The bellows expansion joint is a device with a telescopic function composed of a metal bellows and a component. It can compensate for thermal deformation, mechanical deformation of the pipeline, and absorb various mechanical vibrations, and reduce the deformation of the pipeline and increase the service life of the pipeline.
Classification of bellows expansion joints
1. According to whether it can absorb the pressure thrust (blind plate force) generated by the medium pressure in the pipeline, it can be divided into unconstrained bellows expansion joints and constrained expansion joints.
2. According to the waveform structure parameters of the bellows, it can be divided into U-shape, Ω-shape, S-shape, and V-shape (at present, most domestic manufacturers use U-shape).
3. According to the displacement type of the bellows, it can be divided into axial type, lateral type, angular type and pressure balanced bellows expansion joint (most manufacturers are marked on the manual according to this classification).
(1) Single axial expansion joint
It consists of a bellows and structural parts. It is mainly used to absorb the axial displacement and cannot support the thrust of the medium pressure. The second section of bellows expansion joint selection and pipeline design.
1. The selection of bellows expansion joints must consider the following issues:
1. Nominal size, connection type and flange standard.
2. Design pressure and design temperature.
3. The pressure thrust (blind plate force) generated by the medium determines whether to use an unconstrained expansion joint or a constrained expansion joint.
4. The material and heat treatment of the bellows: It mainly depends on the working medium. For high temperature steam heating network to prevent damage caused by stress corrosion, 316L and solution treatment are recommended. For the bellows for catalytic and cracking high temperature equipment, high nickel alloy is recommended and carried out. Annealing or solution treatment.
5. Fatigue life --- Consider the number of times the bellows expansion joint is operated.
6. Absorption displacement form: axial, lateral, angular.
Supports in the pipeline system
The rational design of the support in the piping system is a necessary condition for the bellows expansion joint to function properly. Different types of bellows expansion joints have different requirements for the support of the piping system.
1. Main Anchor
The main fixed support is installed on a pipe system having one or several unconstrained bellows expansion joints, and it must withstand the forces and moments imposed on it by each pipe segment connected to it. For example, the pressure thrust (blind plate force) generated by the pressure of the medium in the pipeline, the force and moment required for the bellows expansion joint to generate the rated displacement, and the friction generated by the adjustable guide support, the directional guide support, and Weight of pipelines and media, fluid impact forces, etc.
When the unconstrained wave spinning tube expansion joint is selected, the main fixed support must be set in the following cases:
1) Blind end of pipe
2) Where the medium flow direction changes
3) Pipe branch
4) Pipe reduction
5) At the stop valve or pressure reducing valve on the pipeline between the two bellows expansion joints.
2. Secondary anchor (I anchor)
The secondary fixed support is used to bear all loads except pressure thrust (blind plate force).
For straight pipe sections, the secondary fixed support is usually used to divide the longer pipe section between the two fixed supports into several pipe section units, so that only one bellows expansion joint is set between each pipe section to ensure the expansion of the bellows Section works fine.
The guide support is provided in the pipeline to ensure that the bellows expansion joint is displaced in the prescribed direction and to prevent pipeline instability. The general design of the guide support is 10% -15% of the pressure of the medium in the pipeline. consider. On pipe sections with only axial displacement, the guide support only allows axial displacement and restricts displacement in other directions. This type of support is called a general guide support. For pipe sections with lateral displacement and deflection, except for axial displacement In addition, a suitable additional margin should be left in the transverse direction to allow a certain degree of lateral displacement and deflection. Such a guide bearing is called a plane guide bearing.