Specialized in manufacturing compensators, expansion joints, baffle doors

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.

What is a non-metallic compensator unit? Understand these parameters, selection is no longer confused

Two days ago, a customer came over with drawings and said, "I want a DN500 non-metallic compensator with a compensation amount of 300". When we looked at it, the pressure was written "6", and there was no unit. When asked later, he thought it was 6 kilograms, but the actual requirement was 0.6 MPa. By an order of magnitude, the fabric layer will bulge or even tear if done at 6kg. You see, just one unit didn't write it clearly and almost scrapped a piece of equipment. So today, let's thoroughly understand "what is the non-metallic compensator unit".

Direct answer: What units exactly do non-metallic compensators use?

Customers often ask "What is the unit of non-metallic compensator?" Actually, they ask two meanings: one is what to measure the product size (such as diameter DN and length mm), and the other is what to measure the compensation ability (such as displacement mm and pressure MPa). Simply put, common units are:

• Diameter:DN (nominal diameter), such as DN100 and DN200, but it is not the actual inner diameter, so you have to look up the table. This site'sNon-metallic expansion joint (fabric fiber expansion joint)In the product parameters, DN corresponds to the flange connection size.
• Compensation amount:Millimeters (mm), and transverse, axial and angular displacements are all in mm or degrees (°). Note: Although the angular displacement is degree, the rectangular expansion joint is sometimes marked with the angular displacement, which is actually the flange deflection angle.
• Pressure:Megapascals (MPa), occasionally with kilogram force (kgf/cm²), 1 MPa ≈ 10.2 kgf/cm². The old drawings say "6K" and "10K" are Japanese standards, 1K ≈ 0.098 MPa, so don't get confused.
• Temperature:degrees Celsius (℃), the upper temperature resistance limit of non-metallic fabric compensator is usually between 200 and 1200 ℃, depending on silicone cloth, fluorine tape or ceramic fiber. For example, the temperature resistance of ceramic fiber is 1260℃, but the long-term work can only reach 1000℃-if the unit is wrong, the equipment will be scrapped in three months.
• Overall Dimensions:The length, width and height are all in mm,Rectangular non-metallic expansion jointIt is also divided into inner diameter, outer diameter and flange hole pitch. On the drawing, both L and B are mm, and the diameter of the center circle of the flange bolt hole must also be in mm.

When you select the model, these units are marked on the manufacturer's drawings. Don't regard DN as inches or kgf/cm² as MPa. Is that the truth?

Why is the compensator destroyed when the unit is wrong?

• Nominal pressure:PN6, PN10 and PN16 (unit bar or MPa) are commonly used in national standards, but "6K" and "10K" written on the old drawings are Japanese standards, and 1K ≈ 0.098 MPa. I have seen a purchase, holding the drawing of PN10, and the default is 10kgf/cm² (about 0.98MPa). As a result, the supplier does it according to 1.0MPa. The understanding on both sides is actually similar, but if it is higher, there will be problems. In fact, the national standard PN unit is bar, 1 bar =0.1 MPa, and PN10=1.0 MPa.
• Displacement Amount:Axial compression and tension are used in mm, transverse displacement is also used in mm, but angular displacement is used in degree. Rectangular expansion joints are sometimes marked with angular displacement, which is actually the flange deflection angle. For example, you require ±50mm, which is actually determined by the number of folds of the multi-layer fiber cloth. If you need 100mm, you have to widen the folds or increase the number of layers, but the pressure loss will also change.
• Installation Length:Includes flange thickness and compensator effective length in mm. On the drawings of products in the station, such as "rectangular non-metallic expansion joint", L and B are both mm.

So how to avoid it? A suggestion for not rolling over: When confirming with the supplier, write all the units clearly, such as "installation length 300mm, axial compensation amount ±50mm, working pressure 0.1MPa, medium temperature 350℃". Don't come up and throw a number, people can't guess your mind.

What is the difference between the units of non-metallic compensators and metallic compensators?

Some people think that the difference is not big, but in fact, the emphasis is different. Metal expansion joints (e.g.Universal corrugated expansion joint、Direct buried (fully buried) type expansion joint) is more concerned about the pressure grade and the number of ripples, and the units are mainly MPa and wave number. The core of non-metal compensator (also called fabric fiber expansion joint) is temperature resistance and corrosion protection, so the temperature unit (℃) and acid-base concentration (%) are more important.

Used in the cement industryMetal Corrugated Expansion Joints in Cement IndustryMainly cope with high-temperature dust, the pressure is not high, but the temperature may reach 800℃. WhileNon-metallic expansion joint (fabric fiber expansion joint)In the desulfurization flue gas baffle door system, to withstand the acid gas after wet desulfurization, "SO₂ concentration ppm" has to be added to the unit at this time. And guess what? Many purchases only focus on pressure units, ignoring whether the unit marked by the upper temperature limit is long-term operating temperature or instantaneous peak. For example, the high-temperature axial expansion joint is specially designed for power stations, and the temperature is marked accurately to ℃. However, if it is an export order, Fahrenheit (℉) should also be careful-1000°F ≈ 538℃. If it is used as 500℃, the fabric layer will be carbonized.

Three unit pits that are easiest to step on during model selection

Pit 1: Nominal diameter DN ≠ outer diameter of flange.The rectangular non-metallic expansion joint of DN200 has an inner diameter of 200mm, but the diameter of the center circle of the flange bolt hole may be 240mm. If you fit the pipe according to the outer diameter of the flange, it can't be installed. So you must look at it when choosing a modelRectangular non-metallic expansion jointDrawings, mark the flange hole spacing clearly.

Pit 2: The conversion of pressure units is reversed.A customer said "I want PN10", and the supplier defaulted to 1.0MPa, which the customer understood as 10kgf/cm² (about 0.98MPa). The result was similar, but a higher level would cause problems. In fact, the national standard PN unit is bar, 1 bar =0.1 MPa, and PN10=1.0 MPa. If you run into the daily standard "10K", that's another story.

Pit 3: "F" and "C" in the unit of temperature.Export orders are common degrees Fahrenheit (℉), 1000°F ≈ 538℃, if used as 500℃, the fabric layer is carbonized. On-site productsHigh temperature axial expansion jointDesigned for power stations, temperature labeling is accurate to ℃. So when you get the order, look at the unit first, and don't think inertially.

Contrast this site'sNational standard for non-metallic expansion joints(JB/T 12235-2015), which clearly specifies the parameter labeling requirements. Or call the manufacturer directly, don't guess for yourself.

One sentence summary: the unit is the compass of type selection, wrong all bias

The unit system of non-metallic compensator is not complicated, with diameter DN, compensation amount mm, pressure MPa, temperature ℃, plus a flange bolt hole distance mm. However, behind the value of each unit, there are different material layer thicknesses, wave heights and layer numbers. For example, the compensation amount of "non-metallic expansion joint (fabric fiber expansion joint)" is labeled ±50 mm, which is actually determined by the number of wrinkles of the multilayer fiber cloth. If you need 100mm, you have to widen the folds or increase the number of layers, but the pressure loss will also change.

Next time, ask "What is the non-metallic compensator unit?" First, turn through the product page of this site. The four fields of "nominal diameter, displacement, working pressure and working temperature" in the product parameter table are the answer. If you don't understand, just copy the parameters and send them, and we will help you correct them. After all, after more than ten years in this business, I have seen too many cases of rework because of mistakes made by the unit-it is really not worth it.

Why do non-metallic compensators need regular maintenance? Structural characteristics and working environment determine its vulnerability

Non-metallic compensator, also called non-metallic expansion joint or fabric fiber expansion joint, mainly absorbs heat displacement, vibration and noise reduction in pipeline system. It consists of a flexible fabric layer, insulation layer, sealing layer and metal frame. This structure is inherently "tender" than metal bellows-the fabric layer is afraid of high temperature aging, acid and alkali corrosion, and mechanical scratching. What about the work environment? Desulfurization flue gas, hot air pipeline, cement kiln tail... are all working conditions with high temperature, dust and corrosive media. If you think about it, it would be strange if you were burned by smoke and fire every day.

Two days ago, I met the equipment supervisor of a cement factory.Rectangular non-metallic expansion jointIt took two years to leave it alone. As a result, the smoke was directly sprayed out, and the production line stopped for three days. Replacing a compensator itself is not expensive, but the loss of downtime is hundreds of thousands a day. So don't wait for a leak to remember, regular maintenance is about spending a small amount to save a lot of money.

Daily inspection: see, listen and touch, find problems in three steps

You don't need any sophisticated instruments for daily inspections, just use your eyes, ears and hands well.

look

Stand at a safe distance and glance at the whole first. See if the fabric layers are bulging, cracking, delaminating? Is there any rust or deformation in the metal frame? Pay special attention to welds and connecting bolts – usually the first thing that goes wrong is a loose bolt, resulting in a loose seal. Also, see if the deflector (if any) has any signs of wear and tear from the media. You can flip through our previous articles for the specific function of the guide tube, which will not be expanded here.

Listen

A normal non-metallic compensator runs with little to no sound. If you hear a "hiss" of air leakage, or a "click" of metal friction, it is 80% because the seal is broken or the frame is misaligned. Note when listening: Is it in a position with large displacement? For example, near the elbow and next to the fixed bracket.

Touch

After the machine is stopped (or with insulated gloves), touch the surface temperature of the fabric layer with your hand. If the local temperature is significantly higher than the surrounding temperature, it means that the internal insulation may collapse or break, and the heat is transferred directly to the external surface. Don't be careless at this time, the high temperature will accelerate the aging of the fabric, and it won't take long to leak.

Practical maintenance: cleaning, tightening and anti-corrosion, one cannot be missed

What to do after finding a minor problem? Three steps: clean, fasten, and prevent corrosion.

Cleaning: Use a soft brush or compressed air to clean up dust and scale on the surface of the compensator. It is strictly forbidden to scrape with a hard metal blade-once the fabric layer is scratched, it is the future leak point. If the medium is viscous (such as desulfurization slurry), rinse it with clean water and dry it before subsequent treatment.

fastening: Check all connecting bolts and tie rod nuts. Note: How to adjust the expansion joint tie rod nut? It's not that the tighter you screw it, the better. The function of the tie rod is to limit the excessive displacement and at the same time ensure the design compensation amount. If you tighten too tightly, it limits the normal displacement, and the pipe stress will transfer to the weak link. Standard practice: Pre-tighten to the design value and then lock the loose nut. You can refer to the manufacturer's installation instructions, or the Q&A of "The Function of Expansion Joint Tie Rod" we wrote before.

antisepticMetal frames, especially carbon steel, rust quickly in wet or corrosive environments. Find the corrosion spot, polish and remove rust first, and then apply temperature-resistant anti-corrosion paint twice. Pay attention to avoid the fabric layer, the lacquer will swell and harden when it touches the fabric, which is not worth the loss. For stainless steel frames (such asDesulfurization flue gas baffle doorMatching compensator), check pitting and stress corrosion cracks, if they appear, it will be a big trouble.

How to deal with common faults? Leakage, deformation, aging, right seat

Leakage, deformation, aging. It is handled differently.

leak: Confirm the leak location first. If it is on the fabric layer, the small hole can be temporarily treated with a special patch of repair glue (be careful to be temperature and pressure resistant). Don't mend the big tear, just change the components. If the leak is at the connection of the metal frame to the pipe, check that the seal gasket is damaged or that the flange surface is flat. Don't screw the bolts when you come up-if they are uneven, they won't seal them even if they break them.

deformation: Bulging of the fabric layer of the non-metallic compensator, usually due to collapse of the internal insulation, or the operating temperature exceeding the design value. At this time, you have to stop the machine and open it to check the insulation. Don't think about patching, the internal structure is broken and the external fabric won't last long. In addition, the deformation of the frame (such as the corner of the rectangular compensator tilting) is generally caused by excessive pipe thrust or installation deviation, so it is necessary to recalculate the pipe stress and adjust the bracket.

Aging: The fabric layer has a large area of cracking, hardening and loss of elasticity. Don't hesitate to change it directly. Aging compensators have a sharp decrease in strength and may burst at any time. To judge the degree of aging, you can pinch the edge of the fabric with your hand-if it breaks when pinched, it is "osteoporosis".

From the beginning of installation, it determines the ease of later maintenance

This view may be a little counter-intuitive, but the fact is: if you don't install it correctly, the maintenance behind you will exhaust you. There was a chemical factory before,Non-metallic compensatorIt was installed very close downstream of the pipe elbow, and as a result, the compensator was subjected to additional bending moment during operation, and six were replaced in three years. Normal installation considerations include:

• Ensure that the pipes on both sides of the compensator are coaxial and the deviation is within the allowable range (refer to the model and size table of the expansion joint).
• The installation direction should be correct: Pay attention to whether the medium flow direction is consistent with the direction of the arrow of the expansion joint, and the insulation layer will be blown askew if it is reversed.
• Temporary supports to be removed: Tie rods or supports may be installed for the convenience of transportation when leaving the factory, which must be removed after installation, otherwise the compensator will not work.
• Pre-stretching (or pre-compression): If it is cold installation, the compensator should be pre-adjusted according to the ambient temperature. See the design drawings for specific values. If it is not adjusted, the compensator will bear additional tensile stress when the temperature is low in winter.

Think about it, these details are done in place, and the post-maintenance workload is directly halved. Didn't do it? Then just wait to wipe your ass every few months.

When is it time to get a new one? Don't cause trouble just to save money

Many bosses think that "continue to use it if it can still be used", but the non-metallic compensator not only decreases in performance at the end of its life, but also may suddenly burst. Then when do you have to change?

First, achieve the designed service life.According to the national standard for non-metallic expansion joints (JB/T 12235-2015), the service life under normal working conditions is generally 3-5 years. If it is overrun, it is recommended to do regular water or air pressure tests, but don't expect it to last long.

Second, irreparable damage occurs.For example, large-area ablation of fabric layer, serious deformation of metal frame, cracking of weld seam, etc. Don't think about welding and repairing-once the structural integrity of the non-metallic compensator is destroyed, the reliability after repair is greatly reduced.

Third, there is no cure for leakage.Patched more than three times and still leaking? Don't worry about it, get a new one. The indirect cost of leak repair per shutdown is much higher than the cost of replacement. Don't count this account? Ask the cement factory in front.

By the way, when replacing a new one, it is recommended to check the pipe bracket and adjacent equipment (such as flue gas baffle door, electric plug-in insulation door, etc.) simultaneously. Often, the old compensator is broken because the pipe displacement exceeds the standard, and the root problem is not solved, so the new one dies early.

Don't wait for the smoke to remember. Look, listen, touch regularly, tighten what should be tight, clear what should be cleared, and change what should be changed. The non-metallic compensator is actually quite solid-as long as you have given it "due care".