Specialized in manufacturing compensators, expansion joints, baffle doors

织物膨胀节是什么？先给你一句大实话

干管道这行十来年，隔三差五就有人拿着图纸问：这玩意儿是啥？怎么长得跟个帆布口袋似的？你猜怎么着，这就是咱们说的织物膨胀节，也叫非金属膨胀节、织物纤维膨胀节。说穿了，它就是靠一圈柔性织物圈带来吸收管道热胀冷缩、振动位移的装置。你把它想象成管道中间加了一段“软骨头”，管子想往哪儿扭就往哪儿扭，但应力传不出去，设备就安全了。

你别看它名字里带“织物”俩字，就觉得是块破布。这套东西用在电厂、水泥厂的高温风道里，关键时刻比金属波纹管还顶用。不信？往下看。

拆开看：这“软骨头”里到底包着啥？

拿一个标准的矩型非金属膨胀节来说，它通常是四层结构，每层干的活儿都不一样。

• 织物圈带（蒙皮）——最外面这层，也是核心。它一般用氟橡胶、硅橡胶涂层玻璃纤维布或者聚四氟乙烯材料复合而成，负责密封和吸收位移。这层要是破了，整个膨胀节就废了。
• 隔热层——紧贴着圈带内侧，用陶瓷纤维毡或玻璃棉填进去。烟气管道里动辄四五百度，没它隔热，外面的橡胶涂层几分钟就烤化了。
• 导流筒——这玩意儿是金属做的，插在管道内部，把气流导流过去，防止高温烟气直接冲刷织物圈带。别小看它，没有导流筒，圈带寿命能短一半。
• 框架（法兰）——就是上下左右四根角钢或槽钢焊成的框子，跟管道法兰用螺栓拧死。框架强度决定了膨胀节能承受多大压力。

每一层都是配合着干活儿的。你问隔热层能不能省？我劝你别省，省了圈带烧穿，换一次够你买十层隔热棉的。

跟金属波纹膨胀节比，差在哪儿？

既然金属膨胀节那么结实，为什么烟气管道、风道里非得用织物膨胀节？这里头门道很深。

金属波纹膨胀节靠波纹管变形吸收位移，但它有个毛病：对疲劳寿命敏感。烟气管道里温度波动大，还有酸碱腐蚀，金属波纹管一旦疲劳开裂，漏风漏灰是小事，停机检修才是大麻烦。而且金属管的位移量有限，像矩型风道这种大截面的，金属波纹管做起来又重又贵。

织物膨胀节就不一样了。它补偿位移靠的是柔性圈带的形变，三维方向都能动，轴向横向都能吸收。而且它阻尼大，能减振降噪，价格也比同口径的金属波纹管便宜不少。缺点是承压能力差，一般就在几kPa到十几kPa的风道、烟道里用。高压场合？那还是老实用金属的吧。

哪些行业在用？说几个真实场景

我这几年跑现场，见最多的就是这三个地方：

电厂锅炉风道。锅炉送风机出来那截矩形风道，温度高、振动大，热位移靠什么吸收？常用非金属膨胀节。尤其是电站行业用波纹膨胀节，配在低温和高温段都见过，但风道入口段几乎清一色是织物型。

水泥厂窑头窑尾。回转窑出来的烟气温度能到350℃以上，而且含尘量大。水泥行业用金属波纹膨胀节的也不少，但窑尾到除尘器之间那段，基本都是矩型非金属膨胀节。原因很简单：灰尘在金属波纹上积多了会卡死波纹，织物圈带不怕这个，轻微积灰一抖就掉。

脱硫系统。脱硫塔进出口的烟气，湿度大、含硫化物，腐蚀性极强。这时候选金属波纹管，你得盯着材质，成本蹭蹭涨。用织物膨胀节，外层的氟橡胶和四氟涂层本身就耐腐蚀，性价比一下就上来了。

还有那些烟气挡板门、脱硫烟气挡板门旁边，管道连接处也喜欢用织物膨胀节。为啥？挡板门热胀冷缩时，两边管道互相拉扯，没个软连接早把螺栓撕断了。

选型盯住这五个参数，别被销售忽悠

有些销售上来就吹“我们家蒙皮五层夹心，全世界最厚”。你听他的就天真了。选织物膨胀节，盯住这五个数就行：

• 通径尺寸和外形。矩形还是圆形？法兰端口尺寸是多少？这个不量准，后面全部白搭。
• 设计位移量。轴向拉伸量、横向偏移量、角位移，各是多少毫米？你给多少位移，圈带就要用多宽的布，这直接决定价格。
• 介质温度。150℃和500℃用的材料完全是两码事。别只看“耐温800℃”这种上限数，要问长期连续工作温度是多少。
• 压力等级。风道一般是微正压，但万一有负压呢？负压大了圈带吸瘪，一样会失效。
• 介质成分。含不含硫？含不含尘？有没有腐蚀性气体？这对涂层材料选择影响最大。

这五个参数搞不清楚，你听完销售话术，大概率买贵或者买错。

为什么用几年就得换？日常怎么查？

说句实在话，织物膨胀节就是消耗品。金属波纹管能用十几年，织物圈带在高温、粉尘、酸碱腐蚀的环境里，寿命普遍就三到五年，天天高负荷跑，两年换的也见过。你别指望它一劳永逸，设计时就得留更换空间。

日常巡检嘛，重点看三处：一是圈带表面有没有鼓包、龟裂、露纤维，二是法兰螺栓有没有松动，三是看有没有异响漏风。你拿手电筒照照圈带内侧，如果看到隔热层颜色发黑、发脆，那说明跑温了，得赶紧安排更换。

换的时候也有讲究。旧圈带拆下来，框架要清理干净，不得有毛刺。新圈带装上去，螺栓要对角拧，力度均匀，不然受力偏一边，圈带又该扯坏了。

说到底，织物膨胀节不是什么高深技术，但它就是靠那几层布，啃下了金属膨胀节搞不定的硬骨头。下次再有人问你“织物膨胀节是什么？”，你就告诉他：那是管道系统里最懂“让一步海阔天空”的家伙。

一、非金属膨胀节为什么老坏？——织物层老化、划伤、脱层，先搞清楚损伤类型再谈修复

非金属膨胀节（也叫织物纤维膨胀节）在烟气、风道、脱硫系统里用得特别多，它不像金属波纹膨胀节那样靠金属波纹变形吸位移，而是靠多层柔性织物和隔热棉来补偿。坏法也不一样——常见的就三种：织物层老化发脆、外部划伤或磨损、层间脱层鼓包。还有一种隐蔽的，是内部隔热棉被吹蚀掏空，表面看着没破，实际上已经塌了。

所以找修复单位之前，你先自己扒开看看。哪怕只是破了个口子，也要剪开一小块，看看到底是表面硅胶涂层裂了，还是底下玻纤布已经粉化了。损伤类型决定修复方法：表面划伤可以局部补层，但要是脱层范围大、棉层塌陷，那就不是修不修的问题，是整圈都得换。

二、修复还是换新？——算清材料费、停机损失和残余寿命，别一拍脑袋乱花钱

很多用户一听换新要两万，修复只要八千，立马拍板修。但你有没有算过停机成本？一条窑的停机损失可能一小时就是几千块。修复一个非金属膨胀节，拆旧、清灰、打磨、铺层、热合，怎么也得两三天。换新如果现场有备件，一天就能搞定。两边比一比，哪个划算不是单看材料费。

再说了，残余寿命底子得好。如果这个膨胀节已经用了五年，织物层大面积粉化，你花八千修完，再撑一年？那不如直接换新的。反过来，要是只在外部蹭破一小块，内层完好，那你花点钱修一修，再用个三五年没问题。这笔账，算清楚了再决定。

三、找修复单位看什么？——不是有缝纫机就能干，要看非金属膨胀节标准、层间结构和现场工艺

非金属膨胀节这东西，看起来就是个布袋子加法兰圈，但内行都知道，层间结构才是命根子。耐温层、隔热层、气密层、加强层，每一层的材料、厚度、搭接方向都有讲究。国家标准JB/T 12235-2015里写得清清楚楚，修复之后至少得保证位移量、耐压和耐温性能不低于原设计。可有些修复单位连这标准都没听过，拿个工业缝纫机给你把外层布补上就交差，那不是瞎耽误事吗？

所以选修复单位，第一条就是看他懂不懂标准。再一个，问问他能不能提供层间结构图，说不出来的，趁早拉黑。还有，你得问清楚工艺——现场是冷粘还是热合？有没有硫化设备？涂层用什么材料？这些关键点偷工减料了，你根本看不出来。

四、现场修复到底靠不靠谱？——从拆旧到热合、硫化的完整流程，以及常见偷工减料手法

现场修复不是不能干，但得看怎么干。正经流程应该是：先搭架子（如果是高空管道），把旧的失效层彻底拆掉，露出金属法兰面；然后除锈、清理干净，涂粘接剂；接着按原结构逐层铺覆——先铺隔热棉，再铺气密层，再铺加强布，最后是表面耐候层；每层之间要压实排泡，边角用压条和螺栓固定；最后做热合或硫化处理。整个流程下来，一个熟练班组干完也得一天半。

但有些人怎么偷工减料？我见过最离谱的，是把旧的非金属膨胀节外面直接裹一层硅胶布，也不拆旧，也不清理，腻子一抹就完事。还有个作业队，隔热棉都没铺，就两层布缝上去，开机第三天就漏风漏得呜呜叫。你问他们为什么不按标准来？答曰：甲方催得紧。催得紧？那当初别报修复的价啊。

五、修复后怎么验收？——尺寸公差、气密性测试、质保期约定，一条都不能少

修复完不是签字走人就行，你得验收。先量尺寸——膨胀节的长度、法兰间距、法兰面平行度，这些公差如果超了，装上去就憋劲，寿命直接减半。再测气密性，用压缩空气或者烟饼都行，重点看边角压条处有没有漏风。

合同里必须写明质保期。非金属膨胀节修复的质保期业内一般是一年，好点的单位敢写两年。如果对方说“质保？我们不搞质保”，那你连看都不要看，直接换下一家。还有，拿回来的维修报告里，每层材料名称、厚度、搭接量和批号都得列清楚，将来出问题也好追溯。

非金属膨胀节修复单位？好找，凑合事的更多。你先把上面五件事捋清楚，再拿着问题去问对方。答得上来、拿得出方案的，才可以谈下一步。要是不看现场就敢报价的，十有八九是想着先签了再说。设备检修这种事，最怕的就是“说好了”三个字，白纸黑字写清楚，才是对你自己的设备负责。

What are the classifications of expansion joints? First distinguish between metals and non-metals

Many customers ask "What are the classifications of expansion joints?" In fact, the roughest way to divide them is to look at the materials-metal and non-metal. Metal expansion joints are seen most often, likeUniversal corrugated expansion joint、Corrugated expansion joint for power station industry、Large diameter thick wall expansion jointThe bellows inside are all stainless steel or alloy materials, which are hard-core in pressure and temperature resistance. The same cannot be said for non-metallic expansion joints, such asNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion jointThe main body is fiber fabric plus silicone coating, which is mainly used in the occasion of low pressure, large cross section and violent temperature fluctuation of smoke duct.

These two are not substitute relationships. Metal can carry pressure and temperature, but the reaction force is large when compensating displacement; Non-metal has good flexibility and corrosion resistance, but weak pressure bearing capacity. You have to take metal to do non-metal work, and the cost goes up; Taking non-metals to top the high temperature and high pressure is looking for trouble. If the material layer is not selected correctly, no matter how advanced the structure is, it will be useless.

According to the structure: the respective doorways of bellows, sleeve and rotary compensator

The structure determines how the expansion joint absorbs the displacement.Bellows typeIs the absolute mainstream, compensated by ripple deformation. There are many patterns in this, there are single, duplex, with hinges, and with pull rods. LikeCompound hinge transverse expansion joint、External pressure single axial expansion jointIt's all based on this logic.

Sleeve type pipe expansion jointIt relies on the relative sliding of the inner and outer sleeves to compensate the axial displacement, has simple structure and low cost, but the sealing performance is not as good as that of bellows, and is suitable for those pipelines with unclean medium and low pressure.Rotary compensatorIt is another way, which absorbs the axial displacement by converting the axial displacement into rotating motion through the cooperation of a pair of rotating cylinders in the bending section of the pipe. It is especially used in long-distance conveying of steam pipe network, with large compensation amount and small pressure drop.

When choosing a structure, it depends on the direction and space of the pipe. If there are many straight pipe sections, choose axial type; if there are elbows, consider hinge type or rotary compensator. Where the space is compact, the sleeve type is easy to install-it doesn't mean that the more advanced the more suitable, it is the last word that it can be installed and compensated in place.

According to the compensation function: axial, transverse, angular and pressure balance type

This level of classification is the real test of selection skills.

Axial typeThe compensator mainly absorbs the axial expansion and contraction of the pipe, such asUniversal corrugated expansion jointIt is a typical axial product. Several are arranged on straight pipe sections, so thermal expansion and contraction are not afraid.Transverse typeThe good thing is that it absorbs displacement perpendicular to the axis of the pipe,Compound hinge transverse expansion jointThat's what we do.Angular typeWell, with a combination of hinges, the pipe swings at a certain angle, likeDouble hinge expansion joint for air-cooled island vacuum pipelineIt is particularly useful in air-cooled islands with large displacements and multi-directional changes.

If the pressure in the pipeline is high and the blind plate is strong, the ordinary axial compensator will transmit the pressure thrust to the fixed support, which must be made as thick as the city wall. That's when you have to use itStraight pipe pressure balanced expansion jointOrCurved tube pressure balance expansion joint。 Its principle is that a balancing bellows is built in, which eats the blind plate force itself, and the main fixing bracket basically does not bear extra thrust. There are more complicatedCompound straight pipe bypass pressure balanced expansion jointWhich is suitable for the working condition that requires a large compensation amount and does not want the bracket to be stressed. Do you think this classification is important or not? Wrong choice, pipeline vibration, bracket deformation, later is all trouble.

According to the working conditions of the industry: special goods such as power stations, cement and desulfurization

As soon as the industry working conditions come up, the expansion joint has to be "customized". Smoke air duct of power station boiler, high temperature, large cross section, generally usedMetal rectangular expansion jointOrNon-metallic expansion jointWhich not only absorbs thermal displacement but also reduces vibration. Of the cement industryMetal Corrugated Expansion Joints in Cement Industry, that has to be wear-resistant, the dust particles at the head and tail of the kiln are fast, and the material and wall thickness of the bellows have to be increased.

The desulfurization system is more special. The flue gas contains sulfide, and the temperature changes greatly. Ordinary metal bellows can't bear corrosion, so it is commonly usedPTFE compensatorOr a metal hose lined with PTFE, such asPTFE-lined hose。 Also matched with the expansion jointDesulfurization flue gas baffle door、Flue gas baffle doorThese valve equipment have to be considered together when selecting, otherwise the connection size will not match, and the scene will be blinded.

Quick locking categories? Look at these key parameters

Then how do you quickly judge which category to use? Don't rush, just three steps.

The first step is to look at the medium and temperature. High-temperature flue gas and corrosive gas, directly leaning in the direction of non-metal or tetrafluorine lining; High temperature and high pressure steam, honestly choose metal corrugated expansion joint.

The second step is to calculate the compensation amount. Is the axial displacement large? Is there any lateral displacement? If there are multiple directions, preference is given to hinged type or rotary compensators. Like a direct pipeline, then you have to goDirect buried (fully buried) type expansion jointThis goods is directly buried in the soil, and there is a protective sleeve on the outside, so you can't make do with ordinary expansion joints.

The third step is to look at the pipeline constraints. If the position of the bracket has been set, it is necessary to choose the pressure balance type according to the thrust that the bracket can bear. Two days ago, I met a customer who was doing a steam pipe network project. When I came up, I asked, "What are the classifications of expansion joints?" I asked him how to arrange the bracket, and he looked confused. You have to understand that classification is not just a difference in name, each structure corresponds to different force models and installation conditions.

The classification table looks simple, but there are many things involved in the actual selection. The four dimensions of material, structure, function and working condition are cross-combined, and dozens or hundreds of schemes can be discharged. But as long as you grasp the core-the temperature and pressure of the medium, the magnitude of the displacement direction, and the force constraints of the pipeline-you won't deviate. Understanding these, the expansion joint classification is no longer a table, but a selection map in your hand.

Find out first, what kind of equipment is the metal expansion joint?

Metal expansion joints, also called corrugated compensators, are flexible connectors mounted on pipes. It mainly relies on the deformation of the bellows to absorb the displacement and vibration caused by thermal expansion and contraction of the pipeline, so as to avoid the pipeline being cracked or broken. To put it bluntly, it just puts an elastic joint on the pipe.

Are metal expansion joints and corrugated compensators the same thing? Yes, and no. Say "yes" because the core of the vast majority of metal expansion joints is the bellows; Say "no" because there are members of the metal expansion joint family of non-corrugated structures such as sleeve types and rotary compensators. So you can think of corrugated compensators as the mainstream branch of metal expansion joints, but don't draw an equal sign.

Classified by displacement: axial, transverse, angular, you should know these faces

What types of metal expansion joints are included? The most commonly used division method is by absorbing displacement.

Axial typeExpansion and contraction of the absorbent pipe along the axis. Representative products are:

• Universal corrugated expansion joint: The most basic and widely used model, suitable for pipelines with ordinary temperature and pressure.
• High-temperature axial expansion joint: with heat insulation layer and high-temperature resistant material, it can serve hot air ducts above 500℃.
• External pressure single axial type expansion joint: Bellows bear external pressure, good stability, suitable for high pressure steam pipeline.
• Straight Pipe Pressure Balanced Expansion Joint: By balancing the bellows to offset the blind plate force, it is suitable for equipment with fixed ends and unable to bear pressure thrust.

Transverse typeAbsorbs displacement perpendicular to the axis of the pipe. The double hinge transverse expansion joint is typical-two hinge groups are used to restrain the bellows so that it only bends to the side and cannot twist around itself.

Angular typeAbsorbs the angular displacement at the bend of the pipe. Curved pipe pressure balance type expansion joint is a representative of this kind, which is mostly used in the corner of L-shaped or Z-shaped pipe.

Special needs according to working conditions: These "non-mainstream" models specialize in solving difficult problems

Some pipes are unusual, so they have to use special expansion joints.

Direct buried (fully buried) type expansion joint— — The heating pipeline directly buried underground cannot be equipped with an inspection well. The shell of this expansion joint should be made into a structure that can withstand soil pressure, and the interface must be waterproof. It is the only option when directly buried heating pipes are laid.

Sleeve type pipe expansion joint— — Rely on the relative sliding of the inner and outer sleeves to compensate the displacement, which is suitable for low-pressure large-diameter pipelines. The price is much cheaper than that of corrugated pipelines, but the sealing performance is a soft rib and needs regular maintenance.

Rotary compensator— — The displacement is absorbed by the rotation of a pair of rotating arms, and the compensation amount is large. It is especially suitable for long-distance direct burial laying of steam pipelines, which saves brackets compared with traditional expansion.

Large diameter thick wall expansion joint— — The diameter exceeds 1 meter and the wall thickness is increased, which is specially used in large-flow and low-pressure pipelines such as flue gas desulfurization and induced draft fan outlet of power station. Ordinary bellows are easily unstable under this working condition, so it is necessary to use reinforced design.

Does a metal hose count as a metal expansion joint? Close relatives, but don't mix them

This is the easiest pit to step on when selecting a model. Metal hoses and metal expansion joints look similar and have similar names, but their functional emphases are different: expansion joints mainly absorb thermal displacement, and metal hoses are mainly used to connect equipment with relative motion, such as vibration damping joints at pump inlet and outlet, and compensate for installation deviations.

You use the metal hose as an expansion joint, it has few corrugations, short fatigue life, and will crack soon; Conversely, use the expansion joint as a hose, which is not soft enough, and the vibration of the equipment will still be transmitted. When purchasing, read the working condition description clearly: if there is thermal displacement, choose expansion joint; if there is vibration or frequent disassembly, choose metal hose.

Inferred from industry application: Which type should I choose for power station, cement and desulfurization?

Another dimension-the industry pushes back. The working conditions of different industries vary greatly, and products have long been "specialized".

Corrugated expansion joint for power plant industryThe main steam and the reheating steam pipeline have high pressure and high temperature, and the external pressure single axial type or the high temperature axial type are preferably selected; Air-cooled island vacuum pipeline is a large-diameter low-pressure vacuum condition, and the double-hinge expansion joint of air-cooled island vacuum pipeline is needed, which has low stiffness and good seal.

Metal Corrugated Expansion Joints in Cement Industry: The flue gas at the head and tail of the kiln has a large dust content and a drastic temperature fluctuation. When selecting the general-purpose type or the high-temperature axial type, the guide tube should be thickened to prevent the dust from washing and wearing the bellows.

Desulfurization system: The flue gas of wet desulfurization contains acidic corrosive medium, which cannot be carried by ordinary stainless steel, so it is necessary to use PTFE-lined hose or PTFE compensator as an anticorrosive layer; At the same time, the desulfurization flue gas baffle door should be matched with the double seal design. At this time, the expansion joint must be matched with the baffle door.

So, what are metal expansion joints included? The answers are different by displacement, special needs and industry. However, there is one principle that remains unchanged: first find out the pipeline medium, temperature, pressure and displacement, and then compare it with the specific models in the product information of this site. Don't ask "which is cheaper". The wrong choice of expansion joint can lead to air leakage or pipeline overturning. Which one is lighter and which one is heavier, don't I need to say?

What are you most afraid of when choosing metal expansion joints? I am afraid that the customer will only say "Quote me the price of DN600" on the phone. After quoting, ask "why is it so expensive". Because the selection parameters are incomplete, manufacturers can only quote according to the most conservative and largest specifications. Can this price not be high?

What about that? If you want to buy a suitable expansion joint, don't rush to report the caliber. Find out the following 5 things.

Don't be in a hurry to report the caliber, first calculate how much displacement the pipeline should absorb

The core function of the expansion joint is to absorb displacement. The amount of displacement was not calculated clearly, and the rest was all for nothing.

The thermal expansion of a pipeline is generally calculated by multiplying the linear expansion coefficient of the pipeline by the temperature difference and then multiplying the length of the pipeline. The linear expansion coefficient of carbon steel is approximately 0.012 mm/m·°C, and the stainless steel is slightly higher. For example: a 30-meter-long carbon steel pipeline, when the medium temperature rises from 20°C to 200°C, the axial thermal expansion is 30×180×0.012=64.8mm.

This is not over, the ambient temperature during installation, equipment vibration, and displacement caused by pipeline foundation settlement have to be counted. If you only know the diameter of the pipe and don't know how to calculate it, ask the manufacturer for a "Quick Check Table of Pipeline Thermal Displacement" and check it. But only if you have to prepare the pipeline direction diagram and clearly mark the positions of the fixed bracket and sliding bracket.

Media, pressure, temperature: three-piece set that determines the material and number of layers of corrugated pipe

Looking at these three parameters together, the material, wall thickness and number of layers of the bellows are basically determined.

At this end of the medium, 304 stainless steel is enough for ordinary steam, hot water and compressed air; For the medium containing chloride ions, 316L is used; In this strong corrosion condition of desulfurization flue gas, corrosion-resistant alloys or non-metallic expansion joints are often selected. The composition of the medium must be written in full, don't just mention a "smoke". The content of SO₂, NO and dust in the smoke is different, and the corrosiveness is several times worse.

If the pressure is high, the wall thickness has to be added; When the temperature is high, the permissible stress of the material decreases, and the compensation amount is also affected. For example, a steam pipeline with a pressure of 1.6MPa and a temperature of 350°C usually uses 2 to 3 layers of bellows; At the same temperature but the pressure dropped to 0.1MPa, a single layer is enough. The more layers, the greater the stiffness and the higher the price, so there is no need to blindly pursue multiple layers.

On the other hand, don't leak the deflector. The flow rate of the gas medium is high, and the bellows are easily eroded without the guide tube. If the medium contains particulate matter, the anti-wear structure at the front end of the guide tube should also be considered.

Axial, lateral or angular displacement? Choose the universal or hinged type

If the displacement direction is not clear, the chosen structure must be wrong.

The pipeline mainly expands and contracts along the direction of the pipeline, that is, axial displacement. Choose general corrugated expansion joint, also called axial expansion joint. If the pipeline takes an L-shaped or Z-shaped bend, and there is displacement in both horizontal and vertical directions, a single axial type can't be handled at this time, so we have to consider the double hinge transverse expansion joint, or the use of two hinge expansion joints together.

Angular displacement is common at equipment connections, such as steam turbine exhaust port and fan inlet and outlet. Hinge type expansion joint or double tie rod type is a good choice under this working condition.

How to judge? To put it bluntly, just one sentence: telescope and contract along the direction of the tube to choose the general-purpose type; If the pipe is bent and the joint is deflected, you have to use one with hinges or duplex structure. Don't expect to eat all the displacements with a general-purpose type. That's called hard carrying, not compensation.

Tie rod, hinge or pressure balance? Constrained structural relationship support stress

The function of expansion joint is not only "telescopic", but also "controllable force".

The bellows will produce a huge thrust under the action of pressure. If this thrust is all thrown to the fixed bracket, how thick must the bracket be? Therefore, there should be a restraint structure inside the expansion joint to share-this is the meaning of the existence of tie rod, hinge and pressure balance.

The universal expansion joint does not come with its own constraints, and the internal pressure thrust must be carried by the main fixed bracket. Where the pipeline is complicated and the bracket is difficult to make, use straight pipe pressure balance expansion joint or curved pipe pressure balance expansion joint, which can offset the internal pressure thrust, and the force acting on the bracket is much smaller. It is often used on pipelines in cement plants and power stations.

Some people think that the expansion joint with a tie rod can replace the fixed bracket. It wasn't. The tie rod constrains the displacement of the expansion joint itself, not the thrust of the pipeline. The bracket has to do what it needs to do, but the force is different.

High temperature flue gas, large diameter, vacuum pipeline: how to feed in special working conditions

Once the working condition is special, the standard products often can't stand it, so they have to be "added".

High-temperature flue gas, when the temperature reaches above 600°C, metal bellows are basically useless-material creep and oxidative corrosion will quickly shorten the life. At this time, the candidate non-metallic expansion joint (fabric fiber expansion joint) is more suitable, with high temperature resistance, good flexibility and certain sound absorption and vibration isolation effect. Non-metallic expansion joints are often used in desulfurization flues, which are used together with flue gas baffle doors.

Large-diameter pipes, such as flues or air ducts above DN3000, metal bellows are expensive to manufacture, heavy in weight, and laborious in construction and hoisting. Rectangular non-metallic expansion joints are more common schemes under such operating conditions. Of course, if the customer specifies metal, it has to use large-diameter thick-walled expansion joints, and the reinforcing rings and side plates have to be thickened.

The vacuum pipe is different again. Under vacuum conditions, the corrugated pipe should withstand external pressure, and its ability to resist instability is the key. Double hinge expansion joints are often used in air-cooled island vacuum pipelines, which have one more constraint in structure and good stability. The special vacuum hose is equipped with metal mesh sleeves outside the bellows, which is also the truth.

It is much more efficient to give the manufacturer a selection parameter table than to call back and forth

When communicating with the manufacturer, give the following information at once:

• Pipe diameter DN, connection mode (flange or welding)
• Type and value of displacement: What are the axial, transverse and angular displacements in mm/degree
• Name and composition of the medium, especially with corrosive components
• Design pressure MPa, Design temperature °C, Operating temperature °C
• Installation position indication (straight pipe section, near elbow, equipment interface)
• Arrangement of fixed bracket and sliding bracket
• Is there any thermal insulation layer and any outer sheath requirements

All this information is given, and the manufacturer can make the plan and quotation in half an hour. The time saved is much more efficient than calling back and forth to urge questions.

There is no "universal model" for metal expansion joints, only "fit or not". Only when the selection parameters are clear and the working condition boundary is clear can the manufacturer give you a reliable scheme. If you are not sure, send the parameter table directly to the manufacturer-let the engineer judge whether the scheme is valid or not.