Category Archives: Expansion Joints

A User’s Guide to Expansion Joint Control Units

Expansion Joint Control Units

Elongation settings are a vital factor to assembly effectiveness.

Diagram of Control Unit and Control Rod Components

It is no secret that one of the greatest demands for an expansion joint is the expectation to serve a long, leak-free life with little-to-no maintenance. Once installed, these flexible rubber connectors should require little attention. The preservation of this investment (and one’s sanity) can be maximized with an in-depth overview of how control units can prevent a new expansion joint from being overstressed.

The purpose of a control unit is to act as a safety device against excessive movement resulting from pressure thrust. A typical control unit assembly is comprised of threaded rods, steel gusset plates, nuts and washers (see Images 1 and 2).Diagram of Effects of Pressure Thrust

The usage of control units with an expansion joint is always beneficial; pressure spikes during a system upset can cause uncontrolled surges through the expansion joint. This is a prime example of how valuable it is to have control units installed to protect these rubber assets from damage.

Methods to the Madness

A common misconception about control units  is that they are designed to support the weight of pipe members or act as a substitute for adequate mounting. They are not. The sole purpose of a control unit is to allow the expansion joint to move freely within a specific range of movement while preventing the joint from being overstretched from pressure thrust forces.

The control units in no way impede the joint from performing its other duties beyond movement  (vibration absorption, cycling or compensation for misalignment). The few extra steps needed to install the control units with the expansion joint could pay notable dividends in the long run.

Pressure thrust plays a huge role in how an expansion joint functions. While under pressure, the forces acting on the inside walls of the expansion joint actually cause the joint to swell and elongate. In the real world, an expansion joint is held comfortably between two pipe flanges, which in most cases are restrained by a pump lagged to the floor or mounted to a structural beam. Although it may not be apparent to the naked eye, once the expansion joint sees pressure, it produces a thrust force that acts axially on both pipe flanges.

Theoretically, what would be the result if the expansion joint was unrestrained on each end while pressurized?

Without fixed ends, the pressure thrust would force the joint to elongate without bounds.

Most useful in high pressure applications, the control rods will  engage with the gusset plates once a pre-specified amount of growth for the expansion joint has been reached, restricting the joint from stretching any further. At this point, the control rods are absorbing any additional thrust  acting on the pipe flange, thus limiting the amount of stress that is exerted onto adjoining equipment.

The design theory for sizing control unit hardware is based on the pressure thrust. Nominal inside diameter (ID) and arch geometry of the expansion joint are key drivers for calculating the thrust force that will be applied to the pipe at maximum line pressure. Per

Arch Diameter Diagram

industry standards set by the Fluid Sealing Association (FSA), both control rods and gusset plates are designed to withstand no more than 65 percent of the yield strength of the material.

Magnitude of the pressure thrust can be calculated by knowing the internal pressure and the effective area of the expansion joint. Effective area is found using the arch diameter of the expansion joint, which takes into account the size of the arch.

For example, we can calculate the resulting pressure thrust for a 10-inch ID expansion joint using an arch height of 1.5 inches that is rated for a maximum pressure of 250 pounds per square inch (psi).

The equation for pressure thrust “T” is:

Equation for pressure thrust

These design limitations based around yield stress are the reasons why some control units made from lower yield strength stainless steel contain thicker components or more rods per set than the standard carbon steel control units.

Installation & Inspection

For a control unit assembly to be effective, rod positioning and elongation settings are critical during installation. Each control rod should be evenly spaced around the flange to best distribute the load. Elongation settings (see Image 5) are often overlooked, yet are a vital factor to ensure the control units fulfill their intended use.

Every expansion joint comes with movement ratings based on arch size, configuration and number. These movement design ratings of the expansion joint are critical pieces of information that are absolutely required during the installation of control units. The general rule of thumb is the gap between the gusset plate and the nut should be adjusted to match the joint’s elongation rating.

Having this information at hand during installation is great, but what about the existing control units currently in operation? Visual inspections of these components are a basic task that goes a long way toward extending the life of the joint.

Here are the top 4 anomalies to look for when performing a field inspection: Continue reading A User’s Guide to Expansion Joint Control Units

Style 404 Expansion Joint for Abrasive Applications

Abra-Line Style 404The ABRA-LINE™ family of products was developed for highly abrasive applications typically found in the power generation, fertilizer, mining and chemical industries. These may include flue gas desulphurization systems, phosphate mining, dry bulk power transfer systems, tailings and slurry applications. Our proprietary urethane formula was designed to reduce wear and extend
service life.

Style 404 Expansion Joints are specially designed for full vacuum abrasive service applications. The tube material is a proprietary urethane formulation. Style 404 can be constructed as a single or multiple arch design. It can also connect pipe flanges in concentric or eccentric tapers, to join piping of unequal diameters.

Case Study: Chemical Processing

Industry
Chemical Processing

Observation
A stainless hosing was used and would continuously fail due to abrasion on the leading edge of the hose. The hosing would last for 3 to 6 months before replacement.

Continue reading Style 404 Expansion Joint for Abrasive Applications

Expansion Joint Failure Analysis

Failure Analysis - Rubber Expansion JointsGallagher Fluid Seals recently added the Rubber Expansion Joint Surveys & Failure Analysis white paper to our Resources page. This white paper discusses the importance of inspecting your plant’s expansion joints.  Proper design and maintenance of rubber expansion joints plays a major role in the overall preservation and lifespan of a piping system.

It will also discuss failure analysis of rubber expansion joints and some of the leading causes of joint failure.

Below is an except from the white paper, discussing failure analysis of rubber expansion joints, and what it can tell you about the overall health of your piping system.


Failure Analysis

There are perceptible warning signs when an expansion joint is failing:

  • Arch inversion indicating a system vacuum that has exceeded the joint’s specified expansion value.
  • Cracking at the base of the arch, which indicates the joint has been over-elongated and should be replaced with one of the proper length.
  • Ply separation on the outside of the cover. This is an indication the joint has been subjected to excessive movement.
  • Leakage due to over-expansion, mating flange surface issues, or poor installation practices, especially (but not limited to) bolt tightness.
  • Ballooning of arch, which indicates excessive system pressure.

Continue reading Expansion Joint Failure Analysis

NEW Expansion Joint Material – ABRA-SHIELD™

Garlock is excited to announce the launch of ABRA-SHIELD, a new expansion joint material designed for abrasion resistance and sustainability in demanding high temperature operating conditions.

ABRA-SHIELD™As the newest addition to Garlock’s family of abrasion resistant expansion joint materials, ABRA-SHIELD will join ABRA-LINE® and Natural Rubber to provide a variety of liners that cater to increased abrasion protection. ABRA-SHIELD will be an option for use with a number of expansion joint products that Garlock offers – including styles 204, 206, 7250, 8400 and 9394. These expansion joints also provide high levels of protection from stress, misalignment, vibration, noise, shock and corrosion.

In abrasion resistance testing – which provides data to compare materials and predict the lifetime of a material or coating – ABRA-SHIELD provided 50% higher abrasion resistance than standard EPDM (ethylene propylene diene monomer rubber). ABRA-SHIELD will be the recommended solution in abrasive applications (such as slurry, ash and brine) with sustained or spiked temperatures between 180°F and 300°F. For temperatures outside of this range, other materials in Garlock’s family of abrasion resistant expansion joints would be suggested.

Continue reading NEW Expansion Joint Material – ABRA-SHIELD™

How Important are Expansion Joint Surveys?

Expansion Joint SurveysGallagher Fluid Seals recently added the Rubber Expansion Joint Surveys & Failure Analysis white paper to our Resources page. This white paper discusses the importance of inspecting your plant’s expansion joints.  Proper design and maintenance of rubber expansion joints plays a major role in the overall preservation and lifespan of a piping system.

It will also discuss failure analysis of rubber expansion joints and some of the leading causes of joint failure.

Below is an except from the white paper, discussing design and maintenance of rubber expansion joints, as well as the importance of expansion joint surveys.


Elastomeric expansion joints are fabricated from natural or synthetic rubber and fabric, normally consisting of an inner elastomeric tube fused to a metal-reinforced fabric body and an elastomeric cover. These expansion joints accomodate greater pipe movement and provide greater abrasion resistance than metal expansion joints.

Expansion Joint SurveysThe proper design and maintenance of rubber (or elastomeric) expansion joints plays a major role in the overall preservation and lifespan of a piping system. They absorb movement, relieve system strain due to thermal change, stress, pumping surges, wear, or settling, reduce mechanical noise, compensate for misalignment, and/or eliminate electrolysis between dissimilar metals. Poorly functioning joints can lead to major deterioration of the piping system’s integrity, creating safety and environmental issues in your plant and processes. Visible signs of wear and fatigue – including exterior surface cracking, blistering, deformation and delamination, exposure to metal or fabric reinforcement, ply separation of the cover, rubber deterioration, and leakage – can alert observant users to potential failure.

Continue reading How Important are Expansion Joint Surveys?

NEW! Expansion Joint Surveys & Failure Analysis White Paper

Rubber Expansion Joint Surveys & Failure Analysis White PaperGallagher Fluid Seals recently added the Rubber Expansion Joint Surveys & Failure Analysis white paper to our Resources page. This white paper discusses the importance of inspecting your plant’s expansion joints.  Proper design and maintenance of rubber expansion joints plays a major role in the overall preservation and lifespan of a piping system.

It will also discuss failure analysis of rubber expansion joints and some of the leading causes of joint failure.

Download your copy today, and contact our engineering department if you need assistance choosing the right expansion joints for your processes.

When to Use Flue Duct Expansion Joints

Flue Duct - Expansion Joint Design GuideIn July, Gallagher released its Expansion Joint Design Guide, now available for download on our site.  This design guide takes an in-depth look at elastomeric, metal, and flue duct expansion joints.  The excerpt below is a section of our Expansion Joint Design Guide focusing on types of flue duct expansion joints.  To download the entire guide, visit our Resources Page, or click on the image to the right.


Flue Duct Expansion Joints

Used to manage air and gas handling systems, flue duct expansion joints are most widely utilized in the Power Generation, Industrial & Institutional industries:

  • Flue Duct Expansion JointPower Plants
    • Simple Cycle
    • Combined Cycle
    • Co-generation
    • Coal Fired
  • Industrial Operations
    • Steel Mills
    • Paper Mills
    • Cement Plants
  • Institutional Sites
    • Hospitals
    • Schools
    • University Campuses

Continue reading When to Use Flue Duct Expansion Joints

Metal Expansion Joints for High Temperature/Pressure

Expansion Joint Design Guide - Metal Expansion JointsGallagher recently released its Expansion Joint Design Guide, now available for download on our site.  This design guide takes an in-depth look at elastomeric, metal, and flue duct expansion joints.  The excerpt below is a section of our Expansion Joint Design Guide focusing on types of metal expansion joints.  To download the entire guide, visit our Resources Page, or click on the image to the right.


Much like elastomeric expansion joints, metal expansion joints are used to preserve the integrity of a piping system where the piping is subject to changes in temperature, pressure, vibration, compression, extension, cyclical movements or movements required by usage.

Oftentimes, metal expansion joints are used when an elastomeric joint simply cannot handle the extreme conditions – applications where high temperature, large temperature range, or high pressure exists. Generally, metal expansion joints can be used from -450°F to +2000°F, depending on the metallurgy, and can also handle pressures from full vacuum to 3,000psi.

Metal Expansion Joint Components

Though customized and intricate expansion joints can be manufactured for a variety of specialized applications, there are four basic designs that are most commonly used:

Metal Expansion Joints - Basic BellowsBasic Bellows

A bellows can be supplied without end fittings for field installation. The skirt, or straight portion at each end of the bellows, can be sized to fit a flange or pipe. Skirt length can vary depending on your needs and should be specified when ordered.


Metal Expansion Joints - Unrestrained SingleUnrestrained Single

An unrestrained single expansion joint is best used by piping systems which are equipped with proper guides and anchors to absorb axial, angular, and a small amount of lateral movement.

Continue reading Metal Expansion Joints for High Temperature/Pressure

Elastomeric Expansion Joint Installation

Expansion Joint Design GuideGallagher recently released its Expansion Joint Design Guide, now available for download on our site.  This design guide takes an in-depth look at elastomeric, metal, and flue duct expansion joints.  The excerpt below is a section of our Expansion Joint Design Guide focusing on types of elastomeric joint installation, pipe layouts, and joint troubleshooting.  To download the entire guide, visit our Resources Page, or click on the image to the right.


Preparation

Expansion Joint InstallationCheck Service Range
  • Double check expansion joint performance limits against anticipated operating conditions
  • Check temperature, pressure, vacuum recommendations
  • Check total joint deflection—alter as needed to reduce deflection to correct range
  • Anchor lines
Check Location
  • Proper location is usually close to main anchoring point
  • Install pipe guide(s) for proper alignment
  • Joint should absorb pipeline expansion / contraction between fixed anchor points

Continue reading Elastomeric Expansion Joint Installation

Elastomeric Expansion Joint Types & Movement

Expansion Joint Design GuideGallagher recently released its Expansion Joint Design Guide, now available for download on our site.  This design guide takes an in-depth look at elastomeric, metal, and flue duct expansion joints.  The excerpt below is a section of our Expansion Joint Design Guide focusing on types of elastomeric joints and types of pipe movement.  To download the entire guide, visit our Resources Page, or click on the image to the right.


The basic purpose of an expansion joint is to absorb movement and vibration in a rigid piping system, being built to expand, contract, and adjust without straining or breaking the piping or ducting on either side.  They are specially engineered to handle movements due to thermal expansion, vibrations of pumps, and misalignments due to installation tolerances, while also being resistant to the process conditions and the external influences of the application.

Types of Expansion Joints

Expansion Joint - Single ArchSingle Arch

  • Fabric and rubber construction
  • Reinforced with metal/wire rings
  • Full-face flanges integral with joint body
  • Flanges drilled to companion bolt pattern
  • Gaskets not required
  • Offset available

Continue reading Elastomeric Expansion Joint Types & Movement