What Are Metal Expansion Joints?

Networks of piping and tubing are used for every industrial application. You’ll typically see piping installed in any industrial building, and they are used for transmission of airflow, chemicals like ammonia, or for oil or water transmission. Because the fluid transmission is vital to the operation of any industry, piping is required to be well-constituted, leak-proof, and long-lasting. That’s where metal expansion joints come in.

As efficient as piping is, it does suffer from one drawback: rigidity. Unlike hoses, piping cannot compensate for expansion due to temperature or structural shifting, like hoses. However, piping is preferred to hoses in fluid transmission because they don’t sag, are more durable, and they don’t fray or burst as easily. However, piping that is susceptible to swelling and shrinking due to differences in ambient and fluid temperature are prone to distortion or leaking at the flanges after enough movement. Metal expansion joints were designed to solve this problem.

Metal expansion joints were developed to compensate for this restriction. A metal expansion joint is an articulated joint consisting of connecting flanges at both ends, expandable bellows as the body (made from various metals), and a mechanism to help control the movement articulation. The mechanism is usually a tie rod, but reinforcing accessories can be added, such as collars, liners, weld ends, limiting and control rods, and equalizing rings, to name a few. The tie rod and other related accessories allow for axial, longitudinal, and angular shifting, limiting the possibility of a pipe break.

How To Install a Metal Expansion Joint

Before the installation of any metal expansion joints is to take place, it is important to do an initial inspection of all the parts to ensure there are no manufacturing defects or damage from shipping and handling. Look for cracks in the bellows, dents, distortions, chips, or places where components are warped and will not fit properly. Also, check that the alignment of the pipe joint can be properly accommodated by the metal expansion joint. If the joint is not designed to properly compensate for the pipe layout (by the angle being too sharp, for example), the joint is liable to break.

Once the parts pass the initial inspection, it is time to install the metal expansion joint. Ensure that the ends of the pipe to be attached to the joint flanges have been securely anchored to prevent shifting during installation. Make sure that any field pre-positioning conforms to the instructions for installing the joint.

A thin layer of graphite dispersed in glycerin or water should be applied to the rubber seal between the pipe flange and the joint flange before installing to allow for easy removal should the need arise. The joint should not be installed in an expanded or contracted state, as they will not be able to fully compensate for the movement buffer. The metal expansion joint should be continuously supported while bolting the flanges together, and they should not place any excess weight upon the pipe ends.

Finally, tighten bolts with two wrenches to torque specifications. Unlike tightening bolts on a tire where they are usually tightened opposite each other, the bolts on a metal expansion joint flange should be tightened sequentially until the rubber flange bulges uniformly between the backup ring of the flange and the face of the pipe flange. Once all the bolts have been properly torqued, remove any shipping accessories (i.e. stabilizing bars) that are still attached to the joint.

How To Maintain A Metal Expansion Joint

The metal expansion joint must be subject to routine inspection and maintenance by a competent design authority to ensure it remains functional and isn’t going to fail. Since rubber flanges tend to relax, and because of the constant shifting, it is important to check the torque of the bolts routinely to ensure they have not backed off. Routine quality checks should be conducted for possible cracking or distorting. Depending on environmental conditions, checks for chemical or rust corrosion may also be necessary.

Innovations in Metal Expansion Joints

Because pipes come in many sizes, materials, and for several different applications, there are varied selections available in designs and materials for just about every application, including metal expansion joints. To find out what design specifications you need for your project, contact Dannenbaum LLC for a selection and quote. Click here to learn more.