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EXPANSION JOINT SELECTION 73 Expansion joint selection GIMBAL Two gimbals and one hinged expansion joint in a 3D system FP Gn Sp FP Gn Source: Freely adapted from EN 14917 Two gimbals and one hinged expansion joint in a three-dimensional system This often used system absorbs gimbals, while the hinged angular of the vertical distance between the movements in any direction of the expansion joint takes the vertical gimbals. horizontal pipes through use of the movement resulting from the reduction Two gimbals in a 3D system FP Gn Sp FP Gn Source: Freely adapted from EN 14917/EJMA Two gimbals in a three-dimensional system Just as hinged expansion joints offer the illustration. Since the pressure great advantages in single plane loading is absorbed by the gimbal applications, gimbal expansion joints structure, fix points only are provided. are designed to deliver similar benefits Guides are provided to restrict the in multi-plane systems. The gimbal movement of each piping leg. As in expansion joints ability to absorb the case of hinged expansion joints, angular rotation in any plane is most the location of pipe supports is frequently achieved by utilising two simplified by the load carrying ability such units to absorb lateral deflection. of the gimbal structure. Since, in a An application of this type is shown in two gimbal system, the growth of the vertical pipe leg will be absorbed by bending of the longer legs, spring supports (SP) may be required on either or both of these. Guides must be designed to allow for the thermal expansion of the leg containing the expansion joints and for the shortening of this leg due to deflection. B022016-1 – Subject to alterations and eventual misprints www.belman.com
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EXPANSION JOINT SELECTION 75 Expansion joint selection U-PIPE In some pipe systems, the operating conditions can be quite challenging, resulting in special considerations for the design of both the pipe system and for the expansion joints. Large movements can be absorbed in numerous ways, and with different expansion joint types. In many cases installing two or more expansion joints together at natural or contrived offsets in the pipe system can be a good solution to absorb large movement. The same pipe system design can also be used for the absorption of angular movements, which would not be possible in a straight pipe system. Why U-bend/pipe loop? The U-bend is a good solution for absorbing larger movements. The configuration of a pipe loop containing 3-angular (hinged) expansion joints can absorb, at a minimum, three times larger move- ments compared to a traditional pipe loop without angular expansion joints. The hinges on the expansion joints contain the pressure forces from the bellows and simultaneously ensure that movements are controlled, which helps to support the pipe system. The pipe system geometry is determined by the amount of movement to be absorbed and the rotational capability of the expansion joints; the higher the movements the greater the distance required between the centre and end expansion joints. The advantages of this U-pipe system design l Large movements are absorbed l The stress forces on the system fix points are much reduced compared to those from equivalent unrestrained expansion joints l Costs for fix points are reduced l Solutions using restrained expansion joints can prove to be very cost effective, especially when the pipe system is installed at heights. The need for the substantial fix points and guides in the pipe system that are routinely required with un- restrained expansion joints, becomes unnecessary due to the pressure thrust force from the bellows being contained by the hinge structure on the expansion joints l As shown in the on the left, use of expansion joints in loops can reduce the number of loops required from 3 to 1 Tips! l Venting or draining may be required if the loop is fitted vertically l Expansion joints should be fitted as close to the elbows as possible l Guides should be close to the outer expansion joints to direct the pipe growth onto the bend. The guides must allow free travel of the pipe system and expansion joints under all movement conditions l The centre expansion joint in the U-bend should absorb the rotation equally to the rotation of the outer expansion joints l It is advisable to cold pull the U-bend so that the expansion joints work equally from their neutral condition. This maximises the available travel from the bend, minimises the height of the bend and halves the total deflection force applied to the fix points B022016-1 – Subject to alterations and eventual misprints www.belman.com
