Specialized in manufacturing compensators, expansion joints, baffle doors

Can the expansion joint be buried in the ground? Don't jump to conclusions yet

Two days ago, I met a customer, and he was in a hurry on the phone: "Our heating pipeline was buried with ordinary expansion joints, and it leaked in one heating season. Can you help me?" Alas, I have seen this too much. In order to save that procurement cost, many Party A directly buried the general-purpose corrugated expansion joint in the soil, feeling that "it's invisible when buried anyway". And the result? As soon as the groundwater bubbles and the soil is pressured, the bellows become unstable, corroded and fractured by fatigue, and the whole set of pipes have to be dug out and reworked.

Can expansion joints be used buried in the ground?The answer is: ordinary ones can't work, but the "directly buried (fully buried) expansion joint" of this station is specialized in this job.

Why can't ordinary expansion joints bear the underground environment?

Standard metal corrugated expansion joints (such as general corrugated expansion joints and high temperature axial expansion joints) are designed without considering external loads at all. It works by default in overhead pipes or pipe trenches with no soil pressure around, no vehicle crushing, and no groundwater infiltration. You bury it, which is equivalent to asking a man in a suit to carry the sandbag-the bellows are directly deformed by earth pressure, and coupled with poor drainage, the rate of corrosion doubles.

In order to save investment, a thermal power company in the north directly buried the general-purpose corrugated expansion joint, and the backfill soil was mixed with gravel. In the first winter of operation, the bellows was pitted by gravel, coupled with water vapor corrosion, and the weld cracked. Finally, the whole pipe section was scrapped, and the excavator dug for three days before replacing it with new parts. It is more than three times more expensive than buying the direct burial type at the beginning.

What is special about the directly buried expansion joint? To put it bluntly, wearing "body armor"

The "directly buried (fully buried) expansion joint" of this station has three layers of protection in structure:
First, the outer sheath is an integral welded carbon steel or stainless steel casing that directly bears soil pressure and ground dynamic loads (such as car rolling).
Second, the interior is filled with insulation material to prevent heat loss, especially suitable for steam pipes and thermal pipes.
Third, the end seal structure can prevent groundwater from seeping into the bellows and avoid electrochemical corrosion.

Note that it is not the same thing as a "sleeve-type pipe expansion joint" or a "rotary compensator". Sleeve type is sealed by packing, which is easy to leak after long-term operation; The rotary compensator absorbs displacement by rotation, but the installation space requires a large amount. Direct buried expansion joints are specially designed for fully buried environments, so don't mix them.

How many of the three easiest pits to step on when selecting models?

Pit 1: Only look at nominal pressure, regardless of external load.Some people think that since the directly buried expansion joint is called "directly buried", just choose a pressure level. SO WRONG! With a buried depth of 2 meters and a buried depth of 0.5 meters, the soil pressure difference is several times. If a car or excavator passes through the ground, the dynamic load is even more terrible. The pressure bearing capacity must be re-checked according to the actual buried depth and ground use.

Pit 2: Ignoring the axial thrust, the fixed bracket is weak.Both ends of buried pipes must be provided with sufficiently strong fixing brackets. In many projects, in order to save costs, the bracket is welded with thin steel plates. As a result, when the pipeline expands thermally, the axial thrust directly pushes the bracket askew, and the bellows is squeezed to be twisted and deformed. Remember: When the directly buried expansion joint compensates for displacement, the axial thrust must be borne by the fixed bracket, and the strength of the bracket cannot be sloppy.

Pit 3: The anti-corrosion grade is lazy, but the insulation layer accelerates corrosion.If there is an insulation layer in the directly buried part, once the moisture penetrates, the insulation material will become a "water absorber", and the risk of electrochemical corrosion is higher than that of exposed metal. Epoxy coating or cathodic protection is recommended, especially in areas with large burial depth and high groundwater table.

If you don't keep an eye on the installation details, no matter how good the expansion joint is, it will be useless

Backfill soil must be tamped in layers, each layer not more than 30 cm thick, and there must be no large pieces of rubble or sharp objects. At least 50cm of operating space should be left on both sides of the expansion joint to facilitate later maintenance-don't bury the bolts in concrete, and you can't screw them even if you want to.

The soil can be covered only after the pressure test is completed. The pressure test pressure is generally 1.5 times of the design pressure, and the pressure can be kept for 30 minutes without leakage before the soil can be filled. The thickness of the covering soil must be according to the design drawings, and it cannot be thickened at will. We have done a project, and the customer buried the directly buried expansion joint 2 meters deep (the design was only 1.2 meters) to save trouble. As a result, the compensation amount was not enough, and the pipeline collapsed directly from the interface during thermal expansion.

Not all buried pipes need to be buried directly, but thermal steam pipes must be honestly selected

For example, the circulating water pipes of power plants and the conveying pipes of cement plants have low medium temperature and low pressure, so it can be done with "rubber compensator" or "polytetrafluoroethylene compensator" with anticorrosion treatment. However, thermal pipelines and steam pipelines-especially those with a medium temperature exceeding 200℃ and a pipeline length of several hundred meters-honestly choose the "directly buried (fully buried) expansion joint" of this station, and don't joke about its service life.

Not sure about the selection? You can ask our technical department for the parameter table of buried working conditions, fill in the soil type, buried depth, ground load, medium temperature and pressure clearly, and we will give you a calculation book. After all, the final answer to the question "Can expansion joints be buried and used?" Depends on whether you choose the right product or not.

Section 1: The "Safety Illusion" of Overchoosing-Why do many people think bigger is better?

When choosing expansion joints in the project, many people hold the mentality of "rather big than small". I think with a larger caliber and more wavenumber, the compensation ability will definitely be stronger and the system will be safer. Doesn't that sound reasonable? But the actual failure case slapped the face. Two days ago, I talked to a master who did power plant maintenance. He said that several of the corrugated expansion joints replaced on their pipelines were fatigue cracked because of the large selection. The principle is actually very simple: the larger the size of the expansion joint, the greater the stress generated when it is subjected to internal pressure, especially the position of wave peaks and troughs. Moreover, after the selection is large, the actual displacement of the system may be much smaller than the design value, and the corrugation is in a state of "not having enough food" for a long time, so the creep and stress concentration of the material are more obvious. Tsk, is it the opposite of intuition?

Section 2: What trouble will you cause if you elect big? — From instability to air leakage, don't try to hide from any

Let's start with instability. The expansion section is large, especially for large-diameter thick-walled expansion joints or external pressure single axial expansion joints. If the nominal diameter exceeds the actual pipeline by a lot, and the end constraints are not adjusted accordingly, plane instability or columnar instability will easily occur. Once the bellows becomes unstable, it is only a matter of time before the seal fails. Let's talk about fatigue life. The life of the expansion joint depends on the number of cycles and stress levels. If a large expansion joint is selected, the actual stress value of the bellows may exceed the design standard by more than 30%-the original designed life of 100,000 times will crack after 20,000 times. There is also the problem of installation space: the expansion joint is selected to occupy more axial space, and the layout of pipe bracket and guide bracket has to be changed accordingly, or it may interfere with adjacent equipment. Not to mention the cost. Stainless steel materials cost twice as much, and flanges, tie rods and guide tubes are all upgraded, which is pure waste.

Section 3: Under different working conditions, the "lethality" of excessive selection has its own emphasis

The corrugated expansion joint used in the power station industry is often on high-temperature and high-pressure steam pipelines. If it is selected large, the wall thickness of the corrugated pipe will be relatively thin and the pressure resistance will decrease. The metal corrugated expansion joint used in the cement industry contains more dust in the medium. If the flow rate is larger, the dust is easier to accumulate in the trough and the corrosion is aggravated. If a non-metallic expansion joint (fabric fiber expansion joint) is used, the consequence of choosing a large one is more direct-the tension bearing by the fabric layer is uneven, and it will bulge and tear in the short term. For the rubber compensator, choosing a large one will also make the rubber body crack by fatigue. Let's take a look at the rotary compensator and sleeve-type pipe expansion joint. Such products are sealed by packing. If the casing gap is larger, the sealing packing can't be pressed tightly, and air leakage is common. After all, every type of expansion joint has its best working size range, and blindly choosing large is digging a hole for yourself.

Section 4: What exactly is called "choosing the right"? Don't slap your head

Many people get the pipeline layout drawing, and as soon as they see the thermal displacement of 200mm, they directly choose an expansion joint with a rated compensation of 250mm. This approach is only one-third correct. The correct selection process should be: first clarify the medium, temperature, pressure and nominal diameter of the pipeline, then calculate the thermal elongation and cold tightness, and also consider the installation error and additional displacement of the end point. For general-purpose corrugated expansion joints, a safety margin of 10% ~15% should be left when selecting the model, but it should never exceed 20%. If it is a high-temperature axial expansion joint, the allowable stress of the material at the highest operating temperature should also be checked. There is also one that is easy to overlook-the deflector. For example, the diameter of the selected expansion joint is larger than that of the pipeline, and the size of the guide tube has to change accordingly. Otherwise, the medium will directly wash the inner wall of the bellows and wear it out in a few months. Therefore, the selection is not done by looking at the numerical value, but the guide tube, the tie rod and the limit structure have to be taken into account.

Section 5: What if I have already installed it? Can you remedy it if you elect it big?

This problem is case by case. If the expansion joint is only a small amount too large (say one gauge larger than the actual pipe) and space allows, you can limit the amount of compression of the bellows by adjusting the tie rod nut, or add pre-tension/pre-compression to match the actual displacement. For structures with guide barrels, the guide barrels can also be replaced to improve flow path matching. However, if you choose more than two specifications, or there are signs of instability, then don't hesitate to change it directly. The cost of forcibly making do is far greater than that of replacing a new one-the loss of shutdown and production and the risk of safety accidents can't be afforded. In addition, a reminder: the screw and tie rod of the expansion joint are not decorations, and they must be adjusted in place according to the actual displacement before installation. For details, you can check the question and answer "How to adjust the tie rod nut of the expansion joint" we wrote before.

Section 6: The most afraid thing about model selection is "taking it for granted"

The expansion joint is not the bigger the better, nor the smaller the better, it is "just right" the best. Different working conditions, different media and different pipeline layout correspond to different models and sizes of expansion joints. For example, high-temperature axial type is used for high-temperature pipelines, straight pipe pressure balance type is used for large temperature differences, compound hinge transverse type is used for transverse displacement, and directly buried (fully buried) expansion joint is used for buried in soil. Each product has its own "temper". Before the selection, it is best to communicate with the technicians of the manufacturer and give all the working condition parameters. Remember: Does inflated excerpts have an impact when they are big? The answer is clear — not only impactful, but potentially fatal.

First, what is the metal expansion joint used for? — Don't be fooled by the name, the core is two words: compensation

Two days ago, I met a customer who came up and asked, "Is the metal expansion joint the same as the expansion joint on the radiator?" Alas, it means about the same, but it is far from that simple. To put it bluntly, as soon as the temperature in the pipeline system changes, the pipe will expand and contract by heat. The result of hard pulling is that the interface collapses and the equipment is crooked. Metal expansion joints do just that — they absorb displacement and release stress. You can call it compensator. These two words are common in the industry (refer to Article 14 of the FAQ in our site). There are two words at the core: compensation. Compensate for axial expansion and contraction, lateral offset, and even angular torsion. Without it, steam pipes and heat pipe networks will show you a look in minutes.

What we produceUniversal corrugated expansion jointIn chemical pipelines, they are soaked in high-temperature steam every day, and expand and contract hundreds of times all year round, relying on the elastic deformation of the thin walls of the bellows. AndCorrugated expansion joint for power station industryThe temperature of the main steam pipe of the power plant can soar to five or six hundred degrees. Without it, the pipe would have collapsed early.

Second, there are so many structural classifications, which ones are commonly used by us? — Bellows, sleeves, non-metals, each with its own temper

When you stand in our warehouse, you can see that the densely packed expansion joints are actually divided into three categories according to their structure: bellows type, sleeve type and non-metallic type.

Bellows expansion jointIt is the main force, relying on the deflection of ripples to absorb displacement. There are many sub-classes: such asHigh temperature axial expansion jointSpecialized in carrying high temperature;Straight pipe pressure balanced expansion jointIt can balance the blind plate force and be used on large pipes under pressure;Compound hinge transverse expansion jointIt can absorb lateral displacement and fit where the space turns. AndExternal pressure single axial expansion jointExternal pressure structure can withstand higher pressure, which is common in petrochemical industry.

Sleeve type pipe expansion jointIt is another way, which relies on the sliding between sleeves to compensate for the displacement. The structure is simple but the sealing requirements are high. It is generally used in low pressure and large displacement occasions, such as heating pipe network.

Besides, non-metallic ones, we have them on our stationNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion joint。 This thing is made of fabric and rubber, which can absorb multi-dimensional displacement and is corrosion-resistant, especially in smoke ducts and desulfurization systems. Oh, yeah,rubber compensatorAndRubber PTFE compensatorAlso in this category, the vibration damping effect is first-class.

Each structure has its own temper. If you choose the wrong one, the oil and water leakage in two years will be light, and the whole pipeline system may collapse.

Third, if you don't look at these three points in type selection, you will most likely step on pits-medium, temperature and displacement, one cannot be missed

After so many years of explaining metal expansion joints, I have seen too many people who pat their heads and select models. Let me tell you, first figure out these three parameters:

• Medium: What fluid goes? Strong corrosive, must be usedPTFE-lined hoseOrPTFE compensator； For dusty flue gas, wear resistance and guide tube structure should be considered.
• Temperature: Temperature directly determines the material. Use 304 stainless steel at room temperature, and you have to use heat-resistant alloy for five or six hundred degrees. Our oneHigh temperature axial expansion jointThe upper limit of the design temperature can reach more than 1000℃.
• displacement amount: How does the pipeline go? How much is axial telescoping? How big is the lateral offset? Every direction should be calculated clearly. Such asDouble hinge expansion joint for air-cooled island vacuum pipelineSpecially designed for vacuum large diameter pipeline, can absorb large angular displacement.

Don't think that these three values are enough to know. In actual engineering, they will affect each other. For example, high temperature + corrosive media, optical material selection is a knowledge. You choose an ordinary stainless steel bellows, and it won't take long to corrode and perforate. So don't be lazy and give your working condition parameters to the manufacturer honestly.

4. In installation and daily maintenance, the most easily overlooked details-the orientation of the guide tube, the adjustment of the pull rod, and whether the screw can be removed or not

Installing expansion joints looks simple, but the details determine the longevity. The first easy mistake to make is to install the deflector in the reverse direction. We have a FAQ on our siteSpecific Function of Expansion Joint Guide TubeThe guide tube is used to guide the flow direction of the medium and protect the bellows from being washed and worn. The direction of the arrow must be consistent with the flow direction of the medium (refer to Article 10 of Q&A). Install it backwards, and the guide tube is a plug, which will aggravate the wear.

How to adjust the tie rod nut? Many customers receive the expansion joint and find that there are tie rods and nuts fixed at both ends, thinking that it is used for reinforcement, and it will not be disassembled. Wrong! These tie rods (also called transport tie rods) are used to prevent the bellows from deforming during transportation. After being installed in place, the nut should be loosened, adjusted to the working position, or removed directly (refer to Q&A 12 and 13). Otherwise, the expansion joint can't expand and contract freely at all. What is the difference between it and a steel pipe?

AndCorrect installation method of expansion joint of large tie rodThe large tie rod structure is to bear the internal pressure thrust, and the tie rod must be adjusted to the designed length during installation, and cannot be screwed randomly. Routine maintenance is to regularly check the bellows for cracks and corrosion spots, especially thoseDesulfurization flue gas baffle doorNext to the expansion joint, the acidic environment is most prone to problems.

5. Common faults and misunderstandings: Why did it leak after two years of use? — — Fatigue, corrosion, installation stress, take the right seat

"The quality of your expansion joint is not good. It leaked in two years." Every time I heard such words, I always asked about the working condition first. Nine times out of ten, it is a problem of type selection or installation. There are three common reasons for leakage:

• Fatigue failure: If the pipeline vibrates frequently, or the design displacement is smaller than the actual, the bellows bends repeatedly, and the metal fatigue causes cracks. This situation can be consideredMetal hoseOrSpecial hose for vacuumTo dampen the vibration.
• Corrosion perforation: There are chloride ions and sulfide in the medium, and stainless steel still can't bear it. Either reline PTFE or choose high nickel alloy. WeMetal Corrugated Expansion Joints in Cement IndustryOften encounter sulfur-containing flue gas, the surface has to be made with anti-corrosion coating.
• Installation stress: The pipeline is forced to be installed at the opposite side, or the tie rod is not loosened, and the force of the expansion joint exceeds the design. When installing, make sure that the expansion joint is in a free state, and don't pull hard.

Think that the expansion joint is "all-purpose" and can absorb all displacement. Virtually every model has a cap on the ability to compensate. Such asDirect buried (fully buried) type expansion jointSpecially used for directly buried pipelines, the axial compensation is large but the lateral compensation is limited. If the pipe turns too much, you have to cooperateRotary compensatorOrCurved tube pressure balance expansion joint。

This thing of expansion joint, three points depends on quality, seven points depends on selection and installation. Don't just buy a general-purpose model to save money and trouble. When you're not sure, flip through the "Explanation of metal expansion joint"Series articles, or directly find technology to talk about working conditions. Save those few minutes of communication, and the maintenance fee later will be enough for you to buy ten expansion joints.

I met a customer two days ago, and as soon as I came up, I asked, "Which is better, metal expansion joint or non-metal expansion joint?" I asked him what kind of medium was going in the tube, and he was stunned and said, "It's just normal steam." That's the problem-directly comparing the good with the bad regardless of the working conditions, like asking "which is better, a hammer or a screwdriver"-you first have to know whether to nail or screw.

First, don't worry about which one is better, it depends on what is going in your pipe

The expansion joint has one core task: absorbing the displacement caused by thermal expansion and contraction of the pipeline, and by the way, absorbing shock and noise. However, different media, different temperature and pressure, and different selection logic.
Steam pipeline, the temperature is always above 300℃, the pressure starts at 1.6MPa, and the non-metallic fabric fiber layer can't bear it at all; On the other hand, the flue gas pipeline contains sulfur and acid, and the metal bellows will corrode in a few days, while the non-metal is corrosion-resistant.
Therefore, the first step is not to compare good or bad, but to find out the four parameters of medium, temperature, pressure and displacement. Otherwise, if you choose the wrong choice, you can leak at least and explode the pipe at worst.

Second, metal expansion joint: a tough guy resistant to pressure and temperature, but it also has weaknesses

Metal expansion joints (such as oursUniversal corrugated expansion joint、A high-temperature axial expansion joint,Corrugated expansion joint for power station industry) by deformation of stainless steel bellows to compensate for displacement. The advantages are obvious:
-High withstand voltage: Conventional energy to 2.5MPa, special design (e.g.Large diameter thick wall expansion joint,directly buried expansion joint) Can carry higher.
-High temperature resistance: With the guide tube and the heat insulation layer, the high-temperature axial type can reach above 800 ℃.
-Long life: Designed properly, fatigue times can reach tens of thousands.
But the weakness is also eye-catching:
First,Not corrosion resistant。 When it comes to wet chlorine and concentrated sulfuric acid, stainless steel is useless, and it has to be lined with PTFE (such as oursPTFE-lined hose).
Second,Unable to withstand large lateral displacement。 The single-wave compensation amount is generally 10-20mm, which requires multi-wave or double hinges (such asDuplex hinge transverse type expansion joint) to make up for it.
Third,High installation accuracy requirements。 How to adjust the tie rod nut and where to point the direction of the guide tube are all particular, and it is wasteful to install it wrongly.

Look at the structure first: the bellows is the core "spring" of the expansion joint

When you stare at a disassembled metal expansion joint, your first reaction must be: How can this thing "expand"? In fact, the secret is all in the middle circles of bellows. To put it bluntly, a metal expansion joint is a section of thin-walled tube with corrugations, with joints or flanges welded at both ends. The bellows is the equivalent of a metal spring that can be telescoped — but not a coil spring, but an annular ripple that runs in circles. These ripples are elastic in the axial direction, and when subjected to tension or pressure, the peaks and valleys of the ripples will open or close, resulting in displacement.

How much can the bellows stand? It depends on its stiffness. The smaller the stiffness, the easier it is to deform, and the greater the amount of compensation; But the stiffness is too small to hold up internal pressure. Therefore, it is necessary to look at the number of layers, wall thickness, wave height and wave pitch of bellows when selecting the type. For example, the general corrugated expansion joint we often say is generally a single-layer or multi-layer stainless steel bellows, while the high-temperature axial expansion joint under high-temperature working conditions has to be made of heat-resistant alloy and multi-layer structure.

Axial expansion: How does the bellows "expand and contract" when the pipe expands and contracts thermally?

The most common scenario is a steam pipe. When the pipe rises from cold to several hundred degrees, the length will be stretched by several centimeters. At this time, an axial expansion joint is installed in the middle of the pipeline, and the bellows is compressed-the distance between peaks and valleys is reduced, absorbing the elongation of the pipeline. In turn, if the pipe cools and shrinks, the bellows stretches. So you see, how do metal expansion joints expand? In fact, it is more accurate to say "compensate for displacement". The bellows itself does not necessarily really "expand", but eats the thermal expansion and contraction of the pipe through elastic deformation.

The amount of compensation. How many millimeters of axial displacement an expansion energy saver can absorb depends on the wave number of the bellows and the amount of single wave compensation. For example, external pressure single axial expansion joint, because the outside of the bellows bears the medium pressure, the stability is better, and the single wave compensation can be larger, which is suitable for long-distance pipelines. However, the directly buried (fully buried) expansion joint should consider external pressure and soil corrosion, and its structure is more complicated.

Lateral and Angular Displacement: Can Bellows Still "Walk Bending"?

The pipe is not a straight line, and turning, misalignment, and vibration will all produce lateral and angular displacements. Axial compression alone is not enough at this time. What to do? Let the bellows "bend". For example, the double hinge transverse expansion joint uses two sets of bellows to add a hinge structure in the middle, which can absorb transverse displacement and angular displacement. Imagine that two sets of bellows, one bent and the other extended, can make the pipe "drift" in the horizontal direction with the rotation of the hinge.

There is also a curved tube pressure balance type expansion joint, which is specially used in the curved tube part with pressure thrust. It adds a balanced bellows inside to offset the blind plate force and avoid excessive thrust on the pipe support. Two days ago, a customer asked me, saying that the bracket was always broken at the corner of the hot air duct in their factory. When asked, the blind plate force was not counted. Later, the pressure balance expansion joint of the curved tube was replaced, and the problem was directly solved.

Select different "expansion methods" for different working conditions: high temperature type, pressure balance type, double hinge type... Don't choose the wrong one

Choosing the wrong expansion joint is equal to laying a mine. Simply a few points:

• High temperature flue gas pipeline(For example, power stations and cement industries) -use high-temperature axial expansion joints or non-metallic expansion joints. Non-metallic fabric fibers can carry hundreds of degrees, and there is no internal pressure thrust, but the strength is not as strong as metal.
• Steam Supervisor(High pressure, high temperature) -Straight pipe pressure balanced expansion joint or double straight pipe bypass pressure balanced expansion joint. They absorb axial displacement while balancing pressure thrust and do not require a primary fixing bracket.
• Air-cooled island vacuum pipe— — The double hinge expansion joint of air-cooled island vacuum pipeline is used, and the sealing requirement in vacuum environment is extremely high, and the double hinge structure can absorb complex displacement.
• Large diameter thick-walled pipe(For example, desulfurization flue) -large-diameter thick-walled expansion joint, strengthened wall thickness, and guide tube has to be added to prevent scour.
• Insulated parts requiring frequent overhaul— — With manual plug-in type insulation door or electric plug-in type insulation door, use expansion joint to compensate pipeline displacement, and then use baffle door to cut off the medium.

You see, the "expansion method" is different for each working condition. When selecting the model, you have to compare the model and size table of the expansion joint, calculate the compensation amount, pressure and temperature, and don't just look at the price.

"Expansion" doorways in installation and use: the key points of deflectors, tie rods, pre-stretching

Only when the expansion joint is installed correctly can it "expand" normally. Article 1:guide tube。 The guide tube is installed on the inner wall of the bellows, and its function is to guide the flow medium to avoid the direct washing of the bellows by high-speed fluid. Especially in the flue gas pipeline with particulate matter or high flow rate, the bellows will wear out in a few months without the guide tube. The specific function can refer to the question and answer in our station.

tie rod。 Many expansion joints come out of the factory with tie rods or transport screws, which is to prevent the bellows from being crushed or pulled during transportation and installation. How do you adjust the tie rod nut after installing it in place? It is generally required to loosen the nut and allow the tie rod to float freely, but in some cases it is necessary to adjust the tie rod length to pre-compress or pre-stretch the expansion joint. For example, when the temperature of the pipeline is lower than the operating temperature, it has to be pre-stretched. After the temperature rises, the expansion joint just returns to the free length, and the compensation efficiency is the highest. Does the screw of the expansion joint need to be removed? The transportation screw must be disassembled, and the pull rod depends on the situation, and some are reserved as limits.

Pre-stretching。 It's a practical trick. For example, the design compensation amount of an axial expansion joint is 50mm. If the installation temperature is 20℃, the operating temperature is 200℃, and the pipeline is extended by 80mm, the expansion joint has to be pre-stretched by 30mm, installed on the pipeline and then welded. This operates without exceeding the compression limit of the bellows. This is often done in the cement industry and power station industry with corrugated expansion joints.

Don't reverse the installation direction of the expansion joint. The direction of the arrow of the expansion joint refers to the flow direction of the medium. If it is installed backwards, the guide tube will not play the role of diversion, but will become a throttling piece, and the pressure loss will increase greatly. Many on-site accidents are caused by reverse directions.