Fluid Catalytic Cracking Unit Expansion Joints

The types of expansion joints used in Fluid Catalytic Cracking Unit (FCCU) service are some of the most critical expansion joints manufactured. Operating at high pressures, temperatures, large movement conditions and very aggressive media.

Flexider FCCU expansion joints are customized, engineered expansion joints. They are designed and built as per customer specifications and requirements ranging from ND 3” up to ND 100”. The FCCU expansion joint bellows section features a double-ply testable solution of monitoring in the event of an inner ply failure. Each ply is designed to operate independently to avoid external leaks to the environment.

Cold Wall Expansion Joints
These joints use a high density internal vibracast refractory lining to reduce the design temperature of the shell / piping below the temperature of the internal media. Although the temperature of the catalyst or flue gas may be as high as 1,400F, the internal refractory lining reduces the shell temperature below 650F. As a result, carbon steel is usually specified for the piping material of a cold wall expansion joint.

Cold Wall Regenerated Catalyst Standpipe Expansion Joint

Hot Wall Expansion Joints
Hot wall expansion joints are commonly found in the flue gas piping throughout an FCC unit.

Hot wall expansion joints between the Regenerator and the 3rd stage separator are usually lined with hex mesh and an abrasion-resistant lining to protect the piping from the catalyst fines in the flue gas. Hot wall expansion joints on the inlet and outlet piping of an expander are unlined to eliminate loose pieces of the abrasion resistant lining from traveling through the expander.

For both lined and unlined hot wall expansion joints, external insulation is installed around the piping of the expansion joint, requiring the expansion joint piping to be designed for the full temperature of the flue gas.

Hot Wall Single Hinged Expansion Joint

Expansion Joint Hardware
Expansion joint hardware is used in expansion joint applications to control movements and loads.

The gimbal hardware allows the expansion joint to absorb angular movement in all planes. Like the hinge, the gimbal hardware is designed to restrain pressure thrust and other external loads. Gimbal expansion joints are used in pairs or in combination with a hinge expansion joint.

Single Gimbal Exansion Joint

Limit Rods
Limit rods are used on many expansion joints to prevent the bellows from moving beyond the designed limit. In these applications the limit rods are not designed to restrain the pressure thrust load.

Limit Rod

The hinge hardware allows the expansion joint to absorb angular movement in one plane. The hardware is deigned to restrain pressure thrust and other external loads.

Single Hinged Expansion Joint

Pantograph linkages equalize the axial movement each bellows of a universal assembly. The gimbal pantograph expansion joint absorbs lateral deflection in two planes. The centre gimbal ring allows the expansion joint to offset in the opposite plane to the pantograph without the linkage binding.


Tie Rods
Tie rods are commonly used in universal expansion joint assemblies such as the elbow to elbow unit. The expansion joint is capable of absorbing large lateral movements while the tie rods absorb the pressure thrust load.

Elbow to Elbow Tied Universal Expansion Joint

Oversize Clam-Shell Bellows
In the event of a bellows leak through both bellows plies it may be possible to install an oversize clamshell bellows while the unit is online. The bellows is supplied in 180 degree segments that are field welded two places along the longitudinal seam during installation. The bellows has a weld end that allows attachment to existing end plates.

Oversize Clamshell Bellows

Download the Fluid Catalytic Cracking Unit Expansion Joints PDF or more detailed information.

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Balance Media Limited