Specialized in manufacturing compensators, expansion joints, baffle doors

非金属补偿器到底是什么？跟金属波纹膨胀节有啥本质区别？

非金属补偿器（行业里也叫织物纤维膨胀节、非金属膨胀节）跟咱们常见的金属波纹膨胀节，压根儿不是一类东西。非金属补偿器的核心材料是耐高温涂层织物、橡胶、聚四氟乙烯这些柔性非金属材料，做成一个软接头。而金属波纹膨胀节是靠不锈钢波纹管的弹性变形来吸收位移。路子不同，应用场景自然天差地别。

打个比方，金属波纹膨胀节像个硬汉，能扛高压，但怕腐蚀、怕疲劳。非金属补偿器像个柔术高手，扛不住高压，但耐高温、耐腐蚀、还能吸收三维方向的大位移。你让硬汉去干柔术的活儿，不现实吧？反过来也一样。

它凭啥能在高温烟风道、电厂脱硫、水泥窑尾这些恶劣工况里站稳脚跟？

耐、大、好。耐高温——陶瓷纤维层能扛1000℃以上；耐腐蚀——聚四氟乙烯或耐酸橡胶层直接怼酸性气体；大位移——矩型非金属膨胀节能同时吸收X、Y、Z三个方向的位移，金属件往往只能吸收轴向或横向。此外，减振效果一流，风机进出口管道装上它，振动能吃掉一大半。

电厂脱硫烟道里，烟气温度虽然不高但湿气重、含酸性冷凝液，金属波纹膨胀节用不了多久就被点蚀穿孔。换成非金属膨胀节（比如本站的橡胶四氟补偿器或非金属膨胀节(织物纤维膨胀节)），内层四氟抗酸，外层纤维隔热，用了三四年依然完好。是不是这个道理？

短板也很明显，别把它当万能药

非金属补偿器不是没缺点。承压能力低得可怜——一般不超过0.1MPa，也就是一个大气压出头。你要是用在蒸汽管道或者高压油管上，分分钟爆开。另外，它怕尖锐物刮伤，安装时法兰面不平整就容易漏风。寿命方面，纤维和橡胶层会老化，不过按JB/T 12235-2015标准，正规厂家设计寿命都能覆盖机组大修周期（通常3~5年）。

前两天有个水泥厂的采购跟我吐槽，说他们窑尾管道用金属膨胀节一年不到就开裂了，换了几次烦死。我建议他换成矩形非金属膨胀节，温度800℃左右，用陶瓷纤维+硅胶布复合层。你猜怎么着？用了两年多没出过问题。所以说，选型对了一切都好说。

选型时盯准这四个参数

• 设计温度：看织物层的耐受温度。比如陶瓷纤维能到1260℃，但实际使用要留余量。
• 工作压力：非金属补偿器绝大多用在低压烟风道，超过0.1MPa就别想了。
• 位移量：X、Y、Z三个方向都要算清楚，金属件能算横向轴向就行，非金属得算三维。
• 介质成分：脱硫烟气含湿量大、有酸性，必须选耐酸的四氟或橡胶材质，比如本站的橡胶四氟补偿器。如果是水泥窑尾含碱性粉尘，那得用耐碱涂层。

国家标准JB/T 12235-2015对疲劳寿命、气密性都有明确的试验方法，采购时记得问厂家要第三方检测报告。别听销售吹牛，拿报告说话。

什么时候该选非金属补偿器？

低压、大位移、高温、腐蚀性介质的场合，优先考虑非金属。具体场景包括：脱硫烟气挡板门前后的管道、水泥行业风机进出口、电站锅炉烟道、空冷岛真空管道——等等，空冷岛真空管道那边常用空冷岛真空管道双铰链膨胀节，但那是因为真空工况需要金属密封。而烟风道嘛，基本都是非金属的天下，搭配烟气挡板门或者脱硫烟气挡板门一起用，密封和补偿一步到位。

反过来，要是高压管道（比如主蒸汽）、油品介质、或者需要频繁承压的场合，老老实实用金属波纹膨胀节，比如本站的通用型波纹膨胀节或高温轴向型膨胀节。别想着非金属省钱就硬上——选错了，回头维修比买新的还贵，得不偿失。

所以非金属补偿器怎么样？一句话：用对地方是神器，用错地方是废铁。搞懂自己的工况参数，再对照以上几点，选型基本不踩坑。

先泼盆冷水：没有标准答案

金属膨胀节的耐压能力从来不是一个固定数值，它跟波纹材质、层数、壁厚、有没有加强环、工作温度、口径大小都挂钩。你问“最高耐压”，就像问一辆车能跑多快——法拉利和五菱宏光能一样吗？本站有通用型波纹膨胀节，也有大口径厚壁膨胀节，后者专门为高压力场景设计，耐压等级差出好几个量级。前两天碰到个客户，上来就甩一句“给我报个DN200能扛10MPa的膨胀节”，我说您先告诉我温度多少、介质是什么、位移量多大，他还不耐烦。结果一聊，蒸汽管道，500℃，3.5MPa，你猜怎么着？选个电站行业用波纹膨胀节，2.5~6.4MPa的常规设计压力就够用，非要硬上10MPa，疲劳寿命直接砍到脚脖子。

影响耐压的核心参数

波纹材质是第一个门槛。304不锈钢在常温下许用应力大概137MPa，316L稍高一点，但到了600℃，Inconel 625还能保持住强度，304已经软得跟面条似的。波纹层数——单层抗压能力有限，多层波纹可以通过层间摩擦分摊应力，但代价是刚度变大、补偿位移能力变差。壁厚从0.5mm到2.0mm，每增加0.5mm，耐压大约能提升30%~50%，但疲劳寿命也可能下降，因为厚壁波纹更容易在波谷产生应力集中。加强环这东西，说白了就是在波纹之间加个箍，防止波谷过度变形，高压工况下几乎必备。

介质温度是隐藏杀手。温度每升高100℃，材料的屈服强度下降20%~30%。举个例子：DN200的单层波纹膨胀节，常温下能扛1.6MPa，到400℃可能只剩1.0MPa。你按常温选型，现场一跑高温，膨胀节直接鼓包。这个账不算清楚，设计就白做了。

本站产品里哪些能扛高压？

电站行业用波纹膨胀节，常见设计压力2.5MPa~6.4MPa，专门为电厂蒸汽管道、汽轮机组配套，材料多用不锈钢或Inconel，有的还带内衬筒和导流筒。大口径厚壁膨胀节，壁厚做到3mm以上，加上多层波纹和加强环，最高能到10MPa甚至更高。另外还有一类神器——外压单式轴向型膨胀节，结构上把波纹管放在外面，让介质压力从内部顶住一个刚性内筒，波纹管只承受轴向位移产生的弯曲应力，不直接承受内压。所以它的耐压能力比普通内压式膨胀节强不少。不过别以为高压就无敌——压力越高，疲劳寿命越短，这是个死穴。

耐压和疲劳寿命的博弈

你非要让膨胀节扛10MPa，行，但可能循环次数从1万次掉到2000次。实际工程中，很多客户上来就问“最高耐多少”，我通常会反问一句：“你打算用多久？”高压工况下，材料容易在波谷应力集中区萌生裂纹。一个真实的案例：某化工厂高温高压管道，选了耐压8MPa的膨胀节，结果半年就漏了。查原因，设计压力5MPa，但实际运行时压力波动频繁，每天启停一次，疲劳寿命只够300次循环。后来换了外压单式轴向型膨胀节，压力等级降到4MPa，但寿命提升到1万次，用了三年没出问题。选型时得平衡设计压力和预期寿命，而不是傻盯着一个数字。

选型建议：别自己拍脑袋

先明确工作压力、温度、介质、位移量——比如蒸汽管道，满负荷时温度500℃，压力3.5MPa，那得用高温轴向型膨胀节或者电站专用型号，并且要核对疲劳寿命。最好的办法是把工况参数发给厂家，让他们算。本站的旋转补偿器、复式铰链横向型膨胀节也各有适用场景，别拿高压当唯一标准。旋转补偿器适合长距离直埋管道，复式铰链横向型膨胀节可以吸收侧向位移和角位移，但它们的耐压能力一般不会做到像大口径厚壁膨胀节那么高。如果你是水泥行业，烟气管道温度高、含粉尘，水泥行业金属波纹膨胀节带耐磨衬里，耐压反而不是主要矛盾，耐磨和耐温才是。总之，金属膨胀节最高耐压多少？先问设计寿命和工况，再谈压力。

Find out what the silicone cloth is for in a non-metallic compensator-not a simple layer of cloth

When many people hear "non-metallic compensator silicone cloth", their first reaction is: Oh, it's a layer of cloth, which is padded in the middle of the flange to prevent leakage. Tsk, thinking so, the first step is missing.

The role of silicone cloth in non-metallic expansion joints (also called fabric fiber expansion joints) goes far beyond sealing. It has to carry three things at the same time: temperature, pressure and displacement compensation. For example, in the high-temperature flue gas pipeline, the temperature always goes up to 300℃, and ordinary rubber has long been baked. The silicone cloth has been treated with special coating, and the temperature resistance range is usually-60℃ to +300℃. Some models with glass fiber or ceramic fiber layer can withstand more than 600℃ for a short time.

More importantly, the silicone cloth is the core of the flexible compensation layer – it is responsible for absorbing the axial expansion and contraction, lateral offset, and angular displacement of the pipe. If you think of it as a simple gasket, it is equivalent to turning the whole compensator into an iron plate, and all the elasticity that it should have is gone. Two days ago, I met a customer, who said that it had leaked after installing it for only three months. When I took it apart, I saw that the silicone cloth was pressed into a dead fold by the screw, which didn't compensate at all. It's not that the product is not working, it's the wrong usage.

Rollover site before installation: the flange surface is not treated, the size is not checked, and the screw direction is reversed

Before installing non-metallic compensator silicone cloth, three low-level errors can scrap a good set of products.

The first, the flange face is not treated.The flange removed from the old pipe, which is all welding slag, rust and greasy, is directly installed with silicone cloth? That is equivalent to laying carpet on sandpaper-no matter how tight the press is pressed, the leakage point will appear instantly as soon as the medium flushes. Standard practice: Clean it with a wire brush or angle grinder to ensure that the flange surface is flat and smooth without bumps. If there is a pit exceeding 1mm, it must be repair welded and polished.

Second, the size is not reviewed.Don't say "about the same". When installing non-metallic expansion joints, the diameter of flange bolt holes, hole spacing and outer diameter of flange must be measured against the drawings. 5mm more, the bolt can't pass through; It is 3mm less, and the press strip can't cover it. In a case of a power plant, the workers put the silicone cloth on without measuring the hole distance. As a result, the bolts were twisted diagonally, and the silicone cloth was torn directly at the bolt hole, and it was scrapped before it was put into production.

Third, the direction of the screw is reversed.This one is the most hidden. Many non-metallic compensators are equipped with pressing bars and fastening screws on both sides of the flange. The threaded end of the screw should face the outside of the pressing bars to facilitate screwing the nut. However, someone tried to save trouble and threw the screw in from the inside. As a result, the nut was blocked by the flange when it was twisted halfway, and it couldn't be pressed tightly at all. In the end, it could only be disassembled and reinstalled, and the construction period was delayed for two days.

Core four steps: line drawing and positioning → strip pressing → bolt pre-tightening → symmetrical tightening, one step wrong reduces the life by half

So how on earth do you pretend? Don't mess around, go in this order, and rework if the order is wrong.

Draw line positioning.First, lay the silicone cloth flat on the flange surface, and draw a circle along the inner diameter and outer diameter of the flange with a marker to ensure that the silicone cloth is centered and not skewed. Especially for rectangular non-metallic expansion joints, the four sides must be symmetrical. If the offset is 5mm, the compensation amount will be offset by 10%. When drawing the line, pay attention to the fiber direction of the silicone cloth-the warp direction (length direction) corresponds to the axial displacement of the pipeline, and the weft direction corresponds to the lateral displacement. If this direction is reversed, the compensator is equal to uninstalled.

Strip compacting.The strip (usually angle or flat steel) should fit the flange and completely enclose the edge of the silicone cloth. The bead joints are staggered as much as possible to avoid weak spots in the same position. The bolt holes on the press strip must be aligned with the flange holes, and cannot be pulled hard.

Bolt pre-tightening.Many people are fast in this step, so they can directly use the electric wrench to fight it to the end. SO WRONG! Pre-tightening means to first screw all the bolts with a wrench until they just touch and eliminate the gap, probably until they can't be screwed by hand. Don't rush on the torque, there is also symmetrical fastening in the back.

Symmetrical fastening.That's the key. Tighten three times from center outward, diagonally crossed. The first screw to 50% of the design torque, the second to 80%, and the third to 100%. For example, M16 bolts, the recommended torque is 80~100N·m. Do you have to use a torque wrench and screw it by feel? The error can exceed 30%. In this way, the silicone cloth is uniformly stressed, the sealing surface is flat, and the service life is at least doubled.

Should the pre-stretching of silicone cloth be done or not? Don't be led off by the experience of the old master

"You should tighten the silicone cloth first, otherwise it will be loose and baggy when used." Is this correct? According to the situation.

Silicone cloth itself is a flexible material. If it is intentionally stretched during installation, the advantage is that it can apply tension in advance when the pipeline is cold, and it is not easy to wrinkle after thermal expansion. But the disadvantages are more obvious: excessive stretching, early fatigue of internal fibers of silicone cloth, accelerated aging and fracture at high temperature. Especially when the non-metallic compensator is used in high-temperature flue gas or steam pipeline, the amount of thermal expansion is inherently large, and the pre-stretching makes the silicone gel cloth bear additional stress in the hot state.

I checked the installation manuals of several mainstream manufacturers (including the information of rectangular non-metallic expansion joints on this site), and generally recommended:Not pre-stretched。 When the silicone cloth is installed, it can be kept in a natural flat state, and a small margin (1% ~2%) is allowed to cope with fine adjustment. Only when the displacement of the pipe is extremely large and the elasticity of the silicone cloth itself is insufficient, it is necessary to pre-stretch at the stretch ratio given by the manufacturer (usually not more than 5%). Master's experience may apply to old-fashioned asbestos gaskets, and silicone cloth is different. Don't blindly follow the trend.

Three pits that frequently occur in use: media scouring, temperature exceeding limit, and loose beading

Once installed and set and forget? Thinking too much. Three common problems in the running phase, pay attention in advance.

Media flushing.If there is high-speed dusty flue gas in the pipeline (such as desulfurization flue of thermal power plant), and the particulate matter washes the surface of silicone cloth for a long time, the coating will gradually wear out, expose the fiber layer, and then leak. Solution: Add a guide tube or wear-resistant liner inside the non-metal expansion joint (such as the wear-resistant liner matched by the desulfurization flue gas baffle door of this station). If not, then you have to check the windward side of the silicone cloth regularly, and if you find wear, patch the sheet immediately.

Temperature exceeded limit.The temperature resistance of silicone cloth has an upper limit. Some process pipelines occasionally overheat by dozens of degrees during operation, such as 300℃ in design, but 350℃ in actual fact. It may be okay once or twice, but repeated overheat will cause the silicone cloth to become brittle, hard and cracked. Don't expect it to bear the design limit. Over-temperature 10% may reduce its life by 50%. It is recommended to install temperature monitoring points or choose higher grade composite fabrics (such as ceramic fiber cloth + silicone coating).

The bead is loose.The bolts will slowly loosen under high temperature and vibration, especially when non-metallic compensators are used for fan inlet and outlet pipes. Check once a week and tighten the nut with a wrench. Some customers ignore it after installation. After half a year, the strips fell off, and the silicone cloth was blown by the airflow and torn instantly. This is called a small loss.

When is it time to change silicone cloth? Just look at these three points, don't wait for a leak before dismantling

Silicone cloth is not a permanent piece, so you should change it. Don't be reluctant. Three judgment criteria:

• Cracked or hardened surfaces.Press by hand, if the silicone cloth loses its elasticity, cracks will appear when it is gently broken, indicating that the coating has aged and failed. If you don't change it at this time, the next step will be penetrating leakage.
• Local bulging or delamination.The silicone cloth and the reinforcement layer disengaged and bulged like blisters. The reason is the infiltration of the medium or the action of thermal stress, and the bulge will rupture if it is continuously used.
• There are leakage marks at the flange bead.Even if it's just a wet mark, don't wait for a drip. Disassemble and check. If the edge of the silicone cloth has been corroded by the medium and become brittle, it must be replaced.

There is no fixed standard for the replacement cycle, but according to the industry experience of this station, under normal working conditions (temperature ≤250℃, no strong corrosive medium), silica gel cloth can be used for 2~3 years without problem. If the working conditions are bad, such as high sulfur content in flue gas or large pipeline vibration, it is recommended to stop the machine for inspection once a year. Don't wait until it leaks before removing it-at that time, even the flange may be corroded by the medium, and instead of a piece of cloth, the whole expansion joint will be replaced.

How to use non-metallic compensator silicone cloth? Treat it as a precision part of the system, not as a consumable. It takes an extra half hour to install and saves half a year to run.

First, understand the structure of the non-metal compensator before painting-it is not metal, so don't copy the ripple painting method

To be honest, I've seen too many people paint non-metallic compensators the same way they paint metal bellows. And the result? The drawing resembles a stiff pile of iron, completely ignoring the flexible nature of the fabric skin. The core structure of non-metallic compensator (that is, we often call fabric fiber expansion joint) is three layers: the outer layer is temperature-resistant fiber fabric (such as silicone cloth and fluororubber cloth), the middle is heat insulation layer (ceramic fiber blanket or rock wool), and the inner layer has an anti-corrosion lining. The frame is metal — usually a rectangular or circular flanged frame welded from Q235 or 304 angle steel, channel steel. The skin is fastened to the frame by beading and bolting, creating a soft connection segment that can be twisted. To put it bluntly, this thing is a "rigid and soft mix" structure: the rigid one is the upper and lower flanges, and the soft one is the middle section of fabric. When you paint CAD, you would be wrong to still paint the skin corrugated-the non-metallic compensator has no corrugations, it relies on the elastic deformation of the fabric itself to absorb displacement.

2. Confirmation of key parameters: pipe size, compensation amount, skin material and flange connection form

Before you start drawing, set these numbers to death. Otherwise, if you find out that the flange bolt hole is wrong in the middle of the drawing, it will be called a collapse.
Take-over size: OD or ID of pipe? Is it a circular duct or a rectangular air duct? For example, the power station industry commonly uses round shapes, while the cement industry has more rectangular shapes. Our site hasRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)The two products have different dimensioning habits: circles are directly marked with DN, and rectangles are marked with length × width.
Compensation amount: What are the axial, transverse and angular displacements? The compensation capacity of non-metallic compensators is much greater than that of metals, and the axial energy can reach ±50mm or even greater, but you can't blindly paint too thick. There is a standard for the number of skin layers. Referring to the JB/T 12235-2015 standard mentioned in the FAQ of this site, the number of skin layers is generally 3~5, and the thickness of each layer is 0.5~1.5mm.
Skin material: Silica gel cloth + glass fiber for high temperature working condition, polytetrafluoroethylene coating cloth for corrosion working condition. Don't confuse material labeling-for example, this site hasRubber PTFE compensator, that is, rubber and PTFE compound, can't be written as pure fluorine tape.
Flange connection form: Angle steel flange or flat flange? Is the number of bolt holes a multiple of 4 or is it divided equally according to the air duct size? These data must be extracted from the form factor chart provided by the customer, or from the ready-made data on this siteModel and size of expansion jointLook for references in Q&A.

3. Drawing of two-dimensional engineering drawings: from the main view to the cross-sectional view, emphasizing the overlap between the frame and the skin

Two-dimensional drawings are the basis of production drawings. Open CAD, and set the layers: the structure line, the marking line and the section line are separated. Draw the main view first-usually the outer contour of the flange, draw a rectangle for a rectangle, and a circle for a circle. Then the cross-sectional view is the point: you have to cut at least A-A to express the skin lap structure clearly.
How to paint skin? Don't draw it as a continuous arc! The skin of the non-metallic compensator is not corrugated, it is composed of layers of fabric superimposed and pressed against the flange surface by beading and bolting. Therefore, in the cross-sectional view, the skin part should be drawn as several parallel lines (representing different layers of fabric), and both ends should be represented by a schematic diagram of pressing. The press bar is generally flat steel, with a thickness of 4~6mm and a width of 25~40mm. The bolt spacing is usually 150~200mm. This parameter should be confirmed with the customer, and then marked next to the cross-sectional view.
Also, don't forget to markguide tube。 If you are drawing a non-metallic compensator with a deflector (such as one used in a flue gas desulfurization system), the deflector direction must be clearly marked-the arrow points to the direction of the medium flow. There are special topics in the FAQ of this siteSpecific Function of Expansion Joint Guide TubeIf the guide tube is not installed in the right direction, the consequence will be to wear the fabric skin, and the life span will be directly cut in half.

4. Thoughts of 3D modeling: Using lofting and curved surface tools to simulate the twist and wrinkle of fabric skin

Three-dimensional drawings are mainly used to inspect assembly interference or show them to customers. But how to draw the folds of non-metal skin? Stumped a bunch of people.
What I do is: first build two upper and lower flange boxes (stretch solid), then between the two boxes withloftingCommand to generate a connector. However, don't loft directly into a straight contour-the skin will have natural wrinkles under pressure, so add several control points to the loft path to make the surface slightly bumpy. For example, in a rectangular compensator, the central area of the side of the skin can be retracted by 5~10mm to simulate the effect of depression under negative pressure. Of course, this is just a sign, and the real fold shape is ever-changing, but CAD modeling doesn't have to be completely real, so long as customers can understand "this is the flexible section".
For circular fabric compensators, you can useRotating surfaceOrsweepCommand, but pay attention to the thickness of the skin (0.5mm fabric layer can be ignored directly in three dimensions, too thin to show). The key point is to draw the metal parts such as flanges, bolts and strips clearly, and the skin is represented by translucent materials or maps, so that you can see which parts are soft at a glance.

V. Distinguishing Occasions: Drawing Differences between Rectangular Nonmetallic Expansion Joints and Circular Fabric Compensators

Rectangular non-metallic expansion joint (refer to this siteRectangular non-metallic expansion jointProducts) are usually used in flue gas pipes, which are large in size and can reach 5 meters in side length. At this time, the graphic should focus on the arrangement of reinforcing ribs of the frame-the angle steel frame needs to add vertical ribs in the middle of the long side to prevent the skin from bulging. In the cross-sectional view, draw the cross-section of the stiffener.
Circular fabric compensators (that is, we often call non-metallic expansion joints) are mostly used in small-diameter pipes. The flange is a circular ring and the skin is a cylindrical surface. The marking method is closer to the metal compensator, but it should be noted that round products usually need to be marked with "installation length L", which includes flange thickness + skin free length + strip height, while metal compensators generally only mark the length of corrugated section, which is different.
In addition, guide tubes are rarely used for round products (the flow rate of small-diameter pipes is fast, but the guide tubes increase the resistance), but rectangular products must be added with guide tubes in the desulfurization system to prevent dust accumulation. You have to distinguish between scenes when drawing.

6. Common marking traps-don't miss the direction of the guide tube, the thickness of the heat insulation layer and the hole distance of the mounting bolts

Finally checking, these are the most error-prone places:
Direction of guide tube: As mentioned earlier, the arrow points to the flow direction of the medium, and the front end of the guide tube should extend into the inside of the pipe, leaving a gap of 10~20mm between the rear end and the inner wall of the skin. This gap is not marked, and it is easy for workers to push the skin when they install it.
Insulation thickness: The insulation layer of non-metallic compensator is generally only written "xx mm" on the design drawing, but in actual production, customers may require two layers of ceramic fiber + one layer of air. You have to write clearly in the technical description of the drawing: total thickness, material and density of the insulation layer (e.g. 128kg/m³). Otherwise, if you buy the wrong purchase, the insulation effect will be discounted.
Installation Bolt Hole Spacing: The bolt holes in the flange must be marked with center distance and distribution. Circular flanges are generally marked with PCD (pitch circle diameter) and number, while rectangular flanges are marked with adjacent hole spacing and corner hole positions. Many novices only mark the outer contour size of the flange and forget to mark the hole distance. Consequences? It can't be installed on site, and rework takes time and loses money.
In addition,Length of overlap between skin and flangeIt should also be marked-usually 20~30mm, and the width of the strip covers the overlap area. This number is clearly marked on the partial enlargement of the drawing. Don't expect workers to guess for themselves. If they guess wrong, it is a quality accident.

Alas, in the final analysis, drawing a CAD drawing of a non-metallic compensator is completely two sets of ideas than drawing a metal. The metal compensator is deformed by corrugation, and the non-metal is stretched by fabric. You have to have that "soft box" concept in your head before you write. If you just want to draw a picture of a non-metallic expansion joint at hand, you might as well compare the above points and dismantle the structure before starting. The drawn picture in this way can be directly cut by the workshop master after reading it, which is more worry-free.

Once the nonmetallic compensator (that is, we often call the fabric fiber expansion joint) bulges, collapses or twists, many people's first reaction is to remove it and replace it with a new one. Wait a minute – deformed ≠ scrapped. Find out what kind of deformation it is first, and then decide whether to repair or replace it, which can save thousands of shutdown losses and spare parts costs. Today, let's get this out of the way.

Look at the form first, then look for the cause

Bulging, collapse, twisting, localized wear. The bulge is mostly caused by gas expansion inside the fabric fiber layer or damage to the inner lining; Collapse is mostly caused by negative pressure suction or condensate corrosion, which causes the fiber to lose elasticity; The twist is probably due to the misalignment of the pipeline during installation and the shear force of the compensator; Localized wear is common in particle-containing scouring of media. And guess what? Deformations that occur in the same location may have completely different causes. For example, the non-metallic compensator behind the desulfurization flue gas baffle door has been exposed to acidic condensate for a long time, and the fiber layer begins to eat away from the inside. The outside appears to be only slightly collapsed, but when it is disassembled, it is already layered inside. You just change your skin at this time? It's useless, we have to do it with the drainage device and the anti-corrosion coating.

Temperature overruns and pressure fluctuations: the number one killer

The design temperature resistance of non-metallic expansion joints is generally engraved on nameplates, but the local heat radiation or flue gas flow rate changes are often neglected in actual working conditions. Two days ago, I met a cement factory customer. The measured temperature in the pipeline was 50℃ higher than the design value, and the skin was directly carbonized and deformed-the surface felt like a charred biscuit. What about that? Check the heat source and insulation first, and don't dismantle the compensator as soon as it comes up. After lowering the local temperature and restoring the heat insulation layer, as long as the fiber is not broken, adjust the limit bolt (refer to the adjustment method of the expansion joint tie rod nut), so that the compensator can restore part of the pre-compression amount, and it can last for a while. The same is true for pressure fluctuations, especially near the position of electric plug-in type isolation door or manual plug-in type isolation door. The impact at the moment of valve opening and closing may make the compensator bulge instantly. Priority is given to checking the system pressure relief and valve action logic rather than hardening the compensator itself.

Installation deviation: a fault that is slowly worn out

When the pipe is matched, if the flanges at both ends are not in a straight line, the non-metallic compensator will be forcibly pulled to bear the shear force. This deformation is not visible to the naked eye in its early stages-it feels normal when you glance at it during your inspection. But after a few months of operation, one side of the compensator will appear with dense folds, like the wrinkles on the face of an old lady. Why? Because of the long-term uneven stress of the fabric fiber layer, local fatigue. The solution is simple: Readjust the pipe support to release the stress. Don't reinforce the frame of the compensator, it will only transfer the stress to a weaker place.

Corrosion and ash accumulation: comprehensive treatment of chronic diseases

Rubber compensator and rubber PTFE compensator are very common in chemical industry and desulfurization scenes. Rubber is corrosion resistant, but rubber PTFE compensator is easy to age and deform at high temperature. The materials of the two are different, and the processing logic is also different. If the rubber compensator bulges, it is likely that the oil or solvent in the medium penetrates into it and swells the rubber. At this time, you measure its hardness. If it becomes obviously soft, you have to change it. If the rubber PTFE compensator ages and hardens, and the surface cracks, it has to be replaced. However, there is an exception: if the non-metallic compensator behind the desulfurization flue gas baffle door collapses and deforms but is not broken, you can first check whether the drainage device is blocked, clean up the dust by the way, and then adjust the limit bolt to observe the operation.

What conditions can be "conservatively treated"?

If it is slightly bulged and not damaged, it can be saved in this way: the first step is to shut down for cooling and pressure relief; In the second step, gently poke the bulge with a screwdriver. If you feel that there is gas released inside (the fiber layer is just bulging, not tearing), you can adjust the tie rod nut to let the compensator restore a little pre-compression; The third step is to reduce the operation parameters of the system, such as lowering the temperature by 10℃ and the pressure by 0.05MPa, and running for 24 hours for observation. The bulge disappeared? Then keep using it, and arrange regular inspections. Remember: Nonmetallic compensators are different from metallic expansion joints in that their flexibility depends on the fiber layer, which must be replaced once the fibers break or delaminate. If you touch the deformed area with your hand, if it feels loose and baggy like linen, it means that the fiber has broken. Don't hesitate, according to JB/T 12235-2015 standard, continuing operation at this time will only accelerate the fatigue failure of the whole pipeline system-whether it is corrugated expansion joint or straight pipe pressure balance expansion joint, adjacent equipment may suffer.

What circumstances must be shut down for replacement?

Leaked, delaminated, metal frames and pipes detached. For example, the non-metallic compensator on the vacuum pipeline of the air-cooled island of a power plant began to leak after deformation, and the inspector didn't take it seriously. As a result, a month later, the adjacent transverse expansion joint of the compound hinge also cracked. Because after the compensator failed, no one absorbed the thermal displacement of the pipe, and all of it was pushed to the nearby equipment. You must pay attention to two points when replacing: First, the selection should match the original design-rectangular non-metal expansion joint or round fabric fiber expansion joint? The dimensions and interface flanges must be consistent; Second, don't use brute force to force the counter when installing, first adjust the pipe support and then install the compensator. And guess what? Many people try to save trouble. As soon as the new compensator is installed, the bolts are tightened, and as a result, the torsional stress is brought back to the compensator, which is wasting money.

What if the non-metallic compensator is deformed? To put it bluntly, there are three steps: first judge the form and cause, and adjust the limit bolts and working conditions if you can save them; If you can't save it, replace it strictly according to the standard, and repair the installation deviation and corrosion source together. Don't be lazy, and don't mess around. If you use the compensator right, it will last five years, but if you use it wrong, it will be wasted for three months.