A pressure vessel located in the UK was operating under the most challenging circumstances and demanded a special expansion joint solution. To guarantee a reliable performance in these harsh conditions, the only solution was a root ring reinforced high-pressure expansion joint.
Rings to withstand the pressure
At extremely high pressures, rings around each convolution root are needed to ensure the bellow retains the internal pressure. The rings are especially heavy in this case due to the very high pressures involved. Like the bellow, the rings are made from Inconel 625.
Due to the small inside diameter and the diameter of the ring required to contain the pressure forces, the material strength requirements ruled out the use of the standard practice of production from solid round bar, in this case each ring was machined from plate.
Tested at 251 BarG
Normally expansion joints designed according to EJMA 9 are tested at 1½ times the design pressure, but due to the high design temperature (300°C) a higher test pressure was necessary (251 BarG).
This test pressure is just over twice the pressure used to hydraulically form the bellows.
A custom testing setup was designed to pressure test the bellow, within excess of 33t of pressure thrust generated at full test pressure. To avoid unnecessary stress on the bellow or test equipment, the test pressure was gradually increased in 50Bar increments, the full test pressure was held for 30 minutes.
Data:
Dimension: DN 100 | Built-in length: 150 mm | Medium: demineralised water | Design temperature: 300°C | Design pressure: 145 BarG | Test pressure: 251 BarG | AX: +0/-20 mm | Bellow: Inconel 625 | Flange: AISI 304 L | Root rings: Inconel 625