Specialized in manufacturing compensators, expansion joints, baffle doors

Let's break it apart from the name

The compensator is the expansion joint, and they are the same thing. Non-metallic compensator, to put it bluntly, is an expansion joint made of flexible materials such as fabric fiber and rubber. The kind used in the flue of electrolysis plant, which is specially used to deal with the thermal expansion and contraction and pipe displacement caused by high temperature and corrosive flue gas. You run to the scene and take a look, and the bulging, cloth-bag-like thing at the flue interface is it. Don't underestimate this thing. If you choose the wrong thing or use it out, you will lose tens of thousands of dollars at a time of downtime.

Why must electrolysis plants use non-metals?

The metal compensator can't bear it at all under this working condition-the flue gas contains hydrogen fluoride and sulfur dioxide, and the metal bellows will corrode and perforate in a few months at high temperature. I have seen a case where a metal bellows was installed in an electrolysis plant. In less than half a year, yellow smoke began to emit from the weld. When I removed it, it was as thin as paper. Non-metallic multi-layer composite structures, such as fluororubber + glass fiber + polytetrafluoroethylene, can not only withstand the temperature to 300℃ or even higher, but also withstand acid-alkali corrosion. Moreover, it has good elasticity, large compensation amount, and can easily handle the thermal expansion and contraction of the pipeline. Do you say, is it comparable to metal?

Structurally, it is completely different from the metal compensator

There is no ripple, but it is the bending of the fabric fiber layer and the elastic deformation of the rubber layer to absorb the displacement. Typical products like this siteNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion joint, the rectangular section just matches the rectangular flue of the electrolysis plant, the installation flange connection, and the middle is a sandwich fabric. A guide tube has to be added inside to prevent high-speed smoke from directly washing the fabric layer-this point is ignored by many novices, and the consequence is that the fabric layer is blown away and has to be replaced in three months.

Type selection is a technical job

Temperature, pressure, media composition, flue size, required compensation amount, a parameter wrong will wait for air leakage. For example, if the temperature exceeds 250℃, conventional rubber will not work, and fluororubber or pure PTFE layer will be used. At this timeRubber PTFE compensatorAndPTFE compensatorIt would be more appropriate. The pressure is generally low, but the flue of the electrolysis plant runs under negative pressure, so the sealing requirements are high, so the strips and sealing rings should be carefully selected. Two days ago, I met a customer, and randomly bought a general-purpose corrugated expansion joint and installed it. When the negative pressure was sucked, the sealing ring was directly deflated, and the yellow smoke came out, so I had to stop and change it. So don't try to save trouble, the parameters have to be checked one by one.

There is a pit in installation and maintenance that many people step on

Don't hurry to dismantle the limit screw when the non-metallic compensator leaves the factory. It is used to prevent excessive stretching during transportation and installation. After all the pipes are in place and the bolts are tightened, the screw is loosened to allow the compensator to expand and contract freely. This order is reversed, and the compensator is pulled and deformed before it is used. In addition, check the fabric layer regularly for bulging and cracking, especially on the side near the electrolyzer. If you find small damage, make up it in time. Don't wait until the whole flue emits yellow smoke before repairing it. At that time, the downtime loss will be great. It is recommended to inspect once a quarter, and scan the surface temperature with an infrared thermometer to see if there are any local overheating spots-this can find the problem of falling off or internal blockage of the guide tube in advance.

Find out first: What is the difference between non-metallic compensator and metal compensator?

Many customers ask as soon as they come up, "Isn't the compensator just a metal bellows?" Alas, this misunderstanding is big. The materials used in non-metallic compensators (also called non-metallic expansion joints and fabric fiber expansion joints) are glass fiber, silicone cloth and polytetrafluoroethylene, which are not deformed by metal corrugations at all. Its core ability is to absorb the thermal displacement of the pipeline in all directions-axial, transverse and angular directions, and the thrust on the pipeline is particularly small. Think about it. In the big flue of the power plant, when the temperature rises, the iron pipe can jump for several centimeters. If the metal bellows is carried hard, the thrust is so strong that the bracket can be crooked. What about non-metal? Soft connection with almost zero force. So,What does a nonmetallic compensator do?The first is "large displacement, low thrust".

High temperature resistance and corrosion resistance are its special skills

Commonly used non-metallic materials, silicone cloth can withstand more than 300℃, and polytetrafluoroethylene (that is, the PTFE-lined and rubber PTFE compensator in our station) is stable to strong acid, strong alkali and desulfurization flue gas. Look at the pipe connected behind the desulfurization flue gas baffle door. The medium is wet and acid, and the metal bellows will be corroded in less than a few months. Replace withNon-metallic expansion joint (fabric fiber expansion joint)For three or five years. And it is not afraid of dust accumulation, rectangular pipes (likeRectangular non-metallic expansion joint) Especially easy to use. Two days ago, I met a customer from a cement factory, saying that the high-temperature air duct at the end of their kiln had been leaking ash with metal before, and it was directly cured with non-metal. Therefore, the second function: in the harsh working conditions of high temperature, corrosion and dust, non-metal is the only reliable choice.

Reduce vibration and noise, and solve the sealing problem by the way

When such equipment as fans and compressors is turned on, the pipes shake like sieves. Metal compensators can reduce vibration, but they also pose a risk of metal fatigue. Because the material of non-metallic compensator is soft, it is born to absorb vibration, and it can eat a lot of noise. And its sealing performance is critical-a lot of flapper doors (Round flapper door、Double-sealed single-axis circular baffle door) Soft connections are required both front and back to ensure zero leakage. When installing with other products in the station (such asElectric plug-in insulation door) cooperation, the non-metallic section just plays the role of flexible transition. And guess what? Some customers specifically requested a non-metallic compensator insteadrubber compensatorBecause the upper limit of pressure and temperature resistance of fabric fibers is much higher than that of pure rubber. The third function: vibration and noise reduction plus high-grade sealing, three birds with one stone.

Actual scene: power station, cement, desulfurization, none of them can run away

It's useless to just talk about theory. Let's talk about real working conditions. Power station industry: The flue from the boiler outlet to the dust collector, with large temperature change and large pipe section, can only be usedRectangular non-metallic expansion joint。 Cement industry: raw material mill, kiln tail high temperature fan, airflow contains dust, useNon-metallic expansion joint (fabric fiber expansion joint)Most stable. Desulfurization system: inlet and outlet of absorption tower, the medium is gypsum slurry and wet flue gas, which is highly corrosive. The non-metal compensator is equipped with PTFE lining, and its life is three times longer than that of metal. Look at the product list in the station, "Desulfurization flue gas baffle door”、“Corrugated expansion joint for power station industry”、“Metal Corrugated Expansion Joints in Cement Industry"There are all, but the non-metallic models that truly withstand corrosion and high temperature are the key connection points of these systems. Article 4 Function: Specializing in the treatment of stubborn diseases in the industry of high temperature, corrosion and large displacement.

Do not step on pits when selecting models: pay attention to temperature, pressure and displacement

Many customers choose non-metal according to the parameters of metal compensator, and the result is broken in a few months. The weakness of non-metallic compensator is that the pressure bearing capacity is not as good as that of metal, and it is generally only used in flue duct systems with low pressure (below 0.1MPa). The temperature should be distinguished between the medium temperature and the surface temperature. The fabric fiber can carry it to 1000℃, but the lining insulation layer should be calculated well. In terms of displacement, non-metals can be very large (such as 100mm in the axial direction and 50mm in the horizontal direction), but the flange connection and guide tube need to be designed well-you refer to the question and answer on "Specific Function of Expansion Joint Guide Tube" in the station, and non-metals also have to be equipped with guide tubes, otherwise the airflow will directly scour the fabric lining and wear it out quickly. Also, when installing, do not tighten the fastening bolts too tightly to prevent crushing the non-metallic sealing surface. Remember one thing: non-metallic compensators are designed according to the idea of "soft connection", so don't let it suffer. Fifth Function Tip: Choose the right one, it is more durable than metal.

The metal expansion joint, to put it bluntly, is a flexible joint, which absorbs the thermal expansion and contraction of the pipe by the deformation of the bellows. But if you think it can carry any working conditions, it will have to roll over sooner or later. Two days ago, a customer asked me why the expansion joint he installed leaked after only three months. When I removed it, the bellows cracked like a cracked riverbed. What's the problem? When you select a model, you just stare at the compensation amount, and everything else is ignored. Let's break it down today,Disadvantages of Metal Expansion Joints?Where the hell is hidden.

1. Fatigue life: Bellows are not perpetual motion machines, and the number of cycles is the hard threshold

Many people think that the expansion joint can be used for a lifetime, so they dream. Every time the bellows expands or contracts, a micro-damage accumulates inside the material. The fatigue life written in the design standard is usually between a thousand and several thousand cycles-this is not blindly determined, it is measured. If you think about it, steam pipes start and stop once a day, 365 times a year, and thousands of times in three years. If the circulation frequency is high and the displacement amplitude is large, the life time will be cut in half directly.

What about that? Not for you not to use it, but to figure it out. First calculate the total thermal displacement of the pipeline, and then see whether the working condition belongs to low frequency or high frequency. Like those used in the power station industryCorrugated expansion joint for power station industryThe number of cycles requirements must be specified when designing. Don't buy the general-purpose corrugated expansion joint to make do, the fatigue life is not matched, and it is too late to cry later.

2. Media compatibility: There are boundaries in corrosion resistance, so don't use it as a panacea

Stainless steel bellows corrosion resistant? That depends on the medium. Working conditions with high chloride ion content, such as desulfurization flue gas and seawater, 316L will still pitting for you. Two days ago, a case in a chemical plant, usedMetal hoseThrough hydrochloric acid, it leaked within a few months. ChangePTFE-lined hoseOrPolytetrafluoroethylene compensator, instead, lasted for more than two years.

Before the selection, you must get the media composition list, and the temperature, concentration and flow rate must not be less. High-temperature flue gas contains sulfur, ordinary stainless steel can't bear it, have toHigh temperature axial expansion jointOr non-metallicNon-metallic expansion joint (fabric fiber expansion joint)。 Don't gamble on experience, the corrosion boundary is much narrower than you think.

3. Installation and maintenance: pull rod, guide tube, pre-stretching, one step wrong, one step wrong

Installing this thing is really not just a few screws. Let me ask you, what is the tie rod on the expansion joint for? Many workers removed the tie rod directly at the scene, thinking it was a transportation fixture. As a result, as soon as the pipe heated up, the bellows was pulled to the head and torn directly. The correct way is: after installation, adjust the tie rod nut so that the bellows is in the designed position-pre-stretched or pre-compressed, according to the cold tightness requirements of the pipe system.

Let's talk about the guide tube, which not only prevents scour, but also affects the flow direction of the medium. If it is installed backwards or missed, the high-speed fluid rushes directly into the bellows, vibrates and erodes, and the hole will be perforated in less than a month. We have a client usingMetal Corrugated Expansion Joints in Cement IndustryBecause of the reverse installation of the guide tube, three were replaced in three months.

As forCorrect installation method of expansion joint of large tie rodThe tie rod absorbs the internal pressure thrust. During installation, the nuts at both ends of the tie rod should be tightened in place, and the bellows should not be pressurized-this work has to be done step by step according to the instructions, and don't take it for granted.

4. Cost account: Is one-time purchase cheap? Later replacement and downtime losses are deadly

The metal expansion joint itself is not expensive, and a general-purpose corrugated expansion joint may only cost a few thousand yuan. But what about a change? Pipeline venting, thermal insulation dismantling, replacement operation, re-pressurization, plus the loss of production shutdown, six figures per minute. Especially in chemical industry, power plants and cement lines, it is hundreds of thousands to stop a day.

So don't just focus on the money of expansion joints when choosing a model. Working conditions are bad, such as high temperature and high pressure, strong corrosion, rather buyExternal pressure single axial expansion jointOrStraight pipe pressure balanced expansion jointThis structure is more reliable. Although it is twice as expensive, it can be used for five years without accidents. Rubber compensators are cheap, right? However, as soon as the medium temperature exceeds 80℃, it will immediately become soft. You said chooserubber compensatorOr metal? Depending on the working conditions, calculate the general ledger.

5. Special working conditions do not work: vacuum, buried ground, large displacement scenes have to be requested to be smart

Metal expansion joints are not a panacea. Under the vacuum condition, the bellows has a large external pressure and is easily unstable. We have dedicatedSpecial hose for vacuumThe structure is different and can resist external pressure. You take an ordinary metal expansion joint to vacuum, and the bellows are like a flattened can, which is directly scrapped.

What about buried pipes? Buried directly in the soil, corrosion, soil pressure and uneven settlement, the metal expansion joint can't bear it at all. UsefulDirect buried (fully buried) type expansion jointOr simply use a sleeve typeSleeve type pipe expansion joint。 There are also large displacement scenarios-several hundred millimeters of lateral displacement, or axial displacement beyond the bellows limit, then you have to considerCompound hinge transverse expansion jointOrRotary compensatorDon't push on the universal model.

Alas, in the final analysis, choosing an expansion joint is not a set of formulas, but a solution of equations. Media, temperature, pressure, displacement, life, cost, every variable has to be counted. Picked right, it is a buffer for the plumbing system; Wrong choice, it's a ticking time bomb.

Find out one thing first: What role exactly do metal expansion joints play in pipes?

To put it bluntly, it is the "expansion joint" of the pipe-absorbing thermal expansion and contraction, buffering vibration and compensating for installation deviation. There are rubber compensators and non-metallic expansion joints on the market, but metal expansion saves energy and carries high temperature and high pressure, such as the main steam pipeline of power station and the high-temperature air duct of cement industry. Ordinary rubber parts will be wasted when they go up. Then what is its advantage? Let's tear it down layer by layer from the structural design.

The first hard-core advantage: "iron bone clanging" with temperature and pressure resistance

The main body of the metal expansion joint is stainless steel bellows, like our sideUniversal corrugated expansion joint、High temperature axial type expansion joints can operate at temperatures above 600℃, and the pressure level ranges from PN0.6 to PN6.4 or even higher. The rubber compensator begins to age when it exceeds 150℃. Although the non-metallic fabric fiber expansion joint can reach 1000℃, its pressure bearing capacity is weak. Metal expansion joints are just needed in the environment of high temperature, high pressure and medium corrosion such as power station boilers and desulfurization flue gas pipelines. A customer has asked: "What to choose for steam pipe?" We recommend directlyExternal pressure single axial expansion jointOrStraight pipe pressure balance typeThe reason is that it can balance out the internal pressure thrust and the pipe is not subjected to additional axial force. Think about it, if you put a rubber piece on the main steam pipe of a power plant, let alone heat it up, the steam pressure alone can blow it up.

The second advantage: there are many tricks of displacement compensation, which is not a "new trick"

The displacement of the pipeline system is not only linear expansion and contraction, but also may have lateral misalignment and angular deflection. The corrugated structure of the metal expansion joint can naturally absorb the axial displacement, but the composite displacement can be accomplished by adding a tie rod, a hinge and a universal hinge. Such asCompound hinge transverse expansion joint, specializing in absorbing lateral displacement;Curved tube pressure balance type expansion joint is used for simultaneously absorbing axial and transverse displacement at the curved tube;Double-hinged expansion joints of air-cooled island vacuum pipes adapt to large angles of thermal displacement. comparisonSleeve type pipe expansion joint (by sliding seal), metal corrugated expansion joint has no leakage point, small maintenance. Think about it, if the air-cooled island pipeline of the power plant uses a rubber compensator, can the vacuum degree be kept? The rubber will deflate under negative pressure, and the sealing ring will leak as soon as it ages, and the system efficiency will drop a lot.

Third point: Fatigue life is supported by data

The design life of metal expansion joints is usually calculated according to the number of cycles, and the standard ranges from 1,000 to 10,000 times, depending on the waveform, number of layers and material. We have done testing, 304 stainless steel corrugated pipe under reasonable design, the actual operation of 15-20 years a lot. The rubber compensator is affected by ozone and ultraviolet rays, and it has to be replaced in 3-5 years. Two days ago, there was a cement factory customer. The non-metallic expansion joint used in the kiln head pipeline leaked ash in two years, so it was replaced withThe metal corrugated expansion joint of the cement industry has been running for six years without any problems. This is not metaphysics, it is rolling of material science-metal bellows are formed by cold stamping, stress distribution is optimized, plus multi-layer structure increases flexibility, and the fatigue life is more than 5 times that of rubber. Think about it, a production line stops once and loses hundreds of thousands. Who is willing to change the compensator frequently in order to save thousands of dollars?

The fourth hard-core scene: "special students" in extreme working conditions

For example, the expansion joint matched by the desulfurization flue gas baffle door should not only be resistant to SO2 corrosion, but also adapt to the low pressure and large displacement of 0.1MPa. This environmentPTFE compensators can also be used, but the cost is high and the installation is complicated. Metal expansion joints are lined with PTFE liners, or directly with high-nickel alloys (such as Inconel), get it done. AndDirectly buried (fully buried) type expansion joint, directly buried underground, wrapped with anti-corrosion coating and insulation layer, to bear soil pressure and groundwater erosion.Special vacuum hose, the wall thickness is made thin and dense, and it can bear negative pressure without deflating. These non-standard requirements and non-metallic parts are basically stopped. To be honest, choosing expansion joints means choosing "who carries it more". Metal expansion joints are a proper main force in heavy industries such as power stations, cement, chemical industry and metallurgy.

Finally, let's talk about something real: how to pick?

Don't be superstitious about "universal models". Also a metal expansion joint,Corrugated expansion joints for power station industry andMetal corrugated expansion joints in cement industry have different corrugation parameters, end connection forms and guide tube design. For example, the function of the guide tube is to prevent high-speed airflow from washing the corrugated body. When selecting the type, it depends on the flow rate and medium particle size. If there is severe vibration in the pipeline, a tie rod or limit device should be installed. You take a general-purpose corrugated expansion joint and install it on the high-temperature steam pipe. If the angle is wrong, the fatigue life is incorrectly calculated, and it will crack in three months, you can't blame the product. Our product line ranges from general-purpose type, high-temperature axial type, straight pipe pressure balance type toDouble sealed baffle door matching, each model corresponds to specific working conditions. Before the next selection, calculate the temperature, pressure, displacement and medium clearly. Don't think that "metal" is universal. Tsk, if it were that simple, there would be no technical threshold in this business.

How to determine the design temperature of the expansion joint? Three Key Points Engineers Must Understand

Nine times out of ten, people who select expansion joints have stumbled at the design temperature. Either I patted my head to get the medium temperature, or I missed the external heat source. This article is not false, and it directly dismantles the three decisive links.

1. Working temperature and design temperature: Don't regard "highest" as "design"

The maximum operating temperature of pipeline medium is 400℃, which is directly filled in the selection sheet when the design temperature is used. When the corrugated pipe material couldn't bear it, it was discovered that the allowable stress had long failed. The design temperature is not the operating temperature, which is clearly written in the standard-GB/T 12777 and ASME B31.3 both require a safety margin on the operating temperature. But this margin is not a fixed value, depending on the working conditions: continuous operation or intermittent operation? Is there a risk of local overheating? For example, the corrugated expansion joint used in the power station industry (such as the "corrugated expansion joint used in the power station industry" in our station), the temperature of the steam pipeline fluctuates greatly, and the peak value may rush to 550℃, while the average value is only 450℃. If you choose according to the average value, the bellows directly deforms plastically at the peak value. Therefore, the design temperature has to be calculated according to the extreme peak value, and the thermal shock margin at start-up has to be superimposed, generally from +20℃ to +50℃.

2. Internal media vs external environment: who has the final say?

This question is different from the occasion. If it is a high-temperature axial expansion joint, the internal medium temperature is naturally dominant. However, don't ignore the temperature gradient at the flange connection and near the guide tube-where local stress concentrations occur and lead to early cracking of the bellows. On the other hand, like directly buried (fully buried) expansion joints, the external soil temperature and the performance of insulation layer are the keys. Two days ago, a customer who made metal corrugated expansion joints in the cement industry had a medium temperature of only 450℃, but the site was close to the rotary kiln, and the radiant heat made the external temperature soar to 600℃. As a result, the outer wall of the bellows failed first, but the inner wall was still fine. Which do you say the design temperature should be taken? It must be the maximum of the two heat sources, and then the material creep strength is checked. Don't be lazy only measure the medium temperature, the ambient temperature is often the fatal blow.

3. Material selection: When the temperature is high, money and life have to be counted

When the temperature rises, the allowable stress of ordinary austenitic stainless steel (such as 304) cliffs down. Over 550℃, you have to change to a heat-resistant alloy, like Inconel 625. But heat-resistant alloys are expensive, several hundred yuan per kilogram, and the cost doubles. What about that? In some cases, the multi-layer structure of high-temperature axial expansion joint can be used-the inner layer is heat-resistant, the outer layer is pressure-bearing, and the cost is reduced. Or simply put on non-metallic expansion joints (fabric fiber expansion joints), and use temperature-resistant fibers and silica gel coating, which can carry above 1000℃, and the price is lower than that of heat-resistant alloys. Note that the design temperature also directly affects the fatigue life: for every 100°C increase in temperature, the cycle life of the bellows may be reduced by half. Therefore, when selecting the model, the design temperature must be calculated together with the pressure and displacement, so as to determine whether the general-purpose corrugated expansion joint or the large-diameter thick-wall expansion joint should be used. The former is cheap but weak in fatigue resistance, while the latter has large wall thickness and rigidity, which is suitable for high temperature and high cycle.

Here's a common "pitfall": the regulations of temperature cycling and thermal shock in the standard. For example, desulfurization flue gas baffle door and flue gas baffle door, the medium is acidic wet flue gas, and the temperature is not high but fluctuates violently-jumping back and forth from 100℃ to 180℃. If the design temperature is selected only according to the highest value of 180℃, and the thermal fatigue is ignored, the weld will crack after hundreds of cycles under the working condition of high start-stop frequency. National standards JB/T 12235-2015 (non-metal expansion joint) and JB/T 6171 (metal bellows) have detailed regulations on temperature, but in actual projects, I suggest leaving an extra margin of 10% ~15%, especially in working conditions with high start-stop frequency. Don't ask why, I've seen too many live lessons.

4. Actual estimation: What if there is no data?

In the absence of detailed process data, the saturated steam temperature corresponding to the design pressure of the pipeline can be inverted. For example, the pressure is 1.0MPa and the saturated steam temperature is about 180℃, so the design temperature starts at 200℃. Or referring to similar project cases, we have the product pages of "Double Hinge Expansion Joint for Air-cooled Island Vacuum Pipeline" and "Double Hinge Transverse Expansion Joint" on our station, which list the design temperature range for conventional working conditions. Generally, the design temperature of steam pipeline is the medium temperature +20℃, but it depends on the pipeline material and insulation thickness. Finally, a reminder: after the design temperature is determined, don't forget to link with the "guide tube" design. The guide tube can reduce the direct scouring of the bellows by high-temperature medium, which is equivalent to reducing the effective working temperature by 30~50℃. This amount can save a lot of cost when calculating the fatigue life.