded in the carcass which strengthen the expansion joint to withstand high pressure or vacuum.

Tube

A protective, leak-proof lining tube that extends through the bore to the outside edges of the flanges to eliminate the possibility of the fluids penetrating the carcass and weakening the fabric.

Types of Rubber Expansion Joint

 

Arch Type Rubber Expansion Joints

Arch type rubber expansion joints are named from the thick area of elastomer molded into the shape of an arch. The carcass of the joint between the arch is usually supported by metal rings or wire to resist pressure.

Typical arch type rubber expansion joints are single wide arch and multiple wide arch types, the latter for use in longer length joints. As the length of an expansion joint span increases, up to a recommended maximum of four arches can be used to accommodate movement over long lengths.

Rubber arch expansion joints are constructed with an integral flange with fixing holes drilled to match the pipework flanges to form a tight seal without gaskets.

Joint variants may also incorporate lateral offset features or reducer connections to connect pipework of unequal diameters up to a recommended 20-degree reduction along the length of the joint.

PTFE Lined Expansion Joints

Spool Arch type joints are available with fluoroplastic liners of TFE and/or FEP. The liners cover all internally exposed surfaces, and the compounds provide resistance to almost all chemicals carried within the expansion joint.

Sleeved Arch Type

Sleeved joints slide on to the straight ends of an open pipe and are secured with clamps. They incorporate capped sleeve ends with an inside dimension equal to the outside dimension of the pipe. The main application is for low to medium pressure or medium vacuum systems.

Non-Metallic Reinforced Rubber Expansion Joint

Whilst having a similar arch construction to the spool arch type, this type of expansion joint achieves pressure resistance from extended flange rings which enclose part of the body of the joint to compensate for the lack of internal wire or ring reinforcement within the carcass.

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