This week’s featured product is on a hinged universal expansion joint and duct work assembly custom designed for an exhaust duct application in a power plant in Kenya. The hinge hardware was fabricated from carbon steel, while the rest of the unit was fabricated from 316 stainless steel with Inconel 625 bellows. An F-type variable spring was also provided for this project and will be used to support the center spool between the two elbows. The duct work with expansion joint is 36″ in diameter and the distance between the centerline of the two 90 degree elbows is 240″. It is designed for 20 psig at 115°F and 1/2 degree of angular movement. The entire assembly was 100% dye penetrant tested and a soap and air test was performed prior to shipment.
The universal expansion joint consists of two bellows separated by a pipe section or spool. The primary purpose of this arrangement is to have a unit which will accept large amounts of lateral deflection. The amount of lateral deflection they can accept is a function of the amount of angulation each bellows can absorb and the distance between the bellows. For a given bellows element, the amount of lateral deflection capability can be increased or decreased by simply changing the length of the center spool. In our Expansion Joint Catalog, three standard overall lengths are given with their lateral movement capability. If the piping problem requires greater capability, then the overall length can be increased to suit.
Since deflections are the result of piping thermal expansion, and universal expansion joints are usually long, our units are designed so that the thermal expansion within the tie rods is absorbed as axial compression by the two bellows elements. In this way, the overall length of the unit does not change when the piping is in service. The standard units in our Expansion Joint Catalog have all been designed to accept the thermal expansion of their length within the tie rods when the temperature is up to the design temperature shown.
You can view some of our past universal expansion joints on our blog.
Universal expansion joints are usually supplied with tie rods. Tie rods connect the ends of the unit to each other and restrain the pressure thrust load. This unit cannot accept any externally applied axial deflections. The thermal expansion of the distance between the tie rods —within the expansion joint— will be taken by the bellows element, as described above. The tie rods usually come in sets of two or more, equally distributed around the circumference of the expansion joint. When only two are provided, 180 degrees apart, the expansion joint is free to bend, or deflect angularly, as well as laterally. With three or more tie rods, since rods are loaded equally by the pressure thrust, only lateral deflections are possible without significant forces being applied by the adjacent piping.
See more pictures of universal expansion joints in our photo gallery.
U.S. Bellows designed and fabricated a 180″ long double gimbal expansion joint with a 90° elbow and flanged and flued head bellows, and a 114″ long single hinged expansion joint with flanged and flued head bellows. After performing a pipe stress analysis on the line, it was determined that spring supports were necessary, so F-Type variable spring supports were also provided for this project and shipped with the expansion joints.
All material in contact with the service fluid is fabricated from 304 H stainless steel and all external hardware is 304 stainless steel. The expansion joint bellows is designed for 5° angular movement and 1100°F at 10 psig. A spot x-ray test, soap and air test, and 100% dye penetrant examination on all welds were performed prior to shipment.
Thick-wall expansion joints may be a cost-effective option for large-diameter piping systems which operate at low pressure. Metals can be selected to satisfy different temperature conditions. The distribution of axial, angular, and lateral forces will be much higher when thick-wall expansion joints are used. We can provide your design engineers with the calculated forces and movements for proper design of the structural members supporting the system. These joints have a long life which justifies the initial investment.
72 Inch Tied Universal Thick-wall Expansion Joint with 316 Stainless Steel Bellows for a Sulfuric Acid Plant
90 Inch Universal Flanged and Flued Head Expansion Joint and Duct Work Assembly
Thick-wall expansion joints are used primarily in heat exchangers and large diameter piping systems where thin-wall expansion joints would not be sufficient. The bellows are typically fabricated from A516 Grade 70 material, with the thickness ranging from 3/16″ to 1″. Other materials are available to meet different temperature requirements.
108 Inch Diameter Thick Wall Expansion Joint with 2 Convolutions
Thick-wall Flanged and Flued Head Expansion Joints