When the customer called, he asked in the first sentence: What material is cheap and has good sealing for the expansion joint? To be honest, every time I hear this question, I have to ask first: What medium goes in your pipeline here, what is the temperature and what is the pressure? It wasn't an argument, it was a question that really couldn't be answered in one sentence.
As soon as I came up, I rushed to "the cheapest" to choose the material, and eight out of ten turned over the car behind. Let's break up several common materials and crush them into pieces. After reading it, you will know what to choose.
First, recognize these materials
The expansion joints on the market are roughly divided into these categories according to their materials.
- rubber compensator: Suitable for low pressure, normal temperature, large diameter pipeline, mainly depends on elastic deformation of rubber to absorb displacement, the price is generally the lowest.
- Non-metallic expansion joints (fabric fiber expansion joints): It is made of multi-layer fabric fiber composite, and its high temperature resistance is better than that of rubber. It is commonly used in low pressure and high temperature occasions such as flue gas and air duct.
- Universal corrugated expansion joint (metal): Typical stainless steel bellows structure, with strong pressure and temperature resistance, is the main force in complicated working conditions.
- PTFE compensatorAndPTFE-lined hose: PTFE material is resistant to strong corrosion, but the price is also expensive.
In addition to the above, there are various special products such as metal hoses, metal rectangular expansion joints, high-temperature axial expansion joints, etc. It is also to compensate for the displacement of the pipeline. The material is different, and the price can be several times or even ten times different. But the key is not who is cheap, but whether it is suitable or not.
Second, where is the price gap?
Under the same caliber and pressure level, the price ranking is roughly like this:
Rubber compensator cheapestNon-metallic expansion joints are second, general-purpose corrugated expansion joints are more expensive, and PTFE compensators and PTFE-lined hoses are the most expensive. The root reason for the expense lies in the material cost and manufacturing process. PTFE materials are difficult to form, and metal bellows need precision welding and heat treatment, so the price will naturally go up.
However, cheap does not equal a good deal. Rubber compensator does save money on normal temperature water, but if it is used to pass 130℃ steam, the life may be shortened from five years to five months, and the cost will be higher after repeated replacement. Don't just focus on the purchase unit price, the comprehensive life and replacement frequency are reliable.
Third, what does sealing depend on?
The sealing performance is good or bad, the material is the foundation, but the structural design is the key.
The non-metallic expansion joint is compounded by multi-layer fabric fibers and sealed by flange compression. This structure performs well on low-pressure flue gas pipes, but if you force it on high-pressure pipes, the fiber layer will blow through, which is embarrassing.
The medium is guided away to reduce the direct erosion of the fluid to the inside of the bellows and reduce the risk of the bellows being worn out. Think about it, once the bellows breaks and leaks, the whole pipe suffers.
One more word, likeDouble-sealed single-axis circular baffle doorThe sealing effect of this kind of product with double seal structure is much more stable than that of ordinary single seal, which is of great significance to the strict air duct or flue gas system.
Fourth, how to choose?
If the large-diameter pipeline with low pressure and normal temperature is not afraid of corrosion,rubber compensatorOrNon-metallic expansion jointThe price/performance ratio is really high, the price is cheap, and the sealing performance is sufficient.
If the temperature and pressure are high and the medium is corrosive, don't save this money. Choose honestlyUniversal corrugated expansion jointOr simply onPTFE compensator。 Although the initial investment is large, the seal is reliable and durable. For example, the steam pipelines in the power station industry and the kiln head and kiln tail air ducts in the cement industry have very bad working conditions, and the requirements for sealing and durability are extremely high. Generally, metal corrugated expansion joints or high-temperature axial expansion joints with corresponding working conditions are directly used.
Some working conditions are in the middle, such as the flue gas pipeline of desulfurization system, which is not high in temperature but corrosive, so it has to be comprehensively considered. The corrosion resistance of PTFE is indeed good, but if the diameter is large, the non-metallic expansion joint is matched with a suitable anticorrosive material lining, which is more economical and practical. Therefore, there is no universal answer to the selection, and it must be determined according to the working conditions one by one.
Don't use a rubber compensator to top high-temperature steam。 If there is such a plan to save money, it will leak in a few days. When the time comes, the loss of shutdown for maintenance will be enough to buy hundreds of compensators.
5. Finally, pour cold water on a basin
Whether the seal is good or not depends half on the installation. This point goes to the root.
The flange bolts must be tightened evenly and alternately diagonally, and the other side cannot be tightened after one side is screwed to death. The pipeline cannot be biased, and the pre-deformation of the expansion joint must be done according to the requirements given by the manufacturer, so do it right.
Two days ago, I met a customer who said that the expansion joint I bought was leaking, so let us pay for it. As a result, after the sales visit, the bellows was burned by welding slag during installation. Did you say that this matter was caused by material? Not. What's even more outrageous is that some people hoist them with wire ropes directly on the bellows, and the good products are just scrapped.
No matter how expensive the material is, if the installation is not standardized, it will still leak. Save what don't save installation, don't make do with crooked pipelines. Rework when something goes wrong will not only spend more money, but also delay production. Many customers come to the factory to discuss explanations after leaking them. In all probability, the bellows was screwed or bruised during installation, which is not a matter of material at all.
What material expansion joint is cheap and has good sealing performance? The answer is never on the price list, but in your own working condition parameters and installation quality. Know the materials, understand the working conditions, and then take the installation seriously, and the money is worth it.