Two days ago, a buddy who was doing a desulfurization project called to spit, saying that he had looked at the specification sheet of the flue expansion joint for a long time, but he couldn't understand what those numbers meant. As a result, the expansion joint bought back couldn't be installed, the size was wrong, the flange hole was not aligned, the construction period was delayed for three days, and the project manager scolded it. You must be familiar with this situation, right? To be honest, the flue expansion joint specs look like a dense pile of symbols, but just catch a few key points and you can read them through in minutes. Today, I will teach you this set of methods step by step, so that you can choose your own model after reading it.
First, understand the four core numbers on the specification sheet of flue expansion joint: diameter, pressure, temperature and displacement
No matter how much data is on the specification sheet, there are only four that really determine whether you can use it. Everything else is assigned around these four parameters.
First: Diameter (DN/Caliber)
To put it bluntly, it is the inner diameter of the flue or the length and width of the rectangular section. Circular ones are generally labeled DN200 and DN500, while rectangular ones are written, for example, 1000×800 (mm). This parameter directly determines the expansion energy saving cannot be welded to your pipe flange. How to confirm? Take a tape measure to measure the outer diameter of the flue, and then subtract twice the wall thickness, which is the diameter. Note that if there is an insulation layer at the pipe interface, you have to open it a little and measure it again. Don't even count the insulation together.
Second: Design Pressure (PN)
The unit is generally MPa or kPa. The flue system pressure is usually not high, many of which are about a few kPa to 0.1MPa. But you must not think that just pick up an expansion joint will work. There is a common pit: the expansion joint will be "pre-stretched" or "pre-compressed" during transportation and installation, and the actual pressure it bears is not necessarily exactly the same as the specification sheet. Therefore, it is best to leave a 20% margin for pressure when selecting.
Third: Design temperature (T)
Is it hot smoke or cold air in the flue? What's the temperature? This directly determines whether you choose metallic or nonmetallic. Metal expansion energy saving can be carried to 800℃ or even higher, but if it exceeds 400℃, high-temperature resistant alloy must be used. Non-metallic expansion joints are generally used in smoke environment ≤350℃, which is cost-effective. How to choose specifically? Look down.
Fourth: displacement amount
This is the most critical functional parameter of the expansion joint-it absorbs the displacement caused by thermal expansion and contraction of the pipe. The specification sheet usually writes the axial compensation amount, the lateral compensation amount, and the angular compensation amount in mm or degrees. What do you think? You compare the pipe layout diagram and calculate the maximum deformation of the pipe in three directions. For example, if the temperature of a 30-meter-long straight pipe rises by 200℃, the linear expansion coefficient of the steel pipe is about 0.012mm/m·℃, and the axial elongation is 30×0.012×200=72mm. The axial compensation amount of the expansion joint you choose must be ≥72mm, and it is best to multiply it by the safety factor of 1.2.
Tip: If only one "displacement" is written on the specification sheet without direction, it usually refers to axial direction. Other directions need to ask the manufacturer separately or look at the label.
Second, according to the flue medium and temperature, quickly judge whether to choose metal or non-metal? Rectangular or circular?
This question is actually very simple. Let me teach you a formula:High temperature and high pressure depend on metal, low temperature and low pressure use non-metal; Round pipes are used, and rectangular pipes are used for square flues.However, the specific operation depends on the following points.
Temperature is the watershed.If the flue gas temperature exceeds 350℃, the non-metallic expansion joint (fabric fiber material) basically can't bear it, so you have to choose metal. But note that this site hasHigh temperature axial expansion jointSpecially used for high temperature working conditions, there are alsoCorrugated expansion joint for power station industryAndMetal Corrugated Expansion Joints in Cement IndustrySuch subdivided products, these can be given priority when selecting. If the temperature is below 350°C and the medium contains corrosive gases (such as wet flue gas after desulfurization), thenNon-metallic expansion joint (fabric fiber expansion joint)Orrubber compensatorMore suitable-corrosion resistance, good vibration isolation, and cheap price. And guess what? Many power plants use non-metallic compensators for the export of desulfurization towers, because the wet flue gas contains sulfuric acid, which is too corrosive, and the metal can't bear it at all.
Look at the cross-sectional shape.Circular flues are of course equipped with circular expansion joints, but if your flue is rectangular (such as the section from the bottom of the boiler to the dust collector), you have to use itMetal rectangular expansion jointOrRectangular non-metallic expansion joint。 Note: The structural design of the rectangular expansion joint is completely different from that of the circular shape. It cannot be changed by the circular shape, and it must be specially customized according to the rectangular section.
Note: If you need to withstand both axial and lateral displacements and the pipe cannot change its course, considerCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointThey can absorb multi-directional displacement, but the structure is complex and the price is high. Generally, single axial type is enough for small and medium-sized projects.
3. How to match the flange standard, wave number and total length in the specification table? Get you a one-stop checklist
Get a completeFlue Expansion Joint SpecificationTable, in addition to the above four core numbers, the following data also have to be checked one by one. I'll make a list, and you can follow it:
- Flange standards:Are your pipe flanges National Standard (GB), Department of Chemical Industry (HG), Department of Machinery (JB) or American Standard (ANSI)? It must be consistent, otherwise the bolt holes will not align. For example, common desulfurization flue gas pipelines mostly adopt HG/T 20592 standard. This site'sDesulfurization flue gas baffle doorProducts are often equipped with this kind of flange, which can be referred to when selecting.
- Flange Material:Matches the material of the pipe. Carbon steel pipe with carbon steel flange, stainless steel pipe with stainless steel flange. Don't mix it, or electrochemical corrosion will give you a headache.
- Wavenumber:That is, the number of layers or turns of the bellows. The more the wave number, the greater the compensation amount, but the end stability will deteriorate. Generally, the wave number of axial expansion joint is between 2 and 6 waves, which depends on the calculation of displacement. For example, this site'sUniversal corrugated expansion jointThe regular configuration is 4 waves.
- Total length (L):This is the distance between the flange surfaces at both ends of the expansion joint. Are there any limitations on installation space? If there is not enough space and the total length is too long to fit in, you need to useStraight pipe pressure balanced expansion jointSuch short structural forms. Measure the net space reserved on the site, and the total length should be at least 50mm smaller than this space to allow installation allowance.
- Guide tube:If it is flue gas containing particles (such as cement kiln tail), it is best to let the manufacturer matchguide tubeAvoid particles from flushing the bellows directly. Refer to the FAQ of this site "Specific Function of Expansion Joint Guide Tube".
4. Actual combat steps: from flue drawing to final selection, five steps to do it without overturning
It's boring to talk on paper. Let's go through it with a practical case. Suppose you want to give an expansion joint to a circular flue at the outlet of a power plant boiler, the flue is DN1000, the design temperature is 400℃, the pressure is 5kPa, and the total length of the pipe is 40 meters. Follow these five steps:
Step 1: Calculate the displacement amount.
40m pipe, expansion coefficient of 16mm/100℃ (304 stainless steel), temperature rise from normal temperature of 20℃ to 400℃ temperature difference of 380℃, axial elongation =40× (0.016×3.8) =2.432m? Wait, this doesn't work out right. Oh, the linear expansion coefficient should be used, generally carbon steel is about 12×10⁻⁶/℃, so Δ L =40×12×10⁻⁶ ×380=0.1824m =182.4mm. With a safety factor of 1.2, an axial compensation amount of ≥219mm is required. Find when selecting a model High temperature axial expansion jointLook at the column of axial compensation in the specification table, and pick one ≥219mm.
Step 2: Match the diameter and pressure.
DN1000 corresponds to an inner diameter of 1000mm, no problem. The pressure of 5kPa is very low, and the commonly used PN0.1MPa can be used. Note that the flue gas at the boiler outlet may contain sulfur, and 304 stainless steel is recommended for flange material.
Step 3: Determine flange standards.
Check the flange mark on the drawing, for example, it is GB/T 9115-2010, then choose the same standard. If not written, ask the design institute.
Step 4: Check the connection dimensions.
Measure the installation length of the expansion joint reserved on site, if it is 600mm. The total length L selected must be ≤550mm (leaving 50mm operating space). Look at the total length corresponding to each wave number in the expansion joint specification table. For example, if the total length of 4 waves is 500mm, then choose 4 waves. If the number of waves is too small and the amount of compensation is not enough, you have to use more waves or Straight pipe pressure balanced expansion joint(It is compact and compensates heavily).
Step 5: Confirm the attachment.
Do you need to add a deflector? If the dust content of flue gas is high, add it. Do you need to add a pull bar? If the pipeline has a large lateral displacement, it is fitted with Large tie rod expansion jointOrComplex hinge type。 Here, the boiler outlet is mainly axial displacement, so it can be done without adding it.
Does it mean that after walking these five steps, you have a plan in your mind? Two days ago, I was choosing a project in the cement industry. According to this process, it took half an hour to get it done. The manufacturer's quotation was sent for direct check, and I didn't step on a thunder.
5. Three installation pits matching the specifications-no matter how good the expansion joint is, it will be useless
The specifications are selected correctly, but the installation is not correct, which is in vain. You must pay attention to these three pits:
Pit 1: The transport screw is not disassembled.
Many expansion joints will be equipped with transport screws (also called positioning rods) when they leave the factory to prevent bellows from deforming during transportation. It must be removed after installation is complete! Otherwise, the expansion joint is fixed to death by the screw, and the bellows cannot be deformed and directly torn when the pipe is thermally expanded. Dismantle or not? Refer to the FAQ of this site "Does the screw of the expansion joint need to be disassembled".
Pit 2: The flow direction arrow is installed backwards.
The flue has a medium flow direction, and the expansion joint is usually marked with arrows indicating the medium flow direction (such as "←→"). If the guide tube is installed backwards, it will not protect the bellows. The particles will directly wash the bellows, and it will leak in a few months. Before installation, be sure to see that the direction of the arrow is consistent with the flow direction of the smoke.
Pit 3: The flange bolts are tightened too tightly.
Flue expansion joint flange gaskets are generally not metal wound pads, but flexible graphite or PTFE pads. Excessive torque of the bolt crushes the gasket, which leaks. The correct way is to tighten diagonally symmetrically and evenly, and the torque is controlled at about 20-30N·m. If you screw the wrench so hard that it can't be turned, it must have passed.
Finally, if you really can't get the symbols on the specification sheet, send the pipeline drawings directly to the manufacturer and let the technology help you calculate them. This site hasMetal rectangular expansion joint、Non-metallic expansion joint、rubber compensatorWait for dozens of spot products, customer service is knowledgeable, just call and ask. But if you can understand it yourself, the initiative is in your hands, not to be fooled, is this the truth?