Specialized in manufacturing compensators, expansion joints, baffle doors

1. First understand the core parameters: what do you think of stiffness, pressure, temperature and compensation?

I have been in this business for 20 years, and I am most afraid that I will fill in "high temperature resistance" directly on the selection list. There are only a few core parameters of bellows expansion joints, but each one hides pits.

stiffness— — Don't be fooled by the word "stiffness". Simply put, it is the ability of bellows to resist deformation. The greater the stiffness, the greater the thrust generated at the same displacement. If you choose an expansion joint with too high stiffness, the pipe bracket and fixing point may directly push through. This site has a special "Stiffness and Calculation Formula of Bellows", which gives the theoretical algorithm. However, when actually selecting the model, it is recommended to ask the manufacturer directly for the measured stiffness value on the sample, which is the real guy.

pressureAndTemperatureIt's a pair of conjoined babies. The pressure level is easy to understand. Which one should I choose between 0.6MPa, 1.0MPa and 1.6MPa? But as soon as the temperature rises, the permissible stress of the material drops. For example, the bearing capacity of 316L stainless steel at 400℃ and room temperature is quite different. Many peers only look at the design temperature, but ignore the "maximum working temperature × duration"-short-term overtemperature may be fine, and long-term operation at the critical point will directly cut the life of bellows in half. So chooseHigh temperature axial expansion jointWhen, not only look at the nominal temperature resistance value, but also confirm whether the number of corrugated layers and wall thickness meet the fatigue life requirements.

Compensation amountIt's a gimmick hit area. Some manufacturers mark "axial compensation ± 50mm", but that is the theoretical value calculated by multiplying the single wave compensation by the wave number. In fact, the pre-stretching amount, safety factor and cold tightness amount have to be deducted. The correct way is to first calculate the thermal elongation of the pipeline, then multiply it by the insurance factor of 1.2~1.5, and finally check it against the "allowable compensation curve" given by the manufacturer. Don't expect an expansion joint to overcome the world. If the compensation amount is too large, consider using itCompound hinge transverse expansion jointOrStraight pipe pressure balanced expansion jointTo share.

2. Don't pat your head when selecting models: high-temperature axial type, general-purpose type, straight pipe pressure balance type, working conditions determine the model

I met a customer two days ago. The temperature of the steam pipeline is 350℃ and the pressure is 1.0MPa. The direction of the pipeline is simple, but it is necessary to go upStraight pipe pressure balanced expansion joint。 Why? Because I heard that "the pressure balance type is good, and there is no blind board force". However, the pressure balance type has complicated structure, high cost and large installation space requirements. For the working condition that there is no strict thrust limit in the straight pipe section, it is purely a knife for killing chickens.

• High temperature axial expansion joint— — It is suitable for straight pipe sections with high temperature and large axial displacement. The temperature resistance can reach above 600℃, but it can only absorb axial displacement and cannot bear lateral or angular displacement. Note that its guide tube is standard to prevent high-temperature media from directly washing the bellows.
• Universal corrugated expansion joint— — It is often called universal type, which can absorb axial, transverse and angular displacement, and is suitable for pipelines with small and medium diameter, low pressure and temperature no more than 300℃. High cost performance, but the fatigue life is relatively short, so don't use high-frequency vibration occasions.
• Straight pipe pressure balanced expansion joint— — It is mainly used in places where the fixed bracket cannot bear the blind plate force, such as the inlet and outlet of steam turbine and the outlet pipeline of pump. It can balance the thrust generated by internal pressure, but it needs to reserve enough space when installing, and the two bellows need to act synchronously, which requires high welding and assembly accuracy.

Apart from that, there areCurved tube pressure balance expansion jointFits at the elbow,Double straight pipe bypass pressure balance typeSolve the problem of large compensation amount. I just want to tell you that there is no standard answer to model selection, only the working conditions determine the model. Don't save trouble, calculate the design parameters clearly, and then flip through the product library of this site. Each model has the corresponding application scenario description.

3. The three most common pits at the installation site: the direction of the guide tube is reversed, the pre-tension is forgotten, and the tie rod nut is randomly adjusted

If you choose the right model, it will still be useless if you mess up the installation. There are countless pits on the scene, and these three are the most typical ones.

The first pit: the direction of the guide tube is reversed.The function of the expansion joint guide tube is to protect the bellows and avoid direct scouring of the medium. However, many masters think that it is a flow direction sign when they look at the arrow-wrong, the direction of the arrow is the flow direction of the medium, and the open end of the guide tube must face the direction of the incoming flow. If it is installed backwards, the guide tube becomes a gas collecting chamber, and the medium forms a vortex in the tube, which intensifies the vibration, and the bellows is worn out in minutes. Regarding this point, there is a diagram in the question and answer of "Specific Function of Expansion Joint Guide Tube" on this site. It is recommended to take a look before installation.

The second pit: forgot to do the pre-stretch.For axial bellows expansion joints, if pre-tensioning (or cold tightening) is not done during installation, the expansion joints may be directly pulled to the limit after the pipeline heats up, and the bellows may be plastically deformed and scrapped. The amount of pre-stretch is generally half the amount of design compensation. For example, the design compensation amount is 80mm, and the pre-stretching amount is 40mm. How to pull? Use the pull rod and the nut to cooperate, don't pull hard, it is easy to hurt the ripples. Note: Remove the limit screw for transportation after pre-tensioning, otherwise the expansion joint will not work. Some expansion joints (such asExternal pressure single axial expansion joint) Comes with pre-stretching device, confirm before installation.

The third pit: the tie rod nut is randomly adjusted.What is the function of the tie rod of the expansion joint? It is clearly written in the question and answer-limit the excessive expansion and contraction of the bellows and prevent instability. However, some on-site masters think that tightening the nut means fixing, and loosening it means releasing. As a result, the tie rod is adjusted to a dead limit, and the expansion joint completely loses its compensation ability. The correct way is to adjust the nut to the design position according to the drawing before installation (usually with a gap), and then fine-tune it according to the actual needs after installing the pipe. EspeciallyLarge tie rod expansion jointThe tie rod is not a load-bearing part, but a limiting part. Don't use it as a hard support. There are also expansion joints with screws, asking "Do the screws need to be removed"? The answer is: the transport screw must be disassembled, and the tie rod screw remains but the position is adjusted.

4. Industry application comparison: how to set up corrugated expansion joints for power stations, metal corrugated expansion joints for cement industry and desulfurization flue gas baffle doors

Different industries, working conditions vary greatly, and the emphasis of type selection and installation is completely different.

Power station industry: The main steam pipeline, reheating pipeline and water supply pipeline are all large-diameter, high-pressure and high-temperature expansion joints, such asCorrugated expansion joint for power station industryAndDouble hinge expansion joint for air-cooled island vacuum pipeline。 The calculation of pipeline thrust in power stations is extremely strict, and compound hinges or pressure balance types are often used to release the thrust on steam turbines and boilers. Special attention should be paid to when installing: preheating before welding, and slow cooling after welding to prevent stress cracking in the heat-affected zone. Moreover, power station pipelines often have vertical sections, so guide brackets should be set to prevent the expansion joint from twisting.

Cement industry: The high-temperature fan outlet, kiln tail smoke chamber and decomposition furnace inlet and outlet of cement production line, the temperature is 350~500℃ all the year round, with large dust content and serious medium wear. You can't use ordinary stainless steel bellows at this time, you have toMetal Corrugated Expansion Joints in Cement IndustryIn particular, attention should be paid to the lining wear-resistant layer and multi-layer corrugated design. In addition, such occasions are usually associated withRectangular non-metallic expansion jointOrNon-metallic expansion joint (fabric fiber expansion joint)Used on flue gas pipelines, non-metallic materials are corrosion resistant and have high fault tolerance.

Desulfurization flue gas system: The flue gas after wet desulfurization has low temperature but acid corrosion, so it must be usedDesulfurization flue gas baffle doorMatching expansion joint. The most common thing here isDouble-sealed single-axis circular baffle doorAndRound Flap Door (Double Seal), cooperate withrubber compensatorOrPTFE-lined hoseTo isolate corrosive media. Note: The rubber compensator is not resistant to high temperatures and can only be used for clean flue with smoke temperature below 80℃; If the flue gas temperature fluctuates greatly, it is recommended to usePTFE compensator。 The length of the connection between the baffle door and the expansion joint should be sufficient, otherwise the expansion joint will be squeezed and deformed after closing.

5. There is a way to maintain: What is the impact on the service life of the expansion joint? Replacement cycle of rubber compensator and metal hose

Expansion joints are not permanent pieces, but they vary greatly in life. Main factors affecting longevity-by importance:

• Large temperature cycle-frequent start-stop process harms the bellows the most, because the number of thermal stress cycles directly determines the fatigue life.
• Medium corrosion-the chloride ion content exceeds 100ppm, 316L can't bear it, must be replacedPTFE-lined hoseOr higher grade stainless steel.
• Installation error-the initial stress caused by misedging and forced matching of the pipeline is equal to overdrafting the life every day.
• Vibration-Pipe vibration will accelerate the stress concentration at the crest of the bellows, which is prone to cracking.

thatrubber compensatorHow often do you change? Depending on working conditions. The rubber compensator used for desulfurization flue is subject to acid-alkali corrosion and ultraviolet aging, and generally needs to be inspected in 2~3 years. If you find that the rubber surface is hardened, cracked, or even delaminated, replace it immediately. WhileMetal hose(includingSpecial hose for vacuum) The replacement cycle is slightly longer, and it can be used for 5~8 years when there is no obvious corrosion, but the premise is to regularly check the outer surface of the bellows for pitting or wear marks.

Every overhaul cycle, open the insulation layer and visually check the bellows for pits, cracks and scratches; Touch the guide tube with your hand to see if it is loose; Whether the loosening spacer for the tie rod nut is still there. Don't wait until a leak is replaced, by which time you may have damaged nearby brackets and equipment.

To put it bluntly, the bellows expansion joint is worth ten years if it is selected correctly, but it will be scrapped if it is installed wrongly for ten days. I hope these experiences can help you step on fewer pits at the scene.

万向型膨胀节和普通膨胀节，从外观上怎么一眼区分？

干管道这行的，谁还没见过几台膨胀节？但真到了现场，万向型和普通型混在一起，乍一看还真容易懵。前两天一客户发来照片问：“这俩不都带波纹管嘛，怎么价格差一倍？”好嘛，今天就从外观上把这事儿掰扯清楚，管你新老手，看完能秒判。

一、先看波纹管结构——一段还是两段？

最直白的区别就在这。普通膨胀节，比如咱们常见的通用型波纹膨胀节或者轴向型膨胀节，波纹管就是一根完整的、从头通到尾的。你眼睛顺着管子看过去，只有一组波纹，中间没有任何断开的地方。

How to Repair Metal Expansion Joints? Judge the type of fault first, then decide whether to repair or replace

Two days ago, I met a customer. On the phone, I was anxious to say that their factoryUniversal corrugated expansion jointThere was an air leak and asked if it could be repaired. I asked him to take a video first, and at a glance-there was a trachoma the size of a millet grain on the surface of the bellows, but the whole thing was not deformed, and the tie rod nut was not loose. In this case, repair welding can last for two years. But if the crack has already penetrated three or four waves, or the bellows is directly stuck, then sorry, the cost of repairing is higher than replacing.

SoHow to Repair Metal Expansion Joints?The core is one sentence: first find out the type of fault, and then decide whether to repair it partially or scrap it directly. Don't dismantle it as soon as you come up, and don't change it as soon as you leak, which is a waste of money.

First, find out the root cause of the fault-air leakage, stuck or deformation?

Before maintenance, the most taboo thing is to rely on feeling. You have to at least make a judgment with the naked eye and simple tools. Common faults fall into three categories:

• air leakage: The sound can be heard hissing, or use soapy water to paint welds, bellows peaks and valleys, and watch bubbling. The air leakage point is generally at the base metal of the bellows, the end weld, or the connection between the connection and the flange. LikeCorrugated expansion joint for power station industryHigh operating temperature, high pressure, air leakage is mostly fatigue crack, andMetal Corrugated Expansion Joints in Cement IndustryAir leaks are often due to perforations caused by dust wear.
• Stuck (Displacement Failure): The pipe does not expand or contract when it should be expanded or contracted, or the expansion joint is forcibly pulled into a straight line and cannot be pushed by hand. The tie rod nut is too tight, the guide tube falls off and sticks the bellows, or dust accumulates and scales inside, which will cause stuck. LikeHigh temperature axial expansion jointIf the guide tube in the tube falls off and hits the bellows directly, the movement is not small.
• deformation: The bellows has obvious twisting, uneven wave pitch and local bulging. This is often caused by over-displacement operation. You measure the actual displacement, and then compare it with the factory design value, which is clear at a glance.

If you judge these three situations correctly, it will be easier to handle later. If the judgment is wrong, it will be in vain if the cultivation is done.

2. Local damage of corrugated pipe: if it can be repaired, it will not be replaced, but it depends on the material and thickness

If it is only small trachoma or shallow crack, and the material is austenitic stainless steel of 304 or 316L, with a thickness of more than 0.5mm, it can be repaired. Note: Before repair welding, the damaged area must be polished clean to expose the metallic luster. Use argon arc welding, and the welding wire should be made of the same material or more corrosion-resistant (such as 316L welding wire). It must be smoothed after welding, otherwise it will become a new stress concentration point.

But if that thickness of the bellows is less than 0.3mm (such as someSpecial hose for vacuumOr under low pressurePTFE-lined hose), or the material is special alloys such as Hastelloy and Inconel, which ordinary welders can't handle at all. It is recommended to contact the manufacturer directly. There is another situation: the crack is at the root of the bellows (trough), where the stress is the largest, and the life after repair welding can't be long. It is better to replace it with a new one.

Metal rectangular expansion jointAndLarge diameter thick wall expansion jointMost of the corrugated plates are splicing welds, so attention should be paid to thermal deformation control when repairing welding, otherwise the more they repair, the more they leak.

3. The tie rod nut is loose or the guide tube falls off: adjust the minor problems yourself, don't screw it over

These kinds of problems seem small, but they are self-defeating when they are not handled well. Such asHow to adjust the tie rod nut of expansion joint？ The standard practice is to confirm the design displacement first, and symmetrically loosen the adjustment nut with a wrench to restore the bellows to its free length. Don't screw it unilaterally, otherwise the expansion joint will twist. Many teachers screwed to death as soon as they came up. As a result, the bellows couldn't expand and contract normally and stuck directly.

Let's talk about the deflector falling off. The guide tube itself is fixed to the inner wall of the pipeline by bolts or spot welding. If it falls off, it will fall off and jam the bellows, or even be washed away by the medium and smash the downstream valve. During maintenance, open the manhole and re-weld or bolt the fallen guide tube. Be careful that the weld should not be higher than the surface of the guide tube, so as not to affect the flow of media. LikeDesulfurization flue gas baffle doorIn this kind of equipment, once the guide tube falls off, the slurry pours back into the bellows, and the corrosion rate doubles.

4. What circumstances must be scrapped? Fatigue crack, corrosion perforation, excessive displacement

Don't be reluctant. In some cases, forcibly repairing is planting mines.

• Fatigue crack: If the crack extends more than 3 waves along the bellows axial direction, or the circumferential crack length exceeds 1/4 of the circumference, it means that the material has been fatigued and will crack again soon after repair welding. Direct replacement, recommendedExternal pressure single axial expansion jointOrCompound hinge transverse expansion jointThis type of structure has better fatigue resistance.
• Corrosion perforationPerforations caused by pitting and intergranular corrosion often have only a small hole on the surface, but the surrounding metal has been embrittled. Use magnetic particle detection or coloring flaw detection. If you find dense micro-cracks, don't fix them. Especially for chemical pipelinesPTFE compensatorOnce the inner liner is perforated, the media will corrode the outer metal.
• Excess displacement: The actual operating displacement exceeds the design value by more than 120%, and the bellows has produced plastic deformation. Such asDirect buried (fully buried) type expansion jointOver-stretched, the wave pitch is uneven, and repair welding is useless at this time, because the bellows has lost its elasticity.

By the way,Service life of expansion jointGenerally, the design is 1000~2000 full displacement cycles, but many factories have not broken after ten or eight years of use, because the actual displacement is far less than the design value. If the limit is exceeded frequently, the life span will fall off a cliff.

5. How to accept after maintenance? Pressure test and displacement rebound are indispensable

It's not finished after repairing, you have to verify that it still works. Two steps:

The first step, the pressure test.Carry out hydraulic pressure test according to 1.25 times of the design pressure, hold the pressure for 10 minutes, and check whether there is any leakage on the surface of welds, flanges and bellows. Note: It must be thoroughly blow dried after the hydraulic test, esp.Double hinge expansion joint for air-cooled island vacuum pipelineThis kind of vacuum equipment, when the residual moisture is vacuumed, it will freeze and damage the bellows.

The second step is the displacement rebound test.Loosen the tie rod nut, push and pull the bellows by hand, see if it can smoothly expand and contract to the designed displacement, and whether it can rebound automatically after releasing. If the rebound fails to reach its original position, it means that there is a jamming inside, or the bellows has become unstable. ForCurved tube pressure balance expansion jointFor this type of balanced structure, it is also necessary to check whether the tie rod of the pressure balancing ring moves synchronously.

After these two steps, the maintenance is qualified.

6. Keeping an eye on a few details daily can save half of the trouble

After all, maintenance is a passive remedy, rather than prevention. If you keep an eye on the following points, the failure rate will be reduced by at least half:

• Deflector Wear Inspection: Open the manhole every six months, especially the flue gas system and pulverized coal pipeline. When the deflector is worn to less than half the original thickness, replace it in advance, don't wait for it to fall and smash the bellows. LikeNon-metallic expansion joint (fabric fiber expansion joint)Although there is no metal bellows, the deflector is equally afraid of wear.
• Periodic preloading of tie rod nuts: Not for you to tighten it, but to check if it is loose or rusty. ForLarge tie rod expansion jointEvery three months, use the torque wrench to re-tighten according to the design value to prevent the nut from loosening due to vibration.
• Displacement monitoring: Mark the scale on the expansion joint and record the amount of displacement at each shutdown. If you find that a displacement suddenly becomes larger or smaller, it means that the pipe support may be offset. Let's sayStraight pipe pressure balanced expansion jointIf the displacement is abnormal, there is a high probability that the main fixation bracket is loose.
• Heat preservation and corrosion protection: Expansion joints for outdoor installation, especiallyHigh temperature axial expansion jointAfter the insulation layer is damaged, rainwater enters, and the corrosion rate is astonishing. Regularly check the sealing condition of the insulation layer and repair the damaged areas. Also, don't let the corrosive liquid drip directly onto the bellows.

Okay, so aboutHow to Repair Metal Expansion Joints?I was detailed enough. You go back and compare your own expansion joint, look at the type of fault first, and then decide whether to repair or replace it.

Two days ago, a customer from a power station called, and his tone was very urgent, saying that a corrugated expansion joint on their pipeline was leaking and perforated. Asked me if I could just weld it on and make do. This kind of question is too common in the industry, but the answer is really not simply "can" or "can't". What about perforated metal expansion joints? Whether it is repaired or replaced depends on the reason and location of the perforation, and which expansion joint you are using. Let's talk about the conclusion first: blind repair welding will in all likelihood happen bigger things.

The reasons for perforation vary

The most common is corrosion-chloride ions, sulfides in the medium, or high-temperature oxidation. For example, the corrugated expansion joint used in the power station industry is prone to high-temperature oxidation and thinning on the outer wall under high-temperature flue gas for a long time, and finally perforation. Where is the metal corrugated expansion joint in the cement industry, dust abrasion is the main cause. In another case, the tie rod nut is not adjusted properly during installation, which causes the bellows to bear undue torsion or lateral displacement, and fatigue cracks eventually develop into perforations. Think about it, if you weld indiscriminately, there are still media residues sandwiched in the cracks, and it will be virtual when welded.

By the way, there is another reason for perforation that many people ignore-the deflector failure. The specific function of the expansion joint guide tube is to protect the bellows from high-speed medium erosion. Once the guide tube is damaged, the medium directly impacts the bellows, and the local erosion speed can be several times faster. At this time, even if you weld the perforation, the inner wall will continue to thin, and it will leak again soon.

Is there a temporary emergency solution? Yes, but the conditions are harsh

For example, the circulating water pipeline with low pressure and normal temperature has a small perforation (the diameter does not exceed 5mm), so it can be temporarily blocked with a rubber gasket covered with a fixture, or cold solder (metal repair glue) can be used for emergency response. But only if you have to confirm that the medium temperature does not exceed the temperature resistance range of the glue, and the pressure is below 0.5MPa. Don't do this on high-temperature and high-pressure steam pipelines-steam pipelines belong to pressure pipelines, and they can be repaired and welded directly after perforation. Local stress concentration may make the bellows explode.

Many people think that the expansion joint and the compensator are two different things, so they treat them according to the ordinary pipeline repair welding process, and as a result, the elasticity of the corrugation is welded away. Actually, is the expansion joint the same as the compensator? The answer is one thing, it's just called differently. The bellows itself absorbs displacement by elastic deformation, and the welding repair area will harden and lose elasticity, so this expansion joint is basically wasted.

When do you have to change? Don't hesitate to replace it with a new one

Let's put it this way, as long as the diameter of the perforation exceeds 1/3 of the wall thickness of the bellows, or the perforation appears in fatigue sensitive areas such as peaks and troughs, don't hesitate to replace it with a new one directly. EspeciallyLarge diameter thick wall expansion joint、External pressure single axial expansion jointFor those with high pressure, the weld area will become a new weak point after repair welding, and the risk of creep fracture will double. Also, if the perforation is associated with damage to the guide tube, it must be replaced as a whole. Once the guide tube is broken, the internal erosion will be accelerated, and the welding repair is a waste of effort.

And guess what? Some customers feel that it is expensive to replace the expansion joint, so they have to repair welding to save money. As a result, it took two days. On the third day, the weld cracked, and the medium sprayed out and almost injured people. The loss of one equipment shutdown is much more than replacing the expansion joint. Safety first, don't gamble on your luck.

Prevention is more important than remedy

Corrosive medium, preferredPTFE-lined hoseOrPTFE compensator； High temperature flue gas pipe, forHigh temperature axial expansion jointInner lining with temperature-resistant coating; Dusty cement line, useMetal Corrugated Expansion Joints in Cement IndustryOrRectangular non-metallic expansion joint(the kind of fabric fiber), the latter is low replacement cost and convenient maintenance.

The direction of the arrow of the expansion joint points to the direction of the medium flow, and the tie rod (the role of the expansion joint tie rod is to limit excessive tension) can only be loosened after the pipeline pressure test. In daily inspection, check whether there are rust pits and peeling on the corrugated surface, and cooperate with the inspection cycle of non-metallic expansion joints, at least twice a year.

Metal expansion joint perforation, don't treat it as an ordinary leak. It is like a spring. Welding repair is equivalent to tying a knot on the spring. Do you think this spring can still work properly? Leave professional matters to professional people-if you are unsure of the cause of the perforation, or are unsure whether it can be repaired, contact the manufacturer directly to send the on-site photos and media parameters.

Mistaken selection is the number one killer of short lifespan-material and construction determine how many years you will last

Two days ago, I met a customer who complained that the expansion joint in their factory leaked after two years. When I removed it, the bellows were rotten. Ask about the working conditions-high-temperature steam pipeline, with a pressure of 1.6MPa and a temperature of 350℃. As a result, the general-purpose corrugated expansion joint was chosen at the beginning, and the material was 304 stainless steel. Isn't this seeking death?

The matter of model selection, to put it bluntly, is "what horse matches what saddle". High-temperature working condition honestly high-temperature axial expansion joint, the material must be Inconel 625 or at least 321 stainless steel; For corrosive media, such as desulfurization flue gas, you have to consider lining PTFE hoses or non-metallic expansion joints (fabric fiber expansion joints), and even rubber compensators can carry them for a while. In cases where particle erosion is serious, such as air ducts in cement industry, metal corrugated expansion joints in cement industry must have wear-resistant guide tubes, otherwise they will be worn out in less than half a year.

Structurally, don't be sloppy. For pipelines with large axial displacement, straight pipe pressure balance expansion joint or compound straight pipe bypass pressure balance expansion joint is the positive solution; If you need to absorb lateral displacement, compound hinge transverse expansion joint or curved tube pressure balance expansion joint is right. Choosing the wrong type is like letting a sprinter lift weights, and scrapping is a matter of time.

The "invisible killer" of the installation link: the draw rod is not adjusted in place, the guide tube is installed backwards, and no matter how good the expansion joint is, it is useless

You can sit back and relax when you choose the right equipment? That's naive. The pits in the installation link, each deeper than the last. The most common one is that the tie rod nut is not adjusted properly. The function of the expansion joint tie rod is to limit the over-stretching or over-compression of the bellows, but many installation teams directly lock the tie rod, or simply don't dismantle the transportation fixtures. And guess what? As soon as the pipeline heats up, the expansion joint has no space to compensate, and the bellows is directly bulged and scrapped. The correct way is to remove the transport screw after installation, and then adjust the tie rod nut according to the compensation amount. For details, refer to the article "How to adjust the tie rod nut of expansion joint" in our station.

There is a more hidden problem-the deflector is installed backwards. The specific function of the expansion joint guide tube is to guide the flow direction of the medium and protect the bellows from scouring. However, when the direction of the arrow is reversed, the medium directly impacts the root of the bellows, and the rate of corrosion and wear doubles. Remember: The direction of the arrow must coincide with the direction of the media flow. Don't laugh, at least 30% of the installers on the site will make this mistake.

Wear and corrosion in operation: medium temperature, particle erosion, chemical attack, how many of these pits have you stepped on?

During normal operation, the expansion joint can't be laid flat just by installing it. If the medium temperature exceeds the design value of 10℃, the fatigue life of the bellows may be directly discounted by 50%. Particle scour? That's even more like cutting meat with a soft knife. Some cement plants use ordinary metal rectangular expansion joints, and there is no guide tube inside. After half a year, the wall thickness of the bellows is ground from 3mm to 0.5mm. Do you think it can be perforated?

Chemical attack is more headache. The acid condensate in the desulfurization system is a fatal blow to the metal bellows. At this time, either choose a PTFE hose or PTFE compensator, or use a non-metal expansion joint (rubber PTFE compensator is also OK), but we must pay attention to the rubber aging problem. By the way: Is there pitting corrosion and intergranular corrosion on the surface of the expansion joint in your factory? If so, it means that there is a problem with material selection, so change it as soon as possible.

Regular inspection is not a formality: corrugated pipe cracks, rubber aging, non-metal layer peeling, early detection and early treatment

Many factory inspections are to walk around with a flashlight and see nothing. In fact, there is a precursor to the failure of the expansion joint. Fine cracks or "orange peel"-like deformation appear on the surface of metal bellows, which indicates that it is close to the fatigue limit. Rubber compensator or non-metallic expansion joint, pay attention to whether the surface has hardened, cracked, or delaminated peeling. Especially rubber, affected by ozone and ultraviolet rays, has a life span of three to five years. When the time comes, it should be changed. Don't wait for it to leak before stopping.

Also, check for any changes in the pre-tightening forces of the tie rods and bolts. After the expansion joint has been running for some time, the tie rod may loosen, causing the bellows to offset. If the bellows is found to have eccentric wear marks, it means that the pipe support may sink or the compensation direction is wrong. Early detection and early adjustment, it's still too late.

Environmental factors alone? Heat preservation, support and drainage are done correctly, and the life will be doubled directly

Environmental factors are often overlooked, but are often the last straw that crushes the camel. For example, the expansion joint installed outdoors does not do heat insulation, and the metal brittleness increases at low temperatures in winter, so the bellows is easier to crack. Another example is the expansion joint on the steam pipeline. If there is no reasonable drainage design, the condensed water will accumulate at the trough, forming a "water hammer", which will impact and damage the bellows. How to solve it? Set a drain valve at a low position, or choose a sleeve-type pipe expansion joint with drain structure.

Support is also critical. The expansion joint itself does not bear the weight of the pipe, and guide brackets and fixed brackets must be set nearby. Many sites use the expansion joint as a pipe support, but as a result, the bellows is flattened and scrapped in three months. Think about it, is it worth an expansion joint worth tens of thousands of dollars to be scrapped in advance because several brackets worth several thousands of dollars were not done properly?

When to change hard bracing: Precursor judgment of failure and targeted prevention strategies

Expansion joints are not maintenance-free for life. If the following signals appear, change them quickly and don't take chances: First, the bellows has obvious cracks or perforations; Second, the fabric layer of the non-metallic expansion joint peels off in a large area, and the internal thermal insulation cotton or steel wire mesh can already be seen; Third, the surface of the rubber compensator is hardened to the point that it can't be pressed, or there are bubbles bulging; Fourth, the whole expansion joint is obviously distorted, which indicates that the displacement of the pipeline has exceeded the design range.

According to the medium characteristics and working conditions, select the right type in advance (such as special products such as corrugated expansion joints for power station industry, double hinge expansion joints for air-cooled island vacuum pipelines, etc.), strictly implement the specifications during installation, and regularly check and adjust in time during operation. If conditions permit, install displacement monitoring sensors at key positions, and watch the expansion and contraction of the bellows in real time, and you will have a bottom in your heart.

To put it bluntly, there are three words to prolong the life of expansion joints-select, install and raise. Choose the right thing, install it well, and maintain it diligently. To achieve these three points, it is not a dream to serve for more than ten years.