Specialized in manufacturing compensators, expansion joints, baffle doors

Standard life is just a reference value

JB/T 12235-2015 stipulates that the design life of non-metallic expansion joints is usually 10-15 years, but there are many projects that can last for three to five years in actual projects. The life span of this thing is never determined by the manufacturer. The key depends on how you use it. Take the desulfurization flue of power plant as an example. With corrosive gas and high temperature, non-metallic expansion joints (fabric fiber expansion joints) can last for three years, even if they are high-quality products. On the other hand, it is not unusual to use it for more than ten years in clean ventilation ducts. You ask about the lifespan of non-metallic compensators? The standard is the standard, the reality is the reality, don't take the national standard as a life-saving talisman.

Material determines the upper limit, working condition determines the lower limit

Rubber compensator, rubber PTFE compensator, fabric fiber expansion joint-different names, different lives. Rubber is afraid of aging, PTFE is afraid of high temperature, and fabric fiber is wear-resistant but afraid of acid and alkali. Two days ago, I met a customer from a cement factory, who chose the metal corrugated expansion joint in the cement industry. It was not said that the non-metal was cheap and had to be replaced. As a result, the high-temperature dust was washed and it leaked in three months. It's not that non-metals can't be used, you have to find out its temper: when the temperature exceeds 200℃, it begins to lose its life, and the particulate matter in the medium is a life reminder. Alas, in the final analysis, the material just gives you a theoretical ceiling, and the working condition is the real floor.

Installation and maintenance is the real watershed

Whether you put it right or not, the difference is three to five times the life span. There are three common pits: First, the guide tube is installed backwards, and the airflow directly washes the compensation layer; Second, the tie rod nut is adjusted too tightly, which limits the displacement compensation and forcibly cracks the material; Third, there is no pre-deformation left during installation, cold deadlift, and it will explode as soon as it is turned on. You asked how to adjust the expansion joint tie rod? The manufacturer's manual is clearly written, but the on-site master can save trouble and screw it to death directly. No matter how good a non-metallic compensator is, it can't handle this. Is that the truth? If the installation and maintenance are not in place, no matter how good the material is, it will be in vain.

When should I change? Don't wait for it to be completely scrapped

Leaks, surface hardening, fabric delamination, noticeable distortion-don't hesitate to show any of them. Especially the non-metallic expansion joints near the desulfurization flue gas baffle doors corrode faster than you think. It is recommended to check at least once a year, focusing on flange joints and fabric overlap seams. Don't expect it to hold up to fatigue cracks like metal expansion joints, nonmetallic failures are often sudden and more expensive to repair than replace. What about that? Regular inspections are much more cost-effective than mending leaks afterwards.

Let's make one thing clear first: Although non-metallic compensators and metallic compensators are both called compensators, their installation locations are very different

Metals can carry high temperatures and high pressures, such as power station steam pipelines and refinery pipelines, but the strengths of non-metals are low pressure, large displacement and corrosion resistance. The typical scene is smoke duct. Two days ago, a customer called me and asked me if I could install a non-metallic compensator on the steam main pipe. As soon as I heard it, I asked him to stop quickly-the temperature of the steam main pipe started at least 300℃, the pressure was above 0.5MPa, and the non-metallic fabric layer was directly carbonized. I asked him to look at the "high temperature axial expansion joint" on our website, and that was the right answer. Therefore, if the location is not selected correctly, no matter how good the product is, it will be for nothing.

Where is the main battlefield of non-metallic compensators?

The chimney entrance of the power station, the inlet and outlet of the desulfurization tower, the inlet and outlet pipelines of the dust collector, and the kiln head and tail of the cement industry-in these places, the medium temperature is generally below 200℃, the pressure is slightly positive or negative, and the pipeline displacement is large (both lateral and angular). The metal compensator either can't bear the corrosion or the cost is ridiculously high. You go to the 'Non-Metallic Expansion Joints (Fabric Fiber Expansion Joints)' and 'Rectangular Non-Metallic Expansion Joints' on our site, which are specifically designed for these scenarios. For another example, the flue gas baffle door of desulfurization system (such as our 'desulfurization flue gas baffle door') is often equipped with a non-metallic compensator next to it. Why? Because there are sulfur dioxide and water vapor in the flue gas, the metal bellows will rust out in half a year, but the non-metallic fabric layer plus PTFE film can last for three to five years.

Many people think that non-metallic compensators are soft, just find a place to stuff them in. Wrong! It is most afraid of high temperature and high pressure. If the pressure exceeds 0.1MPa, don't put it hard. The non-metallic fabric layer can't bear the high-pressure bulge. We have encountered a customer who installed a non-metallic compensator on a blast furnace gas pipeline with a pressure of 0.2MPa. As a result, it leaked in half a year-the wrong position was selected, and no one could save it.

Rectangular pipes and shaped pipes: What nonmetallic compensators do best

Bellows can be used for round pipes, but rectangular air ducts-such as the rectangular flue of the sintering machine head of a steel mill or the rectangular flue duct of a power plant-metal bellows either can't be made or the price is sky-high. At this time, only non-metallic fabric compensators can be used. Our 'rectangular non-metallic expansion joint' specializes in this, and the installation position is usually in front and behind the fan inlet and outlet, and the baffle door, which is used to absorb thermal expansion and installation deviation. Note: Rectangular pipes are often limited in space, so the installation position of non-metallic compensators should reserve enough maintenance space, otherwise it will be troublesome to die when replaced in the future. I have seen a desulfurization tower renovation project. The compensator is installed close to the wall, and even the wrench can't reach in during maintenance. In the end, it can only smash the wall-tsk, can you die if you leave 30 centimeters more in the design?

Three Forbidden Areas of Non-Metallic Compensators

First, if the medium temperature exceeds 300℃, you don't think about it.Even high-temperature-resistant silicone cloth can't hold it, and the temperature resistance is about 260℃. If it exceeds this number, you have to use 'high-temperature axial expansion joint' or metal products with heat insulation layer. Some customers have to take non-metals to test the export of flue gas heat exchangers, and as a result, they smoke in a month.

Second, there are pipelines with serious accumulation of condensate or dust.Non-metallic compensators are prone to dust accumulation and corrosion. If the location is selected on a horizontal pipe, be sure to consider drainage or ash discharge measures. For example, in the horizontal flue behind the dust collector, there is a lot of dust in the flue gas, and the bottom of the non-metallic compensator will accumulate hard lumps and then wear the fabric layer. What to do? Either install it vertically or open an ash discharge port at the bottom.

Third, the pressure exceeding 0.1 MPa is the red line.Don't believe that "it's okay to exceed it a little". The design pressure of non-metallic compensators is slightly positive pressure. If the system pressure fluctuates greatly, it is necessary to install a pressure relief valve. Remember: the metal can carry 0.5MPa, and the non-metal exceeds 0.1MPa, just wait for the bulge to leak.

Actual Combat Misunderstanding: Non-metallic Compensators Can't Bear Thrust

Some people think that the non-metallic compensator is soft and easy to install, so they install it where it needs to withstand the blind plate force (thrust) of the pipe. Wrong! Non-metallic compensators can only absorb displacement and cannot withstand thrust. For example, at the corner of the pipe or when the valve is closed, the blind plate force will act directly on the compensator, and the non-metallic one can't bear it at all-the fabric layer will be torn apart. At this time, the fixing bracket should be added, or replaced with 'universal corrugated expansion joint' or 'large tie rod expansion joint'. Before selecting the position, calculate the pipe thrust. How does that count? Find the pipeline diagram of the design institute to see the thrust value between the fixed brackets. If it exceeds 0.1MPa, decisively give up the non-metallic scheme.

Final step: three steps to get the installation position

On-site working conditions vary widely. How to locate them specifically? Three simple steps: First, look at the pipeline diagram and find the pipe section between the two fixed brackets with the largest thermal displacement-that place is the candidate location for the non-metallic compensator. Second, confirm that the medium temperature and pressure fall within the parameters of the non-metallic compensator (refer to JB/T 12235-2015 standard). Third, avoid positions where condensation, dust accumulation and mechanical collision are prone to occur. If you are unsure, just ask us about the drawings for sales. The article on our website 'National Standard for Non-Metallic Expansion Joints' has detailed parameters.

By the way, when installing, be sure to align the direction of the arrow with the flow direction of the medium, otherwise the force direction of the fabric layer will be reversed, and it will collapse in less than three months. Alas, this kind of low-level mistake happens several times a year.

Find out what you have in your hand first: round welded non-metallic compensator vs metal expansion joint

Can this thing replace metal? Alas, materials and structure are completely different things. Circular welding non-metallic compensator (that is, the non-metallic expansion joint and fabric fiber expansion joint mentioned in our station) uses composite layers of silicone cloth and fluororubber as circular belts, which rely on flexibility to compensate for displacement. Circular welding type refers to welding short pipes at both ends, which are directly welded to the pipeline. Note-it does not absorb axial thrust, which is very different from metal bellows. If you confuse the position of the guide bracket when installing it, something will go wrong later.

You have to do three things before installation: check the model, check the appearance, and remove the screw or not?

Don't rush to weld. Look at the product nameplate first to confirm whether the caliber and compensation amount are consistent with the design drawings. Is the non-metal ring strip broken or wrinkled? The tie rod nut is locked out of the factory to protect shipping. The tie rod nut must be loosened before installation-how to loosen it? Refer to the question and answer of "Does the screw of the expansion joint need to be removed" in our station. If it is not loose, the ring belt will explode directly as soon as the temperature rises after welding. How much looser is that? Look at the amount of compensation, and generally set aside half of the design displacement. Don't twist by feel, measure with a caliper.

The welding link is the easiest to roll over

The short tube wall thickness of circular welding non-metallic compensator is usually thinner than that of pipe, and the welding electrode is not selected correctly, and it will be worn as soon as it is burned. It is recommended to use DC welding machine, low current, multi-layer welding. After welding, it must be cooled. Don't rush to water the loop-the temperature resistance of the loop is only a few hundred degrees, and it will crack when quenched. Also, the welding sequence is particular: first welding the fixed end, then welding the free end, and finally welding the middle. Why? Prevent thermal expansion from pulling the non-metallic ring tape askew. Think about it, if you weld the middle first, as soon as the two ends shrink, the loop tape will directly wrinkle into a rag.

Finished installation does not mean finished, the tie rod and guide bracket still have to be adjusted

Circular non-metallic compensators generally only absorb axial displacement, and lateral displacement depends on the guide bracket of the pipeline itself. The function of the tie rod is not to bear pressure, but to prevent over-stretching-see the article "The Function of the Expansion Joint Tie Rod" for details. Adjustment method: Twist the nut with a wrench, so that the clearance at both ends of the pull rod is symmetrical. Don't be thick on one side and thin on the other. By the way, how to determine the distance of the guide bracket? Look up the table according to the pipe diameter. We mentioned the influence of the guide tube on the flow direction of the medium in the "Specific Function of the Expansion Joint Guide Tube". The direction of the guide tube must be consistent with the flow direction of the medium. Is it installed backwards? Later cases will tell you the consequences.

How do you judge that it is time to change after it is put into operation?

Non-metallic compensators are most afraid of corrosive media and ash accumulation. In those working conditions in cement industry and desulfurization flue, the aging of the ring belt is easy to harden and crack from the outer surface. Regularly light the interior with a flashlight to see if there are any piercings. Don't think about repairing it if it leaks-the non-metallic band can't be welded and repaired, so it can only be replaced as a whole. The life span is generally 3 to 5 years, which is shorter than that of metal, but the cost is low and the installation is convenient. If you find it troublesome to change it, refer to the "desulfurization flue gas baffle door" and "circular baffle door (double seal)" of our station, which can prolong the life. And guess what? Many power plants are so equipped, and they haven't changed the ring belt for 8 years.

Finally, let's talk about a practical case

Last month, a power plant customer installed a circular welding non-metallic compensator at the outlet of the induced draft fan, and it leaked less than half a year after installation. In the past, the problem was that the guide tube was installed backwards, and the high-temperature flue gas directly washed the inner wall of the ring belt. In addition, the position of the guide bracket was not welded correctly, and the pipe displacement tore the ring belt. After replacing the new parts, it was reinstalled according to our JB/T 12235 standard. Now it has been running for one and a half years without any accident. So, don't underestimate those nuts and brackets. Details are the real skill. Understand "How to use circular welding non-metallic compensator?" Actually, there are two points: First, don't use it as a metal part, and second, the installation sequence and tie rod adjustment must be strict.

If it is not fixed in place, the expansion joint is equivalent to white installation-first understand why the metal expansion joint needs to "control the displacement"

The core role of the metal expansion joint is to absorb the thermal displacement of the pipe, but it is not "free to expand and contract". You have to understand a truth: the expansion joint itself is very thin, and the wall thickness of the bellows is usually only 0.5mm to 3mm. If there is no external constraint, the internal pressure thrust will directly straighten it, resulting in bulging, instability and even rupture of the bellows. Two days ago, a power plant customer sent a photo. They installed itUniversal corrugated expansion jointBecause the fixed bracket is not set, the whole expansion joint is twisted into an S-shape like a snake, and the pipe can't align, so it can only be cut off and re-welded in the end. Therefore, the word "controlling displacement" is the underlying logic of fixing the expansion joint-not only to let the bellows expand and contract freely in the design direction, but also to limit its lateral offset or torsion.

How to set fixed bracket and guide bracket? Different expansion joint type vary greatly

The fixed bracket is a must-have "dead center" near the expansion joint, which catches the pipe firmly and ensures that thermal displacement only occurs on this side of the expansion joint. The guide bracket is responsible for guiding the pipe to move in a straight line to prevent the bellows from being twisted. But different types of expansion joints have completely different setting rules- -

• Universal corrugated expansion joint: Most widely used, main absorption axial displacement. The fixed bracket is generally arranged at one end, and the other end is arranged with a guide bracket, and the spacing is controlled within 4 times the nominal diameter. For example, for DN200 pipes, the spacing between guide brackets should not exceed 800mm.
• High temperature axial expansion joint: The design temperature of this goods can be up to 600℃, and the bellows usually have multiple layers and insulation layers. The fixed bracket must be located on the side close to the heat source, and the spacing between the guide brackets should be reduced to 3 times the nominal diameter. Why? Under high temperature, the material strength decreases, and the bellows is more likely to become unstable, so the support and hanger have to be "more diligent".
• Straight pipe pressure balanced expansion joint: This thing itself has a balance ring, which can withstand internal pressure thrust. In theory, the main fixing bracket can be cancelled. But don't be too happy-in order to save money and space, many projects really don't have fixed brackets, and as a result, the pipes sway back and forth like a pendulum when they run. My suggestion is to set up at least one auxiliary fixing bracket, or useCompound straight pipe bypass pressure balanced expansion jointIts bypass structure can naturally counteract the thrust, and the requirement for the bracket is lower.

Should the tie rod and the limit screw be disassembled? How to adjust the tie rod nut so that it doesn't get stuck or fail?

This question is asked the most by people at the engineering site. The role of the tie rod is to limit the excessive deformation of the expansion joint during transportation and installation, while acting as a "safety rope" to prevent excessive displacement in working condition. But many people screw the tie rod nut to death directly after installation, or simply remove it-both are pits.

Before installation, adjust the tie rod nuts to the initial spacing specified by the design. Like a certainCompound hinge transverse expansion jointThe manufacturer marked "the cold tightness value is 20mm", which means that the nut is screwed to the position where the screw is exposed 20mm during installation. After the pipe heats up in place, the nut will naturally fit the tie rod seat. At this time, if you tighten it again, the bellows will not be able to expand and contract, waiting for it to be cracked.

As for "dismantling or not"-the tie rod is a permanent piece, don't dismantle it. But the limit screw can be removed! The limit screw only temporarily fixes the bellows during transportation, and it must be removed after installation, otherwise it is equivalent to you welding the expansion joint to death. Remember the mantra: "Leave the pull rod, remove the limit, and initially adjust the nut to half open."

Pre-stretching and pre-compression: "Turn back arrow" operation for fixing expansion joints in high temperature pipes

When encountering high temperature conditions (steam pipeline, flue gas pipeline), the expansion joint must be pre-stretched or pre-compressed. For example:High temperature axial expansion jointThe designed compensation amount is 100mm, the operating temperature of the pipeline is 500℃, and the elongation amount is 80mm. If you install it directly without pre-stretching, the bellows will be stretched from 0 to 80mm during operation, and the life will be greatly reduced. The correct way is to pre-stretch the expansion joint to 50% of the design value (that is, pull out 40mm) during installation, so that the actual displacement range becomes-40mm to +40mm during operation, and the bellows always works within the elastic range.

In turn, cryogenic pipes (such as air-cooled island vacuum pipes) need to be pre-compressed. You may ask: Who will do this operation? Generally, the on-site construction team does not dare to make random adjustments. It is suggested that the expansion joint manufacturer preset the length of the tie rod before leaving the factory, and install it directly at the site. Like oursDouble hinge expansion joint for air-cooled island vacuum pipelineWhen leaving the factory, the tie rod is locked according to the cold tightness value provided by the customer, and the installer just takes over the pipeline, which saves a lot of worries.

How to fix special scenes? Direct burial, air-cooled island vacuum pipeline, large-diameter thick-wall expansion joint each has its own special

Let's startDirect buried (fully buried) type expansion joint。 This thing is buried in the soil and can't be inspected on a daily basis. The fixing method is completely different from the above-ground pipeline-it must be "triple fixing": a fixed pier with thrust block is set at both ends of the expansion joint, and a layer of anti-corrosion and waterproof hoop is added in the middle. In order to save trouble, many construction units directly use backfill soil for compaction. As a result, the pipeline sinks and the bellows are flattened. Remember: the fixed pier of the directly buried expansion joint must be higher than the center line of the pipe, and the concrete above C30 should be poured, otherwise the soil creep will push the fixed pier askew.

Air-cooled island vacuum pipeThe pressure is close to negative pressure, but the displacement is large (the temperature difference is more than 50℃). The conventional bracket scheme is easy to make the pipeline unstable, so it is better to use double hinge structure with suspension bracket.Double hinge expansion joint for air-cooled island vacuum pipelineIt comes with two hinges to allow the pipeline to rotate in the plane. The fixed bracket only needs to be set at the corner of the pipeline, and the ordinary hanger can be used for the straight line segment.

Large diameter thick wall expansion jointThe difficulty of (DN1000 or above) lies in self-weight. The bellows themselves are heavy and the guide brackets must bear lateral loads. It is recommended to add a rolling support bracket under the expansion joint. The bottom plate of the bracket is polytetrafluoroethylene plate, and the friction coefficient is only 0.04, which does not affect the axial displacement. We did a steel mill project, DN1400Large diameter thick wall expansion jointIt is by this kind of bracket that the sagging problem is solved.

Common fixed rollover scenes: the bracket position is wrong, the tie rod is not adjusted properly, and the guide spacing is too large.

Of a chemical plantCurved tube pressure balance expansion jointWhen installing, the fixing bracket is set directly above the expansion joint instead of both ends. As a result, when running, the expansion joint bears additional bending moment, and the bellows cracks in half a year. Correct position: The fixing bracket should be 1 times the diameter of the pipe from the end of the expansion joint, neither too far (causing the pipe to become unstable) nor too close (affecting the free expansion and contraction of the expansion joint).

The tie rod nut is screwed dead. There is a garbage incineration project, and the workers finish installing itExternal pressure single axial expansion jointAfter twisting the tie rod tightly, thinking that he was "firm". As soon as the boiler heats up, the bellows can't expand, so the tie rod seat is pulled and deformed directly. Finally, the expansion joint was replaced with a new one, and it was stopped for three days, resulting in a loss of more than 100,000 yuan.

The guide brackets are too spaced apart. According to the national standard, the maximum spacing of guide brackets is 16 times the outer diameter of pipes, but this is for general pipes. The spacing of guide brackets near the expansion joint must be reduced to less than 4 times the outside diameter, otherwise the pipe bending will twist the bellows. Let's not pay tens of thousands of dollars for expansion joints just to save a few brackets.

How to fix metal expansion joints? To put it bluntly, there are three things-control the displacement (fixed bracket + guide bracket), adjust the tie rod (leave the margin for the nut, remove the limit screw), and treat special scenes (pre-stretching, anti-corrosion, bracket). If you follow these points, basically there will be no major problems.

Why does the molding method determine the performance of the expansion joint? — — Start with bellows

"How to choose metal expansion joint?" I always say, don't look at the price first, look at the molding process first. Corrugated pipe is the soul of expansion joint, and the forming method directly determines its fatigue life, pressure bearing capacity and cost. It is also 304 stainless steel, and the hydroformed bellows can carry tens of thousands of cycles, while those with substandard technology may crack hundreds of times. Today, let's talk about several mainstream metal expansion joint forming methods in the market, and by the way, compare the products on our station, such as general-purpose corrugated expansion joint and corrugated expansion joint for power station industry, so that everyone can understand the doorway and choose the type without stepping on pits.

1. Hydroforming-the most classic and default process for most products

Hydroforming is to expand the tube blank into corrugations with liquid pressure. The principle is not complicated, but the process parameters are a little worse, and the result is much worse. It is suitable for manufacturing small to medium caliber (usually below DN600) bellows with thin wall thickness. Our general-purpose corrugated expansion joints, high-temperature axial expansion joints and corrugated expansion joints for power station industry are basically hydroformed. It has the advantages of uniform corrugation, small residual stress, long fatigue life, and can run for more than 10 years under normal working conditions.

The cost of molds is high, with tens of thousands of pieces in a set of molds, and it is not suitable for super-large diameter or thick-walled pipes-the diameter exceeds DN2000 and the wall thickness exceeds 3mm, so hydroforming is difficult. That's when you have to look at the next craft. And guess what? Many customers ask "Why is the metal corrugated expansion joint in your cement industry more expensive than others?" In fact, the difference lies in the control of molding parameters. If the holding time and boosting curve are not adjusted properly, the corrugation will be partially thinned, the thickness tolerance will change from ±0.1mm to ±0.3mm, and the fatigue life will be directly folded in half. Our products have been tested for stiffness before leaving the factory (refer to the stiffness and calculation formula of corrugated pipe) to ensure that the wall thickness reduction rate of each corrugation is controlled within 10%.

2. Mechanical roll forming-good hands on large-diameter and thick-walled tubes

When the diameter exceeds DN2000, or the wall thickness is greater than 3mm, the hydroforming is beyond its capacity. At this time, mechanical rolling forming came to the stage-gradually crushing ripples on the tube blank by rollers, which was a bit like rolling dough, but the accuracy was millimeter-level. Our large-diameter thick-walled expansion joint and external pressure single axial expansion joint are typical representatives, and this process is also used in the high-temperature air duct scene of metal corrugated expansion joint in cement industry.

The biggest benefit of mechanical rolling is that it does not need large molds, which is suitable for single-piece small-batch customization; And it can form high-strength materials, stainless steel 304, 316L and even Inconel 625 are fine. What about the disadvantages? Corrugated surfaces may have minor scratches that require subsequent polishing, but this has little impact on performance. Two days ago, a customer who was doing desulfurization flue had to take the hydroforming scheme. As a result, the ripples cracked during the pressure test-please, the expansion joint matching the flue gas baffle door has been in a sulfur-containing humid environment for a long time, and the material thickness is not enough to bear the corrosion and thinning at all. Mechanical roll forming can easily achieve a wall thickness of more than 4mm, and the corrosion resistance margin is sufficient.

3. Stamping vs. Spinning-An Alternative Solution in the General Scenario

In addition to the previous two mainstream processes, there are stamping and spinning. The stamping efficiency is extremely high, and it is suitable for large batches of standard parts, such as the corrugated sections in our metal hoses and PTFE-lined hoses, which can be punched thousands a day. However, the disadvantages are also there: the mold is expensive, and the corrugation depth is limited by the stroke, so it can't make deep waves. Spinning is more "flexible", and corrugations are extruded by rotating tools. It is often used in metal skeletons in non-metallic expansion joints (fabric fiber expansion joints) or small-batch custom parts. Note that although the main body of the non-metallic expansion joint is fabric, the connecting flange and the metal part of the bead are sometimes spun molded-this point is overlooked by many peers.

Neither stamping nor spinning is a panacea. Stamping is suitable for thin walls and small calibers, and spinning is suitable for complex shapes but with average accuracy. If the customer asks "Why is the lining of my PTFE-lined hose easy to detach?" Nine times out of ten, the stamping corrugation is not handled properly, and the composite layer is not bonded firmly. Our practice is to stamp the corrugation first, then line with PTFE, and finally vulcanize to ensure that the interlaminar shear strength reaches the standard.

4. Special molding process-those uncommon "special forces"

In some extreme scenarios, if the conventional craft can't be handled, you have to invite "special forces". For example, special vacuum hose and double hinge expansion joint of air-cooled island vacuum pipeline require ultra-thin wall (below 0.3mm) and the wall thickness thinning rate to be controlled within 5%. At this time, "inflation molding" or "explosion molding" is used-instantaneous molding with gas shock wave, and a corrugation is completed in 0.1 seconds, and the uniformity of wall thickness is better than that of hydraulic pressure. There are also directly buried (fully buried) expansion joints. In order to meet the seismic requirements of underground pipelines, corrugated pipes are often formed by multi-layer thin-wall superposition, with the inner layer bearing pressure, the outer layer protecting, and anti-corrosion coating. The technical threshold of this piece is high, and the domestic manufacturers who can do well can count it on one hand. Fortunately, these models on our station have detailed parameters and test reports.

Type selection suggestion: The molding method is not determined by patting the head, it depends on the working condition

Having said all that, how do you choose? Direct to dry goods:

• Power plant steam pipeline(Corresponding to the corrugated expansion joint used in power station industry) -Hydroforming is enough, the temperature and pressure are not extreme, cheap and durable, just pay attention to the direction of the guide tube.
• High temperature air duct in cement plant(Metal corrugated expansion joint in cement industry) -mechanical roll forming is recommended, which is wear-resistant, has sufficient wall thickness and can carry dust scour.
• Chemical corrosive media(PTFE-lined metal hose) -You must stamp the corrugation first and then lined with PTFE, otherwise the composite layer will be easily detached, so don't save the process.
• Large diameter desulfurization flue(Flue gas baffle door matching expansion joint) -Mechanical roll forming + thick wall 316L, don't use hydraulic pressure.

Don't just look at the molding method, but also combine the type of expansion joint. For example, the double hinge transverse expansion joint and the curved tube pressure balance expansion joint, although their bellows are shaped the same (probably hydraulic), their structural designs are different and their installation methods are very different. The former needs to reserve lateral displacement space, while the latter relies on pressure balance to eliminate blind plate force. Before selecting, it is best to compare the size table and stiffness calculation formula on our product page, or ask the technology directly, and don't blindly estimate it yourself.