Rubber Expansion Joints

Group 21 Created with Sketch.

What joint do I use for a building joint?

A building joint is installed in a structure so that static loads are not transferred from element of the structure to another due to movement.


When piping crosses a building joint, an expansion joint must be installed to prevent building movement from damaging the piping system.  The expansion joint must be able to handle movements in all directions (X, Y, and Z planes).  The ideal joint for this application is a MetraLoop.  If there is a space constraint the Seismic Gator can be used. Seismic Gators develop much higher anchor loads than Metraloops, see “How do I calculate in line bellows anchor loads”.


Although a building joint may resemble a seismic joint, it is not required to restrain the piping on each side of the building joint.  We recommend using slide guides on each side of the Metraloop.


In many cases the building joint expansion joint will be used to handle the thermal movement of the adjacent piping as well as the design movement of the build joint.  In this case the thermal movement and the building movements must be added together to properly size the expansion joint.

What can I do to protect my rubber expansion joint in an outdoor installation?

If a rubber expansion joint needs to be installed in an outdoors application, we would recommend scheduled inspections and application of CSM / Hypalon paint to the joint.  Additionally, EPDM has shown better resistance to UV degradation that other elastomers, so we would recommend an EPDM joint.

We do not recommend insulating a rubber joint so that they can be continuously inspected.

There are many variables that affect the lifespan of a rubber joint.  Pressure, Temperature, operation, service, and for outdoor applications UV exposure.  We recommend that the guidelines found in the FSA Expansion Joint Technical Handbook (Page 29, Paragraph E.1) that in critical service conditions rubber joints be replaced after 5 years, and for non-critical applications the rubber joints be replaced after 10 years.

How to handle thermal contraction

Standard bellows expansion joints are designed to primarily handle compression resulting from pipe expansion.  In the case of a pipe contracting due to a chilled system media, the expansion joint should be pre compressed at the factory to allow the extension of the joint when the pipe contracts.

What expansion joint do I use on plastic pipe?

Metraloops are an ideal expansion joint for plastic pipe. This is due to the low loads the loop exerts on the pipe. Flanged ends are preferred to prevent cracking of thin wall threaded fittings.

An alternative solution to the Loop is the 711 Plus. The 711 Plus is a full face rubber expansion joint with control rods integrated into the flanges on the joint. The integrated control rods prevent excessive stress from being transferred from the expansion joint’s flanges to the plastic flanges.

Do I need to worry about thermal expansion of natural gas lines?


If a gas line is run across the roof of a building, it will be subject to thermal loads due to the heating and cooling that occurs between day and night and change of seasons. Depending on the location of the installation, you can see a substantial change of temperature that would require additional flexibility.  The ideal product for this is the CSA / AGA Listed Gas Metraloop.

What is the difference between expansion joints that comply with ASTM F-1120 VS ASTM F-2934.

ASTM F-1120 is often used to specify expansion joints because for many years it was the only ASTM standard addressing metal expansion joints.  The specification ASTM F-1120 was developed in the “Ships and Marine Technology” technical committee of ASTM. The intent of this specification is for it to apply to expansion joints that are installed in Naval ships.  There are several requirements in F-1120 that are not necessary for a typical HVAC system, such as 100% radiographic inspection and manufactured with an ASME Section VIII stamp.  (ASME Section VIII (8) establishes rules of safety governing the design, fabrication, and inspection of boilers and pressure vessels, and nuclear power plant components during construction).  This would be what you would want if you were building an aircraft carrier.

ASTM F-2934 that was developed for products intended for HVAC applications.

Metraflex offers expansion joints that meet ASTM F-2934 or ASTM F-1120.

When do I need to add a liner to a hose or expansion joint?

There are three reasons you would want to specify including a liner for a hopes or expansion joint.

1.For internally pressurized bellows the requirement for needing a liner is spelled out in EJMA (Expansion Joint Manufacturers Association) per the table below.

For a hose the requirement for needing a liner is more straight forward.  Any liquid application of 25 feet per second or gas application over 75 feet per second should have a liner.

2.Any applications that are erosive or have particulate matter that may damage the hose.

3.For plumbing applications where the pipe may need to be rodded to clear an obstruction. An example of this would be the DWV Metraloop.

Please note: Externally pressurized expansion joints by design have a built-in liner.  Examples of externally pressurized expansion joints include Metragator, HP, and HPFF.

What kind of liner should I use?

This will depend on the type of product.


For internally pressurized joints, a solid liner is used that will not interfere with the bellows as shown below.  This type of liner can either be permanently welded in place or slipped into place.


Note.  Liners for internally pressurized bellows are flow dependent.

For hose products an interlock hose is used.  This will match the bend radius of the corrugated hose.

Find Your Piping Solution & More

Contact Metraflex
Rep icon Your Local Rep