Specialized in manufacturing compensators, expansion joints, baffle doors

Let's ask a question first: Why use non-metallic ones if the pipeline is equipped with metal compensators?

Friends who have been in contact with power plants and cement plants know that metal parts can't bear corrosion and dust accumulation in high-temperature flue gas pipelines and desulfurization systems. Although the metal bellows has high strength, it will rust out in a few months when it encounters acidic medium and wet smoke. Non-metallic compensators use fabric fibers, rubber, PTFE and other materials to deal with these "soft knives". This site'sNon-metallic expansion joint (fabric fiber expansion joint)Andrubber compensatorIt is to make up for the shortcomings of metal parts-to put it bluntly, it is to wear a layer of "body armor" on the pipeline.

The structure is actually not complicated

A flexible loop strap, plus flanges, frame and insulation. The band material may be silicone cloth, fluororubber,PTFE (rubber PTFE compensator)。 The key lies in design: how can it be resistant to both temperature and pressure? Generally, multi-layer composite, inner layer insulation, outer layer sealing. Two days ago, a customer asked: YouRectangular non-metallic expansion jointDifference from round? To put it bluntly, rectangles are mainly used in square pipes such as smoke ducts, which have large compensation and convenient installation-and the four corners of rectangular pipes are prone to stress concentration, which can be digested by the flexibility of non-metals.

Function Article 1: Absorb multidimensional displacement

During thermal expansion and contraction, the pipe will expand and contract axially, yaw laterally and even twist angularly. Because of its flexibility, the non-metallic compensator can absorb the displacement in these directions at the same time, and is not afraid of twisting like metal bellows. Like those used in the cement industryMetal Corrugated Expansion Joints in Cement IndustryAlthough it can also be compensated, when encountering large rectangular flues, non-metallic rectangular expansion joints are more cost-saving and easier to maintain. Think about it, when the temperature of a flue dozens of meters long changes, the displacement is often more than ten millimeters or even tens of millimeters, and the metal parts will get stuck directly if they are not properly designed. The non-metallic band is like a "soft joint", which is not afraid of twisting.

Function 2: Carry high temperature, carry corrosion, and reduce noise

The pipeline behind the desulfurization flue gas baffle door of the power plant is not high in temperature, but the acid corrosion is serious, and the metal parts will rust through in a few months. useNon-metallic expansion joints (fabric fiber expansion joints)With PTFE lining, the life can be extended by two or three years. In addition, it has a vibration damping effect-the vibration of the fan is transmitted to the pipeline, and the non-metallic band can eat some energy, and the noise is low. Some data show that under the same working conditions, the non-metallic compensator can reduce the noise of pipeline system by 8~12 dB. Tsk, this thing is easier than a silencer.

Compared with metal compensators, what are the advantages of non-metal?

Low pressure capacity, cannot be used in high pressure steam pipeline. Moreover, non-metallic materials will age, and their life span generally has to be replaced after 3-5 years. What about that? Calculate clearly when selecting: the medium temperature exceeds 600℃ or the pressure exceeds 0.1MPa, and honestly use metal parts orHigh temperature axial expansion joint； Low temperature and low pressure, large diameter, corrosive media, non-metal is the first choice. Is that the truth?

Finally, a reminder of the main points of purchasing

The national standard JB/T 12235-2015 stipulates the technical requirements of non-metallic expansion joints, mainly depending on the material of the ring belt, compensation amount and connection mode. Pay attention to the direction of the guide tube during installation-refer to the Q&AArrow direction of expansion jointThe tie rod nut should be adjusted according to the on-site displacement, and do not screw it (see for detailsHow to adjust the tie rod nut of expansion joint）。 If you are not sure, you can compare this siteUniversal corrugated expansion jointAndRectangular non-metallic expansion jointProduct parameters, or just ask the technology – they have more experience than me.

In summary, the role of a universal non-metallic compensator? It is to solve the "difficult and complicated diseases" that metal compensators can't handle: high-temperature corrosion, multi-dimensional displacement, large-diameter special-shaped pipes, vibration and noise reduction. If you choose the right one, the equipment is worry-free; Wrong choice, post-maintenance is enough for you to drink a pot.

1. What exactly is the "welding non-metallic compensator" you asked? — — Clarify the concept first, don't buy the wrong goods

Two days ago, a purchaser called and asked "welding non-metallic compensator". I was stunned for half a second and asked him: By "welding" do you mean welding a non-metallic compensator to a pipe? Or does it mean that the compensator itself has metal welds? The other end of the line was dumbfounded. This thing is often called a bastard in the industry. Today, let's talk about it all at once.

The so-called "welded non-metallic compensator" actually refers to one with metal connectors (such as flanges or stub) at both ends, which is connected to the pipe by weldingNon-metallic expansion joint— That is what we often sayNon-metallic expansion joint (fabric fiber expansion joint)、rubber compensatorOrRubber PTFE compensator。 Its main body is a non-metallic loop band (fabric, rubber, PTFE, etc.), but the ports are usually made of carbon steel or stainless steel for the purpose of welding. So the name itself is a bit "contradictory", but everyone in the industry knows it: it means "non-metallic compensator with welded structure at the port".

Don't underestimate this definition. I have seen people buy pure rubber joints (looper flanges at both ends) and take them for flue welding. As a result, when they are baked at high temperature, the rubber melts away directly. Is it a waste of cost? So figure out that "welding" refers to the port structure, not the whole product is metal.

Second, according to the structure: rectangular and circular, the welding method is very different, rectangular non-metallic expansion joint is the main force

Rectangular and circular. The welding processes of the two are far from each other, and they can't be installed directly if they are selected incorrectly.

1. Circular welded non-metallic compensator

It is more common in pipeline systems, such as smoke air ducts of power stations and hot air ducts of cement plants. The circular structure bears uniform force, and butt welding or fillet welding is generally used during welding. The common practice of ports is: a section of metal stub (or flange) is welded to the pipe, and the other end of the stub is pressed with a non-metal ring band. Note that the non-metallic loop strip itself cannot be welded directly, so "welding" is actually for a metal connection.

2. Rectangular non-metallic expansion joint-absolute shipment workhorse

If you go to the boiler flue site at a power station, 99% of them use rectangles. Why? Because the rectangular flue has high space utilization rate, it is easy to stick to the wall. The welding method is also special: the metal frame of rectangular non-metallic expansion joint is usually made of angle steel or channel steel, which is welded directly to the flue wall panel. The ring belt is fastened to the frame by platen bolts instead of welding. So "welding" only takes place between the metal frame and the flue.

In order to save costs, some manufacturers make the frame thin, and the deformation after welding is serious, resulting in air leakage due to weak pressure of the ring belt. Therefore, when choosing rectangular non-metallic expansion joints, be sure to ask about the thickness and material of the frame plate, and don't just look at the quotation.

Third, according to the material: fabric fiber, rubber, rubber PTFE, which can be welded firmly?

The material of the non-metallic ring belt determines the temperature resistance, corrosion resistance and sealing performance. Here are three mainstream materials, which you can take according to the working conditions.

• Fabric fiber expansion joint: i.e.Non-metallic expansion joint (fabric fiber expansion joint)。 The main body is made of silicone cloth, glass fiber cloth, ceramic fiber cloth, etc., and the temperature resistance can reach 1200℃ (with heat insulation layer). After the port metal parts are welded, the ring belt is pressed mechanically, which is not directly affected by the welding heat. This is the most used in flue and cement kiln tails of power stations.
• rubber compensator: The material is natural rubber, neoprene or EPDM, and the temperature resistance generally does not exceed 150℃. Note when welding: the rubber ring belt must not be close to the high-temperature welding area. The metal parts must be welded first, and then the rubber ring belt must be installed after cooling. Many on-site accidents are caused by welding slag splashing onto the rubber.
• Rubber PTFE compensator: Lined with PTFE layer and rubber, taking into account both corrosion resistance and elasticity. The temperature resistance is a little higher than that of pure rubber (about 200℃), but it is also afraid of high welding temperature. Generally used in desulfurization systems, the medium contains acidic gas or slurry. The welding requirements are the same as the rubber compensator, and the heat source must be isolated.

What are the welding non-metallic compensators? From the material classification, there are these three mainstreams. But some people will ask: Can you weld PTFE directly? Wake up, the melting point of PTFE is only 327℃, and the welding melts directly. Therefore, as long as it is a "non-metal" loop strip, it must pass through the transition of metal parts before it can be welded.

IV. Practical application scenarios: power station flue, cement hot air, desulfurization system, each choose its own goods

Different scenarios have completely different choice logics. The question "What are the welding non-metallic compensators?" When put on the spot, the answer becomes "You can decide after looking at the working conditions".

Scenario 1: Power station flue (boiler outlet, dust collector inlet)

The medium temperature is generally 300-700℃, containing a small amount of dust. PreferredNon-metallic expansion joint (fabric fiber expansion joint)Rectangular structure, high temperature resistance and can absorb multi-directional displacement. Welding method: The wall thickness of the flue is generally 6-10mm, and the frame should be welded directly. The kerosene penetration inspection should be done in the welding seam. Frequent questions: The insulation layer is not done properly, and the temperature of the external metal frame is too high, which leads to thermal stress cracking of the weld.

Scenario 2: Hot air duct (kiln head, grate cooler) in cement industry

The temperature is higher, reaching above 1000℃, and contains a lot of clinker dust. Fabric fiber expansion joints with thermal insulation must be used, and heat-resistant steel (e.g. 310S) should be selected for metal connections. Preheat during welding and heat preservation after welding to prevent cracks. OurMetal Corrugated Expansion Joints in Cement IndustryAlthough mainstream, it is still more economical to use rectangular non-metallic expansion joints for large-section flues.

Scenario 3: Desulfurization system (FGD import and export)

Low temperature (50-80℃), strong corrosion (SO₂, chloride). Circle belt preferredRubber PTFE compensator, or a rubber compensator lined with PTFE. Metal parts must be coated with anti-corrosion coating or duplex stainless steel. Note when welding: Desulfurization pipelines are often lined with rubber or plastic, and welding heat will destroy the lining, so the welding sequence should be designed well: first welding metal connectors, then fill the lining. This detail is wrong, and the later leak will be repaired until you cry.

Speaking of which, do you still think "welding non-metallic compensators" is an easy multiple choice question? Choose the wrong material, and it will leak after welding; Choose the wrong structure and can't fit it; Choose the wrong scene and scrap it in half a year. Doubling the cost is light, and delaying the construction period is really bad.

Next time you communicate with the manufacturer, just report three parameters directly: temperature, pressure and media composition. Leave the rest to us. Oh, by the way, don't forget to confirm whether the port is welded or flanged-don't be like the brother at the beginning, ask "welding non-metallic compensator" when you open the mouth, but when you buy it back, you find that you don't even have welding parts.

Splash cold water first: The non-metallic compensator itself does not leak water, but this structure leaks water

Give the answer directly —Non-metallic compensator(That is what we often sayNon-metallic expansion joint、Fabric fiber expansion joint) The body will not leak. The reason is very simple. Its main body is a composite layer of fabric and rubber, which is not a dense metal. If it was waterproof by itself, it would have leaked into a fountain.

What really carries the waterproof banner is the internalSealing layerAnd externalskinThe cooperation of. The sealing layer is usually made of fluororubber, silicone rubber or polytetrafluoroethylene film, which is responsible for blocking air and water. The skin (several layers of high-strength fiber cloth plus rubber) provides strength and prevents the sealing layer from bursting by pressure. Once one of the two partners dropped the chain, the water found the seam to drill.

By what waterproofing? Cooperation of sealing layer and skin

TakeNon-metallic expansion joint (fabric fiber expansion joint)In terms of structure, it is generally like this from the inside to the outside: the innermost layer is a corrosion-resistant sealing layer, the middle is a heat insulation layer (such as ceramic fiber felt), and the outer layer is a skin. The sealing layer is like a raincoat, and the skin is like a jacket shell-a hole in the raincoat is useless no matter how waterproof the outside is.

So when you ask "Do non-metallic compensators leak?"The correct answer is: it does not leak itself, but once the sealing layer is aged, damaged or selected incorrectly, what leaks is the peace of mind you bought at a large price.

Dismantling of Water Leakage Case: Rectangular Non-metallic Expansion Joint of Cement Plant Drips in Half a Year

Two days ago, a customer from a cement factory reported that they usedRectangular non-metallic expansion jointInstalled on the kiln tail smoke gas pipeline, it began to drip water in less than half a year. The scene was so anxious that he jumped his feet, thinking it was a product quality problem. As a result, when I removed it, I saw that the sealing layer was full of corrosion holes, but the skin was intact.

What's the problem?

• Flue gas temperature fluctuates year-round: In the design, the silicone rubber sealing layer was selected at 180℃. As a result, the actual operation sometimes rushed to 250℃, and the silicone rubber was directly carbonized and brittle.
• There is condensed acid in the medium: The flue gas contains sulfur, and the temperature drops after shutdown to form sulfurous acid. The ordinary sealing layer can't bear it, and it will perforate in a few months.

This pot really shouldn't be left to the non-metallic compensator-the working conditions were not accurately calculated in the selection stage.

Pits buried in the design and selection stage: temperature, corrosion and pressure, none of them can be missed

No matter how cow the sealing layer is, it is also afraid of "cross-border rape". Three key parameters don't match up, and it is only a matter of time before water leaks:

• Flue gas temperature: Select silicone rubber or perfluorororubber at high temperature, and use EPDM with good aging resistance at low temperature (such as wet chimney after desulfurization). Don't take the general-purpose type to carry the high temperature of 300℃, that is, force the sealing layer to commit suicide.
• Medium corrosivityPolytetrafluoroethylene film or fluororubber sealing layer for acidic gas; Alternative formulation for alkaline or oil mist environments. Customers often ignore the corrosion of condensate and choose an ordinary rubber, which leaks in half a month.
• Pressure rating: Non-metallic compensators are generally used in low-pressure or negative-pressure pipelines, but when the pressure fluctuates greatly, the sealing layer will be "blown and bulged" and then torn. Design with a margin at least 20% higher than the actual pressure.

To put it bluntly, the non-metallic compensator is like a custom suit, and only by measuring the body (working conditions) and tailoring (material selection) can it fit. Buy the ready-made universal model when you come up, and don't shout for the leakage.

The most overlooked details of installation and maintenance

Select the right type, install the hand shake, still leakage. Three details are the hardest hit areas:

Has the tie rod nut been adjusted in place?

Non-metallic expansion joints, usually with tie rods, are used to limit displacement. According to the specification, the tie rod nut should be adjusted to the pre-tensioned or pre-compressed position after installation (see the design drawings for specific data). Many workers screwed to death directly, or didn't adjust it at all. As a result, the skin was torn when the pipe was thermally expanded, and the sealing layer suffered. Refer to our site Q&A"How to adjust the tie rod nut of the expansion joint"It should be divided into two steps: first loosen the nut to the free state, and then adjust the positioning nut according to the compensation amount.

Is the deflector in the right direction?

Non-metallic compensator with guide tube, the arrow must point to the direction of media flow. When installed backwards, the airflow directly washes the edge of the sealing layer, and the wear is aggravated. There was once a client who putRectangular non-metallic expansion jointThe guide tube was installed backwards and worn out in three months. We have written about the specific function of the guide tube, and the core is to protect the sealing layer from being damaged by high-speed particulate matter.

Is the bolt torque enough?

The flange bolts can't be tightened, and the water will seep as soon as the sealing surface runs out. But it can't be screwed dead-the strength of non-metallic skin is limited, and the excessive torque of bolts will crush the skin, resulting in local deformation and cracking. The standard practice is to use a torque wrench and tighten it symmetrically three times according to the torque value given by the manufacturer.

What if a non-metallic compensator leaks? Don't be in a hurry to change, check these 4 places first

When you encounter a water leak, don't scold the manufacturer first, and don't rush to place an order for a new one. Sequencing in order:

1. See if the sealing layer is partially damaged: Open the observation port or remove the skin (be careful not to tear it), and check whether there are holes, cracks and bulges on the sealing layer. If it's just a small hole, you can temporarily plug the leak with special repair tape, and then replace it after shutting down.
2. Check if the tie rod nut is loose or stuck: If the tie rod nut is loose and the displacement is uncontrolled, the sealing layer may be torn. Reposition the nut to make sure it is within the set stroke.
3. Verify that the guide tube is detached or installed backwards: The guide tube falls off, and the high-temperature flue gas directly rushes the sealing layer, which can be burned through in a few minutes. Re-fixed or replaced.
4. Measure actual media temperature and composition: Many water leakages are actually due to the change of working conditions-for example, the original burning coal is now mixed with biomass, and the flue gas composition changes, so the sealing layer can't bear it. In this case, the type must be re-selected and the material of the sealing layer must be changed.

80% of the water leakage problems are not the poor quality of the compensator itself, but the hidden pits in the selection, installation and maintenance. After these three links are controlled, the non-metallic compensator will last for three to five years.

By the way, if you still leak after checking, don't hold on. Contact the manufacturer to provide the working condition parameters and let professional technicians recalculate it. It is much cheaper to replace a sealing layer than the entire compensator, and it does not have to move the pipes-this isNon-metallic expansion jointAdvantages of modular design.

What Are Metal Expansion Joints? From structure to application, explain it at once

Two days ago, I met a customer and asked, "What are the metal expansion joints? Which one is suitable?" This question looks simple, but you really need to answer it clearly-you have to know where it is used, what is flowing in the pipe, and what is the temperature and pressure. Today, let's make it clear according to the three dimensions of structure, industry and special working conditions. By the way, let's talk about whether the metal hose is an expansion joint.

1. According to the structure, what do mainstream models look like?

The core of a metal expansion joint is a bellows, but depending on the pipe direction, displacement type, and pressure grade, more than a dozen structures will be derived. Most commonUniversal corrugated expansion jointTo put it bluntly, it is a section of corrugated pipe in the middle of the flange at both ends, which is suitable for the linear pipe between two fixed brackets, absorbs axial displacement, is affordable and simple to install. But if you run into a high-temperature steam pipe, such as the main steam pipe of a power plant, where the temperature soars to five or six hundred degrees, the general-purpose model is not enough-you have to use it at this timeHigh temperature axial expansion jointIts bellows has many layers and heat-resistant materials. It is usually equipped with a guide tube to protect the inner wall and avoid direct erosion by high-temperature media.

When the internal pressure is high to a certain extent, the tube will bend like noodles, which is called "columnar instability". How to treat it?External pressure single axial expansion jointInstall the bellows upside down, let the medium pressure act on the outer shell, and the inner cavity is basically not pressurized, and the pressure level can easily be above 2.5MPa without instability. Do you think it is fragrant or not?

The pipes don't always have to be straight. Where L-shaped and Z-shaped turns, no one can say with certainty which direction the expansion and contraction amount runs.Compound hinge transverse expansion jointJust do the job-the two bellows are hinged between them, allowing only lateral displacement, angular displacement, and axial force to be carried by the tie rod. By the same token,Straight pipe pressure balance typeAndCurved tube pressure balance expansion jointSpecialized device interfaces. For example, the inlet and outlet of pumps, valves and compressors, if the thermal expansion and contraction of the pipeline transmit the thrust, the sealing ring of the equipment will collapse in minutes. There are two sets of bellows against each other inside the pressure balance type, which digests the blind plate force by itself, and the equipment end basically has zero thrust.

And there's an old-school kind of —Sleeve type pipe expansion jointIt is compensated by the sliding seal of the inner and outer tubes. The cost is low and the compensation amount is large, but the sealing packing needs to be changed regularly, and the maintenance amount is large. Nowadays, long-distance directly buried heating pipes like to useRotary compensatorThe axial displacement is absorbed by a pair of rotating cylinders, the footprint is small, the compensation distance can reach several hundred meters, and the leakage point is much less than that of the traditional sleeve type.

Second, according to the industry, what is the special type?

The set of equipment in the power station industry is always high temperature and high pressure. LikeCorrugated expansion joint for power station industry304 or 316L stainless steel is commonly used for bellows, multi-layer structure, and a guide tube is added in the middle. Why add a deflector? It not only diverts the flow, but also reduces the erosion of the bellows by high-speed media and prolongs the life. The cement industry is different. The dusty hot air runs in the pipeline, and the dust particles are like sandpaper. SoMetal Corrugated Expansion Joints in Cement IndustryThere must be a wear-resistant guide tube, the inner wall must be coated with an anti-corrosion layer, and the wave number must be calculated clearly, otherwise the dust will be stuck. Guess why cement plants still like to use non-metallic expansion joints? Because fabric fibers compensate for greater displacement and are not afraid of wear-but that's another topic.

Desulfurization flue gas system, acidic environment, pH as low as 2-3, ordinary stainless steel will corrode through in a few days.Expansion joint for desulfurization flue gas baffle doorGenerally, high-nickel alloys, such as C276, or lined with PTFE are used. By the way, this site has a specialPTFE compensatorAndPTFE-lined hoseThe outer shell is metal, lined with PTFE, and strong acid and alkali can be used casually.

Have you been exposed to air-cooled islands? Vacuum pipeline, run under negative pressure, and it is finished if it leaks.Double hinge expansion joint for air-cooled island vacuum pipelineUsing hinge structure to limit axial displacement and double sealing ring, the vacuum degree can be kept below 0.1Pa. The general-purpose expansion joint of the same specification will probably deflate in the vacuum system.

3. "Special Forces" under special working conditions

What about large caliber and high pressure? For example, the blast pipe of blast furnace in steel mill has a diameter of 1.5 meters and a pressure of more than 1.0MPa.Large diameter thick wall expansion jointThe wall thickness of the bellows can reach 10mm or even thicker, the single wave compensation is small but the pressure resistance is high, and the reinforcing ring is equipped.

Inspection wells cannot be set for directly buried pipelines, and expansion joints must be buried directly in the soil.Direct buried (fully buried) type expansion jointThe outer cover is covered with an anti-corrosion layer, and the moisture drainage pipe is welded on it to drain out soil moisture and prevent electrochemical corrosion. AndSpecial hose for vacuumWith small wave pitch and low stiffness, it is specially used in vacuum coating machines in electronics and semiconductor industries. WhileMetal rectangular expansion jointLook at the inlet and outlet of the boiler air duct and flue gas desulfurization tower. Those square flues have to use rectangular bellows-the round ones can't fit in.

4. Does the metal hose count as an expansion joint?

Strictly speaking,Metal hose(includingPTFE-lined hose) Like the principle of corrugated expansion joint, it absorbs displacement by corrugated deformation. However, the metal hose emphasizes flexible connection, and its diameter usually does not exceed DN300. It is used to connect the pump inlet and outlet, instrument pipeline, and mainly reduces vibration. However, the corrugated expansion joint is often above DN500, which bears the main force of pipeline thermal compensation. In the actual product list, the two are often juxtaposed, and the displacement, pressure level and installation space are seen when selecting the model. Small diameter, large displacement, need frequent bending, choose metal hose; Large diameter, high pressure, mainly axial compensation, choose expansion joint.

Five, choose a tendon, try combination boxing

Thermal pipes are most commonly usedUniversal corrugated expansion jointAdding a guide tube has low cost and good effect. If the cement industry has to use metal, chooseMetal Corrugated Expansion Joints in Cement Industry； If space allows, non-metallic expansion saves energy to handle large displacements at a cheaper cost. Remember one principle: high pressure, high temperature, strong medium corrosion, preference alloy materialsPressure balance typeOrExternal pressure single type； Large displacement, limited space, upperComplex hinge typeOrRotary compensator。

There are many types of metal expansion joints, and there is no universal model. Take the parameters of the pipeline you have-media, pressure, temperature, displacement direction, installation space-and the answer will come naturally. The product page of this site has the detailed parameters of all models, so you can find them correspondingly.

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.