1. What exactly is the "welding non-metallic compensator" you asked? — — Clarify the concept first, don't buy the wrong goods
Two days ago, a purchaser called and asked "welding non-metallic compensator". I was stunned for half a second and asked him: By "welding" do you mean welding a non-metallic compensator to a pipe? Or does it mean that the compensator itself has metal welds? The other end of the line was dumbfounded. This thing is often called a bastard in the industry. Today, let's talk about it all at once.
The so-called "welded non-metallic compensator" actually refers to one with metal connectors (such as flanges or stub) at both ends, which is connected to the pipe by weldingNon-metallic expansion joint— That is what we often sayNon-metallic expansion joint (fabric fiber expansion joint)、rubber compensatorOrRubber PTFE compensator。 Its main body is a non-metallic loop band (fabric, rubber, PTFE, etc.), but the ports are usually made of carbon steel or stainless steel for the purpose of welding. So the name itself is a bit "contradictory", but everyone in the industry knows it: it means "non-metallic compensator with welded structure at the port".
Don't underestimate this definition. I have seen people buy pure rubber joints (looper flanges at both ends) and take them for flue welding. As a result, when they are baked at high temperature, the rubber melts away directly. Is it a waste of cost? So figure out that "welding" refers to the port structure, not the whole product is metal.
Second, according to the structure: rectangular and circular, the welding method is very different, rectangular non-metallic expansion joint is the main force
Rectangular and circular. The welding processes of the two are far from each other, and they can't be installed directly if they are selected incorrectly.
1. Circular welded non-metallic compensator
It is more common in pipeline systems, such as smoke air ducts of power stations and hot air ducts of cement plants. The circular structure bears uniform force, and butt welding or fillet welding is generally used during welding. The common practice of ports is: a section of metal stub (or flange) is welded to the pipe, and the other end of the stub is pressed with a non-metal ring band. Note that the non-metallic loop strip itself cannot be welded directly, so "welding" is actually for a metal connection.
2. Rectangular non-metallic expansion joint-absolute shipment workhorse
If you go to the boiler flue site at a power station, 99% of them use rectangles. Why? Because the rectangular flue has high space utilization rate, it is easy to stick to the wall. The welding method is also special: the metal frame of rectangular non-metallic expansion joint is usually made of angle steel or channel steel, which is welded directly to the flue wall panel. The ring belt is fastened to the frame by platen bolts instead of welding. So "welding" only takes place between the metal frame and the flue.
In order to save costs, some manufacturers make the frame thin, and the deformation after welding is serious, resulting in air leakage due to weak pressure of the ring belt. Therefore, when choosing rectangular non-metallic expansion joints, be sure to ask about the thickness and material of the frame plate, and don't just look at the quotation.
Third, according to the material: fabric fiber, rubber, rubber PTFE, which can be welded firmly?
The material of the non-metallic ring belt determines the temperature resistance, corrosion resistance and sealing performance. Here are three mainstream materials, which you can take according to the working conditions.
- Fabric fiber expansion joint: i.e.Non-metallic expansion joint (fabric fiber expansion joint)。 The main body is made of silicone cloth, glass fiber cloth, ceramic fiber cloth, etc., and the temperature resistance can reach 1200℃ (with heat insulation layer). After the port metal parts are welded, the ring belt is pressed mechanically, which is not directly affected by the welding heat. This is the most used in flue and cement kiln tails of power stations.
- rubber compensator: The material is natural rubber, neoprene or EPDM, and the temperature resistance generally does not exceed 150℃. Note when welding: the rubber ring belt must not be close to the high-temperature welding area. The metal parts must be welded first, and then the rubber ring belt must be installed after cooling. Many on-site accidents are caused by welding slag splashing onto the rubber.
- Rubber PTFE compensator: Lined with PTFE layer and rubber, taking into account both corrosion resistance and elasticity. The temperature resistance is a little higher than that of pure rubber (about 200℃), but it is also afraid of high welding temperature. Generally used in desulfurization systems, the medium contains acidic gas or slurry. The welding requirements are the same as the rubber compensator, and the heat source must be isolated.
What are the welding non-metallic compensators? From the material classification, there are these three mainstreams. But some people will ask: Can you weld PTFE directly? Wake up, the melting point of PTFE is only 327℃, and the welding melts directly. Therefore, as long as it is a "non-metal" loop strip, it must pass through the transition of metal parts before it can be welded.
IV. Practical application scenarios: power station flue, cement hot air, desulfurization system, each choose its own goods
Different scenarios have completely different choice logics. The question "What are the welding non-metallic compensators?" When put on the spot, the answer becomes "You can decide after looking at the working conditions".
Scenario 1: Power station flue (boiler outlet, dust collector inlet)
The medium temperature is generally 300-700℃, containing a small amount of dust. PreferredNon-metallic expansion joint (fabric fiber expansion joint)Rectangular structure, high temperature resistance and can absorb multi-directional displacement. Welding method: The wall thickness of the flue is generally 6-10mm, and the frame should be welded directly. The kerosene penetration inspection should be done in the welding seam. Frequent questions: The insulation layer is not done properly, and the temperature of the external metal frame is too high, which leads to thermal stress cracking of the weld.
Scenario 2: Hot air duct (kiln head, grate cooler) in cement industry
The temperature is higher, reaching above 1000℃, and contains a lot of clinker dust. Fabric fiber expansion joints with thermal insulation must be used, and heat-resistant steel (e.g. 310S) should be selected for metal connections. Preheat during welding and heat preservation after welding to prevent cracks. OurMetal Corrugated Expansion Joints in Cement IndustryAlthough mainstream, it is still more economical to use rectangular non-metallic expansion joints for large-section flues.
Scenario 3: Desulfurization system (FGD import and export)
Low temperature (50-80℃), strong corrosion (SO₂, chloride). Circle belt preferredRubber PTFE compensator, or a rubber compensator lined with PTFE. Metal parts must be coated with anti-corrosion coating or duplex stainless steel. Note when welding: Desulfurization pipelines are often lined with rubber or plastic, and welding heat will destroy the lining, so the welding sequence should be designed well: first welding metal connectors, then fill the lining. This detail is wrong, and the later leak will be repaired until you cry.
Speaking of which, do you still think "welding non-metallic compensators" is an easy multiple choice question? Choose the wrong material, and it will leak after welding; Choose the wrong structure and can't fit it; Choose the wrong scene and scrap it in half a year. Doubling the cost is light, and delaying the construction period is really bad.
Next time you communicate with the manufacturer, just report three parameters directly: temperature, pressure and media composition. Leave the rest to us. Oh, by the way, don't forget to confirm whether the port is welded or flanged-don't be like the brother at the beginning, ask "welding non-metallic compensator" when you open the mouth, but when you buy it back, you find that you don't even have welding parts.