Specialized in manufacturing compensators, expansion joints, baffle doors

Disassembly from the name: thick wall, metal, expansion joint, what exactly do these three words refer to?

The expansion joint, also called the compensator, is, to put it bluntly, the "cushion" in the pipeline system-it absorbs the displacement caused by thermal expansion and contraction, and by the way, digests the mechanical vibration. Think about it, a steam pipe hundreds of meters long, whose temperature rises to hundreds of degrees Celsius, if you keep it from moving, the stress on the wall of the pipe can be so great that the flange can be cracked. At this time, you have to rely on the expansion joint to "give way".

The word "metal" is easy to understand. The most common corrugated pipe materials are stainless steel 304 and 316L. If you encounter high temperature and strong corrosion conditions, you can get high-temperature alloys such as Incoloy 825 or Hastelloy. If the material is not selected correctly, no matter how thick the wall is, it will be for nothing.

Here comes the key – what exactly does "thick wall" mean? Many people think that the shell of the whole expansion joint is thick, but it is not. Specifically, the wall thickness of the bellows is thicker than that of the conventional model. The wall thickness of conventional bellows is generally 0.5~1.5mm, while the thick-walled type can be 2~4mm or even thicker. For example, this site'sLarge diameter thick wall expansion joint, is the fist product specially dealing with high-pressure and large displacement scenes.

What is the essential difference between thick-walled metal expansion joints and ordinary corrugated expansion joints?

Ordinary corrugated expansion joints rely on thin-walled corrugated deformation to absorb displacement, which is well used in low-pressure and small-diameter pipelines, and the price is cheap. However, once it encounters the working conditions of high pressure, high temperature and high cycle times, the thin-walled parts are "crispy skin"-the fatigue life is short, and it will crack for you in a few months.

High withstand voltageAndLong fatigue resistance life。 Take the main steam pipeline of the power plant as an example. The pressure is above 10MPa and the temperature exceeds 500℃. Ordinary thin-walled bellows can't hold it, but thick-walled bellows can hold it for several years.

But thick walls also come at a cost — stiffness. With the same displacement, the thick-walled bellows generates more thrust, so it needs to be matched with a tie rod or hinge structure to share the thrust. This site'sCompound hinge transverse expansion jointIt is typical of this combination, with hinges to absorb lateral displacement while withstanding internal pressure thrust.

Where exactly is it used? Industry cases to help you understand

Selection is not a pat on the head, it depends on the actual working conditions. What scenarios are thick-walled metal expansion joints used in? I'll list you a few typical ones.

• Power industry:Power station boiler outlet, turbine bypass pipeline, high temperature and high pressure are common. Recommend this siteCorrugated expansion joint for power station industryAndHigh temperature axial expansion joint, specially optimized for this working condition.
• Cement industry:The exhaust gas pipeline at the end of the kiln is high in temperature and contains much dust, and the bellows is directly exposed to the dust-containing air flow, which causes serious wear. The thick-wall matching guide tube is standard, and the station'sMetal Corrugated Expansion Joints in Cement IndustryWith this design, the guide tube guides away the high-temperature dust-containing air flow to protect the bellows body.
• Desulfurization system:Upstream and downstream of the flue gas baffle door, the medium is extremely corrosive (containing sulfuric acid and sulfurous acid). Thick-walled bellows can be used with PTFE-lined or metal hoses to withstand corrosion. This site'sDesulfurization flue gas baffle doorAnd PTFE-lined hoses are common combinations.
• Vacuum pipe:For example, in the air-cooled island system, there is negative pressure in the pipeline, and the thin-walled bellows is easily deformed by suction. The thick-walled corrugated pipe has strong external pressure resistance.Double hinge expansion joint for air-cooled island vacuum pipelineIs designed for this kind of scenario.

The 3 Most Common Mistakes to Make in Model Selection

I have been in this business for more than ten years, and I have seen too many people step on pits. Say three of the most common ones.

Mistake 1: Only look at the nominal pressure and ignore the reduction of the allowable stress of the material by temperature.Many people choose models with PN, completely regardless of the temperature. In fact, a piece of 304 stainless steel can be directly discounted by 40% with stress at 400℃. The thick-walled parts you select according to normal temperature may exceed the limit when it reaches high temperature conditions. This can't be sloppy.

Mistake 2: Thinking that thick walls can absorb greater displacement.Quite the opposite! When the wall thickness increases, the single-wave compensation amount decreases. You want to absorb the same displacement by either increasing the wavenumber or switching to a duplex structure. Otherwise, it would be embarrassing to install it and find that the displacement is not enough.

Error 3: Ignore the deflector.Thick-walled expansion joints are commonly used in high-speed fluid pipelines. There is no guide tube, and the bellows are directly subjected to fluid scour-especially for particle-containing media, and the life is cliff-like. About the function of the guide tube, this site has a special articleSpecific Function of Expansion Joint Guide TubeMake it very clear. Make sure to provide media flow rate and particle content data when selecting, otherwise you will dig a hole for yourself.

Installation and maintenance: How are they different from ordinary expansion joints?

Thick-walled parts are of great weight, so special lifting lugs must be used for hoisting during installation, and bellows must be hooked directly? Don't even think about it, once the bellows is deformed, it will be crippled.

The amount of pre-tension/pre-compression needs to be accurately calculated. The cold tightness of ordinary expansion joints is about the same, but the thick-walled parts have great rigidity, so the cold tightness is wrong, and the thrust can pull the bracket crooked after installation. It is recommended to directly find the engineering and technical staff of this site to help you calculate.

For maintenance, check the bellows surface regularly for cracks or corrosion pits. Weld repair is difficult once leakage occurs in thick-walled parts – heat-affected zones can change material properties, and direct replacement is usually recommended. If the design is reasonable, the life of thick-walled metal expansion joint can reach 10~15 years under medium working conditions, which is more than twice that of thin-walled metal expansion joint. Whether it is cost-effective or not, settle your own accounts.

To summarize: Should you spend this money?

If the pipe pressure exceeds 2.5MPa, or the temperature exceeds 400°C, or the medium is corrosive and the flow rate is high — any of these three conditions holds, thick walls are a must. Don't be cheap and buy the universal corrugated expansion joint to make do. It's okay if there is no accident, but if there is an accident, the pipeline will crack and production will be stopped for overhaul. The loss will be enough for you to buy dozens of thick-walled expansion joints.

In this matter of type selection, the first is to understand the principle, and the second is to know the working conditions. Figure out "What does a thick-walled metal expansion joint mean?", and you'll be able to avoid 80% of the pits.

If you choose the wrong material, the expansion joint is a time bomb

Two days ago, a power station customer came back for repair. The reason is very simple: 304 material was used to remove the flue gas containing chloride ions. As a result, the bellows was stress corroded and cracked in less than three months. And guess what? When you take it apart, the crack extends from the trough to the crest of the bellows, and the whole pipe looks like shredded paper. This is not an isolated case-I've seen too many projects end up reworking several times the cost for "saving that little money on materials".

Many people come up and ask "What material is the metal bellows expansion joint made of?"-it seems that just pick one random. However, the reality is that material selection directly determines how high temperature, how strong corrosion and how frequent displacement the expansion energy saving can withstand. Don't just look at the price, first find out exactly what your working condition requires.

Five kinds of mainstream materials, each temper you have to find out

304 stainless steelWith the lowest cost and the best toughness, it can cover 80% of conventional working conditions. For water, steam and air media, the upper temperature limit is 450℃-304 is sufficient for steam pipelines, but don't exceed this temperature, otherwise the risk of intergranular corrosion will soar.

316LWith the addition of molybdenum element, the resistance to chloride ion corrosion is obviously improved. In humid and acidic environments such as desulfurization and chemical industry, 316L is the bottom line. Remember, it's the "bottom line"-if you encounter high chlorine concentrations in wet smoke, 316L just barely copes.

321 stainless steel, containing titanium stabilizing element, specially to deal with intergranular corrosion. When no heat treatment is done after welding or the working temperature fluctuates intermittently between 400-800℃, 321 is more stable than 304 and 316L. In some areas of hot air ducts and power station boilers in the cement industry, 321 is a good choice for money.

Inconel 625 nickel-based alloyIt can withstand high temperatures above 700 ℃ and strong corrosion, and the price is 5-8 times that of 304. High-temperature flue of cement industry, tail flue of power station boiler-the temperature in these places is always 600-800℃, and there are sulfur and chlorine sandwiched in the flue gas. Don't use Inconel 625? The bellows will soon fail due to high temperature oxidation or creep, and it will be too late to regret it.

Duplex stainless steel 2205With outstanding resistance to stress corrosion cracking, seawater or chemical medium containing chloride is the first choice. The fatigue life of air-cooled island vacuum pipe, seawater heat exchanger pipe, 2205 is several times that of ordinary stainless steel.

Medium and Temperature: Two Iron Laws of Material Selection

To put it bluntly, material selection is to compare the media composition with the temperature range. Steam pipes, especially superheated steam, 304 or 316L can handle most working conditions, but don't think about it when the temperature exceeds 450℃-honestly cut to 321 or Inconel 625.

When encountering sulfur and chlorine-containing flue gas, such as wet flue gas after desulfurization, 316L is the starting point. More severe environments require duplex steel or nickel-based alloys. Someone asked: Why can't you use 304? Because chloride ions can cause stress corrosion cracking of 304 above 60℃, can you afford this probability?

The temperature of hot air ducts in cement industry is often between 600-800℃. At this time, when you look through the parameter tables of 304, 316L and 321, you will see "long-term use is not recommended". Go straight to Inconel 625, don't hesitate. Otherwise, the corrugated pipe will fail by high-temperature oxidation and creep, and one will be scrapped in three months. The labor cost of replacing the pipe will be more expensive than the material price difference.

Special scenarios: vacuum, high-frequency fatigue, thick-walled parts

In addition to regular working conditions, there are several types of scenarios that need to be weighed separately.

Vacuum environment— — For example, the double hinge expansion joint of air-cooled island vacuum pipeline, the wall thickness and layer number of corrugated pipe should be designed strongly, and 316L or Inconel 625 are commonly used in materials to ensure pressure stability. Once the bellows is unstable in vacuum, the vacuum degree of the whole system collapses instantly, and the consequences are more serious than leakage.

High frequency fatigue cycle— — The peak shaving unit of the power station starts and stops frequently, and the bellows may have to expand and contract dozens of times a day. Nickel-based alloys, although expensive, have an order of magnitude more cycles than stainless steel. To put it bluntly, ordinary stainless steel may crack after carrying it 30,000 times, but Inconel 625 can reach 300,000 times. You calculate the cost of replacement over the lifecycle of the equipment, who is more cost effective?

Large diameter thick wall expansion joint— — For example, the double straight pipe bypass pressure balance expansion joint has large wall thickness, high weldability and heat treatment requirements. The performance difference between 321 and 316L on thick-walled parts is obvious: 321 has better high temperature strength and 316L has stronger corrosion resistance. Don't get confused. If you don't do solution treatment after welding, 316L thick-walled parts are prone to sensitization in the heat-affected zone, and intergranular corrosion will come to your door.

Don't just focus on bellows-connections and deflectors are just as deadly

Many people only stare at the bellows itself, but ignore the material matching between the connector and the guide tube.

The function of the guide tube is to guide the flow of the medium and protect the inside of the bellows. If the material of the guide tube is not corrosion-resistant, it is perforated first, and the medium directly impacts the bellows-no matter how expensive your 316L bellows is, it is useless. I have seen a case: a carbon steel guide tube was matched with 316L bellows. As a result, the guide tube rotted out for half a year, and the high-temperature flue gas was directly injected into the bellows. A month later, the bellows was also scrapped. The cost of rework is several times higher than directly selecting the right material.

Structural parts such as tie rods, nuts and end pipes should be selected in the same grade or higher as bellows. A single spot of corrosion can drag down the entire system. The expansion joint is a whole, and any short board will become a breakthrough of failure.

In reality: There is no best, only the best match

There is no best material for expansion joints, only the best match. 304 can solve 80% of the normal working conditions, and the remaining 20% of the harsh environment-go to 316L when you should go to 316L, and don't hesitate to change to Inconel when you should go to 316L.

When selecting materials, pull out the data of your own media composition, temperature range, pressure fluctuation frequency and installation space, and match them with the description of the product list of this site (such as high-temperature axial expansion joint, corrugated expansion joint for power station industry and metal corrugated expansion joint for cement industry). If you are really unsure, you should refer to the case when looking for the manufacturer-don't pat your head to determine the material, which is the bottom line of equipment life and safety.

What is the material of metal bellows expansion joint? The answer is hidden in your own operating parameters. Pull out the data, compare it and choose it, and it will be right.

First, take it apart first: What is the layer of cloth outside the non-metallic expansion joint?

You might think that the non-metallic expansion joint is just a normal layer of cloth, like canvas or umbrella cloth. If you really think so, you will stumble when choosing a model.

Take the fabric fiber expansion joint (that is, the "non-metallic expansion joint (fabric fiber expansion joint)" in the product list of this site), which is not a single-layer structure at all. The outermost layer is usually a coated fabric-in human terms, a layer of temperature-resistant, corrosion-resistant rubber or resin is coated on a high-strength fiberglass cloth or other fiber-based cloth. Common coatings include silicone rubber, fluororubber and polytetrafluoroethylene (PTFE). Why not just go to metal? Because non-metallic expansion joints need flexible compensation, vibration reduction and corrosion resistance, once the metal outer layer is put on, these advantages are all wasted, and thermal expansion and contraction are easy to crack.

Therefore, the outer layer of cloth is actually a "composite material", not an ordinary cloth. If you choose the wrong one, the equipment life will be directly discounted in half.

Second, what is the difference between silicone cloth, fluorine tape and PTFE cloth?

These three outer materials are the mainstream of the market, but their temper is completely different. Direct to dry goods:

• Silicone cloth: Wide temperature resistance range (-60℃ ~ +250℃, can carry 350℃ in a short time), good weather resistance and moderate price. Suitable for general hot air duct, air conditioning and ventilation system. If you use it to fight sulfur flue gas, it will be brittle in two months.
• Fluorine tape: The corrosion resistance is much stronger than that of silica gel cloth, and the resistance to acid, alkali and oil media is good. But the price is much more expensive, and the upper limit of temperature resistance is about 200℃. The flue gas of cement industry has a large dust content and frequent temperature fluctuations, and the outer layer is quickly worn out with ordinary silica gel cloth. At this time, fluorine tape has to be thickened, and even a layer of stainless steel wire mesh has to be pressed on the outer layer to strengthen it-just like the working conditions of metal corrugated expansion joints in our cement industry.
• PTFE coated cloth: It can resist almost all strong corrosive media (including sulfuric acid condensate such a killer), temperature resistance-200℃ ~ +260℃, and does not adhere. In the flue gas baffle door of power station desulfurization system (such as the desulfurization flue gas baffle door of this station), the medium contains sulfuric acid condensate, so multi-layer PTFE composite structure must be used. Ordinary silicone cloth will bulge and pierce in three months.

Think about it, if you choose the wrong outer layer, the expansion joint may be scrapped in a few months, and the labor cost of replacing it is more expensive than the material cost. Is it worth it?

Third, the on-site working conditions are different, and the outer layer selection is very different

Two days ago, I met a customer from a cement factory and asked me: Why did the non-metallic expansion joint they bought leak after half a year? I asked him to take a picture and come over to see that the outer silicone cloth was dusted like sandpaper, and the inside fabric was all exposed. Only after asking did I know that the flue gas temperature did not exceed 200℃, but the dust concentration was high and the particle hardness was high. In this working condition, ordinary silicone cloth is paper paste.

For example, the desulfurization system of the power station has sulfuric acid condensate in the flue gas, and the pH value is as low as 1~2. If you use fluorine adhesive tape, although it is acid-resistant, the fluctuation of temperature and repeated infiltration of condensate will also cause the fluorine adhesive to blister and delaminate. The PTFE composite structure must be applied, and the inner layer must be added with an anti-corrosion isolation layer.

On the other hand, if it is just room temperature air in the air conditioning ventilation duct, a layer of silicone cloth is more than enough, and there is no need to waste money on PTFE. Therefore, don't expect one material to dominate the world. The key is the three parameters of medium temperature, corrosiveness and particle concentration. If you don't understand, you can directly ask the manufacturer for the technical parameter table, which is much more reliable than guessing.

4. Can the outer layer be repaired if it is damaged? How to extend life?

The outside of the non-metal expansion joint is bulging. Can you stick a piece of adhesive tape to deal with it? My advice: Look at the breakage location. If the outer coating is partially peeled off and the inner fabric layer has not been injured, it can be temporarily treated with repair tape of the same material (such as silicone repair tape), and it will last one or two maintenance cycles. However, if the fabric layer has been exposed, or the bulge area is more than the size of a palm, then don't mend it, and directly replace it as a whole-because the outer layer is not only decoration, it bears the main task of sealing and isolating the medium. If it is broken, it is equivalent to pipeline leakage, and the corrosive medium directly erodes the internal structure, and it won't take long to be completely scrapped.

Want to live longer? When installing, be careful not to let external machinery scratch. During inspection, regularly check whether the coating has aged and cracked. If you find fine cracks, quickly treat them with special repair glue. In addition, pay attention to whether the displacement of the pipe support exceeds the design value of the expansion joint-we have a case in which the customer regarded the expansion joint as a universal compensator, and the actual displacement exceeded the design value by 30%, resulting in long-term fatigue cracking of the outer layer.

5. Now you should know how to choose the outer material, right?

• Look at the temperature: PTFE or silica gel is preferred when it exceeds 200℃ (silica gel is more stable for short-term high temperature);
• Look at the corrosion: there are strong acids and alkali, and the condensate is directly applied to PTFE;
• Look at wear: for media containing high concentration of particles, choose fluorine tape + stainless steel wire mesh reinforcement layer;
• National standard requirements: JB/T 12235-2015 has clear suggestions on the use conditions of different materials. Please refer to it when designing and selecting, and don't pat your head.

Don't just look at the price. The cheap outer layer often can't last a maintenance cycle. At that time, the shutdown loss and replacement labor cost will add up to more than ten times the saved material cost. If you are not sure, go directly to our manufacturer for a detailed technical parameter table-we have a corresponding recommended scheme for each working condition, which is much more reliable than your own blindness.

What does the "L" after the non-metallic expansion joint model mean? I looked at it, hey, that's a good question. Many people who purchase and install on-site will most likely be confused when they see this letter for the first time. Today, let's make it clear, and by the way, we will also go through the non-metallic expansion joint.

L is the length, but there's a way here

The "L" on the non-metallic expansion joint is, to put it bluntly, the code name of Length. For example, the drawing says "Non-metallic expansion joint L =500mm", which means that the total length of this compensator is 500mm. This length directly determines how much displacement it can absorb-the larger L, the stronger the compensation capacity. Like our commonRectangular non-metallic expansion jointOrFabric fiber expansion jointSize a truth.

But note that the L of non-metallic expansion joints is not randomly marked. There are two kinds of it: one isTotal length from flange face to flange face, also called installation length; The other isEffective compensation length, refers to the elastic segment (that is, the portion that can be telescoped). Be sure to confirm clearly when ordering, otherwise it will be embarrassing if you can't fit it by hand. And guess what? I have encountered several scenes, just because I didn't understand the difference, the flange didn't match, and the welder cursed.

In addition to L, there are W, H, and DN

Are there other letters on non-metallic expansion joints? Yeah, yeah. For example, "W" stands for Width and "H" stands for Height, which are commonly found in rectangular non-metallic expansion joints. Circular non-metallic expansion joints are typically labeled DN (nominal diameter) and L. You remember a principle: letters followed by numbers are most likely size parameters.

A rectangular non-metallic expansion joint is marked with "L =800mm, W =400mm, H =300mm", so you can know its length, width and height at a glance. But if it is circular, it may just write "DN200 L =500mm". So don't panic when you look at the letters, it's simple to sort out the structure.

Why are non-metallic expansion joints used in power plants, cement plants and desulfurization systems?

Because it can withstand high temperature, corrosion resistance and large compensation. The temperature in the flue gas pipe is always three or four hundred degrees, and there are corrosive gases. Where the metal expansion joint can't bear it, it has to be resolved by non-metallic flexible structures. We're standingFlue gas baffle door、Desulfurization flue gas baffle doorOften used in conjunction with non-metallic expansion joints. For example, at the inlet and outlet of the desulfurization tower, the flue gas baffle door is responsible for cutting off the airflow, and the non-metallic expansion joint is responsible for absorbing the thermal expansion, contraction and vibration displacement of the pipeline, both of which are indispensable.

If you choose the wrong L size, it will not fit, or the pipe stress will burst the seal structure. This is not to scare people-last year, a cement factory customer bought the total length as the effective length. As a result, after installation, the compensation was not enough, the corrugated layer was directly torn, and the whole line stopped for three days.

How to communicate with suppliers without overturning?

Next time you see "Non-metallic expansion joint L =...", don't hesitate, it is the length. If the unit is not marked on the drawing, the default is millimeters. Keep that in mind and make at least half the mistakes when communicating with suppliers. However, for the sake of insurance, it is best to let the supplier confirm two sentences when placing an order: is it the total length from flange surface to flange surface, or the effective compensation length? Also, don't forget to check flange bolt hole spacing and sealing surface dimensions.

If there are other letters that you can't understand, please throw them directly and ask, and let's disassemble them one by one. For example, have you encountered the problem "What does the non-metallic expansion joint l mean?"? In fact, I understand L, and the other letters are just a matter of following the gourd and ladle.

By the way, the national standard for non-metallic expansion joints is JB/T 12235-2015, which contains technical requirements and test methods. The products of our station are all produced according to this standard, includingrubber compensator、PTFE compensatorThese non-metallic ones. If you have special working conditions at hand, such as high-temperature dusty smoke, it is recommended to give priority to fabric fiber expansion joints, which have more reliable temperature resistance and compensation ability.

Buy non-metallic expansion joints just look at the price, the size parameters don't match, and no matter how cheap it is, it is also scrap iron. Is that the truth?

How to set and select the expansion joint of metal bellows? Don't wait for the pipe to break before you regret it

Two days ago, I met a friend of a power station project, saying that the expansion joint cracked just half a year after a main steam pipeline in their factory was put into operation. After removing it, it was found that the actual displacement of the high-temperature section was not calculated at all during the selection, and a general-purpose corrugated expansion joint was used. Tsk, this is not saving money, it is clearly laying mines for yourself. Today, let's make it clear how to set up and choose this thing.

1. Before setting up the expansion joint, find out what the pipeline should compensate for

Many people asked "How to choose the expansion joint" as soon as they came up, but after asking, they found that they didn't even understand the compensation object. Pipelines need to deal with nothing more than three things:Thermal displacement、Vibration、Installation error。 But these three things have to be seen separately-thermal displacement is the main cause, accounting for more than 90% of the working conditions. For example, the temperature difference of steam pipes from cold to hot is two to three hundred degrees, and the axial elongation can reach several centimeters or even more than ten centimeters. That's when you have to goAxial expansion jointOrExternal pressure single axial expansion jointThey specialize in this straight-line expansion.

What about vibration? Pump outlet, compressor inlet and outlet pipeline, high-frequency vibration will shake the bellows root out of fatigue crack. This situation is more suitable forMetal hoseOrCompound hinge transverse expansion jointTo absorb the vibration instead of carrying it hard. The installation error is better understood-a few millimeters away from the field welding butt, fine-tune it with the expansion joint to save you from re-cutting the pipe. But don't design the installation error as the main compensation amount, that is to dig a hole for yourself.

Find out what is moving and how in the pipe system first. Is it running in a straight line or swinging up and down? Is it long-term slow displacement or instantaneous impact? Get it backwards, and the rest is all for nothing.

2. Three hard parameters that cannot be avoided in model selection: pressure, temperature and displacement

These three parameters are the bottom line. Don't place an order if one is less. I said it firstPressure rating: The design pressure of the pipeline is 2.5MPa. If you choose a 1.6MPa expansion joint, the on-site pressure will collapse. For example, the main steam pipeline of the power station has high pressure and high temperature, so it can be usedCorrugated expansion joint for power station industryIts pressure-resistant layer and corrugated structure have been strengthened. The air duct pressure in the cement industry is low, but there is much dust and large temperature fluctuation, so you have to go upMetal Corrugated Expansion Joints in Cement IndustryThe guide tube should be thickened and wear-proof.

AgainTemperature range: The upper temperature resistance limit of the corrugated pipe material must be higher than the maximum operating temperature of the pipe. Ordinary austenitic stainless steel 304 is sensitized above 450 ℃, which is prone to intergranular corrosion. If the temperature of the flue gas pipe rushes to 800℃, then useHigh temperature axial expansion jointInner lining with heat insulation layer, outer wall plus heat sink. The temperature is not right, and the bellows will oxidize into slag in a few months.

And finallydisplacement amount: Many design institutes give a general "compensation amount", but is it axial, lateral or angular displacement? It has to be specific to millimeters and angles. For example, a 30-meter-long pipeline, with a temperature rise of 200℃ and an axial elongation of about 72mm, then the expansion joint you choose has enough single-wave compensation ability. If it is not enough, go to multi-wave structure orDouble straight pipe bypass pressure balance type expansion joint. Blind guess displacement, nine out of ten will have an accident.

3. Different industries have huge differences, so don't use general welding to die all working conditions

The universal corrugated expansion joint is indeed cheap, but covering everything is equal to less than covering everything. The pressure level of the main steam pipeline, reheating pipeline and water supply pipeline in the power station ranges from several MPa to more than ten MPa, and the medium temperature ranges from normal temperature to 600℃. The bellows material must be Incoloy 800 or Hastelloy. And you take a general-purpose type made of 304 material to weld, which is called "sending a head".

What about the cement industry? The air duct is full of high-temperature dusty gas, and the bellows are most afraid of wear and dust accumulation. SoMetal Corrugated Expansion Joints in Cement IndustryIt must be equipped with a wear-resistant guide tube, and the direction of the guide tube should be facing the flow direction of the medium-if it is wrong, the dust will directly wash the root of the corrugation, and the hole will be perforated in two months. The chemical industry is more troublesome. Acids, alkalis, organic solvents and corrosive media can be usedPTFE-lined hoseOrPTFE compensatorOrdinary stainless steel can't handle it.

To put it bluntly, there is no cure-all. For flue gas pipelineNon-metallic expansion joint(fabric fiber expansion joint) can be done, but you can try the power station steam pipe? The non-metallic ones blow away directly.

4. Several details of installation settings that are prone to rollover

Will the tie rod be removed or not?Many expansion joints leave the factory with transport rods or adjustment rods-note that the transport rods must be removed after installation, otherwise the expansion joints are locked and cannot compensate for displacement at all. However, some tie rods with limit function (such as large tie rod expansion joint) can't be removed, and only the nut position can be adjusted. How to distinguish? Read the product manual, or ask the manufacturer directly. If you disassemble it wrongly, you can leak or pull off the pipe at worst.

Where is the deflector?The function of the guide tube is to protect the inner wall of the bellows from the medium scour and reduce the flow resistance. Install so that the bell mouth of the deflector is directed in the direction of media flow. In reverse, the medium will directly impact the bellows root, forming vortices and erosion. There was a chemical project before, and the deflector was installed backwards, and it leaked in three months. When welding the end pipe, pay attention to the arrow on the outer wall of the expansion joint. The direction of the arrow is the flow direction of the medium.

The direction of the arrow is particular.The arrow printed on the housing of the expansion joint not only indicates the flow direction, but also indicates the installation direction. Such asSingle-axis double-flapper doorOrRound flapper doorAn arrow pointing to the closing direction or the medium flow direction. Don't take it for granted, just go with the arrows. In addition, when the expansion joint is installed, it is strictly forbidden to forcibly stretch or compress to make up the nozzle distance-that is called "pre-deformation", which must be strictly adjusted according to the designed cold tightness value. How to tune it? Refer to the standard procedure for expansion joint tie rod nut adjustment.

5. Choosing the right is only the first step, daily use and life management are the real way to save money

Expansion joints are not installed once and for all. And guess what? Many factories don't change expansion joints until they leak, and there is not even a patrol inspection in the middle. Bellows belong to pressure pipe components, and their fatigue life is limited. according toService life of expansion jointFrequently asked questions and answers, the number of design cycles under normal working conditions is usually 1000~5000 times, depending on the displacement amplitude and pressure. However, if you have frequent start-and-stop on site and drastic temperature fluctuations, the actual life will be greatly reduced.

What to do? Develop several habits: First, visually inspect at least once a year to see if there are cracks, corrosion pits and deformations on the surface of the bellows. Second, check that the tie rod and limit device are loose-the nut is loose and the displacement is out of control. Third, for the expansion joint with the guide tube, regularly use an endoscope to see the wear of the guide tube. If the wear exceeds half of the wall thickness, replace it directly.

Don't wait until it leaks before replacing it. Regular replacements are much less costly than accident repairs. For example, the expansion joint on high-temperature pipeline, which is rotated one batch in 3~5 years, is far more cost-effective than the shutdown loss caused by sudden pipe burst. Also, in spare parts management, it is best to use the same model in the same working condition to avoid confusion on the spot. Power stations, cement and chemical industries, the models of expansion joints corresponding to each working condition are available in our station-fromDirect buried (fully buried) type expansion jointToCurved tube pressure balance expansion jointAnd then toSleeve type pipe expansion jointIf you choose the right one and use it well, the pipeline will run for decades without fault.

Don't wait for the pipe to break before you regret it. The expansion joint is a small thing, which costs a small amount of money and guarantees a large system. One more step before setting up, ask more when selecting, take a second look when installing, and the maintenance cost saved later is enough for you to drink good tea for ten years.