Specialized in manufacturing compensators, expansion joints, baffle doors

1. "Flexible shield" in high-temperature environment: What does the nonmetallic compensator rely on to withstand hundreds of degrees?

When it comes to high-temperature pipeline compensation, many people's first reaction is metal expansion joints. But there's something calledNon-metallic expansion joint(Also called fabric fiber expansion joint), it relies not on metal bellows, but on a multi-layer composite structure-silicone cloth, fluororubber, ceramic fiber felt and glass fiber cloth are stacked together to form a "flexible shield". askWhat does a high temperature non-metallic compensator do?To put it bluntly, in hundreds of degrees of smoke, hot air and dust pipes, it can both seal and absorb displacement, and is not afraid of corrosion.

Temperature resistance limits depend on the innermost insulation layer. The conventional silicone cloth is used as the inner lining, which can withstand 250 DEG C to 350 DEG C; Replace it with the structure of fluororubber or polytetrafluoroethylene compensator, which can reach 400℃; If ceramic fiber + heat-resistant alloy wire mesh is used, the long-term operating temperature can reach 600℃ or even 1000℃ for a short time. And guess what? In the desulfurization flue of the power plant, the flue gas temperature is only 150℃ ~200℃, but occasionally, high-temperature flue gas will rush into it. Because the non-metallic compensator is multilayered and flexible, it can withstand this temperature shock better than metal-the metal bellows may directly deform plastically when it encounters local overheating, while the non-metallic fabric layer can save its life by ablating the outer layer.

Not that warmer temperatures are better, of course. The maximum continuous service temperature of each material has clear data, and the selection depends on whether the working condition is "continuous high temperature" or "instantaneous peak". Two days ago, I met a customer who used an ordinary silicone cloth compensator on the normally open flue at 350℃. As a result, it was brittle and cracked in three months-that was because the material selection was not clear.

Second, absorbing multi-directional displacement and reducing noise and vibration: How to solve the most difficult problem of "thermal expansion and contraction" in high-temperature pipelines?

The trouble of high-temperature pipelines is not only the temperature itself, but also the displacement caused by thermal expansion and contraction. It is normal for a flue gas pipe tens of meters long, from cold to hot, to extend several centimeters axially and deflect one or two millimeters laterally. Metal expansion joints are usually only good at absorbing axial displacement, and complicated hinge or tie rod structures have to be added when they encounter lateral or angular displacement. WhileNon-metallic expansion jointBorn as a "cartilage head"-its fabric loop band can easily absorb displacement in three directions: axial, transverse and angular, especially suitable for rectangular pipes.

The outlet flue of the induced draft fan of a thermal power unit has a cross section of 3m ×2m and a temperature of 200℃. If installedMetal rectangular expansion jointFor manufacturing, thick steel plates are pressed, weighing several tons, and can only absorb a small angular displacement. modifyRectangular non-metallic expansion joint, which weighs only 1/5 of metal, can even be adjusted by hand during installation. During operation, the low-frequency vibration is almost completely absorbed by the fabric layer-this is its hard work of noise reduction and vibration reduction.

So how to prevent leaks? The structure is generally equipped with two seals: the outer layer is a temperature-resistant flexible skin (such as silicone cloth), the inner layer is a corrosion-resistant fluororubber or polytetrafluoroethylene compensator layer, and the middle is filled with ceramic fiber insulation cotton. Under the triple protection, even if the outer layer burns through, the inner layer can still stand for a while. So in principle,What does a high temperature non-metallic compensator do?It is to use a multi-layer flexible "pocket" to hold the displacement and stress of the high-temperature medium, and by the way, the vibration noise is also eaten.

3. Comparison of metal expansion joints: Which scenes must use non-metals? Pits not to step on when selecting a model

The metal expansion joint relies on the elastic deformation of the bellows, which can withstand high pressure (tens of MPa) and has a long life (tens of thousands of theoretical fatigue times), but its shortcomings are terrible-it is afraid of corrosion and crystallization, and it requires extremely high installation alignment. The bearing pressure of the non-metal expansion joint is generally 0.1~0.3MPa (suitable for low-pressure smoke duct), but the corrosion resistance is extremely strong. For example, the flue gas after wet desulfurization contains a large amount of SO₂, SO₃ and condensed water, and the metal bellows will be perforated in a few months.rubber compensatorOrRubber PTFE compensatorBut it will last two or three years.

Which scenes must use non-metals?

• Low pressure large section rectangular pipeline: The desulfurization flue of power plant and the exhaust gas pipeline at the tail of cement kiln are all non-standard cross-sections with a width of several meters. The metal expansion joint can't make such a large elastic element at all, so only rectangular non-metallic expansion joint can be used.
• Pipes containing corrosive media: Acid flue gas of waste incineration plant and blast furnace gas of iron and steel plant must be made of composite structure of fabric fiber and fluororubber.
• Multidirectional displacement and space constraint: For example, at the corner of the pipeline, the metal expansion joint needs to be set with multiple hinge combinations, and the non-metal one can handle three directions.

The pits not to step on when selecting are mainly the following points. First, don't putNon-metallic expansion joint (fabric fiber expansion joint)When used with metal-it cannot withstand high pressure, if the internal pressure of the pipe exceeds 0.5MPa, it must be used with metal or with a limit tie rod. Second, pay attention to the abrasion of medium particles. If there are hard particles (such as cement raw dust) in the flue gas, wear-resistant lining plate or guide tube should be added to the non-metallic inner layer (you can refer to the function of expansion joint guide tube). Third, the installation must be in the direction of the arrow, and don't install it backwards, otherwise the skin will tear in advance under tension.

IV. Real cases used in power plants, cement and flue gas systems-what media can high-temperature nonmetallic compensators hold?

Talk about a few actual working conditions and you will have an idea.

Case 1: Power Plant Desulfurization FlueIn a 2×300MW unit, the net flue gas temperature after wet desulfurization is 50℃ ~90℃, but it contains a large amount of sulfuric acid condensate. Previously usedUniversal corrugated expansion joint, leakage in half a year. Replace withNon-metallic expansion joint (lined with PTFE compensator), has been running for 4 years without replacement. Medium: SO₂, SO₃, water vapor, acidic condensate. Can carry it.

Case 2: Kiln tail waste gas of cement production lineThe temperature is 350℃ ~400℃, and the dust concentration is as high as 30g/Nm³. useMetal corrugated expansion joint Dust can get stuck in the corrugations and cause fatigue failure. modifyRectangular non-metallic expansion joint, with wear-resistant guide tube inside, dust flows away along the inclined plate, and there is no problem for three years. Medium: High temperature flue gas, cement raw material dust.

Case 3: Primary air duct of waste incineration power plantThe air is preheated to 250 °C, and the pipe has a large cross-section that needs to absorb thermal expansion and vibration. Directly onrubber compensator？ Rubber can't stand 250℃. Must useNon-metallic expansion joint (fabric fiber expansion joint), inner layer of fluororubber + outer layer of silicone cloth + intermediate ceramic fiber, life design of 15 years. Medium: Hot air, a small amount of corrosive gas.

See?What does a high temperature non-metallic compensator do?It is far more than the word "temperature". It has to face four enemies: high temperature, corrosion, dust and vibration at the same time. Choose right, it is the "flexible shield" of the pipeline; If you choose the wrong choice, it will be an accident danger.

5. Life and installation points: If you want it to last for a few more years, these details engineers must keep an eye on

Theoretically, the life of non-metallic compensators can reach 5~8 years, but in fact, many of them are scrapped after two or three years, which is rooted in installation and maintenance.

1. Pipe alignment must be checked before installationThe non-metallic skin has no self-centering ability, and the pipe flange is misaligned by more than 3mm. Forced fixation will lead to skin distortion and local stress concentration. It is best to temporarily fix it with a tie rod, and then tighten the bolts after adjusting it in place.

2. Bolt torque cannot be messed aroundGenerally, flange pressure plate is adopted for screw joint surface, and the bolt tightening torque should be carried out according to the product instructions. Screwing too tight will crush the edges of the skin, and it will be too loose and air leaking. It is recommended to pre-tighten diagonally in three times, and the final torque is controlled at 80~120N·m (depending on the model).

3. Check the guide tube regularlyIf there is a deflector inside, it depends on whether it is worn out. Especially in the cement industry, after the guide tube is worn out, the high-temperature particles directly scour the inner layer of the skin, and the hole can be broken in a few days. You can take a look at it with an endoscope every year when the machine is down.

4. Be careful not to press the insulation layer against the compensatorIn some sites, the thermal insulation cotton is outpaced in the pipeline, and as a result, the thermal insulation cotton is directly pressed on the non-metallic surface, resulting in the heat being unable to dissipate and the local temperature exceeding the standard. The outer surface of the compensator must leave a heat dissipation void of at least 50mm.

The national standard JB/T 12235-2015 clearly states the technical requirements of non-metallic expansion joints, and the selection, installation and inspection should be followed. Don't try to save trouble, and don't be superstitious about imported brands-domestic onesRubber PTFE compensatorIt tends to be more flexible in adapting to complex working conditions.

At the end of the day, find outWhat does a high temperature non-metallic compensator do?It is not to back the definition, but to understand the underlying logic of its "flexibility", "multilayer" and "corrosion resistance". The next time you encounter high temperature and low pressure, corrosion, and large-section pipes, you will know what to do.

What exactly is a non-metallic rectangular compensator? What's the difference with metal ones?

Don't be confused by the name yet. We call this thing in our stationRectangular non-metallic expansion joint, also called fabric fiber compensator. It is completely different from rubber compensators and metal rectangular expansion joints. The rubber compensator is deformed by elastomer, and the metal rectangular expansion joint is expanded and contracted by corrugation. The non-metallic rectangular compensator we are talking about today uses flexible fabric skin to absorb displacement. In short, it is a joint piece specially designed to "loosen" rectangular pipes.

Compared with metal bellows, what is the difference? Metal bellows can't be made of large-size rectangles-in the process, they are either coiled or stamped. The cost of rectangular bellows is sky-high, and the stress concentration after bearing pressure is severe. Non-metal, on the contrary, the larger the size, the more advantageous it is. It can also absorb three-dimensional displacement (up and down, left and right, front and back), and by the way, eliminate vibration and noise. Tsk, isn't that a little counter-intuitive?

The core structure consists of three components: guide tube, insulation layer and skin

Take apart a non-metallic rectangular compensator, and you will find that it is actually quite straight and white. At the very innermost isguide tubeGenerally, stainless steel or carbon steel is welded and formed, and its function is to guide the airflow smoothly to avoid direct washing of the skin. The deflector must be welded firmly, otherwise the high-speed airflow will break the skin in a few weeks. A layer in betweeninsulation layerTypically aluminum silicate fiber cotton or ceramic fiber, the thickness is determined according to the temperature of the medium. The outermost layer isskinThis is the lifegate of the whole product. The skin is made of multi-layer composite materials. The common ones are silica gel cloth, fluorine tape, polytetrafluoroethylene (PTFE) film, and some are reinforced by stainless steel wire mesh. The temperature resistance level depends on the skin-silica gel cloth at 300℃, fluorine tape plus PTFE layer at 500℃. You ask why not use all fluoroadhesive tape? It's expensive, and silicone cloth has a longer fatigue life. Selection is a trade-off problem.

Why do you have to use this for rectangular pipes?

Two days ago, I met a customer. The desulfurization flue of the power plant has a rectangular section of 3 meters ×2 meters, a working temperature of 180℃ and a pressure of only a few kilopascals. His first reaction was to use a metal rectangular expansion joint. An inquiry, the manufacturer's quotation is twice as expensive, and the delivery time is still long. Why? Metal rectangular expansion joints must be stacked with multiple layers of corrugated plates, and each layer must be stamped and welded. Moreover, large-size corrugated plates are easy to become unstable, so reinforcing ribs must be added. Eventually he changedRectangular non-metallic expansion jointThe cost has dropped by 40%, and the installation is fast. And guess what? I used it for two years and didn't come out for a single leak. Instead, the metal cracked once because of weld fatigue. Therefore, in the case of low pressure and large cross section, non-metal is a solid preference.

The displacement caused by thermal expansion and contraction of rectangular pipes can reach tens of millimeters, and the metal bellows can't absorb the displacement in axial, transverse and angular directions at the same time. The non-metallic skin is a flexible fabric that can theoretically withstand displacement in any direction, as long as sufficient margin is left in the design. In addition, the fabric itself has a damping effect, which can attenuate the vibration of the pipe by 70% to 80%. Noise test data: After installing the non-metallic compensator, the noise near the flue is reduced by more than 15dB (A).

Select the three pits that are most prone to rollover

Pressure rating.Non-metallic rectangular compensatorGenerally, it is only suitable for low-pressure systems, within 0.1MPa. Beyond this number, the skin will bulge or the flange bolts will be pulled off. You have to use it on 0.3MPa pipes? Stop thinking about it, change it for metal.

Temperature. The skin material directly determines the upper temperature resistance limit. Silicone cloth ≤300℃, fluorine cloth ≤350℃, plus PTFE layer can reach 500℃. However, it is noted that the overall temperature resistance of the composite skin is subject to the lowest temperature resistance layer. Some manufacturers claim to be resistant to 500℃ with silicone cloth skin, which is nonsense. You have to ask about each layer of material.

Direction of the guide tube. The deflector is usually inserted into the pipe and must be welded in the direction of the airflow. If it is installed backwards or the weld is not firm, the airflow directly impacts the inside of the skin, and it will be scrapped in a few months. We have seen a case: the guide tube was not welded through during installation. Three months later, the skin was torn open by a hole, and the whole flange surface leaked. The labor cost of replacing a set of non-metallic expansion joints is more expensive than the product itself, so why bother?

Maintenance and longevity: 3-5 years for skin replacement, low cost but don't be lazy

Quite frankly, nonmetals have a shorter lifespan than metals. The design life of metal bellows is generally 10 years, and the non-metal skin has to be replaced in 3-5 years because of aging and wear. But the advantage is that the performance can be restored by changing the skin, without dismantling the whole pipe. Once the metal bellows is cracked, it can only be replaced as a whole. So from a life-cycle perspective, non-metals save money — provided you maintain them according to the rules.

The most overlooked thing when changing the skin is the flange bolt torque. Screwing too tight crushed the skin and loosened the air leak. The national standard "Non-metallic Expansion Joint" JB/T 12235-2015 clearly stipulates the range of bolt preloading force, for example, the recommended torque of M16 bolt is 100-120N·m. In practice, it is recommended to tighten it diagonally in three times with a torque wrench. In addition, after the old skin is removed, the flange surface must be cleaned, and the residual glue slag and rust will affect the sealing effect of the new skin.

In addition, the insulation layer should also be checked. If the insulation cotton is damp or coked, it will affect the temperature resistance. In some projects, in order to save money, ordinary carbon steel is used for the guide tube. As a result, the oxide scale falls off and blocks the insulation layer at high temperature, and finally the skin is partially overheated and burned through. You say it was wrong or not?

So,What is a non-metallic rectangular compensator？ It is a flexible joint in a rectangular pipe system that specializes in coping with thermal expansion and contraction and three-dimensional displacement. The structure is simple, the cost is controllable and the installation is fast, but the premise is that the type selection is not stepped on the pit, and the maintenance is not lazy. Are you in the middle of a model selection or are you already having problems? You might as well check yourself against the above points.

Why would anyone ask this kind of question?

To put it bluntly, in everyone's impression, non-metallic compensators (that is, non-metallic expansion joints) are used for hot air and flue gas pipes-such as flues of power stations and cement plants. The temperature is high, the medium is dirty, and the metal bellows can't bear corrosion, so they use compensators made of fabric fiber or rubber. But as soon as I arrived at the water system, hey, the master on the construction site muttered: Can this cloth skin bag be soaked in water? So, "Can non-metallic compensators run water?" This question is asked every three days. The answer? It's not as simple as you think.

First see what kind of "non-metal" you have in your hand

Don't rush to answer "can" or "can't", first distinguish what kind of non-metallic compensator you have in your hand. We have a product on our site calledNon-metallic expansion joint (fabric fiber expansion joint)The main body is multi-layer fabric + silicone/fluoroadhesive coating. The original intention of the design is to resist high temperatures and corrosive gases, but it is not resistant to long-term water immersion-water molecules will penetrate into the fiber layer, resulting in delamination, bulging and even tearing. But if you switch torubber compensatorOrRubber PTFE compensatorThe rubber compound itself is waterproof. EspeciallyPTFE compensator, acid and alkali resistant, water resistant, circulating water is completely fine. So the question is not whether "non-metal" will work, but whether the specific material and structure will work.

You put the fabric fiber expansion joint on the cooling water pipe. Within three months, water begins to drip on the edge of the flange. When you remove it, the inner fabric is completely soaked. However, in the same working condition, it is normal to use a rubber compensator for two or three years. Is that the truth?

Focus on three hard indicators when running water: pressure, temperature and media corrosiveness

Let's talk about the pressure first-the design pressure of non-metallic compensators is generally low, most of which are between 0.1~0.6MPa. If you use it to connect the water pump outlet to make a pressure of 2kg (about 0.2MPa), it depends on the parameters given by the manufacturer. The rubber compensator can usually reach 0.6~1.0MPa, but the fabric fiber is suspended. Talk about the temperature. Generally, the temperature resistance of rubber does not exceed 120℃, and fluororubber can reach 200℃. However, it is common in water systems that the room temperature reaches 80℃, which basically can withstand it. Finally, it is corrosive. Pure water is fine. Wastewater containing chloride ions or acid and alkali has to be lined with PTFE or special rubber. For example, desulfurization wastewater pipelines are sometimes usedRubber PTFE compensatorBecause it is resistant to both dilute sulfuric acid and abrasion.

Speaking of which, two days ago, I met a friend who did HVAC and wanted to install a non-metallic compensator for the air conditioning cooling water pipe, on the grounds that the metal bellows was too expensive. I poured cold water directly: the temperature difference of the cooling water pipe is not big, the displacement is small, and a single ball rubber compensator is completely enough, but if you buy an ordinary fabric fiber non-metallic expansion joint, it will leak in less than three months. He asked back, "That websiteRectangular non-metallic expansion joint"Can I walk away?" — — Rectangles are usually used with flues. If you have to use them at the inlet and outlet of the water tank, it is not impossible, but you have to customize the rubber layer, otherwise the weight of the fabric will double after absorbing water, and the flange bolts will be too much to bear.

Can you run water or not?

In the final analysis, whether a non-metallic compensator can "run water" depends on what kind of "non-metallic" it is. For rubber and tetrafluorine, running water is one of my jobs (provided that the pressure and temperature match); For fabric fibers, try not to touch water. If you really want to use it, you must communicate with the manufacturer to make waterproof lining. Don't pat yourself on the head. If you choose the wrong choice, you can leak and shut down, or the whole pipeline system will suffer.

If you're not sure, just go to the one on our stationrubber compensatorAndPTFE compensatorPage, or make a phone call and ask about technology, is much more reliable than guessing. After all, spending a few minutes figuring it out is more cost-effective than spending thousands on equipment, isn't it?

What exactly is a non-metallic compensator? What is the essential difference with metal corrugated expansion joint?

Non-metallic compensators (also called fabric fiber expansion joints and non-metallic expansion joints in the industry) are not the same thing as our common metal corrugated expansion joints. The core materials of non-metallic compensator are flexible non-metallic materials such as high-temperature-resistant coated fabric, rubber and polytetrafluoroethylene, which are made into a soft joint. The metal corrugated expansion joint absorbs displacement by elastic deformation of stainless steel corrugated pipe. Different ways, application scenarios are naturally different.

For example, the metal corrugated expansion joint is like a tough guy, which can carry high pressure, but it is afraid of corrosion and fatigue. The non-metallic compensator is like a master of jiu-jitsu, which can't bear high pressure, but it is resistant to high temperatures, corrosion, and can absorb large displacements in three dimensions. You're asking tough guys to do jiu-jitsu work, isn't it realistic? The other way around is the same.

Why can it gain a firm foothold in the harsh working conditions of high-temperature flue duct, power plant desulfurization and cement kiln tail?

Resistant, big and good.ResistanceHigh temperature-the ceramic fiber layer can withstand more than 1000℃;ResistanceCorrosion-Polytetrafluoroethylene or acid-resistant rubber layer directly attacks acidic gas;LargeDisplacement-Rectangular non-metallic expansion energy saving absorbs displacement in X, Y and Z directions at the same time, and metal parts can often only absorb axial or transverse directions. In addition, the vibration reduction effect is first-class. If the fan inlet and outlet pipes are installed with it, the vibration can eat more than half.

In the desulfurization flue of power plant, although the flue gas temperature is not high, it is heavy in moisture and contains acidic condensate. It won't take long for the metal corrugated expansion joint to be pitted and perforated. Replace it with a non-metallic expansion joint (such as this station'sRubber PTFE compensatorOrNon-metallic expansion joint (fabric fiber expansion joint)), the inner layer is tetrafluorine acid-resistant, and the outer layer is fiber insulation, which is still intact after three or four years of use. Is that the truth?

The shortcomings are also obvious. Don't treat it as a panacea

Non-metallic compensators are not without drawbacks. The pressure capacity is pitifully low-generally no more than 0.1MPa, that is, just over one atmosphere. If you use it on a steam pipe or high pressure oil pipe, it will explode in minutes. In addition, it is afraid of sharp objects scratching, and it is easy to leak air if the flange surface is uneven during installation. In terms of life, the fiber and rubber layers will age, but according to JB/T 12235-2015 standard, the design life of regular manufacturers can cover the overhaul cycle of the unit (usually 3~5 years).

Two days ago, a cement factory purchaser spat with me, saying that the metal expansion joint in their kiln tail pipeline cracked in less than a year, and it was annoyed to death after several changes. I suggested that he replace it with a rectangular non-metallic expansion joint with a temperature of about 800 ℃ and a composite layer of ceramic fiber + silicone cloth. And guess what? Used it for more than two years without any problems. Therefore, everything is easy to say if the selection is right.

Focus on these four parameters when selecting

• Design temperature: Look at the resistance temperature of the fabric layer. For example, ceramic fiber can reach 1260℃, but the actual use should leave a margin.
• Working pressure: Non-metallic compensators are mostly used in low-pressure smoke ducts, and don't think about them if they exceed 0.1MPa.
• displacement amount: The three directions of X, Y and Z should be calculated clearly. Metal parts can be calculated as transverse axial, and non-metals can be calculated as three-dimensional.
• Media composition: The desulfurization flue gas has a large moisture content and acidity, so acid-resistant PTFE or rubber materials must be selected, such as this station'sRubber PTFE compensator。 If the cement kiln tail contains alkaline dust, then alkali-resistant coating must be used.

The national standard JB/T 12235-2015 has clear test methods for fatigue life and air tightness.

When should you choose a non-metallic compensator?

Low pressure, large displacement, high temperature, corrosive mediaOccasions, preference is given to non-metals. Specific scenarios include: the pipelines in front and behind the desulfurization flue gas baffle door, the inlet and outlet of the fan in the cement industry, the flue of the power station boiler, the air-cooled island vacuum pipeline-and so on. The air-cooled island vacuum pipeline is commonly used thereDouble hinge expansion joint for air-cooled island vacuum pipelineBut that's because the vacuum condition requires a metal seal. As for the Smoke Wind Dao, it is basically a world of non-metals.Flue gas baffle doorOrDesulfurization flue gas baffle doorUsed together, seal and compensate in one step.

Conversely, if high-pressure pipelines (such as main steam), oil media, or occasions where frequent pressure is required, honestly use metal corrugated expansion joints, such as this station'sUniversal corrugated expansion jointOrHigh temperature axial expansion joint。 Don't think about non-metal saving money and hard on it-if you choose the wrong one, it will be more expensive to repair it later than to buy a new one, and the gain will outweigh the loss.

So how about non-metallic compensators? Bottom line: Use it in the right place is an artifact, and use it in the wrong place is scrap metal. Understand your own working condition parameters, and then compare the above points, and basically don't step on pits in the selection.

Splash cold water first: No standard answer

The pressure resistance of metal expansion joint is never a fixed value. It is linked to the corrugated material, the number of layers, the wall thickness, the presence of reinforcing ring, the working temperature and the diameter. You ask "maximum withstand voltage", just like asking how fast a car can go-can Ferrari and Wuling Hongguang be the same? There are general-purpose corrugated expansion joints and large-diameter thick-walled expansion joints in this station. The latter is specially designed for high-pressure scenarios, and the pressure level differs by several orders of magnitude. Two days ago, I met a customer, and he said, "Give me a DN200 expansion joint that can carry 10MPa". I said you should tell me the temperature, what the medium is and how big the displacement is first, but he was still impatient. As a result, steam pipeline, 500℃, 3.5MPa, guess what? Choose a corrugated expansion joint for power station industry, and the conventional design pressure of 2.5~6.4MPa is enough. If it is hard to 10MPa, the fatigue life will directly cut to the ankles.

Core parameters affecting withstand voltage

Corrugated material is the first threshold. The allowable stress of 304 stainless steel is about 137MPa at room temperature, which is slightly higher than that of 316L. However, at 600℃, Inconel 625 can still maintain its strength, and 304 is already as soft as noodles. Number of corrugated layers-the compressive capacity of single layer is limited, and multi-layer corrugation can distribute stress through interlayer friction, but at the cost of increasing stiffness and poor ability to compensate displacement. The wall thickness from 0.5mm to 2.0mm, with every increase of 0.5mm, the withstand pressure can be increased by about 30% ~50%, but the fatigue life may also be decreased, because the thick-walled corrugation is more likely to produce stress concentration in the trough. The reinforcement ring, to put it bluntly, is to add a hoop between the corrugations to prevent excessive deformation of the trough, which is almost necessary under high pressure conditions.

Medium temperature is a hidden killer. The yield strength of the material decreases by 20% ~30% for every 100℃ increase in temperature. For example, the single-layer corrugated expansion joint of DN200 can carry 1.6MPa at room temperature, but may only leave 1.0MPa at 400℃. You select the model according to normal temperature, and the expansion joint will bulge directly when the scene runs at high temperature. If this account is not clear, the design will be in vain.

Which products of this site can carry high pressure?

Corrugated expansion joints used in power station industry, with a common design pressure of 2.5MPa ~6.4MPa, are specially matched for steam pipelines and steam turbine units in power plants. Stainless steel or Inconel are mostly used as materials, and some have lining cylinders and guide cylinders. Large diameter thick-walled expansion joint, the wall thickness is more than 3mm, plus multi-layer corrugation and reinforcing ring, the maximum can reach 10MPa or even higher. In addition, there is a kind of artifact-external pressure single axial expansion joint. Structurally, the bellows is placed outside, so that the medium pressure can resist a rigid inner cylinder from the inside. The bellows only bears the bending stress caused by axial displacement, and does not directly bear the internal pressure. Therefore, its pressure resistance is much stronger than that of ordinary internal pressure expansion joints. But don't think that high pressure is invincible-the higher the pressure, the shorter the fatigue life, which is a dead hole.

The game between pressure resistance and fatigue life

You have to let the expansion joint carry 10MPa, OK, but the number of cycles may drop from 10,000 to 2000. In actual engineering, many customers ask "What is the highest resistance?" I usually ask: "How long do you plan to use it?" Under high pressure conditions, the material is prone to cracks in the trough stress concentration zone. A real case: A high-temperature and high-pressure pipeline in a chemical plant selected an expansion joint with a pressure of 8MPa, but it leaked in half a year. Check the reason, the design pressure is 5MPa, but the pressure fluctuates frequently during actual operation, starting and stopping once a day, and the fatigue life is only enough for 300 cycles. Later, the external pressure single axial expansion joint was changed, and the pressure level was reduced to 4MPa, but the life time was increased to 10,000 times, and there was no problem after three years of use. When selecting a model, you should balance design pressure with life expectancy, rather than staring at a number.

Selection suggestion: Don't pat your head

First, clarify the working pressure, temperature, medium and displacement-for example, for steam pipelines, the temperature is 500℃ and the pressure is 3.5MPa at full load, so you have to use a high-temperature axial expansion joint or a special model for power stations, and check the fatigue life. The best way is to send the working condition parameters to the manufacturer and let them calculate. The rotary compensator and double hinge transverse expansion joint of this station also have their own applicable scenarios. Don't take high pressure as the only standard. The rotary compensator is suitable for long-distance directly buried pipelines, and the double hinge transverse expansion joint can absorb lateral displacement and angular displacement, but their pressure resistance is generally not as high as that of large-diameter thick-walled expansion joint. If you are in the cement industry, the flue gas pipeline has high temperature and dust, and the metal corrugated expansion joint in the cement industry is lined with wear-resistant lining. Pressure resistance is not the main contradiction, but wear resistance and temperature resistance are. In summary, what is the highest pressure resistance of metal expansion joints? Ask about design life and working conditions first, then talk about pressure.