Let's talk about what the hell are fub non-metallic expansion joints?
Two days ago, I met a customer and asked, "What is the difference between your fub non-metallic expansion joint and ordinary fabric fiber expansion joint?" In fact, fub is more a specific name for a certain kind of non-metallic expansion joint in the industry. In essence, it is the "non-metallic expansion joint (fabric fiber expansion joint)" on our station-a compensator made of composite materials such as high silicon fiber and polytetrafluoroethylene. Compared with metal expansion joints, its biggest advantages are corrosion resistance, high temperature resistance (can reach over 1000℃), and can compensate multi-directional displacement. To put it bluntly, chimneys and flues are much more reliable than metal parts in hot and corrosive places.
So how long will this thing last? Take real data: 304 stainless steel corrugated expansion joint used in desulfurization flue of a power plant, and intergranular corrosion crack was found in less than 3 years. After switching to fub non-metallic expansion joints, the fabric layer was still intact at the sixth year inspection. The metal piece is a younger brother in front of the acidic condensate.
Structural dismantling: Why can it withstand high temperatures and corrosion?
Although it is soft, the structure is not simple. The innermost layer is a sealing layer of fluororubber or polytetrafluoroethylene, with aluminum silicate fiber cotton sandwiched in the middle for heat insulation, and a layer of stainless steel wire mesh or glass fiber cloth wrapped on the outside-the implementation standard of this thing is JB/T 12235-2015. Unlike our "metal rectangular expansion joint", the fub non-metallic expansion joint has no corrugated metal shell, so it can absorb greater axial and lateral displacement. By the way, the role of the guide tube is particularly critical in the non-metallic expansion joint, which can guide the medium and prevent the high-temperature airflow from directly washing the fabric layer (refer to the question and answer "Specific role of the guide tube of the expansion joint"). Without the deflector, no matter how good the fabric layer is, it can't last two maintenance cycles.
By the way, some people think that non-metallic expansion joints are "not pressure-resistant", but it is actually not a big problem. When the pressure exceeds 0.1MPa, add a tie rod structure (refer to Q&A "Function of expansion joint tie rod" and "How to adjust expansion joint tie rod nut"), and the fabric layer will not bulge. When the tie rod nut is installed, it must be loosened to allow the compensator to work in a free state, otherwise the stress will all be eaten on the fabric when the temperature rises-this will be described in detail in the installation section later.
Where must it be used? Tell me three real scenarios
The first: the smoke air duct of the power station.Especially when used in conjunction with "flue gas baffle door" and "desulfurization flue gas baffle door", the temperature fluctuates greatly, and there is sulfide corrosion, and the metal expansion joint will rust through after three to five years. fub non-metallic expansion joint with "electric plug-in insulation door" can last for more than ten years. There is a thermal power project in Beijing, which was installed in 2015. So far, the outer glass fiber cloth has only been changed once.
The second: the cement industry.The high-temperature flue gas at the outlet of the clinker cooler can reach 900℃, and the metal bellows is soft early, so only fabric fiber compensator can be used. Moreover, the cement production line shuts down and loses hundreds of thousands a day. Choosing a reliable non-metallic expansion joint is more important than anything else.
Third: desulfurization system.After wet desulfurization, the net flue gas has low temperature but high humidity, and it is entrained by gypsum slurry, which ordinary stainless steel can't bear. At this time, "PTFE compensator" or fub non-metallic expansion joint comes in handy. Note that the desulfurization system is best lined with polytetrafluoroethylene, which has strong permeability resistance.
You can't pat your head when you select a model, these parameters should be picked to death
Temperature, pressure and displacement are iron triangles. If it exceeds 350℃, don't choose an ordinary rubber compensator. You have to use one with aluminum silicate wool. Specifically:
- Temperature: fub non-metallic expansion joints are divided into low-temperature type (≤350℃) and high-temperature type (≤1000℃), and the price difference can be doubled. However, saving money can't be saved in materials. A chemical plant used the low-temperature type on the 500℃ flue for cheap, and it burned through in three months.
- pressure: Tie rod structure must be considered over 0.1 MPa. How to tune it? Refer to the question and answer "How to adjust the nut of the tie rod of the expansion joint". The principle is to reserve more than 30mm space for the tie rod in the displacement direction.
- displacement amount: The advantage of non-metallic expansion joints is that they can absorb axial, lateral and angular displacements at the same time. However, enough space must be left during installation, especially when the "rectangular non-metallic expansion joint" is used on the square pipe flue, and when it is matched with the "circular baffle door (double seal)", the flange connection size must be aligned. If the deviation exceeds 2mm, air may leak.
In addition, the media composition is also critical. Polytetrafluoroethylene must be used for the inner lining when it contains strong acid gas, and wear-resistant guards must be added for the outer layer when it contains dust particles. Manufacturers will not take the initiative to remind them of these details, so they have to pick them themselves.
Installation and maintenance pits to help you avoid in advance
(1) Don't squeeze the ring belt during transportation. If it is damaged, it can't be repaired, so it can only be replaced. A construction site fell when unloading goods, and the band creased, which cracked three months after installation.
(2) When installing, the tie rod nut should be loosened (refer to the question and answer "Does the screw of the expansion joint need to be removed"), so that the compensator is naturally in a free state. Otherwise, the consequence is: once the temperature rises, the fabric layer is directly pulled and torn. I have seen a case where the installer locked the tie rod and it smoked half an hour after turning it on.
(3) Regularly check the outer sheath for wear and cracks. Especially when used in conjunction with "manual plug-in insulation doors", the door panel switch may scratch the fabric layer.
Previously, a power plant installed this fub non-metallic expansion joint in front of the "manual plug-in insulation door". After two years, it was found that the fabric layer was aging and falling off, because it forgot to install the deflector. The existing lining steel plate must not be saved, which is a lifeline to protect the fabric layer from being directly impacted by high-temperature airflow.
Summary: Don't try to be cheap, the cost-performance ratio has to be calculated as the whole life cycle account
Metal expansion joints are cheap but have a short life, while fub non-metallic expansion joints have a higher initial installation cost, but they don't have to move for 8-10 years. Which is cost-effective, counting shutdown losses and replacing labor? For example: the flue expansion joint of a 300MW unit, the purchase price of metal is 5,000 yuan, which is replaced once every two years; fub non-metallic 12,000 yuan, used for eight years. Together with the labor and downtime losses per replacement (hundreds of thousands a day), the total cost of non-metallic solutions is more than 30% lower.
In addition, if it is combined with "double-seal single-axis circular baffle door" and "double straight pipe bypass pressure balanced expansion joint" to form an overall solution, the sealing and compensation effect will be better. Finally, before buying, you must provide the working condition parameters (temperature, pressure, displacement, medium composition) to the manufacturer. Don't take it for granted.