Ash Leakage Is Not Just "Dirty"-How Deadly Is Ash Leakage from Metal Expansion Joints?
Two days ago, I met a customer, and I called in the middle of the night to scold my mother-the metal expansion joint at the tail of their kiln leaked ash, and the ash was sprayed out along the gap of the bellows, and the scene was like snow. The operator can't keep his eyes open when he wears a dust mask, and half a pound of ash can be poured out of his shoes when he comes back from the inspection. You think it's just a hygiene issue? That's naive.
Ash leakage is not a minor problem. The ash is a hard particle that washes the bellows wall at high speed. Guess what the result is? The wall of the pipe is worn and thinned, the stress is concentrated, and finally the pipe is burst by clicking. The pipe burst is not done by blowing it up. High-temperature gas is sprayed out, the production line is shut down, and emergency repair takes several hours or even days. Cement plant, power plant, steel plant, which dares to stop? Stop for a minute is a loss of tens of thousands of dollars.
Moreover, ash leakage will accumulate in the corrugated gap of the expansion joint, occupying the thermal compensation space. As soon as the pipe expands and contracts by heat, the corrugations are squeezed together, the metal fatigue is accelerated, and the life is directly cut in half. Is that the truth?
Where does the ash come from? Find out some common causes of ash leakage first
Don't rush to scold the quality of the expansion joint, the reason for ash leakage is not so simple. Let's break it up and break it up.
- Failure or missing guide tube: There is generally a guide tube inside the metal expansion joint, whose function is to guide the airflow to the middle and prevent high-speed ash from directly hitting the bellows. If the guide tube is worn and perforated, falls off, or is not installed at all during installation, the ash will go straight to the bellows. Over time, the bellows wear out, and ash runs out of the gaps. Look at the common ones we see at our stationMetal Corrugated Expansion Joints in Cement IndustryAndCorrugated expansion joint for power station industry, the deflector is standard, but some bargains will be saved, and the consequences will be endless.
- Installation misaligned or skewed: The pipeline is out of alignment, the expansion joint is twisted by hard screwing the bolts, and the local force of the bellows is excessive, resulting in micro-cracks. Ash seeps out of these cracks. A few days ago, a customer said that they replaced the expansion joint with a new one, and it leaked in less than three months. I went to the scene to see that the flange surface was 5mm misaligned and the bellows had bulged.
- Wrong selection of corrugated pipe material or wall thickness: The working temperature is high and the dust concentration is high, so ordinary 304 stainless steel can't bear it. You have to use the universal corrugated expansion joint to deal with the sulfur-containing flue gas at a high temperature of thousand degrees. It is a matter of time before ash leaks. Such asHigh temperature axial expansion jointHigh temperature resistance upper limit, suitable for high temperature dusty pipeline;Non-metallic expansion joint (fabric fiber expansion joint)It works well in ultra-high temperature and low dust environment, but its life is not as good as that of metal when used in abrasive dust pipes.
- Damage to outer corrosion protection layer or outer sheath: Some expansion joints have rubber or metal sheaths on the outside. If the sheath is broken, ash can get in from the outside. This reason is often overlooked.
On-site Emergency Treatment: Correct Practice of Plugging Leakage, Cleaning Dust and Temporary Reinforcement
Ash leakage has happened and the production line can't be stopped. What should I do? Emergency plans should be reliable and don't mess around.
Let's startplugging: Find a special high-temperature-resistant leak plugging glue or ceramic fiber cotton to plug the leakage point and paste it to death. Note: Do not use ordinary cement or epoxy resin, which will crack as soon as the temperature rises. Temporary measures can be patched with stainless steel skin and fixed by spot welding, but be careful when welding, don't burn through the bellows. Be sure to clean the dust before welding, otherwise the slag will be mixed with ash, and the more you weld, the more you leak.
AgainDust cleaning: Use compressed air to blow off the dust accumulation near the corrugated gap and the guide tube. Don't flush with water! Water enters the inside of the corrugation, accelerating corrosion. After blowing, check the thickness of dust accumulation. If the accumulation is serious, it means that the guide tube may not work.
And finallyTemporary reinforcement: If the expansion joint itself is not broken, but only the connecting flange leaks, it can be installedManual plug-in insulation doorOrElectric plug-in insulation doorCut off the air source and refix the flange bolts. Or use the tie rod to temporarily lock the displacement of the expansion joint to reduce the deformation. But the tie rod must be adjusted according to the specification- -How to adjust the tie rod nut of expansion joint？ Generally, the lock nut should be loosened so that the tie rod is in a free state and cannot bear the thrust of the pipeline. Forced locking can pull out the device.
Radical cure plan: three steps of type selection, installation and maintenance
Emergency is an emergency, and if the root problem is not solved, it will have to leak later. The radical cure should be smoothed out from scratch.
Step 1: The choice of model should be right
Select according to medium temperature, dust concentration, pressure and displacement. First choice for high temperature dusty pipelineHigh temperature axial expansion jointOrMetal Corrugated Expansion Joints in Cement IndustryWith wear-resistant guide tube inside. If space is limited, you can also considerCompound straight pipe bypass pressure balanced expansion jointThe compensation amount is large and the blind plate force is not generated. Flue gas pipeline (e.g. desulfurization system) recommendationDesulfurization flue gas baffle doormatchRectangular non-metallic expansion jointThe non-metallic layer has good elasticity, strong sealing property and low ash leakage rate. Don't be greedy to buy the general-purpose type for cheap, and do it professionally.
Step 2: Installation should be standardized
Check the direction of the guide tube before installation-the direction of the arrow refers to the flow direction of the medium, and if the guide tube is installed backwards, it is a display. Ensure coaxiality during flange connection, and the deviation does not exceed 2-3mm. Tighten the bolts evenly with a torque wrench. Don't tighten them and loosen them. Tie rod and adjustment nut are pre-tensioned or pre-compressed according to product drawing, and the positioning bolt should be loosened before running. For details, refer toCorrect installation method of expansion joint of large tie rod。
Step 3: Maintenance should be regular
Check the wear of the guide tube when the machine is shut down for maintenance, and replace it immediately if the wear exceeds 50%. The wall thickness of the bellows is sampled by ultrasonic thickness gauge, and it is found that it is thinned to 80% of the design thickness, which is included in the replacement plan. In addition, clean the external ash regularly to keep the heat dissipation good-ash is the insulation layer, and the temperature of the bellows increases after a long time of accumulation, and the stress increases. In the stationMetal rectangular expansion jointIt is commonly used on large-section flues, and ash is easier to accumulate, so it is best to set a dust cleaning port.
When should I change? Don't wait until the pipe bursts to regret it
Some factories thought of "supporting another maintenance cycle", but only changed it when the pipe burst. It is several times more expensive to exchange than to repair. Don't hesitate if any of the following signals appear:
- The amount of cracks, perforations and ash leakage visible to the naked eye increased obviously;
- Bulging, twisting and local deformation appear on the bellows surface;
- The guide tube falls off or is perforated and cannot be repaired;
- The wall thickness is reduced by more than 30%;
- Significant radial displacement or axial deviation of the expansion joint (indicating fatigue failure).
At this time, go directlyCompound hinge transverse expansion jointOrCurved tube pressure balance expansion joint, cooperate withFlue gas baffle doorCut off isolation and replace the most efficiently. Don't feel bad about that little money. Think about the loss of shutting down the kiln after the pipe burst-take a cement plant as an example. It takes two or three days for the rotary kiln to stop once and then heat up to normal production, and the cost of coal and electricity alone is hundreds of thousands. This account, you do it yourself.
Anyway,Ash Leakage Treatment of Metal Expansion JointIt's not a trivial matter. Only by understanding the root cause, making a solid temporary emergency response, and putting the radical cure plan in place in one step can the pipeline be clean and the workshop safe. Don't wait for the ash to reach the ceiling before you remember to repair it. At that time, you will lose not only money, but also people's hearts.