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金属膨胀节怎么维修？先判断故障类型，再决定修还是换

前两天碰到个客户，电话里火急火燎说他们厂里的通用型波纹膨胀节漏气了，问能不能修。我让他先拍个视频过来，一看——波纹管表面有个小米粒大的沙眼，但整体没变形，拉杆螺母也没松。这种情况，补焊一下还能撑两年。但要是裂纹已经穿透了三四条波，或者波纹管直接卡死，那抱歉，修的成本比换还高。

所以金属膨胀节怎么维修？核心就一句话：先搞清楚故障类型，再决定是局部修还是直接报废。别上来就拆，也别一漏就换，浪费钱。

一、先搞清楚故障根源——漏气、卡死还是变形？

维修之前，最忌讳的就是凭感觉。你至少得肉眼加简单工具做个判断。常见的故障分三类：

• 漏气：声音能听到嘶嘶声，或者用肥皂水涂焊缝、波纹管波峰、波谷，看冒泡。漏气点一般在波纹管母材、端部焊缝或者接管与法兰的连接处。像电站行业用波纹膨胀节运行温度高、压力大，漏气多半是疲劳裂纹，而水泥行业金属波纹膨胀节漏气往往是因为粉尘磨损导致的穿孔。
• 卡死（位移失效）：管道该伸缩时不伸缩，或者膨胀节被硬拉成一条直线，手推不动。拉杆螺母拧太死、导流筒脱落卡住波纹管、或者内部积灰结垢，都会造成卡死。像高温轴向型膨胀节里的导流筒如果脱落，直接撞在波纹管上，那动静可不小。
• 变形：波纹管出现明显的歪扭、波距不均、局部鼓包。这往往是超位移量运行造成的。你量一下实际位移量，再对照出厂设计值，一目了然。

这三种情况，判断对了，后面就好办。判断错了，修了也是白修。

二、波纹管局部损坏：能补焊就不换，但得看材质和厚度

如果只是小沙眼或者浅表裂纹，且材质是304、316L这种奥氏体不锈钢，厚度在0.5mm以上，那完全可以补焊。注意：补焊前必须把破损区域打磨干净，露出金属光泽，用氩弧焊，焊丝要选同材质或更耐腐蚀的（比如316L焊丝）。焊后必须打磨平滑，不然这里会成为新的应力集中点。

但要是波纹管厚度小于0.3mm（比如一些真空专用软管或低压工况的衬四氟金属软管），或者材质是哈氏合金、因科镍尔这类特种合金，普通焊工根本搞不定，建议直接联系厂家处理。还有一种情况：裂纹在波纹管根部（波谷），这里应力最大，补焊后寿命也长不了，不如换新的。

金属矩形膨胀节和大口径厚壁膨胀节的波纹板大多是拼接焊缝，补焊时要注意热变形控制，否则越补越漏。

三、拉杆螺母松动或导流筒脱落：小问题自己调，别拧过了

这类问题看着小，但处理不好反而弄巧成拙。比如膨胀节拉杆螺母怎么调整？标准做法是：先确认设计位移量，用扳手对称拧松调整螺母，让波纹管恢复到自由长度。千万别单边拧到底，否则膨胀节会歪扭。很多师傅一上来就拧死，结果波纹管无法正常伸缩，直接卡死。

再说导流筒脱落。导流筒本身是用螺栓或者点焊固定在管道内壁上的，如果脱落，它会掉下来卡住波纹管，甚至被介质冲走砸坏下游阀门。维修时打开人孔，把脱落的导流筒重新焊接或螺栓固定即可。注意焊缝不要高出导流筒表面，免得影响介质流动。像脱硫烟气挡板门这类设备，导流筒一旦脱落，浆液倒灌进波纹管，腐蚀速度翻倍。

四、哪些情况必须报废？疲劳裂纹、腐蚀穿孔、超位移量

别舍不得，有些情况强行修就是埋雷。

• 疲劳裂纹：如果裂纹沿着波纹管轴向延伸超过3个波，或者周向裂纹长度超过圆周的1/4，说明材料已经疲劳，补焊后很快会再裂。直接换新的，推荐用外压单式轴向型膨胀节或复式铰链横向型膨胀节，这类结构抗疲劳性能更好。
• 腐蚀穿孔：点蚀、晶间腐蚀造成的穿孔，往往表面看只有一个小洞，但周围金属已经脆化。用磁粉检测或者着色探伤，如果发现密密麻麻的微裂纹，那就别修了。特别是化工管道用的聚四氟乙烯补偿器，内衬一旦穿孔，介质会腐蚀外部金属。
• 超位移量：实际运行位移超过设计值的120%以上，波纹管已经产生塑性变形。比如直埋(全埋)型膨胀节被过度拉伸，波距都不均匀了，这时候补焊也没用，因为波纹管已经失去弹性。

顺便说一句，膨胀节的使用寿命一般设计在1000~2000次全位移循环，但很多厂用了十年八年都没坏，那是因为实际位移远小于设计值。如果频繁超限，寿命断崖式下跌。

五、维修完怎么验收？打压测试和位移回弹一个不能少

修完不是完事了，你得验证它还能不能干活。两步走：

第一步，打压测试。 按照设计压力的1.25倍进行水压试验，保压10分钟，检查焊缝、法兰、波纹管表面有没有渗漏。注意：水压试验后必须彻底吹干，特别是空冷岛真空管道双铰链膨胀节这类真空设备，残留水分抽真空时会结冰损坏波纹管。

第二步，位移回弹测试。 把拉杆螺母松开，用手推拉波纹管，看它是否能顺利伸缩到设计位移量，松手后能否自动回弹。如果回弹不到原位，说明内部有卡阻，或者波纹管已经失稳。对于曲管压力平衡型膨胀节这类平衡型结构，还要检查压力平衡环的拉杆是否同步移动。

这两步都过了，才算维修合格。

六、日常盯紧几个细节，能少去一半麻烦

维修终归是被动补救，不如预防。以下几个点你但凡盯住了，故障率至少降一半：

• 导流筒磨损检查：每半年打开人孔看看，特别是烟气系统、煤粉管道。导流筒磨损到厚度不足原始一半时，提前更换，别等它掉下来砸坏波纹管。像非金属膨胀节(织物纤维膨胀节)虽然没有金属波纹管，但导流筒一样怕磨损。
• 拉杆螺母定期预紧：不是让你拧紧，而是检查有没有松动、锈死。对于大拉杆膨胀节，每隔三个月用扭矩扳手按设计值复紧一下，防止振动导致螺母松脱。
• 位移量监控：在膨胀节上标记刻度，记录每次停机时的位移量。如果发现某次位移突然变大或变小，说明管道支架可能偏移了。比方说直管压力平衡型膨胀节如果位移失常，很大概率是主固定支架松动了。
• 保温与防腐：室外安装的膨胀节，尤其是高温轴向型膨胀节，保温层破损后雨水进入，腐蚀速度惊人。定期检查保温层密封情况，修补破损处。还有，别让腐蚀性液体直接淌到波纹管上。

好了，关于金属膨胀节怎么维修？我说的够细了。你回去对照自家的膨胀节，先看故障类型，再决定修还是换。实在拿不准的，拆机拍个照片发给我，我帮你一眼定生死。

前两天有个电站的客户打电话来，语气挺急，说他们管线上一个波纹膨胀节漏了，穿孔。问我能不能直接焊上凑合用。这种问题在行业里太常见了，但答案真不是简单的“能”或“不能”。金属膨胀节穿孔怎么办？是补是换，得看穿孔的原因、位置、还有你用的是哪种膨胀节。先说结论：盲目补焊十有八九会出更大的事。

穿孔的原因五花八门

最常见的是腐蚀——介质里的氯离子、硫化物，或者高温氧化。比如电站行业用的波纹膨胀节，长期在高温烟气下，外壁容易发生高温氧化减薄，最后穿孔。水泥行业的金属波纹膨胀节呢，粉尘磨蚀是主因。还有一种情况，是安装时拉杆螺母没调好，导致波纹管承受了不该有的扭转或侧向位移，疲劳裂纹最终发展成穿孔。你想想，如果不分青红皂白就焊，裂纹里还夹着介质残留，焊上去也是虚的。

对了，还有一种穿孔原因很多人忽略——导流筒失效。膨胀节导流筒具体的作用是保护波纹管免受高速介质冲刷，一旦导流筒破损，介质直接冲击波纹管，局部冲蚀速度能快好几倍。这时候就算你焊住了穿孔，内壁还在继续减薄，过不了多久又会漏。

有没有临时应急的办法？有，但条件苛刻

比如低压常温的循环水管路，穿孔不大（直径不超过5mm），可以用夹具包覆橡胶垫片临时堵一下，或者用冷焊剂（金属修补胶）应急。但前提是你得确认介质温度不超过胶的耐温范围，而且压力在0.5MPa以下。千万别在高温高压蒸汽管道上这么干——蒸汽管道属于压力管道，穿孔后直接补焊，局部应力集中反而可能让波纹管炸开。

很多人以为膨胀节和补偿器是两回事，就按普通管道补焊工艺来处理，结果把波纹的弹性给焊没了。其实膨胀节跟补偿器一样吗？答案是一回事，只是叫法不同。波纹管本身就是靠弹性变形来吸收位移的，焊补区域会硬化、失去弹性，这根膨胀节基本就废了。

什么时候必须换？别犹豫，直接换新的

这么说吧，只要穿孔直径超过波纹管壁厚的1/3，或者穿孔出现在波峰、波谷这些疲劳敏感区，别犹豫，直接换新的。尤其是大口径厚壁膨胀节、外压单式轴向型膨胀节这类承压较高的，补焊后焊缝区会成为新的薄弱点，蠕变断裂风险翻倍。还有，如果穿孔伴生导流筒损坏，更得整体更换。导流筒一旦破裂，内部冲蚀会加速，焊补等于白费功夫。

你猜怎么着？有些客户觉得换个膨胀节贵，非要补焊省钱。结果用了两天，第三天焊缝开裂，介质喷出来差点伤到人。设备停机一次损失比换个膨胀节大多了。安全第一，别赌运气。

预防比补救更重要

有腐蚀性介质，优先选衬四氟金属软管或聚四氟乙烯补偿器；高温烟气管道，用高温轴向型膨胀节加内衬耐温涂层；粉尘大的水泥线，用水泥行业金属波纹膨胀节或者矩型非金属膨胀节（织物纤维的那种），后者更换成本低、维修方便。

膨胀节的箭头方向指向介质流向，拉杆（膨胀节拉杆的作用是限制过度拉伸）在管道试压后才能松开。日常巡检多看波纹表面有没有锈坑、起皮，配合非金属膨胀节的检查周期，一年至少两次。

金属膨胀节穿孔，别当成普通漏洞来处理。它就像一个弹簧，焊补相当于在弹簧上打了个结，你觉得这弹簧还能正常工作吗？专业的事交给专业的人——如果你不确定穿孔原因，或者拿不准能不能修，直接联系厂家把现场照片和介质参数发过来。我们见过太多本来换个波就能解决的事，硬生生补成了整根报废。

Mistaken selection is the number one killer of short lifespan-material and construction determine how many years you will last

Two days ago, I met a customer who complained that the expansion joint in their factory leaked after two years. When I removed it, the bellows were rotten. Ask about the working conditions-high-temperature steam pipeline, with a pressure of 1.6MPa and a temperature of 350℃. As a result, the general-purpose corrugated expansion joint was chosen at the beginning, and the material was 304 stainless steel. Isn't this seeking death?

The matter of model selection, to put it bluntly, is "what horse matches what saddle". High-temperature working condition honestly high-temperature axial expansion joint, the material must be Inconel 625 or at least 321 stainless steel; For corrosive media, such as desulfurization flue gas, you have to consider lining PTFE hoses or non-metallic expansion joints (fabric fiber expansion joints), and even rubber compensators can carry them for a while. In cases where particle erosion is serious, such as air ducts in cement industry, metal corrugated expansion joints in cement industry must have wear-resistant guide tubes, otherwise they will be worn out in less than half a year.

Structurally, don't be sloppy. For pipelines with large axial displacement, straight pipe pressure balance expansion joint or compound straight pipe bypass pressure balance expansion joint is the positive solution; If you need to absorb lateral displacement, compound hinge transverse expansion joint or curved tube pressure balance expansion joint is right. Choosing the wrong type is like letting a sprinter lift weights, and scrapping is a matter of time.

The "invisible killer" of the installation link: the draw rod is not adjusted in place, the guide tube is installed backwards, and no matter how good the expansion joint is, it is useless

You can sit back and relax when you choose the right equipment? That's naive. The pits in the installation link, each deeper than the last. The most common one is that the tie rod nut is not adjusted properly. The function of the expansion joint tie rod is to limit the over-stretching or over-compression of the bellows, but many installation teams directly lock the tie rod, or simply don't dismantle the transportation fixtures. And guess what? As soon as the pipeline heats up, the expansion joint has no space to compensate, and the bellows is directly bulged and scrapped. The correct way is to remove the transport screw after installation, and then adjust the tie rod nut according to the compensation amount. For details, refer to the article "How to adjust the tie rod nut of expansion joint" in our station.

There is a more hidden problem-the deflector is installed backwards. The specific function of the expansion joint guide tube is to guide the flow direction of the medium and protect the bellows from scouring. However, when the direction of the arrow is reversed, the medium directly impacts the root of the bellows, and the rate of corrosion and wear doubles. Remember: The direction of the arrow must coincide with the direction of the media flow. Don't laugh, at least 30% of the installers on the site will make this mistake.

Wear and corrosion in operation: medium temperature, particle erosion, chemical attack, how many of these pits have you stepped on?

During normal operation, the expansion joint can't be laid flat just by installing it. If the medium temperature exceeds the design value of 10℃, the fatigue life of the bellows may be directly discounted by 50%. Particle scour? That's even more like cutting meat with a soft knife. Some cement plants use ordinary metal rectangular expansion joints, and there is no guide tube inside. After half a year, the wall thickness of the bellows is ground from 3mm to 0.5mm. Do you think it can be perforated?

Chemical attack is more headache. The acid condensate in the desulfurization system is a fatal blow to the metal bellows. At this time, either choose a PTFE hose or PTFE compensator, or use a non-metal expansion joint (rubber PTFE compensator is also OK), but we must pay attention to the rubber aging problem. By the way: Is there pitting corrosion and intergranular corrosion on the surface of the expansion joint in your factory? If so, it means that there is a problem with material selection, so change it as soon as possible.

Regular inspection is not a formality: corrugated pipe cracks, rubber aging, non-metal layer peeling, early detection and early treatment

Many factory inspections are to walk around with a flashlight and see nothing. In fact, there is a precursor to the failure of the expansion joint. Fine cracks or "orange peel"-like deformation appear on the surface of metal bellows, which indicates that it is close to the fatigue limit. Rubber compensator or non-metallic expansion joint, pay attention to whether the surface has hardened, cracked, or delaminated peeling. Especially rubber, affected by ozone and ultraviolet rays, has a life span of three to five years. When the time comes, it should be changed. Don't wait for it to leak before stopping.

Also, check for any changes in the pre-tightening forces of the tie rods and bolts. After the expansion joint has been running for some time, the tie rod may loosen, causing the bellows to offset. If the bellows is found to have eccentric wear marks, it means that the pipe support may sink or the compensation direction is wrong. Early detection and early adjustment, it's still too late.

Environmental factors alone? Heat preservation, support and drainage are done correctly, and the life will be doubled directly

Environmental factors are often overlooked, but are often the last straw that crushes the camel. For example, the expansion joint installed outdoors does not do heat insulation, and the metal brittleness increases at low temperatures in winter, so the bellows is easier to crack. Another example is the expansion joint on the steam pipeline. If there is no reasonable drainage design, the condensed water will accumulate at the trough, forming a "water hammer", which will impact and damage the bellows. How to solve it? Set a drain valve at a low position, or choose a sleeve-type pipe expansion joint with drain structure.

Support is also critical. The expansion joint itself does not bear the weight of the pipe, and guide brackets and fixed brackets must be set nearby. Many sites use the expansion joint as a pipe support, but as a result, the bellows is flattened and scrapped in three months. Think about it, is it worth an expansion joint worth tens of thousands of dollars to be scrapped in advance because several brackets worth several thousands of dollars were not done properly?

When to change hard bracing: Precursor judgment of failure and targeted prevention strategies

Expansion joints are not maintenance-free for life. If the following signals appear, change them quickly and don't take chances: First, the bellows has obvious cracks or perforations; Second, the fabric layer of the non-metallic expansion joint peels off in a large area, and the internal thermal insulation cotton or steel wire mesh can already be seen; Third, the surface of the rubber compensator is hardened to the point that it can't be pressed, or there are bubbles bulging; Fourth, the whole expansion joint is obviously distorted, which indicates that the displacement of the pipeline has exceeded the design range.

According to the medium characteristics and working conditions, select the right type in advance (such as special products such as corrugated expansion joints for power station industry, double hinge expansion joints for air-cooled island vacuum pipelines, etc.), strictly implement the specifications during installation, and regularly check and adjust in time during operation. If conditions permit, install displacement monitoring sensors at key positions, and watch the expansion and contraction of the bellows in real time, and you will have a bottom in your heart.

To put it bluntly, there are three words to prolong the life of expansion joints-select, install and raise. Choose the right thing, install it well, and maintain it diligently. To achieve these three points, it is not a dream to serve for more than ten years.

Non-metallic compensator leaking? Don't be in a hurry to change, try these steps to fix the leak first

I answered a phone call two days ago, and the customer said that the non-metallic expansion joint of their dust removal system began to smoke after half a year. When disassembled, the particulate matter in the smoke grinds a hole in the skin-this kind of thing is too common in cement and electric power industries. The non-metallic compensator (also called fabric fiber expansion joint) is leaking. Your first reaction is to replace it with a new one? Don't worry. Find out the leak point first. 80% of the cases can be fixed on site.

Where's the leak? Three common locations

Non-metallic compensator is used in flue gas pipeline and desulfurization system. The medium temperature is high and corrosiveness is strong, and the leakage is basically in three positions: one is the overlap joint between layers, the other is the sealing surface at the connection of flange, and the third is the riveting point or weld between the guide tube and the skin. And guess what? Many times it is not the skin itself that is broken at all, but the bolts are loose-the flange surface leaks, which can be solved by tightening. So the first step is not to rush to buy new pieces. First, take a flashlight and brush it with soapy water to see where the bubbles come from.

The medium contains sulfur or strong acid and alkali, and the sealing gasket becomes brittle after aging, and it will break when touched. At this time, you have to judge the type of leak: is it pitting perforation (small hole), sealing surface failure, or overall fatigue cracking? The countermeasures are completely different in different situations.

Preparation before mending leaks: Wrong material selection is equal to dry for nothing

Don't put any glue on it. This site hasrubber compensator、Rubber PTFE compensator、Non-metallic expansion jointAnd other products, leak repair materials must match the working conditions. High-temperature flue gas pipeline uses high-temperature resistant silicone rubber or fluororubber sealant, and ceramic fiber repair materials have to be replaced when the temperature exceeds 300℃. If the medium contains acid and alkali, use PTFE sealing tape, refer to this sitePTFE-lined hoseCorrosion resistance ideas.

Be sure to clean up before repairing the leak. Oil, dust accumulation and old glue layer have to be shoveled off to expose fresh substrate. Wipe it with acetone or alcohol, and wait until it is completely dry before starting. Otherwise, if you make it up, it will drop in two days.

By the way, if the flange surface leaks, check the bolts first-in many cases, it's just thermal expansion and contraction that causes loosening. Just take a torque wrench and re-tighten it according to the original torque. Don't get major surgery right up there.

Three Methods of Leakage Mending in Actual Combat

Method 1: Small perforations or cracks are patched with temperature-resistant cement + glass fiber cloth in multiple layers.Apply the glue to the break first, stick the cut fiberglass cloth, and then scrape it flat with a scraper to ensure that there are no bubbles. Apply one layer until it dries (usually 4-6 hours), then apply a second layer, at least three layers. Finally, brush a layer of temperature-resistant sealant on the outer surface to form a protective film. This method is suitable for perforations less than 20 mm in diameter.

Method 2: The local damage area is large, and the skin of the same material is cut and replaced.This site has ready-madeNon-metallic expansion jointSkin material, cut according to the damaged area, overlap width at least 50mm. Apply high-temperature-resistant adhesive to the overlap surface, and rivet and fix it with stainless steel press strips and self-tapping screws after pasting. Note that the spacing of the pressing strips should not exceed 150mm, and the riveting points should be staggered out of the original structural holes to avoid stress concentration.

Method 3: Total Outsourcing? Don't mess around.Someone asked if you could just wrap a metal compensator on the outside? No way. This site hasHigh temperature axial expansion joint、Universal corrugated expansion jointHowever, these metal parts are used for pipe displacement compensation, and their structure is completely different from that of non-metallic skin. Hard wrapping will limit thermal displacement, but accelerate damage. A more reliable way is to customize a short-joint non-metallic expansion joint to replace the damaged section. The size should match the original pipeline. Just provide the diameter, temperature, pressure and displacement when ordering.

Testing and routine maintenance after leak repair

It can't be put into operation directly after repairing, so do the airtightness test first. Brush soapy water or foaming agent on the repair area, introduce 0.05~0.1MPa compressed air (the design pressure of non-metallic compensator is low, so don't overpressure), and observe whether there are bubbles. If there is no air source, feel the air leak point with your hands after running, or use infrared thermal imaging to see the temperature abnormality-the temperature at the leak will be significantly lower.

Check the skin surface quarterly for blistering, delamination, and hardening. Especially in cement plants,Metal Corrugated Expansion Joints in Cement IndustryNext to the non-metal segment, dust wear is fatal. It is recommended to establish a ledger, record the location of each leak and the number of repairs, and accumulate data to judge when to completely replace it.

When should I give up patching and replace it with a new one?

If the same part is repaired more than twice, or the leakage area exceeds 30% of the total area, don't worry about it. The design life of non-metallic compensator is generally 3~5 years, and the aging will be accelerated by temperature, corrosion and mechanical fatigue. Also note that if the leak occurs in connection with this siteFlue gas baffle door、Electric plug-in insulation doorWhen connecting, consider whether the system vibrates too much. Vibration will cause fatigue cracking of the skin, which is useless. You have to install damping or switch to non-metallic expansion joints with reinforcing nets.

Don't save hundreds of dollars to make up for the leakage. As a result, the leakage expands and leads to the shutdown of production-the loss starts with tens of thousands of dollars. If you need to change, you will not lose money in the general ledger.

Metal expansion joint desoldering? Don't hurry to scold the manufacturer, the problem may lie in this

Two days ago, I met a customer who said that the metal expansion joint weld of their pipeline was cracked, and asked me if the quality was not good. Alas, who is not in a hurry when it comes to such things-media leakage, production line shutdown, or safety accidents. But let's say, don't rush to throw the blame on the manufacturer. For the problem of desoldering, we must first look at where the welding is located. Is it the bellows and end pipe connection? Or a deflector weld? Or is it a tie rod mount? The causes of desoldering in different positions vary a hundred and eighty thousand miles.

The cracking of the circumferential weld between the bellows and the end pipe is most likely due to fatigue or stress concentration. If the weld of the guide tube is cracked, it is mostly because the guide tube is worn through by the medium or the guide tube is installed backwards, causing the airflow to directly scour the weld. Tie rod bearing desoldering? You have to check whether the tie rod nut is loosened during installation, and whether the limit is regarded as a fixed support. And guess what? Many so-called "quality accidents" were checked over and over again. Either the installation team was fooling around, or the selection didn't match the working conditions at all.

The three most common pits for desoldering

First, fatigue.The pipeline system expands and contracts thermally every day, and the expansion joint expands and contracts repeatedly. Once the stress concentration at the weld exceeds the allowable value, cracks will slowly grow out. Especially the large-diameter thick-walled expansion joint or high-temperature axial expansion joint, the more extreme the working condition, the more sensitive the fatigue life. For example, the temperature of high-temperature flue gas pipelines in the cement industry often fluctuates above 400℃. Every time the bellows expands and contracts, the welds accumulate damage.

Second, corrosion.When there are chloride ions and sulfide in the medium, the weld seam will be corroded preferentially, and the strength will drop linearly. The expansion joint behind the desulfurization flue gas baffle door has a bad corrosion environment. If the right material is not selected or the corrosion resistance treatment is not done, the weld will become slag in less than half a year.

Third, the installation error.When leaving the factory, the tie rod nut was not loosened, the guide tube was installed backwards, and the cold drawing amount of the pipeline was not enough... These operations caused additional stress to be fully pressed on the weld. Many customers complained that "it took three months to desolder". As a result, when they went to the scene, they found that the direction of the guide tube arrow pointed to the opposite direction of the medium flow, and the airflow directly hit the bellows. Tsk, is this pot manufacturer wronged?

What about that?

Let's see the working conditions first. If it is a pipeline at normal temperature and low pressure, such as a general-purpose corrugated expansion joint, the cracking of the weld joint is probably a problem of the welding quality itself-the current is excessive, the welding electrode is wrong, and the groove is not handled properly. You have to re-weld if you should cut it off and re-weld it. Don't feel distressed. However, if it is a high-temperature steam pipeline or a high-temperature flue gas pipeline in the cement industry, desoldering is often a wrong selection. At this time, we have to consider changing the high-temperature axial expansion joint or the external pressure single axial expansion joint, so that the bellows can avoid the high-temperature area. Another situation: the displacement of the pipeline is too large, and the general-purpose type can't bear it at all, so it is necessary to use the double hinge transverse expansion joint or the straight pipe pressure balance expansion joint to share the stress.

On-site emergency treatment is also particular. Small cracks can be repaired in non-critical parts, but they must be welded with the same material electrode, preheated and controlled cooling speed. If the bellows itself is cracked, don't repair welding-the wall thickness of the bellows is thin, and it will burn through as soon as it is repaired, so replace it directly. In addition, it should be noted that before repair welding, check whether the guide tube is in good condition. If the guide tube is also worn out, the medium will directly wash the inner wall of the bellows, and desoldering is only a prelude. When replacing, it is best to check the adjustment status of the expansion joint tie rod nut simultaneously to ensure that the pre-tension or pre-compression meets the design requirements. As for how to adjust the tie rod nut? After screwing the nut to the limit position, reverse back half a turn to one turn, so that the expansion energy saving can expand and contract freely. Look at the design drawings for specific values, don't screw them blindly by hand feel.

Prevention is really worry-free

The selection stage is not cheap. When providing information to the design institute, write clearly the temperature, pressure, displacement and corrosive medium. For example, the expansion joint behind the flue gas baffle door has a high sulfur content in the medium, so corrosion-resistant alloy or PTFE-lined scheme must be used. In the installation stage, be sure to look at the direction of the arrow on the expansion joint (flow direction mark), and one end of the guide tube faces the direction of the medium. During the operation stage, check the appearance of the weld regularly, tap and listen to the sound, and do penetration testing if conditions permit. Don't forget, the life of the expansion joint is directly tied to maintenance-you let it run over the limit, and it will strike sooner or later.

In the final analysis, 80% of the desoldering of metal expansion joints are not deliberately cut corners by manufacturers. Find the root cause, prescribe the right medicine, change the type, repair the welding, don't curse your mother as soon as you come up. Pipeline safety depends on the cooperation of three rings of selection, installation and maintenance, and one less ring will lead to moths.