1. Find out first: Why do you have drainage holes in your flue expansion joint?
To be honest, many people don't even think about this problem at first-isn't the flue expansion joint used to absorb thermal expansion and contraction? What does it have to do with the drain hole?
But think about it, what's running in the flue? Smoke! The flue gas discharged from coal-fired, gas-fired and biomass boilers will condense as soon as the temperature drops. Especially those clean flue gas after wet desulfurization, the temperature is low, the humidity is high, and the condensed water is surging. If this water accumulates in the trough of the expansion joint, it will not only corrode the bellows over time (such asCorrugated expansion joint for power station industryOrMetal rectangular expansion joint), and it is easy to freeze and damage the structure in winter. I met a friend from a power plant two days ago, and they usedUniversal corrugated expansion jointNo drainage hole was opened, and as a result, the condensed water poured back into the insulation layer, and the whole expansion joint froze and cracked. Tsk, the loss was not small.
So, uh,Flue expansion joint drain holeIt's not chicken, it's life-saving. Its core task is one: to drain the accumulated fluid away, and not to let the water stay in the trough.
2. Step 2: Where and how big is the drainage hole? Step-by-step teaching you how to size
Okay, since we decided to make a hole, how do we choose the location? What is the right size? Don't worry, follow these steps.
Location: Find the lowest point
The reason is simple-the water flows low. The drainage hole must be opened at the lowest point of the expansion joint, that is, the bottom of the trough. If you install it on the side or on the high side, the water will not drain clean, which is equivalent to boiling for nothing. Usually forCompound hinge transverse expansion jointOrExternal pressure single axial expansion joint, there will be an inclination angle when installing, so the lowest point should be confirmed according to the actual inclination direction.
Size: Not too big or too small
The opening diameter is generally DN15~ DN25 (that is, 15mm to 25mm). Too small is easy to block, too large affects the structural strength. If it is a large diameter flue (e.g. more than 1 m in diameterLarge diameter thick wall expansion joint), two holes can be opened and symmetrically distributed to ensure drainage efficiency.
Tips:After opening the hole, remember to polish the edge and remove the burrs, otherwise it is easy to scratch the sealing gasket or cut the drain pipe in the future.
3. Step 3: Install the drain pipe and valve to prevent the condensate from flowing back
The hole is opened and the mouth is open? That's not okay. Smoke will leak out of the holes, and cold air from outside pouring in will exacerbate the condensation. So it has to be fitted with drain pipes and valves.
How to connect the drain pipe?
Use a piece of metal hose (like the one in the stationMetal hose) or stainless steel pipe, welding a stub from the drain hole and then leading to a sump or gutter. A ball valve or globe valve should be installed on the stub. Usually, the valve is always open, so that the condensed water flows away naturally; Close the valve during maintenance to prevent smoke from escaping.
Don't forget the water seal
If your flue is running under negative pressure, it is not enough to rely on the valve alone. You have to set up a water seal device. The easiest way is to make a U-shaped bend at the end of the drain pipe to maintain a certain water level, which can both drain and seal. Alas, this piece is easily ignored by many old drivers. As a result, the condensed water poured back into the expansion joint and the bellows was soaked.
Note:If you are usingNon-metallic expansion joint (fabric fiber expansion joint)The drainage hole is best made of corrosion-resistant materials, such as PTFE-lined hoses, because the non-metallic expansion joint itself is afraid of acid, and the condensed water is often acidic.
4. Step 4: Don't be sloppy in daily inspection. What should I do if the drainage hole is blocked?
The drain hole is not opened once and for all. It is inevitable that there will be dust and scale in the smoke, and the drainage hole may be blocked over time. What about that?
Inspection frequency
Check it at least once a month. Focus on whether there is water flowing out of the drain outlet. If there is no water for a long time, it may be blocked or the valve is not open. Also touch the bottom of the expansion joint for any water bulging-especiallyRectangular non-metallic expansion jointThe water at the bottom will bulge, which can be seen at a glance.
How to dredge a blockage?
Close the valve first, remove the drain pipe, and poke with thin wire or compressed air from the inside out. If the blockage is severe, it can be rinsed with water. Note: Do not hurt the inner wall of the bellows when dredging. If it doesn't work, you have to enlarge the drainage hole a little or re-open the hole.
And guess what? In order to save trouble, some factory maintenance personnel directly welded the drainage hole to death. Doesn't that mean laying a mine for yourself?
5. Attachment: When selecting the model, you can directly tell the manufacturer to have an expansion joint with a drainage hole
To be honest, the most hassle-free way is not to open holes yourself in the later stage, but to ask the manufacturer when purchasing. For example, if you buyMetal Corrugated Expansion Joints in Cement IndustryOrDesulfurization flue gas baffle doorWhen matching the expansion joint, clearly tell the manufacturer: "I want one with drainage hole, open it at the lowest point of the trough, with DN20 pipe and ball valve."
Factory portraitHigh temperature axial expansion joint、Straight pipe pressure balanced expansion jointSuch standard products can actually customize drainage holes. Say in advance that you can also do a good job in anti-rust treatment, which is much safer than on-site hot opening.
Whether you open the hole yourself or let the manufacturer customize it, don't make do with the drainage hole. The flue is full of real money. A stagnant water ruins the expansion joint, and the cost of replacing it with a new one plus the loss of downtime is enough for you to buy several dozen drain valves. Is that the truth?