Nonmetallic Expansion Joint Internal Z-Deflector: What Exactly Is It Protecting Against?
Two days ago, I met a customer. The non-metallic expansion joint of desulfurization flue took less than half a year, and the skin was worn out. He asked: Haven't the deflectors been installed? Why is it still so crisp? This matter is really not the pot of the guide tube-ordinary straight guide tube is okay to deal with clean gas, but when it comes to dusty smoke, especially our non-metallic expansion joint is made of flexible fabric fibers, and high-speed particulate matter is like sandpaper, which pierces the skin in a few strokes. This brings us to today's true owner —Z-shaped deflector inside non-metallic expansion joint。
Why do non-metallic expansion joints need internal diversion structures?
Let's talk about the basic functions of the deflector first. This siteSpecific Function of Expansion Joint Guide TubeIt is clear in the question and answer: the guide tube is to protect the corrugation or fabric from direct erosion by high-speed media. But the problem is that the bellows in the metal expansion joint is metal, and its wear resistance is okay; Instead of metal expansion joints (such as this station'sRectangular non-metallic expansion joint、Fabric fiber expansion joint) The interior is made of flexible material, and the skin is usually a few layers of silicone or fluororubber plus fiberglass cloth, which doubles the wear rate when facing dusty smoke.
What about that? The Z-shaped deflector is specifically designed to solve this pain point. It is not a simple curved steel plate, but a special-shaped piece that has been bent twice. If you think about it, the airflow rushing to the first bend, the speed being cut off partly, and then turning through the second bend is the equivalent of putting two brakes on the high-speed medium — is it not much more secure than a sudden brake?
Structural Characteristics and Working Principle of Z-shaped Deflector
Typically made of temperature-resistant metal, the Z-plate is mounted on the media inlet side inside the non-metallic expansion joint. Compared with the straight deflector, its trump card is the S-shaped channel formed by the two bends.
When the airflow hits the first bend, the kinetic energy is converted into pressure energy, and the velocity drops sharply; As the flow follows towards the second bend, the direction is changed again, and the inertia of the particulate matter is further consumed. And guess what? After these two rounds of tossing, the flow rate of the medium reaching the skin surface may have dropped below one third of its original level. This design is especially useful for the pipelines in front and behind the desulfurization flue gas baffle door-those gypsum particles with a diameter of less than 20 microns are stopped by the Z-shaped plate and thrown directly to the bottom of the pipeline, without touching the skin at all.
Tsk, isn't it much smarter than a straight plate deflector?
Which operating conditions are Z-deflectors standard?
You don't have to get a Z-plate everywhere. However, in the following three cases, the ordinary guide tube basically can't hold it:
- Flue gas pipelines in power stations, cement and steel industries: The medium temperature is 200~600℃, the dust content is high, and the flow rate exceeds 15m/s. For example, if the Z-shaped plate is not installed in the kiln tail flue of cement plant, the skin may be worn out in half a year. This siteMetal Corrugated Expansion Joints in Cement IndustryThe supporting flue gas pipeline is a typical case.
- Rectangular section pipe: Like this siteRectangular non-metallic expansion jointWith large internal space, Z-shaped plates can be arranged in sections to adapt to displacements in different directions. The straight guide tube can't evenly guide the flow in the rectangular pipe at all, but it is easy to form local vortex.
- Frequent start-and-stop conditionsWhen the temperature changes drastically, the straight plate guide tube is prone to thermal stress concentration, while the Z-shaped plate can be somewhat cushioned because of the elasticity of the bending structure.
In addition, this siteDesulfurization flue gas baffle doorThe front and rear expansion joints, because they have to be switched on and off frequently, the airflow impact is more severe, and the Z-shaped deflector is already a standard option.
Several Key Points in Selection and Installation
Although the Z-shaped board is easy to use, it is a disaster if it is not installed properly. Here are a few pits you have to avoid:
Material matching: Use Q235 when the medium temperature is below 300℃, 304 stainless steel can be obtained at 300~500℃, and heat-resistant alloy (such as Inconel 625) must be used when the medium temperature exceeds 500℃. Don't use ordinary steel in the high-temperature section in order to save cost-after softening and deformation, it will block the airflow channel and accelerate wear.
Arrow Direction: The Z-plate is marked with arrows and must be installed in the same direction as the media flow. This siteThe direction of the arrow of the expansion joint refers toIt was specifically mentioned in the question and answer that if the direction is reversed, it is not called diversion, it is called destructive vortex generator. You imagine that the airflow rushes in and is bounced back by the reverse bend, creating turbulence inside the expansion joint-it is strange that the skin is not perforated.
Fixation mode and thermal displacement: The connection between the Z-shaped plate and the expansion joint frame should reserve a thermal expansion gap, otherwise the displacement compensation function of the non-metallic expansion joint itself will be wasted when the pipeline is hot and the plate will resist the frame. When installing horizontal pipes, remember to open drainage holes at the bottom of Z-shaped plates-there is always condensed water in the flue, which can crush the board after accumulating ash and clumping.
Practical Influence of Z-shaped Deflector on Expansion Joint Life
According to the national standard JB/T 12235-2015 for non-metallic expansion joints in this station, the diversion structure is an optional component. However, the actual case illustrates that the difference in life is more than three times when adding or not adding.
This station is used in the desulfurization flue of a power plantNon-metallic expansion joint (fabric fiber expansion joint)With Z-plate, the skin was inspected after 25 months of operation, and it was intact without any penetrating wear. However, another pipeline in the same power plant without Z-shaped plate was partially worn out after 8 months, and was forced to shut down for replacement. Although it is not expensive to replace the skin, how much electricity is lost in a day of downtime? It will be clear as soon as the account is settled.
Do you think adding a Z-shaped board will cost thousands more dollars, but in exchange for one installation for three years, saving two maintenance hours and spare parts costs?
Therefore, don't just stare at the expansion joint body when you select the model next time. The internal diversion structure is the hidden Boss that really determines the life. Especially for the working conditions with high dust content and fast flow rate, directly assign the Z-shaped deflector to the supplier-don't ask why, asking is to save worry and money. By the way, this site'sElectric plug-in insulation doorAndManual plug-in insulation doorThere is also a similar wear-resistant design.