Installation Requirements for Corrugated Metal Expansion Joints
Release time:
2021-05-20
Bellows metal expansion joints, regardless of their structural design and installation configuration, are used to accommodate relative displacement between two fixed supports along a pipeline. In other words, only one bellows expansion joint is permitted between any two fixed supports; otherwise, the compensation capacity of the expansion joint would become uncertain. Among these requirements, the primary fixed support must be capable of withstanding the combined forces exerted on it under operating conditions—namely, the thrust from the pipeline and its internal medium, elastic forces, frictional forces, the weight of the pipeline itself, as well as any additional forces resulting from wind loads.
When the straight-buried pipeline bend has a length less than 30D or a pipe diameter greater than 325, fixed supports and fully balanced bellows expansion joints shall be provided. The main fixed supports on both sides need only bear the elastic force and frictional force acting on the fixed supports themselves; however, they must not be used in combination with partially balanced bellows expansion joints. If such mixed use is unavoidable, the two main fixed supports must be designed based on the internal pressure thrust—that is, the forces exerted by blind flanges must be taken into account. For axial displacement bellows expansion joints (except for pressure-balanced types), an intermediate fixed support and a main fixed support should be installed at the blind end of the pipeline. When the forces at the second end of the pipeline are perfectly symmetrical or when the pressure and thrust are entirely borne by the expansion joint itself, the branch pipe equipped with a compensator shall connect to the main pipe. In large rod-type expansion joints and angular expansion joints, the pressure and thrust are borne by the rods and hinges, respectively.
If a hydrostatic pressure test is conducted on the entire pipeline, the secondary fixed pipe supports at the ends of pipelines equipped with bellows expansion joints should be reinforced. To prevent pipeline movement or rotation, it is necessary to verify that the fixed supports at both ends of the bellows expansion joint’s compensating section are securely welded to the pipeline and pressure-bearing components according to design specifications, and that the main fixed supports are designed to withstand a load equal to 1.5 times the internal pressure thrust.
If the supports and pipe sections are not properly secured or if the supports do not have sufficient load-bearing capacity, the hydrostatic pressure test must not be carried out. Otherwise, the corrugated expansion joint could be damaged by the internal pressure thrust. The auxiliary components on the corrugated expansion joint cannot be considered as substitutes for fixed supports in bearing the internal pressure thrust. Since there is a small amount of unbalanced force in pressure-balanced bellows expansion joints, the requirements for fixed supports can be designed based on factors such as the bellows’ pressure thrust, frictional forces, and rebound forces.
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