Expansion Joint Internal Liner

What are Internal Liners?

Internal liners or baffles are a recommended accessory to extend the life of many metallic pipe expansion joints because of their ability to protect the convolutions from direct flow impingement, which can cause erosion and flow-induced vibration. Internal sleeves shall be specified for all pipe expansion joints, regardless of the metal of the bellows in the following cases:

• Where it is necessary to hold friction losses to a minimum and smooth flow is desired.

• Where flow velocities are high and could produce resonant vibration of the bellows. Sleeves are recommended when flow velocities exceed the following values:

Air, Steam and other Gases

1) up to 6-inch dia. – 4 ft/sec per inch of dia.

2) over 6-inch dia. – 25 ft/sec.

Water and other Liquids

1) up to 6-inch dia. – 1-2/3 ft/sec per inch of dia.

2) over 6-inch dia. – 10 ft/sec.

When turbulent flow is generated within ten pipe diameters of the pipe expansion joint by changes in flow direction, valves, tee or elbow sections, cyclic devices, etc., the actual flow velocity should be multiplied by four prior to utilizing the criteria of the Standards of the Expansion Joint Manufacturers Association Sections C-3.1.2 and C-3.1.4.

• Where there is a possibility of erosion, such as in lines carrying catalyst or other abrasive media. Heavy gauge sleeves should be used, as at no time should the relatively thin bellows be directly exposed to erosion.

• Where there is reverse flow. Heavy gauge sleeves may be required.

• Where high temperatures are present in applications. An internal liner should be used to decrease the temperature of the bellows and enable the metal to retain its higher physical properties. (To obtain a maximum effect, the expansion joint should not be externally insulated.)

• Internal sleeves should NOT be used where high viscosity fluids such as tar are being transmitted, since these fluids may cause “packing up,” “coking” and “caking” which, in turn, may cause premature pipe expansion joint failure. If the fluid is such that purging will effectively prevent the “packing up,” internal sleeves may be used in conjunction with purge connections.

Internal Liner Materials

The standard PT&P internal liner is made of 300 Series stainless steel. If corrosion or temperature considerations dictate, the liner can be made of the same material specified for the bellows.

The liner is a longitudinally welded tube attached at one end to the upstream end connection. The diameter of the liner is small enough that the free, downstream end will not interfere or contact the downstream end connection during lateral or angular deflections. When a standard pipe expansion joint is selected from this catalog with the internal liner accessory, the expected lateral deflection should be stated so that the liner diameter can be properly sized.

If expected flow rates will be very high, such as at steam safety relief valves or in turbine exhaust and extraction steam applications, the internal liner should be of heavier construction. Usually, the liner material can be the same as the system pipe material, such as carbon steel, with liner thickness’ of 1/8-inch and greater depending upon flow rate and diameter.

Internal liners are almost always welded into the pipe expansion joint. However, if the Van-Stone flange end connection is specified, the PT&P liner will have its own flange and will be captured between the flanges at the upstream connection into the piping.

Reliability with Internal Liners

Internal liners are an important accessory for metallic expansion joints in systems where flow conditions could otherwise cause issues. By reducing turbulence, shielding the bellows from abrasive or high-velocity media, and maintaining more stable operating temperatures, liners help extend the service life of the expansion joint and protect the overall piping system.

If your piping system suffers from one of the issues above, an internal liner will be essential to keep any premature issues from occurring. 

Not sure if you have an internal liner or not? Meet with one of our engineers to find out more and if you need to have one installed. 

Did you know that US Bellows is a Piping Technology Company?
We are proud to be a one-stop solution from expansion joints to pipe supports and engineering services. We work hard to simplify your supply chain, and ensure system reliability with quality assurance.