Let's talk about the conclusion first: Is the non-metallic compensator resistant to high temperatures?
Resistant, and can carry better than metal compensators under some working conditions. But there is a premise-you have to choose the right material. When many people hear the word "non-metal", the first reaction in their minds is "plastic things are soft when exposed to heat". Tsk, that impression has to be changed. Non-metallic compensators (also called fabric fiber expansion joints and non-metallic expansion joints) are not simple plastic at all. Its main body is composite materials: multi-layers of fabric fiber cloth, rubber, fluoroplastics and insulation cotton are superimposed together, and each layer performs its own duties. Therefore, whether it is resistant to high temperatures or not depends entirely on which "formula" you pick.
The secret of high temperature resistance is hidden in materials: how many degrees can it carry from silica gel to tetrafluorine?
Let's take apart several kinds of fabrics commonly used in nonmetallic compensators, and the upper temperature limit is clear at a glance:
- Silicone cloth/fluororubber cloth: The continuous working temperature is 200℃ ~250℃, and it can reach 300℃ in a short time. Suitable for hot air duct, low pressure steam.
- Polytetrafluoroethylene (PTFE/Tefluoro): Temperature resistance range-200℃ ~ +250℃, but above this temperature, PTFE will decompose to produce toxic gases. This site'sPTFE compensatorAndPTFE-lined hoseIs a typical representative, suitable for corrosive media and low temperature occasions.
- Ceramic fiber cloth (aluminum silicate fiber): This thing is the real main force of high temperature resistance, and the long-term use temperature can reach more than 1000℃. With stainless steel wire reinforcement, it is commonly used in flue gas pipeline and boiler exhaust system. stationaryNon-metallic expansion joint (fabric fiber expansion joint)Use this kind of material in large quantities.
- Glass fiber cloth + silicone rubber coating: The common temperature resistance range is 250℃ ~400℃, taking into account both flexibility and sealing.
So you see, there are corresponding products for the temperature resistance span of non-metallic compensators from 150℃ to 1200℃, and the key lies in the thickness of the middle insulation layer and the number of fabric layers. Listed in the stationHigh temperature axial expansion jointIt belongs to the metal category, but if you need super-large displacement and high temperature, non-metals are more flexible.
The scenario decides the choice: Which kind to use for flue gas pipes? Which kind of high-temperature steam should I use?
Two days ago, I met a customer who was doing desulfurization project. When I came up, I asked, "Is the non-metallic compensator resistant to high temperatures? The flue gas temperature is 350℃". I said no problem, but it has to be equipped with ceramic fiber lining + stainless steel wire mesh reinforcement layer, and the outer layer is protected against acid corrosion with fluororubber cloth. This operating condition is selectedRectangular non-metallic expansion jointThe most suitable, can absorb three-dimensional displacement, flange installation also saves space.
Conversely, if it is high temperature steam (such as the main steam pipe of a power station, the temperature is 540℃), guess what?Non-metallic expansion joints N/A。 High-temperature and high-pressure steam has strong permeability, and the non-metallic layer is easy to bulge and delaminate. At this time, honestlyCorrugated expansion joint for power station industryOrHigh temperature axial type expansion joint. Non-metallic compensator is most used for low-pressure saturated steam (≤150℃) on steam pipeline. If it exceeds this number, metal compensator is the correct solution.
Compared with metal compensators, what is the advantage of non-metal high temperature resistance?
The upper limit of temperature resistance of metal compensators (such as stainless steel bellows) is very high. Ordinary 304 stainless steel can carry 600℃, and Inconel alloy can even reach 900℃. But nonmetallic compensators have a unique skill- -Thermal shock resistance。 Metals are prone to fatigue cracks under quenching and sudden heating, while non-metals are more solid because of their soft material and multilayer structure that can buffer thermal stress. For example, the temperature of the flue gas pipeline of the waste incinerator instantly drops from 800℃ to 200℃, and the metal expansion joint may crack in two or three years.Non-metallic expansion joint (fabric fiber expansion joint)It's normal to use it for five or six years. In addition, the non-metal compensator also has its own vibration and noise reduction function, and the metal compensator has to be added with an additional damper. But what about the cost? Non-metals have weak pressure bearing capacity, so they are generally only used at low pressure (≤0.1MPa), and they still have to be used when high pressure is neededUniversal corrugated expansion jointOrStraight pipe pressure balanced expansion joint。
Select and avoid pits: Don't just look at temperature, but also at pits such as pressure, medium and life
Many people think that "it's enough to withstand temperature", but it leaks after three months of installation. Why? The pressure is over the limit! The pressure rating of non-metallic compensators usually does not exceed 0.1MPa, and if there is a positive or negative pressure fluctuation inside the pipe, the flange sealing surface can easily be blown open. Besides, the flue gas containing acidic gas must be lined with PTFE or fluororubber, otherwise the fiber cloth will be corroded through. From our stationRubber PTFE compensatorIt is to solve this corrosion + medium temperature working condition.
There is also the problem of life-the fabric layer of non-metallic compensator is a consumable, and the normal life is 3~5 years, while the metal compensator can do it for more than 10 years. Therefore, if it is a key pipeline that runs non-stop for a long time (such as the main steam of a power plant), don't use non-metals cheaply; If it is an auxiliary pipe that is easy to maintain and replace (such as dust removal system and flue bypass), non-metal will be very fragrant. And don't forgetNational Standard for Non-Metallic Expansion Joints JB/T 12235-2015When selecting, compare the temperature-pressure curve in the standard, and don't use it beyond the parameters.
In one sentence: Non-metallic compensators do withstand high temperatures, but it depends on how high, what medium and how much pressure. Don't be fooled by the name, it's the exact opposite of "intolerant to high temperatures"-it's pressure, not temperature, that really limits positioning.