Two days ago, a buddy who was doing a desulfurization project called and said that the non-metallic expansion joint in their factory was torn apart after less than half a year. I asked him how the deflector was installed, and he was stunned for a moment-deflector? Isn't that something that metal compensators only have?
Well, I really don't blame him for this. Many people get a non-metallic compensator, and their attention is all on the fabric band, thinking that is the core. As for the board inside, it is a windshield at best. But the truth is,Non-metallic compensator internal deflectorIn case of design or installation problems, the life of the entire compensator is directly discounted in half. Today, we'll break it apart and crumble it into pieces.
1. What does the deflector do? — — Not just "blocking the wind"
Think about it, the pipeline is running with high-temperature flue gas or dust gas, and the flow rate is always more than ten meters per second. Without the deflector, the airflow directly impacts the inner wall of the fabric loop, with two consequences:
One is wear and tear. The particles rubbed against the band like sandpaper and wore out in a few months.
The second is vortex. The airflow swirls inside the compensator, causing vibration, flange bolts may loosen, or even cause the entire expansion joint to fail.
Therefore, the first function of the deflector is to guide the airflow smoothly and reduce the direct erosion of the ring belt. But that's not over, it has to take on a more stealthy task:Prevent dust accumulation。 Non-metallic expansion joints are used on flue gas pipes, and dust is easy to settle in corrugated gaps. Once the ash accumulates more, the circle belt loses its activity space, and the compensation amount is gone. The deflector has a reasonable shape and angle, so that the airflow forms a sweep inside and carries the ash away.
To put it bluntly, this board is like an invisible bodyguard, carrying beatings and sweeping ash.
2. Material and structure: How to choose the "skeleton" under the fabric band?
You say the loop is the skin, and the deflector is the bone. The bones are not hard, and the skin is useless no matter how thick it is.
The commonly used material is carbon steel or stainless steel, depending on the medium temperature. Generally, Q235B is used below 350℃, and 304 or 316L has to be replaced if it exceeds 350℃. Some working conditions contain sulfur or chlorine, so consider duplex stainless steel or more corrosion-resistant alloys (such as C276). But don't be superstitious about stainless steel at the beginning-in some alkaline dust environments, carbon steel is more able to withstand it, because corrosion products can form a protective film.
In terms of thickness, 3mm ~5mm is enough in most cases, but if the medium is mixed with iron chips or large particles (such as clinker dust in cement industry), it is recommended to add it to more than 6mm.
Structurally, we're standingRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)The internal deflector is usually formed in a conical tubular shape or a bell mouth shape. The advantage of the cone is that the resistance is small, and the bell mouth can better cover the circumferential direction of the ring belt. There is another detail: there should be a gap between the deflector and the flange, and it should not be welded to death, otherwise thermal expansion and contraction will tear the ring belt.
3. Difference with metal compensator guide tube: don't apply it with experience
Old masters who are used to metal expansion joints can easily move the set of metal compensator guide tubes directly. But the logic of these two things is completely different.
The guide tubes of metal compensators are mostly thin-walled tubes (1~2mm), whose main function is to separate the medium from the bellows and reduce the direct contact of the bellows with the fluid. Because the metal bellows is afraid of corrosion and wear, the guide tube is a sacrificial layer. Moreover, metal compensators generally have tie rods or hinges to bear the pressure thrust, and the guide tube is not stressed much.
Nonmetallic compensators are different. The ring belt itself is very soft, and the pressure and thrust are carried by the flange and frame. Although the internal deflector is also called a deflector, it actually also bears the responsibility ofSupport ring belt shapeThe function of. Especially under negative pressure, the ring belt will be deflated, and the deflector must provide a rigid inner wall profile to prevent the ring belt from collapsing. Therefore, the thickness should not be too thin, and the rigidity should be enough.
In addition, the end of the internal deflector of the non-metallic compensator is usually flanged or crimped to avoid sharp corners scratching the band. The guide tube of the metal compensator is directly rolled into a cylinder, polished and done. Manufacturing costs and process requirements vary.
4. The three easiest pits to step on during model selection (flow rate, medium, installation direction)
Flow rate.
Some people think that the deflector, just choose a size. Tell you, when the flow rate exceeds 15m/s, the front end of the board will be flushed out of a slot. If the speed is higher, such as the flue gas pipeline on the dry cement production line, the wind speed often reaches 25m/s, and the leading edge of the deflector has to be hardened-either cemented carbide surfacing or ceramic lining. Otherwise, it will be pierced in half a year.
The second pit: the medium.
Two days ago, a customer boughtDesulfurization flue gas baffle doorAt the same time, several non-metallic compensators were equipped, which were used after wet desulfurization. The wet flue gas contained a lot of sulfuric acid condensate, and as a result, the deflector was made of carbon steel, which rusted out in two months. The correct approach is to either use stainless steel (such as 316L) or make an anti-corrosion coating on the surface of carbon steel, but the coating is easy to fall off, so simply use acid-resistant non-metallic materials as deflectors-such as FRP or PP. However, note that the temperature should not exceed 80℃, otherwise fluoroplastics should be considered.
Third Pit: Installation direction.
This one is the most injustice. There is generally an arrow on the deflector, pointing to the direction of the medium flow. But many people pretend backwards! If the direction of the arrow is wrong, the bell mouth of the deflector becomes a windshield, and the airflow is directly held in the ring belt, which will blow up the ring belt when the pressure is high. Refer to our website aboutArrow direction of expansion jointThe answer, that arrow is the flow direction of the medium, can't be wrong.
5. Installation and maintenance: the strength of screwing is particularly important
The deflector is usually bolted to the flange, but some manufacturers weld it directly to the inside of the flange to save trouble. Never do this! Welding deformation will cause the flange plane to be uneven, the sealing gasket will not be pressed tightly, and it is a trivial matter to run and leak. After a long time, the stress concentration at the root of the ring belt will tear.
The correct way to do this is:
The bolts should be twisted symmetrically, and the torque should be according to the value given by the manufacturer-generally, the bolt torque of M16 is between 80~120N·m. If it is too large, the flange edge will be pulled and deformed, and if it is too small, the ring band will not be sealed tightly.
In addition, when installing, pay attention to leaving enough gap between the deflector and the ring belt, usually 10~20mm. If the gap is too small, the ring belt will push against the board when it expands, which will affect the compensation amount; The gap is too large, and the airflow is easy to rush in from the side, losing the diversion effect.
In terms of maintenance, don't forget to check whether the deflector is warped or perforated every time you overhaul. It doesn't matter if there is a little bulge on the surface of the ring belt, but if the deflector is found broken, it must be replaced immediately-the debris may get stuck in the pipe and block the equipment downstream.
And guess what? Sometimes customers complain that the compensator is leaking, and after checking for a long time, it is found that the ring belt is punctured after the deflector is broken. So I'll see you next timeNon-metallic compensator internal deflectorDon't think of it as an optional accessory.