Specialized in manufacturing compensators, expansion joints, baffle doors

Find out how the outer skin is broken

The outer skin of large non-metallic compensators is damaged for the same reasons: aging, mechanical scratches and media corrosion. But which one is specific, directly determines how you fix it later. For example, if high-temperature flue gas runs in the flue gas pipeline for a long time, coupled with the erosion of acidic gases (such as SO₂ and H₂S), the skin will gradually become brittle and hard, and fine cracks will appear on the surface-this is called aging damage. If pulverized coal or particulate material is transported in the pipeline, high-speed scour will partially wear the skin, forming small holes or strip-like scratches-this is mechanical damage. There is also chemical corrosion, such as the wet flue gas behind the desulfurization tower. The pH value of the condensate is low, the skin is soaked, and the surface is blistered and delaminated.

Are there any curls around the edges? Did it change color? Is the interior insulation cotton exposed?If the skin has become brittle as a whole and drops slag when touched, it is of little significance to repair it. It is more cost-effective to directly replace the whole non-metallic expansion joint (fabric fiber expansion joint) or rectangular non-metallic expansion joint. Repairs are only valuable if they are localized piercings or scratches.

What preparation work can't be saved before patching?

Safety comes first. Shutdown, pressure relief, power failure – these three steps are the bottom line. Non-metallic compensators are usually used in the environment of high temperature, dust and corrosive media. If the knife is moved without relieving pressure, an accident may occur. After the pressure relief is completed, wait for the pipeline temperature to drop to the ambient temperature (generally lower than 40℃), and then use a blade to clean all the dust accumulation, loose fibers and residual glue layer in the damaged area to expose the fresh substrate surface. The surface should be dry without water stains or oil stains.

In terms of materials, the commonly used accessories in our station are fluororubber cloth, silicone cloth and stainless steel wire mesh, which can be selected according to the same color and material of the original skin. If we can get a sample of the old skin on site,Be sure to measure the total thickness and number of layers。 The outer skin of non-metallic expansion joints is usually a multi-layer composite structure, such as the outermost layer is fluororubber cloth, sandwiched with aluminum silicate fiber cotton in the middle, and the inner layer is reinforced with stainless steel wire mesh. If the thickness is poor, the strength of making up is not enough, and it is easy to tear twice in the later stage.

Hands-on repair, divided into three common situations

Small area perforation (less than 50mm in diameter)

Cut a piece of composite material 30-50mm larger than the damaged area, and stick one layer inside and outside. The inner patch is attached to the inside of the pipe (sticking through the opening), and the outer patch is covered on the outside. High-temperature vulcanized glue is used for adhesive, and epoxy resin glue can be used if it is not available on the spot, but attention should be paid to the curing time. After the patch is attached, press the edge with mechanical strips (such as stainless steel flat strips), fix them with bolts, and apply a layer of sealant on the back of the strips in advance. Pay attention to the ambient temperature: when it is lower than 5℃, the adhesive effect will be discounted, so you have to preheat the repair area to above 15℃ with a hot air gun in advance.

Large area tear

If the tear length exceeds 200mm, or there are multiple tears, the double-sided patch will not be enough. It is necessary to cut a brand new skin, an area larger than the damaged area,Lap width at least 100mm。 Note: The non-metallic compensator is a multi-layer structure. Each layer should be staggered, and the overlap seams of all layers should not be stacked together, which will create weak points. When cutting a new skin, stick it layer by layer according to the lamination order of the original skin-first stick the inner fiber layer, then stick the middle insulation layer, and finally stick the outer fluororubber cloth. Each layer is compacted with a roller to drain air bubbles. Finally, tighten with strips and bolts, and control the spacing of strips at 150-200mm. Don't forget to apply high temperature resistant sealant on the back of the strip and around the bolt holes to prevent air leakage.

Edge breakage

Broken edges are easiest to fix. The compensator presses the skin tightly on the metal flange by the pressing bar. If the edge is broken, the old pressing bar is directly removed, the damaged section is cut off, a new skin is replaced and inserted again, and then the pressing bar is used to screw the bolts. During operation, pay attention to the new skin to leave sufficient flange length, at least 50mm, the press strip should be evenly pressed, and the torque should be according to the recommended value given by the manufacturer (generally, the torque of M12 bolts is 50-70N·m).

Don't be in a hurry to turn it on after replenishing

After the repair work is finished, do an airtightness check first: get some soapy water and spray it on the repair area and the gap between the strips, turn on the low-pressure air source (or blow it with compressed air) to see if there is any bubbling. Conditionally, do a low-pressure airtight test, control the pressure at about 1.2 times of the design pressure, and hold the pressure for 10 minutes without dropping the pressure. Check the torque of the strip bolt again-the torque attenuation is the main cause of later leakage, especially the thermal expansion and contraction under high temperature conditions can easily lead to bolt loosening.

Finally,Record repair location, date, material model used on equipment ledger。 Focus on this patch area the next time you shut down for maintenance, because the life of patches is usually only 60% to 80% of the original skin. Don't expect to do it once and for all.

When should I just replace it with a new one?

Patching is not a panacea. If the following occurs, don't hesitate to replace it with a brand-new non-metallic compensator or rectangular non-metallic expansion joint:

• The whole skin has reticular cracks, which feel brittle and breaks as soon as it is broken-indicating that the substrate has aged in an all-round way, and it will break if it is repaired here and there.
• The internal insulation cotton layer has rotted to black slag, or it absorbs water seriously-the failure of the insulation layer will cause the skin to be directly exposed to high temperatures, and the life will be shortened.
• There are more than three leakage points, and the spacing is less than 500mm-this porous state indicates that the skin has been fatigued in a large area and cannot be repaired.

The non-metallic expansion joints (fabric fiber expansion joints) and rectangular non-metallic expansion joints in our station are shipped from the factory according to JB/T 12235-2015 standard, and the warranty period and life are much more reliable than those of repair parts. Don't save hundreds of dollars, and you lose tens of thousands at a time when you shut down. Do you think that's true?

1. Let's start with the structure: What is the difference between non-metallic waveform compensator and metal expansion joint?

Many people think "non-metal" is a cheap substitute when they hear it, but it's just the opposite. Non-metallic waveform compensator (also called in our stationNon-metallic expansion jointOrFabric fiber expansion jointInstead of a metal bellows, the main body is a composite of multiple layers of flexible materials-usually including silicone/fluororubber coated fiberglass cloth, PTFE film, ceramic fiber insulation, plus stainless steel wire mesh reinforcement. This structure gives it a natural ability that a metal expansion joint can't do:Barely transmitting thrust。

Think about it, although the metal bellows can absorb displacement, it will still produce elastic reaction force itself, which has additional requirements for the pipe support; The non-metallic compensator depends on the flexible deformation of the fabric, and the reaction force is very small, so it is especially suitable for those thin-walled pipelines or equipment interfaces that can't bear large thrust. Two days ago, there was a customer who made a dust removal system. The wall thickness of the pipe was only 3mm. Every time he drove with a metal expansion joint, the bracket was crooked and replaced with oursRectangular non-metallic expansion jointThe problem is solved directly.

2. Temperature resistance and corrosion resistance: What working conditions must it be?

Strong acid and alkali corrosion and ultra-high temperature flue gas. But nonmetallic waveform compensators happen to play in both fields. From our stationRectangular non-metallic expansion joint、rubber compensator、Rubber PTFE compensatorAll are targeted designs: the outer layer is made of polytetrafluoroethylene (PTFE) or special fluororubber as an anti-corrosion barrier, and the inner layer is made of ceramic fiber or aluminum silicate cotton as heat insulation. The long-term temperature resistance can be above 1000℃ (such as the smoke duct of power plants).

There is a customer in the cement industry. The temperature of the flue gas at the tail of their kiln fluctuates greatly, and it also contains sulfur. The metal expansion joint is perforated in one year. Replace it with oursMetal Corrugated Expansion Joints in Cement Industry？ Of course, it works, but the cost is high-later, non-metallic expansion joints were used, which saved half the cost and prolonged the life. The principle is simple: the non-metallic material itself is corrosion resistant and does not produce stress corrosion cracking.

3. Displacement compensation ability: large displacement and multi-direction are its home field

Metal expansion joints are usually good at axial displacement, while lateral and angular displacement depend on complex structures (such as compound hinge type and universal type). What about non-metallic waveform compensators? It is itself a piece of "soft connection" that can absorb axial, lateral and angular displacements simultaneously-as long as the structure is properly designed. For example, ourRectangular non-metallic expansion jointIt is often used in rectangular flues of power plants and steel plants, and can compensate for the deviation in various directions caused by thermal expansion and contraction.

Moreover, its compensation amount can be made very large, and some can reach more than 100mm. To reach this amount, a metal expansion joint of the same size may have to be made into several waves or even with a tie rod. So you have to ask what is the biggest feature of non-metallic compensators? One word:soft。 It can resist large displacements and is not afraid of multiple directions.

4. Hidden advantages of installation and maintenance: light, easy to change, and not afraid of installing wrong

Everyone who does engineering knows that the fault tolerance rate of equipment installation is very important. Non-metallic waveform compensators are usually 30%-50% lighter than metal expansion joints of the same caliber, which can be moved by one person, and are convenient for on-site welding or flange connection. More importantly, in case the pre-stretching is not accurate during installation, or the pipeline deviates, the forced adjustment of the metal expansion joint may screw the bellows; The elasticity of non-metal is good, and it can still work if it is slightly biased.

And in our product structure, likerubber compensatorAndNon-metallic expansion jointThey are all modular designs, and the inner lining, insulation and outer cladding can even be replaced separately-which layer is broken and which layer is replaced without dismantling the whole pipe. Don't underestimate this. The maintenance window period of power plants is so short. It may take half a day to weld a metal expansion joint. Once the non-metal one is tightened with bolts, it will take half an hour to get it done.

5. The easiest pit to step on when selecting a model: don't treat non-metals as a panacea

Having said so many advantages, I have to pour some cold water. Non-metallic waveform compensators do not work everywhere. First of all, its pressure bearing capacity is inherently weak, and it is generally used in low-pressure systems (usually below 0.1MPa, and higher special designs can reach about 0.5MPa). If you are steam pipes, high pressure oil pipes, honestly choose metal- -like oursUniversal corrugated expansion jointOrHigh temperature axial expansion joint。

Secondly, the fatigue life of non-metallic compensators is not as good as that of metal bellows-the fabric layer always has an aging period, and the general design life in the industry is 10-15 years, while the metal expansion joint can reach more than 20 years under ideal working conditions. In addition, some media contain hard particles (such as pneumatic ash transportation pipelines), and high-speed scour will wear the fabric. At this time, wear-resistant lining or direct metal has to be added. To sum up: When selecting the model, see the four parameters of pressure, temperature, medium and displacement clearly. Don't just listen to "non-metal is cheap" and use it indiscriminately. We have so many product lines in our station, fromNon-metallic expansion jointToHigh temperature axial expansion joint、Universal corrugated expansion joint, is to let you match on demand.

All right,What are the features of non-metallic waveform compensator?Simply put, it is: flexible structure, high-temperature corrosion resistance, multi-direction large displacement, worry-free installation and maintenance, but low pressure and limited life, so you must look at the working conditions when selecting the type. If you have a specific project on hand and aren't sure which one to use, feel free to flip through the product page on our site- -Rectangular non-metallic expansion joint、rubber compensator、Rubber PTFE compensatorThey all have detailed parameters, so just take your seat.

Let's break it apart from the name

The compensator is the expansion joint, and they are the same thing. Non-metallic compensator, to put it bluntly, is an expansion joint made of flexible materials such as fabric fiber and rubber. The kind used in the flue of electrolysis plant, which is specially used to deal with the thermal expansion and contraction and pipe displacement caused by high temperature and corrosive flue gas. You run to the scene and take a look, and the bulging, cloth-bag-like thing at the flue interface is it. Don't underestimate this thing. If you choose the wrong thing or use it out, you will lose tens of thousands of dollars at a time of downtime.

Why must electrolysis plants use non-metals?

The metal compensator can't bear it at all under this working condition-the flue gas contains hydrogen fluoride and sulfur dioxide, and the metal bellows will corrode and perforate in a few months at high temperature. I have seen a case where a metal bellows was installed in an electrolysis plant. In less than half a year, yellow smoke began to emit from the weld. When I removed it, it was as thin as paper. Non-metallic multi-layer composite structures, such as fluororubber + glass fiber + polytetrafluoroethylene, can not only withstand the temperature to 300℃ or even higher, but also withstand acid-alkali corrosion. Moreover, it has good elasticity, large compensation amount, and can easily handle the thermal expansion and contraction of the pipeline. Do you say, is it comparable to metal?

Structurally, it is completely different from the metal compensator

There is no ripple, but it is the bending of the fabric fiber layer and the elastic deformation of the rubber layer to absorb the displacement. Typical products like this siteNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion joint, the rectangular section just matches the rectangular flue of the electrolysis plant, the installation flange connection, and the middle is a sandwich fabric. A guide tube has to be added inside to prevent high-speed smoke from directly washing the fabric layer-this point is ignored by many novices, and the consequence is that the fabric layer is blown away and has to be replaced in three months.

Type selection is a technical job

Temperature, pressure, media composition, flue size, required compensation amount, a parameter wrong will wait for air leakage. For example, if the temperature exceeds 250℃, conventional rubber will not work, and fluororubber or pure PTFE layer will be used. At this timeRubber PTFE compensatorAndPTFE compensatorIt would be more appropriate. The pressure is generally low, but the flue of the electrolysis plant runs under negative pressure, so the sealing requirements are high, so the strips and sealing rings should be carefully selected. Two days ago, I met a customer, and randomly bought a general-purpose corrugated expansion joint and installed it. When the negative pressure was sucked, the sealing ring was directly deflated, and the yellow smoke came out, so I had to stop and change it. So don't try to save trouble, the parameters have to be checked one by one.

There is a pit in installation and maintenance that many people step on

Don't hurry to dismantle the limit screw when the non-metallic compensator leaves the factory. It is used to prevent excessive stretching during transportation and installation. After all the pipes are in place and the bolts are tightened, the screw is loosened to allow the compensator to expand and contract freely. This order is reversed, and the compensator is pulled and deformed before it is used. In addition, check the fabric layer regularly for bulging and cracking, especially on the side near the electrolyzer. If you find small damage, make up it in time. Don't wait until the whole flue emits yellow smoke before repairing it. At that time, the downtime loss will be great. It is recommended to inspect once a quarter, and scan the surface temperature with an infrared thermometer to see if there are any local overheating spots-this can find the problem of falling off or internal blockage of the guide tube in advance.

Find out first: What is the difference between non-metallic compensator and metal compensator?

Many customers ask as soon as they come up, "Isn't the compensator just a metal bellows?" Alas, this misunderstanding is big. The materials used in non-metallic compensators (also called non-metallic expansion joints and fabric fiber expansion joints) are glass fiber, silicone cloth and polytetrafluoroethylene, which are not deformed by metal corrugations at all. Its core ability is to absorb the thermal displacement of the pipeline in all directions-axial, transverse and angular directions, and the thrust on the pipeline is particularly small. Think about it. In the big flue of the power plant, when the temperature rises, the iron pipe can jump for several centimeters. If the metal bellows is carried hard, the thrust is so strong that the bracket can be crooked. What about non-metal? Soft connection with almost zero force. So,What does a nonmetallic compensator do?The first is "large displacement, low thrust".

High temperature resistance and corrosion resistance are its special skills

Commonly used non-metallic materials, silicone cloth can withstand more than 300℃, and polytetrafluoroethylene (that is, the PTFE-lined and rubber PTFE compensator in our station) is stable to strong acid, strong alkali and desulfurization flue gas. Look at the pipe connected behind the desulfurization flue gas baffle door. The medium is wet and acid, and the metal bellows will be corroded in less than a few months. Replace withNon-metallic expansion joint (fabric fiber expansion joint)For three or five years. And it is not afraid of dust accumulation, rectangular pipes (likeRectangular non-metallic expansion joint) Especially easy to use. Two days ago, I met a customer from a cement factory, saying that the high-temperature air duct at the end of their kiln had been leaking ash with metal before, and it was directly cured with non-metal. Therefore, the second function: in the harsh working conditions of high temperature, corrosion and dust, non-metal is the only reliable choice.

Reduce vibration and noise, and solve the sealing problem by the way

When such equipment as fans and compressors is turned on, the pipes shake like sieves. Metal compensators can reduce vibration, but they also pose a risk of metal fatigue. Because the material of non-metallic compensator is soft, it is born to absorb vibration, and it can eat a lot of noise. And its sealing performance is critical-a lot of flapper doors (Round flapper door、Double-sealed single-axis circular baffle door) Soft connections are required both front and back to ensure zero leakage. When installing with other products in the station (such asElectric plug-in insulation door) cooperation, the non-metallic section just plays the role of flexible transition. And guess what? Some customers specifically requested a non-metallic compensator insteadrubber compensatorBecause the upper limit of pressure and temperature resistance of fabric fibers is much higher than that of pure rubber. The third function: vibration and noise reduction plus high-grade sealing, three birds with one stone.

Actual scene: power station, cement, desulfurization, none of them can run away

It's useless to just talk about theory. Let's talk about real working conditions. Power station industry: The flue from the boiler outlet to the dust collector, with large temperature change and large pipe section, can only be usedRectangular non-metallic expansion joint。 Cement industry: raw material mill, kiln tail high temperature fan, airflow contains dust, useNon-metallic expansion joint (fabric fiber expansion joint)Most stable. Desulfurization system: inlet and outlet of absorption tower, the medium is gypsum slurry and wet flue gas, which is highly corrosive. The non-metal compensator is equipped with PTFE lining, and its life is three times longer than that of metal. Look at the product list in the station, "Desulfurization flue gas baffle door”、“Corrugated expansion joint for power station industry”、“Metal Corrugated Expansion Joints in Cement Industry"There are all, but the non-metallic models that truly withstand corrosion and high temperature are the key connection points of these systems. Article 4 Function: Specializing in the treatment of stubborn diseases in the industry of high temperature, corrosion and large displacement.

Do not step on pits when selecting models: pay attention to temperature, pressure and displacement

Many customers choose non-metal according to the parameters of metal compensator, and the result is broken in a few months. The weakness of non-metallic compensator is that the pressure bearing capacity is not as good as that of metal, and it is generally only used in flue duct systems with low pressure (below 0.1MPa). The temperature should be distinguished between the medium temperature and the surface temperature. The fabric fiber can carry it to 1000℃, but the lining insulation layer should be calculated well. In terms of displacement, non-metals can be very large (such as 100mm in the axial direction and 50mm in the horizontal direction), but the flange connection and guide tube need to be designed well-you refer to the question and answer on "Specific Function of Expansion Joint Guide Tube" in the station, and non-metals also have to be equipped with guide tubes, otherwise the airflow will directly scour the fabric lining and wear it out quickly. Also, when installing, do not tighten the fastening bolts too tightly to prevent crushing the non-metallic sealing surface. Remember one thing: non-metallic compensators are designed according to the idea of "soft connection", so don't let it suffer. Fifth Function Tip: Choose the right one, it is more durable than metal.

The metal expansion joint, to put it bluntly, is a flexible joint, which absorbs the thermal expansion and contraction of the pipe by the deformation of the bellows. But if you think it can carry any working conditions, it will have to roll over sooner or later. Two days ago, a customer asked me why the expansion joint he installed leaked after only three months. When I removed it, the bellows cracked like a cracked riverbed. What's the problem? When you select a model, you just stare at the compensation amount, and everything else is ignored. Let's break it down today,Disadvantages of Metal Expansion Joints?Where the hell is hidden.

1. Fatigue life: Bellows are not perpetual motion machines, and the number of cycles is the hard threshold

Many people think that the expansion joint can be used for a lifetime, so they dream. Every time the bellows expands or contracts, a micro-damage accumulates inside the material. The fatigue life written in the design standard is usually between a thousand and several thousand cycles-this is not blindly determined, it is measured. If you think about it, steam pipes start and stop once a day, 365 times a year, and thousands of times in three years. If the circulation frequency is high and the displacement amplitude is large, the life time will be cut in half directly.

What about that? Not for you not to use it, but to figure it out. First calculate the total thermal displacement of the pipeline, and then see whether the working condition belongs to low frequency or high frequency. Like those used in the power station industryCorrugated expansion joint for power station industryThe number of cycles requirements must be specified when designing. Don't buy the general-purpose corrugated expansion joint to make do, the fatigue life is not matched, and it is too late to cry later.

2. Media compatibility: There are boundaries in corrosion resistance, so don't use it as a panacea

Stainless steel bellows corrosion resistant? That depends on the medium. Working conditions with high chloride ion content, such as desulfurization flue gas and seawater, 316L will still pitting for you. Two days ago, a case in a chemical plant, usedMetal hoseThrough hydrochloric acid, it leaked within a few months. ChangePTFE-lined hoseOrPolytetrafluoroethylene compensator, instead, lasted for more than two years.

Before the selection, you must get the media composition list, and the temperature, concentration and flow rate must not be less. High-temperature flue gas contains sulfur, ordinary stainless steel can't bear it, have toHigh temperature axial expansion jointOr non-metallicNon-metallic expansion joint (fabric fiber expansion joint)。 Don't gamble on experience, the corrosion boundary is much narrower than you think.

3. Installation and maintenance: pull rod, guide tube, pre-stretching, one step wrong, one step wrong

Installing this thing is really not just a few screws. Let me ask you, what is the tie rod on the expansion joint for? Many workers removed the tie rod directly at the scene, thinking it was a transportation fixture. As a result, as soon as the pipe heated up, the bellows was pulled to the head and torn directly. The correct way is: after installation, adjust the tie rod nut so that the bellows is in the designed position-pre-stretched or pre-compressed, according to the cold tightness requirements of the pipe system.

Let's talk about the guide tube, which not only prevents scour, but also affects the flow direction of the medium. If it is installed backwards or missed, the high-speed fluid rushes directly into the bellows, vibrates and erodes, and the hole will be perforated in less than a month. We have a client usingMetal Corrugated Expansion Joints in Cement IndustryBecause of the reverse installation of the guide tube, three were replaced in three months.

As forCorrect installation method of expansion joint of large tie rodThe tie rod absorbs the internal pressure thrust. During installation, the nuts at both ends of the tie rod should be tightened in place, and the bellows should not be pressurized-this work has to be done step by step according to the instructions, and don't take it for granted.

4. Cost account: Is one-time purchase cheap? Later replacement and downtime losses are deadly

The metal expansion joint itself is not expensive, and a general-purpose corrugated expansion joint may only cost a few thousand yuan. But what about a change? Pipeline venting, thermal insulation dismantling, replacement operation, re-pressurization, plus the loss of production shutdown, six figures per minute. Especially in chemical industry, power plants and cement lines, it is hundreds of thousands to stop a day.

So don't just focus on the money of expansion joints when choosing a model. Working conditions are bad, such as high temperature and high pressure, strong corrosion, rather buyExternal pressure single axial expansion jointOrStraight pipe pressure balanced expansion jointThis structure is more reliable. Although it is twice as expensive, it can be used for five years without accidents. Rubber compensators are cheap, right? However, as soon as the medium temperature exceeds 80℃, it will immediately become soft. You said chooserubber compensatorOr metal? Depending on the working conditions, calculate the general ledger.

5. Special working conditions do not work: vacuum, buried ground, large displacement scenes have to be requested to be smart

Metal expansion joints are not a panacea. Under the vacuum condition, the bellows has a large external pressure and is easily unstable. We have dedicatedSpecial hose for vacuumThe structure is different and can resist external pressure. You take an ordinary metal expansion joint to vacuum, and the bellows are like a flattened can, which is directly scrapped.

What about buried pipes? Buried directly in the soil, corrosion, soil pressure and uneven settlement, the metal expansion joint can't bear it at all. UsefulDirect buried (fully buried) type expansion jointOr simply use a sleeve typeSleeve type pipe expansion joint。 There are also large displacement scenarios-several hundred millimeters of lateral displacement, or axial displacement beyond the bellows limit, then you have to considerCompound hinge transverse expansion jointOrRotary compensatorDon't push on the universal model.

Alas, in the final analysis, choosing an expansion joint is not a set of formulas, but a solution of equations. Media, temperature, pressure, displacement, life, cost, every variable has to be counted. Picked right, it is a buffer for the plumbing system; Wrong choice, it's a ticking time bomb.