How to choose the metal expansion joint of desulfurization flue? Follow these 4 steps to spend less money

First, find out how "ruthless" your desulfurization flue is-the characteristics of the working conditions determine what you should use

To be honest, the environment of desulfurization flue is "acid, hot and dirty". Think about it, the flue gas carries sulfuric acid, sulfurous acid, high and low temperatures, and a lot of dust particles. If you just buy an ordinary expansion joint and install it, hey, it will leak in less than three months.

Then how to judge "fierce or not"? You have to figure out at least these three things:

• Temperature Range:The inlet temperature of the desulfurization system is generally 130~180 ℃, and the outlet temperature drops to 50~80 ℃. If it is close to GGH (flue gas heat exchanger), it may rush above 200℃ locally. That's when you have to considerHigh temperature axial expansion jointOrCorrugated expansion joint for power station industryThe material has to be heat-resistant stainless steel (such as 316L and 254SMO). Don't believe that "general-purpose" can take it all-that's all fooling.
• Corrosive Components:After wet desulfurization, there is a large amount of condensed water in the flue gas, which is extremely acidic. Ordinary carbon steel rust wears in two days. At this timePTFE-lined hoseOrPTFE compensatorThat would come in handy. If you are afraid that PTFE will not withstand negative pressure, then useMetal rectangular expansion jointThickened wall design, lined with anti-corrosion coating.
• Displacement Type:Does the flue go straight or with turns? Is there any device vibration? Is there more axial displacement or lateral displacement? If it is a large diameter flue (such as a rectangle of 2 meters ×3 meters), it is recommended to useMetal rectangular expansion jointAnd can absorb multidimensional displacements. If the pipe is slender and limited in space,Compound hinge transverse expansion jointMore flexible.

Tips:Don't just look at the data sheet given by the manufacturer. It's best to write down the highest temperature, lowest temperature and pressure fluctuations at your site. Some customers have encountered "instantaneous overtemperature", and the design temperature is 150℃. As a result, the flue gas rushes in at 200℃, and the bellows directly burns out of the hole. You think about it, is this wrongful money spent unjustly?

Second, don't just look at the price in the selection. If you don't understand these three key parameters, you will suffer a loss

Two days ago, I met a buddy from a thermal power plant. The picture was cheap, but it leaked after half a month of installation. When I removed it, I saw that the wall thickness of the bellows was only 0.8mm, and the deflector was not anticorrosive. Do you think it's irritating? When selecting, you have to keep an eye on these three parameters:

• Bellows wall thickness:Desulfurization flue is generally not less than 1.2mm. If the pressure is high or it contains abrasive dust, it is recommended to be above 1.5mm. It's too thin, and it cracks after fatigue after a few high-frequency vibrations. From our stationLarge diameter thick wall expansion jointThe wall thickness can be more than 3mm, which is specialized in treating bad working conditions.
• Guide tube:This stuff is not a decoration. The guide tube can guide the air flow and avoid the high-speed smoke gas directly washing the bellows. You will understand if you go to the question and answer on the function of the expansion joint guide cylinder. But note-the material of the guide tube must also be corrosion-resistant. Don't use ordinary carbon steel, at least 316L or higher duplex steel.
• Compensation amount:Don't just look at the nominal "compensable 100mm", but the actual needs. How to calculate? Simply put: pipe length × linear expansion coefficient × temperature difference. For example, for a 50-meter-long carbon steel flue, with a temperature difference of 100℃ and a linear expansion coefficient of 0.012mm/ (m·℃), the total elongation is 50×0.012×100=60mm. You leave a 20% margin when choosing a model, such as choosing a model with a compensation amount of 75mm. If there is not enough space, you can useCompound straight pipe bypass pressure balanced expansion jointIt can balance the axial force itself without transmitting it to the pipe support.

Note:Some sellers will deliberately increase the amount of compensation.

3. Don't let the workers fool around when installing. Remember that these 5 actions can be used for several years

If you choose the right product, if you install it wrong, it will still be useless. The most outrageous thing I've ever seen is that the worker screws the expansion joint tie rod nut so hard that the bellows can't move at all, so why install it? It's better to weld the root steel pipe. Remember these 5 actions:

1. Check the mounting clearance first:When the expansion joint leaves the factory, the manufacturer will preset a pre-stretch or pre-compression amount. For example, the direction of the compensator arrow (you see that question and answer) points to the direction of thermal displacement, so it must be aligned when installing it, so don't install it backwards.
2. Removal of transport support:Some expansion joints (especiallyStraight pipe pressure balanced expansion joint) Will come with a temporary support screw, which must be removed before installation. Otherwise, the bellows will be pressed all the time, and the compensation amount will not be enough after turning on.
3. Design fixed bracket:The pipes at both ends of the expansion joint must be provided with fixing brackets (main fixing brackets) and guide brackets. If you let the pipe run around on its own, the expansion joint will be pulled apart in minutes. Specific referenceCorrect installation method of expansion joint of large tie rodThat article, there are detailed steps in it.
4. The direction of the guide tube is toward the direction of the flue gas:Don't reverse this. The bell mouth of the deflector should be facing the direction of the airflow, so that the bellows can be protected. If it is installed backwards, the smoke directly impacts the root of the bellows, and the life is shortened by half.
5. Finally check bolt torque:All flange bolts should be tightened in diagonal order, and the torque value should refer to the manufacturer's specification. It's too tight to crush the flange sealing surface, it's too loose to leak air. The commonly used torque value range is 70~120N·m, depending on the bolt specifications.

By the way, there is another small detail: after installation, do the airtightness test first, check the leakage with soapy water at low pressure (such as 0.1MPa), and don't turn it on as soon as it comes up. In case of leakage, you have to peel open the insulation layer and dry it again.

Fourth, don't panic in daily inspection, teach you a few tricks to judge whether to change or not

The expansion joint is usually inconspicuous, but if it breaks, the whole desulfurization system may shut down. You can't wait for it to leak sour water all over the floor before you fix it, can you? Learn to read these signals yourself:

• Look at the corrugated surface:Take a flashlight. If there are cracks, corrosion pits and bulges, it means that the material has reached its limit. In particular, it is distinct from that spiral corrugation of a metal hose,Metal rectangular expansion jointThe U-shaped corrugation is more prone to dust accumulation and corrosion, so you have to take a look.
• Listen to the sound:If you hear a "hissing" sound during operation, nine times out of ten it is an air leak. Sweep with a portable ultrasonic leak detector to locate the leakage point.
• Touch temperature:The infrared temperature measuring gun measures the surface temperature of the expansion joint. If the temperature in a certain section is abnormally high (for example, 30℃ higher than the side), it may be that the guide tube falls off or is blocked internally.
• Check the displacement:After shutdown, measure the actual compression/elongation of the expansion joint. If the design compensation amount is 80mm, you find that it has been stretched to 90mm, then you have to change it quickly, because there is no margin.

If you decide it's time to change, don't panic. We have complete alternatives in our site, such asNon-metallic expansion joint(Fabric fiber) can replace metal in some low temperature segments, with lower cost and more convenient installation. But that high temperature section still have to be usedUniversal corrugated expansion jointOrExternal pressure single axial expansion joint。 When you are not sure, dump this article directly to the manufacturer and let him help you choose-anyway, in our business, experience is more useful than theory.

Don't save hundreds of dollars. Once there is a problem with the metal expansion joint of desulfurization flue, maintenance costs, shutdown losses and environmental fines. You can calculate that number, enough to buy ten good ones. Follow the above four steps, spend less wrongful money, and be stable for a few years-isn't it good?