Specialized in manufacturing compensators, expansion joints, baffle doors

What exactly is a non-metallic compensator? What is the essential difference with metal corrugated expansion joint?

Non-metallic compensators (also called fabric fiber expansion joints and non-metallic expansion joints in the industry) are not the same thing as our common metal corrugated expansion joints. The core materials of non-metallic compensator are flexible non-metallic materials such as high-temperature-resistant coated fabric, rubber and polytetrafluoroethylene, which are made into a soft joint. The metal corrugated expansion joint absorbs displacement by elastic deformation of stainless steel corrugated pipe. Different ways, application scenarios are naturally different.

For example, the metal corrugated expansion joint is like a tough guy, which can carry high pressure, but it is afraid of corrosion and fatigue. The non-metallic compensator is like a master of jiu-jitsu, which can't bear high pressure, but it is resistant to high temperatures, corrosion, and can absorb large displacements in three dimensions. You're asking tough guys to do jiu-jitsu work, isn't it realistic? The other way around is the same.

Why can it gain a firm foothold in the harsh working conditions of high-temperature flue duct, power plant desulfurization and cement kiln tail?

Resistant, big and good.ResistanceHigh temperature-the ceramic fiber layer can withstand more than 1000℃;ResistanceCorrosion-Polytetrafluoroethylene or acid-resistant rubber layer directly attacks acidic gas;LargeDisplacement-Rectangular non-metallic expansion energy saving absorbs displacement in X, Y and Z directions at the same time, and metal parts can often only absorb axial or transverse directions. In addition, the vibration reduction effect is first-class. If the fan inlet and outlet pipes are installed with it, the vibration can eat more than half.

In the desulfurization flue of power plant, although the flue gas temperature is not high, it is heavy in moisture and contains acidic condensate. It won't take long for the metal corrugated expansion joint to be pitted and perforated. Replace it with a non-metallic expansion joint (such as this station'sRubber PTFE compensatorOrNon-metallic expansion joint (fabric fiber expansion joint)), the inner layer is tetrafluorine acid-resistant, and the outer layer is fiber insulation, which is still intact after three or four years of use. Is that the truth?

The shortcomings are also obvious. Don't treat it as a panacea

Non-metallic compensators are not without drawbacks. The pressure capacity is pitifully low-generally no more than 0.1MPa, that is, just over one atmosphere. If you use it on a steam pipe or high pressure oil pipe, it will explode in minutes. In addition, it is afraid of sharp objects scratching, and it is easy to leak air if the flange surface is uneven during installation. In terms of life, the fiber and rubber layers will age, but according to JB/T 12235-2015 standard, the design life of regular manufacturers can cover the overhaul cycle of the unit (usually 3~5 years).

Two days ago, a cement factory purchaser spat with me, saying that the metal expansion joint in their kiln tail pipeline cracked in less than a year, and it was annoyed to death after several changes. I suggested that he replace it with a rectangular non-metallic expansion joint with a temperature of about 800 ℃ and a composite layer of ceramic fiber + silicone cloth. And guess what? Used it for more than two years without any problems. Therefore, everything is easy to say if the selection is right.

Focus on these four parameters when selecting

• Design temperature: Look at the resistance temperature of the fabric layer. For example, ceramic fiber can reach 1260℃, but the actual use should leave a margin.
• Working pressure: Non-metallic compensators are mostly used in low-pressure smoke ducts, and don't think about them if they exceed 0.1MPa.
• displacement amount: The three directions of X, Y and Z should be calculated clearly. Metal parts can be calculated as transverse axial, and non-metals can be calculated as three-dimensional.
• Media composition: The desulfurization flue gas has a large moisture content and acidity, so acid-resistant PTFE or rubber materials must be selected, such as this station'sRubber PTFE compensator。 If the cement kiln tail contains alkaline dust, then alkali-resistant coating must be used.

The national standard JB/T 12235-2015 has clear test methods for fatigue life and air tightness.

When should you choose a non-metallic compensator?

Low pressure, large displacement, high temperature, corrosive mediaOccasions, preference is given to non-metals. Specific scenarios include: the pipelines in front and behind the desulfurization flue gas baffle door, the inlet and outlet of the fan in the cement industry, the flue of the power station boiler, the air-cooled island vacuum pipeline-and so on. The air-cooled island vacuum pipeline is commonly used thereDouble hinge expansion joint for air-cooled island vacuum pipelineBut that's because the vacuum condition requires a metal seal. As for the Smoke Wind Dao, it is basically a world of non-metals.Flue gas baffle doorOrDesulfurization flue gas baffle doorUsed together, seal and compensate in one step.

Conversely, if high-pressure pipelines (such as main steam), oil media, or occasions where frequent pressure is required, honestly use metal corrugated expansion joints, such as this station'sUniversal corrugated expansion jointOrHigh temperature axial expansion joint。 Don't think about non-metal saving money and hard on it-if you choose the wrong one, it will be more expensive to repair it later than to buy a new one, and the gain will outweigh the loss.

So how about non-metallic compensators? Bottom line: Use it in the right place is an artifact, and use it in the wrong place is scrap metal. Understand your own working condition parameters, and then compare the above points, and basically don't step on pits in the selection.

Splash cold water first: No standard answer

The pressure resistance of metal expansion joint is never a fixed value. It is linked to the corrugated material, the number of layers, the wall thickness, the presence of reinforcing ring, the working temperature and the diameter. You ask "maximum withstand voltage", just like asking how fast a car can go-can Ferrari and Wuling Hongguang be the same? There are general-purpose corrugated expansion joints and large-diameter thick-walled expansion joints in this station. The latter is specially designed for high-pressure scenarios, and the pressure level differs by several orders of magnitude. Two days ago, I met a customer, and he said, "Give me a DN200 expansion joint that can carry 10MPa". I said you should tell me the temperature, what the medium is and how big the displacement is first, but he was still impatient. As a result, steam pipeline, 500℃, 3.5MPa, guess what? Choose a corrugated expansion joint for power station industry, and the conventional design pressure of 2.5~6.4MPa is enough. If it is hard to 10MPa, the fatigue life will directly cut to the ankles.

Core parameters affecting withstand voltage

Corrugated material is the first threshold. The allowable stress of 304 stainless steel is about 137MPa at room temperature, which is slightly higher than that of 316L. However, at 600℃, Inconel 625 can still maintain its strength, and 304 is already as soft as noodles. Number of corrugated layers-the compressive capacity of single layer is limited, and multi-layer corrugation can distribute stress through interlayer friction, but at the cost of increasing stiffness and poor ability to compensate displacement. The wall thickness from 0.5mm to 2.0mm, with every increase of 0.5mm, the withstand pressure can be increased by about 30% ~50%, but the fatigue life may also be decreased, because the thick-walled corrugation is more likely to produce stress concentration in the trough. The reinforcement ring, to put it bluntly, is to add a hoop between the corrugations to prevent excessive deformation of the trough, which is almost necessary under high pressure conditions.

Medium temperature is a hidden killer. The yield strength of the material decreases by 20% ~30% for every 100℃ increase in temperature. For example, the single-layer corrugated expansion joint of DN200 can carry 1.6MPa at room temperature, but may only leave 1.0MPa at 400℃. You select the model according to normal temperature, and the expansion joint will bulge directly when the scene runs at high temperature. If this account is not clear, the design will be in vain.

Which products of this site can carry high pressure?

Corrugated expansion joints used in power station industry, with a common design pressure of 2.5MPa ~6.4MPa, are specially matched for steam pipelines and steam turbine units in power plants. Stainless steel or Inconel are mostly used as materials, and some have lining cylinders and guide cylinders. Large diameter thick-walled expansion joint, the wall thickness is more than 3mm, plus multi-layer corrugation and reinforcing ring, the maximum can reach 10MPa or even higher. In addition, there is a kind of artifact-external pressure single axial expansion joint. Structurally, the bellows is placed outside, so that the medium pressure can resist a rigid inner cylinder from the inside. The bellows only bears the bending stress caused by axial displacement, and does not directly bear the internal pressure. Therefore, its pressure resistance is much stronger than that of ordinary internal pressure expansion joints. But don't think that high pressure is invincible-the higher the pressure, the shorter the fatigue life, which is a dead hole.

The game between pressure resistance and fatigue life

You have to let the expansion joint carry 10MPa, OK, but the number of cycles may drop from 10,000 to 2000. In actual engineering, many customers ask "What is the highest resistance?" I usually ask: "How long do you plan to use it?" Under high pressure conditions, the material is prone to cracks in the trough stress concentration zone. A real case: A high-temperature and high-pressure pipeline in a chemical plant selected an expansion joint with a pressure of 8MPa, but it leaked in half a year. Check the reason, the design pressure is 5MPa, but the pressure fluctuates frequently during actual operation, starting and stopping once a day, and the fatigue life is only enough for 300 cycles. Later, the external pressure single axial expansion joint was changed, and the pressure level was reduced to 4MPa, but the life time was increased to 10,000 times, and there was no problem after three years of use. When selecting a model, you should balance design pressure with life expectancy, rather than staring at a number.

Selection suggestion: Don't pat your head

First, clarify the working pressure, temperature, medium and displacement-for example, for steam pipelines, the temperature is 500℃ and the pressure is 3.5MPa at full load, so you have to use a high-temperature axial expansion joint or a special model for power stations, and check the fatigue life. The best way is to send the working condition parameters to the manufacturer and let them calculate. The rotary compensator and double hinge transverse expansion joint of this station also have their own applicable scenarios. Don't take high pressure as the only standard. The rotary compensator is suitable for long-distance directly buried pipelines, and the double hinge transverse expansion joint can absorb lateral displacement and angular displacement, but their pressure resistance is generally not as high as that of large-diameter thick-walled expansion joint. If you are in the cement industry, the flue gas pipeline has high temperature and dust, and the metal corrugated expansion joint in the cement industry is lined with wear-resistant lining. Pressure resistance is not the main contradiction, but wear resistance and temperature resistance are. In summary, what is the highest pressure resistance of metal expansion joints? Ask about design life and working conditions first, then talk about pressure.

Find out what the silicone cloth is for in a non-metallic compensator-not a simple layer of cloth

When many people hear "non-metallic compensator silicone cloth", their first reaction is: Oh, it's a layer of cloth, which is padded in the middle of the flange to prevent leakage. Tsk, thinking so, the first step is missing.

The role of silicone cloth in non-metallic expansion joints (also called fabric fiber expansion joints) goes far beyond sealing. It has to carry three things at the same time: temperature, pressure and displacement compensation. For example, in the high-temperature flue gas pipeline, the temperature always goes up to 300℃, and ordinary rubber has long been baked. The silicone cloth has been treated with special coating, and the temperature resistance range is usually-60℃ to +300℃. Some models with glass fiber or ceramic fiber layer can withstand more than 600℃ for a short time.

More importantly, the silicone cloth is the core of the flexible compensation layer – it is responsible for absorbing the axial expansion and contraction, lateral offset, and angular displacement of the pipe. If you think of it as a simple gasket, it is equivalent to turning the whole compensator into an iron plate, and all the elasticity that it should have is gone. Two days ago, I met a customer, who said that it had leaked after installing it for only three months. When I took it apart, I saw that the silicone cloth was pressed into a dead fold by the screw, which didn't compensate at all. It's not that the product is not working, it's the wrong usage.

Rollover site before installation: the flange surface is not treated, the size is not checked, and the screw direction is reversed

Before installing non-metallic compensator silicone cloth, three low-level errors can scrap a good set of products.

The first, the flange face is not treated.The flange removed from the old pipe, which is all welding slag, rust and greasy, is directly installed with silicone cloth? That is equivalent to laying carpet on sandpaper-no matter how tight the press is pressed, the leakage point will appear instantly as soon as the medium flushes. Standard practice: Clean it with a wire brush or angle grinder to ensure that the flange surface is flat and smooth without bumps. If there is a pit exceeding 1mm, it must be repair welded and polished.

Second, the size is not reviewed.Don't say "about the same". When installing non-metallic expansion joints, the diameter of flange bolt holes, hole spacing and outer diameter of flange must be measured against the drawings. 5mm more, the bolt can't pass through; It is 3mm less, and the press strip can't cover it. In a case of a power plant, the workers put the silicone cloth on without measuring the hole distance. As a result, the bolts were twisted diagonally, and the silicone cloth was torn directly at the bolt hole, and it was scrapped before it was put into production.

Third, the direction of the screw is reversed.This one is the most hidden. Many non-metallic compensators are equipped with pressing bars and fastening screws on both sides of the flange. The threaded end of the screw should face the outside of the pressing bars to facilitate screwing the nut. However, someone tried to save trouble and threw the screw in from the inside. As a result, the nut was blocked by the flange when it was twisted halfway, and it couldn't be pressed tightly at all. In the end, it could only be disassembled and reinstalled, and the construction period was delayed for two days.

Core four steps: line drawing and positioning → strip pressing → bolt pre-tightening → symmetrical tightening, one step wrong reduces the life by half

So how on earth do you pretend? Don't mess around, go in this order, and rework if the order is wrong.

Draw line positioning.First, lay the silicone cloth flat on the flange surface, and draw a circle along the inner diameter and outer diameter of the flange with a marker to ensure that the silicone cloth is centered and not skewed. Especially for rectangular non-metallic expansion joints, the four sides must be symmetrical. If the offset is 5mm, the compensation amount will be offset by 10%. When drawing the line, pay attention to the fiber direction of the silicone cloth-the warp direction (length direction) corresponds to the axial displacement of the pipeline, and the weft direction corresponds to the lateral displacement. If this direction is reversed, the compensator is equal to uninstalled.

Strip compacting.The strip (usually angle or flat steel) should fit the flange and completely enclose the edge of the silicone cloth. The bead joints are staggered as much as possible to avoid weak spots in the same position. The bolt holes on the press strip must be aligned with the flange holes, and cannot be pulled hard.

Bolt pre-tightening.Many people are fast in this step, so they can directly use the electric wrench to fight it to the end. SO WRONG! Pre-tightening means to first screw all the bolts with a wrench until they just touch and eliminate the gap, probably until they can't be screwed by hand. Don't rush on the torque, there is also symmetrical fastening in the back.

Symmetrical fastening.That's the key. Tighten three times from center outward, diagonally crossed. The first screw to 50% of the design torque, the second to 80%, and the third to 100%. For example, M16 bolts, the recommended torque is 80~100N·m. Do you have to use a torque wrench and screw it by feel? The error can exceed 30%. In this way, the silicone cloth is uniformly stressed, the sealing surface is flat, and the service life is at least doubled.

Should the pre-stretching of silicone cloth be done or not? Don't be led off by the experience of the old master

"You should tighten the silicone cloth first, otherwise it will be loose and baggy when used." Is this correct? According to the situation.

Silicone cloth itself is a flexible material. If it is intentionally stretched during installation, the advantage is that it can apply tension in advance when the pipeline is cold, and it is not easy to wrinkle after thermal expansion. But the disadvantages are more obvious: excessive stretching, early fatigue of internal fibers of silicone cloth, accelerated aging and fracture at high temperature. Especially when the non-metallic compensator is used in high-temperature flue gas or steam pipeline, the amount of thermal expansion is inherently large, and the pre-stretching makes the silicone gel cloth bear additional stress in the hot state.

I checked the installation manuals of several mainstream manufacturers (including the information of rectangular non-metallic expansion joints on this site), and generally recommended:Not pre-stretched。 When the silicone cloth is installed, it can be kept in a natural flat state, and a small margin (1% ~2%) is allowed to cope with fine adjustment. Only when the displacement of the pipe is extremely large and the elasticity of the silicone cloth itself is insufficient, it is necessary to pre-stretch at the stretch ratio given by the manufacturer (usually not more than 5%). Master's experience may apply to old-fashioned asbestos gaskets, and silicone cloth is different. Don't blindly follow the trend.

Three pits that frequently occur in use: media scouring, temperature exceeding limit, and loose beading

Once installed and set and forget? Thinking too much. Three common problems in the running phase, pay attention in advance.

Media flushing.If there is high-speed dusty flue gas in the pipeline (such as desulfurization flue of thermal power plant), and the particulate matter washes the surface of silicone cloth for a long time, the coating will gradually wear out, expose the fiber layer, and then leak. Solution: Add a guide tube or wear-resistant liner inside the non-metal expansion joint (such as the wear-resistant liner matched by the desulfurization flue gas baffle door of this station). If not, then you have to check the windward side of the silicone cloth regularly, and if you find wear, patch the sheet immediately.

Temperature exceeded limit.The temperature resistance of silicone cloth has an upper limit. Some process pipelines occasionally overheat by dozens of degrees during operation, such as 300℃ in design, but 350℃ in actual fact. It may be okay once or twice, but repeated overheat will cause the silicone cloth to become brittle, hard and cracked. Don't expect it to bear the design limit. Over-temperature 10% may reduce its life by 50%. It is recommended to install temperature monitoring points or choose higher grade composite fabrics (such as ceramic fiber cloth + silicone coating).

The bead is loose.The bolts will slowly loosen under high temperature and vibration, especially when non-metallic compensators are used for fan inlet and outlet pipes. Check once a week and tighten the nut with a wrench. Some customers ignore it after installation. After half a year, the strips fell off, and the silicone cloth was blown by the airflow and torn instantly. This is called a small loss.

When is it time to change silicone cloth? Just look at these three points, don't wait for a leak before dismantling

Silicone cloth is not a permanent piece, so you should change it. Don't be reluctant. Three judgment criteria:

• Cracked or hardened surfaces.Press by hand, if the silicone cloth loses its elasticity, cracks will appear when it is gently broken, indicating that the coating has aged and failed. If you don't change it at this time, the next step will be penetrating leakage.
• Local bulging or delamination.The silicone cloth and the reinforcement layer disengaged and bulged like blisters. The reason is the infiltration of the medium or the action of thermal stress, and the bulge will rupture if it is continuously used.
• There are leakage marks at the flange bead.Even if it's just a wet mark, don't wait for a drip. Disassemble and check. If the edge of the silicone cloth has been corroded by the medium and become brittle, it must be replaced.

There is no fixed standard for the replacement cycle, but according to the industry experience of this station, under normal working conditions (temperature ≤250℃, no strong corrosive medium), silica gel cloth can be used for 2~3 years without problem. If the working conditions are bad, such as high sulfur content in flue gas or large pipeline vibration, it is recommended to stop the machine for inspection once a year. Don't wait until it leaks before removing it-at that time, even the flange may be corroded by the medium, and instead of a piece of cloth, the whole expansion joint will be replaced.

How to use non-metallic compensator silicone cloth? Treat it as a precision part of the system, not as a consumable. It takes an extra half hour to install and saves half a year to run.

First, understand the structure of the non-metal compensator before painting-it is not metal, so don't copy the ripple painting method

To be honest, I've seen too many people paint non-metallic compensators the same way they paint metal bellows. And the result? The drawing resembles a stiff pile of iron, completely ignoring the flexible nature of the fabric skin. The core structure of non-metallic compensator (that is, we often call fabric fiber expansion joint) is three layers: the outer layer is temperature-resistant fiber fabric (such as silicone cloth and fluororubber cloth), the middle is heat insulation layer (ceramic fiber blanket or rock wool), and the inner layer has an anti-corrosion lining. The frame is metal — usually a rectangular or circular flanged frame welded from Q235 or 304 angle steel, channel steel. The skin is fastened to the frame by beading and bolting, creating a soft connection segment that can be twisted. To put it bluntly, this thing is a "rigid and soft mix" structure: the rigid one is the upper and lower flanges, and the soft one is the middle section of fabric. When you paint CAD, you would be wrong to still paint the skin corrugated-the non-metallic compensator has no corrugations, it relies on the elastic deformation of the fabric itself to absorb displacement.

2. Confirmation of key parameters: pipe size, compensation amount, skin material and flange connection form

Before you start drawing, set these numbers to death. Otherwise, if you find out that the flange bolt hole is wrong in the middle of the drawing, it will be called a collapse.
Take-over size: OD or ID of pipe? Is it a circular duct or a rectangular air duct? For example, the power station industry commonly uses round shapes, while the cement industry has more rectangular shapes. Our site hasRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)The two products have different dimensioning habits: circles are directly marked with DN, and rectangles are marked with length × width.
Compensation amount: What are the axial, transverse and angular displacements? The compensation capacity of non-metallic compensators is much greater than that of metals, and the axial energy can reach ±50mm or even greater, but you can't blindly paint too thick. There is a standard for the number of skin layers. Referring to the JB/T 12235-2015 standard mentioned in the FAQ of this site, the number of skin layers is generally 3~5, and the thickness of each layer is 0.5~1.5mm.
Skin material: Silica gel cloth + glass fiber for high temperature working condition, polytetrafluoroethylene coating cloth for corrosion working condition. Don't confuse material labeling-for example, this site hasRubber PTFE compensator, that is, rubber and PTFE compound, can't be written as pure fluorine tape.
Flange connection form: Angle steel flange or flat flange? Is the number of bolt holes a multiple of 4 or is it divided equally according to the air duct size? These data must be extracted from the form factor chart provided by the customer, or from the ready-made data on this siteModel and size of expansion jointLook for references in Q&A.

3. Drawing of two-dimensional engineering drawings: from the main view to the cross-sectional view, emphasizing the overlap between the frame and the skin

Two-dimensional drawings are the basis of production drawings. Open CAD, and set the layers: the structure line, the marking line and the section line are separated. Draw the main view first-usually the outer contour of the flange, draw a rectangle for a rectangle, and a circle for a circle. Then the cross-sectional view is the point: you have to cut at least A-A to express the skin lap structure clearly.
How to paint skin? Don't draw it as a continuous arc! The skin of the non-metallic compensator is not corrugated, it is composed of layers of fabric superimposed and pressed against the flange surface by beading and bolting. Therefore, in the cross-sectional view, the skin part should be drawn as several parallel lines (representing different layers of fabric), and both ends should be represented by a schematic diagram of pressing. The press bar is generally flat steel, with a thickness of 4~6mm and a width of 25~40mm. The bolt spacing is usually 150~200mm. This parameter should be confirmed with the customer, and then marked next to the cross-sectional view.
Also, don't forget to markguide tube。 If you are drawing a non-metallic compensator with a deflector (such as one used in a flue gas desulfurization system), the deflector direction must be clearly marked-the arrow points to the direction of the medium flow. There are special topics in the FAQ of this siteSpecific Function of Expansion Joint Guide TubeIf the guide tube is not installed in the right direction, the consequence will be to wear the fabric skin, and the life span will be directly cut in half.

4. Thoughts of 3D modeling: Using lofting and curved surface tools to simulate the twist and wrinkle of fabric skin

Three-dimensional drawings are mainly used to inspect assembly interference or show them to customers. But how to draw the folds of non-metal skin? Stumped a bunch of people.
What I do is: first build two upper and lower flange boxes (stretch solid), then between the two boxes withloftingCommand to generate a connector. However, don't loft directly into a straight contour-the skin will have natural wrinkles under pressure, so add several control points to the loft path to make the surface slightly bumpy. For example, in a rectangular compensator, the central area of the side of the skin can be retracted by 5~10mm to simulate the effect of depression under negative pressure. Of course, this is just a sign, and the real fold shape is ever-changing, but CAD modeling doesn't have to be completely real, so long as customers can understand "this is the flexible section".
For circular fabric compensators, you can useRotating surfaceOrsweepCommand, but pay attention to the thickness of the skin (0.5mm fabric layer can be ignored directly in three dimensions, too thin to show). The key point is to draw the metal parts such as flanges, bolts and strips clearly, and the skin is represented by translucent materials or maps, so that you can see which parts are soft at a glance.

V. Distinguishing Occasions: Drawing Differences between Rectangular Nonmetallic Expansion Joints and Circular Fabric Compensators

Rectangular non-metallic expansion joint (refer to this siteRectangular non-metallic expansion jointProducts) are usually used in flue gas pipes, which are large in size and can reach 5 meters in side length. At this time, the graphic should focus on the arrangement of reinforcing ribs of the frame-the angle steel frame needs to add vertical ribs in the middle of the long side to prevent the skin from bulging. In the cross-sectional view, draw the cross-section of the stiffener.
Circular fabric compensators (that is, we often call non-metallic expansion joints) are mostly used in small-diameter pipes. The flange is a circular ring and the skin is a cylindrical surface. The marking method is closer to the metal compensator, but it should be noted that round products usually need to be marked with "installation length L", which includes flange thickness + skin free length + strip height, while metal compensators generally only mark the length of corrugated section, which is different.
In addition, guide tubes are rarely used for round products (the flow rate of small-diameter pipes is fast, but the guide tubes increase the resistance), but rectangular products must be added with guide tubes in the desulfurization system to prevent dust accumulation. You have to distinguish between scenes when drawing.

6. Common marking traps-don't miss the direction of the guide tube, the thickness of the heat insulation layer and the hole distance of the mounting bolts

Finally checking, these are the most error-prone places:
Direction of guide tube: As mentioned earlier, the arrow points to the flow direction of the medium, and the front end of the guide tube should extend into the inside of the pipe, leaving a gap of 10~20mm between the rear end and the inner wall of the skin. This gap is not marked, and it is easy for workers to push the skin when they install it.
Insulation thickness: The insulation layer of non-metallic compensator is generally only written "xx mm" on the design drawing, but in actual production, customers may require two layers of ceramic fiber + one layer of air. You have to write clearly in the technical description of the drawing: total thickness, material and density of the insulation layer (e.g. 128kg/m³). Otherwise, if you buy the wrong purchase, the insulation effect will be discounted.
Installation Bolt Hole Spacing: The bolt holes in the flange must be marked with center distance and distribution. Circular flanges are generally marked with PCD (pitch circle diameter) and number, while rectangular flanges are marked with adjacent hole spacing and corner hole positions. Many novices only mark the outer contour size of the flange and forget to mark the hole distance. Consequences? It can't be installed on site, and rework takes time and loses money.
In addition,Length of overlap between skin and flangeIt should also be marked-usually 20~30mm, and the width of the strip covers the overlap area. This number is clearly marked on the partial enlargement of the drawing. Don't expect workers to guess for themselves. If they guess wrong, it is a quality accident.

Alas, in the final analysis, drawing a CAD drawing of a non-metallic compensator is completely two sets of ideas than drawing a metal. The metal compensator is deformed by corrugation, and the non-metal is stretched by fabric. You have to have that "soft box" concept in your head before you write. If you just want to draw a picture of a non-metallic expansion joint at hand, you might as well compare the above points and dismantle the structure before starting. The drawn picture in this way can be directly cut by the workshop master after reading it, which is more worry-free.

Once the nonmetallic compensator (that is, we often call the fabric fiber expansion joint) bulges, collapses or twists, many people's first reaction is to remove it and replace it with a new one. Wait a minute – deformed ≠ scrapped. Find out what kind of deformation it is first, and then decide whether to repair or replace it, which can save thousands of shutdown losses and spare parts costs. Today, let's get this out of the way.

Look at the form first, then look for the cause

Bulging, collapse, twisting, localized wear. The bulge is mostly caused by gas expansion inside the fabric fiber layer or damage to the inner lining; Collapse is mostly caused by negative pressure suction or condensate corrosion, which causes the fiber to lose elasticity; The twist is probably due to the misalignment of the pipeline during installation and the shear force of the compensator; Localized wear is common in particle-containing scouring of media. And guess what? Deformations that occur in the same location may have completely different causes. For example, the non-metallic compensator behind the desulfurization flue gas baffle door has been exposed to acidic condensate for a long time, and the fiber layer begins to eat away from the inside. The outside appears to be only slightly collapsed, but when it is disassembled, it is already layered inside. You just change your skin at this time? It's useless, we have to do it with the drainage device and the anti-corrosion coating.

Temperature overruns and pressure fluctuations: the number one killer

The design temperature resistance of non-metallic expansion joints is generally engraved on nameplates, but the local heat radiation or flue gas flow rate changes are often neglected in actual working conditions. Two days ago, I met a cement factory customer. The measured temperature in the pipeline was 50℃ higher than the design value, and the skin was directly carbonized and deformed-the surface felt like a charred biscuit. What about that? Check the heat source and insulation first, and don't dismantle the compensator as soon as it comes up. After lowering the local temperature and restoring the heat insulation layer, as long as the fiber is not broken, adjust the limit bolt (refer to the adjustment method of the expansion joint tie rod nut), so that the compensator can restore part of the pre-compression amount, and it can last for a while. The same is true for pressure fluctuations, especially near the position of electric plug-in type isolation door or manual plug-in type isolation door. The impact at the moment of valve opening and closing may make the compensator bulge instantly. Priority is given to checking the system pressure relief and valve action logic rather than hardening the compensator itself.

Installation deviation: a fault that is slowly worn out

When the pipe is matched, if the flanges at both ends are not in a straight line, the non-metallic compensator will be forcibly pulled to bear the shear force. This deformation is not visible to the naked eye in its early stages-it feels normal when you glance at it during your inspection. But after a few months of operation, one side of the compensator will appear with dense folds, like the wrinkles on the face of an old lady. Why? Because of the long-term uneven stress of the fabric fiber layer, local fatigue. The solution is simple: Readjust the pipe support to release the stress. Don't reinforce the frame of the compensator, it will only transfer the stress to a weaker place.

Corrosion and ash accumulation: comprehensive treatment of chronic diseases

Rubber compensator and rubber PTFE compensator are very common in chemical industry and desulfurization scenes. Rubber is corrosion resistant, but rubber PTFE compensator is easy to age and deform at high temperature. The materials of the two are different, and the processing logic is also different. If the rubber compensator bulges, it is likely that the oil or solvent in the medium penetrates into it and swells the rubber. At this time, you measure its hardness. If it becomes obviously soft, you have to change it. If the rubber PTFE compensator ages and hardens, and the surface cracks, it has to be replaced. However, there is an exception: if the non-metallic compensator behind the desulfurization flue gas baffle door collapses and deforms but is not broken, you can first check whether the drainage device is blocked, clean up the dust by the way, and then adjust the limit bolt to observe the operation.

What conditions can be "conservatively treated"?

If it is slightly bulged and not damaged, it can be saved in this way: the first step is to shut down for cooling and pressure relief; In the second step, gently poke the bulge with a screwdriver. If you feel that there is gas released inside (the fiber layer is just bulging, not tearing), you can adjust the tie rod nut to let the compensator restore a little pre-compression; The third step is to reduce the operation parameters of the system, such as lowering the temperature by 10℃ and the pressure by 0.05MPa, and running for 24 hours for observation. The bulge disappeared? Then keep using it, and arrange regular inspections. Remember: Nonmetallic compensators are different from metallic expansion joints in that their flexibility depends on the fiber layer, which must be replaced once the fibers break or delaminate. If you touch the deformed area with your hand, if it feels loose and baggy like linen, it means that the fiber has broken. Don't hesitate, according to JB/T 12235-2015 standard, continuing operation at this time will only accelerate the fatigue failure of the whole pipeline system-whether it is corrugated expansion joint or straight pipe pressure balance expansion joint, adjacent equipment may suffer.

What circumstances must be shut down for replacement?

Leaked, delaminated, metal frames and pipes detached. For example, the non-metallic compensator on the vacuum pipeline of the air-cooled island of a power plant began to leak after deformation, and the inspector didn't take it seriously. As a result, a month later, the adjacent transverse expansion joint of the compound hinge also cracked. Because after the compensator failed, no one absorbed the thermal displacement of the pipe, and all of it was pushed to the nearby equipment. You must pay attention to two points when replacing: First, the selection should match the original design-rectangular non-metal expansion joint or round fabric fiber expansion joint? The dimensions and interface flanges must be consistent; Second, don't use brute force to force the counter when installing, first adjust the pipe support and then install the compensator. And guess what? Many people try to save trouble. As soon as the new compensator is installed, the bolts are tightened, and as a result, the torsional stress is brought back to the compensator, which is wasting money.

What if the non-metallic compensator is deformed? To put it bluntly, there are three steps: first judge the form and cause, and adjust the limit bolts and working conditions if you can save them; If you can't save it, replace it strictly according to the standard, and repair the installation deviation and corrosion source together. Don't be lazy, and don't mess around. If you use the compensator right, it will last five years, but if you use it wrong, it will be wasted for three months.