Specialized in manufacturing compensators, expansion joints, baffle doors

Last summer, the desulfurization flue of a coastal power plant was shut down for maintenance. The reason was dumbfounded-the flange gasket was aging, and the bolt preloading force was uneven. The flue gas came out of the gap, and the whole line was forced to land the load. Lao Wang, who is in charge of the maintenance, told me, "The corrugated pipe material cost a lot of money, and the result was planted in the connection method." Indeed, non-metallic expansion joints (fabric fiber expansion joints, rubber compensators, rectangular non-metallic expansion joints) are good at carrying heat expansion and cold contraction in flue ducts and desulfurization systems, but if the connection method is not selected correctly, none of them can run away from air leakage, running and shutdown.

1. Flanged connection: the most common pit, often the deepest

Flange connection is the most commonly used way of non-metallic expansion joints, none of them. Regardless of the siteNon-metallic expansion joint (fabric fiber expansion joint)StillRectangular non-metallic expansion jointThe mating flanges will be equipped when they leave the factory. But when installed on site, three details are prone to rollover.

flange surface flatness— — I have seen the on-site pipe flange tilt up by 3mm after welding, and the workers firmly plugged the asbestos gasket flat. As a result, it leaked one week after it was put into operation. Correct practice: the flatness error of the matching flange is ≤1mm/m, otherwise it should be leveled with sealant or machining.

bolt preload force-Many people think that "the tighter it is screwed, the less it leaks", which may be right for metal pipes, but it is a disaster for non-metal expansion joints. The loop tape (fabric fiber layer) is pressed too tightly by the bolt, the edge stress is concentrated, and it tears in a few months. This site'sRectangular non-metallic expansion jointClearly mark the torque value in the installation manual. For example, the preload force of M16 bolts should be controlled at 80-100N·m. Don't rely on the feel.

Gasket selection— — The flue gas temperature is high and contains sulfur, so ordinary rubber gaskets can't bear it.Rubber PTFE compensatorCommonly used integral flange + PTFE gasket, corrosion resistance and good fit. But note: the gasket should not be too thick, otherwise the bolt will not be compressed firmly; It should not be too thin, otherwise the compensation joint will be easily displaced when vibrating. According to JB/T 12235-2015 standard, the gasket compression ratio is controlled at 25%-30% to be the most stable.

Used in a cement plantNon-metallic expansion joint (fabric fiber expansion joint)Connecting the cyclone outlet, the workers tried to save trouble and screwed all the flange bolts to the maximum torque. As a result, the ring belt tore a hole along the bolt hole, and the smoke was sprayed with dust for half an hour. Later, I changed the preload wrench and never happened again.

2. Connection between clamp and buckle edge: save money? Temperature resistance passes first

Many people like to connect low-pressure large-diameter pipelines with clamps or buckles, which are cheap and convenient to disassemble. But here's the paradox: You think clamps save money and hassle? Wrong, the temperature resistance rating does not match the fastener material, and it will come loose in a few months.

Clamps are mostly used in circular pipes, such as the flue section behind the flue gas baffle door. However, the bolts and spring sheets of the clamps will creep at high temperatures-when the temperature exceeds 200℃, the elastic modulus of ordinary carbon steel buckles decreases by 30%. A stainless steel 304 clamp was used in a desulfurization project. Half a year later, the bolts were loosened due to thermal cycle, and acid fog emerged at the interface. Later, it was replaced with a 310S clamp to stabilize.

This site'sRectangular non-metallic expansion jointThe structure of buckling edge + strip is mostly used: the edge of the expansion joint band is flanged, embedded in the flange groove, and the outside is fixed with an entire strip. This design is particularly friendly to the four corners of a rectangular pipe, and there will be no case where the clamp can't press the R corner. However, if the material of the strip is not selected well, it will also roll over-ordinary galvanized strip will rust and wear in the wet desulfurization environment for three months. It is recommended to use 316L or FRP composite strips.

Have you ever used a failed clamp case on your project? Chat in the comments section.

3. Hot vulcanization bonding and integral molding: Don't be superstitious about the word "sticky"

Rubber non-metallic expansion joints, such as this station'srubber compensatorAndRubber PTFE compensatorThe connection method is commonly bonding or integral vulcanization molding. However, many purchases are biased by sales talk: "We use imported glue, which sticks firmly!"-Not enough bonding strength? That's because you didn't follow the standards.

High temperature flue gas section (> 120℃) must use hot vulcanization process。 The essence of vulcanization is that rubber molecules are crosslinked with reinforcing materials to form chemical bonds, and the peel strength can reach more than 50N/mm. In the normal temperature section (≤80℃), cold adhesion and special primer can be used, and the peel strength can also reach ≥25N/mm as required by JB/T 12235-2015.

I met a customer who used a cold-stick rubber compensator in a hot air duct (180℃) of a power plant, and the bonding surface degummed after two weeks. During the maintenance, it was discovered that the cold adhesive glue softened at high temperature and couldn't hold it at all. So,Not all non-metallic expansion joints can be bonded— — When selecting the model, be sure to ask clearly: What is the medium temperature? Is it frequent start and stop?

Integral molding is to directly mold rubber or PTFE into a compensator with flanges, such as this station'sPTFE compensator, the flange and the corrugated body are formed at one time, there is no bonding interface, and the reliability is higher. But the cost is also high, and it is not suitable for oversized sizes (such as rectangular sections above 5 meters).

4. Special structure: pipe welding and composite seal

In some operating conditions, the standard connection method is simply not sufficient. For example, double seal structure-learn from this siteRound Flap Door (Double Seal)The idea that the non-metallic expansion joint can also be made into two layers of seal inside and outside. The inner layer is covered with fabric fiber skin to absorb displacement, and the outer layer is protected by metal deflector + temperature-resistant sealing strip. This structure is commonly found in high temperature fan inlets and outlets that require zero leakage.

Such asHigh temperature axial expansion jointNon-metal alternative-welded to the pipe with stainless steel through pipe, covered with multiple layers of skin (silicone cloth + ceramic fiber + stainless steel wire mesh), the design logic of layered overlap is simple: each layer is responsible for a function-the innermost layer is insulated, the middle layer is pressurized, and the outer layer is corrosion-resistant. The weld position must be staggered to avoid thermal stress concentration. After one project did so, it was extended from quarterly maintenance to biennial maintenance.

In addition,Double hinge expansion joint for air-cooled island vacuum pipelineAlthough it is mostly used in metal pipes, its hinge compensation concept can also be transplanted to non-metals: the universal joint structure allows the displacement in three directions, and the composite gasket is added at the connecting flange, which has a very stable effect.

To summarize – there is no best way to connect, only the most suitable. If the medium temperature is lower than 150 ℃ and the pressure is slightly positive, the flange connection is sufficient; Large-diameter low-pressure buckling strip; Vulcanization or integral molding for high temperature; If you want zero leakage, go to double seal. This site'sNon-metallic expansion jointCovering fabric fiber, rubber, PTFE and other materials, the connection methods can be customized from flange, clamp to vulcanization bonding. The key is to select according to parameters-the temperature, pressure and displacement are clearly reported, and we will help you match the scheme without running.

How exactly do metal expansion joints expand? Physical processes from bellows deformation to displacement absorption

When many people come into contact with the metal expansion joint for the first time, they will stare at the circle of corrugated pipes in a daze: this thing looks like the drain pipe of a washing machine. How can it swallow the thermal expansion and contraction of tens of millimeters of pipes? In fact, the core principle is very simple-relying on the elastic deformation of the bellows itself to "eat" the displacement. Think of it as a retractable spring tube, except that the spring is made of stainless steel or alloy, and the shape of the corrugations has been specially calculated to bend repeatedly without fatigue fracture while withstanding internal pressure and temperature.

Each corrugation (also called crest and trough) of the bellows will bend and stretch when stressed, and multiple corrugations are accumulated together, and the compensation amount comes out. Take what we always sayUniversal corrugated expansion jointFor example, the single wave compensation amount is typically between 2 and 8 mm, depending on the wave height and wall thickness. A set of more than ten waves of expansion joints can easily handle tens of millimeters of axial expansion and contraction. To put it bluntly, this is to accumulate small deformations into macroscopic displacements-the same principle as stacking Arhats. One person doesn't have much height on tiptoe, but more than a dozen people can reach the roof after stacking them. Isn't this the principle?

The direction of displacement in the pipe is not only axial. The steam pipe heats up and the pipe elongates along the length, which is axial. However, sometimes the pipeline is deformed or turned due to the bracket, and there will be lateral misalignment or angular deflection. At this time, it is not easy to rely on the axial expansion joint alone. Hard installation is equivalent to letting the bellows twist to work, and it will crack in a few cycles.

What to do? Engineers added tie rods, hinges or universal rings outside the bellows to forcibly limit the deformation direction of the bellows. Such asCompound hinge transverse expansion jointTwo sets of bellows are used to cooperate with the hinge structure to absorb the lateral displacement;Curved tube pressure balance expansion jointThen the internal pressure of the bellows on both sides is self-balanced, and the angular displacement is absorbed, while the pressure thrust is not transmitted to the fixed bracket. You see, the same bellows, with different restraints, can make more than a dozen functions-the products listed on our website, likeStraight pipe pressure balance type、Double straight pipe bypass pressure balance type、External pressure single axial expansion jointThey are all derived from this idea.

The elastic limit of metal is just that little. Will it not crack when bent repeatedly? Good question. Here we have to talk about the fatigue life design of the expansion joint. The bellows will be pre-strained before leaving the factory, and the wall thickness at the trough is usually a little thicker than the peak, in order to transfer the stress concentration zone to the peak position. In addition, the guide tube is an accessory-the guide tube is sleeved on the inner wall of the bellows, which can not only guide the flow of the medium without washing the ripples, but also reduce the vibration caused by turbulence (for specific functions, please refer to the Q&A in our station).

The service life of the expansion joint is generally calculated according to 1,000 to 10,000 full cycles in design. Under actual working conditions (such as how many times a year the power plant pipeline starts and stops), it is no problem to use it for twenty or thirty years. Two days ago, a customer asked the gas bellows to be changed every few years. In fact, it was civil gas hoses, which are different from industrial metal expansion joints. Civil gas hoses have age requirements, and the type test used in industry is carried out according to the standard JB/T 12235. As long as it does not exceed the design displacement and pressure, it can be checked regularly, and there is no need to pat your head to change them.

When installing the expansion joint, what exactly is that arrow direction and tie rod nut for? The direction of the arrow refers to the direction of the flow of the medium, and its main function is to prevent the direct impact of the medium on the ripples caused by the reverse installation of the guide tube. The tie rod nut is locked in the transportation and installation stage, and the purpose is to pre-compress or pre-stretch the expansion joint to the middle position to avoid the on-site pipeline being misaligned; After all the pipes are connected and the fixing bracket is welded, loosen the nut to the specified position (usually the product description will give the distance between the two nuts), otherwise the expansion joint is locked and there is no room for expansion at all. You say it was wrong or not?

To put it bluntly, the principle of metal expansion joint expansion is not mysterious. The difficulty is to choose the right model and install it correctly according to whether it is axial, transverse or angular displacement in the pipeline system. Like those used in the power station industryCorrugated expansion joint for power station industryCement industryMetal Corrugated Expansion Joints in Cement Industry, the working temperature is high, the dust is heavy, and it will be equipped with heat insulation layer and wear-resistant lining-but in the final analysis, the corrugations of the bellows are still bending honestly, bearing all the thermal stress for the pipe. Therefore, the next time you see the bulging bellows on the pipe, you will know that it is not a beautiful decoration, but a hard-core part that actually carries displacement with your body.

Why do you have to have regular inspections? — Don't wait until you miss it to regret it

Two days ago, I met a brother from a power plant. Their desulfurization tower was exportedNon-metallic expansion joints (fabric fiber expansion joints)Suddenly it was torn, and the hot smoke was wrapped in slurry and directly leaked out. After the production line was stopped for 3 days, the light loss was a small million. You say it was wrong or not? In fact, this kind of accident can be completely avoided-as long as it is checked regularly, it will only take a few hours to replace one if the signs of aging of the fabric layer and corrosion of the metal frame are found in advance.

Non-metallic compensators (also called non-metallic expansion joints and fabric fiber expansion joints) are widely used in smoke and air ducts, desulfurization systems and cement production lines, because they are resistant to high temperatures, corrosion resistance and can absorb large displacements. However, its soft belt is tossed by high temperature, dust, acid and alkali gases all the year round, and its aging rate is much faster than that of metal parts. When you see air leakage, smoke leakage and abnormal noise before dealing with it, the internal structure is often hurt. SoHow to check a non-metallic compensator?This problem is actually one of the core lessons of pipeline maintenance.

Appearance inspection: Seeing, touching and listening, three steps to find out the big fault

Look-scan details with your eyes

Standing on the side of the compensator, first look at the surface of the fabric for bulging, scratches, fluffing, and whitening. Bulging usually means debonding between layers, and scratches deep may have damaged the inner PTFE or rubber film. Pay special attention to the corners of rectangular non-metallic expansion joints-that position has the most stress concentration and is most likely to crack first. Look at whether the metal flange is corroded and the weld is cracked.

Touch-to feel with your hands

Put on the gloves and touch the circle along the surface of the circle band. If it feels hard and sticky locally, it means that the material has degraded. Rubber compensator or rubber PTFE compensator is especially afraid of this-it will be brittle and cracked when it is hard, and it will be corroded by the medium when it is sticky. The normal feel should be uniform elasticity and smooth surface.

Listen-Find abnormalities with your ear

When the equipment is running, get closer and listen to whether there is a hissing air leak or a puff bulge. Experienced masters know where they leak as soon as they hear it-the hissing sound is mostly due to the fabric needle eye being enlarged, and the puff sound may be the displacement of the internal cushion.

After these three steps are completed, 70% to 80% of the surface problems can be found out. However, some internal injuries have to rely on these methods.

Dimension and displacement compensation ability check-measure to know whether there is failure

Nonmetallic compensators are not only soft connections, they absorb the thermal expansion and mechanical displacement of the pipe. Think about it, the pipe can stretch tens of millimeters when it is hot, and it all depends on this soft guy's deformation to digest it. If it loses its elasticity due to aging, or does not leave enough margin during installation, the consequence will be pipe stress hard top, flange crack, or even equipment.

How to check? Simple: Measure the actual length and width of the compensator under shutdown, and compare with the factory design dimensions. If the amount of compression has exceeded 80% of the design maximum, or the amount of stretch is almost to the end, then you have to consider replacing it. Common standards, such as JB/T 12235-2015 "Non-metallic Expansion Joints", specify the displacement limit and fatigue life.

In addition, don't forget to look at the guide tube (if any) -the specific function of the expansion joint guide tube is to protect the fabric from being washed by high-speed airflow. If it corrodes and collapses, the compensator life is directly discounted in half.

Sealability and airtightness test-a dozen pressures, all leaks appear

The front ones are all visual and feel, and the real tough battle is the airtightness test. Especially in the desulfurization flue gas baffle door, air-cooled island system and other occasions with high sealing requirements, the high air leakage rate not only increases the energy consumption, but also may lead to scaling and corrosion of peripheral equipment.

Close the valves on both sides of the non-metallic compensator, seal one end with a blind plate, and give 0.05~0.1MPa compressed air to the other end (don't overpressure, the fabric can't bear to rush), and then coat each seam, flange surface and bolt hole with soapy water. Where bubbles are the leakage spots.

Before the test, confirm that the compensator has no obvious bulge or tear, otherwise it will collapse directly when the wind takes a dozen, which will be dangerous. The pressure holding time should be at least 5 minutes, and the pressure should not drop before it is qualified. If there are not many leaks, you can try to plug them with special repair glue; But if the fabric leaks in a large area, or several leaks are strung together, don't toss it, just replace it with a new one.

Judgment and treatment of common faults-which can be repaired by themselves and which must be replaced

Come on, go straight to the dry goods:

• Small scratches and slight fluffing on the fabric surface: Apply a layer with silicone rubber or fluororubber repair agent, and it can top for a while when it dries. However, the premise is that the covering layer is not damaged, and the medium temperature does not exceed the temperature resistance range of the repair agent.
• Air leakage due to loose flange bolts: This can be tightened by itself, and the torque value is tightened 2~3 times in diagonal order. Don't screw to death at once, it will easily deform the flange.
• Local bulging and delamination of circular zone: It indicates that the fabric and inner layer have been detached. Don't fix it, just change it. Because the bulge will get bigger and bigger and break sooner or later.
• Metal frame corrosion perforation: Look at the corroded area. If it is only a small piece, you can apply anticorrosive paint after repair welding and polishing; If a large area is thinned, the whole frame has to be replaced.
• Fabric distortion due to displacement exceeding limit: First check whether the pipe support is displaced or the original selection is too small. If it is a bracket problem, adjust the bracket; If it is a type selection problem, the expansion joint with a larger compensation amount must be replaced.

At the end of the day,How to check a non-metallic compensator?Not going through the motions, but turning "examination" into "diagnosis". Each inspection records the appearance status, size data, and leakage, and compares the historical trend. For example, the compression amount in the last quarter was only 40%, and this time it reached 60%, which means that the aging has accelerated-the spare parts replacement plan can be arranged six months in advance.

Don't wait for the smoke to panic. Follow this list, and your non-metallic compensator (whether it is a rectangular non-metallic expansion joint, rubber compensator, or PTFE compensator) will last three or five more years, and it will be perfectly fine.

First, find out what "too long" is all about-common cause investigation

Many people ask as soon as they come up, "What should I do if the metal expansion joint is too long?", but we have to first see whether this "too long" is not calculated correctly by design, or it is forced in during installation. There are three common reasons: First, the thermal elongation of the pipeline is considered large during design and selection, or the cold tightness is not considered at all; Second, there is a deviation between the actual center distance of the on-site pipeline and the drawing, such as support settlement and flange misalignment; Third, the factory length of the expansion joint itself is too large-for example, you ordered a general-purpose corrugated expansion joint, but the supplier delivered it according to the standard length, and did not customize and shorten it. Two days ago, a customer of a power plant took an external pressure single axial expansion joint. The actual installation space was only 300mm, but the one he bought was 400mm long. Do you think this can be installed?

Second, don't hurry to cut, try "adjust the installation position" and "change the bracket" first

The expansion joint is too long, and it is not the only way to cut. In many cases, adjusting the pipe bracket or adding a bias can solve the problem. For example, if your pipe has installation allowance, you can retract the fixing bracket a little, so that the connectors at both ends of the expansion joint extend more into the pipe. Alternatively, if the expansion joint has a tie rod nut (like a large tie rod expansion joint), try loosening the nut to allow the bellows to compress-be careful not to exceed the allowable amount of compression. Don't forget what the expansion joint guide does: it both protects the bellows and limits excessive compression. If you use a double hinge transverse expansion joint, it itself can absorb angular displacement through the hinge, and a slight adjustment of the angle can "eat" part of the length. If it doesn't work, you can add a short section to the pipe to fill up the space.

3. Wrong selection? Then switch to an expansion joint construction-recommended alternative

If the installation and adjustment can't be done, the problem is probably in the selection. At this time, it is necessary to change a more suitable model according to the pipeline displacement, pressure, temperature and other parameters. For example: you originally used a general-purpose corrugated expansion joint, but thought it was too long, so you can replace it with a straight tube pressure balanced expansion joint or a double straight tube bypass pressure balanced expansion joint, which is more compact in structure and has a shorter axial length. If it is a high-temperature steam pipeline, consider the high-temperature axial expansion joint, which has less corrugations, large stiffness and shorter length under the same compensation amount. There is also an extreme practice: instead of the axial expansion joint, the rotary compensator is a sleeve-type structure with a fixed length and is not affected by bellows compensation. Note, however, that rotary compensators are not suitable for high-pressure applications. Here is a reminder that you must check the pipeline thrust before changing the model, otherwise it is easy to pull the bracket.

4. The last way: Cut or return to the factory-but the risks must be clear

Some old masters say, "Saw off a piece of isn't it over?" Don't do this! Each wave of the bellows of the metal expansion joint is calculated according to the design pressure, and cutting will destroy the end structure and stress distribution, which directly leads to the instability or leakage of the bellows. Only a few circumstances are possible: if the manufacturer reserves a cut allowance and you have accurate welding process documentation on hand, you can short-circuit it-for example, large-diameter thick-walled expansion joints sometimes leave a straight edge section on the end tube, allowing you to cut off the excess and re-weld the joint. However, in most cases, it is recommended to contact the manufacturer directly to return to the factory for modification, or change to a customized length. For example, the directly buried (fully buried) expansion joint of this station is made according to the measured length of the construction site after leaving the factory, so there is no problem of being too long at all. Remember: cutting the bellows is equal to scrapping, and cutting the end pipe should also ensure the welding quality. Don't save small money and suffer big losses.

5. How to avoid "too long" from the beginning-3 key points in the design selection stage

Instead of remediating afterwards, it is better to get stuck in the front. First, when calculating the thermal elongation of the pipeline, it should be calculated according to the difference between the actual working temperature and the installation temperature, and don't leave too much margin; Second, preference is given to the type of expansion joint with compact structure-for example, in the pipe gallery with limited space, the double hinge transverse expansion joint or the curved pipe pressure balance expansion joint is much shorter than the single axial type; Third, before ordering, let the manufacturer produce according to the measured size on the spot, or mark the cold tightness on the installation drawing. For example, the corrugated expansion joints for power station industry and metal corrugated expansion joints for cement industry in this station all support non-standard customized length according to working conditions. In addition, don't ignore the non-metallic expansion joint (fabric fiber expansion joint), which occupies little space and is light in weight, and can replace the metal expansion joint under some working conditions.

How to pick the expansion joint manufacturer? A 10-Year Selection Consultant's Guide to Avoiding Pitfalls

Two days ago, I met a customer. As soon as he came up, he threw me a drawing and asked, "How much is this expansion joint?" I said, don't worry. Is your working condition steam pipe or flue gas pipe? What's the temperature? He was stunned for a moment and said, "Oh, it's just ordinary pipes. Can't you use your general-purpose corrugated expansion energy-saving type?"-I can run into this kind of conversation dozens of times a year. If you choose an expansion joint manufacturer, if you only stare at the price, you will probably roll over. Today, I'll talk to you about the pits I've stepped on and the thunder I've seen in these 10 years of selection.

1. Don't just look at price: product line breadth is the first sieve

Many purchases ask, "How much is your expansion joint per meter"-as soon as I hear this, I know that I am either a novice or just want to be cheap. What is the "universal price" of expansion joints? The same caliber,High temperature axial expansion jointAndThe materials and processes of general-purpose corrugated expansion joints are completely different, and the price difference is three or five times too normal.