Form division of metal expansion joints: structure, working conditions and type selection, explain clearly at one time
Metal expansion joints, to put it bluntly, are flexible joints used in pipelines to absorb thermal displacement, vibration, and even installation errors. Although it has a simple structure, it meets dozens of models-general-purpose type, high-temperature axial type, double hinge type, straight pipe pressure balance type... Is it a big head? In fact, starting from the structural form, all metal expansion joints can be classified into several categories. If you understand this, you will not be blind in the selection.
Structural form: single, duplex, angular, sleeve, which category do you belong to?
The most basic is single bellows, with only one bellows section. Such asUniversal corrugated expansion jointThe invention has the advantages of simple structure, mainly attacks axial displacement, and is suitable for occasions where the pipeline is short and the compensation amount is not large. The duplex is different — two bellows with an intermediate pipe in between, likeCompound hinge transverse expansion joint, this design can absorb transverse displacement, but also rely on hinge structure to limit axial force, the pipe can swing in the horizontal plane casually. If you encounter a scenario where you need to compensate for angular displacement, angular expansion joints come into play. Common ones areCompound straight pipe bypass pressure balanced expansion joint、Curved tube pressure balance expansion jointThese guys come with their own balanced bellows, which can digest the pressure and thrust away and protect the fixed bracket. And don't forget that there'sSleeve type pipe expansion jointIt is compensated by the sliding of the inner and outer sleeves, which is completely different from the bellows-the sleeve structure is more resistant to high pressure, but the sealing requirements are high, so it is suitable for large-diameter steam pipelines.
Then how is it divided? Actually, there is a more practical angle —Divided by displacement direction。 Axial types are most common, such asExternal pressure single axial expansion jointThe bellows is subject to external pressure, and the risk of instability is less, so it is suitable for large-diameter and high-pressure steam lines. What about the horizontal type?Double hinge expansion joint、Double hinge expansion joint for air-cooled island vacuum pipeline, the two hinges cooperate to allow the pipe to swing back and forth in the horizontal plane. Angular type is a single hinge or universal hinge structure, which specifically absorbs angle changes. Here I want to talk about it in particularPressure balance type— — Straight pipe pressure balance type and curved pipe pressure balance type, their names sound mysterious, but in fact, the principle is to add a set of balanced bellows to offset the blind plate force generated by internal pressure, so that the thrust of the equipment port can be ignored. Two days ago, I met a customer. The steam pipeline was used with ordinary axial type. As a result, the fixed bracket was pulled away after half a meter thick concrete, so it was replaced withStraight pipe pressure balanced expansion jointIt never went wrong again. Is that the truth?
Different working conditions, different type selection
Under high temperature conditions, ordinary stainless steel bellows can't bear it, so it has to be usedHigh temperature axial expansion jointThe material is heat-resistant alloy, and the heat insulation layer or guide tube is added on the structure. What about low temperature or vacuum environment?Direct buried (fully buried) type expansion jointSpecially designed for underground pipe, with anti-corrosion layer and moisture drainage pipe;Double hinge expansion joint for air-cooled island vacuum pipelineFor the condenser vacuum system, the sealing grade requirements are extremely high. In terms of pressure, high-pressure pipelineLarge diameter thick wall expansion jointThe bellows has a large number of layers and a thick wall; Just use the general-purpose type for low-voltage systems. There is also a demand for corrosion resistance-the expansion joint followed by the desulfurization flue gas baffle door. The medium contains sulfur and acid, so stainless steel or PTFE-lined should be selected. When it comes to lining PTFE, this site hasPTFE-lined hoseAndPTFE compensator, also essentially a variation of metal expansion joints, with fluoroplastics as the liner to solve the corrosion problem. Cement industry and power station industry also have special products, such asMetal Corrugated Expansion Joints in Cement IndustryAndCorrugated expansion joint for power station industryThese are usually customized non-standard parts, designed individually according to working conditions.
And guess what? Some customers want to save trouble. A steam pipe only uses the general type from beginning to end. As a result, the bellows is washed and worn by the medium, and it leaks in two years. The role of the guide tube is reflected at this time-it can reduce the direct erosion of the bellows by high-speed fluid and prolong the life. Therefore, don't forget the guide tube and protective sleeve when selecting the model, which is the most easy to overlook but the most critical link in the matching accessories.
Connection methods and accessories, don't underestimate these details
The metal expansion joint may be a flange, a connector, or a quick coupling at both ends. In addition, people often putMetal hoseConfused with expansion joints-metal hoses are also considered flexible connectors, but strictly speaking it is not an expansion joint: expansion joints mostly absorb axial or angular displacements, while metal hoses are better at absorbing vibrations and lateral offsets. There are both products in this siteMetal hoseThere are alsoSpecial hose for vacuum, the use is different, don't choose the wrong one. In addition, expansion joints are often used with baffle doors, such asFlue gas baffle door、Round Flap Door (Double Seal)、Electric plug-in insulation door、Manual plug-in insulation doorThese valves are used to cut off or regulate the medium, and the expansion joint is responsible for absorbing the thermal expansion and contraction of the pipe. If you need to switch media channels,Single-axis double-flapper doorOrDouble-sealed single-axis round baffle doorIs the best partner.
Let's pull the topic backForm division of metal expansion jointsThis core. In fact, no matter how you classify it, there is only one ultimate goal: to find the one that best matches your working conditions. There is no universal expansion joint, only the most suitable one. Next time you communicate with the supplier, don't just report a model of "expansion joint". Make the medium, temperature, pressure, displacement direction and installation space clear, so that the other party can recommend the correct product to you. Have you learned it?