Metal vs. Rubber Expansion Joints: What Is the Difference?

Expansion joints, also referred to as bellows, play an integral part in piping systems. They absorb excessive vibrations and correct misalignment to keep exhaust systems working correctly. There are two different types of expansion joints: metal and rubber. Determining which type of expansion joint will work best in your company's system depends on a few factors.

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When you're deciding between metal vs. rubber expansion joints, you'll need to know: What is the difference? Here are the advantages and disadvantages of both types.

Rubber Expansion Joints

Rubber expansion joints consist of a flexible connector that can consist of fabric and, sometimes, internal metallic reinforcements. Here are the main advantages of rubber bellows:

• More mobility: Typically, rubber expansion joints offer more lateral movements than metal.

• Superior noise dampening abilities: Rubber joints are more effective at reducing noise from vibrations in piping systems.

• Easy installation: Additional gaskets aren't needed to install rubber joints, making the joints easier to install and maintain over time.

Metal Expansion Joints

Metal expansion joints are used in applications much more frequently than rubber expansion joints. When you're exploring metal vs. rubber expansion joints, what is the difference in using either in applications? Rubber joints may offer more mobility and less maintenance, but metal expansion joints are necessities in most systems. Constructed from a thin-gauge material that will absorb mechanical and thermal movements, they can handle extreme temperatures and pressures that rubber joints cannot.

Here are the advantages of metal expansion joints:

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• Ability to withstand extreme temperatures: Metal bellows can withstand a greater range of temperatures than rubber can. They can handle a range of -420 degrees Fahrenheit to 1,800 degrees Fahrenheit. Rubber joints can only accommodate up to 400 degrees Fahrenheit. If your project requires extreme temperatures, then you'll need metal expansion joints.

• Ability to withstand pressure: Another critical factor of stainless steel bellows is their ability to withstand significant stress. Since they're made from stainless steel, they can deal with far more force than rubber joints can. A rubber joint can withstand up to 250 psi, whereas a metal joint can withstand pressures up to 1,000 psi.

Deciding between metal and rubber bellows isn't so much about which is better but which expansion joint provides the most support to a particular application.

Elastomer Choices, Pressure Ratings, Sizes

Choice of elastomer is very important when your pipeline is conveying liquids other than water. Various elastomers, fluoroelastomers, and fluoroplastics have differing compatibility to chemicals and abrasive slurries. For instance, expansion joint liners can be formulated to handle raw sewage, acids, alkaline, hot air, pure drinking water, abrasive slurry, and many other chemicals and media. Tube liners of natural or pure gum rubber are ideal for use with abrasive material. Synthetic Nitrile rubber is best for raw sewage, EPDM is a good choice for many hot air applications. For chemical applications, your best choice may be Viton, PTFE, or Hypalon. Unisource does not recommend rubber expansion joints for use with compressed gases, steam, or extreme temperature liquids. For shipboard service for commercial vessels, we offer rubber expansion joints that meet the requirements of the U.S. Coast Guard and the Code of Federal Regulations. Our U.S. Navy mil-spec joints can be built with ANSI flange drilling or Navy drilling.

Also, look carefully at the maximum pressure that your piping system will see, It may be during the system hydro-test. Standard rubber expansion joints are made in working pressures of 150 to 225 PSI in most sizes. High pressure products can be manufactured upon request. Keep in mind that higher pressure expansion joints will be heavier and more stiff than lower pressure joints. Generally, rubber expansion joints are reinforce with polyester fabric plies along with steel hoops for vacuum rating. For higher-pressure ratings, Kevlar reinforcing might be indicated.

Rubber expansion joints are readily available in sizes from 1-1/2 inch to 36 inch. Single and double rubber spheres are made in hydraulic molds and range in size from 1-1/2 inch to 16 inch, with larger sizes to 20' available upon special order. Spool-type or arch-type expansion joints can be made in much larger sizes. Sizes on these products vary from 1-1-/2' to 102' diameter.

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