What is the cause of the deformation of the compensator? The old master only talks about these four points
Two days ago, I met a customer and called in a hurry, saying that a batch of newly installed products in their factoryUniversal corrugated expansion jointAfter only three months of operation, the bellows began to bulge and twist, and some directly cracked. The other end of the phone was obviously anxious: "Is there something wrong with the quality of your products?"
I asked him about the working condition parameters and installation details, and he didn't make a sound-the compensation given by the selection was nearly half less than the actual thermal displacement, the medium temperature exceeded the design value of 40℃, and the material was still ordinary 304. And guess what? This is not a product problem. It is obviously that the account was not clearly calculated in the early stage. In fact, the deformation of the compensator is not a metaphysics at all. The old masters can count four pain points for you with their eyes closed. Today, we will break them open and crush them to talk thoroughly.
1. Selection rollover: insufficient compensation, wrong material, deformation is only a matter of time
Let's talk about the selection first. Many people think that the compensator is just a corrugated pipe. Just buy a similar size and install it. That would be a big mistake. The first major reason for the failure of the compensator is that the mine has been buried in the selection stage.
A cement factory used the pipeline at the end of the kilnMetal Corrugated Expansion Joints in Cement IndustryThe working temperature of the pipeline is 650℃, and the design thermal displacement is 80mm. As a result, a model that can only compensate 40mm was chosen at the time of purchase. After two months of operation, the bellows was forcibly stretched to the limit, and cracks appeared directly at the trough-this was not deformation, it was pulled off.
Let's talk about the material. Many users can't distinguish the corrosiveness of the working medium. For example, if the flue gas pipe contains sulfide, if you choose ordinary stainless steel, the inner wall will quickly be penetrated by pitting. The correct approach is to directly go to the flue gas desulfurization scenarioDesulfurization flue gas baffle doorOrPTFE compensatorOr internally lined with fluorine. Like oursPTFE-lined hose、Rubber PTFE compensatorIs specially designed to deal with strong corrosive media. The material is wrong, the deformation is just the appearance, and the inside has collapsed long ago.
Second, installation and digging: the guide frame is installed randomly, cold tightening is not done, and the pipeline stress is all carried by the compensator
If you choose the right model, everything will be fine? Thinking too much. There are more problems in the installation process than in the selection and rollover.
Guide frame and cold tight.
First, the guide frame is not something you can install casually if you want. Many field workers install the guide frame too far from the compensator, or simply don't install it, causing the pipeline to deflect laterally while axially displacing. Should have been created byCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointThe angular displacement bearing is fully pressed on the bellows. And the result? The bellows bulge sideways, expanding and deforming like blowing a balloon.
Second, cold tightness. Steam pipes and high-temperature flue gas pipes must be pre-stretched by cold tightness before operation. But some construction teams are too troublesome, so they save it directly. For example, a 300℃ steam pipeline, the ambient temperature is 20℃ when installed. If it is not cold and tight, the thermal elongation during operation is all carried by the bellows. The elongation per meter of pipeline is calculated as 0.012mm/℃, and a 50m pipeline is 168mm-you let aHigh temperature axial expansion jointTo withstand the displacement beyond the design value, it is strange not to deform.
Another point, check the tie rod nut of the expansion joint when installing. OurLarge tie rod expansion jointAfter installation, the tie rod nut must be loosened to the designated position, otherwise it is equivalent to locking the expansion joint, and the pipe stress is all suppressed on the bellows. Before, I encountered a customer who didn't dismantle the transportation protection nut, and as a result, the bellows was directly broken as soon as the temperature rose-it was distressed. A pipe cost tens of thousands because a screw was not unscrewed.
3. Corrosion and scaling: It looks good, but in fact the interior is riddled with holes
Deformation is not necessarily caused by mechanical stress. Chemical corrosion is the killer of "boiling frogs in warm water".
TakeNon-metallic expansion joints (fabric fiber expansion joints)For example, when used in flue gas pipelines, the acidic condensate in the flue gas will slowly penetrate into the fiber layer, resulting in delamination and bulging. But on the outside, it may just look a little discolored on the surface, and when you press it with your hand, the inside is already crispy.
Metallic ones are more obvious. Such asCorrugated expansion joint for power station industryThe corrosion resistance of 304 stainless steel will decrease rapidly due to long-term exposure to sulfur-containing flue gas in the tail flue of the boiler. Chloride ions and sulfur ions will induce stress corrosion cracking in the wet environment of 60-80℃. Instead of watching the deformation, the grain boundaries are first corroded, and then the bellows break along the intergranular cracks. Another exampleThe directly buried (fully buried) expansion joint is buried in the soil. If the anticorrosive layer is damaged, the chloride ions in the groundwater directly contact the bellows, and the perforation speed is very fast, and the bellows with a wall thickness of 1.2mm can be eroded in half a year.
Therefore, the anti-corrosion piece should be selected according to the characteristics of the medium. Preferred choice for strong acid and alkali environmentPTFE compensatorOrPTFE-lined hose； High temperature flue gas preferredNon-metallic expansion joint； If wear resistance and erosion resistance are required, considerLarge diameter thick wall expansion joint。 Don't wait until the interior is riddled with holes to regret it, by then the compensator deformation will be irreversible.
4. Fatigue and over-limit: it is not broken once, but it is too many cycles to bear it
Some compensators seem to have no problems in installation and selection, but bellows cracks still appear after two years of operation. What is the reason for this? Fatigue.
Note that fatigue is not a violent operation, but repeated cycles of small displacements. Such asDouble hinge expansion joint for air-cooled island vacuum pipelineThe pressure fluctuates frequently in the vacuum system, and the pipeline has to experience dozens of thermal expansion and contraction every day. Each node of the bellows is repeatedly stretched-rebounded, hundreds of times a day, or hundreds of thousands of times a year. By the time the design fatigue life is reached (usually 100,000 or 200,000 times), microcracks will naturally occur.
Exceeding the limit is more straightforward. Sometimes the pipeline system will have instantaneous overtemperature and overpressure due to process fluctuations. The compensation amount you designed is 50mm. Under a certain sudden working condition, the pipeline is displaced by 70mm, and the bellows is directly pulled to the plastic deformation zone, and it can never go back. Each cycle afterwards exacerbates this deformation until it breaks.
For this case, a safety margin must be allowed when selecting the model. For example, the design temperature is 300℃, and it is best to choose 400℃ gradeHigh temperature axial expansion joint； The design pressure is 0.6MPa, and the specification of 1.0MPa is selected. In addition, for frequent start-and-stop pipeline systems, you can chooseCompound straight pipe bypass pressure balanced expansion jointOrStraight pipe pressure balanced expansion jointThey can reduce the axial force of the main bellows through the internal pressure balance structure, thus prolonging the fatigue life.
To summarize: Don't let the compensator take the blame for you
Writing this, you should understand: compensator deformation reason? In the final analysis, it is the superposition of four dimensions: selection, installation, environment and fatigue. To be honest, the vast majority of compensator failures are not the problem of the product itself, but the user fails to understand the working conditions thoroughly.
The compensator you use in your plumbing system, isUniversal corrugated expansion jointStillSleeve type pipe expansion joint？ Are there regular checks for corrosion on the inner walls of the bellows? If you haven't done it, take one apart and have a look when it is down for maintenance next week. There will definitely be a surprise. Tsk, don't ask me how I know.
If you have questions about the selection and installation of compensator, welcome to our website to see the product information,Metal hose、rubber compensator、Rectangular non-metallic expansion joint…There are specific parameters for the whole range. Choose the right way, use the right way, transform? Nonexistent.