Specialized in manufacturing compensators, expansion joints, baffle doors

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.

How to cut metal expansion joint? 5 Key Points and Precautions of On-site Practice

Two days ago, a customer called, and his tone was very urgent: they cut a double hinge transverse expansion joint by 20mm, and after installing it, the tie rod nut was directly suffocated to death, and the compensation amount was completely insufficient. Do you think this sucks or not? Metal expansion joints, especially general-purpose corrugated expansion joints, high-temperature axial joints, large-diameter thick-walled expansion joints, are calculated with good design, material and corrugation parameters. On-site cutting is not a job that can be done by an angle grinder. Today, let's talk about these five key points, so as to save you from stepping on pits later.

1. Find out which expansion joint you have in your hand before cutting

Different structures, cutting strategies are very different. You have to confirm the material first-is it stainless steel, carbon steel or alloy steel? Look at the wall thickness, corrugation shape (U-shaped, ω-shaped or S-shaped), and end connection mode (flange, welding or thread). For example, universal corrugated expansion joint, the corrugation is generally thin, so carefully avoid the root of the corrugation when cutting; The high-temperature axial expansion joint usually has a guide tube and a heat insulation layer. Before cutting, the outer sheath must be opened to see where the wave peak is; Large-diameter thick-walled expansion joints, the wall thickness is always more than ten millimeters, and the cutting tool is not selected correctly.

Measure the total length and compensation requirements, and leave 3~5mm margin when marking the cutting line on the pipe body. Why? Because there is no way to make up for it when you cut too much at once. You cut it short and either scrap it or add a short section, but that again involves weld distortion and stress concentration. We have aMetal expansion joint weight tableChecking can roughly estimate the size margin, but the most reliable thing is to find the manufacturer to confirm the minimum length requirement-especially the models with tie rods such as double hinge transverse type and straight pipe pressure balance type. The length of the tie rod determines the maximum compensation amount, and cutting it short is equal to wasting half of the function.

2. How to choose cutting tools? Don't burn bellows with oxyacetylene

This is the most common mistake. Some people tried to save trouble and directly cut the bellows with oxyacetylene flame. As a result, the stainless steel was partially overheated to above 450℃, resulting in the precipitation of chromium carbide and direct scrapping of intergranular corrosion. Tell me, did you do that before?

• Plasma cutting: Suitable for thick-walled carbon steel parts, such as straight pipe sections with large diameter thick-walled expansion joints, with fast cutting speed and small heat affected zone.
• Laser or waterjet: Most friendly to stainless steel bellows. Especially for the ultra-thin wall (0.5~1.5mm) universal corrugated expansion joint, the edge of laser cutting is smooth, and the waterjet can not only cut multi-layer composite structure without heat influence. However, the cost is high, and it is not realistic to operate in small batches.
• grinding wheel cutting blade: Small-size thin-walled parts (such as DN100 or below) are enough, but they will produce burrs. They must be deburred after cutting, otherwise the burrs will scratch the sealing surface after installing it.
• OxyacetyleneIt is only suitable for cutting straight carbon steel pipe sections, and leave at least 200mm distance from the corrugation. Don't touch the bellows, don't touch the deflector, don't touch the stainless steel.

3. How to cut the corrugated part? Avoid stress concentration zones

If you are cutting a straight section near the corrugation, be careful not to cut to the root of the corrugation-there is a stress concentration zone, and the risk of crack propagation is extremely high if you cut it. It is recommended to cut the outer sheath or insulation first, touch your finger to confirm the crest position (or sweep it with a flaw detector), and then cut the knife on your desired cutting line.

In addition, the expansion joint typically has a flow guide tube (a structure that prevents the medium from washing the corrugations) inside. You have to mark the position of this thing separately, because the guide tube is usually longer than the bellows. If you cut it directly according to the external dimensions, it is likely that the guide tube will be cut off. As a result, the medium directly washes the corrugated wall and wears out in three months. Before, a customer of a cement factory cut a metal corrugated expansion joint in the cement industry, didn't pay attention to the length of the outcrop of the guide tube, and changed it one year after installing it. Go to our website and searchSpecific Function of Expansion Joint Guide TubeYou can see the structure diagram.

4. Treatment after cutting: deburring, pickling and beveling are indispensable

Cut is not finished. First use a file or angle grinder to clean the burrs (the edge R angle is at least above R1.5), and then use a magnifying glass to check for any micro-cracks or ripples near the incision. Stainless steel incisions must be passivated by pickling-otherwise fresh metal will be exposed at the incisions, and there will be no passivation film protection, which will pitting in a few days in the chloride ion environment. The pickling solution can be a citric acid-nitric acid mixture, applied and waited for 15 minutes before rinsing.

In the case of expansion joints for high-temperature steam pipelines (such as corrugated expansion joints used in the power station industry), welding grooves are also involved after cutting. The groove angle (common V-shaped groove and U-shaped groove) of the original design drawing must be referred to, and the roughness of the groove surface should reach within Ra3.2, otherwise unfusion will easily occur during welding. Don't guess for yourself, on our websiteWhat category do steam pipes fall intoAs mentioned in that article, the welding requirements of high-temperature and high-pressure pipelines are particularly strict, and the groove angle is 2° different, so the post-welding heat treatment parameters will be completely changed.

5. Real Lessons: The Consequences of Cutting 20mm Shorter

I asked carefully about the case of the double hinge transverse expansion joint mentioned at the beginning. They found the wrong size in the warehouse and wanted to cut it shorter themselves. Results not checkedMetal expansion joint weight tableI didn't find the manufacturer to confirm the minimum length, but cut 20mm directly according to the installation space. After installation, the tie rod nut is pushed to the limit block, and the compensation amount is reduced by 15%. As soon as the thermal expansion of the pipeline comes up, the nut is directly deformed.

Therefore, directly contact the supplier to customize the length in non-emergency situations, and the risk of on-site cutting is really not low. If you have to cut on site, at least do: check the weight table, measure three times, leave a margin, choose the right tool, and handle the cut. If you are really unsure, take a photo and send it, and we will help you see the model number. It's better than cutting it away.

How to cut metal expansion joint? The answer is actually-don't cut if you can. If you need to cut, remember these 5 points above and avoid detours.

Let's talk about the conclusion first: Should the metal expansion joint be wrapped with heat insulation?

The answer is-it is needed in most cases, but it depends on the specific working conditions. Two days ago, a purchaser from a power plant asked me that the bellows on their steam pipe cracked after two years of use. Was the insulation not done well? When I heard it, it was probably. The core function of the metal expansion joint is to absorb heat displacement, but it is also a guy who is afraid of cold and heat. Today, let's talk about this logic.

Why do most metal expansion joints have to be insulated? Three hard truths

First, anti-condensate corrosion.The medium temperature in the steam pipeline is high, and the ambient temperature is low. When the temperature difference is large, the surface of the expansion joint will condense. When water bubbles, especially the corrugated roots where stress is concentrated, the corrosion rate doubles up. The power station industry in our station uses corrugated expansion joints and general-purpose corrugated expansion joints. Most of the corrugated pipes are stainless steel, and austenitic stainless steel is the most afraid of chloride ion stress corrosion. A package of insulation layer can suppress the dew point problem.

Second, prevent the medium from freezing and blocking.In northern winter, if the pipeline is water or condensate, once the inside of the expansion joint is frozen, the bellows will directly crack. Think about it. On a day of minus 20 degrees, the water is still flowing in the pipe, the insulation is not done well, and it is frozen. That's no trivial matter. Like the double hinge expansion joint of air-cooled island vacuum pipeline, the medium temperature is low and it belongs to the negative pressure condition. It pays more attention to antifreezing and heat insulation, which is often done with polyurethane foaming.

Third, maintain the thermal compensation effect.Thermal insulation can ensure that the body temperature of the expansion joint is consistent with that of the pipeline, and prevent the deviation of displacement calculation caused by local temperature drop. The compensation amount of the expansion joint design is calculated according to the thermal expansion of the whole pipe system. If the temperature of the expansion joint itself is lower than that of the pipe, the deformation amount of the bellows will be wrong, and the fatigue failure will occur after a long time. It's the same as wearing clothes-your arms are cold, your whole body shrinks, and your movements are unnatural.

But in some cases, thermal insulation is bad

For example, high-temperature axial expansion joints and external pressure single axial expansion joints are designed to allow the outer wall of the bellows to be directly exposed to high-temperature flue gas or steam. If the insulation is blindly wrapped, the bellows will be wrapped dead, which will affect its free expansion and contraction. There are also those expansion joints with guide cylinders (see the article in the station for the specific function of the expansion joint guide cylinder). The guide cylinder itself has separated the high-temperature medium, and the outside does not need additional heat insulation. For example, the metal corrugated expansion joint in the cement industry is used in the kiln tail dust removal pipeline. The medium temperature is high but the dust is large, and the insulation layer is easy to accumulate dust and scale, which increases the difficulty of maintenance-in this case, the pros and cons have to be weighed. Some customers want to save trouble, and all of them cover heat insulation. As a result, the high-temperature axial expansion joint is stuck and can't be displaced. Finally, it has to be disassembled and redone, spending more money and missing work period.

If you decide to do insulation, what should you pay attention to during construction? Two things must be kept an eye on

First, the insulation layer cannot limit the displacement of the expansion joint.The design displacement of the metal expansion joint is realized by the deformation of the bellows. If the insulation material is stuck too dead and stuffed too tightly, it is equivalent to adding a "tightening curse" to it. The correct way to do this is: use elastic insulation felt or rock wool, leave an expansion joint, or make a slidable structure when wrapped with iron sheet. We have seen a project in which the construction team stuffed rock wool tightly. As soon as the expansion joint expanded and contracted, the insulation layer directly broke the iron sheet, and the water vapor went in, and the corrosion was faster than not wrapped.

Second, never let the insulation layer seep water.Once rainwater drills in through the insulation seam, and the water vapor is sealed inside and can't come out, the corrosion rate is faster than without insulation. Although the directly buried (fully buried) expansion joint in the station has an anti-corrosion layer, the insulation layer also needs waterproof treatment. The outer iron sheet should be tightly overlapped with the seams facing down to avoid rainwater backflow. If possible, it is safer to brush another layer of waterproof coating on the outside of the insulation layer.

How to choose insulation scheme for different products? Take an example

The corrugated expansion joint used in the power station industry equipped with the steam pipeline of the power station has high medium temperature and high pressure, so it must be insulated with composite silicate or aerogel felt, plus galvanized iron sheet. However, the double hinge expansion joint of air-cooled island vacuum pipeline has low medium temperature and negative pressure, so it pays more attention to antifreeze and heat insulation, so it can be foamed with polyurethane. Another example is the expansion joint next to the desulfurization flue gas baffle door. The flue gas has high humidity and sulfur. The focus of heat insulation is to prevent condensation corrosion, and anti-corrosion coating has to be added outside the insulation layer. These details are directly related to the life of the equipment. Some factories are cheap, using ordinary glass wool, which collapses within two years and has to be reworked, which is more expensive.

Finally, a common misconception

Since the metal expansion joint needs to be insulated, can I paint a thick layer of paint on the outside of it? No way. Paint is an anti-corrosion coating, not an insulation layer, with high thermal conductivity and thin thickness, which can't stop the heat loss at all. Insulation must be made of materials with low thermal conductivity, and the thickness is calculated according to the design temperature of the pipeline. Others say that the non-metallic expansion joints (fabric fiber expansion joints) we use don't have to be insulated? Non-metal itself has limited temperature resistance, such as rubber compensator and polytetrafluoroethylene compensator. Instead, the medium needs external insulation or protective sleeve when it exceeds the tolerance range. In a word: whether thermal insulation is not thermal insulation depends on the matching relationship between the medium temperature, ambient temperature and the material of the expansion joint. If you are not sure, ask the manufacturer directly for the design parameters, which is more reliable than guessing.

Budget Step 1: Find out the parameters of working conditions, and don't let the quotation become "artistic creation"

Flue non-metallic compensator, also called non-metallic expansion joint, fabric fiber expansion joint. The core of the budget of this thing is four words: working condition parameters. Temperature, pressure, diameter, displacement-these four numbers are not determined, and the quotation given to you by the supplier is probably "slapping your head". For example, in the desulfurization flue of power station, the flue gas temperature is generally 80~120℃, but the acid is extremely corrosive; The temperature of the cement kiln tail flue directly soared above 400℃. Different temperatures, the materials used for loops are completely different-silicone cloth, fluorine tape or ceramic fiber cloth, and the price difference starts from three times. Pin these figures to the paper first, and all the quotes later will be accurate.

Don't ignore the pressure. The flue system is mostly slightly negative pressure or low pressure, but in case of positive pressure fluctuation, the number of belt layers and flange strength must be adjusted accordingly. Not to mention the diameter size, the processing hours of the DN200 and DN2000 vary by several orders of magnitude. What about the amount of displacement? Mark the axial, horizontal and angular directions respectively. Don't write "compensation amount 50mm" in general-that's digging a hole for yourself.

The material cost is the big head: ring belt, insulation layer and metal frame, how do you estimate them?

The cost of a non-metallic compensator is divided into three large pieces. The first piece is a non-metallic loop band, which is a multi-layer composite fabric. The more belt layers and the higher the temperature resistance grade, the more expensive the unit price. The national standard JB/T 12235-2015 has requirements for the minimum number of layers of the ring belt, but some manufacturers secretly reduce two layers, which is 30% cheaper and has a life span of less than one year. The second piece is internal insulation cotton, which is commonly used as aluminum silicate fiber blanket. The thickness is calculated according to the surface temperature requirements-generally, the outer wall temperature is required to not exceed 50℃, and the thickness of insulation layer starts from 50~100mm. The third piece is the metal flanges or connectors on both sides. There is an easy pit here: the stress at the four corners of the rectangular non-metallic expansion joint is concentrated, which requires additional reinforcement of the structure, and the processing difficulty is much greater than that of the round one. Q235 or 304 stainless steel for metal frames? For desulfurization systems with strong flue gas corrosion, 316L or even higher nickel alloys have to be considered. The selection of materials directly determines the cost of a single unit, so there is no way to be lazy.

For example, in the product information on our siteNon-metallic expansion joint (fabric fiber expansion joint)Commonly used fluorine tape + alkali-free glass fiber cloth + polytetrafluoroethylene film composite, temperature resistance 260℃; WhileRectangular non-metallic expansion jointBecause of the special structure, angle steel reinforcements will be installed around the flange. For the same caliber, rectangle is 15~25% more expensive than round.

Don't ignore the "hidden costs": deflectors, insulation, anti-corrosion coatings

Two days ago, a customer purchased a non-metallic compensator for flue, and cut off the guide tube because the price was high. As a result, the ring belt was worn out by high-speed flue after three months of installation. Re-assembly plus shipping, double the money saved in the first place. What is the role of a deflector? See what we wrote in our FAQ-the protective ring belt is protected from direct erosion by high-temperature smoke, especially when the wind speed exceeds 15m/s. What about insulation? If the thickness of aluminum silicate wool is not enough and the surface temperature exceeds the standard, it may not only burn people but also burn the ring belt. Do you want to make anti-corrosion coating on the flange surface? The sulfur dioxide concentration in the desulfurization system is high, and the ordinary carbon steel flange will rust through in half a year, so it must be coated with epoxy resin or lined with PTFE. The sealing air interface for the linkage of the smoke baffle door also has to be reserved-this detail has no place in many budget tables at all.

Install bolts, gaskets, sealant. The unit price of these bits and pieces is not high, but the quantity is also money, and the price difference between different materials is great. For example, heat-resistant alloy steel bolts should be used in high-temperature working conditions, and a set is four or five times more expensive than ordinary 8.8 grade.

Size and displacement: Why can the quotation be half the difference for the same caliber?

It is also a rectangular flue with a length of one meter. If it only absorbs 20mm axial displacement, a single wave structure is enough; If you need to compensate the displacement in three directions (axial + transverse + angular) at the same time, you must design a composite structure or increase the wavenumber. With more wave numbers, the number of circle layers may also be added, and the flange width will change accordingly. There is also the installation length-when the site space is limited, the compensator is short and the compensation amount is not enough; If the long flange bolt holes don't match, it will cost money to weld and repair the holes on the spot. These parameters must be clearly marked on the drawing: wave number, compensation per wave, total length, flange screw hole distribution. Only when the supplier gets these parameters can he quote a reliable price, otherwise he can only quote a "benchmark price", and a bunch of additions are waiting for you.

And guess what? Some customers only give a diameter size and let them quote. As a result, after getting the price comparison sheet, they found that A quoted 5000, B quoted 8500, and C quoted 12,000-how to choose? In fact, B and C may have given enough safety margin according to the standard design, and A cut corners. Therefore, when budgeting, we must write the displacement and installation size to death, and then let the supplier calculate according to the national standard. Inside our stationCorrugated expansion joint for power station industryAndHigh temperature axial expansion jointThere are clear displacement compensation curves, so you can refer to the design logic.

Inquiry Comparison: Several quotations are put in front of you, and these three points are focused on

First, is it implemented according to the national standard JB/T 12235-2015? This standard specifies hard indexes such as the number of bands, tensile strength and airtightness test of non-metallic expansion joints. If there is no standard implementation, the default is according to the industry minimum standard-be careful. Second, what does the offer contain? Some only report bare parts, and the freight, on-site welding and installation, bolts and gaskets are all calculated separately; Some quote all-inclusive price, but the warranty period is only half a year. Third, the warranty period and after-sales service-once the flue compensator fails, the exhaust gas leakage directly affects the environmental protection emissions, and the loss of hundreds of thousands a day after production is stopped. So don't just stare at the cheapest one, list these three items clearly, and then let the three companies compare prices. How to do it? Build a comparison table.

Here, the practical template: seven columns are built in Excel-working condition parameters, material selection scheme, structural size, quantity, accessory list, freight installation and warranty terms. Take this form and ask the supplier. If the other party can't report or is vague, just pass. For example, you say you want to add a deflector and he asks "What is a deflector?"-then don't talk about it.

Budget Template: From Zero to Issue Order, One Table Does It

If you estimate it yourself, there is a simple formula: the unit price of rectangular non-metallic compensator ≈ (belt area × belt unit price + flange weight × steel unit price) ×1.2 (machining factor). How to calculate the area of the circle belt? Perimeter × width (the effective width of the band). Look up the table for flange weight according to section steel specification. Ask several suppliers for specific figures, and take the median as the bottom line of the budget. Similarly for circular non-metallic compensators, the area is calculated according to the circumference, and the machining coefficient can be lowered to 1.1.

A 1000×800mm rectangular flue with a band width of 300mm and a temperature resistance of 300℃ is made of fluorine tape composite structure. The unit price of the band is about 800 yuan/m², the band area (1.0+0.8) ×2×0.3=1.08m², and the band cost is 864 yuan. The flange is made of Q235 angle steel, the weight is about 150kg, the unit price is 6 yuan/kg, and the cost is 900 yuan. Total 1764 yuan ×1.2=2117 yuan. This is just a bare estimate, plus the guide tube (about 500 yuan), the insulation layer (about 300 yuan) and the freight (depending on the distance), and the total budget is about 3,000 yuan. The actual quotation may fluctuate by 20%, but if you have a bottom in your heart, you won't be pitted.

Don't use low-grade materials in key parts to save money. Once the flue non-metallic compensator fails, the maintenance window is short, and the loss of shutdown is far greater than the price difference of equipment. Bookmark this article, and go through the list next time you make a budget, at least no items will be missed.