How to choose the insulation type of flue expansion joint? Follow these four steps to select and install without error
Two days ago, I met a customer, and the flue temperature soared to 650℃. As a result, I bought an ordinary metal expansion joint and installed it. In less than three months, the bellows cracked, and the insulation layer was burned to the point where there was no slag left. Tsk, thousands were spent for nothing. Actually chooseFlue expansion joint insulation typeThis matter is not that mysterious. As long as you follow the following four steps, you can handle it.
Step 1: Find out your flue operating conditions first-temperature, pressure, and medium concentration must all be missing
Don't come up and ask the seller, "How much can this expansion joint withstand?" You have to find out your own family first. Specifically, note down three data:
- Maximum operating temperature: Is it steady state temperature or instantaneous peak? For example, the desulfurization flue sometimes reaches 180℃, but it may rush to 250℃ in an instant, so the selection has to be considered according to 250℃.
- Working pressure: Positive or negative pressure? Some flues are slightly negative pressure (-3kPa to-5kPa), and some positive pressure can reach 0.1MPa. Different pressures, bellows wall thickness and reinforcing ring design are completely different. Like oursCorrugated expansion joint for power station industryThe positive pressure condition will be equipped with a reinforcing ring.
- Media composition: Are there corrosive gases such as SO₂ and HF in the flue gas? What is the concentration? Stainless steel still rust when it encounters high concentration of chloride ions. If the medium contains high sulfur, it is recommended to use corrosion-resistant alloy or PTFE-lined scheme, you can refer to ourPTFE-lined hose。
Writing these three parameters on a note, taking photos and sending them to the manufacturer is more useful than saying a hundred sentences of "complicated working conditions".
Step 2: Choose metal or non-metal for insulation layer? Plate according to displacement and temperature resistance
This step is the watershed. Many people come up and ask, "Is the thermal insulation type a layer of cotton on the outside"? Yes, but what cotton to wrap, how to wrap, the gap is big.
Metal insulation layer (such as stainless steel shell + aluminum silicate fiber cotton): Suitable for high temperature and large displacement occasions. And guess what? Two days ago, there was a customer of a cement factory. The flue expansion joint insulation type needs to absorb an axial displacement of 150mm, and the temperature is 850℃, so it can only be put onHigh temperature axial expansion jointEquipped with metal insulation sleeve. Because the non-metallic insulation layer is easy to collapse at high temperature, the insulation cotton is crushed when it is displaced.
Non-metallic insulation layer (e.g. fabric fiber + multilayer insulation felt): Suitable for scenarios with low and medium temperature (≤350℃) and small displacement. Like oursNon-metallic expansion joint (fabric fiber expansion joint)It can withstand a certain temperature itself, and it is enough to wrap a layer of insulation felt on the outside. What are the advantages? Cheap, easy to install, good shock resistance. The disadvantage is that it is not resistant to high pressure and easy to wear.
When the temperature exceeds 400 DEG C and the displacement exceeds 50 mm, the metal insulation type is preferably selected; On the contrary, non-metals are enough.Don't worry about it. If you choose the wrong choice, you will repair it every day.
Step 3: Three details that must be confirmed before installation: direction of guide tube, tie rod nut, insulation dressing
Many expansion joints are not worn out, but installed. You must avoid these three pits:
- The direction of that guide tube must be opposite to the direction of the medium flow。 The function of the guide tube is to guide the flue gas to pass smoothly and avoid directly flushing the bellows. If it is installed backwards, the flue gas will directly hit the bellows, and the life will be at least halved. How to judge? Look at the arrow on the expansion joint. The arrow points to the flow direction. OurUniversal corrugated expansion jointAndThe metal rectangular expansion joints are all marked, don't be silly.
- Don't screw down the tie rod nut。 Many people screw the tie rod nut to death in order to "fix it". As a result, as soon as the pipe expands, the tie rod pulls the expansion joint and deforms it. Correct practice: When installing, adjust the nut so that the expansion joint is at a free length, and loosen it a little appropriately after the pipe is connected, leaving a 3-5mm gap. How exactly to adjust? Refer to our question and answer "How to adjust the tie rod nut of the expansion joint".
- Expansion joints must be left for thermal insulation dressing。 The insulation layer cannot be wrapped too tightly, otherwise the insulation layer will squeeze the expansion joint when the pipe expands, causing the bellows to be stressed. Generally speaking, an empty section of 50mm at each end of the expansion joint is not covered with heat insulation, or a detachable heat insulation sleeve is used. Have you ever seen one of those packs that squeezes the bellows flat at the end? Alas, it's all a lesson of blood.
If it isDouble-sealed single-axis circular baffle doors orFlue gas baffle doorFor this type of flange, check the flatness of the flange surface before installation, and don't shake the gasket.
Step 4: Don't step on pits in routine maintenance-check the damaged insulation layer and fatigue of corrugated pipe regularly
- Damaged insulation layer: Especially outdoor flue, wind blows, sun and rain, once the insulation layer is cracked, cold air enters the interior, thermal expansion and contraction are uneven, and the bellows are quickly fatigued. It is recommended to inspect once a quarter, and use a flashlight to show whether there is any white leakage (the insulation cotton is exposed) and whether there is any rust trace. If you find any damage, repair it quickly. Don't delay it.
- Fatigue crack of bellows: This doesn't look good to the naked eye, but there is a stupid way: listen to the sound. Gently tap the bellows with a screwdriver. Normally, it is a crisp metallic sound. If it is stuffy or has a hoarse sound, it means that there may be cracks inside. In addition, observe whether the tie rod nut is loose. If the nut is loose, it means that the displacement exceeds the design value. If the pressure is unstable, you can consider installing a pressure gauge for monitoring.
Don't say that in order to save trouble, some power plants only inspect it once every two or three years. As a result, the heat insulation type of the flue expansion joint directly collapses, and the flue gas leaks. The environmental fine is ten times more expensive than that of the equipment. So, regular maintenance is about saving money.
Don't just look at the price when choosing a model,Flue expansion joint insulation typeIt's about the safety of the entire plumbing system. If you are unsure, send the working parameters directly to the manufacturer and ask them to recommend specific models-such asHigh temperature axial expansion joint、Non-metallic expansion jointOrCorrugated expansion joint for power plant industryThere's always one for you. Following these four steps will help you avoid at least 80% of the pits.