What exactly is a welded non-metallic compensator? How is it different from ordinary non-metallic expansion joints?
To put it bluntly, welding a non-metallic compensator is to replace the connection method of flange bolts with direct welding to the pipeline. Think about it, omitting flanges, bolts and gaskets not only reduces leakage points, but also saves installation space-especially in those cases where the temperature and pressure are high or the pipes are next to the wall and the equipment is crowded, the flange can't fit in at all, and welding becomes the only way out. Moreover, the welding seal is naturally stronger than that of bolted connection, and the risk of media running outside is much lower.
Is it essentially the same thing as ordinary non-metallic expansion joints? Expansion joint and compensator are actually different names for the same type of equipment (refer to Article 14 of Q&A on this site), but the connection mode has changed. Non-metallic expansion joints (fabric fiber expansion joints), rubber compensators, PTFE compensators, if the customer requires welding connection, we can still weld the structure. So stop asking "Is the welding non-metallic compensator a new product"-it is a variant, and the key is to see if the non-metallic materials inside are selected correctly.
Material determines longevity: fabric fiber, rubber or PTFE?
Select the welding non-metallic compensator, and 80% of the pits are planted on the material. You have to keep an eye on the hard indicators of medium temperature and corrosiveness.
- Non-metallic expansion joints (fabric fiber expansion joints): The main material is glass fiber, silicone cloth, fluorine adhesive cloth and other fabrics laminated composite. Wide range of temperature resistance, conventional products can achieve 200~400℃, special design can rush up to 800℃. It is suitable for high-temperature flue gas pipelines such as power station boiler, cement kiln tail and desulfurization flue. The disadvantage is that it is not resistant to long-term soaking of strong acids and alkalis.
- rubber compensator: Mainly EPDM, butyl rubber and neoprene rubber. Good elasticity, vibration and noise reduction are strong points, and the working temperature generally does not exceed 120℃. It is suitable for circulating water system, sewage pipeline, pump inlet and outlet. But don't use it against steam above 150°C-the rubber will carbonize and crack.
- PTFE compensator: PTFE materials are resistant to almost all chemical media except molten alkali metals and fluorine gas. Applicable temperature-50~250 ℃. The chemical industry preferred when dealing with highly corrosive media (hydrochloric acid, sulfuric acid, hydrofluoric acid). However, PTFE itself has great rigidity and small compensation, so it is usually made into bellows structure or compounded with rubber.
Calculate, when you bought it, the picture was cheap, so you chose a rubber compensator to deal with 300℃ smoke. After three months, when you removed it, it burned like crispy rice-the maintenance cost was enough to buy three regular products.
Three pits that are easiest to plant during type selection
The pressure rating is not correct。 Although the welded non-metallic compensator is not as high as the metal bellows, many designers choose the type according to the nominal pressure of the pipeline-for example, the design pressure of the pipeline is 0.25MPa, so he chooses the compensator of 0.25MPa. Wrong! Does the pressure rating of a non-metallic compensator refer to "internal pressure bursting pressure" or "working pressure"? Many manufacturers target the blasting value, and the actual safety factor is only 2~3 times. Correct practice: Multiply the working pressure by the safety factor (usually 3~4) and then select against the product sample.
Deflector is omitted。 Two days ago, I met a customer. The rectangular non-metallic expansion joint for desulfurization flue was too expensive for the guide tube, saying, "There is a fabric fiber layer in it anyway, so I am not afraid of wear". As a result, in less than half a year, the high-speed dusty smoke wore the fabric layer, and ash leaked everywhere. The function of the guide tube (Article 7 of Q&A on this site) is to guide the airflow to avoid the main body of the compensator and protect non-metallic materials. Especially for flue gas pipelines containing particles, the money of the guide tube cannot be saved.
Blind adjustment of tie rod nut。 The tie rod nut is generally locked when welded non-metallic compensators leave the factory, which is used to prevent excessive compression or stretching during transportation and installation. Some people remove the screw directly after installation (Article 13 of Q&A on this site), or tighten the tie rod nut too tightly, which causes the compensator to lose its displacement function-then welding it is equivalent to welding a dead knot. Correct approach: Pre-compress (see below) before installation, then loosen the nut to leave space for the design compensation and allow the compensator to expand and contract freely.
Pay attention to installation and welding: pre-compression is not done, which is equal to white installation
The welded non-metallic compensator must be "pre-compressed" or "pre-stretched" before installation. What do you mean? For example, when the pipeline is running, it will expand (thermal displacement), so when installing, compress the compensator to half of the designed displacement, and then weld it. When the pipe is hot, the compensator goes from the semi-compressed state to the elongated direction, and both ends are safe. If this step is not done, wait until the compensator is either pulled off or crushed to death at runtime.
In addition,How to adjust the tie rod nut？ Article 12 of Q&A is very detailed: first loosen the locking nut, adjust the adjustment nut to the designated position, and then re-lock it. After installation, the screw does not need to be disassembled, but the nut must be loosened to the design clearance to allow the compensator to move freely. Many project site drawings save trouble, and the screw is not loose. As a result, the compensator becomes a rigid connection, and the thermal stress of the pipeline is all transmitted to the equipment, which cracks the base of the fan and pump.
How to pick between different industries? The working conditions of power stations, cement and desulfurization flue gas pipelines are very different
Power station industry: Commonly used in hot and cold air ducts and flue ducts of boilersCorrugated expansion joint for power plant industry(metallic), but non-metallic compensators have more advantages in waste heat boilers and denitrification inlet sections-high temperature, strong corrosion, useNon-metallic expansion joint (fabric fiber expansion joint)CooperateDouble-sealed round flapper doorOrDesulfurization flue gas baffle doorSo that zero leakage isolation can be achieved.
Cement industry: The outlet of high-temperature fan and preheater at the end of the kiln, the flue gas temperature is above 400℃, containing raw material dust. Metal corrugated expansion joints can be oxidized and worn by high temperatures, whileRectangular non-metallic expansion jointCan absorb three-dimensional displacement, cooperate withManual plug-in insulation doorOrElectric plug-in insulation doorDo maintenance partitions. The metal corrugated expansion joint in cement industry of this station is mainly used in coolers, pulverized coal pipelines and other occasions where the pressure is slightly higher and the temperature is slightly lower.
Desulfurization flue gas pipeline: The flue gas after wet desulfurization has high humidity and acid liquid, and the metal parts corrode very quickly. Preferredrubber compensatorOrPTFE compensator, cooperate withDouble-sealed single-axis circular baffle doorImplement flue switching. Note: The desulfurization flue is usually low pressure (-3~ +5kPa), but the requirements for air tightness are extremely high. 100% non-destructive testing can be done to ensure no leakage in the welding seam of the non-metallic compensator.
Finally, let's be honest
National standard JB/T 12235-2015 for non-metallic compensators is the bottom line. If you compare, those products that are ridiculously cheap either have substandard materials, or cut corners to save the deflector and lack compression strips. When buying a welding non-metallic compensator, don't just stare at the price, and ask the manufacturer if there is any actual case-the same working condition, three years of operation is no problem, which is more effective than verbal guarantee. If the warranty period is less than two years, it will be directly excluded. Save two or three hundred yuan, in exchange for shutting down every day for maintenance, is it a loss?
Choose the right one and save ten years of worry. If you choose the wrong one, you have to figure out how to remove it and fix it every month.