The material of non-metallic compensator, first understand the structure
Many people think the whole piece of equipment is a piece of rubber or cloth when they hear "non-metal"-ridiculously wrong. A qualified non-metallic expansion joint (also called fabric fiber expansion joint) is actually a composite of multiple layers of materials:The outer layer is a temperature-resistant fiber clothFor example, silicone cloth, fluorine cloth;Insulating cotton with intermediate clipBlocking heat transfer;The inner layer is an anti-corrosion sealing layerTo deal with media corrosion. These three floors each perform their own duties. If the material is not selected correctly, the pipeline system will be waiting to suffer.
What are the materials of non-metal compensators? Don't worry, take it apart layer by layer.
Fabric Fiber Circle: Temperature-resistant "facade" and the easiest place to step on pits
The outer fiber cloth directly faces the smoke or hot air, and the temperature can't bear everything in vain. Several common kinds:
- Silicone glass fiber cloth— — Temperature resistance is about 250℃, cheap, suitable for ordinary ventilation ducts.
- Polytetrafluoroethylene glass fiber cloth— — Temperature resistance is about 300℃, and corrosion resistance is improved by a section.
- Ceramic fiber cloth— — The trump card that can reach above 1000℃ and high temperature working conditions.
But don't just look at the nominal temperature. In actual working conditions, the medium flow rate, pressure fluctuation and dust washing will compromise the actual tolerance temperature. Two days ago, I encountered a cement plant project. The temperature of the kiln head flue gas pipeline was nominal to 350℃, and ordinary silica gel cloth was selected. As a result, it was brittle and cracked for three months-it lasted for more than two years after replacing it with ceramic fiber cloth. The reason is simple: dust washing thinns the surface of the fiber, and thermal aging accelerates. Selecting materials regardless of working conditions means digging holes for Party A.
Rubber and PTFE: the two main forces of sealing layer, their uses are very different
The inner sealing layer is responsible for corrosion protection, and common materials are rubber and polytetrafluoroethylene (PTFE).
rubber compensator(For example, EPDM, neoprene) has good elasticity and low cost, which is suitable for room temperature ventilation and dust removal system. I've seen a lot of dusting pipes use EPDM, which has a life span of three to five years without any problem. But if the smoke is acid and the rubber becomes brittle directly, you have to change the scheme.
Rubber PTFE compensatorA PTFE film is compounded on the rubber substrate, which takes into account the flexibility of rubber and the corrosion resistance of tetrafluorine. This "hybrid" scheme is cost-effective-acid-, alkali-and temperature-resistant (about 200℃), and the price is much lower than that of pure PTFE.
As forPTFE compensatorIt has no elasticity and is deformed entirely by the corrugated structure. It has the strongest corrosion resistance, and is not afraid of almost any strong acid and alkali, but the price is also the highest. Moreover, it cannot bear large axial displacement, so it must be calculated clearly when selecting the model.
Then how to choose? To put it roughly: if the smoke is acid, it will be PTFE or rubber PTFE; It's just that the temperature is high and there is no corrosion. Fabric fiber plus insulation cotton is enough. Don't use an anti-aircraft gun to shoot mosquitoes, and don't use a slingshot to shoot off an airplane.
Different working conditions, different material matching schemes
It is also a non-metallic compensator, which is used in desulfurization system and hot air duct of power station. The material combination is completely different.
Back section of desulfurization flue gas baffle door: The medium contains sulfide, high humidity, and acid condensation. In this condition, acid-resistant rubber PTFE composite layer must be used, and the outer layer must be prevented from aging by fluorine adhesive tape. We have supplied several power plantsDesulfurization flue gas baffle doorThe matching non-metal expansion joint, the sealing layer must be PTFE or FEP, otherwise it will be perforated in half a year.
Hot air duct system of power station: The temperature always moves five or six hundred degrees, and the medium is hot air, which is not corroded but has pressure. Then you have to use ceramic fiber + stainless steel wire mesh reinforcement layer, and the middle insulation cotton should be thick enough to avoid heat transfer to the flange bolts. OurCorrugated expansion joint for power station industryIt is more metal, but the non-metal compensator in the inlet section of hot air duct uses ceramic fiber cloth with high silicon oxide cloth, and the service life can reach more than 3 years.
Cement industryMore headache-high temperature dust wear heavily. Wear-resistant lining plate should be added to the inner layer, and high silicon oxide cloth or mullite fiber should be selected for the fiber cloth. And guess what? In order to save costs, many manufacturers sell general-purpose non-metallic expansion joints to high temperature and high dust conditions. As a result, they break three times a year, which is more expensive than customized models. Alas, there are too many cases of greed for small gains and big losses.
There is another hidden pit in material selection: the gap between standard and actual measurement
National standard JB/T 12235-2015 specifies the test methods for pressure resistance, temperature resistance and leakage rate of non-metallic expansion joints. But there is a loophole in the standard: it allows short-term experimental data to be replaced with long-term aging data. Some manufacturers take short-term qualification reports at 300℃ to promote sales, but the actual continuous operation at 120℃ will age. Tsk, this isn't a lie.
What to do? Suppliers are required to provide accelerated aging test reports of the same material and thickness. For example, ASTM D573 hot air aging test, aging at the specified temperature for 72 hours, see the strength retention rate. If the manufacturer can't even take this out, just rule it out.
Choosing the material of the non-metallic compensator is not choosing the parameter, but choosing the long-term reliability. Don't be fooled by a "qualifying report".
If you are unsure about a certain working condition, ask the manufacturer directly for cases in the same industry. OurNon-metallic expansion joints (fabric fiber expansion joints)AndRubber PTFE compensatorThere are detailed selection tables, but more importantly, the media composition, temperature fluctuation range and pressure level are clearly stated. Only when the material is matched can the equipment give you worry-free.