Find out one thing first: What role exactly do metal expansion joints play in pipes?
To put it bluntly, it is the "expansion joint" of the pipe-absorbing thermal expansion and contraction, buffering vibration and compensating for installation deviation. There are rubber compensators and non-metallic expansion joints on the market, but metal expansion saves energy and carries high temperature and high pressure, such as the main steam pipeline of power station and the high-temperature air duct of cement industry. Ordinary rubber parts will be wasted when they go up. Then what is its advantage? Let's tear it down layer by layer from the structural design.
The first hard-core advantage: "iron bone clanging" with temperature and pressure resistance
The main body of the metal expansion joint is stainless steel bellows, like our sideUniversal corrugated expansion joint、High temperature axial type expansion joints can operate at temperatures above 600℃, and the pressure level ranges from PN0.6 to PN6.4 or even higher. The rubber compensator begins to age when it exceeds 150℃. Although the non-metallic fabric fiber expansion joint can reach 1000℃, its pressure bearing capacity is weak. Metal expansion joints are just needed in the environment of high temperature, high pressure and medium corrosion such as power station boilers and desulfurization flue gas pipelines. A customer has asked: "What to choose for steam pipe?" We recommend directlyExternal pressure single axial expansion jointOrStraight pipe pressure balance typeThe reason is that it can balance out the internal pressure thrust and the pipe is not subjected to additional axial force. Think about it, if you put a rubber piece on the main steam pipe of a power plant, let alone heat it up, the steam pressure alone can blow it up.
The second advantage: there are many tricks of displacement compensation, which is not a "new trick"
The displacement of the pipeline system is not only linear expansion and contraction, but also may have lateral misalignment and angular deflection. The corrugated structure of the metal expansion joint can naturally absorb the axial displacement, but the composite displacement can be accomplished by adding a tie rod, a hinge and a universal hinge. Such asCompound hinge transverse expansion joint, specializing in absorbing lateral displacement;Curved tube pressure balance type expansion joint is used for simultaneously absorbing axial and transverse displacement at the curved tube;Double-hinged expansion joints of air-cooled island vacuum pipes adapt to large angles of thermal displacement. comparisonSleeve type pipe expansion joint (by sliding seal), metal corrugated expansion joint has no leakage point, small maintenance. Think about it, if the air-cooled island pipeline of the power plant uses a rubber compensator, can the vacuum degree be kept? The rubber will deflate under negative pressure, and the sealing ring will leak as soon as it ages, and the system efficiency will drop a lot.
Third point: Fatigue life is supported by data
The design life of metal expansion joints is usually calculated according to the number of cycles, and the standard ranges from 1,000 to 10,000 times, depending on the waveform, number of layers and material. We have done testing, 304 stainless steel corrugated pipe under reasonable design, the actual operation of 15-20 years a lot. The rubber compensator is affected by ozone and ultraviolet rays, and it has to be replaced in 3-5 years. Two days ago, there was a cement factory customer. The non-metallic expansion joint used in the kiln head pipeline leaked ash in two years, so it was replaced withThe metal corrugated expansion joint of the cement industry has been running for six years without any problems. This is not metaphysics, it is rolling of material science-metal bellows are formed by cold stamping, stress distribution is optimized, plus multi-layer structure increases flexibility, and the fatigue life is more than 5 times that of rubber. Think about it, a production line stops once and loses hundreds of thousands. Who is willing to change the compensator frequently in order to save thousands of dollars?
The fourth hard-core scene: "special students" in extreme working conditions
For example, the expansion joint matched by the desulfurization flue gas baffle door should not only be resistant to SO2 corrosion, but also adapt to the low pressure and large displacement of 0.1MPa. This environmentPTFE compensators can also be used, but the cost is high and the installation is complicated. Metal expansion joints are lined with PTFE liners, or directly with high-nickel alloys (such as Inconel), get it done. AndDirectly buried (fully buried) type expansion joint, directly buried underground, wrapped with anti-corrosion coating and insulation layer, to bear soil pressure and groundwater erosion.Special vacuum hose, the wall thickness is made thin and dense, and it can bear negative pressure without deflating. These non-standard requirements and non-metallic parts are basically stopped. To be honest, choosing expansion joints means choosing "who carries it more". Metal expansion joints are a proper main force in heavy industries such as power stations, cement, chemical industry and metallurgy.
Finally, let's talk about something real: how to pick?
Don't be superstitious about "universal models". Also a metal expansion joint,Corrugated expansion joints for power station industry andMetal corrugated expansion joints in cement industry have different corrugation parameters, end connection forms and guide tube design. For example, the function of the guide tube is to prevent high-speed airflow from washing the corrugated body. When selecting the type, it depends on the flow rate and medium particle size. If there is severe vibration in the pipeline, a tie rod or limit device should be installed. You take a general-purpose corrugated expansion joint and install it on the high-temperature steam pipe. If the angle is wrong, the fatigue life is incorrectly calculated, and it will crack in three months, you can't blame the product. Our product line ranges from general-purpose type, high-temperature axial type, straight pipe pressure balance type toDouble sealed baffle door matching, each model corresponds to specific working conditions. Before the next selection, calculate the temperature, pressure, displacement and medium clearly. Don't think that "metal" is universal. Tsk, if it were that simple, there would be no technical threshold in this business.