Wavy metal expansion joints are used to compensate for the relative displacement of pipelines between two fixed supports, regardless of their structure and installation form. Only one wavy expansion joint is permitted between the two fixed supports; otherwise, the compensation value of the expansion joint becomes uncertain. The main fixed support of the compensator must meet the working conditions, including the thrust, elasticity, friction force, weight, and other resultant forces from wind load on the fixed supports exerted by the pipeline and the medium inside the pipeline.
When the bend direction length of the buried pipeline is less than 30D or the pipe diameter is greater than 325, fixed supports and full-balance bellows expansion joints should be installed. The main fixed supports on both sides of the compensator only need to bear the elastic force and friction on the fixed supports, but should not be mixed with partially unbalanced bellows expansion joints. If they must be mixed, the two main fixed supports should be designed based on the internal pressure thrust, which means considering the blanking plate force. For bellows expansion joints with axial displacement compensation (except pressure-balanced type), intermediate fixed supports and main fixed supports should be set at the pipeline blind ends. When the forces at the second end of the pipeline are completely symmetrical or when the pressure and thrust are completely borne by the expansion joint, the branch pipe with the compensator enters the main pipe. The pressure and thrust of large-diameter rod expansion joints and angular expansion joints are borne by the rods and hinges.
If an overall hydrostatic test is to be conducted on the compensator pipeline, the secondary support brackets at the ends of the pipe with bellows expansion joints should be reinforced. To prevent pipe movement or rotation, it is necessary to check whether the fixed brackets at both ends of the bellows expansion joint compensating section are securely welded to the pipeline and pressure-bearing components as per design requirements, and whether the main fixed bracket is designed with a load-bearing capacity of 1.5 times the internal pressure thrust.
If the supports and pipe sections are not securely fastened or the support's load-bearing capacity is insufficient, hydrostatic testing is prohibited. Otherwise, the bellows compensator may be damaged by internal pressure thrust. Auxiliary components on the bellows expansion joint cannot be considered as substitutes for fixed devices to bear internal pressure thrust. Due to the slight unbalanced forces in the bellows expansion joint for pressure balance of the compensator, the requirements for the fixed supports can be designed based on factors such as the pressure thrust, friction, and rebound force of the bellows.
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