Specialized in manufacturing compensators, expansion joints, baffle doors

First, the core value of metal expansion joint: it is not just "compensating displacement"

When many people mention metal expansion joints, their first reaction is "absorbing thermal expansion". Yes, this is the basic skill. But its benefits go beyond that – vibration and noise reduction, preventing pipeline thrust from damaging equipment, adapting to complex spatial layouts…To put it bluntly, it is the "flexible joint" of the entire pipeline system. Without it, as soon as the high-temperature steam pipe is hot, the flange weld will crack; When the equipment vibrated, the whole pipeline shook. Two days ago, I met a customer. The pump unit in the factory building always had problems. I changed the machine seal three times, and finally found that the pipeline stress was not eliminated. Add a universal corrugated expansion joint, and the problem is solved directly. So don't underestimate this thing. It is an "invisible life-saving talisman" in power stations, cement, chemical industry and desulfurization industries.

Second, how to "save life" of metal expansion joint under high temperature and high pressure working conditions

The thermal expansion and contraction of pipelines are physical laws, and hard carrying will only lead to accidents. Metal expansion joints rely on bellows structure and absorb displacement by elastic deformation. For example, high-temperature axial expansion joint, which is specially used to deal with axial expansion and contraction; The transverse expansion joint of compound hinge solves the transverse offset. For example, the corrugated expansion joint used in the power station industry has a steam temperature of five to six hundred degrees and a pressure of more than ten MPa. Ordinary rubber compensators can't bear it at all, so stainless steel or heat-resistant alloy metal bellows must be used. Here's a key point: the deflector. Many customers don't know what it is for-it can guide high-speed airflow away, prevent the bellows from being directly washed, and its life can be several times worse. To put it bluntly, if you choose the right model and material, the metal expansion joint is the "fuse" of the system.

3. Selection of different scenarios: from power station to cement, don't choose the wrong one

And guess what? Many people hold an expansion joint parameter and want to be universal in all occasions. That's a dream. In the flue gas pipeline of power station industry, the temperature is high and the pressure fluctuates greatly. Double-sealed single-axis circular baffle door is commonly used with large-diameter thick-walled expansion joint. In the cement industry, there is much dust and severe wear. The metal corrugated expansion joint in the cement industry has to be lined with wear-resistant lining. There are also desulfurization flue gas baffle doors, which are highly corrosive, and lined with PTFE hose or PTFE compensator is the correct solution. As for the vacuum pipeline of air-cooled island, the double hinge expansion joint of air-cooled island vacuum pipeline has to be used to resist negative pressure. So don't think about it once and for all, you have to choose according to the medium, temperature, pressure and displacement direction. If you are not sure, go directly to the manufacturer for the model selection table, or refer to the metal expansion joint weight table to estimate the model.

4. Installation does not mean completion: those pits of installation and post-maintenance

The screw must be removed! Many novices are afraid of trouble, so they leave the tie rod nut unremoved. As a result, the expansion joint can't expand and contract freely, so it is installed for nothing. The role of the expansion joint tie rod is to protect the bellows during transportation, and once in place, it must be loosened or removed. There is also the direction of the arrow-that is the direction of the medium flow, and the guide tube will block if it is installed backwards. Also pay attention to the coaxiality when installing, deviation will lead to stress concentration. What about post-maintenance? Regularly check whether there are cracks and corrosion points on the surface of the bellows, especially the external pressure single axial expansion joint with external sleeve, which is easy to accumulate water and rust. To put it bluntly, three points for selection and seven points for installation, and the remaining ninety points for daily inspection. Don't wait until it leaks before replacing it, it will be expensive.

V. Life and cost: How long can an investment last?

The design life of metal expansion joints is usually calculated by the number of cycles, such as 10,000 or 20,000. How long can it actually run? Depends on working conditions. It is also stainless steel bellows, which may be fine for more than ten years when used on clean steam pipes; Used in desulfurization flue gas containing chloride ions, it will be perforated in half a year. So don't just look at the price, but whether the material matches. For example, vacuum special hoses are used in high vacuum systems, which have extremely strict requirements for leakage rate, and are expensive but must be used. Rubber compensators are cheap but have limited temperature and pressure resistance. The initial investment of metal expansion joint is high, but the frequency of maintenance and replacement is low, and the whole life cycle cost is cost-effective. You taste, you taste. Finally, let me add: the expansion joint and the compensator are the same thing, so don't be fooled by different names. Anyone who knows the business knows that if you choose the right thing, the system will be safe and stable; Wrong choice, headache every day.

First, find out what kind of metal expansion joint you are facing

The name metal expansion joint is actually a general term. What you have in your hand may beUniversal corrugated expansion joint、High temperature axial expansion joint, could also beDirect burial type、External pressure single type axial type, even large-diameter thick-walled expansion joints. Different structures correspond to different working conditions: high-temperature axial type for high-temperature steam pipeline, direct burial type for buried pipeline, and occasions where transverse displacement needs to be absorbedCompound hinge transverse expansion joint。 Get the wrong model, and it will be a ticking time bomb.

Before selecting, look at the pipeline medium temperature, pressure and compensation direction-is it axial, transverse or angular displacement? For example, the power station industry usesCorrugated expansion joint for power station industryHigh temperature resistance and fatigue resistance are usually required, while the cement industryMetal Corrugated Expansion Joints in Cement IndustryTo deal with dust and abrasion. Each product has a clear application scenario, so don't mix it.

2. Four things before installation: arrow, guide tube, pull rod and bracket

Many people's first reaction when they get the expansion joint is to weld it to the pipe. Stop it. The first step is to look at the direction of the arrow on the expansion joint cylinder. That arrow represents the flow direction of the medium. If the direction is installed in the opposite direction, the guide tube will become a throttle plate, which will increase the pressure loss at least and cause the bellows to flush and fail at least —The direction of the arrow of the expansion joint refers toMedia flow, this common sense rollover case I have seen no less than ten times.

The second step is to check whether the guide tube is in good condition. The role of the deflector is to protect the bellows from being directly washed by high-speed media, especially fluids with particles (such as the pipe behind the smoke baffle door). Once the guide tube falls off, the bellows life plummets. Step 3, confirm the position of the tie rod nut. Adjustment nuts on tie rods are usually in a pre-tensioned or pre-compressed state when they leave the factory to compensate for installation errors. Once installed in place, these nuts should be loosened or adjusted according to the design requirements-how exactly? refer toHow to adjust the tie rod nut of expansion jointThe core principle of that question and answer is: let the expansion joint be in the design pre-displacement in the cold state, and only in the hot state can it work normally.

Step 4, check the pipe support. The expansion joint itself does not bear the weight of the pipe, so it is necessary to set up a fixing bracket and a guide bracket. The lack of guide brackets can cause the expansion joint to twist, which is the most overlooked mistake in installation. And guess what? Some construction sites did not install guide brackets, and three months later, the bellows was directly twisted into a twist.

3. Hard rules of upper pipe welding: torque and misalignment are not allowed

Before welding the expansion joint to the pipe, make sure that both ends of the pipe have been adjusted to the same axis. Forcibly using expansion joints to compensate for pipeline installation deviations (such as non-parallel flanges and uneven gaps) is equivalent to keeping the bellows in a torsional state after welding. The biggest fear of metal bellows is torsional loads-it is good at tensile compression, but its ability to resist torsion is almost zero.

The correct thing to do is to position the pipe with a jack or a reversed chain so that the flanges or welded joints at both ends of the expansion joint are naturally aligned. After welding, remember to review the straightness of the expansion joint. If the deviation exceeds 1% of the nominal diameter of the pipe, it should be reworked. Also, if you useDouble-sealed single-axis circular baffle doorOrElectric plug-in insulation doorIn this type of sealed structure, welding heat may damage the internal seal and require cooling measures. Alas, I've seen cases where seals melt directly after welding on site, and the rework cost is enough to buy three new expansion joints.

4. Debugging stage: Is the tie rod disassembled or not?

It was the most asked question on the scene.Do you need to remove the screw of the expansion joint？ First of all, be clear: the tie rod (or screw) plays a protective role during transportation and installation, preventing the bellows from excessively elongating or compressing. Once installed in place, whether to remove it depends on the expansion joint type.

For general-purpose corrugated expansion joints, if the design allows for axial displacement, then the locking nut on the tie rod needs to be loosened to allow the bellows to expand and contract freely. But if the tie rod is used aslimit tie rodDesign (such as double hinge transverse expansion joint), it cannot be removed at will, but the nut position should be adjusted according to calculation. How to judge? Look at the product nameplate or drawing: If the value of "pre-deformation" is marked, it is usually necessary to adjust the nut to the specified scale in the cold state. For specific operation, first loosen the nut on one side, and then symmetrically adjust the other side to avoid force on one side. After adjustment, check the bellows for skew. To put it bluntly, whether the pull rod is removed or not depends on whether it plays a "bodyguard" or a "traffic police"-the bodyguard can be withdrawn, but the traffic police have to keep the command.

5. Fatal misunderstanding in operation: the insulation layer cannot wrap the bellows

In order to keep heat at many sites, the expansion joints are wrapped tightly with rock wool. This is a big no-no. The inside of the bellows is a cavity structure, which needs heat dissipation. If the insulation layer is directly applied to the bellows surface, local superheating zones will be formed and material fatigue will be accelerated. The correct way is: the insulation layer should only be made on the pipes at both ends of the expansion joint, and the expansion joint itself should be exposed, or a detachable insulation sleeve should be used.

In addition, for high-temperature axial expansion joints and corrugated expansion joints used in power station industry, we should also pay attention to whether there is condensed water accumulation inside the bellows-when starting at low temperature, if the medium is steam, the condensed water may form a water hammer and impact the bellows instantly. The solution is to set the trap in the low position. Is that the truth? Just like when a person wears a cotton-padded jacket, he can't wrap his head around him, so he must leave the heat dissipation port.

6. The maintenance cycle is very simple: look at the displacement and fatigue times

Metal expansion joints are limited life components.Service life of expansion jointDepends on the actual number of cycles rather than simply the time. For example, an expansion joint with a design life of 1,000 full displacements can be used for about three years if it starts and stops once a day; But if the pipe vibrates frequently (like connecting the pump outlet), it can fail in a few months.

During maintenance, focus on checking whether there are cracks at the crest of the bellows and corrosion pits on the surface. ForLarge diameter thick wall expansion jointAnddirectly buried expansion joint, due to being buried in the soil or difficult to disassemble, it is recommended to reserve inspection holes or use models with leak detection during installation. If you useRotary compensatorOrSleeve type pipe expansion jointThe maintenance method is different-this type of product relies on sliding seals and needs regular grease injection. In short, different structures have their own rules. Don't apply the same maintenance method to all expansion joints.

Two days ago, I met a customer who installed a general-purpose expansion joint on the steam main pipe, without a guide bracket, and the insulation layer was still wrapped tightly. Three months later, the bellows cracked, and I came to ask "How to use the metal expansion joint?"-I can only say that the wrong installation is equal to white installation, and one step of type selection, installation and debugging can't be saved.

What Are the Ways of Fabric Connection? Complete solution of connection process of fabric fiber expansion joint in industrial pipeline compensation

The "fabric connection" we talk about, in the field of industrial pipelines, most likely refers to the joint treatment between non-metallic expansion joints (fabric fiber expansion joints) and pipelines. This type of equipment is usually used in flue gas, hot air and dust ducts, and relies on flexible bands of multi-layer fiber fabric and rubber composite. The connection method determines the sealing and life of the whole compensation system. If you choose the wrong one, the later maintenance can make people collapse.

Flanged connection: the most versatile, but the details cannot be sloppy

Flange connection is the most common way in the field-welding flanges at both ends of the expansion joint, flanges on the pipeline, gaskets in the middle, and the bolts are tightened. It is convenient to disassemble and assemble, and does not need to move the pipeline during maintenance, and directly loosen the bolts and change the ring belt. But the pit is also here: the flange surface and bolt materials are not selected correctly, and it will rust to death in half a year. For example, the PTFE-lined metal hose matching the desulfurization flue gas baffle door has strong acidic medium in the flue gas. The flange has to be made of 316L stainless steel, and the bolts have to be coated with Dacro. Otherwise, it will be too late to break the bolts when disassembling them. The sealing gasket is also cheap. Graphite composite gasket is used for high-temperature flue gas and PTFE gasket is used for low-pressure and normal temperature, otherwise the leakage rate will double directly.

Welding connection: once and for all, but don't expect to change it later

Welding connection is to weld the metal frame of the expansion joint directly to the pipe, without bolts and gaskets. Advantages? Extremely low leakage rate, suitable for high temperature, high pressure and long-term non-maintenance occasions. For example, the power station industry uses corrugated expansion joints, high-parameter steam pipelines, with a temperature above 500℃ and a pressure of 10MPa. Do you dare to use flanges? The spacer blew off long ago. There are also high-temperature axial expansion joints, and the working conditions are continuously stable, so they don't have to be cared for for ten or eight years after welding. The cost is that you have to cut the pipe during maintenance, welding, flaw detection and heat treatment, and the labor cost is more than 3 times higher than that of flange. Therefore, welding is only suitable for those scenarios where "install it and don't plan to disassemble it".

Clamp/hoop connection: a money-saving tool with low voltage and large diameter

The clamp connection looks simple-apply sealant to the end faces of the two pipes, put a rubber compensator or rubber PTFE compensator on it, and use a hoop on the outside. Quick installation, one person can do it in half an hour. It is especially suitable for smoke and air ducts with low pressure (below 0.1MPa) and large diameter (above DN1000). Cement plant denitrification flue loves to use this trick, saving money and construction period. However, the disadvantages are also obvious: the sealing ring is a consumable part, and the rubber ages quickly. If the ambient temperature exceeds 80℃, it can't bear it, so it has to be replaced every two or three years. If the medium contains particulate dust, it will wear faster. To put it bluntly, the clamp is a combination of "cheap, fast and short-lived".

Adhesive connection: Patching is the technical job

The loop belt of non-metallic expansion joint (fabric fiber expansion joint) itself is multi-layer composite, and the loop belt and the metal frame have been vulcanized or bonded into one body when the manufacturer leaves the factory. The scene is just docking the frame with the pipe flange. But what if the ring belt is partially damaged during maintenance? Can't change the whole thing, can you? The sheet has to be patched on site with a special adhesive. This job looks simple, but it is actually very demanding on curing time and temperature. I met a customer two days ago, saying that it opened the glue after two months of mending. I asked: What is your curing temperature? He said that the workshop was 5℃ in winter, and it was used directly after gluing. That certainly won't work! Cure at room temperature for at least 24 hours, and ensure that the ambient temperature is not lower than 15℃. If it is a high-temperature zone, it is necessary to use heat-resistant epoxy glue, which can withstand the temperature above 150℃ after curing. Tsk, not many people pay attention to this detail.

Three elements of model selection: temperature, pressure and space

Which one do you choose? There is no "best", only "most suitable". Staring at three numbers first —Medium temperature: Basically say goodbye to rubber and ordinary bonding when it exceeds 300℃. Flange bolts should pay attention to high-temperature creep, and welding is more reliable.Pressure rating: Flanges or welding are preferred above 0.1MPa, and clamps below 0.1MPa can also be made up.Installation space: The narrow clamp is easier to use than the flange, such as the double hinge expansion joint of air-cooled island vacuum pipeline, which has a compact space and can't be sealed with a clamp, so it can only be welded.

Cement industry metal corrugated expansion joint, pipeline temperature fluctuation large, dust. Some people tried to save trouble with welding. As a result, two years later, the ring belt wore out and had to be replaced. The pipe had to be cut, and the kiln was shut down for three days, resulting in a loss of millions in output value. If the flange connection was used at the beginning, with the double-sealed single-axis circular baffle door, the sealing grade could reach more than 99.9%, and it would take half a day to change the ring belt. On the other hand, the double hinge expansion joint of air-cooled island vacuum pipeline, welding is the only choice in high vacuum scenario, and the flange leakage rate can't pass the test at all. Once the vacuum degree drops, the power generation efficiency plummets.

Don't be fooled, turn your own standards

To put it bluntly, many people can't even figure out the temperature threshold. If you are not sure, go directly to this site"National Standard for Non-Metallic Expansion Joints"Or compare the article "The Specific Function of Expansion Joint Guide", which is much more realistic than listening to bragging. The way of fabric connection seems simple, but behind it is the comprehensive consideration of material science, thermodynamics and sealing technology. If you choose the right one, the pipeline will run safely for ten years; If you choose wrong, half a year will make you doubt your life.

DN1000 not 1000mm in diameter? Understand the definition of nominal diameter first

When many people saw DN1000 for the first time, their first reaction was "the diameter of the tube is 1 meter". To be honest, I thought so when I first entered the industry, but I was fooled once by the drawings-the flange I actually bought couldn't fit. The "DN" in DN1000 is an abbreviation for Nominal Diameter, which is essentially aNominal size, not measured values. Take steel pipe as an example. The outer diameter corresponding to DN1000 is commonly 1016mm or 1020mm (see the standard, such as GB/T 1047 or ASME B36.10), while the inner diameter depends on the wall thickness. For example, a pipe with an outer diameter of 1020mm with a wall thickness of 10mm has an inner diameter of 1000mm; If the wall thickness is 12mm, the inner diameter will be 996mm. So here's the question: When you buy the expansion joint or hose of DN1000, do you have the flange according to the outside diameter, or do you have the flow according to the inside diameter? The answer is – look at the FLAND standard. If you are equipped with the national standard PN series flange, the sealing surface size of DN1000 flange and the center circle diameter of bolt hole are fixed, which has nothing to do with the actual wall thickness of the pipe. But if you come across the American Standard Class series, you have to count separately. Bottom line: Don't regard DN as the measured value. It is a code name. When selecting the model, be sure to check the detailed size of the connection end.

How to use DN1000 in large diameter pipe compensation?

DN1000 is particularly common in large-diameter pipelines in thermal power, steel and chemical industries. Which products will be marked with this size? Just a few examples:Large diameter thick wall expansion joint、Metal hose、Desulfurization flue gas baffle door。 Two days ago, the purchase of a desulfurization project asked me: Is the flue gas baffle door of DN1000 1 meter in diameter? I said you should understand it this way, but the actual door panel size depends on the inner diameter of the air duct and the thickness of the lining. The door frame size of the baffle door is usually larger than the DN1000 by a circle, because it needs to leave a sealed space. Another exampleMetal hoseThe metal hose of DN1000 is usually used for circulating water pipelines or flue gas pipelines in power plants. The number of bellows layers and the number of net strands are directly linked to the pressure resistance grade. WhileDesulfurization flue gas baffle doorThe DN1000 (list number 19) refers more to the standard diameter of the flange connection port. You have to confirm whether it is a single-axis double-baffle or a double-seal single-axis circular baffle door. Their structure and sealing methods are completely different.

Field case: DN1000 corrugated expansion joint for power station industry for steam pipeline in a power plant

A while ago, I went to the site of a 660MW unit project, and several steam pipelines were installedCorrugated expansion joint for power station industry(5th in the list), the specification is DN1000. When the installation team finished hoisting according to the drawings and was ready to tighten the tie rod nut, the technician suddenly found that the wave number and pressure level on the expansion joint nameplate did not match the design. And guess what? The drawing requires 4 waves with a withstand pressure of 2.5MPa, while the actual arrival is 6 waves and 1.6MPa. Although the flange hole spacing is all right, more wave number means that the axial stiffness becomes smaller, and it is easy to be compressed and unstable under the large thrust of steam pipeline. In the end, I could only return it for exchange, and the construction period was delayed for three days. So don't think that everything will be fine if DN1000 is matched. The wave number, pressure level and temperature compensation must be checked item by item. Especially for high-temperature steam pipelines, it depends on the material of the guide tube (lining tube) -if it is ordinary carbon steel, it can't withstand more than 500℃, so stainless steel has to be used.

Are metal hoses and rubber compensators interchangeable for DN1000?

Basically not, hard change is equivalent to digging a hole for yourself.Metal hose(The first in the list) relies on bellows and stainless steel mesh sleeve to bear pressure, and the maximum temperature resistance can reach above 600℃ (depending on the material, such as 316L or Incoloy 800), and the pressure resistance can also reach more than ten MPa. Whilerubber compensator(List 9) The main body is rubber + ply, and the temperature resistance is generally over 100℃, and the pressure does not exceed 1.6MPa. You said it was used on the steam pipe of the power plant, and the rubber one melted directly as soon as it was put on. On the other hand, for some low-pressure and normal-temperature circulating water pipes, metal hoses are ok, but the cost is several times higher, so it is unnecessary. There is also a pit: rubber compensators usually have hard flanges at both ends and a rubber sphere in the middle, which cannot bear the weight of the pipe when installed; Metal hoses can be properly supported. Be sure to ask about the medium temperature, working pressure and displacement type before selecting the model. Don't just look at the word DN1000 to place an order.

Three Must-Ask Questions When Purchasing DN1000 Products

First question: What is the connecting flange standard?Is it the national standard GB/T 9119 or the Ministry of Chemical Industry HG/T 20592? Or is it the American Standard ANSI B16.5? Each standard flange outer diameter, number of bolt holes, hole center circle diameter are different. The same supplier may match the national standard by default, but what you get is the American standard flange, and the on-site nozzle has to be reprocessed if it doesn't match. Second question: How to calculate the compensation amount? The expansion joint of DN1000, with axial compensation amounts of 50mm and 100mm, is completely two structures, and the wave number, layer number and wave height are different. Don't just listen to verbal promises. Third question: Does the guide tube have to be fitted? Many people ignore this.Specific Function of Expansion Joint Guide Tube(From Article 7 of FAQ on this site) is to protect the bellows from being washed by high-speed media, while reducing the flow resistance. For flue gas or steam pipelines containing particles, the life of bellows without guide tube is cut in half directly. However, having a guide tube will increase the pressure drop, which can be omitted if the medium is clean and the flow rate is low.

Let's talk about what is expansion joint plane instability

To put it bluntly, when the bellows is subjected to internal pressure, the corrugations are not axially compressed or stretched honestly, but like a flattened can, the plane direction of the corrugations is twisted, wrinkled or even bent laterally. This thing is called plane instability in engineering, and it is also called "bellows instability" in the industry. Have you ever seen the kind of ripples that were originally neat in circles suddenly turn into crooked twists? That's the typical symptom. Understanding this can avoid big problems in the pipeline system.

For example, if the pressure of the corrugated expansion joint used in the power station industry is not accurately calculated in the design, it will change from a ring to an ellipse with corrugation, or even partially deflate. That's not a cosmetic problem, it's a precursor to structural failure.

Where did the plane instability come from?

Excessive internal pressure and insufficient design stiffness. For example, when selecting the type, the working pressure is not accurately calculated, or the corrugated plate is too thin, or the ratio of wave height and wave pitch is unreasonable. When you think about it, bellows are inherently dependent on the geometry of corrugations to absorb displacement. Once the pressure exceeds its critical value, it is like a human spine suddenly bends under excessive compression-it can't hold up. In addition, if there are additional lateral forces or torsional stresses during installation, instability can also be induced. Two days ago, I met a customer, saying that the general-purpose corrugated expansion joint used in power stations was crooked after half a year of use. When I checked the drawings, the wave number was large but the wall thickness didn't keep up, and the typical pressure exceeded the limit.

The external pressure single type axial expansion joint was selected, but the actual operating pressure exceeded the design pressure by 1.5 times, and the instability probability increased greatly. The design pressure is 1.0MPa, but when it actually runs to 1.6MPa, 80% of them will have problems-this is not metaphysics, but common sense of mechanics.

The dangers of plane instability are no joke

Failure and air leakage are mild, and pipe burst is severe. Especially in some high-temperature and high-pressure pipelines, such as corrugated expansion joints and high-temperature axial expansion joints used in power station industries, once they become unstable, the corrugation breaks and leads to media leakage, which may directly cause shutdown accidents and even personal safety risks. Do you think the loss is big? Moreover, instability often does not happen suddenly, and there will be deformation accumulation in the early stage, but once it passes the critical point, the collapse speed is extremely fast. So don't wait until you hear an abnormal noise or see a noticeable distortion before dealing with it, it's already too late.

A cement factory used a batch of metal corrugated expansion joints in cement industry. In the third month after installation, it was found that the corrugations were partially depressed, and the operator didn't take it seriously. As a result, it burst directly on the sixth day, and high-temperature gas was ejected. Fortunately, no one came close at that time. This matter was later resumed, that is, the wave height ratio exceeded the standard and the plane stability was not enough.

How to judge whether the expansion joint has plane instability?

The simplest and crudiest way-eyes. If it is found that the corrugations of the bellows have irregular wavy wrinkles and local depressions, or the whole bellows rotates like a twist, it is basically unstable. More professionally, you can measure the change of outer diameter and wave pitch of bellows, or monitor it with a strain gauge. In addition, it is also critical to compare the design parameters: if the actual operating pressure exceeds 1.5 times the design pressure, the probability of instability increases greatly. For example, the external pressure single axial expansion joint, with a design pressure of 1.0MPa, actually runs to 1.6MPa, and 80% of them will have problems.

Scratches or abnormal wear on the inner wall of the guide tube. Because the corrugation deforms after instability, it will rub the guide tube. Therefore, regularly checking the state of the guide tube is also one of the basis for judgment. The product information of this site mentions the specific functions of the expansion joint guide tube, one of which is to protect the corrugation, but it can also reflect the health of the corrugation.

To prevent plane instability, the core is four words: choose the right one and use it well

When selecting the type, don't just look at the pressure grade and diameter, but also check the stability coefficient of the bellows. Like straight pipe pressure balance expansion joint or double hinge transverse expansion joint, because the structure itself has constraints, the risk of instability will be lower. However, if it is a general-purpose corrugated expansion joint or a large-diameter thick-wall expansion joint, special attention should be paid to the matching of wave height and wall thickness. Install a guide tube when necessary-the guide tube can not only protect the inner wall, but also reduce the direct impact of the medium on the corrugation, indirectly reducing the risk of instability. Concentricity should also be ensured during installation, and the pipe should not be pulled and dragged.

In some scenarios, such as the double-hinged expansion joint of air-cooled island vacuum pipeline for air-cooled island vacuum pipeline or the high-temperature axial expansion joint for high-temperature pipeline, the stability check must be done during design, and it can't only rely on experience. In addition, although the materials of metal rectangular expansion joints and non-metal expansion joints are different, the principle of plane instability is the same-the instability of corrugated structure is a geometric problem and does not change due to the material.

The product drawings of many small factories are cheap with thin materials, or they are not designed according to standards. It doesn't take long for users to buy them back and use them before they go wrong. When making products in our industry, such as metal rectangular expansion joints and non-metal expansion joints, stability must be regarded as a hard index. If you find that the expansion joint on the pipe looks wrong one day, don't hesitate to stop it and check it quickly. After all, a pipeline costs millions and an expansion joint costs thousands of pieces. Is it a loss to scrap the whole line because of instability?

For expansion joints that have been installed, strain gauges can be attached to the bellows surface to record the deformation regularly. Once it is found that the strain value of a certain side corrugation continues to increase, it indicates that instability is occurring. This is much more reliable than observing it with the naked eye. Especially for high-risk scenarios such as power stations and chemical industries, early warning saves too much money than remediation afterwards.