1. How did the leak happen? Material fatigue, corrosion or installation buried mine
When many people see the leakage of the metal expansion joint, their first reaction is "it's over, you have to change it". Don't rush yet. This matter of leakage was probably not suddenly exploded, but slowly saved up. You think about it, metal expansion joints- -whether they areUniversal corrugated expansion joint、High temperature axial expansion jointStillCorrugated expansion joint for power station industry— — In the pipeline system, it is pulled, compressed and heated every day. Over time, the wall thickness of the bellows will gradually become thinner, which is called material fatigue. Especially thoseLarge diameter thick wall expansion jointAlthough it looks strong, once micro-cracks appear at the weld position, leakage is a matter of time.
Let's talk about corrosion. Tsk, this one is the biggest headache. If the medium in the chemical pipeline is a little acidic and alkaline, or the environmental humidity on the site is high, pitting and intergranular corrosion will occur on the surface of the bellows. I met a client two days ago, and theirStraight pipe pressure balanced expansion jointIt began to leak after three years of use. When I removed it, I saw that the inner wall was full of hemp spots-the medium was chlorine-containing wastewater, and I didn't pay attention to the material when selecting the model.
And the installation of buried mines. Such asLarge tie rod expansion jointThe tie rod nut is not adjusted to the pre-tensioned position, orexpansion joint guide tubeIf the direction is reversed (the function of the guide tube is to guide the flow direction of the medium and reduce erosion), the leakage rate will be doubled directly. Don't ask me how I know it. I have more experience on the spot, and there are all kinds of weird things.
2. Plugging with pressure, welding repair or overall replacement? The cost performance of the three schemes
When there is a leak, there are usually three ways: pressure plugging, welding repair and overall replacement. Let's break down their respective costs and applicable scenarios.
Pressure plugging— — Suitable for micro-leakage, low-pressure, non-hazardous media. Use a special fixture with sealant to enclose the leakage point. The advantage is that the downtime is short and it can be done in a few minutes; The disadvantage is that it treats the symptoms rather than the root cause, and the internal corrosion continues. Like someFlue gas baffle doorThe nearby expansion joint, the medium temperature is low, the pressure is low, and the pressure plugging can last one and a half years.
Welding repair— — RightMetal Expansion Joint Leakage RepairSpeaking, this is the most cost-effective option, but only if the leak point is not on the bellows crest or trough. If the crack is on the end straight pipe section or reinforcing ring, it can be repaired directly. A real case on the scene: a chemical plantExternal pressure single axial expansion jointWhen the weld cracked, the welder repaired it with argon arc welding with stainless steel electrode for 20 minutes, and it didn't leak again for two years. It costs about 2,000 yuan, and it costs 20,000 yuan to replace it with a new one. However, note that welding will produce heat-affected zones and reduce local strength, so it is necessary to do local heat treatment or polish smooth after welding.
Overall replacement-It has to be replaced only in the following cases: the corrugated pipe is corroded and thinned in a large area, the fatigue crack propagates into a web, or the medium is toxic and harmful. Such asDouble hinge expansion joint for air-cooled island vacuum pipelineOnce it leaks and can't be repaired, the vacuum system requires extremely high sealing, so it is safer to replace it directly with a new one. When replacing, be sure to check the model, size and pressure level of the old and new parts, don't buy the wrong one (this site hasModel and size of expansion jointInformation can be referred to).
3. Key points of on-site operation: Don't ignore the details of guide tube, tie rod nut and weld position
It's really time to get hands on patching, and there are a few details that can save you a lot of rework time.
- guide tube: Confirm whether the guide tube has fallen off before repairing. Some leakages are actually caused by the erosion and perforation of the guide tube by the medium, resulting in the medium directly washing the bellows. In this case, change the guide tube alone, without moving the bellows. This site has an article dedicated toSpecific Function of Expansion Joint Guide TubeIt is recommended to flip through.
- tie rod nut: Many people find that the expansion joint elongation is wrong after repair, and it can't be installed back. The reason isExpansion joint tie rod nutNot marked. Write down the current position of the nut before operation, and restore it to its original state after repair. If it isCompound hinge transverse expansion jointThe tie rod also assumes the function of limiting position, and once loosened, the bellows may be permanently deformed.
- Weld position: When repairing welding, do not directly overlay welding on the crest of the bellows-the stress is concentrated there, and it will crack when welded. The correct way is to drill crack stop holes at both ends of the crack, and then weld from the crack stop holes to the middle. If the crack is on the bellows body and the length exceeds 1/3 of the wave pitch, it is recommended to give up the repair and replace it directly.
Commonly used equipment on site — —Metal hoseAs a temporary connection pipe to bypass the leak point, it is also a smart emergency solution. Such as inDesulfurization flue gas baffle doorIn the system, a section of PTFE-lined hose is temporarily connected, which can support until the furnace is shut down for maintenance.
4. The key to cure the root cause: from selection to regular inspection, avoid missing again next time
Repairing is just a stop loss. To really avoid repeated leakage, we have to solve the problem from the root. First of all, the selection should not be sloppy. Media contains corrosive gases? Then usePTFE compensatorOrPTFE-lined hose。 High temperature? chooseHigh temperature axial expansion joint, material at least 316L. Large vibration?rubber compensatorOrNon-metallic expansion joint (fabric fiber expansion joint)It may be better to carry, but be aware of the pressure limits.
Secondly, don't try to save trouble when installing. Such asDirect buried (fully buried) type expansion jointInstalled underground, if drainage and anti-corrosion are not done well, it may have been rusted out after a few years. AndElectric plug-in insulation doorThe nearby expansion joint must be insulated after installation to prevent condensed water from accumulating and corroding.
Finally, regular inspections are indispensable. Don't wait until you leak to rush. It is recommended to check the bellows surface every six months for rust, bulge and crack; Measure each year whether the compression or stretching of the expansion joint is within the allowable range (refer toStiffness and Calculation Formula of Bellows）。 LikeSleeve type pipe expansion jointThis kind of structure, focus on the wear of the sealing packing, timely compression or replacement.
In the final analysis, if you can repair the leakage of the metal expansion joint, don't rush to dismantle it, but after repair, you have to remember: think more about the next selection, take a second look during installation, and spend ten more minutes during inspection. There is no conflict between money and saving trouble, but the conflict is luck.