EXPANSION JOINTS WITH PANTOGRAPHIC GIMBAL Belman has delivered 35 expansion joints with up to four bellows and pantographic gimbal for a district heating pipeline in France.
Placed in the outer pipeline The district heating pipeline, in which the expansion joints are placed, is constructed so that it consists of a double pipe. In the inner pipe the app. 300 ºC hot district heating water flows. This pipe is surrounded by another pipe, which makes up the outer pipeline. Belman's expansion joints are all placed in this outer pipe. Vacuum exists between the two pipes, which causes the air between the pipes to stand still and thus have an insulating effect. This constellation not only means that the insulation is better than by use of ordinary insulating material; the construction is also safer as the tightness has been optimised. If any leak should mean that district heating water escapes from the inner pipe it will be collected in the outer pipe. This minimises the risk of leaking district heating water seeping into the underground, which would be very impractical here as the district heating pipeline is placed under a big city.
High requirements of the expansion joints The construction means that the expansion joints from Belman are not in contact with the medium, which explains why the medium is air. However, the construction makes heavy demands on the tightness of Belman's expansion joints, which meant that comprehensive testing had to be carried out prior to delivery.
The distance determines the number of bellows As the district heating pipeline is buried and in many places this restricts the possibility of placing fixed points, relatively few expansion joints are installed over great distances. This means that some expansion joints must absorb much larger movements depending on the distance between the expansion joints. Therefore Belman have delivered expansion joints with one, two, three or four bellows depending on where they are to be placed and the size of movements they are to absorb.
Why pantographic gimbal? More bellows allow the absorption of very large movements but in order to ensure uniform running of the bellows and thus equal absorption of movements pantographic gimbal have been mounted. In this way it can be avoided that some bellows absorb larger movements than others and wear out prematurely. The large number of bellows leads to instability, which the pantographic gimbal cannot compensate for, but the construction of the pipeline brings about a stabilisation of the expansion joint. This is due to the fact that it has been possible to place Teflon sliding blocks between the two pipes, which add stability to the expansion joints.
Technical data The expansion joints have the following technical data: Dimension: NB 600, NB 900 and NB 1000. Installation length: 260 mm to 3600 mm. Medium: Air. Design temperature: 120 ºC. Design pressure: -1/ 1 bar. Movements: Axial movement: From +30/-0 mm to +1500/-0 mm. Material: Bellows: W.1.4541 Welded ends: P265GH Intermediate pipes: P265GH
