Specialized in manufacturing compensators, expansion joints, baffle doors

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.

First, recognize what this silicone cloth in your hand is for-the core component of non-metallic expansion joint

When many people get the non-metallic compensator silicone cloth, their first reaction is "Isn't this just a cloth? Just screw it on". Tsk, if it were that simple, there would be less leaks, tears, or even shutdowns in the industrial pipeline system. This silicone cloth, to be exactNon-metallic expansion joints (fabric fiber expansion joints)The flexible body bears the heavy responsibility of absorbing the thermal displacement of the pipeline, reducing vibration and noise, and compensating the installation error. Think about it, the flue gas pipe can be extended by tens of millimeters at high temperature, and it all depends on this piece of cloth to "expand and contract". If it is not installed properly, it is not a compensator, but a breaker.

Two days ago, I met a customer, saying that their factory had changed the silicone cloth three times, and every time it cracked in less than half a year. I asked him how to install it, and he said, "Just tighten the four corners." As soon as you hear it, you know what the problem is-the wrong way of pretending, no matter how expensive the cloth is, it will be for nothing. So let's understand first: silicone cloth is not just hung casually, it needs accurate pre-stretching, symmetrical fastening, and treatment of flange surface.

2. Hardcore preparation before installation: flange surface treatment, dimension check, bolt preload estimation

First, the flange surface must be clean and flat.Old flanges often have weld slag, rust, and even residual glue from a silicone cloth. These bumps will break through the silicone cloth, and even the burr of only 0.5mm will become a stress concentration point under high temperature and pressure. Polish with an angle grinder and then check flatness with a ruler-repair welding or flange replacement if clearance exceeds 1mm. This work can't be saved. If you save it, you will dig a hole for yourself.

Second, size check.Silicone cloth has a durability limit and cannot be deadlifted when installed. Measure the inside diameter of the flange and the effective width of the silicone cloth. The standard practice is: the free length of silicone cloth should be 10~20mm shorter than the flange spacing (see the design displacement). For example, if the axial compensation amount is designed to be ±50mm, the length of silicone cloth should be about 15mm shorter than the flange spacing during installation, leaving pre-stretching space. This piece of data is usually obtained fromNational Standard for Non-Metallic Expansion Joints JB/T 12235-2015You can find it in, don't be lazy.

Third, bolt preload estimation.Many people screw bolts all by hand feel, and as a result, they either loosen or deform the flange. Silicone cloth is generally fixed by pressure plate, and the preloading force of pressure plate bolts is recommended to be controlled at 40~60 N·m (with torque wrench). For M16 bolts, the torque value is approximately 50 N·m. If the flange is a thin-walled piece (such as the flange of a smoke baffle door), it must be lowered to 30 N·m to prevent the platen from deforming and cutting the edges of the silicone cloth. There is no standard answer for this data? Yes, ask the manufacturer for installation specifications, or refer to the product information on this siteRectangular non-metallic expansion jointThe installation instructions page.

3. Step-by-step installation practice: from the fixed end to the free end, screw the bolts diagonally to avoid accidents

All right, preparations done, start loading. Remember one principle:Fix one end first, then center it gradually, and finally tighten it diagonally.The order is wrong, and the silicone cloth is quasi-skewed.

Step 1, spread the silicone cloth onto the flange and align the bolt holes. Put the pressure plate on the free end (usually the displaced end of the pipe) first, and tighten two bolts slightly (don't tighten them, as long as they can fix the position). Then use a crowbar or manual hoist to align the flange at the fixed end (such as the equipment side) with the pressure plate, put all the bolts on this end, and screw it snugly against the pressure plate by hand.

The second step is to adjust the position of the free end. Use a flashlight to check whether the silicone cloth is centered-the gap difference between the two sides should not exceed 2mm. If there is an offset, fine tune the position of the free end flange with a crowbar. At this time, don't be lazy to smash it hard with a hammer, it will smash the silicone cloth out of wrinkles.

Step 3: Twist the bolts diagonally. This is too critical. Assume that there are 16 bolt holes in one circle of the flange, first screw the four points 1, 9, 5 and 13, and hit the torque to 30 N·m; Screw again 3, 11, 7, 15, again 30 N·m; Then fill all the bolts in sequence, and finally add to the target torque uniformly. Why do you want this? Because if you twist it one by one along a circle, the silicone cloth will be "squeezed" aside, and wavy wrinkles appear. During operation, these wrinkles are stress concentration zones and will quickly wear out.

And guess what? Many on-site workers directly twisted the electric wrench from 1 to 16 in order to get fast. It took five minutes to get it done. The consequence is: after three months, the silicone cloth cracks at the edge of the bolt hole, and they will blame the poor quality of the product-in fact, the fault lies in the installation technique.

4. The installation and rollover sites we saw in those years: over-stretching, deflection and unilateral compression

After working for more than ten years, I can write a book about the rollover cases I have seen. Pick three typical ones and say:

1. Over-stretching.There is a rotary kiln flue in a cement plant. When the silicone cloth is installed, it is pulled too tightly, so it is directly used as a "bandage". As a result, the pipe was elongated after heating up, and the silicone cloth had no margin, which was torn at the edge of the platen. Correct practice: Let the silicone cloth be in a "slightly loose" state when installing, retaining at least 10mm of axial relaxation. Criteria of judgment? Press the middle of the silicone cloth with your hand, and it is normal to easily press 5~10mm.

2. Deflection.A brother who was doing a desulfurization project loaded the silicone cloth 8mm crooked. As soon as the transverse displacement of the pipeline occurs during operation, the silicone cloth bears tension on one side, and the side collapses directly after three months. How to solve it? After installation, check the flange alignment with a laser measuring instrument. If the deviation exceeds 3mm, it must be adjusted.

3. One-sided compression.In order to catch up with the construction deadline, some sites only screwed half of the bolts of the flange, thinking "test it first, and make up if it leaks". As a result, as soon as the fan is turned on, the negative pressure sucks in the silicone cloth on the unfastened side and tears it in half directly. Therefore, every bolt must be in place during assembly, and no one can leak.

How many of these pits have you stepped on? Don't think it's all the fault of a novice. I've seen twenty-year-old masters still make it. In the final analysis, the silicone cloth is treated as an "ordinary gasket".

5. Don't rush to go after installation: pressure test, displacement check, and how to make silicone cloth use for two more years

The bolts are screwed, not the end. There are three more barriers to pass:

First, test the pressure.For pipelines under pressure (such as the non-metallic section next to the corrugated expansion joint used in the power station industry), perform a hydraulic test with 1.25 times of the design pressure, hold the pressure for 30 minutes, and observe that there is no leakage at the flange connection. If it is a negative pressure pipe (such as the flue before and after the smoke baffle door), check all bolt holes and joints with soapy water, no air bubbles.

Second, displacement check.Mark several reference points on the silicone cloth (for example, draw an alignment line between the cloth surface and the edge of the flange with a marker), then simulate the temperature rise and fall under the working condition, and measure the actual displacement with a caliper. If the measured displacement exceeds 80% of the design value, it means that the installation reserve is not enough, and it must be readjusted.

Third, the SAO operation to extend the life.Want to make silicone cloth last two more years? A few tips:

• Applying a temperature-resistant and waterproof coating (such as silicone rubber varnish) on the outer surface of silicone cloth can greatly slow down the aging.
• If it is outdoor installation, add stainless steel protective cover to prevent direct UV rays.
• Check the torque of the platen bolts periodically-thermal cycling causes attenuation of the preload force, re-tighten every six months.

After all, how to install non-metallic compensator silicone cloth? There is no standard answer to this question, but there is a standard process. If you follow the above five steps, you won't make a mistake. If you want to save trouble and pretend blindly, then this piece of cloth will only last half a year if it dies, and the money for shutting down the machine and changing the cloth will be enough to buy several sets of good ones. This account, you can settle it yourself.

Non-metal compensator, can it be used in the second construction examination and engineering?

Find out what "second construction" refers to first. The second-level construction engineer examination is divided into professional directions, and mechanical and electrical, municipal and highway will all involve pipeline engineering. Non-metallic compensators (also called non-metallic expansion joints) are very common in industrial pipes, heat pipes and flue gas pipes. Many candidates think that metal bellows is the key point, ignoring products such as fabric fiber expansion joints. Two days ago, a friend who took the electromechanical test asked me, "Did the book mention non-metallic compensators? I had no impression at all when I was reviewing." In fact, flipping through GB50235 of the Construction Code of Industrial Pipeline Engineering, the compensator chapter clearly contains the non-metallic type, but some tutorial books have mentioned it in a stroke.

Will it be taken or not in the exam? Real Questions Speak

Will the non-metallic compensator be examined in the second construction examination? Say it directly: test. Multiple-choice questions and case questions may appear, especially scenarios involving thermal pipeline displacement compensation, desulfurization system and dust removal pipeline. For example, in 2021, a provincial real question asked "Which compensator is more suitable for flue gas pipelines", and the answer was non-metallic expansion joints. Why? Because the non-metallic material is resistant to high temperature and corrosion, it can absorb multi-directional displacement and is cheap. The products of this station are specialized in "non-metallic expansion joint (fabric fiber expansion joint)" and "rectangular non-metallic expansion joint", which are designed for flue gas pipelines of power plants and cement plants. Although the exam syllabus does not list this term separately, the scope of application has long been covered. Think about it, the flue gas pipe is high in temperature and corrosive, and the metal bellows can hold it? Not at all.

Do you dare to use it in actual engineering? Don't be biased by "weak"

Let's talk about actual engineering. The second construction licensee usually serves as the project manager or technical leader, and needs to select the compensator in the construction organization design. Some peers feel that the non-metallic compensator is "weak" and dare not use it. Actually, it is not the case-non-metallic compensators (such as rubber compensators and PTFE compensators) perform well in low-pressure, large-diameter pipelines with a temperature of no more than 600℃, especially the pipelines behind the desulfurization flue gas baffle doors. Metals for corrosive gases are easy to break. The "rubber PTFE compensator" in our station is specially designed to deal with acid-base media. When selecting the model, you should calculate the compensation amount and pressure level, and don't exceed the limit. It is recommended to confirm the model parameters according to the national standard JB/T 12235-2015. No, two days ago, a cement factory project used a "rectangular non-metallic expansion joint", and there has been no problem for three years. So don't listen to anyone's nonsense, non-metallic compensators are much more durable than metals in specific scenarios.

The two easiest pits for beginners to step on. Have you fallen for it?

However, the second construction candidates or engineers who have just entered the industry are prone to stepping on two pits: First, the non-metallic compensator is regarded as a universal piece, and it dares to be used in high temperature and high pressure situations; Second, there is not enough space for the guide tube during installation, or the tie rod nut is screwed to death, resulting in failure. The function of the expansion joint guide tube is discussed in our question and answer-to prevent the medium from washing the fiber layer. Although the non-metallic expansion joint does not have a tie rod (different from the metal bellows), the bolt torque of the frame and pressure plate is particular. Be sure to read the instructions before installation, don't mess around with experience. If you are preparing for the second construction exam, it is recommended to save the question and answer of "National Standard for Non-metallic Expansion Joints" on this site, and turn it over before the exam. If the case questions get the installation details, you can get points. Tsk, don't get blind in the examination room then.

After all, the second construction of non-metallic compensators is like a carpenter who can only use a hammer

In the final analysis, non-metallic compensators can not only be used in the context of second construction, but should also be used. From the examination point of view, it is a must-know point for industrial pipeline installation; From the engineering point of view, it is a mature scheme to solve the displacement compensation of high temperature flue gas and corrosive media. The second construction of non-metallic compensators is like a carpenter who can only use a hammer-he can do his job, but he may not do his job well. Think about it, if a desulfurization flue project is hard on the metal expansion joint, it will rust through in half a year, and it is weird that the owner does not complain. On the other hand, choosing the right non-metallic expansion joint (such as our "rectangular non-metallic expansion joint") can save worry and effort for three to five years. Therefore, don't worry about "whether you can use it", learn when you need to learn, and use when you need to use it. After thoroughly understanding JB/T 12235-2015, and then remembering the parameters of "rubber PTFE compensator", the examination and project will be stable.

How to choose a metal expansion joint? Understand these 5 steps and buy the right goods for less money

Two days ago, I met a customer and bought a batch of general-purpose corrugated expansion joints and installed them on high-temperature steam pipelines. As a result, they exploded within three months. After asking, he found out that he only looked at the nominal diameter, not the actual temperature at all. This happens a few times a year. How to choose a metal expansion joint? Don't just look at the price, you have to follow the following five steps, and the probability of wasting money can be reduced by more than half.

Step 1: Understand the working conditions of the pipeline thoroughly-pressure, temperature and displacement must be missed

Many purchases ask "How much is DN200" as soon as they come up, and the price is too expensive after quotation. But when you tell him, "Is your pipe pressure 1.6MPa or 2.5MPa? Is the temperature 300℃ or 600℃?", the opposite side often froze. The first pit of selection is here:Does the pressure depend on the design pressure or the maximum working pressure?The design pressure is usually 10% ~20% higher than the highest working pressure, but the selection of expansion joints should be based on the highest working pressure, and the safety factor should be sufficient. Don't blindly choose bigger, it is not cost-effective to double the cost.

The temperature is even worse.Medium temperature plus thermal radiation and pipe outer wall temperature, the actual corrugated pipe may bear a temperature of 50~100℃ higher than the medium temperature. For example, the steam pipe medium is 450℃, but there is no heat insulation near the bellows, and the heat radiation directly bakes it, and the surface temperature of the bellows can reach 550℃. At this time, you take the ordinary 304 material to carry it, and the intergranular corrosion will accelerate, and it will crack in half a year. High temperature operating condition preferredHigh temperature axial expansion jointOrExternal pressure single axial expansion jointThe material is heat-resistant alloy.

Don't just focus on axial expansion and contraction.The thermal expansion and contraction of pipelines not only exist in axial direction, but also in horizontal and vertical directions. After installing at many sites, it is found that the expansion joint is twisted into a twist because only the axial vector is counted. Therefore, before selecting the type, you must get the pipe system stress analysis report, or at least draw a sketch to mark the displacement in all three directions.

Step 2: Don't confuse the structure type-choosing the wrong is equal to buying for nothing

There are many patterns of metal expansion joints on the market, but there are only a few core structures. Using them in the wrong place is a disaster.

• High temperature and high pressure steam pipeline: Decisive external pressure single axial expansion joint or high temperature axial expansion joint. Why? The universal corrugated expansion joint is easy to lose stability in the bellows under high temperature, the external pressure structure can disperse the stress, and the guide tube has its own heat insulation layer, so the service life is directly doubled.
• Large diameter smoke duct: For example, the desulfurization flue of a power plant has a diameter of two or three meters.Metal rectangular expansion jointOrNon-metallic expansion joints (fabric fiber expansion joints)。 Rectangular expansion joints absorb a large amount of displacement, and non-metallic joints can also resist acid and alkali corrosion. However, it should be noted that the national standard JB/T 12235-2015 for non-metallic expansion joints stipulates that the fatigue life should meet the design requirements.
• Need to absorb lateral displacement: There are many turns in the direction of the pipeline and large lateral displacement, withCompound hinge transverse expansion joint。 It has two hinge structures that absorb large lateral displacements, but note that it does not absorb axial displacements.
• High-pressure pipeline to prevent blind plate force: For example, before and after the pump outlet and the valve, if there is blind plate force in the pipeline, selectStraight pipe pressure balanced expansion jointOrCurved tube pressure balance expansion joint。 This expansion joint has a balanced bellows inside, which can cancel out the blind plate force, otherwise the pipe support will be pushed down.

And guess what? Some small factories take general-purpose corrugated expansion joints to connect with pressure balance conditions, but as a result, they are directly broken after installing them for pressure test. If you choose the wrong structure, you can't make up for it no matter how much money you spend later.

Step 3: Materials and Connection Methods – Saving money is not on materials

The media is corrosive, so don't think about saving money with 304. For example, in the desulfurization flue gas environment, the chloride ion concentration is high, and the conventional 304 pits and perforates in less than three months. That's the time to goCorrugated expansion joint for desulfurization flue gas baffle doorThe material is 316L or even duplex steel, or simply lined with PTFE. The PTFE-lined metal hose and PTFE compensator are particularly good for dealing with strong corrosive media, but note that the PTFE-lined metal hose is not resistant to negative pressure, so it should be used in vacuum conditionSpecial hose for vacuum。

How to choose the connection method?The flange is convenient to connect, easy to overhaul and disassemble in the future, and is suitable for low-pressure large-diameter pipelines. Butt welding connection has good sealing performance, suitable for high pressure and small diameter. However, if you use butt welding with low pressure and large diameter, the on-site welding volume is large and the construction period is long, which saves flange money and spends more installation cost. On the other hand, if you use a flange for high pressure and small diameter, the flange gasket is easy to leak, so it is better to direct butt welding. Remember one principle: don't spend 2000 to repair the air leak in order to save 200 yuan of flange money.

Step 4: Accessories and Installation Details That Are Easy to Overlook

Some installers welded the expansion joint to the nozzle when they came up, and they didn't even know if the direction of the guide tube was installed backwards. The direction of the arrow of the expansion joint usually refers to the direction of media flow, not the direction of displacement. The function of the guide tube is to guide the medium to flow smoothly and prevent high-speed fluid or particulate matter from directly impacting the bellows. If it is installed backwards, the guide tube will become a baffle, and the medium will directly hit the bellows, which will wear as fast as cutting. Especially for working conditions containing granular media, such as ash transportation pipelines in power plants, guide tubes must be installed.

How to adjust the tie rod nut?Pre-stretching and pre-compression are realized by it. Adjust the nut according to the displacement given by the manufacturer during installation. Don't forget to remove the limit screw after installation. Some construction teams don't dismantle the limit screw, and the expansion joint can't play a role at all. The pipeline is thermally expanded and hard, and finally the weld joint cracks. AndDirect buried (fully buried) type expansion jointThere must be a moisture drainage pipe buried underground, otherwise the groundwater will seep in and the bellows will not know if it is corroded.

BTW, does the screw of the expansion joint need to be removed? The answer is: the limit screw must be removed, but the tie rod nut cannot be moved. The function of the tie rod is to prevent the bellows from over-stretching, not for fixing. For details, see the article "How to Adjust the Tie Rod Nut of the Expansion Joint" on this site.

Step 5: Avoid fakes and low-price traps

Those stainless steel expansion joints on the Internet that are cheaper than steel prices have a high probability of 201 pretending to be 304. How to tell? Regular products haveMetal expansion joint weight tableFor reference, for example, the general corrugated expansion joints of DN200 and PN16 have a standard weight of about 15~18 kilograms. If the weight quoted by the seller is only 10 kilograms, it will be directly blackened, and the wall thickness will shrink. In addition, look at the wave height and wave pitch of the bellows, and take a caliper to measure it to know if you have cut corners.

Working conditions with high fatigue life requirementsFor example, frequent start-and-stop of power plants and rotary kiln pipelines in cement plants, don't buy general corrugated expansion joints. UsefulCorrugated expansion joint for power station industryOrMetal Corrugated Expansion Joints in Cement Industry。 After structural strengthening and wave number optimization, the design life of these corrugated pipes is 2~3 times that of the general type. The selection is not to look at the beauty of the sample book, but to see whether the application scenario can live up to it. You bought the general-purpose model cheaply, but the result was to change it once every two years. The total cost was higher than buying the special-purpose model.

How to buy metal expansion joint? In the final analysis, it is: understand the working conditions thoroughly, choose the right structure, do not save materials, keep an eye on accessories, and avoid fakes. After five steps, he basically wouldn't step on a pit.

What is a large size non-metallic compensator? Let's break the name into three pieces

Don't be fooled by the phrase "large-size non-metallic compensator". When disassembled, it is a straightforward industrial part: the compensator is the expansion joint, and its function is to absorb the displacement caused by thermal expansion and contraction of the pipeline; Non-metal means that the main body of the ring belt does not need metal bellows, but uses flexible materials such as fabric, rubber and fluoroplastics instead; Large size refers to a rectangle or circle with a large cross section-a side length of one or two meters or even larger, which is specially fitted to air ducts and flues. You go to our station "non-metallic expansion joint (fabric fiber expansion joint)" and "rectangular non-metallic expansion joint", which are typical representatives. To put it bluntly, it is a flexible connection that can be telescoped, specializing in serving large-diameter pipes.

Why can non-metals get bigger, but metals can't?

The metal expansion joint depends on the deformation of the bellows to absorb the displacement, but think about it, when the diameter exceeds one or two meters, how much does the wall thickness of the bellows have to be added? The difficulty and cost of processing are soaring up like a rocket, and the materials are easy to become unstable-yesterday, I heard from a friend in a steel mill that they tried a 3-meter diameter metal bellows, and it bulged within two months of installation. There is no such problem with non-metallic belts: silicone cloth, fluororubber and glass fiber cloth. These materials can be stacked into a large format of dozens of square meters, and it is no problem to do it on the spot. More importantly, it is corrosion resistance. The sulfur-containing flue gas in the desulfurization flue of power stations, the metal bellows will erode in a few months, and it is common for non-metals to last for three to five years. And guess what? Some foreign appliance plants use the non-metallic compensator in our station, and the ring belt is changed only once every ten years, which saves a lot of downtime losses.

There are three layers of structure: ring belt, frame and heat insulation. Don't think about complicated

The internals of large-sized non-metallic compensators are far less intimidating than the name. The ring belt is the core, and a layer of sealing film is sandwiched between the multi-layer fiber cloth, just like wearing a leakproof jacket for the pipeline; The frame is welded with metal angle steel or steel plate and is subjected to system pressure; The insulation layer is tucked between the loop belt and the frame to prevent the high temperature from spreading outside. Some working conditions require a guide tube to adjust the direction of airflow-the specific function of the guide tube of the expansion joint, as we talked about in the question and answer, is to reduce vortex erosion. The "rectangular non-metallic expansion joint" in our station is designed according to this logic. By the way, the national standard JB/T 12235-2015 specifically stipulates the strength and sealing requirements of these components. When you buy a product, if the other party doesn't even dare to mention the national standard, just pass.

The three most headache numbers in model selection: temperature, pressure and displacement

When making technical selection, customers like to ask these three parameters. Let's talk about the temperature first: the conventional silicone ring is fine to 250℃, and the fluororubber layer can carry it above 300℃, but don't exceed 400℃. After this thread, the fabric begins to carbonize, and the whole ring belt will be wasted. Stress? Large-size non-metallic compensators are generally used in low-pressure air duct systems, and the design pressure does not exceed 0.1MPa. If it is really high-pressure working condition, obediently choose metal expansion joints. What about the amount of displacement? Axial ± 100mm and horizontal ± 50mm are easy to do, depending on the number of circle layers and wrinkle design. Two days ago, a customer set the parameters of metal expansion joints. Tsk, it was completely confused-metal deforms elastically by bellows, and non-metal slides by fabric folds. The calculation formulas are different, and chaos will cause big problems.

Practical application scenarios are very concentrated: desulfurization in power plants, blast in steel plants, and cement kiln tail

You can see the shadow of large-size non-metallic compensators in any pipeline with large temperature fluctuation, strong medium corrosion and oversized cross section. Desulfurization flue of thermal power plant, blast furnace blast of iron and steel plant, kiln head and tail of cement plant, and waste gas pipeline of chemical plant-it is almost standard in these occasions. Moreover, it is often used in conjunction with baffle doors: for example, the "desulfurization flue gas baffle door" and "circular baffle door (double seal)" of our station are responsible for cutting off the airflow, and the compensator absorbs the thermal strain of the pipeline, which is indispensable. Rectangular air ducts must use rectangular non-metallic expansion joints, and circular air ducts can be rounded. Remember one sentence when installing: the ring belt cannot be twisted, the bolts must be symmetrically tightened, and the insulation layer should not be compacted-compaction will affect expansion and contraction.

Maintenance is simple enough to surprise you

Routine maintenance is to check whether there are aging cracks on the surface of the ring belt and whether the frame bolts are loose. Found a partial breakage? Treat it temporarily with special repair tape, but in severe cases, you have to change the tape as a whole. Don't worry about the money-a non-metallic compensator costs only 1/3 of the price of the same caliber metal, and it can be changed as fast as hell: loosen the bolts, pull out the old ring belt, stick in the new one, and tighten it again, and two or three people can do it in a day. You have to ask about longevity? Depending on the working conditions: the indoor clean air duct is 8-10 years, and the outdoor corroded smoke is 3-5 years, but compared with the 1-2 years of metal bellows, is it much stronger?