Have you really figured out the role of acid and alkali resistant non-metallic compensators?

As the old saying goes, if you choose the wrong compensator, the pipe will be repaired every day. Especially when encountering acid-base media, a bunch of people come up and ask: Do you use metal or non-metal? Today, let's talk about acid-alkali-resistant non-metallic compensator, and explain its functions, doorways and pits. Don't be too long-winded, you will have a spectrum in your heart after reading it.

Let's start with the name: What is it?

To put it bluntly, compensators and expansion joints are the same thing-they are both devices used to absorb the thermal expansion and contraction, vibrational displacement of pipes. The "acid-alkali-resistant non-metallic compensator" is the kind that specializes in carrying corrosive media, and the material completely draws a clear line with metal hoses and corrugated expansion joints.

This kind of product is usually called in our businessrubber compensator、PTFE compensatorOrNon-metallic expansion joint (fabric fiber expansion joint)。 There are also compound types, such asRubber PTFE compensator, lined with PTFE outer bread rubber. There are many names, but the actual core is one: the main body is not metal, and it relies on polymer materials or fiber fabrics to achieve elastic compensation and corrosion resistance.

Isn't it better for metal compensators to withstand temperature and pressure? Just look down and you will see.

Acid and alkali resistance, why can't metals work, and how can non-metals do it?

No matter how awesome the metal is, it has to kneel when it encounters strong corrosive media such as concentrated sulfuric acid, hydrofluoric acid and wet chlorine. 316L stainless steel won't last a few days in front of hydrochloric acid, let alone ordinary carbon steel. Corrosion not only causes leakage, but also causes hydrogen embrittlement, stress corrosion cracking, especially headache.

Non-metallic materials take a different approach-Polytetrafluoroethylene (PTFE)Known as the king of plastics, except for molten alkali metals and high-temperature fluorine, he is almost not afraid of any acid and alkali;Rubber(Mainly EPDM, butyl and chloroprene) can carry dilute acid and alkali, and the price is cheap and elastic;Fabric fiber(Glass fiber, silicone rubber coated cloth) High temperature resistance, but mainly used to compensate for displacement.

For example, the flue gas in the desulfurization system is not high in temperature but contains a large amount of sulfurous acid and chloride ions.rubber compensatorOrNon-metallic expansion jointIt's much more reliable than metal bellows. And guess what? Some customers saved money on stainless steel, but as a result, it was perforated in half a year, and the renovation cost was twice as expensive as buying non-metal.

What kind of work does it do for you in actual working conditions?

Acid and alkali-resistant non-metallic compensator not only solves corrosion, its daily work includes at least the following three things:

• Displacement compensation:The axial, transverse and angular displacements caused by thermal expansion and contraction of pipelines and deviation of equipment installation are absorbed by corrugations or fabric wrinkles in non-metallic layers. Especially on rectangular pipes (such as flue of power plants and dust removal pipes of steel plants),Rectangular non-metallic expansion jointAlmost standard.
• Vibration isolation and noise reduction:The rubber material itself has damping properties, which can absorb the vibration transmitted by pumps and fans. On the contrary, metal bellows are easy to conduct high-frequency vibration.
• Sealing and pressure bearing:Many conditions require zero leakage. flangedRubber PTFE compensatorOrPTFE compensatorWith the special lining layer, it can withstand the pressure of 0.6~2.5MPa while preventing a drop of acid from seeping out.

Two days ago, I met a buddy who did chlor-alkali engineering. They directly usedPTFE-lined hoseDo pipe connections, but places with many elbows still rely onrubber compensatorSaid it had been used for five years without changing it-tsk tsk, worry-free.

Don't scratch at the selection: rubber, PTFE, fabric fiber, how to pick?

Many purchases ask "Which is best" as soon as they come up? There is no best, only the most suitable. I list a generic selection logic:

• The medium temperature is lower than 100℃, dilute acid and alkali, and the vibration is large:userubber compensator(EPDM or neoprene), which is cheap and has good vibration damping effect. But don't touch strong oxidizing acids (concentrated nitric acid, concentrated sulfuric acid) and organic solvents, the rubber will swell.
• Medium temperature-30~200℃, strong acid and strong alkali, requiring extremely high chemical resistance:UpperPTFE compensatorOrPTFE-lined hose。 PTFE is invincible in corrosion resistance, but has poor elasticity, limited displacement, and cannot be used in vacuum (easily deflated).
• Wide temperature range (-40℃ ~1000℃), large diameter rectangular pipe, containing dust and flue gas:chooseNon-metallic expansion joint (fabric fiber expansion joint)。 The structure is multi-layer fabric + insulation cotton, which can compensate for displacement and insulate heat. For example, high-temperature air ducts in power plant flues and cement industries are used more.
• It should be acid and alkali resistant and have good comprehensive elasticity:ConsiderationRubber PTFE compensator, lined with PTFE contact media, and the outer rubber plays a sealing and compensating role. The price is somewhere between pure rubber and full PTFE.

Isn't it a little messy? Simple note: the pieces with "PTFE" are corrosion resistant, the pieces with "rubber" are elastic and cheap, and the pieces with "fabric" are high-temperature and large-diameter. When selecting, be sure to give the composition, temperature, pressure and displacement of the medium. Don't just throw "acid and alkali resistance" and be done.

Installation and routine maintenance, say a few words if you have stepped on the pit

Say a thousand words and ten thousand, pretending to be wrong is equivalent to buying it for nothing. I've seen too many cases of compensators being scrapped early because of sloppy installation. Here are a few pits you have to bypass:

• The pre-stretch/compression is backwards:Non-metallic compensators usually leave the factory with installation length markings. Pre-stretching is required if the ambient temperature is lower than the design temperature during installation; Otherwise, pre-compression. Many people don't care about the hard installation of 3721, but as a result, it will either crack or explode once it runs.
• Ignore deflector and limit rod:Having a guide tube (e.g.expansion joint guide tube) Must ensure that the media flow direction is consistent with the arrow. Tie rod (expansion joint tie rod) is for transportation protection, and it should be loosened after installation, otherwise the compensator will not move. Otherwise, the stress concentration will tear off the takeover.
• Flange bolts are not screwed by torque:The rigidity of the sealing surface of rubber and PTFE is poor. If the bolts are tightened too tightly, the compensator body will be crushed, and if they are tightened too loosely, they will leak. It is recommended to use a torque wrench and tighten it symmetrically in 3 times according to the value given by the manufacturer.
• Daily inspection does not check displacement indication:Some compensators are marked with displacement scales. Glance at them every quarter. If you find abnormal deformation (such as exceeding the maximum stroke), quickly check whether the pipeline support and hanger have been displaced.

Finally, let's say it-the acid-and alkali-resistant non-metallic compensator, reliable suppliers and installation teams are much more important than the price difference saved. You save 500 yuan in purchase fees and may lose 5,000 yuan in discontinued production losses. Taste yourself.

aboutFunction of acid and alkali resistant non-metallic compensator?The core is four words: erosion and inflation. Choose the right materials, install the right method, and use it for another ten years without panic.

Why use a non-metallic compensator? These five scenes metal really can't do

Dry pipeline compensation has been in the business for a long time, and you will find a heartbreaking fact: metal expansion joints (such as metal corrugated expansion joints and metal hoses) are indeed solid, but when encountering high-temperature flue gas, corrosive media and super-large displacement, the shortcomings of metal are completely exposed-short fatigue life, high cost and limited installation. At this time, non-metallic compensators (that is, non-metallic expansion joints, including fabric fiber expansion joints, rectangular non-metallic expansion joints, rubber compensators and rubber PTFE compensators) have become life-saving straws. Why? Look down.

If metal can't carry it, why can non-metal carry it?

The greatest confidence of non-metallic compensators comes from the materials themselves. The temperature resistance range is ridiculously wide-some fabric fibers expand and save energy to work for a long time above 1000℃, and metal bellows start to swing when they reach 600℃. In terms of corrosion resistance, in the face of acidic and alkaline flue gas and desulfurization system, stainless steel can't bear pitting corrosion, but PTFE compensator is like nothing. More importantly, non-metals can absorb multi-dimensional displacements-eating them all in axial, transverse and angular directions, unlike metal bellows, which are prone to fatigue cracking. Think about it for yourself, as soon as the pipe vibrates, the metal bellows bends back and forth, and the stress concentration point will crack sooner or later; The non-metal loop belt is flexible and can be twisted how you want.

In addition, the weight is light, the load on the pipe support is small, and the installation is also hassle-free. The vibration and noise reduction effect is much stronger than that of metal-this is not metaphysics, fiber fabric itself has damping properties. Two days ago, I met a buddy in a cement factory. He used to use metal corrugated expansion joints, and the noise made workers complain. After replacing them with non-metal expansion joints (fabric fiber expansion joints), the noise directly dropped by 10 decibels.

Five scenes, metal is really bad

Specific to actual projects, non-metallic compensators are almost just needed in several industries, and hard metal is to find trouble for yourself.

1. Power station industry: front and rear of boiler flue duct and desulfurization flue gas baffle door

The flue gas temperature of the power station is high, and the sulfur-containing corrosion is heavy. In the desulfurization system, the temperature of the pipelines in front and behind the flue gas baffle door fluctuates greatly, and there is still a large amount of acidic condensate in the medium. Would you try it with a metal corrugated expansion joint? Corroded perforations in a few months. Non-metallic expansion joints (specifically rubber PTFE compensators or PTFE compensators) are acid and alkali resistant and can absorb large displacements. The desulfurization flue gas baffle door of this station is a standard flue configuration with non-metallic compensator.

2. Cement industry: hot air ducts at the head and tail of the kiln

At the head and tail of the cement rotary kiln, the temperature fluctuates drastically and the amount of dust is extremely large. The surface of metal bellows is easy to accumulate dust. Once the ash block falls off and gets stuck in the corrugation, the expansion joint will be wasted. The surface of the non-metallic compensator is smooth, the dust is not easy to adhere, and it can adapt to frequent temperature changes. Cement industry metal corrugated expansion joints are also available, but only in branch pipes with lower temperatures and less dust. Trunk hot air duct, honestly use non-metal.

3. Iron and steel industry: blast furnace gas pipeline, dust removal system

Blast furnace gas pipeline contains a lot of dust and corrosive gas. Although the temperature is not high (usually 300-500℃), the medium is extremely corrosive. The life of metal bellows here is generally less than a year. The non-metallic compensator (fabric fiber expansion joint) with the guide tube can effectively isolate the medium and easily double the life. The dust removal system is the home field of non-metals-low pressure, large displacement, serious wear, and the rubber compensator is cheap and doesn't feel distressed to change.

4. Chemical industry: acid-base media pipeline

Concentrated sulfuric acid and concentrated hydrochloric acid run in the chemical pipeline, and even if the metal hose is lined with PTFE, it is inevitable that there is a risk of pinhole leakage. The rubber PTFE compensator in the non-metal compensator is made of PTFE composite material as a whole, which is corrosion resistant and has no dead angles. Moreover, low-pressure pipelines do not need to bear much pressure, and non-metals are completely enough.

5. Rectangular large section flue

Many flue gas pipelines are rectangular, such as the inlet and outlet of desulfurization towers in power stations. Although the metal rectangular expansion joint can be made, it is expensive, heavy and difficult to install. Designed for rectangular flues, the rectangular non-metallic expansion joint is lightweight and compensates for less than half the price of metal. Which do you want to choose?

The structure is not so mysterious, and the core of the selection is a few points

Non-metallic compensators typically consist of non-metallic loop belts (fabric fiber, rubber or PTFE composite) and metal frames (deflectors, platens, bolts, etc.). The rectangular non-metallic expansion joint in our product line is specially equipped with rectangular flue, while the rubber compensator and rubber PTFE compensator are biased towards low-pressure, corrosive liquid or gas pipelines. Don't look at the fancy name when selecting the model. The core is to look at the medium temperature, pressure, chemical properties, and the displacement required by the pipeline. For example, the desulfurization system should not use ordinary rubber, but use an acid-and alkali-resistant PTFE compensator. Otherwise, the rubber will be softened by corrosion, and it will leak in less than two months.

It's not a panacea. High pressure and low temperature still depend on metal

Nonmetallic compensators aren't panacea either. If the pressure is too high (say over a few MPa) or the temperature is extremely low (cryogenic embrittlement), it won't be able to handle it. What about that? Metallic, such as general-purpose corrugated expansion joints or high-temperature axial expansion joints. There is no absolute choice of who is better or worse, only whether it is suitable or not. After all, the national standard JB/T 12235-2015 also makes it clear that non-metallic expansion joints have clear technical boundaries. What we do in engineering is to choose the most cost-effective plan within the boundaries.

Find out first: What exactly is the skin non-metallic compensator?

Look at the name-skin non-metal compensator. Do you feel tall and confused when you hear it? In fact, to put it bluntly, it is the soft connector responsible for "flexible compensation" in the pipeline system. Structurally simple: a circle of metal flanges or carbon steel frames with a special flexible skin sandwiched between them, that's it. And metal expansion joints (like the one in our stationUniversal corrugated expansion joint、Metal rectangular expansion joint), the difference is bigger-those metals deformed by bellows, with high rigidity and small displacement, which are suitable for high-pressure clean media; The skin relies on the elastic deformation of fabric and rubber layer, which can compensate for large displacement in three dimensions and hardly transmit thrust. If you want to draw a picture, the left side is a rigid bellows, and the right side is a soft skin laminated structure. You will understand its "soft" truth at once.

Cough, in practical applications, flue gas pipelines, desulfurization systems, air ducts and other places have high temperature, strong corrosion, alternating hot and cold, and dust particles-do you let metal bellows carry it? It can't handle it for a few days before it cracks from fatigue. At this time, you have to rely on non-metallic compensators to play. So don't be fooled by the name, it's a flexible joint specialized in "dirty work".

Why can it withstand high temperatures and corrosion resistance? — — The mystery of the core material "skin"

The skin is not a piece of cloth, it is a composite of layers of materials. The most common is: the outermost layer is silicone cloth or fluororubber coated cloth, with glass fiber cloth and polytetrafluoroethylene film sandwiched in the middle, and a layer of acid-resistant rubber may be added to the inner layer. Each layer performs its duty-silicone cloth carries temperatures above 200℃, fluororubber is resistant to acid and alkali corrosion, glass fiber provides tensile strength, and polytetrafluoroethylene is anti-adhesion. Let's put it this way, the acid-alkali condensate and high-temperature steam in the flue gas pipeline have long been rusty through the single-layer metal plate, but the skin is forcefully supported by these laminated combinations.

Talk about the desulfurization system. Although the flue gas temperature after wet desulfurization drops to about 50℃, it contains a large number of sulfuric acid and sulfurous acid droplets. The fluororubber layer in the skin non-metallic compensator can directly resist acid-alkali corrosion, and the skin itself does not conduct heat, which can also reduce the heat bridge effect of pipelines. That's why our stationNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion jointThe appearance rate in desulfurization projects of power plants and cement plants is so high. Is that the truth?

Don't step on pits in model selection: how much displacement with how thick skin?

You really can't slap your head when it comes to selection. Two days ago, I encountered the purchase of a cement factory, and I chose a thin skin for the air duct cheaply. As a result, it bulged and leaked in less than half a year-losing dozens of tons of cement output. There are three core principles: compensation amount, pressure level and medium temperature. Take the one from our stationRectangular non-metallic expansion jointFor those with large angular displacement, the skin has to be reinforced, and the number of glass fiber layers is increased from two layers to four layers; If the amount of axial stretching is large, the depth of the preset folds of the skin must be sufficient. The pressure level-low-pressure air duct (below 0.1MPa) can be reinforced with a single layer of skin, but if it is a positive pressure environment above 0.2MPa at the inlet of desulfurization tower, it is necessary to choose a double layer of skin and stainless steel wire mesh to reinforce it.

Medium temperature is a ruthless character. A silicone cloth-glass fiber combination is sufficient below 150°C; If it exceeds 300℃, you have to change the configuration of fluororubber-ceramic fiber. Real case: The raw material grinding ventilation pipe of a cement plant, the temperature is 280℃, the silica gel cloth skin is selected, and it will be layered in half a year. Later, it was replaced with fluororubber skin, and it is still in use for three years now. The wrong layer of material is selected, and the life difference is more than five times.

Install that little thing: to make it work, you have to untie it first

When installing a skin non-metallic compensator, the most taboo thing is "thinking that you can install it when you bring it". Remember three points, one less, and half the equipment will be scrapped.

• Transport tie rod must be removed: In order to fix the skin when the manufacturer delivers the goods, several temporary tie rods will be installed. Connect the pipe directly without dismantling it? Hey, the compensator can't move at all, the thermal expansion is all stuck in the pipes, and the equipment quickly deforms. After installation, confirm that the flange bolts are tightened, and immediately remove the tie rod.
• Pre-stretched (or pre-compressed): According to the design drawings, give the skin an initial displacement amount during installation. For example, if the pipeline is installed at ambient temperature, it will expand when the operating temperature rises, so the skin should be pre-compressed a little during installation, so that the compensation amount is enough. This value is given by the design engineer, so don't guess for yourself.
• Flange centering: The flanges on both sides of the compensator must be aligned parallel with a deviation of no more than 2mm. If forcibly straightened with bolts, the skin will be unevenly stressed, the angular deformation will exceed the limit, and the life will be directly cut in half. Besides, we have to talk to the people in our stationFlue gas baffle door、Round flapper doorIn case of cooperation, pay attention to the compensator to be installed downstream of the baffle door (according to the flow direction of the medium), so that in case of skin leakage, it will not directly rush to the sealing surface of the baffle door.

Once the installation is done, check again-is the tie rod removed? Is the flange bolt torque uniform? Is the pre-stretch amount in place? If this step is done wrong, the compensator will basically hang up. Tsk, we have seen too many cases of equipment being scrapped on site because we forgot to remove the tie rod.

How long is the lifespan? How to fix it if it is broken?

Under normal operating conditions, the design life of the skin non-metallic compensator is 3 to 5 years. But the actual life span is related to the conditions you serve-the medium contains acid and alkali, frequent start and stop, and large temperature fluctuations, so the life span will be shortened to one and a half years; If it is used to clean air ducts, it may be seven or eight years. How do you tell if it's time to change it? Two tricks on-site inspection: first, see if there is any bulging, delamination and cracking on the skin surface; Second, see if the flange bolt is loose (loose means that the skin creeps and deforms). As long as you find bulging or layering, change it quickly and don't delay it.

The first step is to loosen the flange bolt and remove the old broken skin (take care to protect the flange sealing surface). Step 2, clean the flange surface and apply temperature-resistant sealant (silicone rubber or fluorine rubber glue). The third step is to put on the new skin, pay attention to the direction not to install the reverse, and use the diagonal tightening method when tightening the bolts, and the torque is uniform. The whole process is done in half a day, and you don't have to stop production for too long. If there are multiple compensators in the pipeline system, it is recommended to replace them all at once, so as to avoid problems one by one in the future.

From our stationrubber compensatorAndRubber PTFE compensatorIt also belongs to the non-metallic category, but the structure is slightly different-the rubber compensator focuses on vibration damping, and the skin compensator focuses more on high temperature and corrosion. Which one to choose? It depends on the working conditions.

Find out if you want a non-metallic compensator

Two days ago, I met a customer who was anxious to buy a "large-diameter non-metallic compensator" on the phone. As a result, after chatting for ten minutes, I found out that he was using a rubber compensator on the spot, and the temperature had soared to 350℃-the rubber had been carbonized early. I've seen this happen a lot.

Non-metallic compensators (also called fabric fiber expansion joints) are completely different from metal bellows and rubber compensators. The metal bellows absorbs displacement by deformation of stainless steel corrugated body, and has high pressure resistance but limited compensation; Rubber compensator relies on rubber elasticity, corrosion resistance but fear of high temperature and high pressure. WhileNon-metallic compensatorThe main body is flexible loop belt (multi-layer fabric + fluororubber/silicone coating), and the frame is metal, which is specially designed to deal with high temperature, large displacement and low pressure working conditions. If you buy the wrong one, it will leak at least and the pipe will be broken at worst.

Then how to judge? Look at three indicators: the temperature is higher than 150℃, the pressure is lower than 0.1MPa, and the pipe diameter exceeds DN500-it is the home field of non-metals. If you don't believe me, check JB/T 12235-2015. It is clearly written in the standard.

The first step of model selection: medium, temperature and pressure, you dare to fill in these three numbers, and you will wait for problems later

The most common mistake made by purchasers is to say "probably" and "almost" when reporting parameters to suppliers. Tsk, if one of these three numbers is not accurate, the compensator will not be able to use it.

• Medium: Acidic condensate in the flue gas? The outer surface of the band must be filled with a PTFE anti-corrosion layer. Contains hard particles? The inner layer must be made of wear-resistant ceramic cloth. We have them in our stationNon-metallic expansion joint (fabric fiber expansion joint)Is specialized in dealing with this kind of working condition.
• Temperature: Don't just report "working temperature", but report "maximum instantaneous temperature". The instantaneous temperature of desulfurization flue in many power plants can rush to 400℃, and the ordinary silicone ring belt burns through directly. Here, you must confirm the number of layers of the belt material and the temperature gradient of the supplier-such as a three-layer structure: outer layer of fluororubber (250℃), middle layer of fiberglass cloth (550℃), inner layer of steel wire mesh (support).
• pressure: The design pressure of non-metallic compensator generally does not exceed 0.1MPa. If you report 0.2MPa, you have to use a metal frame with reinforcing ribs, or simply change the metal expansion joint.

You ponder, these three numbers are filled in, do you have to spend money on rework later?

When the caliber is large, the structure has to change accordingly: What is the difference between rectangular and circular design?

Many people think that circles and rectangles are just different in shape, and the choice is universal-a big mistake. After the caliber exceeds 1 meter, the design logic of the two structures is completely different.

Circular non-metallic compensator: Mainly used in round pipe flue, the ring belt is annular integral, and the flange is usually angle steel or flat steel coiled. Because the force is symmetrical, the band thickness can be relatively thin. However, it should be noted that the large diameter circular guide tube must be designed to be tapered, otherwise the fluid will scour the inner wall of the ring belt.

Rectangular non-metallic expansion joint: Square pipe flue is commonly used, such as sintering machine head in steel plant. The biggest problem with rectangular structures isCorner stress concentration。 The loop belt is easy to tear at the corner, so it should be molded with a special die when manufacturing, or a reinforcing layer should be added at the corner. In addition, the four sides of the rectangular frame should be designed separately with pressing strips, which can't be simply rounded.

If you are purchasing large diameter rectangular compensator, be sure to ask the supplier: How to seam the corner band? Is it a lap or a docking? Has the lap length exceeded 50mm? These details determine whether it will last five years or eight months.

What are the hard indicators hidden in the national standard JB/T 12235-2015 that purchasers must know?

Many purchases regard national standards as decorations. JB/T 12235-2015 "Non-Metallic Expansion Joints" I pick a few must-see hard requirements:

• Belt withstand voltage test: Before leaving the factory, an air pressure test of 1.5 times the design pressure must be done, and the pressure must be kept for 5 minutes without leakage.
• Displacement compensation amount mark: The allowable compensation amounts in axial, transverse and angular directions must be clearly marked on the expansion joint. Don't look at the unmarked.
• Flange flange length: The connection between the non-metallic ring belt and the flange must be flanged, the length of the flange shall not be less than 20mm, and fixed by pressing strips. The flanges are too short, and the ring band will slip out of the flange groove during the run.

By the way,Expansion joints and compensators are the same thing, it is also mixed in the standard, so you don't have to worry about the title problem.

Don't just look at the price: the supplier's manufacturing process, the number of layers of belt material, and the length of flange are the real skills

And guess what? Many small factories report bargains, the circle belt has only two layers of cloth and one layer of glue, and the flange flange is folded by 10mm. Loaded it up and ran for three months, leaked. You spend another amount of downtime changing it, which is three times more expensive than buying good goods.

How to judge the manufacturer's real ability? Ask three questions:

1. Number of belt material layers: At least three layers, the inner layer is high-temperature resistant fabric, the middle layer is heat insulation, and the outer layer is sealing anti-corrosion layer. What is the thickness of each layer? What grade of silicone/fluorine is used?
2. Flange flange length: The measured flange side length is not less than 25mm before it is considered qualified. Have you installed stainless steel strips at the flange? Is the spacing of the beading screws not greater than 150mm?
3. Frame welding process: Do corner welds of large-diameter frames do flaw detection? Did you do overall hot dip zinc anti-corrosion? These determine whether the frame will rust out within two years.

By the way, this kind of product in our site is calledRectangular non-metallic expansion joint, andNon-metallic expansion joint (fabric fiber expansion joint)All have been verified by multiple working conditions.

Acceptance of arrival and installation precautions: direction of guide tube, whether the tie rod nut should be removed or not, and how to pre-stretch

• Direction of guide tube: The guide tube must be directed downstream of the medium flow direction. When installed backwards, the fluid directly impacts the loop belt, and the hole is pierced in one week. There are generally arrows on the expansion joint to mark the direction, and if there is no mark, let the manufacturer make up.
• Do you remove the tie rod nut or not?Transport tie rods are used to prevent deformation during transportation and must be loosened or removed before installation. But note: Some designs have limit rods, and that one can't be removed. How to distinguish? Read the instructions. Really confused, just ask the manufacturer: "Does the screw of the expansion joint need to be disassembled?" Generally, the manufacturer will tell you clearly.
• Pre-stretching: The compensator needs to be pre-stretched to the specified length if there is a cold tightening requirement when the pipe is installed. The pre-stretching amount is carried out according to the design value, and after stretching, it is fixed with temporary supports, and then released after the pipe is connected. Don't pull blindly, pull the headband strap and scrap it directly.

Also, check whether the flange surface is flat and the sealing gasket is centered when installing. When tightening the bolts, tighten them diagonally and sequentially, and the torque should not be too large to prevent crushing the flange.

Purchasing is three things in the final analysis

First, confirm the medium/temperature/pressure, don't pat your head; Second, selecting the right structure according to the caliber and shape; Third, inspect the goods and check the process details. Do these three things,How To Buy Large Caliber Non-Metallic Compensator?This question is a sure thing.

If you are unsure of anything, you can directly compare the product information of this site, such asNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion jointThe pages all have detailed parameters. Don't be afraid to ask, asking clearly saves money than buying the wrong one.

How harsh is the working environment of a high temperature expansion joint? The bellows itself can't carry it

Tell me the truth. Two days ago, the equipment supervisor of a cement plant called me and said that the expansion joint on their kiln tail flue cracked in less than four months. I asked him did you make castables? The other party was stunned for a moment. "You still need castables? Isn't the bellows able to withstand high temperatures?"

The flue gas temperature is often 800℃-1100℃, and some even rushes to 1300℃ instantaneously. There are also a lot of dust and corrosive gases (SO₂, NO₂) trapped in the medium. The stainless steel materials used in the bellows itself, such as 304 or 316L, will experience carbide precipitation, intergranular corrosion and cliff-like decrease in strength under long-term high temperature-this is called high-temperature failure. Even if you use a nickel-based alloy like Inconel 625, the surface temperature exceeds 650℃ and you have to stop.

Streaking bellows are consumables under high temperature conditions. What about that? It must be dressed with a piece of "armor"-castable.

The first layer of protection of castables: thermal insulation to prevent high temperature failure of corrugated pipes

Castables are first and foremost thermal insulation. Its thermal conductivity is typically between 0.3-0.8 W/m K, while the thermal conductivity of corrugated stainless steel is above 15 W/m K. What's the meaning? Castables can block most of the heat radiation and heat conduction. For example, we giveCorrugated expansion joint for power station industryWhen designing castables, the inner surface temperature should be controlled below 200℃, so that the yield strength of bellows can be maintained at the design value.

At the expansion joint at the outlet of the induced draft fan of a thermal power plant, the temperature of the outer wall of the bellows before castable was 480℃, and after 80mm thick lightweight mullite castable was placed, the outer wall dropped to 180℃. The lifespan has been pulled directly from 9 months to 5 years and still hasn't broken. Thermal insulation can't pass, and the rest is all nonsense.

The second layer of protection: diversion and anti-scour, blocking the wear of high-speed dusty airflow

You think only the heat is the killer? High-speed dusty airflow is the real "taking your life". The flow rate of the air duct on the cement production line is often 18-25m/s, which is mixed with clinker particles. When that thing hits the bellows, it is like sandblasting. The geometric structure of the peaks and valleys of the bellows itself is a "ash nest", and the dust accumulates in the valleys and rubs them repeatedly, and wears them out quickly.

After the castable is hit, a smooth flow channel will be formed on the inner side, without groove dead angles, and the airflow will pass smoothly. At the same time, the wear resistance of castable is 3-5 times that of ordinary carbon steel (high aluminum castable, Mohs hardness above 7). OurMetal Corrugated Expansion Joints in Cement IndustryBefore leaving the factory, the diversion design is done, but the diversion tube plus castable is the double insurance-the diversion tube blocks most of the frontal impact, and the castable fills the gap to prevent vortex erosion.

Think about it, if you don't hit castable, how fast will the bellows be worn out at the crest? We have measured that the unprotected bellows perforates in an average of 3 months at the outlet of the cement mill. After beating the castable, carry it for at least two years.

The third layer of protection: structural support and anti-corrosion, isolating corrosive media from the bellows

Acidic condensation in high-temperature smoke is a hidden killer. In some projects, the temperature drops below the dew point after the furnace is shut down, and SO₃ and water vapor combine to form sulfuric acid, which adheres to the inner wall of the bellows. Stainless steel is most afraid of chloride ions and concentrated sulfuric acid, pitting corrosion and stress corrosion cracking follow one after another. Castables are alkaline or neutral materials (such as corundum) that keep acidic media out of the bellows.

Additionally, the castable also provides structural support. Especially for large fluesNon-metallic expansion joint(Fabric fiber expansion joint), although it is temperature-resistant but has poor rigidity, the castable can fix the shape and prevent negative pressure deflation. InHigh temperature axial expansion jointThe castable layer can share a part of the axial pressure and reduce the stress concentration at the root of the bellows. It can be said that castable is not only a protective layer, but also a part of the load-bearing structure.

How to beat castables to be qualified? Construction details and material selection determine life

After discussing "why to fight", let's talk about "how to fight" next-there are more people stepping on pits here.

Material selection:Select different materials for different working conditions. High aluminum castable for flue gas temperature ≤800 DEG C; Corundum mullite for 900-1100 DEG C; High temperature resistant castables containing silicon carbide must be used above 1200℃. Don't listen to the manufacturers saying "general-purpose type", that's all fooling laymen. We giveDesulfurization flue gas baffle doorFor matching expansion joints, we should also consider acid resistance, and choose castables combined with low calcium aluminate cement.

Construction Details:First, the anchors must be welded firmly, 304 stainless steel anchor nails, with a spacing of less than 200mm, are distributed in a plum blossom shape. Second, before pouring, the bellows surface must be removed from rust and brushed with anti-oxidation coating. Third, curing-it can't be baked immediately after pouring. It must be naturally cured for 24 hours before baking according to the temperature rising curve (usually, the temperature is raised to 600℃ every 50℃/h for 4 hours). If the curing is not in place, the castable will crack and fall off, and dry for nothing.

Thickness control:Not that the thicker the better. Too thick will increase the weight and affect the compensation ability of the expansion joint. Experience value: 40-60mm in the center, and the edge can be as thin as 20mm. Use special molds to ensure uniform thickness. In addition, the end of the guide tube should leave an expansion gap, otherwise the castable will bend the top of the guide tube as soon as it expands.

To put it bluntly, playing castables looks simple, but in fact, it tests the understanding of working conditions and the seriousness of construction. We have seen too many customers buy castable paste by themselves, and the result is that slag falls in two months. I regret that I didn't find a professional manufacturer to mix itUniversal corrugated expansion jointThe castable scheme of.

Why Should High Temperature Expansion Joints Be Castable?Because the bellows is a "crispy skin" under the attack of high temperature, erosion and corrosion, the castable is the human shield that can carry and fight. No pouring, compulsory within six months; If you water it right, you don't have to worry about it for five years.