Step 1: Find out where the water leak is first-Quick judgment of three common fault types
The flue expansion joint is leaking, which is quite annoying. But don't dismantle it as soon as you come up. Take 10 minutes to judge the type of fault first, which can save more than half of your wrongful money. There are three common situations of water leakage:
- Weld cracked: The body of the metal bellows is not broken, but water seeps at the weld position. Shine a flashlight around and you can see fine cracks or water stains. This is mostly because the tie rod is not adjusted properly during installation, or the pipe vibrates too much.
- Bellows perforation: Needle holes or corrosion pits appear on the metal expansion joint, and even water can be seen directly spewing out. Friends engaged in chemical industry and desulfurization are common, because the flue gas contains acidic condensate.
- Nonmetallic layer agingNonmetallic expansion joints (fabric fibers) are bulged, delaminated, or the rubber compensator is hard and cracked. This leak tends to be a large area seepage, not a spray.
Stop the furnace or machine first, wait for the flue to cool, take a flashlight to shine from the outside, and look inside with a mirror reflection (or simply drill in and check). Alas, don't trouble, this step is wrong, and the rest is all in vain.
Step 2: Different leakage methods and different treatment methods-targeted repair steps of metal/non-metal expansion joint leakage
See where the leak is? Okay, let's prescribe the right medicine.
Metal expansion joint (general corrugated expansion joint, corrugated expansion joint for power station industry, etc.)
- Weld leakage: Clean up and repair welding with argon arc welding. Pay attention to the temperature control when welding, don't bake the bellows deformed. Do a colored flaw detection inspection after repairing.
- Bellows perforation: Don't think about welding, it is useless to weld. The correct way is to temporarily plug the leak with a special patch (stainless steel sheet) and high-temperature-resistant sealant, and then arrange a new part. If you are in a hurry, you can try to use clamps and rubber gaskets for emergency response first, but it won't last long.
Non-metallic expansion joints (rectangular non-metallic expansion joints, rubber compensators, etc.)
- Fabric layer damaged: Cut a piece of non-metallic compensator fabric of the same material (don't use messy substitutes), bond it with high-temperature glue or silicone sealant, and press a layer of stainless steel strip to fix it on the outside. Remember: The glue should be selected to withstand the temperature of smoke, otherwise it will fall off as soon as it is baked.
- Aging and cracking of rubber: Just change the rubber compensator. It doesn't make sense to make it up. The aging rubber is not strong enough to last for three months.
And guess what? Two days ago, a client told me that he pasted glass glue three times, and each time it couldn't last for a week. Tsk, this isn't fooling around.
Step 3: How to choose when changing parts? — — Match the products of this site according to the working conditions (with pit avoidance reminder)
When it comes to the step of replacing the expansion joint with a new one, many people's first reaction is to "buy the same one and install it". Wrong! You have to look at the working conditions, otherwise it will leak when replaced. Keep these three core parameters in mind:
- Medium temperature: Flue gas temperature exceeds 200°C? Don't use rubber compensators, choose honestlyMetal rectangular expansion jointOrHigh temperature axial expansion joint。 Flues below 150°C, withNon-metallic expansion joint (fabric fiber expansion joint)More cost-effective, corrosion resistant and good to install.
- pressure: Positive pressure flue (such as induced draft fan outlet) selectionUniversal corrugated expansion jointOrExternal pressure single axial expansion jointStrong pressure resistance. Negative pressure flue (such as in front of dust collector) has high sealing requirements, so it is recommendedDouble-sealed single-axis circular baffle doorUse with expansion joints.
- Corrosivity: The flue of the desulfurization system contains acidic water vapor? Must usePTFE-lined hoseOrPTFE compensatorOrdinary stainless steel bellows will be scrapped after one year.
Pit avoidance reminder:Don't be cheap and buy expansion joints without deflectors. The guide tube can prevent the airflow from directly washing the bellows. Many leakage cases are caused by the guide tube being too short or not. From our stationStraight pipe pressure balanced expansion joint、Curved tube pressure balance expansion jointAll with deflectors, you can confirm with customer service when selecting the model.
Step 4: Don't go in a hurry after repair-Key points of pressure test and preventive maintenance
After replacing the new expansion joint, you think it's done? Too naive. Ignition directly without testing, and rework if something goes wrong. Get it done in two steps:
- Pressure test: Seal both ends of the flue with blind plates and pass compressed air (the pressure is 1.25 times the design pressure). Hold pressure for 15 minutes and brush all welds and bellows surfaces with soapy water to see if there are bubbles. No? OK, deflate and prepare for production.
- Preventive maintenance: ① Check whether the tie rod nut is loose, and tighten it according to the method in our previous article "How to adjust the tie rod nut of expansion joint". ② See if there is any dust or water around the expansion joint, and clean it in time. ③ Twist the bolts once a quarter to prevent loosening caused by thermal expansion and contraction. Isn't it simple?
Also, don't forget to install one near the flue expansion jointFlue gas baffle doorOrElectric plug-in insulation door。 In this way, the airflow can be cut off during maintenance, and the whole line does not need to be stopped every time.
Step 5: What if you leak repeatedly? — — Type selection and transformation ideas of eradicating from the source
If you repair it according to the above steps and replace it with a serious product, but it leaks again within a few months-then you have to find the reason from the design level. There are three common root causes:
- The selection is small: The compensation of the expansion joint is not enough, and the pipeline is thermally expanded and contracted to deadpull the corrugated pipe, resulting in fatigue cracking. Check the total displacement of the pipeline. If it exceeds 70% of the rated compensation of the expansion joint, you have to change to the model with a larger compensation. For example, change the single form toCompound hinge transverse expansion jointOrCompound straight pipe bypass pressure balanced expansion jointAnd can absorb displacement in multiple directions.
- Pipeline vibration source is not eliminated: The vibration of the fan or pump is transmitted directly to the expansion joint. The solution is to add installationMetal hoseOrrubber compensatorAs a vibration damping section, the vibration is separated.
- Media corroded more than expected: For example, the sulfur content of flue gas was not high in the original, but later the coal type was changed, and the acid concentration skyrocketed. At this time, you have to upgrade the material: replace ordinary stainless steel with 316L or duplex steel, or use it insteadPTFE-lined hoseThoroughly withstand the corrosion.
Flue expansion joint water leakage treatment, seven points in type selection, three points in installation. You spent half a day figuring out the working conditions in the early stage, and you can save several years of worry later. If you are really unsure, please send the on-site photos and parameters to our technical department to help you match the most suitable plan-don't guess blindly, waste money and delay production if you guess wrong.