Specialized in manufacturing compensators, expansion joints, baffle doors

A non-metallic compensator is a skin? Stop mixing up!

Is a non-metallic compensator a skin? If you go to the maintenance site and ask around, eight out of ten old masters may point to the layer of cloth and say, "Isn't this the skin?" But if you understand it this way, then the procurement and design links will lead to a big mess. Today, let's get this straight.

Find out one thing first: What exactly is a non-metallic compensator?

Start with the product name. Non-metallic compensators, also known asNon-metallic expansion joint、Fabric fiber expansion jointDefinitely not a single layer of fabric. It is a set of multi-layer composite flexible pipeline compensation device, which is specially used to absorb thermal displacement, reduce vibration and noise. To put it bluntly, it is a "system", not a "part". If you just take a skin to replace it, that's called changing the coat, not the compensator.

Two days ago, I met a customer, and urgently called and asked, "Your non-metallic compensator, if the skin is broken, can you only change the cloth?" I said yes, but I have to find out which layer you changed first. He was stunned: "Isn't it just a layer of skin?" – you see, this is the typical misconception.

Take it apart to see the interior

Take a complete non-metallic compensator apart, and you'll find something inside:

• outer layer: Skin (temperature-resistant and corrosion-resistant fabric layer), which is the "skin" that everyone is most familiar with.
• intermediate: Heat insulating cotton, sealing film. Insulating cotton is responsible for blocking high temperature, and sealing film prevents smoke from leaking out.
• inner layer: Wire mesh, flange frame. Wire mesh is used to enhance overall strength, and flanged frames are responsible for hard connections to pipes.

So, the skin is just the outermost layer of "skin", which is equivalent to a coat. There are also cotton-padded jackets, underwear and skeletons inside. When you say a person wears a down jacket, can you say that a down jacket is a person? A truth.

Function of skin and material selection

Temperature, corrosion, aging. Common materials are silicone rubber, fluororubber, PTFE fabric. The material selection must be based on the working conditions:

• Silicone rubber skin: Temperature resistance around 200℃, suitable for general smoke environment.
• Fluorine rubber skin: Temperature resistance 250-300℃, acid and alkali resistance, commonly used in desulfurization system.
• PTFE fabric: Higher temperature resistance, extremely strong corrosion resistance, but also expensive.

However, it is easy to cause problems by changing the skin without changing the overall structure. Take a real case: a power plant only changed the skin, and did not check whether the insulation cotton in the middle was hardened. As a result, after three months of operation, the internal insulation failed, the outer flange was baked and deformed at high temperature, and the whole set of equipment was scrapped. You say it's a pity or not?

Non-Metallic Compensator vs Skin: Don't Confuse It

The compensator is a complete set of components, including the frame, guide tube, insulation cotton, bead, bolts, and so on. The skin is just a replaceable consumable in it. It is true that only the skin can be changed when replacing, but the design selection must be based on the overall performance.

For example, you bought aRectangular non-metallic expansion jointThen its compensation amount, temperature resistance grade and pressure grade are all calculated for the whole structure. Looking at the skin thickness alone (such as 2mm or 3mm), the reference value is limited. Just like buying a car, you can't judge the performance of the whole car just by looking at the tire tread thickness, can you?

Why do people often call it wrong?

Because the repair site often only changes the skin. Over time, everyone thought that "compensator = skin". In addition, many small manufacturers sell skin as a standard product, and writing "skin compensator" on the drawing deepens the misunderstanding.

In fact, we have bothNon-metallic expansion joint (fabric fiber expansion joint)This typical representative, there are alsorubber compensator、Rubber PTFE compensatorAnd other variants, but their core advantages are in multilayer composite structures. Single-layer skin simply can't withstand the high-temperature and high-pressure smoke erosion.

Purchase recommendations

Don't just focus on the thickness and material of the skin, ask these points clearly:

• Insulation thickness: At least 50 mm or more, otherwise the heat bridge effect will burn out the flange.
• Frame Material: Carbon steel or stainless steel? Is the surface anti-corrosion treatment done?
• Installation dimensions: The flange bolt hole distance and the pipe center are high, all of which can't be wrong.

Standard referenceJB/T 12235-2015。 The overall temperature resistance and compensation amount are the key indicators. For example, if your working temperature is 400℃, you can't just look at the nominal 450℃ of the skin and place an order. You have to confirm whether the heat insulation layer and the sealing film can match.

If the next time someone asks "Is a non-metallic compensator a skin?", you can ask him rhetorically: "Then do you think people are clothes?"-this analogy is rough, but not rough.

Is the metal expansion joint model? The answer is yes, and there are enough models to make your scalp tingle. The reason is simple-pipeline working conditions vary widely, and it is simply unrealistic for one model to dominate the world. Temperature, pressure, displacement direction, medium corrosiveness, any variable changes, the required expansion joint has to be replaced. Two days ago, I met a customer and asked, "Is there a universal expansion joint?" I can only tell him: The universal type you want is actually just one of the models, and you have to make the diameter, pressure and wave number clear, otherwise you can't install it.

Classification by structure and compensation mode, which is the most commonly used division method

The axial type expansion joint is specifically responsible for absorbing the thermal expansion and contraction of the pipe along the axis direction. Like the most commonUniversal corrugated expansion jointAnd when the pipe diameter is large and the pressure is highExternal pressure single type axial type expansion joint-This structure can hide the bellows in the external shell, avoid the medium directly washing the wave crest, and is suitable for high temperature steam pipeline. Lateral and angular types deal with lateral displacement and angular deflection.Compound hinge transverse expansion jointThe lateral displacement is absorbed by the cooperation of two sets of hinge groups, and is often used at the corner of L-shaped or Z-shaped pipes. Pressure balanced type (Straight pipe pressure balanced expansion joint、Curved tube pressure balance type expansion joint) can offset the blind plate force generated by internal pressure, and is suitable for high-pressure large-diameter pipelines, such as the main steam pipeline of power plants. Each structure has its applicable scenario-if you choose the wrong one and install it, it will either be broken or leaked. Think about it, if a DN600 steam pipe is incorrectly installed with an axial type without pressure balance, the blind plate force can push the fixing bracket down.

More targeted by application industry and media

The power station industry has dedicatedCorrugated expansion joint for power station industryThe material and fatigue life requirements are according to the DL/T standard; The cement industry has its ownThe metal corrugated expansion joint in cement industry is wear-resistant and high-temperature resistant, and the problem of dust accumulation has to be considered. In the desulfurization system, the flue gas contains sulfide and moisture, and the common metal expansion joint can't bear the corrosion at all, so it has to be usedDesulfurization flue gas baffle doorCooperateNon-metallic expansion joints (fabric fiber expansion joints)。 At high temperatureHigh-temperature axial expansion joint, the working temperature can reach above 800℃, the bellows must use Inconel 625 or GH3030. Large-diameter and thick-wall situations, such as hot air ducts, have to beLarge-diameter thick-walled expansion joint, the wall thickness should be enough, and a guide tube must be added to prevent vortex erosion. And vacuum pipes, like those used for air-cooled island vacuum pipesThe double hinge expansion joint of air-cooled island vacuum pipe, the ordinary model can't bear the negative pressure at all-the bellows will be sucked flat. The standards and material requirements of different industries vary greatly, so don't mix them. Two days ago, a chemical factory used the model selected for the steam pipeline on the acid pipeline, and the result was perforated in two months.

Classified according to special functions and materials, it specializes in treating various "difficult and complicated diseases"

PTFE-lined hoseAndPTFE compensatorSpecially dealing with strong corrosive media-lined with PTFE, it can withstand almost all strong acids and alkalis, but the temperature cannot exceed 200℃.Special hose for vacuumIt has reinforcing ring and special sealing structure, which can ensure that the bellows will not be unstable under negative pressure.The directly buried (fully buried) type expansion joint is directly buried underground, and the shell has been treated with anti-corrosion and waterproof, which is suitable for directly buried heating pipelines without compensation.rubber compensatorAndThe rubber PTFE compensator is good at absorbing vibration and noise-the rubber section can reduce the vibration transmission of the pipeline, and it is most used in the fan inlet and outlet and pump outlet pipelines. These special models are often not found in ordinary selection manuals, so they have to be customized with manufacturers. You said that if a heating pipe buried under the road surface uses an above-ground expansion joint, it will rust through in half a year. Is this the truth?

Then how do you understand the doorway in the model?

General expansion joint models include nominal diameter (DN), pressure class (PN), wave number, material code, connection mode and other information. For example, "DN200 PN1.6 304 8 wave" can basically describe aUniversal corrugated expansion jointCore parameters-diameter 200mm, pressure 1.6MPa, material 304 stainless steel, 8 waves. But don't expect to conquer the world with a string of letters. Manufacturers usually provide detailed size diagrams and technical parameter tables. When selecting a model, check the displacement (axial, transverse and angular), fatigue life (how many cycles can withstand in the design life) and the guide tube design-these are more critical than the model itself. If the guide tube is installed backwards or the material is wrong, the high-speed airflow will directly split the bellows. There is also the adjustment of the tie rod nut, which should be locked before installation and loosened after operation, otherwise it will limit the displacement.

Finally, a suggestion: Don't think about the model yourself

The actual working conditions (medium, temperature, pressure, displacement direction and quantity, connection mode) are sorted out clearly, and directly thrown to professional manufacturers to let them match the most suitable model. After allMetal expansion jointOnce installed wrong, the cost of replacing is much more expensive than buying a new one-you have to stop the pipe, empty it, cut it, and re-weld it, not counting the loss of construction time. Remember, the model is the result, and the working condition is the source. You tell me what medium is going through your pipeline, how high it is, how much pressure it is, which way it goes, how much it moves, and I can tell you to use itCompound hinge transverse type orStraight pipe pressure balanced type. Don't be too troublesome. The more you fear trouble, the easier it is to get into trouble.

1. Where is the gasket hidden in the non-metallic compensator structure?

The non-metallic compensator not only has gaskets, but also the position and selection of gaskets directly determine whether the equipment can be used normally。 Many people get non-metallic compensators (that is, what we often call non-metallic expansion joints and fabric fiber expansion joints), and when they unpack them, they are blinded-why are there no gaskets? Did the manufacturer miss it?

Don't hurry. Instead of lying alone in the case waiting for you to discover, the spacers are hidden on the flanged connection surface. The body of the non-metallic compensator consists of a skin (usually multi-layered composite fiber fabric), thermal insulation cotton, and an internal support frame (such as wire mesh or steel plate). A layer of gasket is usually pre-installed on the flange surface, or a special groove is opened to place the gasket. The function of this layer of gasket is to fill the tiny gap between the flange and the pipe and prevent media leakage. That soft, black or gray strip you see that sticks to the flange is the spacer.

For the convenience of transportation, some manufacturers will make the gasket into a split structure, bag it separately when leaving the factory, and stick it on the spot. At this time, if the workers are sloppy, or the list is not clearly written, there will be the embarrassment of "no gasket". So customers who ask "Do non-metallic compensators have gaskets?", in all likelihood, have encountered this situation.

Second, why do some people say that non-metallic compensators don't need gaskets? It's a pit

I met a customer two days ago, who made hot air ducts, and purchased a batch of rectangular non-metallic expansion joints. Their installation master insisted: "The non-metallic compensator itself is soft, and the flange is tight when pressed, so there is no need for extra gaskets." The result? As soon as the machine is turned on, the air leaks, the hot air whistles out, and the flange surface is still smoking. Later, after checking, there was no rubber pad attached to the flange surface, all by the elasticity of the skin itself.

Alas, this statement is pure pit. The elasticity of the non-metallic skin does provide some sealing compensation, but that is for the thermal expansion and contraction displacement of the pipe, not for the microscopic irregularity of the flange surface. Stainless steel flange will be deformed after welding, only by skin compression, over time, bolt pre-tightening force attenuation, air leakage is inevitable. What's more, some non-metallic expansion joints (such as those used in desulfurization flue gas pipelines) have negative pressure inside, and the flange sealing surface is directly deflated without installing gaskets, and the consequences are more serious.

So don't believe the "no spacers" nonsense. Regular manufacturers, such as the non-metallic expansion joints (fabric fiber expansion joints) provided by us, clearly mark the gasket installation area on the flange surface when they leave the factory, and some even vulcanize the gaskets on the flange.

3. How to choose the gasket material? High temperature, corrosion and low pressure are different

The wrong choice of gasket is more scary than not installing it. Different working conditions, gasket materials are completely two worlds.

• High temperature conditions (> 400℃): For example, flue gas pipelines in power stations and cement industries. Ordinary rubber gasket burns when it goes up, so you have to use ceramic fiber paper gasket or graphite composite gasket. The temperature resistance of ceramic fiber can reach 1200℃, but the texture is brittle, so the tightening force of bolts should be well controlled and cannot be crushed. Graphite gasket has better flexibility, but it is easy to be oxidized, so it is not suitable for strong oxidizing media.
• Corrosive media (acid, alkali, salt spray): For example, the non-metallic compensator behind the desulfurization flue gas baffle door. Gaskets must be resistant to chemical corrosion, commonly used are polytetrafluoroethylene (PTFE) coated gaskets, or PTFE composite gaskets. Note: The PTFE compensator itself has a flange surface seal, but most non-metallic expansion joint flanges still need additional gaskets, so don't get confused.
• Low pressure and normal temperature (: For example, ventilation and dust removal system, ordinary nitrile rubber gasket or asbestos-free compression fiber gasket is enough. Cheap and easy to install, replace if it breaks.

Gasket thickness. Too thick bolts can't be pressed tightly, too thin to fill the depression. Generally, if the flange surface has good flatness, use 1.5-2mm; If the weld is raised, it is recommended to use more than 3mm. Do not use a 1mm standard gasket for one-cut cutting.

4. If the gasket is not placed correctly during installation, the compensator is equivalent to white installation

If the gasket is installed in the wrong position, the displacement function of the compensator will be scrapped directly. For example: Once the field worker attached the gasket to the inner ring side of the non-metallic compensator, that is, the inner side of the skin. As a result, the pressure of the operating medium blew the gasket displaced, blocking the expansion gap of the compensator. The rectangular non-metallic expansion joint was originally designed to compensate ±50mm in the axial direction, but it stuck at 15mm, and the tie rod was bent.

There are three correct ways to do it:

First, the gasket must be attached to the inside of the bolt hole on the flange face, but not into the inner diameter of the pipe. That is to say, the outer diameter of the gasket should be smaller than the distribution circle of the bolt hole, and the inner diameter should be larger than the inner diameter of the pipe. Otherwise, the media will scour the edges of the gasket, resulting in early failure.

Second, for round or rectangular non-metallic expansion joints, if there is a stop groove (groove) on the flange surface, the gasket should be embedded in the groove to prevent lateral slippage. If there is no stop slot, it is recommended to apply a layer of sealant to assist in positioning.

Third, the order of bolt tightening should be particular. Screw diagonally first, afterburn it three times, and the final torque reaches 80% of the design value. Don't screw it to death. The flange frame of the non-metallic compensator is relatively thin, and excessive bolt force will cause the flange to deform, and the gasket will not be compacted.

Since it's so troublesome, why not seal with a monolithic molded flange? Because the non-metallic compensator has to bear multi-directional displacement when working, the connection between the flange and the pipe must be soft and adjustable, but the integral seal ring will limit the displacement. So spacers are the necessary price.

V. Summary: There are gaskets, but it depends on how the manufacturer matches them

Do non-metallic compensators have gaskets?Yes, but there are three situations：

• Most regular manufacturers install gaskets on the flange surface when they leave the factory (or distribute them with accessories);
• In order to save costs, a few low-priced products may not be equipped with gaskets, so customers need to buy them themselves;
• Very few unprofessional installation teams cancel the gaskets on their own, resulting in leaks.

Are flange gaskets standard or optional? What is the material? What is the thickness? Check this article during on-site installation, and don't let a few cents of gaskets pit tens of thousands of yuan of equipment.

By the way, we have both non-metallic expansion joints (fabric fiber expansion joints) and rectangular non-metallic expansion joints in our station, as well as matching rubber compensators, PTFE compensators and other products. If you are unsure about the selection of gaskets, send the working condition parameters directly to technical support, and we will help you set the specifications. After all, do non-metallic compensators have gaskets? The answer is yes, but it is called yes when used correctly.

How on earth do you build that large non-metallic compensator? It's more than two meters wide at every turn, and it can withstand hundreds of degrees of high temperature. Is it reliable? I told him that this thing looked like a cloth cover, but it actually had many ways. Today, I simply break the whole process apart and crush it, from material selection to factory delivery to installation, and explain it clearly bit by bit.

Find out the details first: temperature, pressure, medium and displacement. These parameters determine what materials are used

The first step in building a compensator is not to draw a picture, but to settle accounts. You have to know whether smoke or hot air runs in the pipeline, whether the temperature is 200℃ or 600℃, whether the pressure is slightly positive or negative, and whether the displacement is axial stretch or lateral offset. These data directly determine the number of layers and materials of non-metallic bands, and also determine the thickness and corrosion protection grade of metal frames.

The flue gas pipeline used in the cement industry has a temperature of around 350℃ all the year round, containing sulfur and dust. Therefore, a temperature-resistant layer and an airtight layer must be added to the belt, and the skeleton must be made of weather-resistant steel and high-temperature paint. If it is used on the pipeline before and after the desulfurization flue gas baffle door, and the medium is still corrosive, the anti-corrosion grade has to be raised. To put it bluntly, the parameters started to cut the material without figuring out, and the rest was all in vain-there are many people in this industry who have stepped on this kind of pit.

The skeleton is the beam of the house: how can the metal frame be designed, welded and prevented from corrosion to hold it?

The skeleton of the non-metallic expansion joint (fabric fiber expansion joint) is, to put it bluntly, a steel structure frame. This thing has to hold the entire ring, and it has to withstand pipe thrust and external loads. When designing, calculate the cross-sectional moment of inertia of the frame according to the displacement and pipe diameter, and the place of the stiffened plate cannot be saved.

For welding, I have seen many factories do not polish or do non-destructive testing after welding in order to catch up with the construction deadline. As a result, the frame is deformed, and it can't match the flange when installed, so it can only be smashed with a sledgehammer. Do you say it is upsetting or not? The good practice is to spot welding the frame first, then fully welding, and annealing to relieve stress or vibration aging after welding. Don't be sloppy in anti-corrosion-hot-dip galvanizing, epoxy zinc-rich primer plus topcoat, or directly use stainless steel, depending on the working conditions.

Non-metallic tape is the soul: How to match fabric lamination, adhesive process and temperature resistant layer

The loop band is the heart of a large non-metallic compensator. And guess what? Many laymen think it's just layers of cloth sewn together. In fact, the band is a multi-layer composite material: the outermost layer is usually silicone rubber cloth or fluorine rubber cloth, which is used to insulate the temperature and wind; Add glass fiber felt or ceramic fiber blanket in the middle for heat insulation; The inner layer is made of tetrafluorine membrane or a material similar to a polytetrafluoroethylene compensator as an airtight layer. Each layer should be pressed with high-temperature adhesive, no bubbles, no wrinkles.

The lamination process is also very particular. Staggered seams should be made between layers to avoid overlapping weak points. The pressing temperature, pressure and time must be supported by data-for example, when silicone rubber cloth and glass fiber felt are compounded, the temperature is controlled at about 150℃ and the pressure is 0.3MPa for 20 minutes. Each manufacturer of these parameters has its own process manual, but the factory that fooled people directly brushed the matter with cold glue, and the ring belt cracked in layers within half a year.

It is not so simple to install: sealing strips, pressure plates, tension structures, one less all leak

How to fix the loop band to the skeleton when it is done? The usual practice is to use plates and bolts to press the ring belt to the frame flange. But here's the problem-if the platen is not designed well, the edge of the loop band will be crushed or slip off. Therefore, the inside of the pressure plate should be rounded, the bolts should be evenly tightened, and the torque wrench should be adjusted properly, so that no air leakage can be made.

Sealing strips are equally critical. Between the contact surface of the ring belt and the skeleton, a temperature-resistant sealing gasket, such as graphite sandwiched metal mesh or PTFE coated gasket, must be padded. In addition, the four corners of rectangular non-metallic expansion joints are most likely to leak, so special corner sealing strips should be used, or the ring belt should be made into an integral corner in advance to avoid splicing seams. It is also very important to tighten the structure, especially the negative pressure pipeline. The ring belt will be deflated, so it is necessary to add an internal support ring or external tension bar. One less detail and the site has to be reworked.

Before leaving the factory, you have to go through the court one by one: withstand pressure test, air tightness test, displacement simulation, one can't be missed

Factory trials are not a formality. Before leaving the factory, the large non-metallic compensator must be tested for pressure resistance, inflated to 1.5 times of the design pressure, and held for 10 minutes to see if the ring belt is bulging and the frame is deformed. The airtightness inspection is stricter-use soapy water or helium to detect leaks, and the leakage points must be repaired and redone.

Displacement simulation is a link that many factories are unwilling to do because it is troublesome. But there is a big difference between having done it and not having done it. Install the compensator on the test bench, pull and compress it to the designed displacement, then offset it laterally, and charge it at the same time, and observe whether the ring belt is twisted and the pressure plate is rubbing. I have personally seen a manufacturer who didn't do displacement simulation. When it was installed at the site, the guide tube interfered with the ring belt, and it was directly scrapped. Alas, is this money not injustice?

Doorways installed on site and pits stepped on in those years: How to adjust pre-stretching, guide tube and expansion gap

Finally on the scene. When good things arrive at the construction site, if they are not installed correctly, they will be finished. Let's talk about pre-stretching first: if there is thermal expansion when the pipeline is running, the compensator should be pre-stretched by a certain amount when it is cold, equal to half the amount of thermal expansion. How much to pull? The data is marked on the drawing, so don't feel it.

The deflector is also an easy place to overlook. What is the specific function of the expansion joint guide tube? It allows the medium to flow smoothly through the interior of the compensator and prevents the vortex from washing the ring belt. The direction of the deflector must be the same as the direction of the media flow when installed-the direction of the arrow is the direction of flow. Never install it backwards. If it is installed backwards, the loop belt will wear out quickly.

The expansion gap needs to be more attentive. If there is no sufficient gap between the frame and the pipe, the compensator will fail when it is directly pushed to death during thermal expansion. In addition, it is mentioned in the correct installation method of the expansion joint of the large tie rod that the tie rod nut should be loosened for a certain stroke after installation, so that the compensator can expand and contract freely. Don't screw the nut to death, that's a common mistake for newbies.

How to make a large non-metallic compensator? It is not knocked out by one person, but an engineering work from parameters, materials and processes to testing and installation. Those who want to save trouble often end up trouble. Those who want to save money tend to burn more money in the end. Is that the truth?

1. Is the current market cold or hot? — — Real voices on both sides of supply and demand

What is the market of desulfurization non-metallic compensator? This question, I just talked with the purchase of several desulfurization projects last week. To be honest, the market is not simply cold or hot now, but sharply differentiated.

Look at the demand side first. In the final stage of ultra-low emission transformation of domestic thermal power, steel and cement industries, there are indeed fewer replacement parts for old projects, but what about new projects? In coking, chemical and waste incineration industries, desulfurization systems are still being launched. Especially for some central heating projects in industrial parks, the standard equipment of flue gas desulfurization is non-metallic compensator. From the inquiry volume, the first half of this year increased by about 15% compared with the same period of last year-mainly supported by small and medium-sized projects.

Look at the supply side again. Small and medium-sized compensator manufacturers are having a hard time. The price increase of raw materials is on the one hand, and more importantly, the payment cycle has been extended to 6 months or even one year, and many factories dare not take big orders. However, the head enterprises are expanding production instead, because end users are becoming more and more picky: not any non-metallic expansion joint can be exported to the desulfurization tower.

So you have to ask whether the market is hot or cold? For manufacturers who can come up with the new national standard and have actual operating performance, the order is scheduled for three months; For factories that are still making up numbers with old fabric fibers, they can only rely on low prices to grab bulk orders, and their profits are as thin as paper.

Second, driven by the policy, what hard indicators does the desulfurization system put forward for non-metallic compensators?

The environmental protection policy has not been loosened in recent years. In 2023, the Ministry of Ecology and Environment revised the Air Pollutant Emission Standard for Thermal Power Plants, which directly forced the upgrading of the desulfurization system. What used to be made do with metal expansion joints is now required to be replaced with non-metallic ones-for a simple reason: corrosion resistance, zero leakage, and the ability to absorb multidimensional displacement.

• Temperature resistance class must be defined: The temperature of the original flue gas side of desulfurization is generally 120~160℃, but it may rush above 200℃ when encountering bypass conditions. The skin of the non-metallic compensator (that is, the fabric fiber layer) must give a third-party inspection report to prove that it will not fail after continuous operation for 10,000 hours at the set temperature. Don't trust the manufacturer's verbal promise, ask for paper documents.
• Sealability Requirements: The new design code requires a compensator leak rate of less than 0.1%. By what? Multi-layer construction + fluororubber sealing layer. Like the one in our stationNon-metallic expansion joint (fabric fiber expansion joint)It is made of fluororubber, polytetrafluoroethylene and glass fiber fabric, and is sealed in three layers. Before leaving the factory, air tightness test is done one by one.
• Anti-corrosion requirements: The wet flue gas after desulfurization contains acidic condensate water, and the pH value can be as low as 2. If the interior of the compensator uses a carbon steel frame, it must be lined or enameled to a high standard. Some projects specify stainless steel frames lined with PTFE, which is costly but long-lasting.

These hard indicators directly determine the difference in procurement cost by more than 30%. But there is no way, the acceptance fails, and rework is more expensive.

Third, buy it or buy a metal expansion joint? — — The irreplaceability of non-metallic compensators in desulfurization scenarios

Why don't metal corrugated expansion joints be used directly for desulfurization flue? It is cheap and has a high pressure resistance.

Alas, I've seen this pit too many times. The diameter of the desulfurization flue pipe is large (DN1000~ DN4000 is very common), and it is low pressure (usually below 0.1MPa) and large displacement (axial energy reaches 50mm and transverse energy is more than 20mm). The metal corrugated expansion joint has two dead points under this working condition: First, the thrust is huge, and the pipe support can't stand it; Second, it is easy to crack by stress corrosion-the bellows has a thin wall, and it will crack in a few months as soon as chloride ions come.

The flexible structure can almost neglect the thrust on the pipeline; The multilayered laminated fabric fibers are inherently not afraid of dilute acids; But also can simultaneously absorb axial, transverse and angular displacement. More importantly, its noise reduction effect is incomparable to metal parts.

In the desulfurization project of sintering machine in a steel mill, the original design used metal rectangular expansion joint. After half a year of operation, it was found that the weld seam frequently leaked. Later replaced withRectangular non-metallic expansion jointNever had any problems. This is not to say that the metal expansion joint is bad, it is used in the wrong place. Desulfurization scenario, non-metal is just needed.

IV. Behind price fluctuations: Who is at work with raw materials, processing cycle and project account period?

In the last two months, the price of fluororubber has increased by 20%, and so has PTFE. These are the main raw materials for the compensator skin. Aluminum silicate fiber cotton is stable, but the labor cost is high-the daily salary of a good skin master is almost catching up with that of an engineer.

The processing cycle is another variable. The standard cycle of custom parts is 30~45 days from blanking to factory. However, if you require the frame to be hot-dipped zinc for corrosion protection, or the skin requires imported fluororubber (such as DuPont's Viton), the cycle will be directly stretched to more than 60 days. In case of a project that rushes to the deadline, the manufacturer's expedited fee can eat 5% of the profit.

Then there is the accounting period. The industry practice is "3-3-3-1": 30% for advance payment, 30% before delivery, 30% after installation and commissioning, and 10% after expiration of warranty. However, many owners delay the payment until after acceptance, and even settle it with acceptance bills. When manufacturers' cash flow is tight, they will either increase prices or degrade quality.

So when you see a 20% difference between the two quotes, don't rush to pick the cheaper one. First ask clearly: Is there any difference in raw material batches? How long is the processing cycle? How to negotiate payment terms? These things are the essence of price fluctuations.

5. A few honest words for purchasing and engineers: how to pick, how to test and how to save

Something dry at last. What is the market of desulfurization non-metallic compensator? Quotes are dead, people are alive. If you master the following points, you will be able to step less on pitfalls:

How to pick?

First, confirm the working condition parameters: temperature, pressure, displacement amount, and medium composition. Don't just give a caliber and ask the manufacturer to quote. Second, manufacturers are required to provide running cases of the same type of projects, preferably in the past two years.

How to test?

When the goods arrive on site, don't just look at the appearance. Cut a small piece of skin sample and burn it with a lighter: real fluororubber flame retardant, self-extinguishing from fire; The counterfeit ones will drip oil and emit black smoke. Put the compensator flat and measure the difference of diagonal length. If the difference exceeds 3mm, the welding deformation exceeds the standard. Also, check the gap between the guide tube and the bellows, not less than 20mm, otherwise it will be damaged by friction after operation.

How to save?

Don't think about saving money on materials – all the money saved will turn into repair costs. The real way to save money is to choose a standard sizeNon-metallic expansion jointAvoid non-standard customization. In addition,Desulfurization flue gas baffle doorPackaging and purchasing with the compensator can often negotiate discounts. Finally, sign a warranty agreement with a reliable manufacturer: if it is damaged by people during the warranty period, it will be replaced for free. That's a lot more practical than the 5% of your hard-earned money you save.

What is the market of desulfurization non-metallic compensator? In the final analysis, the market is not good or bad in the total market volume, but in how professional you are. Think about this industry thoroughly, and you can deal with it calmly no matter the ups and downs.