Rubber & PTFE expansion joints have been commonly used in piping systems for over 50 years. The main purpose of an expansion joint in a piping system is to provide stress relief. In order to ensure that the expansion joints operate safely, and as intended, it is imperative to follow proper installation practices.
By Eric Blazej, National Industrial Distribution Sales Manager, Proco Products Inc.
General Properties
The ability to move in three directions (compression, extension, and lateral), coupled with the ability to assist with sound dampening and minimizing vibration, are just some of the factors that make rubber expansion joints extremely versatile. The majority of expansion joints are located on both the suction and discharge side of a pump. They can also be found on boilers, heat exchangers, cooling towers, tanks, as well as in the middle of pipe runs.
The average lifespan of a rubber expansion joint is roughly 7-10 years. Depending on the application, however, some joints only last a couple months, while other can function well for 25+ years. When determining the application specific requirements of a rubber expansion joint, most manufacturers require the acronym STAMPED (Size, Temperature, Application, Media/Movement, Pressure, End Fittings, Delivery) to quote the proper expansion joint for any given application. This will ensure the best possible longevity for the expansion joint.
As many rubber expansion joints have standardized lengths, they are often pre-fabricated and kept in stock.
Rubber joints are not the only solution for providing relief in piping systems; both a stainless-steel bellows expansion joint and a stainless-steel flexible connector can be installed to provide relief. To determine which type of expansion joint should be used, it is best to start with the Rule of 250. For any application that has under 250 PSI, or 250F, a rubber expansion joint will usually be the best selection. Stainless-steel will, however, typically be a better option for anything that has over 250 PSI or 250F. For aggressive medias, such as acids or caustics, PTFE or stainless-steel should always be used. As applications that use stainless-steel expansion joints tend to have a wider range of specifications, they are commonly custom made per application.
Common Installation Mistakes to Avoid
Once a joint is selected proper installation is imperative to avoid premature failures. Common types of improper installations include the following:
Incorrect bolt usage
If the bolts used for installation are too long or facing the wrong direction, they will protrude into the rubber arch in the bellows. Three solutions to this issue are: a shorter bolt that is no more than two turns past the nut, turning the bolts outward, or using all thread.
Over-extension
The natural reaction of a rubber expansion joint once a piping system is turned on is to extend outward. Properly installing anchors or using control units will prevent the joint from extending past its limitations.
Over-compression
There are commonly other pieces of equipment, such as check valves or strainers, which may be placed on top of a rubber joint in a vertical pipe run. The weight of the equipment could over-compress the expansion joint. An improperly supported pipe and the weight of the column could cause similar issues. Control units can also be used to prevent over-compression.
Extending or squeezing joints
It is important to install rubber expansion joints as close to neutral length as possible. Extending or squeezing joints into place will put stress on the joint prior to the system being turned on. Custom length joints or expansion joints built with an offset are available from most manufacturers.
Rubber-to-rubber seals
If connecting to any center guided style silent check valve, it is important to install rubber joints on the discharge side (away from the trim). If a rubber joint must be installed on the intake side a Transition or Spacer Flange must be used. Avoid a rubber-to-rubber seal. The use of a spacer flange is advised.
Improper bolt torque procedures
Please follow the proper bolt torque procedures that are specified by each manufacturer. Information of bolt torque pressure will be in the installation instructions. This will be different for all companies. It is also important to re-torque the bolts 24 hours after initial installation. Rubber ‘relaxes’ so additional torquing may be required.
Inappropriate use of gaskets
Most of the time rubber expansion joints do not require the use of a gasket. The gasket will create a potential leak path. It is best to allow the rubber of the expansion joint to create the seal with the mating flange.
Solids present in media
For applications where 20% or more solids are present in the media, it is important to use a filled arch expansion joint. Solids could cause failures due to abrasion of the bellows inside the expansion joint. Important note: filled arch joints movement values are reduced by 50%. Finally, as a reminder, it is important to make sure that the pressure, temperature, and media are compatible with the style of joint as well as the elastomer. Failure to take these into consideration could lead to a catastrophic failure.
Final Thoughts
The nine scenarios listed above are the most common types of installation issues for rubber expansion joints. Should a user have any additional questions about specific expansion joint related scenarios, it is always best to reach out to a manufacturer directly and they can provide further assistance. It is best to work with manufacturers of rubber expansion joints that are members of the Fluid Sealing Association as well. Rubber expansion joint manufacturers who are members of the FSA are recognized as the primary source of technical information for the industry; they help influence and support the development of related standards, and provide education in the fluid sealing area.
ABOUT THE AUTHOR
Eric Blazej, National Industrial Distribution Manager at Proco Products, has more than 10 years of sales experience of rubber expansion joint products in both HVAC & Industrial piping applications. His primary focus is assisting distribution at the end user level via rubber expansion joint surveys.