Specialized in manufacturing compensators, expansion joints, baffle doors

How much does the metal expansion joint DN250 expand and contract exactly? Stop being fooled by parameter tables

Expansion and contraction amount of metal expansion joint DN250, no fixed value。 You are holding a model and wondering how long it will stretch? That's the same as asking "how fast can this car go"-depends on whether it's a 1.5L self-priming or a 4.0T twin-turbo. The DN250 is only a nominal diameter, and the amount of expansion and contraction depends on wave number, wave height, wall thickness, material, pressure class, and temperature. Take the usual ones on our stationUniversal corrugated expansion jointFor example, the axial compensation amount is usually between a few tens of millimeters and two hundred millimeters, but when changed toHigh temperature axial expansion jointOrExternal pressure single axial expansion jointAnd the data is completely different.

"Why can your DN250 only compensate 80mm, but that one can reach 150mm?" I said you should first see whether the working pressure of his target is 0.1MPa or 1.6MPa, and whether the temperature is normal temperature or 500℃. The same pipe, the working condition is three times different, can the expansion and contraction amount be the same? This is not a fraud of the parameter table, but the selection logic is not right at all.

To understand the scaling amount, first understand these key parameters

The first one iswavenumber-The number of twists and turns on the bellows. The more waves, the greater the expansion and contraction, but the pressure bearing capacity will decrease. The second isWave height and wall thicknessThe higher the wave and thinner the wall, the better the flexibility, but the fatigue life will be shortened. And the third isMaterials-Stainless steel 304, 316L or high temperature resistant alloy? When the temperature exceeds 400℃, the allowable stress of ordinary 304 should be folded in half, and the temperature correction coefficient must be included in the calculation of expansion and contraction.

The same DN250 is used on 0.25MPa flue gas pipeline and 1.0MPa steam pipeline, and the design safety factor is completely different. Think about it, if the low-pressure expansion joint is forced into the high-pressure pipeline, and the bellows will crack as soon as it deforms, it will be useless no matter how much expansion and contraction is. We have a customer in the cement industryMetal Corrugated Expansion Joints in Cement Industry, the medium temperature is 600℃, ask if DN250 can achieve 120mm compensation amount-of course, but you have to use double-layer bellows and guide tube, and you have to pressPressure balance typeDesign. Simply heap wave number? If it can't bear the high temperature and internal pressure, it will be scrapped in three months.

How to calculate the expansion and contraction amount of DN250 expansion joints with different structural types?

This is the easiest place to overlook.Single axial type(For example, the general corrugated expansion joint) can only absorb axial displacement, and the expansion and contraction amount mainly depends on the wave number stacking. But if you need to absorb lateral displacement or angular displacement at the same time, you have to useCompound hinge transverse typeOrDouble straight pipe bypass pressure balance type。 For example, for the same DN250, the axial compensation amount of the single axial type may be 150mm, but if it is replaced with the double hinge type, its axial compensation may only be 30mm, but it can absorb the angular displacement of ±5°-these are completely two kinds of compensation logics.

AndStraight pipe pressure balanced expansion jointIt relies on two sets of bellows to offset the internal pressure thrust, and no matter how large the expansion and contraction is designed, the pipe will not fly. When you choose a model, you have to ask clearly what direction of displacement the pipeline should compensate, otherwise you can't install it when you buy it back, and the rework cost is much more expensive than the expansion joint itself.

Actual selection: How to determine the expansion and contraction according to the thermal displacement of the pipeline?

Don't check Baidu, calculate the thermal elongation first. The formula is simple: Δ L = α × L × Δ T. Carbon steel pipeline α ≈0.012mm/m·℃. Assuming that DN250 pipeline is 30m long and the temperature difference is 200℃, the thermal elongation is 0.012×30×200=72mm. Then the axial compensation amount of the expansion joint you choose should be at least greater than 72mm, leaving 20% safety margin, that is, about 90mm.

But it is not enough to look at the axial direction-if the line has elbows that cause lateral displacement, then considerCompound hinge transverse expansion jointOrUniversal hinge type。 We have products on our site that deal with this combined displacement. In addition, don't forget the internal pressure thrust: DN250 has a blind plate force of about 49kN at 1.0MPa. If you don't use the pressure balance type, the fixed bracket has to hold this force, otherwise the pipe will fly out. Last year, there was a case in a power plant. They chose the ordinary axial type to install it in the position of a large-diameter thick-walled expansion joint, but the bracket collapsed during pressure test-a painful lesson.

Don't make mistakes about the pits that are easy to step on during installation, the guide tube and the tie rod

Let's startguide tubeIt is on the inner wall of the bellows, and its function is to guide the high-speed fluid away to avoid the bellows from being washed and worn. weFAQThe role of the guide tube is talked about in detail. Don't underestimate the thin plate-without it, the expansion joint of DN250 is used in the dusty flue gas pipe, and it will be worn out in half a year. Againtie rod nut adjustmentMany construction teams do not disassemble the transportation fixings after installation, or screw the tie rod nut to death, resulting in the expansion joint losing its compensation function. On expansion jointArrow DirectionIt is the flow direction of the medium, and the guide tube will not play a role if it is installed backwards. We still have clients who putDouble-sealed single-axis circular baffle doorIt's used as an expansion joint. Laughing to death. That thing is used for truncation, not compensation. Therefore, be sure to check the product nameplate before installation to confirm whether it is a general-purpose type or a high-temperature axial type, and do not mix it.

In addition,Do you need to remove the screw of the expansion joint？ The transportation fixing parts must be disassembled, but the adjusting nut on the pull rod should not be disordered-how to adjust it specifically,FAQThere are also instructions in. In short, installation is not by brute force, but by looking at nameplates and drawings.

Summary: Don't just look at parameters in type selection, working conditions are the fundamental

The diameter of DN250 can be expanded from 30mm to 300mm. The key is that you should give the working pressure, temperature, medium, pipe direction and fixed bracket position. Instead of guessing blindly on the parameter table, it is better to directly find the manufacturer to produce a calculation book. All expansion joint products on our station-includingUniversal corrugated expansion joint、High temperature axial expansion joint、Straight pipe pressure balanced expansion joint、Large diameter thick wall expansion joint、Compound hinge transverse expansion jointAnd so on-all support customization according to GB/T 12777 standard. You provide the working conditions, and we will calculate them for you. The data speaks for itself, and it is not false.

How much expansion and contraction of the metal expansion joint DN250 does not depend on the model, but what exactly your pipe wants it to carry. Wrong choice, no matter how beautiful the parameters are, they are still scrap iron.

What are single and triple waves? Find out the structure before choosing

The core of the metal expansion joint is that bellows, and the wave number is the number of corrugations. Single-wave expansion joints have only one ripple, and three waves are three ripples-it sounds like crap, but many people run to ask for the price without even figuring it out.

Structurally, the single-wave expansion joint is more like a "spring sheet", and the wall thickness, wave height and wave distance are all fixed. The three-wave expansion joint is formed by three single waves welded in series or integrally, and there is a transition section between each wave. To put it bluntly, a single wave is "one section" and a three wave is "three sections strung together".

But don't think that three waves are as simple as three single waves stacked. The wave number has changed, and the stiffness, compensation amount and pressure resistance of the whole expansion joint are all another set of logic. And common products on the market, such as ourUniversal corrugated expansion jointSingle-wave and three-wave are also different in end structure and guide tube design.

Performance Differences: How Different Are Compensation Amount, Stiffness and Pressure Resistance

The axial displacement absorbed by single wave energy is usually only a few millimeters to more than ten millimeters, and the three wave energy is up to tens of millimeters. But what about the cost? The stiffness drops with the wave number-single wave stiffness is high, three wave stiffness is low. Some people think that low stiffness is so soft and wrong.

Low stiffness means that under the same pressure, the bellows is easier to deform, and it is easy to fatigue if the deformation is large. What about pressure resistance? Because the wall thickness of single wave is relatively thicker (under the same caliber), the withstand voltage is usually higher than that of three wave. For example, with the same design of DN200 and 0.6MPa, the blasting pressure of a single wave can reach more than 3MPa, while the blasting pressure of three waves may only be 2.5MPa. It's not an absolute value, but the trend is there.

When the three-wave expansion joint is subjected to lateral displacement, each wave will "share" the deformation, but at the same time, it is also prone to inter-wave interference. We doExternal pressure single axial expansion jointIt has been encountered that if the wave distance design of the three waves is unreasonable, the outer wave will be deflated. That's a real thing.

Application scenario disassembly: Which working condition must use single wave? Which scenario is more stable with three waves?

Is the medium in your pipes under high pressure? Does the temperature fluctuate a lot? If the answer is "high pressure, small displacement", then a single wave is the lifeblood. For example, the compact space on the steam pipeline has a displacement of 5mm and a pressure of 1.6MPa. If you use three waves, it will be easy to tremble. We've done it for the power station industryCorrugated expansion joint for power station industry, the main steam pipeline is all single wave plus external pressure structure, why? Because the safety margin is sufficient.

On the other hand, if it is low pressure and large displacement-such as flue gas pipes and air-cooled islands, three waves are the right way. For example,Double hinge expansion joint for air-cooled island vacuum pipeline, the tube is tens of meters long, the thermal expansion and contraction are tens of millimeters, and the single wave can't hold it at all. The three waves cooperate with the hinge structure, which is stable. There are also hot air ducts in the cement industry, which have high temperature but low pressure, and three-wave belt guide tubes, which can double their life.

The pressure is not high but frequent vibration compensation is required. For example, the pump outlet can absorb multi-directional displacement with three waves, but be careful not to choose the wrong model — —Compound hinge transverse expansion jointThis is what it does specifically, and it has nothing to do with wave number.

The most common mistake made in model selection: blindly pursuing wave number or looking only at price

Two days ago, I met a customer and said, "I want three waves because the compensation is large"-as a result, his pipeline pressure was 2.5MPa and the temperature was 400℃, and the three waves cracked after three months. Later, the columnar instability caused by internal pressure was checked. You say it was wrong or not?

Just look at the price. Single wave is cheap and three wave is expensive, so choose single wave. As a result, the displacement was not enough, and the tube deformed the expansion joint by hard pulling, and the guide tube flew. Tsk, we see too many of these things.

Selecting the wave number is not a pat on the head. You have to calculate the compensation requirement first, then inverse the stiffness, and then check the pressure and fatigue life. We have an internal formula: single wave for small displacement and high pressure, three waves for large displacement and low pressure, and double waves or multi-layer waves for the middle zone. Oh, yeah,Large diameter thick wall expansion jointSometimes single wave is also used, because the wall thickness can be very thick and the pressure resistance is easy.

Professional advice: Introduce the wavenumber from the pipeline parameters, and place an order after calculating it clearly

How on earth is that calculated? The first step is to get the pipeline design parameters: medium, pressure, temperature, pipe diameter, pipe length and fixed bracket position. The second step is to calculate the amount of thermal displacement. Step 3, determine if you need axial, lateral, or angular compensation.

A section of DN300 steam pipeline with a length of 20 meters, a temperature difference of 200℃ and an axial displacement of about 30mm. Pressure 0.8 MPa. If a general-purpose corrugated expansion joint is used, the rated compensation amount of single wave is up to 10mm, and three single waves need to be connected in series, but the stiffness increases after series connection, and multiple sets of tie rods are required. It's better to go straight to three waves and get it done in one. However, it should be noted that the three waves at 0.8MPa should be checked whether plane instability will occur. Usually, we will add a guide sleeve or selectStraight pipe pressure balanced expansion joint。

Don't believe that "three waves are definitely better than single waves" or "single waves are safer". Each wavenumber has its reason for existence. We doHigh temperature axial expansion jointWhen, the wave number will be adjusted for different temperature segments: three waves below 600℃, and a single wave is used to thicken the wall above 600℃, because the material creeps at high temperature, and multiple waves are easy to be uneven.

If you are still unsure, send the pipeline parameters to our technical department, and they will calculate it with finite element, which is ten times better than slapping your own head. After all, which is better, single-wave or three-wave metal expansion joints, is never a multiple-choice question, but an arithmetic question.

Just say the answer: What exactly is the common temperature tolerance range?

The temperature resistance limit of high-temperature non-metallic expansion joints is not a fixed value, but depends on which fiber material you choose. The mainstream high-temperature non-metallic expansion joints on the market (that is, we often call fabric fiber expansion joints) mainly use three kinds of fabrics:

• Silicone cloth: The continuous working temperature is generally around 250℃, and it can reach 300℃ instantly. Suitable for ventilation ducts with low flue gas temperature, such as boiler tail flue.
• Fluorine tape: The temperature resistance can reach 300℃-350℃, and the corrosion resistance is stronger than that of silica gel cloth. Fluorine tape is the first choice when it comes to flue gas containing sulfur and acid.
• Ceramic fiber cloth: This is the real high temperature resistant player. The limit temperature can be above 1000℃, but in actual engineering, we generally design according to 800℃-1000℃. The ceramic fiber itself is fine with temperature resistance, but the outer sealing layer (such as the silicone rubber coating) will limit the overall temperature resistance.

Many manufacturers name "temperature resistance 1200℃", but you have to ask whether it is a short-term peak or a continuous working condition. We have done a case in the power station industry-the flue temperature of a power plant is designed to be 850℃, and we chose ourNon-metallic expansion joint (fabric fiber expansion joint)The inner layer is made of ceramic fiber felt + multi-layer insulation layer, and the outer layer is made of high-temperature resistant coating. At present, it has been in stable operation for 3 years. The temperature parameter does not depend on how much it can carry at the highest, but whether it can carry "continuous drying".

Three "Invisible Killers" Affecting Temperature Resistance

Just because the temperature number looks good doesn't mean it can be used. I have encountered it several times, and the customer took the parameter of 800℃ to select the model, but the result was leaked in less than half a year. Why? Because temperature is only a basic indicator, these three things are really fatal:

Medium corrosivity

High-temperature flues often carry sulfur dioxide, hydrogen chloride, and even alkali vapor. Ceramic fiber can withstand 1000℃, but encounter strong acid corrosion, the fiber structure will be destroyed. At this time, you have to choose fluorine tape or add corrosion-resistant coating. weDesulfurization flue gas baffle doorThe matching non-metal expansion joint, the lining is made of polytetrafluoroethylene film to prevent corrosion.

Pressure fluctuation

The fabric layers of non-metallic expansion joints have no strength themselves and rely on metal frames and platens. Once the pressure exceeds the design value (generally, the design pressure of non-metallic expansion joint does not exceed 0.1MPa), the fabric will bulge or even tear. The higher the temperature, the faster the tensile strength of the material decreases. For example, the strength of the same silicone cloth is about 60% of that of normal temperature at 200℃, but it may only remain 30% at 300℃. So don't just look at temperature, pressure and temperature should be calculated together.

Number of cyclic displacements

The high-temperature non-metallic expansion joint compensates for thermal expansion and contraction, and every time the unit starts and stops, it is a large displacement. Fibrous materials are subject to fatigue aging under repeated bending. We have a customer in the cement industry. The kiln tail pipeline uses ordinary non-metallic expansion joints, which are replaced twice a year. Later, we put on oursMetal Corrugated Expansion Joints in Cement Industry(Strengthened design is made for high temperature and multi-displacement working conditions), and the service life is directly doubled.

Non-Metallic Expansion Joints vs Metallic Expansion Joints: Who is More Reliable?

When many engineers hear about high temperature, their first reaction is to "put on the metal expansion joint". However, the metal expansion joint also has shortcomings at high temperature: the bellows will cause fatigue cracks due to thermal stress, and the installation accuracy is extremely high. OurHigh temperature axial expansion jointIt performs well below 600℃, but when it exceeds 700℃, nickel-based alloys have to be used, and the cost will rise.

Low cost, light weight, large amount of compensation and good corrosion resistance。 Especially in the scenario of large-diameter flue (more than 2 meters in diameter), using metal expansion joints is not only expensive, but also a problem in manufacturing and transportation. Non-metallic expansion joints can be assembled on site, and the maintenance is simple-if they are broken, only the fabric loop belt is changed, and the pipe is not removed.

Then when to choose non-metallic? Remember two principles: one is that the temperature is high but the pressure is low (Corrugated expansion joint for power station industryIt is used a lot at the outlet of the boiler (temperature 500-600℃), but at the inlet of the desulfurization tower (temperature 120-180℃, containing corrosive flue gas), the non-metallic expansion joint is the optimal solution.

The easiest pits to step on when selecting a model

Pit 1: "All non-metals are resistant to 800℃"

This is the biggest misconception. You take a silicone cloth to carry 800℃, and it will burn to ash in less than an hour. Only ceramic fiber substrate is resistant to 800℃, and multi-layer insulation layer must be designed: inner ceramic fiber blanket, middle fire barrier layer and outer sealing cloth. Without any layer, the temperature parameter is waste paper.

Pit 2: Ignore the insulation design

The insulation of non-metallic expansion joints is not just stuffed with asbestos. We doRectangular non-metallic expansion jointWhen, the insulation layer thickness is calculated according to the flue section and the temperature gradient. For example, the flue temperature is 600℃, and the external surface temperature is required to not exceed 60℃. The thermal insulation layer must be at least 150mm thick, and multi-layers of staggered seams should be laid to prevent thermal bridges.

Pit 3: Ignoring the air or water cooling requirements of the installation location

Some high-temperature pipes are close to the steel structure, and radiant heat can bake the peripheral equipment. At this time, it is necessary to install an air-cooled jacket or a water-cooled jacket. We encountered a machine in the cement industryMetal Corrugated Expansion Joints in Cement IndustryAlthough the metal part itself is fine, the adjacent non-metallic compensator causes the fabric to age prematurely because there is no ventilation gap. Later, an air guide hood was added, and the problem was solved.

High Temperature Application in Power Station, Cement and Desulfurization

• Power station industry: The temperature of the boiler flue is usually 400-600℃, ourCorrugated expansion joint for power station industryUse with non-metallic compensators. The non-metallic part is used between the outlet of the induced draft fan and the desulfurization tower, and the temperature drops to 120-180℃, but contains SO2 and dust. It is used with fluorine tape + wear-resistant lining plate, and the life span is 3-5 years.
• Cement industry: The temperature of the kiln tail exhaust gas is as high as 900-1000℃, but the pressure is extremely low (slightly negative pressure), and there is a lot of alkaline dust. At this time, non-metallic expansion joints are the only option. We made it for a cement factoryMetal Corrugated Expansion Joints in Cement IndustryIn fact, it is used for the circulation pipeline of raw mill (temperature 150℃), and the kiln tail is the world of non-metals. Note: High-temperature non-metallic expansion joints in cement industry must have wear-resistant guide tubes, otherwise dust directly washes the fabric layer, and it will be perforated in half a year.
• Desulfurization industry: This scenario is the most complex-the temperature is not high (80-150℃), but the medium is a strongly corrosive slurry or wet flue gas. Metal expansion joints can't withstand pitting corrosion with 316L, while non-metallic expansion joints have a longer life because they are lined with PTFE or rubber. OurDesulfurization flue gas baffle doorThe matching non-metallic expansion joint is designed with a liquid drainage port at the bottom, which solves the problem of liquid accumulation corrosion.

Summary: The selection checklist behind the high temperature numbers

At this point, you should understand:How many degrees is the high temperature of the high-temperature non-metallic expansion jointNot a simple number, but a set of working condition matching logic. Keep these three in mind:

1. Look at the media: Smoke or hot air? Does it contain corrosive ingredients? Decide to choose silicone cloth, fluorine tape or ceramic fiber.
2. Look at displacement: Use non-metal when the displacement is large and the frequency is low; Use metal when displacement is small and pressure is high. Don't mix it.
3. See attachment: The thickness of the insulation layer, the cooling method, the anti-corrosion lining these details determine success or failure.

Selection is not about whose parameters are bright, but about who runs longer. Next time I see the advertisement of "Temperature Resistance 1000℃", let me ask first: What is the continuous temperature? How much pressure? What are the ingredients of media? — — After asking these three questions, the manufacturer will know that you are an expert.

How to choose metal expansion joint for chemical plant? Understand these 4 hard indicators first

How harsh are chemical plant pipelines? Temperature, medium, pressure, any of them can kill you. Two days ago, I met a customer, who bought a general-purpose expansion joint for cheap and installed it on the sulfuric acid pipeline. As a result, it was perforated and leaked in three months-it was a mess. Find out the bottom line of the working condition before selecting the model, and don't use the general-purpose model as a panacea. The 'universal corrugated expansion joint' in our station is suitable for conventional steam pipelines, but when it encounters strong corrosive media, it depends on 'PTFE-lined hose' or 'PTFE compensator'. This thing is acid and alkali resistant, but the upper temperature limit is stuck, and it hangs when it exceeds 200℃.

1. Material and structure: 316L is just the beginning, and high chloride ion gets 2205

After doing this for a long time, I found that many engineers heard about metal expansion joints, and their mouths were stainless steel 304. But how is it that simple in a chemical plant? In the environment where the chloride ion content exceeds 200ppm, 304 will be stress corroded and cracked in less than half a year. Stainless steel 316L is the starting price, and further up, the high chloride ion environment gets 2205 duplex steel. Not only the material, but also the number of bellows layers, wall thickness and wave number directly determine the fatigue life-how to choose between single layer and multi-layer? Single layer has good flexibility and low cost, but poor pressure resistance. The multi-layer wall is thin, the wave number energy is more under the same outer diameter, and the absorption displacement is more flexible. High pressure occasions? Then use 'external pressure single axial expansion joint', the outside of the bellows is compressed, and the stability is good. What about high temperature and large displacement? The 'high-temperature axial expansion joint' specializes in this, and the structure is insulated, so that the heat will not be directly transmitted to the bellows. Don't get confused. If you choose the wrong parameter, the whole pipeline may be wasted.

By the way, the stiffness thing has to be counted. We have a question and answer "Stiffness and Calculation Formula of Bellows" on our station, which is very thorough. Chemical plant pipeline vibration is large, too high stiffness will transmit stress, too low and easy instability. Check it according to the formula when designing to save trouble.

2. Displacement mode: axial, transverse, angular displacement, or combined displacement?

The way of absorbing displacement is particular. Not all expansion joints can do everything at once. If a pipe has only axial displacement of thermal expansion and cold contraction, then a single axial type is sufficient. However, the pipe system of chemical plants is complicated, with a pile of corners, corners and branches, which often need to absorb lateral displacement and angular displacement. At this time, the 'double hinge transverse expansion joint' comes in handy. Two hinge groups can withstand transverse displacement without blind plate force. If the pipe system has limited space and has to absorb a large amount of combined displacement, then the 'double straight pipe bypass pressure balanced expansion joint' can handle it. Another headache-large-diameter, high-pressure pipes, blind plate force can push the pipe support down. What to do? The 'straight pipe pressure balanced expansion joint' counteracts the blind plate force by built-in pressure balancing element, so the equipment does not have to bear additional thrust. Is that the truth?

III. Installation and fixation: How to match the tie rod, guide bracket and fixed bracket?

Choosing the right model is only the first step. If there is a problem with installation and fixation, it will still be useless. We have a question and answer "How to adjust the tie rod nut of the expansion joint", which makes it very clear: the function of the tie rod is to limit the over-stretching of the expansion joint and bear the internal pressure thrust at the same time. During installation, the nut cannot be screwed to death, and the margin for cold or hot tightening must be allowed. The distance between the guide bracket and the fixed bracket must also be calculated according to the design, otherwise the pipeline will be unstable and the expansion joint will sway. In addition, the role of the guide tube is to prevent scour, especially when the medium contains particles or the flow rate is fast. We have an article "The Specific Function of the Expansion Joint Guide Tube", which is very thorough. Simply put, it is to protect the inner wall of the bellows from being worn. Chemical plant pipeline vibration is large, don't forget to calculate the stiffness, refer to 'Bellows stiffness and calculation formula'.

4. Decision list: first look at temperature, pressure and medium, and then calculate the displacement

First confirm the design temperature, design pressure and medium type (corrosiveness, chloride ion content, whether it is flammable or explosive), then calculate the displacement (axial, transverse and angular displacement magnitude and direction) that the pipeline needs to absorb, and then choose the model. For example, the 'general corrugated expansion joint' is used for steam pipelines, the 'high-temperature axial expansion joint' is used for high-temperature flue gas, the cement industry has a specially customized 'metal corrugated expansion joint for cement industry', and the power station industry corresponds to the 'corrugated expansion joint for power station industry'. This kind of industry-specific model is more tasty than the general model-the manufacturer has already figured out the working conditions. If you are really unsure, ask the manufacturer for a case first, and don't guess yourself. There are also 'metal hoses', 'rubber compensators' and 'non-metal expansion joints' in the product library of our station, each of which has its own applicable scenarios, but the core part of the chemical plant is mainly metal expansion joints.

Alas, a last long-winded sentence: don't bother. How to choose metal expansion joint for chemical plant? To put it bluntly, four words: take the right seat. Each parameter corresponds to a product model, and there is no panacea. Looking at a few more cases and asking a few more why is much more hassle-free than patting your head.

First, the name with "metal" does not mean that it is all stainless steel-first understand the basic concepts

Many people think that metal expansion joints are made of stainless steel, and even some purchasing calls ask, "Quote me the price of stainless steel expansion joints." Let's not laugh at people, after all, with the word "metal" in the name, the first reaction is shiny stainless steel, right? But the fact is that "metal expansion joints" are a big category. For example, there are general-purpose corrugated expansion joints, external pressure single axial expansion joints, and directly buried (fully buried) expansion joints on our website... These all belong to metal expansion joints, but their materials are various.

The core of the metal expansion joint is that telescopic bellows. Corrugated pipes can be made of stainless steel, carbon steel, alloy steel or even nickel-based alloys, depending entirely on the working conditions. For a practical example: if you use it in a flue gas desulfurization system, the medium contains sulfur, so you have to use corrosion-resistant stainless steel or higher-grade materials; If it is used in ordinary steam pipelines, the temperature is less than 200℃, and the carbon steel bellows can be completely carried with proper anti-corrosion treatment. Therefore, don't default to stainless steel as soon as you hear "metal". If this misunderstanding is not clear, it will be easy to overturn after the selection.

Second, stainless steel is only one of the "top students" in the metal expansion joint family

The reason why stainless steel is most used in metal expansion joints is simple-the medium transported by most industrial pipelines is corrosive, or the environmental humidity is high and the temperature changes drastically, so stainless steel can carry it. But look at the corrugated expansion joints used in power station industry and metal corrugated expansion joints in cement industry on our website. The working conditions are high temperature, dusty and worn. At this time, 304 and 316 stainless steel alone may not be enough-heat-resistant steel or duplex stainless steel must be used.

PTFE-lined hose. This product is a metal bellows inside, and the outside or inner wall is lined with polytetrafluoroethylene (PTFE). The real contact medium is PTFE, and the metal is only responsible for bearing pressure. At this time, carbon steel can be used for the metal part. Why? Because the corrosion problem has been solved by PTFE, it is a waste to use stainless steel. Therefore, the equation of "metal expansion joint = stainless steel" is simply untenable in engineering. If the material is chosen wrong, it will leak at least and the whole pipeline system will have an accident at worst.

Third, non-metallic expansion joints and metal expansion joints are fundamentally different things-don't confuse them

Sometimes customers take non-metallic expansion joints (that is, fabric fiber expansion joints) and ask, "Can your stainless steel replace that cloth?" This is the classic conceptual confusion. The metal expansion joint absorbs the displacement by the elastic deformation of the bellows, which can withstand high pressure and high temperature, but it has great rigidity and is not suitable for large displacement. Non-metallic expansion joints (we also have rectangular non-metallic expansion joints and non-metallic expansion joints (fabric fiber expansion joints) on our station) rely on flexible fabrics and rubber to absorb displacement, and have weak pressure resistance, but large compensation and good vibration reduction. They are often used in scenes with low pressure and large displacement such as flue gas pipes and air ducts.

Therefore, the relationship between the two of them is not one that replaces the other, but one that manages each other. In other words, metal expansion joints are not all "stainless steel", while non-metal expansion joints are not "metal" at all. When selecting the type, first find out the pipeline medium, pressure, temperature and displacement direction, and then look at the material. Don't ask "is it stainless steel".

4. Look at the material selection from the products of this station: the same expansion joint, different "steel and iron bones"

Open the product page of our website, you will find the same called "corrugated expansion joint", but the materials are varied. For example, the high-temperature axial expansion joint is used on the boiler outlet or hot air duct, and the medium temperature may be above 800℃. At this time, the heat resistance limit of 304 stainless steel is only about 700℃, which can't hold it at all. Another example is the vacuum special hose, which is used on air-cooled island vacuum pipelines. The pressure is low but the sealing performance is extremely high. The material is often 316L stainless steel to ensure corrosion resistance and welding quality.

There is also a sleeve-type pipe expansion joint, which relies on the sliding compensation of the inner and outer sleeves, and the sealing packing and steel are matched. The material can be stainless steel or carbon steel, mainly depending on the cost and use environment. There is also a compound three-way expansion joint in the cement industry. The working condition is high temperature and dust, so the material has to be wear-resistant and heat-resistant alloy. Simply put: Don't think of "stainless steel" as a universal option. Choosing materials is like matching keys, and one key opens a lock.

5. Figuring out this problem can help you save 30% of the purchase cost

"Is the metal expansion joint stainless steel?" This question is not just a conceptual question, but a real cost question. You choose the right material, the equipment has a long life and less maintenance; If you choose the wrong choice, you will either waste your money or fail every three days. When engaging in engineering, don't be led by the name. Look at the working conditions and check the parameters. If you are not sure, just look through the product descriptions on our website-the materials, applicable temperatures and pressure ranges of each model are clearly written.