What counts as a "large" metal expansion joint? Let's see where it's used first
Boiler outlet of power station, cement kiln tail, high-temperature pipeline of petrochemical plant... The big guys you see in these scenes are basically classified as "large metal expansion joints". In our product listCorrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement Industry、Large diameter thick wall expansion jointAll of them are typical representatives. Where's the threshold? Usually, metal corrugated compensators with nominal diameter DN ≥3000mm, design pressure ≥2.5MPa, or operating temperature exceeding 1000℃ are considered large. Once these things go wrong, the maintenance cost is enough to buy several new ones-don't ask me how I know. Two years ago, the expansion joint at the boiler outlet of a power plant burst, and the replacement plus shutdown loss was enough to buy three of the same specifications.
Four Parameters Most Easily Overlooked During Type Selection
Temperature, pressure, compensation amount, medium-these four parameters look simple, but 80% of selection accidents are planted on them. Let's talk about high-temperature working conditions first: do you think it's done to choose a temperature-resistant material? You have to calculate the fatigue life of the bellows. weCalculation formula of bellows stiffness(available in the FAQ) determines how many heat cycles it can carry. For example, a general-purpose corrugated expansion joint was used in the kiln tail pipeline of a cement plant, and the result was that it cracked in three months-the problem was that the medium contained sulfur, corroded and high temperature, and the material couldn't hold it. Media corrosive? Don't hesitate,PTFE-lined hoseOrPTFE compensatorThat's the right answer. In order to save thousands of dollars and choose the general-purpose type, is it cost-effective to finally lose hundreds of thousands of maintenance fees? Weigh it yourself.
Let's talk about the compensation amount. Many people only give the theoretical value on the drawing, and the actual pipeline deformation on site is often greater. Pressure is also a pit-the nominal pressure marked by some manufacturers is at room temperature, and the pressure level should be discounted at high temperature. We have encountered a petrochemical plant with a design pressure of 2.0MPa and an actual operating temperature of 600℃. We chose an ordinary axial type, and as a result, the bellows was unstable. How to avoid it? chooseHigh temperature axial expansion jointOrExternal pressure single axial expansion jointAnd the pressure resistance is stronger.
Preparation work before installation, one step of mistake will lose all
Look at the direction of the guide tube before installation. In FAQArrow direction of expansion jointThere is a detailed explanation-the arrows must be aimed at the direction of the media flow. Install backwards? The medium directly impacts the bellows, and the life is cut in half. Next is the tie rod nut:How to adjust the tie rod nut of expansion joint？ Remember that the screw is locked during transportation and must be loosened when installed in place, leaving for pre-tension or pre-compression amounts. And guess what? Some construction sites did not dismantle the screw, and after the pipeline heated up, the expansion joint became a rigid connection, and the flange collapsed directly. Alas, such low-level mistakes are heard every year.
AndCorrect installation method of expansion joint of large tie rodIt has been emphasized that the function of the tie rod is to bear the blind plate force and lateral displacement, and the nut cannot be screwed to death during installation, leaving a gap of 10~20mm. Also don't forget to check the amount of pre-stretch-high temperature pipes should be cold drawn and low temperature pipes should be cold pressed. Don't understand? Flip through our FAQFunction of expansion joint tie rodThat one.
Post-installation debugging and inspection: How to see if the installation is in place?
Don't be in a hurry to suppress it when it's finished. First, see if the bellows is twisted-twisted means that the force is uneven and has to be re-adjusted. Then see if the guide tube is centered, and if it is biased, scrape the bellows. ForLarge diameter thick wall expansion jointIt is also necessary to measure the parallelism of the flange surface. If the deviation exceeds 2 mm, it will not be qualified. There was a case in a cement plant before. There was no gap when the guide tube was welded. After operation, the thermal expansion and contraction directly pushed through the tube, and a whole section of the pipeline was wasted.
Let the pipeline settle naturally for a day or two, then tighten the bolts, and finally do a pressure leak test. The leak test pressure should not exceed 1.5 times of the design pressure, hold the pressure for 30 minutes, and observe whether the weld and bellows have leakage. By the way,directly buried expansion jointThe insulation layer and waterproof layer must be done before the pressure test, otherwise the water will freeze and the bellows will directly freeze and crack-the counterparts in the north of this pit should have a deep understanding.
Routine Maintenance and Life Extension
The metal expansion joint is not installed, so you don't have to worry about it. Check the bellows surface every six months-see if there are cracks, corrosion pits, and listen to abnormal vibration sounds. In FAQService life of expansion jointIt is mentioned that the design life can reach 15 years under normal working conditions, but it is often scrapped in advance due to water hammer, overtemperature or installation deviation. How to prevent water hammer? Install on a pipeRotary compensatorOrSleeve type pipe expansion jointWhich can effectively buffer the impact.
Additionally noteDirect buried (fully buried) type expansion jointThe waterproof layer is damaged. Once the groundwater seeps into the ice, even the gods can't save it. Andrubber compensatorAndNon-metallic expansion joint (fabric fiber expansion joint)Also check the aging regularly-don't think everything will be fine with metal, corrosion, fatigue, stress corrosion cracking are all silent killers.
The longer it takes to select and install, the more worry-free the later maintenance. Don't try to save trouble. The stiffness that should be calculated is clearly calculated, the gap that should be left is enough, and the screw that should be disassembled is disassembled-you respect the equipment, and the equipment will save your life.