Step 1: Get down on the flue and see where the tear is first-determine the type and location of the tear
If you find that the original flue expansion joint is torn, don't rush to call the maintenance team. You first lean over by yourself, get down to the edge of the flue, turn on the flashlight, and see where the breach is. No joke-when many old masters heard of "tearing", their first reaction was to dismantle it and replace it with a new one. As a result, they were replaced and torn again, and it was dry for nothing.
YesThe metal part split, orThe non-metallic fabric layer is torn？
- If the crack is in a metal bellows, it is usually an elongated straight split, or a tortoise crack appears at the bottom of the corrugated valley. This is mostly fatigue fracture, or thinning by corrosion.
- If the break is on the skin of the non-metallic expansion joint (fabric fiber expansion joint), it is often the edge of the line, the middle burned through, or scratched by hard objects. Pay attention to whether it is close to the guide tube-the guide tube falls off or wears out, and the high-temperature smoke is sprayed directly on the skin, and it burns through in a few strokes.
Tips: Take a photo and mark the size of the break from the edge of the flange. When selecting or repairing later, the manufacturer asks you for these data, and you can report them casually, saving you from running back and forth on the scene.
Step 2: Don't rush to change, first find out the culprit-temperature, corrosion and displacement. Which one is doing the trick?
Expansion joint tears are never unprovoked. Think about it, the working conditions of the original flue: high temperature, sulfur, and sometimes a little negative pressure. There are only three common "murderers":
- Temperature exceeds standard: The designed temperature resistance is 400℃, but it actually runs to 500℃. The skin of the non-metallic expansion joint can't bear it, and it is carbonized and cracked. The metal may undergo high-temperature creep, and the bellows slowly deforms until it tears.
- Corrosion leakage: The condensed water in the flue gas is acidic. If the PTFE-lined hose or metal bellows is not treated with anti-corrosion treatment, local pitting corrosion will develop into perforation and then tear.
- Displacement exceeding limit: Pipe thermal expansion and contraction or foundation settlement, causing the expansion joint to be stretched or compressed beyond the design stroke. Do you see if the tie rod nut has been pushed dead? If the nut is already attached to the end plate, it is too much displacement and it is torn by deadlift.
How to check? Take a thermometer gun to hit the surface temperature of the expansion joint and compare the design value. Use PH test paper dipped in condensed water to measure acidity and alkalinity. As for the displacement, find a ruler to measure the current length of the expansion joint, and then compare it with the original length at the time of installation. Too much difference, that is the pot of pipes.
attention: If you find that there is a problem with the pipe bracket (such as the spring hanger stuck), it is useless to replace a hundred expansion joints-fix the bracket first, then replace the parts.
Step 3: Cramming-How to plug it in an emergency if it leaks?
As soon as the original flue leaked, the environmental protection data immediately went red. Spare parts are still on the way, what to do? Plug the leak first and buy time.
- Small cracks or pinholes: Use high-temperature resistant cement (alumina-based, which can carry to 800℃) to rub it directly, wrap it with a layer of ceramic fiber cloth, and tighten it with stainless steel cable ties. Don't use regular epoxy, it will melt as soon as you open the smoke.
- Large break (such as non-metallic skin tearing more than 30cm): Find a piece of non-metallic expansion joint scrap or high-temperature canvas of the same material, cut it into a shape larger than the break, stick it to the break with high-temperature-resistant sealant, press a steel plate on the outside, and tighten it with bolts. There is really no material, so temporarily stack several layers with asbestos cloth and hold hoops outside-but note that asbestos cloth can only last for a few hours, so you have to change it as soon as possible.
- Broken tie rod or bolt: Don't screw hard, first pull both sides of the pipe with a manual hoist, so that the expansion joint is not stressed, and then dismantle the old bolts and replace them with new ones. Otherwise, once the tie rod is broken, the pipe will bounce open with a "bang", and people may be injured.
Plugging is just a symptom, and you should know it in your heart: it lasts for up to 72 hours, and you must arrange for shutdown and replacement.
Step 4: Which one can handle it? — — Select metal rectangle or non-metal expansion joint according to working condition
The new expansion joint was chosen wrong, and the tear will be worse next time. Original flues are mostly rectangular in section, so the common choice isMetal rectangular expansion jointAndRectangular non-metallic expansion joint。 How to choose? Look at three points:
- Temperature: If the flue gas temperature exceeds 300℃ for a long time, metal rectangular expansion joints are preferred, such as corrugated expansion joints (with guide tubes) used in power station industry. When the temperature is lower than 300 ℃, non-metallic expansion joints (fabric fiber expansion joints) can be used, which is low cost and convenient to install.
- Corrosivity: If the flue gas contains high sulfur and condensed water, the metal bellows is easily corroded. At this time, the non-metallic expansion joint is more corrosion-resistant-the skin is fluororubber or PTFE coated, and acid can't do anything about it. Or you use PTFE-lined hoses for partial connections, which can also be carried.
- displacement direction: The pipeline is mainly axial expansion and contraction, and the menu axial type is selected. If there is also horizontal or vertical displacement, the double hinge transverse or universal type is required. Don't use the universal corrugated expansion joint to resist lateral displacement, it will tear the fastest.
Take an example: Two days ago, there was a customer of a cement plant. The original flue temperature was 280℃, there was a small amount of condensed acid, and the displacement was mainly 20mm in the axial direction. We recommended himMetal Corrugated Expansion Joints in Cement Industry(with internal liner), used it for two years with no problems. He bought a general-purpose one himself before, and it cracked in three months.
If you are not sure, directly take the photos taken in the first step and the data measured in the second step to consult the manufacturer. Don't pat yourself on the head.
Step 5: Install it and stop tearing it-install the clearance, guide tube and pull rod, none of them can be careless
The new expansion joint was bought back, and three pits were noted when installing:
- Installation clearance: Expansion joints usually leave the factory in a pre-stretched or pre-compressed state. You want to adjust the tie rod nut according to the ambient temperature at the time of installation so that the actual length of the bellows is equal to the designed length. Only when it is installed in the cold state can it expand and contract normally in the hot state. How exactly to adjust? Refer to the article "How to Adjust the Tie Rod Nut of Expansion Joint" we wrote earlier. Simply put, it is: remove the transportation fixture, screw the tie rod nut to the marked position, and then lock it. Don't screw too hard, leave a displacement allowance.
- Direction of guide tube: The deflector must be directed toward the medium flow direction! The direction of the arrow is the direction of the flow. Install it backwards, and the smoke directly washes away the ripples, which will wear out in less than half a year. Moreover, a gap of 3~5mm should be left between the guide tube and the bellows, which cannot be stuck to death, otherwise it will get stuck after thermal expansion.
- Tie rod locking: If the expansion joint comes with a tie rod, after installation, be sure to screw the backup nut on the outside of the tie rod nut to death. Otherwise, vibration in operation, the nut itself will loosen, the expansion joint will lose its restraint, and instantly over-displacement will tear.
Final Check: After installation, manually disc the expansion joint (if available) to see if there is any sticking. Verify that the flange bolts are symmetrically tightened and the torque is uniform. Then heat up the smoke, and check it again after half an hour to see if there is any abnormal noise or local overheating.
Raw flue expansion joint tearing is no trivial matter, but by following these five steps, you will go from discovery to done in no more than one shift. Next time you have a similar problem, you will have the bottom in your heart.