Specialized in manufacturing compensators, expansion joints, baffle doors

The expansion joint leaks, which is upsetting to watch and more troublesome to deal with. But don't rush to dismantle it, first find out where the water came from. The location of the leakage point is different, and the reason is completely different from the modification of the method.

First distinguish the leakage point: bellows, weld, flange or connection

Get a leaky expansion joint and turn around it first. Water stains, rust, crystalline salt, will help you guide the way. There are only four common leakage points: bellows body, circumferential weld, flange sealing surface, and the connection between pipe and pipe.

Bellows leaks, usually with pinholes, cracks, or corrosion pits in the walls. Weld leakage mostly occurs on longitudinal seams or annular seams. If you look closely, you can find pores and unfused. Flange leaks, usually at the gasket position, with wet marks or dripping. As for the leakage of the pipe, it is often where the pipe butts with the expansion joint, and there is a problem with the weld or thread. And guess what? Many users report for repair and say that "the expansion joint is leaking", which is actually a flange leak, which has nothing to do with the half dime of the bellows.

Corrugated pipe leakage: corrosion, fatigue and stress corrosion cracking are the main causes

The bellows is the heart of the metal expansion joint. If it leaks, the problem is usually more serious. Three conditions are the most common.

The first is corrosion. There are chloride ions, sulfide in the medium, or improper chemicals are used during cleaning, and the inner wall of the bellows will pitting and intergranular corrosion. 304 stainless steel is very fragile in chlorine-containing environment, so you have to change 316L or higher grade material at this time.

The second is fatigue. The pipeline expands and contracts repeatedly, and every time the bellows expands and contracts, the corrugated root bears alternating stress. The number of cycles is more, and the crack will initiate from the trough and slowly penetrate the wall thickness. In particular, it should be noted that the constraints underground are more complicated than those above ground, and the fatigue life may be much lower than the design value.

The third is stress corrosion cracking. If the tie rod nut is adjusted too tightly and forcibly matched during installation, the bellows will take on duty with extra stress. If you encounter corrosive media again, the crack will break through in a few days. Here is a data: the 304 bellows of the circulating water pipeline of a power plant leaked after less than eight months. After metallographic analysis, it shows transgranular cracks and typical stress corrosion. Later, it was replaced with 254SMO material resistant to chloride ions, and the problem was solved.

Leaky welds and flanges: improper installation, loose bolts and gasket failure

Weld leakage is most likely a problem of welding quality. In the ring seam between the bellows and the connecting pipe, if the current is too large during welding, the welding wire is damp, or the slag is not thoroughly cleaned, there will be pores and slag inclusions. This kind of leakage point, all defects must be dug out before repair welding, otherwise it will be repaired in vain.

Flange leakage, don't blame the gasket yet. Check the bolts first. Have you ever encountered this situation: tightening the bolts a few turns, it didn't leak at the time, and then it leaked again two days later? That's because the flange is unevenly stressed, one side is crushed to death, and the other side is still open. The correct way to do this is to tighten diagonally, adding to the specified torque in two or three times. Gasket failure should be distinguished whether it is aging, creep or corroded by the medium. The rubber gasket quickly hardens in front of high-temperature oil products, so it can be held by replacing it with a metal winding pad or a PTFE pad.

The expansion joint was in use, and the weld between the connector and the pipe cracked. This is often due to the lack of pipe frame support in the pipeline system, and the expansion joint is regarded as a force bearing member. The expansion joint compensates for displacement, it is not responsible for load-bearing. The addition of sliding brackets is different.

Non-metallic expansion joint water leakage: fabric layer aging, skeleton corrosion and lax sealing

Don't think that only the metal expansion joints will leak. The non-metallic expansion joint (fabric fiber expansion joint) leaks, and the precursor is more concealed. It generally has several layers of structure: fluororubber or silicone coated cloth as airtight layer, ceramic fiber as heat insulation layer, and the outermost is stainless steel wire mesh and skin. Water seeped out, indicating that the airtight layer was broken.

Airtight layer aging is a common occurrence. The flue gas temperature fluctuates greatly, and the coated cloth alternates hot and cold repeatedly, and it begins to become brittle and cracked in about two years. If you notice powdery shedding on the surface of non-metallic expansion joints, that's a sign of aging. At this time, when it rains again, water seeps in along the fibrous layer.

Don't ignore skeletal corrosion either. The frames and platens of non-metallic expansion joints, if stainless steel, will still rust in sulfur-containing flue gas. If the platen bolts are rusty and the skin can't be pressed tightly, water will seep from the edges. The treatment method is to clean the bolts regularly, apply anti-jamming agent, and change to high-strength alloy bolts if necessary.

The problem of lax sealing mostly lies in the installation link. The sealant between the skin and the flange is not evenly applied, or the wave shape of the pressure plate is wrong, which will leave gaps. When installing, it must be pressed tightly according to the manufacturer's torque sequence. Don't try to save trouble and only screw a few points.

Treatment plan and prevention: explain from type selection, material to installation and maintenance

Water leaks are not done once and for all by plugging them. You have to hold it down from the source.

In the selection stage, first see the working conditions clearly. What is the medium? What's the temperature? How stressful? Is it corrosive? If it is a flue gas pipeline, it has to use non-metallic expansion joints (fabric fiber expansion joints) to absorb three-dimensional displacement, which is resistant to high temperature and has large compensation. If it is a steam pipe, metal corrugated expansion joints are more suitable, such as general purpose corrugated expansion joints or high temperature axial expansion joints, which can withstand higher pressures and temperatures. Wrong choice, it is only a matter of time before the water leaks.

In terms of material, for media with high chloride ion content, don't use 304, use 316L or 254SMO. When the temperature exceeds 400℃, stainless steel bellows should consider high-temperature creep. At this time, heat-resistant alloy can be selected. If the medium is particularly dirty and there are many particles, add a guide tube to avoid direct flushing of the bellows.

In terms of installation and maintenance, remember three things: First, the expansion joint tie rod nut, adjust it according to the requirements after installation, some need to be removed, some need to be loosened, don't screw it. Second, the flange connection should be symmetrically tightened and the moment should be uniform. The third is to make regular inspections, touch your hands and see, and find rust spots or wet marks, so deal with them as soon as possible. Small leaks do not make up, big leaks suffer.

In case of urgent work and no suitable spare parts on hand, can you temporarily block it? You can use pipe hoops and rubber plates to hoop the leakage point of the bellows first, but that is only an emergency and can't last for a month. What is really reliable is to replace the leaky expansion joint. Even if it is just a weld leak, it is recommended to replace it as a whole. Welding quality is such a matter, the site conditions are difficult to guarantee, and the risk of repair is much greater than that of replacing it with a new one.

Expansion joint leaks are no trivial matter and involve pipeline safety and production continuity. Distinguish the leakage points, see the working conditions clearly, choose the right products, and standardize the installation. After this set of combination boxing is played down, the probability of water leakage can be reduced by more than half. If you are annoyed by this matter, go through the above steps first, and there is a high probability that you can find out the root cause of the disease.

Are metal compensators pipe fittings? Not. But if you go around the construction site, eight out of ten purchasers will buy it as a pipe fitting. Why? It looks like it-with flanges at both ends and a stainless steel bellows in the middle. When welded to the pipe, it looks like an elbow and a tee. But if you really choose the type according to the idea of pipe fittings, trouble will come.

Pipe fittings do "connect" and compensators do "compensate"

Let's talk about what pipe fittings are first. Elbow, tee, four-way, flange, blind plate, these things do the work of connecting and changing direction. They are rigid parts, and the shape they are when installed is whatever, and the thermal expansion and contraction of pipes have nothing to do with them. What about metal compensators? Its serious name is corrugated expansion joint, which belongs to the flexible element of pipeline. Its core function is to absorb thermal displacement, reduce vibration and noise. You can see from the product classification of this site that general-purpose corrugated expansion joints, external pressure single axial expansion joints and straight pipe pressure balance expansion joints are all under the category of compensator, and they don't go along with pipe fittings at all.

To put it bluntly, the pipe fitting is rigid connection, the compensator is flexible compensation, and the force in the pipeline is completely different. You weld a compensator at the elbow and want it to absorb the displacement that the elbow can't absorb? The direction is reversed.

Why do people keep confusing them?

On the one hand, the metal compensator does have connectors and flanges at both ends, and the installation method is almost the same as the pipe fitting-welded, bolted, and done. On the other hand, some manufacturers themselves scream, mixing "metal compensator" with "metal hose". This station is clearly distinguished: metal hose and PTFE-lined metal hose are specially designed to absorb vibration and lateral displacement; Whether the compensator is a general-purpose type or a high-temperature axial type, it mainly carries axial displacement. The two things look alike, but the functional emphasis is completely different. Confused, the selection straight away.

Two days ago, a customer came to me with the drawing of a metal hose and asked me if it could be used as an expansion joint. I said that if there is axial thermal displacement at your installation position, the hose can't hold it at all, and the corrugated pipe will become unstable as soon as it is compressed. Only then did he realize that he had taken the two things seriously.

Ask Yourself Three Questions Before Choosing a Model

Ordinary pipe fittings have no displacement compensation ability, which is the most essential difference between it and compensator. Metal compensators are divided into particularly fine displacement types: axial type, transverse type, hinge type and pressure balance type, each with its own applicable scenarios. When selecting, ask yourself three questions first: How much thermal displacement does the pipe go? What is the pressure rating? What is the medium?

Take an example. The steam pipeline has high temperature and large expansion amount, so it is necessary to use high-temperature axial expansion joint or external pressure single axial expansion joint; If the space available in the middle of the pipe is limited, it is necessary to consider the double hinge transverse expansion joint or the curved pipe pressure balance expansion joint. If you only report the nominal diameter and pressure and let the manufacturer deliver the goods, it is equivalent to asking the doctor to prescribe the medicine based on his height, which is unreliable. The medium has to be made clear. If the corrosive medium should be lined with PTFE, it has to be lined with PTFE. Take ordinary stainless steel to carry it hard, and it will leak in less than two years.

The installation link can better see that it is not a pipe fitting

Pipe fittings are simple to install, welded or threaded, and the position is right. Compensators are different. Before installation, check the amount of pre-stretching or pre-compression. When hoisting, the bellows can't be stressed, let alone take it to bear the self-weight of the pipeline. For example, sleeve-type pipe expansion joints and rotary compensators, the installation requirements are stricter, and they are slightly sloppy, ranging from leakage to direct scrapping of bellows instability. You said it was a pipe fitting. How could there be so much attention to pipe fittings?

So, exactly how to buy it?

Back to the topic – are metal compensators pipe fittings? The answer is clear: no. The difference between it and pipe fittings is not only that its functions are different, but that the whole design logic is different. Pipe fittings are standard parts and can be chosen at will; The compensator is a non-standard customized part, and the compensation amount must be calculated according to the working conditions.

If you buy the compensator as a pipe fitting in the pipeline design stage, only look at the nominal diameter and pressure, and there is a high probability that something will go wrong. The correct way is to hand over the parameters of pipeline layout, medium temperature and installation position to the manufacturer, and let them help you calculate the compensation amount and choose the appropriate model. Each of the double hinge transverse expansion joints and straight pipe pressure balance expansion joints in this station is designed for specific working conditions. Just take a pipe fitting instead, and don't even think about it.

What are fabric expansion joints? I'll let you know the truth first

In the dry pipeline industry for more than ten years, every once in a while, someone asks with drawings: What is this thing? Why does it look like a canvas pocket? Guess what, that's what we're talking aboutfabric expansion joint, also called non-metallic expansion joint, fabric fiber expansion joint. To put it bluntly, it is a device that absorbs the thermal expansion, contraction and vibration displacement of the pipe by a ring of flexible fabric. You think of it as a "cartilage head" added in the middle of the pipe, and the pipe can twist wherever it wants, but the stress can't be transmitted, and the equipment is safe.

You don't look at the word "fabric" in its name, you think it's a rag. This set of things is used in high-temperature air ducts of power plants and cement plants, and it is more useful than metal bellows at critical moments. Don't believe it? Look down.

Take it apart and see: What is wrapped in this "cartilage head"?

Take a standard rectangular non-metallic expansion joint, for example. It is usually a four-layer structure, and each layer does a different job.

• Fabric band (skin)— The outermost layer was also the core. It is generally made of fluororubber, silicone rubber coated glass fiber cloth or polytetrafluoroethylene material, which is responsible for sealing and absorbing displacement. If this layer breaks, the whole expansion joint will be wasted.
• Thermal insulation-Close to the inside of the loop band and fill it with ceramic fiber felt or glass wool. The flue gas pipe is often four to five hundred degrees. Without its insulation, the rubber coating on the outside will melt in a few minutes.
• guide tube— — This thing is made of metal. It is inserted into the pipe to divert the airflow and prevent the high-temperature smoke from directly washing the fabric band. Don't underestimate it. Without the guide tube, the life of the loop can be shortened by half.
• Frame (flange)— — That is, the upper, lower, left and right four angle steel or channel steel welded frames, and the pipe flange is screwed to death with bolts. Frame strength determines how much pressure the expansion energy saving is subjected to.

Each floor is coordinated with the work. You asked if the insulation can be saved? I advise you not to save it, save the circle belt burning through, and change it once enough for you to buy ten layers of insulation cotton.

Compared with the metal corrugated expansion joint, what is the difference?

Since metal expansion joints are so strong, why do you have to use fabric expansion joints in flue gas ducts and air ducts? There's a deep doorway here.

The metal corrugated expansion joint absorbs displacement by the deformation of the bellows, but it has a fault: it is sensitive to fatigue life. The temperature fluctuates greatly in the flue gas pipeline, and there is acid-alkali corrosion. Once the metal corrugated pipe is cracked by fatigue, air leakage and ash leakage is a trivial matter, and shutdown for maintenance is a big trouble. Moreover, the displacement of metal pipes is limited, and metal bellows with large cross-sections such as rectangular air ducts are heavy and expensive to make.

The same cannot be said for fabric expansion joints. It compensates the displacement by the deformation of the flexible ring belt, which can move in three dimensions and absorb in axial and transverse directions. Moreover, it has great damping, can reduce vibration and noise, and its price is much cheaper than that of metal bellows of the same caliber. The disadvantage is that the pressure bearing capacity is poor, and it is generally used in air ducts and flues from several kPa to more than ten kPa. High pressure occasions? Then you should honestly use metal.

Which industries are using it? Tell me a few real scenarios

In the past few years, I ran the scene, and I saw these three places the most:

Boiler air duct of power plant。 The rectangular air duct that comes out of the boiler blower has high temperature and big vibration. What does the thermal displacement rely on to absorb? Commonly used non-metallic expansion joints. Especially the corrugated expansion joint used in the power station industry has been seen in both low-temperature and high-temperature sections, but the air duct inlet section is almost all fabric type.

Cement plant kiln head and kiln tail.The temperature of the flue gas from the rotary kiln can reach above 350℃, and the dust content is large. There are many metal corrugated expansion joints in the cement industry, but the section between the kiln tail and the dust collector is basically rectangular non-metallic expansion joints. The reason is simple: too much dust accumulates on the metal ripples, which will jam the ripples. The fabric band is not afraid of this, and the slight dust accumulation will fall off as soon as it is shaken.

Desulfurization system.The flue gas at the inlet and outlet of the desulfurization tower has high humidity, contains sulfide, and is extremely corrosive. At this time, candidate metal bellows, you have to keep an eye on the material, and the cost will rise. With fabric expansion joints, the outer layer of fluororubber and PTFE coating itself is corrosion-resistant, and the cost performance will come up.

There are also those flue gas baffle doors and desulfurization flue gas baffle doors next to, and fabric expansion joints are also liked at pipe connections. Why? When the baffle door expands and contracts, the pipes on both sides pull each other, and no soft connection has ripped the bolts early.

Focus on these five parameters in model selection, and don't be fooled by sales

Some sales come up and blow "our family has five layers of skin sandwich, the thickest in the world". You would be naive to listen to him. When choosing fabric expansion joints, just keep an eye on these five numbers:

• Diameter dimensions and profile.Rectangular or circular? What is the flange port size? This is not accurate, and the rest is all useless.
• Design displacement amount.Axial stretch, lateral offset, angular displacement, how many millimeters are each? How much displacement you give, how wide cloth you have to use for the loop belt, which directly determines the price.
• Medium temperature.The materials used at 150℃ and 500℃ are completely different things. Don't just look at the upper limit of "temperature resistance 800℃", but ask what is the long-term continuous working temperature.
• Pressure rating.The air duct is generally slightly positive pressure, but what in case there is negative pressure? If the negative pressure is large, the ring belt will deflate, and it will fail.
• Media composition.Does it contain sulfur? Does it contain dust? Are there any corrosive gases? This has the greatest impact on coating material selection.

These five parameters are not clear. After listening to the sales speech, you have a high probability of buying expensive or wrong.

Why do you have to change it after a few years of use? How to check daily?

To be honest, fabric expansion joints are consumables. Metal bellows can be used for more than ten years. In the environment of high temperature, dust and acid-alkali corrosion, the life span of fabric belts is generally three to five years. They run with high load every day, and they have been changed in two years. Don't expect it to be done once and for all. You have to leave room for replacement when designing it.

For daily inspection, we focus on three places: first, whether there are bulges, cracks and exposed fibers on the surface of the ring belt, second, whether the flange bolts are loose, and third, whether there is any abnormal noise and air leakage. You take a flashlight to shine on the inside of the ring belt. If you see that the color of the insulation layer is black and brittle, it means that it is running warm, and you have to arrange a replacement quickly.

There is also particular attention when changing. The old loop is removed, and the frame should be cleaned without burrs. When the new ring belt is installed, the bolts should be twisted diagonally and the force should be even, otherwise the force will deviate to one side, and the ring belt should be torn again.

In the final analysis, fabric expansion joints are not advanced technology, but they rely on those few layers of cloth to chew hard bones that metal expansion joints can't handle. The next time someone asks you, "What's a fabric expansion joint?", you tell him: That's the guy in the plumbing system who knows the best "make the sea brighter".

1. Why are non-metallic expansion joints old and bad? — — Aging, scratching and delamination of fabric layer, first find out the type of damage before talking about repair

Non-metallic expansion joints (also called fabric fiber expansion joints) are widely used in flue gas, air duct and desulfurization systems. They do not rely on the deformation of metal corrugations to absorb displacement like metal corrugated expansion joints, but rely on multi-layer flexible fabrics and thermal insulation cotton to compensate. Bad methods are also different-there are only three common ones: aging and brittleness of the fabric layer, external scratches or wear, and delamination and bulging between layers. There is also a hidden one, which is that the internal insulation cotton has been blown out and hollowed out. On the surface, it looks unbroken, but in fact it has collapsed.

So before looking for a restoration unit, you should open it yourself and have a look. Even if it's just a hole, cut a small piece to see if the surface silicone coating is cracked or the fiberglass cloth underneath has been powdered. The type of damage determines the repair method: surface scratches can be repaired locally, but if the delamination range is large and the cotton layer collapses, it is not a question of whether to repair it or not, but the whole circle has to be replaced.

2. Repair or replace? — — Calculate material costs, downtime losses and residual life, and don't spend money with a slap on your head

Many users hear that it costs 20,000 yuan to replace it and 8,000 yuan to repair it, and they immediately make a decision to repair it. But have you calculated downtime costs? The shutdown loss of a kiln may be several thousand dollars an hour. It takes two or three days to repair a non-metallic expansion joint, dismantle the old, clean the dust, polish, lay up and heat close. If there are spare parts on site, it can be done in one day. Compare the two sides, which is cost-effective is not just the material cost.

Besides, the residual life has a good foundation. If this expansion joint has been used for five years, and the fabric layer is powdered in a large area, you spend 8,000 to finish it and last another year? Then it's better to just replace it with a new one. On the other hand, if only a small piece is rubbed on the outside and the inner layer is intact, then you spend some money to repair it, and it will last for another three to five years. This account should be settled clearly before deciding.

Third, what to look for in a restoration unit? — — It is not possible to do it with a sewing machine, it depends on the standard of non-metallic expansion joints, interlayer structure and field process

The non-metallic expansion joint looks like a cloth bag with flanges, but experts know that the interlayer structure is the lifeblood. Temperature-resistant layer, heat insulation layer, airtight layer and reinforcement layer, the material, thickness and overlap direction of each layer are particular. The national standard JB/T 12235-2015 clearly states that after repair, at least the displacement, pressure resistance and temperature resistance should be guaranteed not lower than the original design. But some restoration units have never even heard of this standard. Isn't it a blind delay to take an industrial sewing machine to fill the outer layer of cloth for you?

Therefore, when choosing a repair unit, the first thing is to see if he understands the standard. Another, ask him if he can provide the interlayer structure diagram. If he can't say it, he will block it as soon as possible. Also, you have to ask about the process-is the site cold glued or heat bonded? Is there any vulcanization equipment? What material is used for coating? These key points are cut corners and you can't tell at all.

4. Is on-site repair reliable? — — The complete process from demolition to heat-sealing and vulcanization, as well as common corner-cutting techniques

On-site repair is not impossible, but it depends on how to do it. The serious process should be: first set up a shelf (if it is a high-altitude pipeline), completely remove the old failure layer, and expose the metal flange surface; Then remove rust, clean up, and apply adhesive; Then lay layer by layer according to the original structure-first lay insulating cotton, then lay airtight layer, then lay reinforcing cloth, and finally lay surface weather-resistant layer; Each layer should be compacted and bubble removed, and the corners should be fixed with pressing strips and bolts; Finally do heat sealing or vulcanization treatment. It takes a day and a half for a skilled team to finish the whole process.

But how do some people cut corners? The most outrageous thing I have ever seen is to wrap the outside of the old non-metal expansion joint directly with a layer of silicone cloth, and not tear down the old one or clean it up. Just a rub of putty is done. There is also a work team, and the insulation cotton is not laid, so two layers of cloth are sewn on it. On the third day of starting the machine, the air leaks and whines. You ask why they don't come by the standards? Answer: Party A urged tightly. Squeezing? Then don't quote the price for the repair.

5. How to accept after repair? — — Dimensional tolerance, airtightness test and warranty period agreement, all of which must be missed

After the repair, you don't just sign and leave. You have to check and accept it. Prerequisite the size-the length of the expansion joint, the flange spacing and the parallelism of the flange surface. If these tolerances are exceeded, it will be stiff when installed, and the life will be directly reduced in half. Measure the airtightness again, use compressed air or smoke cakes, and focus on whether there is any air leakage at the corner strips.

The warranty period must be stated in the contract. The warranty period of non-metallic expansion joint repair is generally one year in the industry, and better units dare to write two years. If the other party says "warranty? We don't engage in warranty", then you don't even look at it, just change to the next one. In addition, in the maintenance report taken back, the name, thickness, overlap amount and batch number of each layer of materials must be clearly listed, so that future problems can be traced back.

Non-metallic expansion joint repair unit? Easy to find, more to make do with. You first clear out the above five things, and then ask the other person with questions. Only those who can answer and come up with a plan can talk about the next step. If you dare to quote without watching the scene, most likely you want to sign it first. Equipment maintenance, the most afraid thing is the three words "said yes", written clearly in black and white, is responsible for your own equipment.

What are the classifications of expansion joints? First distinguish between metals and non-metals

Many customers ask "What are the classifications of expansion joints?" In fact, the roughest way to divide them is to look at the materials-metal and non-metal. Metal expansion joints are seen most often, likeUniversal corrugated expansion joint、Corrugated expansion joint for power station industry、Large diameter thick wall expansion jointThe bellows inside are all stainless steel or alloy materials, which are hard-core in pressure and temperature resistance. The same cannot be said for non-metallic expansion joints, such asNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion jointThe main body is fiber fabric plus silicone coating, which is mainly used in the occasion of low pressure, large cross section and violent temperature fluctuation of smoke duct.

These two are not substitute relationships. Metal can carry pressure and temperature, but the reaction force is large when compensating displacement; Non-metal has good flexibility and corrosion resistance, but weak pressure bearing capacity. You have to take metal to do non-metal work, and the cost goes up; Taking non-metals to top the high temperature and high pressure is looking for trouble. If the material layer is not selected correctly, no matter how advanced the structure is, it will be useless.

According to the structure: the respective doorways of bellows, sleeve and rotary compensator

The structure determines how the expansion joint absorbs the displacement.Bellows typeIs the absolute mainstream, compensated by ripple deformation. There are many patterns in this, there are single, duplex, with hinges, and with pull rods. LikeCompound hinge transverse expansion joint、External pressure single axial expansion jointIt's all based on this logic.

Sleeve type pipe expansion jointIt relies on the relative sliding of the inner and outer sleeves to compensate the axial displacement, has simple structure and low cost, but the sealing performance is not as good as that of bellows, and is suitable for those pipelines with unclean medium and low pressure.Rotary compensatorIt is another way, which absorbs the axial displacement by converting the axial displacement into rotating motion through the cooperation of a pair of rotating cylinders in the bending section of the pipe. It is especially used in long-distance conveying of steam pipe network, with large compensation amount and small pressure drop.

When choosing a structure, it depends on the direction and space of the pipe. If there are many straight pipe sections, choose axial type; if there are elbows, consider hinge type or rotary compensator. Where the space is compact, the sleeve type is easy to install-it doesn't mean that the more advanced the more suitable, it is the last word that it can be installed and compensated in place.

According to the compensation function: axial, transverse, angular and pressure balance type

This level of classification is the real test of selection skills.

Axial typeThe compensator mainly absorbs the axial expansion and contraction of the pipe, such asUniversal corrugated expansion jointIt is a typical axial product. Several are arranged on straight pipe sections, so thermal expansion and contraction are not afraid.Transverse typeThe good thing is that it absorbs displacement perpendicular to the axis of the pipe,Compound hinge transverse expansion jointThat's what we do.Angular typeWell, with a combination of hinges, the pipe swings at a certain angle, likeDouble hinge expansion joint for air-cooled island vacuum pipelineIt is particularly useful in air-cooled islands with large displacements and multi-directional changes.

If the pressure in the pipeline is high and the blind plate is strong, the ordinary axial compensator will transmit the pressure thrust to the fixed support, which must be made as thick as the city wall. That's when you have to use itStraight pipe pressure balanced expansion jointOrCurved tube pressure balance expansion joint。 Its principle is that a balancing bellows is built in, which eats the blind plate force itself, and the main fixing bracket basically does not bear extra thrust. There are more complicatedCompound straight pipe bypass pressure balanced expansion jointWhich is suitable for the working condition that requires a large compensation amount and does not want the bracket to be stressed. Do you think this classification is important or not? Wrong choice, pipeline vibration, bracket deformation, later is all trouble.

According to the working conditions of the industry: special goods such as power stations, cement and desulfurization

As soon as the industry working conditions come up, the expansion joint has to be "customized". Smoke air duct of power station boiler, high temperature, large cross section, generally usedMetal rectangular expansion jointOrNon-metallic expansion jointWhich not only absorbs thermal displacement but also reduces vibration. Of the cement industryMetal Corrugated Expansion Joints in Cement Industry, that has to be wear-resistant, the dust particles at the head and tail of the kiln are fast, and the material and wall thickness of the bellows have to be increased.

The desulfurization system is more special. The flue gas contains sulfide, and the temperature changes greatly. Ordinary metal bellows can't bear corrosion, so it is commonly usedPTFE compensatorOr a metal hose lined with PTFE, such asPTFE-lined hose。 Also matched with the expansion jointDesulfurization flue gas baffle door、Flue gas baffle doorThese valve equipment have to be considered together when selecting, otherwise the connection size will not match, and the scene will be blinded.

Quick locking categories? Look at these key parameters

Then how do you quickly judge which category to use? Don't rush, just three steps.

The first step is to look at the medium and temperature. High-temperature flue gas and corrosive gas, directly leaning in the direction of non-metal or tetrafluorine lining; High temperature and high pressure steam, honestly choose metal corrugated expansion joint.

The second step is to calculate the compensation amount. Is the axial displacement large? Is there any lateral displacement? If there are multiple directions, preference is given to hinged type or rotary compensators. Like a direct pipeline, then you have to goDirect buried (fully buried) type expansion jointThis goods is directly buried in the soil, and there is a protective sleeve on the outside, so you can't make do with ordinary expansion joints.

The third step is to look at the pipeline constraints. If the position of the bracket has been set, it is necessary to choose the pressure balance type according to the thrust that the bracket can bear. Two days ago, I met a customer who was doing a steam pipe network project. When I came up, I asked, "What are the classifications of expansion joints?" I asked him how to arrange the bracket, and he looked confused. You have to understand that classification is not just a difference in name, each structure corresponds to different force models and installation conditions.

The classification table looks simple, but there are many things involved in the actual selection. The four dimensions of material, structure, function and working condition are cross-combined, and dozens or hundreds of schemes can be discharged. But as long as you grasp the core-the temperature and pressure of the medium, the magnitude of the displacement direction, and the force constraints of the pipeline-you won't deviate. Understanding these, the expansion joint classification is no longer a table, but a selection map in your hand.