Specialized in manufacturing compensators, expansion joints, baffle doors

What is radial force? Why do so many people fall on this

Anyone who designs pipelines knows that the biggest function of metal expansion joints is to absorb heat displacement. However, when the radial force was mentioned, many people began to be confused. Radial force, to put it bluntly, is the force that pushes the bellows perpendicular to the axis of the pipe, from the center outward or from the outside inward. Wrong direction, light bulge, worse bracket collapse, pipeline twist. Two days ago, I met a customer. A DN600 steam pipe was equipped with a universal corrugated expansion joint. As a result, the radial force was not calculated accurately. After three days of production, the corrugated pipe bulged like a toad's belly. Alas, this kind of thing is not rare.

Radial forces under internal pressure: Outward expansion is mainstream, but not so simple

As soon as the pressure inside the pipe comes up, the bellows expands outward like a balloon-this is the most intuitive direction of radial force, pointing from the central axis to the outer wall. But don't think it's just evenly outward. withUniversal corrugated expansion jointFor example, the radial force generated by internal pressure will make the wave peak expand outward and the wave trough contract inward. The magnitude of this force is directly related to the pressure and wave diameter. If the medium is high temperature and high pressure steam, the radial force has to be doubled instantly. What's more troublesome is that this force will be transmitted to the whole pipeline system, and if the constraint is not good, it can push the fixing bracket askew.

Don't ignore end effects

Where the ends of the bellows are close to the end pipe, the radial force distribution will change abruptly. Stress is concentrated there, and the ripples are more likely to crack. So a lotHigh temperature axial expansion jointThickened walls or reinforcing rings may be provided at the ends in order to hold the non-uniform radial forces of this piece.

Radial force reversal under displacement condition: axial compression, transverse tension, direction change accordingly

Internal pressure is only the basic working condition, and what really makes the radial force "discolor" is displacement. When the pipe is heated and elongated, and the expansion joint is axially compressed, the relative positions of the peaks and valleys of the bellows change, and the direction of the radial force will be partially reversed-the place that originally wanted to be pushed out may be retracted inward at this time. Conversely, if it is a lateral displacement (such as a pipe route turning), the radial force will become a complicated state of "pulling and pressing at the same time". At this time, useCompound hinge transverse expansion jointOrLarge tie rod expansion jointCan effectively restrain and avoid the radial force runaway.

I've seen a case in the cement industry, usingMetal Corrugated Expansion Joints in Cement IndustryOriginally, the axial displacement was handled well, but the radial force reversal was not considered after the lateral displacement was added, and the spacing between the guide brackets was too large, so the bellows was directly twisted into a twist. Tsk, it's more expensive to fix than to buy a new one.

Differences in Radial Force of Different Types of Expansion Joints: From Universal Type to Pressure Balance Type

Different structural designs, the performance of radial force is very different.

• Universal corrugated expansion joint: The radial force caused by internal pressure is the largest. If there is no guide tube, the bellows will easily become unstable under high pressure.
• Straight pipe pressure balanced expansion jointAndCurved tube pressure balance expansion joint: Most of the internal pressure thrust is offset by balancing the bellows, and the radial force mainly comes from media flow disturbance and installation deviation, which is relatively easy to control.
• Compound hinge transverse expansion joint: The radial force is concentrated on the hinge structure, and the bellows itself is more stressed, but special attention should be paid to the fatigue life of the hinge.
• External pressure single axial expansion joint: On the contrary, its bellows is compressed on the outside, and the radial force generated by the internal pressure is squeezed inward, in the entire reverse direction. Don't get confused when designing.

You see, it is also called an expansion joint, and the direction of radial force varies widely. When you don't see clearly when you select the model, you have to cry at the scene as soon as you sign the drawings.

Common consequences of misdesigning radial forces: bulging, twisting, stent collapse

The radial force is not counted correctly, how serious are the consequences? Tell me a few real things:

• bulge: The internal pressure radial force is too large, the bellows peak excessively expands outward, and the material forms permanent bulge after yielding. Common inLarge diameter thick wall expansion jointAlthough the wall thickness is large, the stress is concentrated in the zone of abrupt curvature change.
• Twisted: The direction of the radial force is inconsistent during lateral displacement, causing the bellows to twist like twisting a towel. Generally occurs in the middle of long pipelines, when the spacing between guide brackets exceeds the standard.
• Stent collapsed: The radial force is transmitted to the fixed bracket through the end tube, and if the bracket is not designed according to the thrust, it will tear the base directly. There was a desulfurization flue project last year, usingDesulfurization flue gas baffle doorAndNon-metallic expansion jointCombination, just because the radial force is not counted, the fillet weld of the steel support is broken.

These problems can actually be avoided by preliminary calculation. The point is, you have to know exactly where the radial force is pushing.

How to judge the direction of radial force during installation? Look at arrows, calculate thrust, set guidance

Don't have time to do finite elements for on-site installation? There are shortcuts, too.

First, look at the arrows.Products in the station (such asUniversal corrugated expansion joint) Before leaving the factory, arrows are basically made, and the direction of the arrows is the flow direction of the medium, which also corresponds to the main direction of the radial force after installation-the flow direction side is the peak expansion side, and the reverse side is the trough contraction side. Don't act backwards.

Second, count thrust.The internal pressure thrust formula is not complicated: F = p × A (A is the effective area of the bellows). However, the radial force has to be multiplied by a coefficient, which is related to the shape and height of the wave. In the stationStiffness and Calculation Formula of BellowsThe detailed algorithm is listed in the question and answer, so just apply it directly.

Third, set the guidance.Whether the radial force can be controlled or not, the guide bracket is the key. normalUniversal expansion jointThe first set of guide brackets is required to be Direct buried (fully buried) type expansion jointIt is another set of calculation logic to consider the influence of soil lateral constraint on radial force.

How many hundreds can a piece of cloth carry? Talk about the underlying logic of the temperature range of non-metallic expansion joints

When many people come into contact with non-metallic expansion joints for the first time, they will think that this thing is just a piece of "cloth"? If you can hold a hundred or two hundred degrees, it will top the sky. But the reality is that in places such as cement kiln tail and boiler flue, it has to work in flue gas at 300 to 400 degrees Celsius or even higher. Isn't it a little counter-intuitive?
In fact, the truth is very simple: non-metallic expansion joints do not rely on a single layer of fabric to carry the temperature at all. Its temperature capability depends on the synergy of the entire composite structure-fabric, insulation, sealing layer, each with its own division of labor. But the outermost layer of cloth determines "whether you can carry it", and the hidden insulation layer inside determines "how long you can carry it". If you don't understand this logic, the selection is blind.

Silicone cloth, fluorine tape, polytetrafluoroethylene-where is the temperature ceiling of different fabric layers

Let's go straight to the hard goods. There are only a few kinds of fabrics most commonly used for non-metallic expansion joints, and the upper temperature limit is basically the industry consensus:

• Silicone cloth: The continuous working temperature is about 200~250 DEG C. The advantages are good flexibility and aging resistance, but once it exceeds 250 ℃, the silicone coating begins to decompose and the fabric becomes brittle. Therefore, silicone cloth is suitable for compensators from room temperature to medium temperature, such as air conditioning air duct and drying equipment.
• Fluorine tape: Can carry it to the beginning of 300℃. The high temperature resistance of fluororubber is stronger than that of silica gel, and it is also resistant to oil, acid and alkali. It is often used for the front flue of the desulfurization tower, but it won't work further up.
• Polytetrafluoroethylene (PTFE) film or coated cloth: This is the "carrying handle" in non-metallic fabrics at present. The long-term service temperature of pure PTFE can reach about 260℃, but the glass fiber cloth + PTFE composite layer after special impregnation treatment can reach 350℃ or even higher in a short time. Note, it is short-term. When continuous operation exceeds 300℃, PTFE will slowly soften and creep, resulting in leakage.

Many people look at this table and run to choose PTFE cloth, thinking that everything will be fine. Hey, don't worry-the fabric is only the first line of defense, and the real trick is in it.

Don't just look at the fabric: insulation and sealing structures are the real protagonists of high-temperature conditions

Two days ago, I met a customer, saying that his non-metallic expansion joint at the tail of the cement kiln leaked after less than half a year. On disassembly, the fabric layer is intact, but the insulation layer in the middle — ceramic fiber felt — has been sintered to powder by high temperatures. This is the typical "strong outside but dry inside".
The function of the insulation layer is to block the heat flow inside through porous materials (ceramic fibers, aluminum silicate wool, glass fiber felt). If the insulation layer is not thick and dense enough, the heat penetrates directly into the inner surface of the fabric, and the fabric soon becomes unbearable. A standard non-metallic expansion joint such as oursNon-metallic expansion joint (fabric fiber expansion joint)It is usually designed in 3~5 layers: an outer layer of fluorine tape or PTFE cloth, 2~3 layers of heat insulation felt in the middle, and an inner layer of corrosion-resistant sealing film (such as F46 film).
More critical is the sealing structure. At high temperature, the pressing force between the metal flange and the cloth surface will be loosened due to thermal expansion, so it is generally necessary to match stainless steel pressing strips and high-temperature sealing gaskets. Don't underestimate this. The root cause of many leaks is the failure of the seal at the flange, not the broken fabric itself.

Temperature and pressure are husband and wife, who has the final say when fighting? Synergistic Relationship Must Be Considered in Model Selection

When the temperature goes up, the pressure goes down. These two parameters are like a couple fighting-one is always pressing the other. For example, the same PTFE fabric compensator can withstand 0.3MPa at 200℃, and it may not even be able to withstand 0.1MPa at 300℃. Why? Because the strength of the fabric decreases with the increase of temperature, and at the same time the aging rate of the seal ring accelerates.
Therefore, when selecting the model, we must get the "temperature-pressure" combination of working conditions, instead of simply asking "how many degrees can this expansion joint withstand". For example:rubber compensatorGenerally used for normal temperature and low pressure (0.1~0.2MPa), andRectangular non-metallic expansion joint350 ℃ and slightly positive pressure are common in the boiler flue. If you throw the rubber compensator into the 250℃ flue, it will be wasted in less than a month. Conversely, if high-temperature resistant non-metallic expansion joints are used on high-pressure pipes, the flange connections will also be pushed open.

Cement kiln tail, boiler flue, desulfurization tower-three real cases teach you to calculate the applicable temperature

It's boring to talk about theory. Let's look at the case directly:

• Cement kiln tail: The typical temperature is 350~400 ℃, and the flue gas contains dust and alkaline substances. The selection scheme isNon-metallic expansion joint (fabric fiber expansion joint), PTFE impregnated glass fiber cloth for the fabric, three layers of ceramic fiber felt in the middle (20mm each), and an inner F46 film for corrosion protection. The sealing structure adopts stainless steel corrugated press strip + graphite gasket. The actual operating temperature is 380℃, the pressure is-3kPa, and the life can reach more than 2 years.
• Boiler flue: The temperature is generally 150~250℃, but an instantaneous peak of 300℃ may occur when starting and stopping. At this time, silicone cloth or fluorine tape is enough, and the price is also cheap. However, it should be noted that the boiler flue gas has a large moisture content, so waterproof fabrics should be selected, such asRubber PTFE compensator(lined with PTFE) can be solved well.
• Desulfurization tower import and export: The temperature is 80-120 DEG C, but the medium contains dilute sulfuric acid, which is highly corrosive. Conventional non-metallic expansion joint fabrics are prone to corrosion, so it is recommendedPTFE compensatorOr rubber compensator lined with PTFE, although the temperature is low, anti-corrosion is the first priority.

Do you see the doorway? Each working condition should be calculated separately: first set the temperature section, then look at the medium and pressure, and finally combine the number of layers.

Three-step self-examination method: You can also judge by yourself that non-metallic expansion energy saving can't be used in your working condition

Well, after talking about so many dry goods earlier, finally give me a grounded self-examination method, so as to save you from being fooled by sales:

1. Step 1: Find out the working condition parameters-Maximum continuous operating temperature, instantaneous peak temperature, medium (whether containing acid, alkali, particles), working pressure (positive or negative pressure?). These data are indispensable.
2. Step 2: Check fabric and insulation— — Take a product sample and ask what material the outer cloth is made of (silica gel? Fluorine glue? PTFE?), which kinds of felt are used for the insulation layer, and how thick each layer is. If the total thickness is less than 50mm, it basically can't bear long-term operation above 250℃.
3. Step 3: Look at the seal and connection structure-Is the flange surface flat or with stops? Stainless steel 304 or 316 for beading? Is the gasket asbestos rubber or expanded graphite? If the seal is not good, no matter how good the fabric is, it will be for nothing.

After these three steps, he felt confident in his heart. Finally, the national standard for non-metallic expansion joints is JB/T 12235-2015, which can be used as a reference when selecting. However, the practical application depends on practical experience. After all, the standard is only the lower limit.

Two days ago, a customer called and asked, "Which is the radial direction of the expansion joint?" I asked him back, did you use the arrow as a radial reference when you installed it? He froze for a moment. In fact, this problem is particularly typical. Many field engineers and technicians will confuse radial and axial directions. The consequence of confusion is very direct-the selection is wrong, the pipeline will still be broken after installation, and the compensator will be installed for nothing. Today, let's make this direction clear at once.

Let's make it clear: What is radial?

The radial direction of the expansion joint refers to the direction perpendicular to the centerline of the pipe, that is, the direction radiating outward from the center of the circle. For example, if you take a round tube, the direction along the length of the tube is axial, the direction around the tube is called circumferential, and the radial direction is along the radius, pointing from the inner wall to the outer wall. Used on expansion joints, radial displacement is the compression or stretching of the bellows in a direction perpendicular to the axis. For example, when the pipeline shifts up and down or left and right, the compensator bears radial displacement. Isn't it intuitive? But why do 90% of people do the opposite? Because everyone stares at the "axial direction", the main direction of thermal expansion and contraction, ignoring the lateral offset.

What does the direction of the arrow on the expansion joint mean?

Many products, such as general-purpose corrugated expansion joints and high-temperature axial expansion joints, will be marked with an arrow on the shell. This arrow points to the direction of the medium flow, and it also reminds you that the expansion joint mainly compensates for axial displacement-that is, thermal expansion and contraction in the direction of the arrow. Arrows are not radial markers. There are no arrows in the radial direction, because the radial displacement is absorbed by the lateral stiffness of the bellows, and the amount of radial compensation allowed by expansion joints of different structures varies greatly. And guess what? Some customers took the arrow as a radial reference, and forced the expansion joint to be crooked. As a result, the bellows was twisted into a twist before it was pressurized. Alas, sorry for the tube.

What kind of expansion energy saving carries radial displacement?

Look at the type. For example, the compound hinge transverse expansion joint is specially used to absorb transverse (radial) displacement. Its structure has two sets of bellows plus hinges, so that the tube can swing in the vertical direction. There are also expansion joints of large tie rod structure (such as straight pipe pressure balance expansion joints). The function of tie rod is to limit axial displacement and guide compensation force to radial direction. Conversely, like external pressure single axial expansion joint, its design mainly eats axial displacement, radial capacity is very weak. When selecting, if the direction is reversed, the bellows will be twisted, and the flange will be cracked. This is not to scare people. There have been enough accidents at the scene to write a case book.

How to judge in actual operation?

Here are three stupid ways for you to remember and not step on pits:

• First, look at the product nameplate or drawings.It will be marked with "lateral compensation amount" or "radial displacement", generally in millimeters. If not, look for the technical parameter table, which is written separately in the axial and radial directions.
• Second, find the guide tube of the expansion joint.The guide tube is usually along the axis direction. If there is a significant gap between the guide tube and the inner wall of the pipe, this expansion joint allows certain radial deflection. On the contrary, with minimal or even no clearance, it is a pure axial type.
• Third, look directly at the structure.There is a high probability that those with tie rods and hinges can eat radial, while those without such constraints are mostly pure axial. For example, in our products, compound hinge transverse expansion joint and straight pipe pressure balance expansion joint are good at radial compensation, while general-purpose corrugated expansion joint and external pressure single axial expansion joint should not be expected to carry radial direction.

Whichever of these three methods you use is better than blind guessing. One more detail: How to adjust the expansion joint tie rod nut? If you buy the model with a tie rod, be sure to loosen the tie rod nut to the designed position before installation, otherwise the tie rod locks the radial displacement and becomes a rigid connection. For specific adjustment methods, please refer to the FAQ of this site.

One last word of reminder

Don't use the radial direction as the axial direction, and don't expect a general-purpose expansion energy saver to hold a few millimeters of pipe misalignment. When installing, if you find that there is a deviation from the pipeline and forcibly tighten the expansion joint with bolts to make do, you are sentencing the bellows to death. The correct approach is to use double hinge transverse expansion joints or large tie rod expansion joints to specifically absorb this radial deviation. I really can't figure it out. Looking through the product information of this site, the displacement parameters of each model are clearly written-how much in the axial direction and how much in the radial direction, at a glance. For example, for straight pipe pressure balance expansion joints, the radial compensation amount is clearly marked in the selection table, so just follow the selection.

Alas, the direction is right, and expansion and energy saving will help you carry it for ten years; If the direction is reversed, it will leak in three months.

What are the expansion joint insulation liner structures? One article clarifies three mainstream schemes

The temperature of the medium in the high-temperature pipeline is always five to six hundred degrees, or even thousands of degrees. When the bellows is directly exposed to this environment, the material strength will drop by a cliff, and the fatigue life will not be sustained. The insulation lining is like putting an insulation suit on the expansion joint, separating the heat source from the bellows. Common scenes: smoke duct of power plant, cement kiln tail, blast furnace gas pipeline of iron and steel plant-if bare bellows are used in these places, they will have to be scrapped in a few months.

What are the expansion joint insulation lining structures? Don't worry, break up the three mainstream schemes and break them into pieces to explain them clearly, with real cases and product benchmarking.

Scheme 1: Lined Castable Structure

This stuff is most common in the cement industry and power station industry. To put it bluntly, a layer of high-temperature resistant concrete is poured on the spot inside the expansion joint, with a thickness of generally 50-150mm. The advantages are high temperature resistance (up to more than 1200 ℃), wear resistance and good integrity. The disadvantages are also obvious-heavy, and the curing cycle of castables is long, so it is anxious to die during emergency repair.

The "Metal Corrugated Expansion Joint for Cement Industry" and "Corrugated Expansion Joint for Power Station Industry" of our station are equipped with this structure as standard, and with the guide tube, it can effectively prevent the medium from directly washing the bellows. However, it should be noted that castable cracking is an old problem, which must be controlled by the design and construction quality of anchors. Two days ago, I met a customer of a cement plant. During the maintenance, I found that the castable was partially peeling off. It was found that the spacing between the anchors was too large. Later, the cloth welding was re-welded at a spacing of 150mm, and there was no accident again.

Option 2: Ceramic fiber/non-metallic insulation

This solution is much lighter, and is mainly used in high temperatures but non-abrasive media. For example, flue gas pipelines and desulfurization systems. The structure is simple: fill ceramic fiber felt or aluminum silicate wool between the bellows and the guide tube, and wrap a layer of stainless steel wire mesh on the outside.

Our "non-metallic expansion joint (fabric fiber expansion joint)" and "rectangular non-metallic expansion joint" use this idea. The advantages are fast installation, low cost and good thermal insulation effect (thermal conductivity below 0.1W/m·K). However, there is a pit-fiber materials are afraid of water vapor, and the performance of flue gas will decay when the moisture content is high, so it has to be matched with waterproof layer. How to prevent it? Usually a layer of PTFE film or stainless steel foil is added on the outside. If the budget allows, go directly to the "PTFE-lined hose" scheme, and you won't be afraid of sour gas.

By the way, don't think that you can choose just because the temperature and pressure are low. There was once a desulfurization project with a temperature of only 150℃, but the condensed water of wet flue gas soaked the ceramic fiber into mud, and it collapsed in three months. Later, it was replaced with aluminum silicate cotton + PTFE cladding, which has not been changed for three years now.

Option 3: Composite thermal insulation lining

This is a combination of the first two schemes, specializing in the treatment of various difficult and complicated diseases. For example, the medium is high temperature and dusty, or the temperature fluctuates violently periodically. Structurally, the innermost layer is castable anti-scour, the middle layer is ceramic fiber insulation, and the outer layer is guide tube to protect bellows.

Two days ago, a customer asked, saying that their pipeline temperature circulated from normal temperature to 800℃, and it cracked in the first week if only castables were used. Later, it was replaced with a composite structure and used it for three years without any problems. Well, the cost is 30% more expensive, but the life span has doubled by 5 times, which is cost-effective.

Composite structures are not simply stacked and done. The difference of expansion coefficient between the layers must be calculated well, otherwise it will be peeled off in layers after several cold and hot cycles. Solution? A layer of stainless steel expansion mesh is added between the castable and the fibers, and the elasticity of the mesh absorbs the displacement.

Don't just look at the temperature when selecting a model

Pressure, media corrosiveness, installation space and maintenance frequency must be considered. For example, desulfurization flue gas pipeline, the temperature is not high but the acid corrosion is strong, so it is better to choose non-metallic insulation layer with PTFE lining. Our "desulfurization flue gas baffle door" and "PTFE-lined metal hose" are for this working condition.

In addition, the thickness and material of the guide tube also directly determine the heat insulation effect-if the guide tube is too thin, it will easily be burned through, and if it is too thick, it will increase the cost. It is recommended that it be determined according to the medium flow rate and particle hardness, generally 304 or 316L, with a thickness of 3-6mm. If the medium contains hard particles (such as coal powder and slag), it is best to add a layer of wear-resistant lining plate, such as high chromium cast iron or ceramic patch, to the inner wall of the guide tube.

Don't forget to reserve access

Access port reserved for insulation liner. Many projects have installed expansion joints, but when they are broken, they find that the lining can't be changed. In the design stage, space should be allowed, or split structure should be used. Our Round Flap Doors (Double Seal) and Manual Insulated Doors have a quick-service design-bolted end caps that remove the liner module.

All in all, thermal insulation lining has no universal solution, it has to be tailored to the working conditions. If you are not sure, directly take the parameters to find the manufacturer to come up with a plan, and don't make it yourself. After all, if the bellows is burned through, it is not as simple as changing a piece-the loss of the whole pipeline may be hundreds of thousands.

What is the price of non-metallic compensator? Find out what it is

What is the price of non-metallic compensator? Anyone who has been in the purchasing circle for several years has asked this sentence. But if you only focus on the quotes and compare the numbers, nine times out of ten you will step into a pit. To put it bluntly, the non-metallic compensator (also called fabric fiber expansion joint, rubber compensator) is not a standard screw, it is a customized flexible pipe fitting. It relies on glass fiber cloth, silicone cloth, polytetrafluoroethylene, fluororubber and other non-metallic materials to absorb the thermal displacement, vibration and noise of the pipeline.

Two days ago, I met a friend who was doing a flue gas desulfurization project, saying that the quotation ranged from several thousand to tens of thousands, and he was completely confused. In fact, the "value basis" of non-metallic compensator is hidden in its structure-ring belt, flange, insulation layer and sealing layer, each layer is a cost. Like what we always sayNon-metallic expansion joint (fabric fiber expansion joint)If the ring belt is coated with fluororubber, the price will be doubled directly; Made of ordinary silicone clothrubber compensatorIt's much cheaper. So don't cut fabric and fiber goods at the price of rubber, it's not the same thing.

The five elements are the vital gates of pricing, and the quotation sheet will not write them all

1. Material: Every layer of cloth is money

The outermost layer is corrosion-resistant fluororubber or polytetrafluoroethylene, the middle layer is glass fiber or ceramic fiber for reinforcement, and the inner layer may be high-temperature resistant aluminum silicate wool. And guess what? Compensators of the same size, with temperature resistance of 200℃ and temperature resistance of 1000℃, can have a cost difference of 3 times. OurHigh temperature axial expansion jointEven multiple layers of stainless steel wire mesh need to be sandwiched in the ring belt, and the price will naturally rise. And there's anotherPTFE compensatorPerfluorinated material is acid-and alkali-resistant, but it is difficult to process, and the unit price is close to that of metal parts.

2. Size: the bigger the more expensive, but not as linear as you think

The little guy with a diameter DN100 can do it for a few hundred bucks. But like the ones used in power plantsRectangular non-metallic expansion jointWith a side length of two or three meters or even larger, the light flange is thickened and the ring belt is widened, and the cost will rise exponentially. Moreover, rectangular parts are more material-consuming than round parts-if you taste it carefully, the same cross-sectional area, the rectangular circumference is longer, the amount of ring belt is more, and the mold fee is calculated separately. It is the norm that the price increases by 30% to 50% for each larger gear of size.

3. Working conditions: temperature, pressure, medium, one parameter and one pit

Working conditions are the deepest hidden cost assassins. Common air ducts, withRubber PTFE compensatorYou can handle it. However, if you encounter sulfur-containing flue gas, high-temperature steam, acid-alkali liquid, you have to change fluororubber coating or even full tetrafluorine lining. Pressure is also the key. Low pressure (below 0.1MPa) should be used with a single layer of ring belt, and medium pressure (0.1~0.5MPa) should be added with steel wire skeleton or even another layerUniversal corrugated expansion jointMetal mesh sleeve. Not to mention corrosive media – ourDesulfurization flue gas baffle doorWith the matching non-metallic compensator, the band must be resistant to SO₂ and chloride ions, which directly doubles the cost of this material.

4. Customized design: there is no "average price" for non-standard parts

Eighty percent of non-metallic compensators on the market are non-standard parts. For example, for smoke ducts in power plantsRectangular non-metallic expansion jointThe flange hole spacing, thickness and number of circle layers have to be according to the drawing. If you ask the manufacturer to change a size, open the mold, adjust the production line and change the blade, these hidden costs will be spread into the unit price. And something likeCompound hinge transverse expansion jointThe design with tie rod has high structural complexity and long processing period, so the price is naturally more expensive than the ordinary straight pipe type.

5. Installation and after-sales service: Free installation? never mind

Many quotations only quote the bare price. But think about it. When installing the non-metallic compensator, it is necessary to pre-stretch, adjust the parallelism of the flange and tighten the torque. If you don't pay attention, you will leak inside. OurElectric plug-in insulation doorThe matching compensator has to cooperate with the debugging sealing performance during installation. If the manufacturer packages installation, labor costs, travel expenses and hoisting expenses are added, it is not surprising that the price will rise by 20%. So don't just compare the bare price, ask clearly to the total price including installation in place.

Why are some non-metallic compensators more expensive than metal ones? Just take it apart and see

In the same project, the metal expansion joint was quoted at 10,000 yuan, while the non-metal one was quoted at 15,000 yuan. The first reaction is that the manufacturer is slaughtering you? Don't worry, just disassemble a non-metallic compensator and you'll understand. The core values of non-metallic compensators lie in "flexibility" and "corrosion resistance". Metal bellows are prone to stress corrosion cracking at high temperatures, whereas non-metallic bands consist of multiple layers of functional materials — such asSilicone cloth + ceramic fiber + PTFE film, each layer has a different role: heat insulation, sealing, and corrosion resistance. Moreover, the non-metallic compensator has no fatigue life limit (unlike metal bellows, which has cycle times), and the maintenance cost is low.

A power plant flue gas piping system, if usedStainless steel corrugated expansion joint, may corrode perforation in two or three years; Replace withNon-metallic expansion joint (fabric fiber expansion joint)Seven or eight years, no problem. If you calculate the general ledger, non-metals are more cost-effective. And something likeHigh temperature axial expansion jointThis specially designed non-metallic part, filled with heat-resistant fiber inside and covered with stainless steel mesh, has complicated processing technology and is no cheaper than metal parts.

How to avoid being pitted when purchasing? Three Practical Tips

Tip 1: Don't just look at the price, first see if the manufacturer has a "working condition confirmation sheet"
Regular manufacturers will confirm the medium temperature, pressure, corrosive components and displacement with you before placing an order. If the manufacturer comes up and quotes a fixed price, even without asking about the working conditions, 80% of them are fooling you with generic products. When we met a customer who said "just ordinary air", it actually turned out to be oily steam, and the ordinary rubber compensator bulged after three months.

Tip 2: Require to provide "three or more layers of band samples"
The ring belt is the vital gate of the non-metallic compensator. Good bands have high interlayer bonding strength and cannot be torn apart. You can ask the manufacturer to send a small circle band sample, take the blade to cut and see-if the layers are chipped, it is inferior quality goods. Also, check the flange material: the price difference between carbon steel and stainless steel is 3 times. Don't be confused by the low quotation of "carbon steel flange". Stainless steel or PTFE must be used when the working conditions are corrosive.

Tip 3: Ask about the warranty period and maintenance plan
Non-metallic compensators are most afraid of "leakage" (internal leakage). Be vigilant if the warranty period is less than 1 year. And if offset is found after installation, does the manufacturer provide on-site adjustment? One of our customers bought a compensator from a small factory. When it was installed, the tie rod was not adjusted properly, and it leaked after three months. The manufacturer didn't answer the phone. So before signing the contract, write "Installation Guide" into the terms.

You asked him, "How to ensure that the loop does not shrink at 800℃"? If the other party is hesitant, quickly substitute.

Want an accurate quote? Just have these four parameters ready

Stop sending "I want a non-metallic compensator" demands to manufacturers. If you give him these four parameters, he will make a quote in a second:

• Pipeline Media and TemperatureFor example, "flue gas, containing SO₂, the highest temperature is 650℃, and the long-term operation is 450℃".
• Design and test pressures: For example, "0.3 MPa, hydraulic pressure test 0.6 MPa".
• Nominal diameter of pipeline and connection mode: For example, "DN600, flange connection, flange standard HG/T 20592".
• Axial displacement, radial displacement and angular displacementFor example, "axial compensation amount ± 50 mm, transverse direction ± 20 mm".

If rectangular pipes are involved, add two more parameters: length-width dimensions and allowable deflection. With these, the manufacturer can match you with the most economical band structure (such as glass fiber or ceramic fiber, and whether to add stainless steel wire mesh), instead of directly quoting and estimating it higher. OurHigh temperature axial expansion jointAndRectangular non-metallic expansion jointAfter the customer provides the complete parameters, the quotation error can be controlled within 5%.

What is the price of non-metallic compensator? The key depends on how much you are willing to pay for reliability. Don't buy cheap supplies, customize when you need to customize. Remember, the loss of one shutdown is enough for you to buy ten compensators.