How to remove square flue expansion joint? Look at the type before you do it
Two days ago, a customer called and said that a square flue expansion joint in the factory was leaking, and he was anxious to change it. As a result, it was stuck halfway through the dismantling-the bolts were rusty, the tie rod couldn't be twisted, and the fabric layer was torn. He asked me: How should you dismantle this thing when you sell it?
Good question. How to disassemble the square flue expansion joint is really not just a matter of twisting it with a wrench. Before dismantling, regardless of the type and working conditions, hard dismantling will only pull and deform the flange surface, and even make the pipe bracket crooked. Today, I will explain the two common methods of disassembling square expansion joints, breaking them apart and crumbling them.
First, there are two main types of square flue expansion joints: metal rectangular and rectangular non-metal
Metal rectangular expansion jointAndRectangular non-metallic expansion joint。
Metal rectangular expansion joint, structurally is corrugated pipe plus flange, with tie rod and nut. Used for high-temperature and high-pressure flue gas pipelines, such as power station boiler outlets and desulfurization flues. The material of corrugated pipe is usually stainless steel, and the temperature resistance can reach above 600℃.
Rectangular non-metallic expansion joint, the main body is a fabric fiber layer (non-metallic expansion joint, also called fabric fiber expansion joint), with a guide tube inside and clamped by a metal frame outside. It has lower temperature resistance, but a large amount of compensation, which is suitable for low-pressure, large-size flues, such as dust collection pipes in steel mills.
These two things, the disassembly method is completely different things. You take the idea of dealing with metal parts to dismantle non-metal, and the fabric layer is ripped off as soon as you pull.
2. Three issues that must be clearly understood before disassembly: medium, pressure and bolt state
Before you start, ask yourself three questions. If you can't answer them, don't touch the wrench.
First, what is the medium?Is it hot smoke, cold air, or corrosive gas? If it is wet flue gas after desulfurization, which contains sulfuric acid condensate, the metal bolt may have been corroded so that only one layer of skin is left, and it will break when twisted.
Second, is there still pressure in the tube?Some maintenance drawings save trouble, and the flange is removed before the system is completely relieved. If the square flue expansion joint is disassembled under pressure, the flange surface suddenly separates, and the high-pressure gas will collapse the bolt like a bullet. It's no joke, every year there are cases of injuries as a result.
Third, what is the current state of the bolt?First, take a flashlight to see if there is rust, deformation, and whether the tie rod nut has been welded to death. There's a simple way to judge: tap the head of the bolt with a wrench and listen to the sound-crisp instructions have room for loosening, stuffy instructions have rusted to death.
3. Disassembly of metal rectangular expansion joint: loosen the tie rod first, and then disassemble the flange
There is a core principle in the disassembly sequence of metal rectangular expansion joints:Release the pre-tightening force first, then remove the connecting bolts。
Step 1: Loosen the tie rod nut.The metal rectangular expansion joints are equipped with tie rods, which are used to limit the excessive stretching of the bellows. When disassembling, first loosen all the nuts at both ends of the pull rod, so that the bellows is in a free state. Be careful not to dismantle all, leave one or two buckles to prevent falling off.
Step 2: Diagonal method to remove flange bolts.Many people are used to dismantling them one by one from one side. As a result, the flange is unevenly stressed, and the remaining bolts are stuck. The correct way to do this is: first remove the two bolts of the diagonal, then remove the other pair of diagonals, step by step like removing a tire. Every time you remove one, check the flange surface for misalignment.
Step 3: Top off the flange surface.After the bolts are all removed, the flanges may still stick together because the gaskets will carbonize and bond after high-temperature operation. Gently wedge with a flat shovel from the flange gap and shake left and right to separate the two flange surfaces. Don't smash the flange ear plate with a sledgehammer, which will deform the bolt hole.
The worker cut the bolt directly with a cutting gun. As a result, the cutting flame burned through the bellows and the whole expansion joint was scrapped. The wall thickness of the corrugated pipe of the metal rectangular expansion joint is usually only 0.5~1.5mm, and it is worn as soon as it is ironed.
4. Disassembly of rectangular non-metallic expansion joint: Pay attention to the fabric layer and guide tube
Rectangular non-metallic expansion joints are much more delicate. It is a metal press frame on the outside, a fabric fiber layer on the inside, and a flow guide tube in the middle.
Step 1: Remove the bolts of the press frame.First remove the metal press frame bolts that hold down the fabric layer. Note: This kind of bolts are usually large in number and closely spaced, so it is easy to leak when disassembled by one person. It is recommended to use a marker to make a mark between the press frame and the flange, so that it can be aligned when put back.
Step 2: Carefully separate the fabric layers.After using the fabric fiber layer for a period of time, it will be smoked hard by smoke and lose its elasticity. Do not pull hard when disassembling. Use scissors to cut off the attached spacer along the edge of the press frame. If there are tar-like deposits, spray some loosening agent first.
Step 3: Take out the guide tube.Rectangular non-metallic expansion joints usually have a guide tube inside, which is used to guide air flow and protect the fabric layer. The guide tube is inserted in the flue. When pumping out, it should follow the axial direction and not skew, otherwise it will scratch the anticorrosion layer on the inner wall of the flue.
If the fabric layer of non-metallic expansion joint has been broken, the insulation cotton inside will leak out. Before dismantling, confirm whether there is any insulation cotton leakage. If so, you need to wear a dust mask and goggles first-the glass fiber sticks to the skin and itches unbearably.
5. What about the bolts that can't be removed? Several practical treatment methods
When removing square flue expansion joints, screw rust is the most common pit. I'll list a few measured methods that work:
- Osmotic loosening agents.Spray WD-40 or special bolt loosener on the root of the thread and wait 15 minutes before screwing. If it is a high-temperature bolt, it works better with bolt coolant (instantaneous cooling creates cold shrinkage gap).
- The tapping method.Use a copper or wood hammer to tap the side of the bolt head a few times to shatter the rust layer. Don't use a hammer, it will round the bolt head.
- Heating method.Heat the nut part with oxyacetylene flame (be careful to avoid bellows), use the principle of thermal expansion and contraction to expand the nut, and then twist it quickly. This method can be used for the tie rod nut of the metal rectangular expansion joint.
- Grooving method.If it can't be twisted, use an angle grinder to cut a straight slot in the head of the bolt, and then screw it with a large screwdriver. This is a destructive means. After removing the bolts, it is wasted, but it keeps the flange.
Don't try to clamp the bolt rod with a pipe plier and turn it hard, which will break the screw rod and make it harder to remove it if it breaks in the bolt hole.
6. Don't rush to suit after dismantling, check these parts first
It was finally removed, so don't try to put on new pieces quickly. Spend 10 minutes checking the following places to save you the hassle of reworking later.
Is the flange surface flat?Lean against it with a ruler to see if there is any deformation. The flange of the square flue expansion joint may warp after long-term use because it is subjected to thermal stress. If the deformation exceeds 1mm/m, the new expansion joint will not be sealed tightly.
Are the bolt holes elongated?The bolt holes will become oval at high temperatures. When this is found, it is necessary to ream the hole with a reamer or re-drill the hole after repair welding.
Is the deflector intact?If it is a rectangular non-metallic expansion joint, check the removed deflector for wear. The head of the guide tube is the easiest to wear. Once perforated, the airflow will directly scour the fabric layer, resulting in the newly replaced expansion joint breaking in half a year.
Is there a settlement in the bracket?Settlement of the pipe supports at both ends of the expansion joint can cause the new expansion joint to be forcibly twisted when installed. Measure the actual distance between the two flanges, and compare it with the length of the new expansion joint. If the error exceeds 5mm, the bracket should be adjusted first.
In the final analysis, the disassembly of the square flue expansion joint depends on strength and experience. You have mastered these steps, and the next time you meet them, you will have the bottom in your heart. If you encounter particularly tricky working conditions-for example, all the bolts are rusted in the blind hole and the flange is seriously deformed-you should find technical support from the manufacturer, and don't carry it hard.