1. Why is the installation direction a "fatal" problem? How severe are the consequences of reverse installation?
Two days ago, I met a customer who made desulfurization pipelines, saying that they had installed a batch of non-metallic expansion joints (fabric fiber expansion joints) on the spot, and as a result, air leakage began to occur within a few days of operation. When I removed it, I saw that the guide tube was blown over by the airflow-it was directly rolled into a twist. After asking, I found out that they had reversed the direction of installation.
Non-metallic compensators are not as "durable" as metal hoses. Its fabric layer and deflector design have definite directionality. If the arrow is pointed backwards, the high-temperature flue gas will directly wash the fabric layer, which will lead to seal failure, air leakage and air leakage, and the whole set will be scrapped-the fabric will burn through, the guide tube will fall off, and even the flange may be deformed. What's even more headache is that the replacement of non-metallic compensators often requires shutting down the furnace and production, and the loss is not a matter of thousands of dollars. The loss of shutting down production in one day may be 100,000.
Isn't it just a direction? How much difference can it make? I'm telling you, it's a big difference. If the guide tube is installed backwards, the medium directly impacts the compensator body, and the layer of fiber fabric can't withstand the erosion of high temperature and particulate matter at all. It can take as short as one or two months or as long as half a year, and problems will happen. Therefore, the installation direction is really no joke.
Second, understand the arrow-the "hidden rule" of the flow direction of the guide tube and the medium
Most non-metallic compensators, including rectangular non-metallic expansion joints, leave the factory with arrows on the tubes. That arrow is pointing to the direction of the medium flow. Why so particular? Because there is usually a guide tube inside the compensator, its function is to divert the medium to the center of the pipe, avoiding direct washing of corrugations or fabrics.
Think about it, wherever the deflector opening is, the medium will go. The arrow is the "instructions" of the guide tube. If the arrow points opposite, the opening of the guide tube faces the medium, which is equivalent to directing the medium directly to the fabric layer-what is the difference between sanding and sanding?
In addition, some rubber compensators or rubber PTFE compensators have no arrows, which depends on the eccentric structure of the flanges at both ends-usually the flange aperture on the upstream surface is slightly larger or chamfered, which can be judged by the position of the sealing surface. How to judge? Simply put, the side with the large inner hole of the flange is the upflow surface, and the sealing surface faces the backflow surface. Really unsure, flip through JB/T 12235-2015 standard, which writes the installation orientation requirements of non-metallic expansion joints. This national standard, people engaged in installation should have a copy at hand.
3. Under different working conditions, there are "additional questions" in the installation direction
It is not enough to look at the direction of the media flow. For example, near the desulfurization flue gas baffle door used on the flue gas pipeline, the non-metallic compensator usually matches the opening and closing direction of the baffle door. If there is backward flow when the baffle door is closed, the compensator must be designed as a two-way compensation type or an inner bushing-otherwise, once the door is closed, the compensator will be disabled once.
Another example is the non-metallic compensator used next to the metal corrugated expansion joint in the cement industry. Because there is much dust, the installation direction of the guide tube should avoid dust accumulation-generally, the opening of the guide tube is required to face downward or laterally, so that the dust can slide down naturally, instead of piling up at the root of the guide tube. If it is installed backwards, the dust will accumulate inside the compensator, and it will clump over time, which will directly lead to the failure of the compensator.
For non-metallic compensators with high-temperature axial expansion joints, attention should be paid to the direction of thermal expansion. Pre-stretching or pre-compression need to be taken into account during installation-for example, the compensator needs to be compressed when the pipe is thermally expanded, so you have to reserve compression space during installation, instead of tightly installing it, otherwise it will be directly dead after operation. These details should be clearly confirmed by manufacturers and customers in the selection stage, and on-site installers must not "follow their feelings".
4. Installation details determine success or failure-those easily overlooked "pits"
Let's talk about how to adjust the expansion joint tie rod nut first. If there are tie rod bolts on the non-metallic compensator (such as the structure of large tie rod expansion joint), the nut needs to be loosened before installation to leave displacement space for the compensator. After the pipe is installed and fixed, adjust the nut according to the design value, do not screw it to death. And guess what? Some workers try to save trouble, and the factory nut is what it is. As a result, the compensator has no room to move at all, and it collapses as soon as the heat expands.
Also, does the screw of the expansion joint need to be disassembled? Remember one principle: the transport bolts must be removed after installation, otherwise the compensator will not work properly; However, the limit screw (such as the one that controls the amount of axial tension) should be kept and adjusted to the designated position. I've seen this case of confusion more than once-someone removed the limit screw as a transport bolt, and as a result the compensator overstretched and tore directly.
In addition, the flange connection of non-metallic compensator, the gasket must be made of the right material-corrosion-resistant polytetrafluoroethylene pad for flue gas system and metal winding pad for steam pipeline. The bolt tightening torque should also be uniform, and it should be tightened diagonally two to three times to prevent leakage caused by warping of the flange. This is no trivial matter-the flange is warped, and even changing the gasket can't plug the leak, so it has to be reworked.
5. Two small on-site cases to help you avoid the same pit
Case A:A rectangular non-metallic expansion joint was used in the waste heat recovery pipeline of a steel mill. During installation, the workers didn't pay attention to the direction of the arrow, and as a result, the guide tube was installed backwards. After three months, the fabric layer was burned through by high-temperature smoke. When removed, the deflector port has been washed out into a "bell mouth"-the edges are thin as paper. Solution: Re-install in the correct direction, and add wear-resistant layer to the flow-up surface of the guide tube. With just one small change, the lifespan has been extended from three months to three years.
Case B:The rubber compensator of a chemical plant (the medium is corrosive gas) is installed in the right direction but the ambient temperature is ignored-the compensator is next to the steam pipe, and the heat radiation causes the rubber to age accelerately. And guess what? In less than half a year, the rubber surface was all cracked, and the air leakage was a mess. Later, the insulation was added and the installation position was adjusted, and the life span was extended from half a year to three years. You see, direction is only the first step, and working condition matching is the key.
In the final analysis, the installation direction of non-metallic compensators is not a matter of glancing at the arrow. Media flow direction, guide tube structure, working conditions, flange connection, tie rod adjustment... every ring has to be kept a close eye. Don't wait for the air leak to regret it. That little time cost is enough for you to ask a professional team to do a comprehensive training. Don't believe it? You calculate how much you lose by shutting down the furnace for a day.