What exactly is the use of a large size non-metallic compensator? Understand these points and spend less money
Two days ago, I met a customer who was doing desulfurization project. The original scheme used metal expansion joints. As a result, the cost was high and the leakage was frequent under large diameter. I changed a large-size non-metallic compensator, and the problem was solved. I have seen too many similar examples-many projects are selected and slapped on their heads, either fooled by suppliers to buy expensive ones, or cheap ones are wrong, and they have to be reworked in the end. Today, let's break it up and crush it, and make clear the functions, applicable scenarios and selection pits of large-size non-metallic compensators.
1. What do large-size non-metallic compensators do? Let's talk about the core functions first
Large-size non-metallic compensator, also called in the industryNon-metallic expansion jointOrFabric fiber expansion joints, mainly used to absorb thermal displacement, vibration and installation errors of pipes or equipment. Compared with metal, its biggest advantage is that it can handle large-diameter and low-pressure flue gas pipes-such as desulfurization systems in power plants and air ducts in cement industries. The diameter always rushes to 2 meters and 3 meters. The price of metal bellows can go to the sky there, and the lateral displacement is greatly limited.
- Compensate for multidimensional displacement: It can be absorbed in axial, transverse and angular directions. Metal bellows have great restriction on lateral displacement, and non-metallic flexible structure is naturally suitable for multi-directional compensation.
- Vibration isolation and noise reduction: The fabric fiber layer itself has damping, which can effectively attenuate mechanical vibration and airflow pulsation-the buzz of the power plant fan outlet, which can drop several decibels after installation.
- Corrosion resistance and high temperature resistance: Non-metallic materials (fluororubber, silica gel, polytetrafluoroethylene, etc.) with heat insulation layer can carry sulfur-containing flue gas, acid-alkali corrosion and high temperature. Think about the flue gas coming out of the desulfurization tower. The SO₂ concentration is high, and metal parts will rust through in three months, but non-metals can hold up.
- Easy to install: Lightweight, flange can be screwed, no complicated guide bracket is required. On-site workers don't have to move heavy equipment, and the construction period can be saved by half.
So don't underestimate this thing, it is not a cheap substitute for metal, but an optimal solution under certain working conditions.
2. Which scenarios must use large-size non-metallic compensators?
Not everywhere is suitable, but three typical scenarios are its home:
- Desulfurization flue gas system of power plant: The flue gas temperature is high (120~180℃), contains corrosive SO₂, and the pipe diameter often exceeds 2 meters. Metal expansion joints are too heavy, too expensive, and less resistant to corrosion than non-metals. Cooperate with this siteDesulfurization flue gas baffle doorUse, seal compensation is integrated, and the air leakage rate can be controlled within 1%.
- Air duct in cement industry: The hot air ducts and dust collection ducts on the cement production line have large temperature fluctuations (from normal temperature to 400℃) and lots of dust. Large size non-metallic compensator can prevent pipe from cracking due to thermal expansion and cold contraction. Although this site'sMetal Corrugated Expansion Joints in Cement IndustryIt can also be used, but non-metal is much more cost-effective in large sizes-the same diameter is 2 meters, and the price of non-metal is only 1/3 of that of metal.
- Flues in the chemical and metallurgical industriesFor example, the blast furnace gas pipeline in steel mills has a diameter of 3 meters and a pressure lower than 0.1MPa. Using non-metallic compensators is economical and reliable. You can refer to this siteRectangular non-metallic expansion jointProducts, specially designed for rectangular flue, measure the dimensions on site and customize them directly.
Conversely, if you use it on high-pressure steam pipes, the non-metal will stop-the fabric layer will bulge as soon as the pressure comes up. Each product has its own territory, don't force it.
3. What is the difference between large-size non-metallic compensator and metal?
Since non-metal is so good, why are there metal expansion joints? Here we have to clarify our own territories.
- Pressure rating: Non-metallic compensators are generally used below 0.1 MPa, and the limit does not exceed 0.3 MPa. Metal expansion joints (e.g.Universal corrugated expansion joint、External pressure single axial expansion joint) Can bear pressure to several MPa. You take non-metals to connect to the steam main? It won't last a day.
- Upper temperature limit: Non-metal usually does not exceed 600℃ (the limit is slightly higher after adding heat insulation layer), and metal bellows with heat-resistant alloy can reach above 1000℃. In places like the outlet of blast furnace hot blast furnace, use metal obediently.
- Service life: The non-metallic fabric layer will age, generally 5-10 years; Metal bellows have a longer fatigue life, but problems can occur with welds — especially with high welding stresses under large diameters. When selecting a model, you must calculate the full life cycle cost, not just the initial purchase price.
- Price: Under the same caliber, the price of non-metals is only 1/3 to 1/2 of that of metals, especially when the diameter exceeds 1 meter, the advantage is more obvious. A non-metallic compensator with a diameter of 3 meters may buy three non-metallic compensators at the price of one metal.
Therefore, when selecting a model, look at the pressure and temperature first. Low pressure, low temperature, large pipe diameter, non-metal is the first choice; High pressure, high temperature, small pipe diameter, and metal. Don't be superstitious about a certain kind, suitability is king.
4. I have summarized the three pits that are easy to step on when selecting a model
According to the project experience I have contacted, the selection of large-size non-metallic compensators is most likely to roll over in these three points:
- Ignoring the guide tube design: If there is high-speed airflow in the flue gas pipe (for example, the wind speed at the outlet of the fan is more than 15m/s), no guide tube will directly wash the fabric layer, and it will leak in a few months. This site'sexpansion joint guide tubeThe relevant technical information is clearly written-according to the flow rate and medium particle size, installing 316L or carbon steel guide tube can prolong the life by more than three times. Don't save this money.
- Ignoring installation pre-stretch: Non-metallic compensators usually need to be pre-stretched or pre-compressed when installed to absorb thermal displacement. Many people install it directly, but as a result, the expansion and contraction amount is not enough after operation, and the flange is pulled and deformed. You can refer to the FAQ of this site "How to adjust the tie rod nut of expansion joint". In fact, the operation is not difficult-calculate the pre-stretching amount according to the design temperature, and then loosen the tie rod nut after installation.
- Wrong number of layers: The non-metallic compensator consists of multiple layers-fluororubber/silicone inner lining, insulating cotton, outer sheath. The combination of layers is completely different in different working conditions. For example, desulfurization flue gas contains acid, and PTFE must be used for the lining; High temperature conditions need to add ceramic fiber insulation layer; If there is dust wear, a wear-resistant layer should be added. Don't listen to suppliers fooling the unified configuration, but according to the actual media. If you are really unsure, send samples to them for matching testing.
5. How to maintain large-size non-metallic compensators to last longer?
Many customers ignore it when they buy it back, and wait until it leaks before changing it. In fact, the daily maintenance is very simple:
- Check flange bolts periodically: Large-size pipes vibrate heavily and bolts are easy to loosen. Tighten with a torque wrench once a quarter, and the torque is as standard (M16 bolts are usually about 120N·m). Loose bolts can cause air leakage on the flange surface and accelerate the aging of the fabric layer.
- Observation of outer sheath damage: The outer sheath of non-metallic compensator is generally silicone cloth or PTFE film. If there are cracks or scratches, stick it with special repair tape in time, so as not to let moisture enter and corrode the heat insulation layer. Even if it is just a small hole, the acidic condensate seeps in, and the insulation cotton inside will clump and fail.
- Pay attention to peripheral thermal radiation: If there are high-temperature pipes nearby (for example, the distance between steam heat tracking pipes is less than 500mm), radiant heat will accelerate the aging of non-metallic materials. Installing an insulated baffle can extend life — less than a tenth of the cost of getting a new compensator.
- Empty during shutdown: After the wet desulfurization system is stopped, acidic condensate will accumulate in the pipeline. If it is not emptied, the non-metallic compensator will rot if it is soaked in acidic solution for a long time. Open the bottom drain valve after more than a week of outage, or blow dry with compressed air.
After all, this thing is like a tire. With daily maintenance in place, it can last for two or three years. Don't wait until the air leaks and smoke to remember to fix it, it's already too late.