U.S. Bellows refurbished a 54″ dia. custom crossover expansion joint for a power plant in Kansas. The flow end and balancing end bellows were replaced. The pressure balanced expansion joint was designed for 1″ axial movement at 700°F and 150 psig. The bellows longitudinal weld seams were 100% x-rayed and the assembly was hydro-tested at 180 psig prior to shipment. The refurbishment was completed in three weeks to meet the customer’s outage requirements.
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These expansion joint components were fabricated for a pressure balanced expansion joint in a nuclear power facility in Pennsylvania. They are 46″ square, fabricated from carbon steel duct with Inconel 625 bellows, and 321 stainless steel liner. The design conditions were +/- 0.875″ axial compression, 1,346 lb./in. lateral spring rate and 15 psig at 250°F. All welds were 100% dye penetrant examined and a pneumatic pressure test at 15 psig was conducted prior to shipping.
The pressure thrust produced by low pressures can be tremendous in large diameter systems, just as it can be at normal pressure ratings in small pipes. To avoid expensive anchors, to keep long pipe runs in tension, to prevent buckling, or reduce reaction forces on equipment, the pressure in the pipe can be used to generate balancing forces within the expansion joint. These combinations of bellows and thrust restraining structural components can accept almost any combination of movements, as shown in the following examples.
The pressure balanced elbow is ideal for absorbing the thermal expansion of equipment, such as turbines, pumps and compressors, which rely upon low reaction forces on their inlet and exhaust flanges. In this example, only an intermediate anchor is provided at the elbow, to isolate the equipment from any forces produced in the remaining piping.
The pressure thrust force produces tension on the equipment flange, but the only forces produced by the deflection, are the spring resistance of the bellows within the expansion joint. The spring rate of these units is the sum of the spring rates of the bellows on each side of the elbow, and care must be taken to provide a unit which produces spring forces low enough to satisfy the equipment maximums as stated by the equipment manufacturer. Bellows may also be cold sprung to reduce these forces even lower.
Example of how the flange is subjected to an axial force equal to the pressure thrust. In this example, which may be typical for a turbine exhaust application, the force on the machine’s flange is the spring reaction of the bellows in lateral deflection, as described in the above example. Again, the flange is also subjected to an axial force equal to the pressure thrust, as if it were capped, but the turbine’s mounts are not. The pipe guide between the expansion joint and the equipment flange absorbs the forces produced by the thermal expansion of the pipe, along its axis.
View all the examples in the full article on, Pressure Balancing Expansion Joints.
The existing pressure balanced elbow expansion joint with liners was re-designed with turning vanes to eliminate the vibration impact on the bellows. U.S. Bellows performed a computational fluid dynamics (CFD) analysis to determine the design of the turning vanes.
The turning vanes redirect the flow stream, which creates a smoother flow, thus eliminating the flow induced vibration. The bellows and liner were fabricated from 321 stainless steel and the rest is fabricated from carbon steel. An air and soap test was performed prior to shipping it to a power plant in Washington.
U.S. Bellows, Inc. specially designed and fabricated two 770 lb. pressure balanced expansion joints for a company in Ohio. These expansion joints, designed for 450 PSIG and 1350 °F, will be used for wind tunnel testing of airplanes and engines. With an overall length of 70, these expansion joints consist of four 8 diameter bellows with 3 plies of Inco 625 Gr1 material, an 8 diameter Inco 800 HT elbow, four 74 A193 B8 tie rods, and four 2 thick A240 tp304H rings. To ensure quality, 100% x-ray and 100% dye-penetran tests were performed on the bellows. A pneumatic test at 550 PSIG was conducted on the entire assembly prior to shipping.