First, the name with "metal" does not mean that it is all stainless steel-first understand the basic concepts
Many people think that metal expansion joints are made of stainless steel, and even some purchasing calls ask, "Quote me the price of stainless steel expansion joints." Let's not laugh at people, after all, with the word "metal" in the name, the first reaction is shiny stainless steel, right? But the fact is that "metal expansion joints" are a big category. For example, there are general-purpose corrugated expansion joints, external pressure single axial expansion joints, and directly buried (fully buried) expansion joints on our website... These all belong to metal expansion joints, but their materials are various.
The core of the metal expansion joint is that telescopic bellows. Corrugated pipes can be made of stainless steel, carbon steel, alloy steel or even nickel-based alloys, depending entirely on the working conditions. For a practical example: if you use it in a flue gas desulfurization system, the medium contains sulfur, so you have to use corrosion-resistant stainless steel or higher-grade materials; If it is used in ordinary steam pipelines, the temperature is less than 200℃, and the carbon steel bellows can be completely carried with proper anti-corrosion treatment. Therefore, don't default to stainless steel as soon as you hear "metal". If this misunderstanding is not clear, it will be easy to overturn after the selection.
Second, stainless steel is only one of the "top students" in the metal expansion joint family
The reason why stainless steel is most used in metal expansion joints is simple-the medium transported by most industrial pipelines is corrosive, or the environmental humidity is high and the temperature changes drastically, so stainless steel can carry it. But look at the corrugated expansion joints used in power station industry and metal corrugated expansion joints in cement industry on our website. The working conditions are high temperature, dusty and worn. At this time, 304 and 316 stainless steel alone may not be enough-heat-resistant steel or duplex stainless steel must be used.
PTFE-lined hose. This product is a metal bellows inside, and the outside or inner wall is lined with polytetrafluoroethylene (PTFE). The real contact medium is PTFE, and the metal is only responsible for bearing pressure. At this time, carbon steel can be used for the metal part. Why? Because the corrosion problem has been solved by PTFE, it is a waste to use stainless steel. Therefore, the equation of "metal expansion joint = stainless steel" is simply untenable in engineering. If the material is chosen wrong, it will leak at least and the whole pipeline system will have an accident at worst.
Third, non-metallic expansion joints and metal expansion joints are fundamentally different things-don't confuse them
Sometimes customers take non-metallic expansion joints (that is, fabric fiber expansion joints) and ask, "Can your stainless steel replace that cloth?" This is the classic conceptual confusion. The metal expansion joint absorbs the displacement by the elastic deformation of the bellows, which can withstand high pressure and high temperature, but it has great rigidity and is not suitable for large displacement. Non-metallic expansion joints (we also have rectangular non-metallic expansion joints and non-metallic expansion joints (fabric fiber expansion joints) on our station) rely on flexible fabrics and rubber to absorb displacement, and have weak pressure resistance, but large compensation and good vibration reduction. They are often used in scenes with low pressure and large displacement such as flue gas pipes and air ducts.
Therefore, the relationship between the two of them is not one that replaces the other, but one that manages each other. In other words, metal expansion joints are not all "stainless steel", while non-metal expansion joints are not "metal" at all. When selecting the type, first find out the pipeline medium, pressure, temperature and displacement direction, and then look at the material. Don't ask "is it stainless steel".
4. Look at the material selection from the products of this station: the same expansion joint, different "steel and iron bones"
Open the product page of our website, you will find the same called "corrugated expansion joint", but the materials are varied. For example, the high-temperature axial expansion joint is used on the boiler outlet or hot air duct, and the medium temperature may be above 800℃. At this time, the heat resistance limit of 304 stainless steel is only about 700℃, which can't hold it at all. Another example is the vacuum special hose, which is used on air-cooled island vacuum pipelines. The pressure is low but the sealing performance is extremely high. The material is often 316L stainless steel to ensure corrosion resistance and welding quality.
There is also a sleeve-type pipe expansion joint, which relies on the sliding compensation of the inner and outer sleeves, and the sealing packing and steel are matched. The material can be stainless steel or carbon steel, mainly depending on the cost and use environment. There is also a compound three-way expansion joint in the cement industry. The working condition is high temperature and dust, so the material has to be wear-resistant and heat-resistant alloy. Simply put: Don't think of "stainless steel" as a universal option. Choosing materials is like matching keys, and one key opens a lock.
5. Figuring out this problem can help you save 30% of the purchase cost
"Is the metal expansion joint stainless steel?" This question is not just a conceptual question, but a real cost question. You choose the right material, the equipment has a long life and less maintenance; If you choose the wrong choice, you will either waste your money or fail every three days. When engaging in engineering, don't be led by the name. Look at the working conditions and check the parameters. If you are not sure, just look through the product descriptions on our website-the materials, applicable temperatures and pressure ranges of each model are clearly written.