Two days ago, I met a customer and asked, "What is the maximum degree that your flue metal expansion joint can bear?" I asked him about the working parameters, and he looked dumbfounded. Yes, he is another master who flips through the parameter table when he comes up. In fact, it is really not so mysterious to choose the flue metal expansion joint. Follow these five steps to ensure that you don't step on the pit.
Step 1: Find out your flue operating conditions. Don't just flip through the parameter table
Think about it, what's running in the flue? Smoke. But flue gas is different from flue gas-the temperature difference between the flue gas behind the desulfurization tower of the power plant and the flue gas at the cement kiln head is hundreds of degrees Celsius. There are also corrosiveness, particulate matter content, and whether it contains moisture... If you don't find out these first, the parameters selected later are purely blind.
Make a list, and you fill it in:
- Medium type (flue gas, steam, dusty gas?)
- Maximum operating temperature (long-term and short-term peaks)
- Maximum working pressure (positive or negative?)
- Flue direction (straight pipe? with elbow?)
- Installation location (indoor or open? Is there any vibration?)
Take this list to the manufacturer, and they can recommend the appropriate type of expansion joint for you. For example, the flue gas temperature of the desulfurization system is low but the corrosion is strong, so it may be necessary to use PTFE-lined or non-metallic; If the cement industry contains dust at high temperature, it is necessary to consider the high-temperature axial expansion joint or the metal rectangular expansion joint with wear-resistant guide tube.
Step 2: First determine the caliber and connection method. If this is wrong, it will be all in vain
Alas, some brothers struggled with the number of corrugated layers and the amount of compensation when they came up, and as a result, the tube size was wrong. What is the inner diameter of the flue interface? What is the flange standard? Is it welding or flange connection? If these parameters are wrong, the expansion joint can't be installed, and your front is all in vain.
How exactly? Use a tape measure to measure the outer diameter (or inner diameter) of the flue, and pay attention to the wall thickness of the flue. Connection method this block:
- Flanged connection: Confirm the flange standard (national standard JB/T81, American standard ANSI...), and measure the diameter of the center circle of the bolt hole.
- welded connection: Confirm the welding groove form and leave the welding gap.
- Sleeve connection: Generally used for large flue, pay attention to sleeve length and seal form.
If the on-site flue has been installed, it is best to measure the flange spacing, because pipeline installation errors are common. Don't just look at the drawings and place an order.
Step 3: Select the number of corrugated layers according to the temperature and pressure, and don't be biased by "the thicker the better"
And guess what? I have seen a project manager who insisted on letting the manufacturer use 5-layer bellows, thinking that the thicker the safer. As a result, the stiffness of the pipe is too large, and the compensation amount is not enough at all. When the pipe expands thermally, the expansion joint is directly cracked. The principle is simple: the more corrugated layers, the thicker the wall thickness, the greater the stiffness, and the worse the elastic deformation ability. Thicker wall thicknesses are required at high temperatures and high pressures, but at the expense of reduced compensation.
Then how?
- Low temperature and low pressure (≤100℃, ≤0.1MPa): Single-layer bellows will do, which is cheap and flexible.
- Medium temperature and medium pressure (100~300℃, 0.1~0.6MPa): 2~3 layers of bellows, material 304 or 316L.
- High temperature and high pressure (> 300 °C,> 0.6 MPa): 4 layers or even more, material on Incoloy 825 or Superalloy. For example, the corrugated expansion joint used in the power station industry often uses multi-layer design and external insulation in the high-temperature section.
Don't pat your head, give the temperature and pressure data to the manufacturer, let them use software to calculate the fatigue life, and then determine the number of layers and materials.
Step 4: Is the amount of compensation calculated correctly? Teach you how to use the simplest formula directly
In fact, the compensation amount (also called displacement amount) has three parts: thermal expansion amount, installation error and vibration displacement. 90% of the time you just need to calculate the amount of thermal expansion. The formula is just one:
Δ L = α × L × Δ T
- Δ L — — Thermal expansion amount (mm)
- α-Linear expansion coefficient of pipe material (carbon steel approximately 0.012 mm/m·℃)
- L — — Length of flue between two fixed points (m)
- Δ T — — Difference between operating temperature and installation temperature (℃)
A section of 10-meter-long carbon steel flue, the working temperature is 200℃, 20℃ during installation, and the temperature difference is 180℃, then Δ L =0.012×10×180=21.6mm. That is to say, the axial compensation of your expansion joint should be at least 21.6mm. Of course, you also have to consider lateral and angular displacements, but that's what is needed for complicated pipe directions. Generally, for straight pipe sections, choose axial expansion joints.
The bigger the compensation amount, the better. If the bellows is chosen, it is easy to become unstable. Moreover, the allowable compensation amount of different types of expansion joints is also different. For example, the parameters of general corrugated expansion joints and straight pipe pressure balance expansion joints are different. Find the manufacturer to compare and select the parameter table.
Step 5: Don't forget the deflector and the tie rod. These two details can save you half a year's maintenance cost
Tsk, many people choose the expansion joint only to stare at the bellows itself, thinking that the guide tube is a baffle, and the tie rod is a few iron bars. SO WRONG!
guide tube: If there is high-speed dusty airflow in the flue, there is no guide tube, and the bellows is directly exposed to the airflow scour, which will wear out in a few months. Especially in the cement industry and desulfurization system, the material of the guide tube should be wear-resistant (such as 316L or wear-resistant lining), and it should be designed as a plug-in type to reduce vortex and vibration. Take a look at this siteSpecific Function of Expansion Joint Guide TubeThat article, illustrated and explained very clearly.
tie rod: The tie rod is not used to reinforce the expansion joint, its function is to limit the excessive tension or compression of the bellows and protect the bellows from being damaged. For example, during installation, the tie rod nut can adjust the amount of pre-tension. Think about it, if the pressure of the pipeline exceeds during pressure test, and there is no tie rod, the bellows will bulge and be scrapped directly. In addition, the installation method of the expansion joint of the large tie rod is also particular, and the tie rod must be loosened and adjusted after the pipeline is fixed. The question and answer on this siteFunction of expansion joint tie rodYou will see if you have a look.
Select the guide tube to see whether there are particles in the flue gas, and select the tie rod to see whether the pipeline needs to be limited. Choose these two correctly, and the life of the equipment will double.
Okay, five steps, isn't it as complicated as you think? Next time someone asks you "How to determine the parameters of flue metal expansion joint", dump this article directly to him. If you are still unsure, please look through the more than 30 kinds of product information in our site, such asHigh temperature axial expansion joint、Desulfurization flue gas baffle door、Compound hinge transverse expansion joint…There's always one that suits your working conditions.