Rubber Expansion Joint: Enhancing Piping Flexibility and Performance

Why Use a Rubber Expansion Joint?

Rubber compensators are widely applied in a variety of industrial pipelines, in power plants, in heating networks (heat transfer stations) and sanitary installations (sewage treatment plants and pumping stations, water treatment stations and machines). Basically, they are mounted near components that produce vibrations (pumps, engines, turbines, compressors etc.). They absorb different movements: axial, lateral and angular that result from thermal expansion of the pipelines or misalignment. They dampen vibration and noise and absorb the energy of pressure variations.

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:

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:

Construction Terms for Rubber Expansion Joints

A rubber expansion joint generally consists of inner tube, cover and carcass. The inner tube shall be made of natural rubber, synthetic rubber, or blend of synthetic rubber. It is a seamless protective, leak-proof lining that extends through the bore to the outside edges of the joint. Since the inner tube is in direct contact with the flowing media, it shall be designed to cover service conditions for chemical, petroleum, sewage, gaseous and abrasive materials. The purpose of the tube is to eliminate the possibility of the materials being handled penetrating the carcass and weakening the fabric. The cover is the exterior surface of the joint that is formed from natural or synthetic rubber. The prime function of the cover is to protect the carcass from outside damage caused by atmospheric chemicals, oils, air, sunlight, vapor, etc. The carcass or body of the rubber expansion joint is the flexible and supporting member between the tube and cover. It is the structural framework of the joint and is made from multiple plies woven fabric or tire cord impregnated with synthetic rubber. Steel wires or solid metal rings are often embedded in the carcass to provide additional reinforcement to the body fabric.

Miscellaneous design patterns of rubber expansion joints are available:

(1) Integral Rubber Flanges – The end connection flanges of the joint are integrally formed as a part of the elastomeric bellows. It is also called “spool arch type rubber expansion joint”.

(2) Floating Metallic Flanges – The metal flanges shall have a groove to accept the molded bead in the body at each end of the expansion joint bellows.

(3) Spherical Type – Long radius arch, either single sphere or twin sphere, to provide better movement capability and strength.

(4) Control Units – Tie rods or control rods are provided to minimize possible damage to the expansion joint caused by excessive motion of the piping system.

(5) Custom Designs – rectangular flange connection, threaded union connection, tapered reducer type, no-arch U type, hinged type, gimbal type, sleeve type, PTFE lined type.

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.

Specification of Rubber Expansion Joints

Function & Performance

As illustrated in the picture, rubber expansion joints are primarily designed to absorb and compensate for various movements and vibration in a piping systems:

• Axial Compression – The dimensional reduction or shortening of in face-to-face parallel length of the joint measured along the longitudinal axis.
• Axial Elongation – The dimensional increase or lengthening of face-to-face parallel length of the joint measured along the longitudinal axis.
• Lateral Movement – The movement of relating displacement of the two ends of the joint perpendicular to its longitudinal axis.
• Vibration – Mechanical oscillations in the piping system, usually in high frequency.
• Angular Movement – The angular displacement of the longitudinal axis of the joint from its initial straight line position, measured in angle degrees. One half of the joint has axial elongation and the other has axial compression.
• Torsional Movement – One end of the expansion joint is twisted around the longitudinal axis while the other end is held fixed.

Rubber expansion joints for piping systems

Rubber Expansion Joints for Piping Systems provide time-tested ways to accommodate pressure loads, relieve movement stresses, reduce noise, isolate vibration, compensate for misalignment after plants go on stream, and prolong the life of motive equipment. Rubber expansion joints are available in a variety of styles and are used to convey fluid under vacuum pressure conditions in piping systems. Flanged rubber expansion joints are most common and are available in single – and multi-arch designs. They can be custom-engineered to fit your application requirements. Our rubber expansion joints are particularly beneficial due to their flexible nature, which makes them suitable for many functions, including the absorption of sound, thermal energy and shock. They are specifically designed to reduce the need for maintenance, repair and manual assistance.

Benefits of flexible rubber expansion joints

Flexible rubber expansion joints offer several benefits in piping systems, contributing to the overall performance, reliability, and longevity of the system. Here are some key advantages:

Changes in temperature and pressure in piping systems connected to pumps lead to thermal expansion and contraction within the pipes. Rubber expansion joints and connectors are the ideal choice for many piping situations, and they have several uses. Rubber expansion joints are most often used as a flexible connector between a vibrating piece of mechanical equipment and the pipeline. They can also be used to absorb pipe movements. Rubber connectors will also provide for a reasonable amount of pipe offset caused by equipment settling.

Available options include PTFE-lined, eccentric reducing, concentric reducing, filled arch, lightweight and off-set configurations. They can be designed to operate up to 200 psi and withstand temperatures up to 500º F. Sizes available from 1/2″ to 144″.

Careful selection of the expansion joint design and material for a given application, as well as properly engineered installation are important factors in determining performance. These factors should be fully evaluated by each person selecting and applying expansion joints for any application.

Main data of rubber expansion joint

According to the connection method, there are three kinds of flange type, fixed flange type and thread type; according to the structure, it can be divided into five types: single sphere, double sphere, different diameter body, curved sphere and wind pressure coil. The tubular rubber piece is composed of inner and outer rubber, ply and traveler, and is formed by vulcanization molding and loosening with metal flange or parallel joint. This product can reduce vibration and noise, and can compensate for thermal expansion and contraction caused by temperature changes, and is widely used in various piping systems.

Which rubber is used in expansion joints?

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.

Why rubber expansion joints are used?

Rubber expansion joints are used in piping installations to compensate for thermal growth, relieve piping stress during operation, and reduce vibration and noise caused by rotating equipment.

How long do rubber expansion joints last?

The majority of expansion joints can be found off the suction and discharge side of every pump; however, they can also be found near boilers, tanks, cooling towers, heat exchangers and the middle of pipe runs. The average life span of a rubber expansion joint is roughly seven to 10 years.

Can you fill expansion joints with silicone?

Installing expansion joints and using a high-quality silicone-based sealant is one important step you can take to ensure that your work will last for years to come. Expansion joints allow space in which concrete can contract and expand without causing cracks.