How to choose expansion joint
All components and system requirements must be considered when choosing an expansion joint for the particular application. Uncovering all the factors that may influence reliable performance provides for the most ideal selection.
Piping Plan
Before addressing the expansion joint itself, ensure that adjacent piping and equipment conforms to Good, solid piping engineering practices. Basically, this means the proper placement and design of the anchors, guides and supports are important for the expansion joint to function properly.
Joint Movement
Since expansion joints and pump flexible connectors are employed to absorb axial, lateral and angular pipe movement, as well as vibration, careful consideration should be made to correctly calculate those movements. It is important that the correct coefficient of thermal expansion (CTE) is used.
The specific pipe material must be known since the CTE differs greatly between pipe materials. These differences can affect calculated movement to a point that the pipe movement may greatly exceed the expansion joint’s capability when initial calculations show that they are within its limits.
Pumped Media
Determining the process media is also important since new chemicals are processed every year. The media is one of the most important determining factors for compatible elastomer selection. Material selection must not be compromised during the specifying process. Choosing a marginal tube material is risky and invites high replacement costs and/or downtime.
Any abrasive material in the media should also be investigated since even minute amounts of abrasive material at high velocity can wear out a tube prematurely. A protective liner or filled arch design should be investigated. Conservatism is the best policy since a compromised product can lead to rapid deterioration and failure.
It is recommended that severe service joints carry material certification requirements and that material properties are checked to confirm that the material certification matched the pumped fluid.
Pressure and Temperature
Accurate temperature and pressure data is important and should be included in the analysis of the application’s requirements. When temperatures exceed 200 degrees Fahrenheit (93 degrees Celsius), proper pressure de-rating should be made to ensure that the expansion joint or flexible connector can handle the system working pressure at the maximum elevated temperature. Pressure de-rating is required to prevent potential deterioration of the reinforcing fabric.
When connectors are used at discharge, pulsating or shock pressure should be investigated. A general rule is that the expansion joint or flexible connector should be rated to withstand four times the system working to compensate for shock pressure.
Anchors
High quality, reliable anchors should be employed that will withstand the joint pressure thrust and force resulting from the pipe motion. The use of control rods or limit bolts is also recommended as a backup for the possibility of anchor failure. These rods prevent the joint from extending or pulling apart if a restraint anchor were to fail or blow out. The use of control rods is an inexpensive insurance policy.
Non-metallic expansion joint systems, when designed properly and applied correctly, can last 30 years or more. One example is an application in which high pressure cooling water was passing through an ethylene propylene diene monomer (EPDM)expansion joint with a 132-inch internal diameter at more than 200 degrees F (93 degrees C) in a nuclear power facility. When removed, the expansion joint showed little wear and increased durometer hardness after more than 25 years of service.
Reliability is almost always tied directly to correct joint selection along with sound adjacent piping design. Consideration of all factors that can affect performance will almost guarantee long life for expansion joints or flexible connectors.
What factors should be considered when selecting an expansion joint?
When choosing an expansion joint, several factors must be taken into account to ensure optimal performance. These include the piping plan, which should adhere to good engineering practices by ensuring proper placement and design of anchors, guides, and supports. Additionally, consider the operating conditions such as temperature, pressure, and the type of media being transported, as these will impact the material selection and design of the expansion joint.
How does the type of expansion joint influence its performance?
The type of expansion joint selected—whether metallic, rubber, or fabric—will directly affect its ability to absorb movement and accommodate thermal expansion. Each type has its own characteristics, such as flexibility, pressure ratings, and resistance to chemicals, which must align with the specific needs of the piping system. For instance, metal expansion joints are often preferred in high-temperature applications due to their durability and strength.
What maintenance considerations should be taken into account for expansion joints?
Regular inspection and maintenance of expansion joints are crucial for ensuring their longevity and reliability. Look for signs of wear, such as cracking or leakage, and assess the joint's alignment within the piping system. Implementing a routine maintenance schedule can help identify potential issues early. Additionally, consider the ease of access to the expansion joint for maintenance purposes when designing the piping layout.