DN1000 not 1000mm in diameter? Understand the definition of nominal diameter first
When many people saw DN1000 for the first time, their first reaction was "the diameter of the tube is 1 meter". To be honest, I thought so when I first entered the industry, but I was fooled once by the drawings-the flange I actually bought couldn't fit. The "DN" in DN1000 is an abbreviation for Nominal Diameter, which is essentially aNominal size, not measured values. Take steel pipe as an example. The outer diameter corresponding to DN1000 is commonly 1016mm or 1020mm (see the standard, such as GB/T 1047 or ASME B36.10), while the inner diameter depends on the wall thickness. For example, a pipe with an outer diameter of 1020mm with a wall thickness of 10mm has an inner diameter of 1000mm; If the wall thickness is 12mm, the inner diameter will be 996mm. So here's the question: When you buy the expansion joint or hose of DN1000, do you have the flange according to the outside diameter, or do you have the flow according to the inside diameter? The answer is – look at the FLAND standard. If you are equipped with the national standard PN series flange, the sealing surface size of DN1000 flange and the center circle diameter of bolt hole are fixed, which has nothing to do with the actual wall thickness of the pipe. But if you come across the American Standard Class series, you have to count separately. Bottom line: Don't regard DN as the measured value. It is a code name. When selecting the model, be sure to check the detailed size of the connection end.
How to use DN1000 in large diameter pipe compensation?
DN1000 is particularly common in large-diameter pipelines in thermal power, steel and chemical industries. Which products will be marked with this size? Just a few examples:Large diameter thick wall expansion joint、Metal hose、Desulfurization flue gas baffle door。 Two days ago, the purchase of a desulfurization project asked me: Is the flue gas baffle door of DN1000 1 meter in diameter? I said you should understand it this way, but the actual door panel size depends on the inner diameter of the air duct and the thickness of the lining. The door frame size of the baffle door is usually larger than the DN1000 by a circle, because it needs to leave a sealed space. Another exampleMetal hoseThe metal hose of DN1000 is usually used for circulating water pipelines or flue gas pipelines in power plants. The number of bellows layers and the number of net strands are directly linked to the pressure resistance grade. WhileDesulfurization flue gas baffle doorThe DN1000 (list number 19) refers more to the standard diameter of the flange connection port. You have to confirm whether it is a single-axis double-baffle or a double-seal single-axis circular baffle door. Their structure and sealing methods are completely different.
Field case: DN1000 corrugated expansion joint for power station industry for steam pipeline in a power plant
A while ago, I went to the site of a 660MW unit project, and several steam pipelines were installedCorrugated expansion joint for power station industry(5th in the list), the specification is DN1000. When the installation team finished hoisting according to the drawings and was ready to tighten the tie rod nut, the technician suddenly found that the wave number and pressure level on the expansion joint nameplate did not match the design. And guess what? The drawing requires 4 waves with a withstand pressure of 2.5MPa, while the actual arrival is 6 waves and 1.6MPa. Although the flange hole spacing is all right, more wave number means that the axial stiffness becomes smaller, and it is easy to be compressed and unstable under the large thrust of steam pipeline. In the end, I could only return it for exchange, and the construction period was delayed for three days. So don't think that everything will be fine if DN1000 is matched. The wave number, pressure level and temperature compensation must be checked item by item. Especially for high-temperature steam pipelines, it depends on the material of the guide tube (lining tube) -if it is ordinary carbon steel, it can't withstand more than 500℃, so stainless steel has to be used.
Are metal hoses and rubber compensators interchangeable for DN1000?
Basically not, hard change is equivalent to digging a hole for yourself.Metal hose(The first in the list) relies on bellows and stainless steel mesh sleeve to bear pressure, and the maximum temperature resistance can reach above 600℃ (depending on the material, such as 316L or Incoloy 800), and the pressure resistance can also reach more than ten MPa. Whilerubber compensator(List 9) The main body is rubber + ply, and the temperature resistance is generally over 100℃, and the pressure does not exceed 1.6MPa. You said it was used on the steam pipe of the power plant, and the rubber one melted directly as soon as it was put on. On the other hand, for some low-pressure and normal-temperature circulating water pipes, metal hoses are ok, but the cost is several times higher, so it is unnecessary. There is also a pit: rubber compensators usually have hard flanges at both ends and a rubber sphere in the middle, which cannot bear the weight of the pipe when installed; Metal hoses can be properly supported. Be sure to ask about the medium temperature, working pressure and displacement type before selecting the model. Don't just look at the word DN1000 to place an order.
Three Must-Ask Questions When Purchasing DN1000 Products
First question: What is the connecting flange standard?Is it the national standard GB/T 9119 or the Ministry of Chemical Industry HG/T 20592? Or is it the American Standard ANSI B16.5? Each standard flange outer diameter, number of bolt holes, hole center circle diameter are different. The same supplier may match the national standard by default, but what you get is the American standard flange, and the on-site nozzle has to be reprocessed if it doesn't match. Second question: How to calculate the compensation amount? The expansion joint of DN1000, with axial compensation amounts of 50mm and 100mm, is completely two structures, and the wave number, layer number and wave height are different. Don't just listen to verbal promises. Third question: Does the guide tube have to be fitted? Many people ignore this.Specific Function of Expansion Joint Guide Tube(From Article 7 of FAQ on this site) is to protect the bellows from being washed by high-speed media, while reducing the flow resistance. For flue gas or steam pipelines containing particles, the life of bellows without guide tube is cut in half directly. However, having a guide tube will increase the pressure drop, which can be omitted if the medium is clean and the flow rate is low.