Although sometimes overlooked or treated like an afterthought in process design, expansion joints are critical elements in chemical process industries (CPI) operations for providing flexibility and stress relief to piping systems. Failures in expansion joints can result in leaks of process fluids, with implications for personnel safety, environmental protection and operational uptime. Selecting the correct type of expansion joint for the process conditions will maximize the longevity of the joint and reduce downtime for replacing it, while also maintaining the joint’s integrity. By considering a full set of process characteristics when selecting expansion joints, plants can maximize production and operational uptime while still maintaining safety and environmental stewardship.
For the selection process, plant engineers should consider taking advantage of expansion-joint vendors, who can offer specialized expertise and on-the-ground experience to guide users to the optimal type of expansion joint for certain process conditions. Vendor companies serve as a valuable resource for arriving at the best expansion-joint choice.
With competitive price and timely delivery, HESPER sincerely hope to be your supplier and partner.
Expansion Joint Types
Expansion joints can be split into three general categories: rubber expansion joints, stainless steel expansion joints and hose-and-braid flex connectors. Each type has its own advantages and limitations, and each category can be further broken down into subcategories, because there are several different types of elastomers used for expansion joints, as well as multiple types of stainless steel. In addition, there are multiple design variations with different joint geometries that help their performance in certain specific applications.
Figure 1. Expansion joints can be divided into three general categories, as shown here: Rubber, hose and braid, and stainless steel
For rubber expansion joints, the most common elastomers are ethylene propylene diene monomer (EPDM) rubber, polytetrafluoroethylene (PTFE), polychloroprene (Neoprene), nitrile rubber, butyl rubber, natural rubber, & synthetic elastomers. Rubber expansion joints are generally more versatile than other types of joints, although issues of chemical compatibility, pressure and temperature may preclude them from being used under some process conditions. Rubber expansion joints effectively handle compression (movement inward), and extension (movement outward), as well as lateral offset motion, vibration and sound dampening in a short overall length.
Stainless steel expansion joints are also available in several variants, such as 304, 316, and 321 stainless steel grades. Expansion joints made from other metals, such as titanium, or high-temperature alloys, such as Hastelloy and Inconel, are also available. Stainless steel expansion joints are good for handling compression, extension, lateral motion and vibration, but they will exert a larger overall force on the piping system and are longer in overall length
Stainless steel expansion joints should not be confused with stainless steel flex connectors, which are hose-and-braid-style connectors with a stainless steel braided material on the outside. They can address lateral movement and vibration in pipe and equipment joints.
Figure 2. Rubber expansion joints shown on a process pump and piping setup
Factors For Selecting Expansion Joints
When selecting expansion joints for process pipes and equipment, engineers should begin by following a set of criteria that has been generally agreed upon by the industry as a method of taking a comprehensive look at the requirements of the joint. The set of criteria is known by the acronym “STAMPED.” By gathering information according to this set of factors and questions will provide an excellent basis for which expansion joints should be used. The components of the acronym are defined here:
The STAMPED criteria can go a long way toward narrowing down the choices in expansion joints to steel or rubber, but there are still a wide variety of choices within each of those categories, and different designs available for particular conditions and applications. For example, if an application requires a great deal of movement, there are joints with more convolutions or arches built into the bellows of the joint. Again, expansion joint vendors can be a resource here.
Selection Recommendations
Once you have established the information for the questions associated with STAMPED, there a several additional considerations to help arrive at the final selection of expansion joints. They are discussed here:
Rule of 250. The “Rule of 250” concerns pressure and temperature of the media. If the pressure is lower than 250 psi and temperature lower than 250°F, then rubber expansion joints should be used, but for pressures above 250 psi and temperatures over 250°F amount probably requires stainless steel.
Figure 3. Rubber expansion joints can be used in applications where temperatures are lower than 250°F
Specific temperature requirements. Beyond the so-called Rule of 250, the selection of expansion joint material should get more specific. EPDM and butyl rubber expansion joints are suitable up to 250°F, but Neoprene is only good to 220°F and nitrile rubber up to 212°F.
MSDS. Material safety data sheets (MSDS) provide details on various compounds that might be present in process media. The information can include details about the potential health and environmental hazards of the components, as well as chemical compatibility. It is highly recommended that users consult MSDS before selecting an expansion joint. Two similar compounds used in a process, such as ethylene glycol and propylene glycol, could require different expansion joints. For example, ethylene glycol is suitable for EPDM expansion joints, while propylene glycol works with nitrile rubber. The degree of specificity that users can have for the type of media that the expansion joint will encounter can have huge impact on the type of elastomer selected.
Concentrations. Beyond the identity of the process media that is present, concentrations of various components within the media are also important. For example, a 5% solution of a caustic substance might be suitable for a particular type of elastomer, but if the concentration of the same caustic material is increased to 20%, for instance, the rubber material might break down. In these cases, stainless steel expansion joints might be required.
Gas handling. For processes involving gases, the material should be considered carefully also, since rubber expansion joints are somewhat permeable to gases. Cases where gas escape would be a problem might also require the use of stainless-steel expansion joints.
Life expectancy. It can be useful to identify factors that might reduce or extend the lifetime of an expansion joint. The average lifespan of a rubber expansion joint is roughly 7-10 years. Depending on the particulars of an application, however, expansion joints might only last a matter of 2-3 months, while other joints might function well for 25 years or more. Some of the factors that can contribute to a shorter life expectancy are high pressure, high temperature, aggressive or abrasive media, exposure to outdoor weather and extensive levels of movement.
Expansion joint surveys. Although there are lengths of time that expansion joints can be expected to last, a definitive method for determining exactly when to replace expansion joints or to identify the exact moment when they will fail does not exist. The best way to prepare for an expansion joint failure, and to limit downtime in the event of a failure, is an expansion joint survey. Member companies of the Fluid Sealing Association (FSA; Wayne, Pa.; www.fluidsealing.com) offer expansion joint surveys. These surveys can be critical for plant maintenance, especially with plants that are trying to maximize productivity and profits while also limiting downtime. Surveys have the potential to help a plant avoid environmental concerns associated with expansion joint failures.
No matter what process details are found in a process, expansion-joint manufacturers will be able to guide users toward the correct type of expansion joint for given operational conditions.
Expansion joints are a critical component for any industrial application which includes piping or ducting. With a wide variety of designs and materials to choose from, the correct selection and optimal installation of expansion joints are vital to ensure reliable and safe operations.
Commercial and industrial installations which feature any kind of pumping, piping, or ducting will also almost invariably include expansion or movement joints too. Mitigating against the effects of thermal expansion, movement induced by vibration or even external factors such as seismic activity or ground settlement, expansion joints are a necessary safety component.
Manufactured from a wide variety of materials such as stainless steel, rubber, or Polytetrafluroethylene (PTFE), expansion joints help to ensure structural integrity. For instance, where industrial processes require large changes in temperature, thermal expansion of metal components can introduce stresses which may cause fatigue. Expansion joints can eliminate this potential source of failure.
What Is The Right Kind Of Expansion Joint?
Rubber expansion joints possess many particularly beneficial characteristics due to an inherent flexibility, provided it meets the application temperature/pressure requirements. This makes them suitable for many applications, including the absorption of sound, thermal energy and shock. Known for their durability and capability to withstand extreme environments, rubber expansion joints are commonly found in harsh applications such as pulp and paper, chemical processing, water and wastewater, mining and metals, as well as in pumping applications. Rubber expansion joints are also commonly found being used to reduce fluid noise from rotating equipment they are attached to.
Typically fabricated of natural or synthetic oil-based elastomers, materials used in rubber flexible joints include EPDM, Neoprene, Chlorobutyl and Hypalon, Nitrile and Natural Rubber combined with other materials, including metal or wire reinforcing, nylon, polyester, aramid fiber or PTFE.
In some extreme environments, such as high PH or low PH chemical systems, expansion joints are constructed from molded PTFE or PTFE lined rubber. As a non-reactive material, PTFE has some advantageous properties for the chemicals processing industry where highly corrosive substances may be in play. Molded PTFE or PTFE lined rubber expansion joints are specifically designed to protect pipes which come in contact with strong industrial and reactive materials.
Systems which feature braided metal hose are designed to control vibration, reduce noise, relieve stress and compensate for potential misalignment while withstanding higher operational temperature/pressures. Suitable for many different mechanical applications, such as pumps, compressors and other heavy equipment, these connectors are made from a variety of different metals, including copper and stainless steel, to suit even the most extreme applications.
Selecting The Right Expansion Joint
Given that expansion joints are frequently found operating in potentially rigorous processes such as the power, steel, pulp & paper, mining and chemical industries, correct selection, installation and maintenance is key to ensuring reliability and maximizing performance, getting the best service life. Where failure of an expansion joint could lead to downtime of a system, materials selection and optimal installation are key. Rubber expansion joints, for example, if incorrectly used at excessively high temperature or are improperly installed will lose flexibility over time as oils within the rubber are lost. This will lead to the expansion joint becoming brittle and prone to accelerated failure.
Do review the expansion joint manufacturerexpansion joint manufacturer’s performance characteristics and seek help with design considerations based on the manufacturer’s experience for the application to lessen failure possibilities. Some initial considerations when selecting an expansion joint are to choose one which is suitably sized for the application and the available footprint, as well as rated for the anticipated range of temperatures and pressures that the equipment will see during its operational life. Other factors may include the viscosity of the pumped fluid, if it includes solids, and if there are any potential incompatibility issues between the process fluids and the expansion joint materials. Total cost of ownership is also a critical element in choosing the best expansion joint for any given application.
Correct Expansion Joint Installation
Even the best and most expensive product will become more prone to failure if it is badly installed. Conversely, installing the right product correctly can not only extend the life of a system, but can also enhance the total lifespan of the whole system.
Correct piping alignment is high on the list of priorities. An offset installation automatically puts the expansion joint in a difficult situation and may create very real hazards for both product and operators. Expansion joints are not designed to compensate for inaccuracies in piping installation and should not be used to correct them. Similarly, vibration should be minimized and expansion joints should be located as close as possible to fixed anchors or control rods which should be used in un-anchored piping systems. Sufficient pipe support is also critical as the expansion joint should not carry the weight of adjacent piping/equipment in order to operate correctly.
Siting (site selection) of expansion joints is another key consideration. Ideally, expansion joints should not be installed in areas where inspection is not possible. Furthermore, where expansion joints are transporting hazardous materials, the use of an external metal shield should be considered to protect personnel in the event of leakage or failure as fluid will run parallel to the pipe system and not radially out.
It is also important to consider the type of expansion joint and its materials. For example, while it is common practice to place piping insulation over metallic expansion joints, when using rubber expansion joints this practice should be avoided. Thermal insulation can allow heat to build up and dry out the rubber making it become more brittle, enhancing the failure mode.
On a more mundane level, during the expansion joint installation operators should check for any damage to the expansion joint, install external hardware properly and ensure that it is torqued properly to ensure leak free operation.
Following a few simple guidelines and taking every effort to ensure an expansion joint is installed correctly will inevitably pay operational dividends.
Maintaining Expansion Joints
While an expansion joint that is correctly sized, specified and installed should not require any maintenance, a regular inspection program is nonetheless highly recommended. Inspections can identify any issues such as leaks, corrosion or blisters and cracks in rubber expansion joints. Checking for signs of wear does not guarantee that damage will not occur but identifying any potential problems early does significantly reduce the total value at risk. As with all equipment, following the manufacturer’s recommended maintenance schedule is likely to yield the optimal result in terms of securing a maximized service life. When installed and maintained correctly, expansion joints may reasonably expect a 7 to 10-year service life, though specifics are dependent on the application. However, this does require sticking to a policy of strictly following manufacturer’s recommendations.
Used correctly, expansion joints are an effective solution to manage movement, vibration and the cyclic motion associated with temperature changes. Available in a broad range of sizes, styles, materials and specifications, suitable expansion joints are available to service even the most demanding applications. But to get the most out of any expansion joint choose the right one and ensure it is installed correctly.
Proco Products are leading expansion joint manufacturers with an extensive inventory of expansion joints for piping and ducting systems. Find out more about expansion joints at https://www.procoproducts.com.
Although sometimes overlooked or treated like an afterthought in process design, expansion joints are critical elements in chemical process industries (CPI) operations for providing flexibility and stress relief to piping systems. Failures in expansion joints can result in leaks of process fluids, with implications for personnel safety, environmental protection and operational uptime. Selecting the correct type of expansion joint for the process conditions will maximize the longevity of the joint and reduce downtime for replacing it, while also maintaining the joint’s integrity. By considering a full set of process characteristics when selecting expansion joints, plants can maximize production and operational uptime while still maintaining safety and environmental stewardship.
For the selection process, plant engineers should consider taking advantage of expansion-joint vendors, who can offer specialized expertise and on-the-ground experience to guide users to the optimal type of expansion joint for certain process conditions. Vendor companies serve as a valuable resource for arriving at the best expansion-joint choice.
Expansion Joint Types
Expansion joints can be split into three general categories: rubber expansion joints, stainless steel expansion joints and hose-and-braid flex connectors. Each type has its own advantages and limitations, and each category can be further broken down into subcategories, because there are several different types of elastomers used for expansion joints, as well as multiple types of stainless steel. In addition, there are multiple design variations with different joint geometries that help their performance in certain specific applications.
Figure 1. Expansion joints can be divided into three general categories, as shown here: Rubber, hose and braid, and stainless steel
For rubber expansion joints, the most common elastomers are ethylene propylene diene monomer (EPDM) rubber, polytetrafluoroethylene (PTFE), polychloroprene (Neoprene), nitrile rubber, butyl rubber, natural rubber, & synthetic elastomers. Rubber expansion joints are generally more versatile than other types of joints, although issues of chemical compatibility, pressure and temperature may preclude them from being used under some process conditions. Rubber expansion joints effectively handle compression (movement inward), and extension (movement outward), as well as lateral offset motion, vibration and sound dampening in a short overall length.
Stainless steel expansion joints are also available in several variants, such as 304, 316, and 321 stainless steel grades. Expansion joints made from other metals, such as titanium, or high-temperature alloys, such as Hastelloy and Inconel, are also available. Stainless steel expansion joints are good for handling compression, extension, lateral motion and vibration, but they will exert a larger overall force on the piping system and are longer in overall length
Stainless steel expansion joints should not be confused with stainless steel flex connectors, which are hose-and-braid-style connectors with a stainless steel braided material on the outside. They can address lateral movement and vibration in pipe and equipment joints.
Figure 2. Rubber expansion joints shown on a process pump and piping setup
Factors For Selecting Expansion Joints
When selecting expansion joints for process pipes and equipment, engineers should begin by following a set of criteria that has been generally agreed upon by the industry as a method of taking a comprehensive look at the requirements of the joint. The set of criteria is known by the acronym “STAMPED.” By gathering information according to this set of factors and questions will provide an excellent basis for which expansion joints should be used. The components of the acronym are defined here:
The STAMPED criteria can go a long way toward narrowing down the choices in expansion joints to steel or rubber, but there are still a wide variety of choices within each of those categories, and different designs available for particular conditions and applications. For example, if an application requires a great deal of movement, there are joints with more convolutions or arches built into the bellows of the joint. Again, expansion joint vendors can be a resource here.
Selection Recommendations
Once you have established the information for the questions associated with STAMPED, there a several additional considerations to help arrive at the final selection of expansion joints. They are discussed here:
Rule of 250. The “Rule of 250” concerns pressure and temperature of the media. If the pressure is lower than 250 psi and temperature lower than 250°F, then rubber expansion joints should be used, but for pressures above 250 psi and temperatures over 250°F amount probably requires stainless steel.
Figure 3. Rubber expansion joints can be used in applications where temperatures are lower than 250°F
Specific temperature requirements. Beyond the so-called Rule of 250, the selection of expansion joint material should get more specific. EPDM and butyl rubber expansion joints are suitable up to 250°F, but Neoprene is only good to 220°F and nitrile rubber up to 212°F.
MSDS. Material safety data sheets (MSDS) provide details on various compounds that might be present in process media. The information can include details about the potential health and environmental hazards of the components, as well as chemical compatibility. It is highly recommended that users consult MSDS before selecting an expansion joint. Two similar compounds used in a process, such as ethylene glycol and propylene glycol, could require different expansion joints. For example, ethylene glycol is suitable for EPDM expansion joints, while propylene glycol works with nitrile rubber. The degree of specificity that users can have for the type of media that the expansion joint will encounter can have huge impact on the type of elastomer selected.
Concentrations. Beyond the identity of the process media that is present, concentrations of various components within the media are also important. For example, a 5% solution of a caustic substance might be suitable for a particular type of elastomer, but if the concentration of the same caustic material is increased to 20%, for instance, the rubber material might break down. In these cases, stainless steel expansion joints might be required.
Gas handling. For processes involving gases, the material should be considered carefully also, since rubber expansion joints are somewhat permeable to gases. Cases where gas escape would be a problem might also require the use of stainless-steel expansion joints.
Life expectancy. It can be useful to identify factors that might reduce or extend the lifetime of an expansion joint. The average lifespan of a rubber expansion joint is roughly 7-10 years. Depending on the particulars of an application, however, expansion joints might only last a matter of 2-3 months, while other joints might function well for 25 years or more. Some of the factors that can contribute to a shorter life expectancy are high pressure, high temperature, aggressive or abrasive media, exposure to outdoor weather and extensive levels of movement.
Expansion joint surveys. Although there are lengths of time that expansion joints can be expected to last, a definitive method for determining exactly when to replace expansion joints or to identify the exact moment when they will fail does not exist. The best way to prepare for an expansion joint failure, and to limit downtime in the event of a failure, is an expansion joint survey. Member companies of the Fluid Sealing Association (FSA; Wayne, Pa.; www.fluidsealing.com) offer expansion joint surveys. These surveys can be critical for plant maintenance, especially with plants that are trying to maximize productivity and profits while also limiting downtime. Surveys have the potential to help a plant avoid environmental concerns associated with expansion joint failures.
No matter what process details are found in a process, expansion-joint manufacturers will be able to guide users toward the correct type of expansion joint for given operational conditions.