First, what is the metal expansion joint used for? — Don't be fooled by the name, the core is two words: compensation
Two days ago, I met a customer who came up and asked, "Is the metal expansion joint the same as the expansion joint on the radiator?" Alas, it means about the same, but it is far from that simple. To put it bluntly, as soon as the temperature in the pipeline system changes, the pipe will expand and contract by heat. The result of hard pulling is that the interface collapses and the equipment is crooked. Metal expansion joints do just that — they absorb displacement and release stress. You can call it compensator. These two words are common in the industry (refer to Article 14 of the FAQ in our site). There are two words at the core: compensation. Compensate for axial expansion and contraction, lateral offset, and even angular torsion. Without it, steam pipes and heat pipe networks will show you a look in minutes.
What we produceUniversal corrugated expansion jointIn chemical pipelines, they are soaked in high-temperature steam every day, and expand and contract hundreds of times all year round, relying on the elastic deformation of the thin walls of the bellows. AndCorrugated expansion joint for power station industryThe temperature of the main steam pipe of the power plant can soar to five or six hundred degrees. Without it, the pipe would have collapsed early.
Second, there are so many structural classifications, which ones are commonly used by us? — Bellows, sleeves, non-metals, each with its own temper
When you stand in our warehouse, you can see that the densely packed expansion joints are actually divided into three categories according to their structure: bellows type, sleeve type and non-metallic type.
Bellows expansion jointIt is the main force, relying on the deflection of ripples to absorb displacement. There are many sub-classes: such asHigh temperature axial expansion jointSpecialized in carrying high temperature;Straight pipe pressure balanced expansion jointIt can balance the blind plate force and be used on large pipes under pressure;Compound hinge transverse expansion jointIt can absorb lateral displacement and fit where the space turns. AndExternal pressure single axial expansion jointExternal pressure structure can withstand higher pressure, which is common in petrochemical industry.
Sleeve type pipe expansion jointIt is another way, which relies on the sliding between sleeves to compensate for the displacement. The structure is simple but the sealing requirements are high. It is generally used in low pressure and large displacement occasions, such as heating pipe network.
Besides, non-metallic ones, we have them on our stationNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion joint。 This thing is made of fabric and rubber, which can absorb multi-dimensional displacement and is corrosion-resistant, especially in smoke ducts and desulfurization systems. Oh, yeah,rubber compensatorAndRubber PTFE compensatorAlso in this category, the vibration damping effect is first-class.
Each structure has its own temper. If you choose the wrong one, the oil and water leakage in two years will be light, and the whole pipeline system may collapse.
Third, if you don't look at these three points in type selection, you will most likely step on pits-medium, temperature and displacement, one cannot be missed
After so many years of explaining metal expansion joints, I have seen too many people who pat their heads and select models. Let me tell you, first figure out these three parameters:
- Medium: What fluid goes? Strong corrosive, must be usedPTFE-lined hoseOrPTFE compensator； For dusty flue gas, wear resistance and guide tube structure should be considered.
- Temperature: Temperature directly determines the material. Use 304 stainless steel at room temperature, and you have to use heat-resistant alloy for five or six hundred degrees. Our oneHigh temperature axial expansion jointThe upper limit of the design temperature can reach more than 1000℃.
- displacement amount: How does the pipeline go? How much is axial telescoping? How big is the lateral offset? Every direction should be calculated clearly. Such asDouble hinge expansion joint for air-cooled island vacuum pipelineSpecially designed for vacuum large diameter pipeline, can absorb large angular displacement.
Don't think that these three values are enough to know. In actual engineering, they will affect each other. For example, high temperature + corrosive media, optical material selection is a knowledge. You choose an ordinary stainless steel bellows, and it won't take long to corrode and perforate. So don't be lazy and give your working condition parameters to the manufacturer honestly.
4. In installation and daily maintenance, the most easily overlooked details-the orientation of the guide tube, the adjustment of the pull rod, and whether the screw can be removed or not
Installing expansion joints looks simple, but the details determine the longevity. The first easy mistake to make is to install the deflector in the reverse direction. We have a FAQ on our siteSpecific Function of Expansion Joint Guide TubeThe guide tube is used to guide the flow direction of the medium and protect the bellows from being washed and worn. The direction of the arrow must be consistent with the flow direction of the medium (refer to Article 10 of Q&A). Install it backwards, and the guide tube is a plug, which will aggravate the wear.
How to adjust the tie rod nut? Many customers receive the expansion joint and find that there are tie rods and nuts fixed at both ends, thinking that it is used for reinforcement, and it will not be disassembled. Wrong! These tie rods (also called transport tie rods) are used to prevent the bellows from deforming during transportation. After being installed in place, the nut should be loosened, adjusted to the working position, or removed directly (refer to Q&A 12 and 13). Otherwise, the expansion joint can't expand and contract freely at all. What is the difference between it and a steel pipe?
AndCorrect installation method of expansion joint of large tie rodThe large tie rod structure is to bear the internal pressure thrust, and the tie rod must be adjusted to the designed length during installation, and cannot be screwed randomly. Routine maintenance is to regularly check the bellows for cracks and corrosion spots, especially thoseDesulfurization flue gas baffle doorNext to the expansion joint, the acidic environment is most prone to problems.
5. Common faults and misunderstandings: Why did it leak after two years of use? — — Fatigue, corrosion, installation stress, take the right seat
"The quality of your expansion joint is not good. It leaked in two years." Every time I heard such words, I always asked about the working condition first. Nine times out of ten, it is a problem of type selection or installation. There are three common reasons for leakage:
- Fatigue failure: If the pipeline vibrates frequently, or the design displacement is smaller than the actual, the bellows bends repeatedly, and the metal fatigue causes cracks. This situation can be consideredMetal hoseOrSpecial hose for vacuumTo dampen the vibration.
- Corrosion perforation: There are chloride ions and sulfide in the medium, and stainless steel still can't bear it. Either reline PTFE or choose high nickel alloy. WeMetal Corrugated Expansion Joints in Cement IndustryOften encounter sulfur-containing flue gas, the surface has to be made with anti-corrosion coating.
- Installation stress: The pipeline is forced to be installed at the opposite side, or the tie rod is not loosened, and the force of the expansion joint exceeds the design. When installing, make sure that the expansion joint is in a free state, and don't pull hard.
Think that the expansion joint is "all-purpose" and can absorb all displacement. Virtually every model has a cap on the ability to compensate. Such asDirect buried (fully buried) type expansion jointSpecially used for directly buried pipelines, the axial compensation is large but the lateral compensation is limited. If the pipe turns too much, you have to cooperateRotary compensatorOrCurved tube pressure balance expansion joint。
This thing of expansion joint, three points depends on quality, seven points depends on selection and installation. Don't just buy a general-purpose model to save money and trouble. When you're not sure, flip through the "Explanation of metal expansion joint"Series articles, or directly find technology to talk about working conditions. Save those few minutes of communication, and the maintenance fee later will be enough for you to buy ten expansion joints.