The bellows expansion joint is a telescopic function composed of metal bellows and components. It can compensate the thermal deformation, mechanical deformation and absorption of various mechanical vibrations of the pipeline, and can reduce the deformation of the pipeline and improve the service life of the pipeline.
Classification of the first section of bellows expansion joint
1. According to whether it can absorb the pressure thrust (blind plate force) generated by the pressure of the medium in the pipeline, it can be divided into unconstrained bellows expansion joint and constrained expansion joint.
2. According to the wave structure parameters of the bellows, it can be divided into U shape, Ω shape, S shape, V shape (mostly domestic manufacturers use U shape).
3. According to the displacement type of bellows, it can be divided into axial type, transverse type, angular direction type and pressure balance type bellows expansion joint (most manufacturers are marked according to this classification in the manual).
(1) Single axial expansion joint
It consists of a bellows and structural members. It is mainly used for the expansion section of the second section of bellows expansion joints and pipeline design that absorb axial displacement and cannot withstand medium pressure thrust.
First, the bellows expansion joint selection must consider the following issues:
1. Nominal size, joint type and flange standard.
2. Design pressure, design temperature.
3. The pressure thrust (blind plate force) generated by the medium determines whether an unconstrained expansion joint or a constrained expansion joint is used.
4. Material and heat treatment of bellows: mainly depends on the working medium. It is recommended to use 316L and solution treatment for the damage caused by high temperature steam heat network to prevent stress corrosion. For high-nickel alloys for corrugated tubes for catalytic and cracking high-temperature devices, it is recommended. Annealing or solution treatment.
5. Fatigue life - consider the number of times the bellows expansion joint is working.
6. Absorb displacement form----axial, lateral, angular.
Second, the support in the pipeline system
Reasonable design of the support in the pipeline system is a necessary condition to ensure the normal operation of the bellows expansion joint. Different types of bellows expansion joints have different requirements for the support of the piping system.
1, the main fixed support (Main Anchor)
The primary fixed mount is mounted on a tubular system having one or more unconstrained bellows expansion joints that must withstand the forces and moments exerted thereon by each of the sections connected thereto. For example, the pressure thrust (blind plate force) generated by the medium pressure in the pipe, the force and moment required for the bellows expansion joint to generate the rated displacement, and the friction force generated by the adjustable guide support and the directional guide support, and Pipeline and media weight, fluid impact, etc.
When using an unconstrained wave tube expansion joint, the main fixed support must be provided in the following cases:
1) Blind end of the pipe
2) Change in media flow
3) Pipe branch
4) Pipe diameter reduction
5) On the pipe between the two bellows expansion joints, the shut-off valve or the pressure reducing valve.
2, secondary fixed support (I anchor)
The secondary fixed bearing is used to withstand all loads except the pressure thrust (blind plate force).
For a straight pipe section, the secondary fixed bearing is usually used to divide the longer pipe section between the two fixed supports into a plurality of pipe section units, so that only one bellows expansion joint is provided between each pipe section to ensure the bellows expansion. The section works fine.
3, the guide bearing
The guide support is arranged in the pipeline to ensure the displacement of the bellows expansion joint in a specified direction and to prevent the instability of the pipeline. The design strength of the general guide support is 10%-15% of the pressure of the medium pressure in the pipeline. consider. On a pipe section with only axial displacement, the guide abutment only allows axial displacement and limits displacement in other directions. This type of support is called a general guide abutment. For axial sections with lateral displacement and deflection, in addition to axial displacement In addition, a suitable additional margin should be left in the lateral direction to allow for a certain degree of lateral displacement and deflection. This guide support is called a planar guide abutment.