Step 1: Find out if your flue is round or square-choose the right expansion joint type
Two days ago, a customer told me that he bought the expansion joint and found that it couldn't be installed, and the size difference was more than ten millimeters. I asked him if it was round or square, and he froze for a moment and said "I didn't pay attention". You see, if you take this wrong step, you will work for nothing.
The flue expansion joint, to put it bluntly, is the "shock absorber + expansion joint" on the pipe. If your flue is round, you have to chooseUniversal corrugated expansion jointOrHigh temperature axial type expansion joint; If it's square, you have to use itMetal rectangular expansion jointOrRectangular non-metallic expansion joint。 Don't get confused-it's common sense that the round ones don't fit the flange above, and the square ones don't fit into the round pipe.
Tips:When you are unsure, look directly at the cross-sectional shape of the flue interface. There is no way to judge, so use a rope to measure the circumference and then calculate the diameter. The circumference of the circle divided by 3.14 is the diameter, and the length and width of the square will do.
Step 2: Measure these 3 key dimensions: diameter, length, and flange hole pitch
Okay, the shape is clear, now take out the tape measure and work. Remember three numbers:Diameter, length, flange screw hole pitch。
- Diameter:Is the inner diameter of the pipe. Don't measure the outer diameter. The outer diameter is the tube itself, and the expansion joint interface is matched according to the inner diameter. If it is a rectangle, measure the width and height, denoted as W × H.
- Length:The net distance between the flanges at both ends of the expansion joint. Attention! This length is not a random measurement-you have to consider the position of the pipe after thermal expansion and contraction. In the fourth step, the compensation amount will be detailed. Here, we first measure the original installation length.
- Flange screw hole pitch:Take a caliper to measure the center distance of two adjacent bolt holes, and then count the number of bolt holes. For round flanges, they are usually based on the standard pressure grade (PN0.6, PN1.0), but there are some non-standard goods if they are not fully guaranteed. I've seen an old power plant, and their flange hole distance is 2mm different from the national standard. As a result, the bolts can't go in. Do you think it's irritating?
Note:The screw hole distance is the center of gravity distance, not the edge distance. Many people take a ruler to measure from the edge of the hole to the edge of the hole, which doesn't match. Correct way to do it: Measure the center distance of two symmetrical holes and divide by 2 to get the radius, and then find the position of adjacent holes.
Step 3: Don't ignore the deflector and tie rod-they directly affect the mounting size
What is the relationship between the deflector and the tie rod and the installation size? It matters a lot.
guide tubeIt is a metal cylinder installed inside the expansion joint, which is used to guide the medium and protect the bellows. Its length is shorter than the expansion joint itself, but if the installation space is particularly compact, the protruding part of the guide tube may push against the elbow or valve. We have an article on our site dedicated toFunction of Expansion Joint Guide TubeIt is mentioned that the diameter of the guide tube is usually 10-20mm smaller than the inner diameter of the pipe, and this gap should not be too large, otherwise the diversion effect will be poor. Therefore, when you set the installation size, you must add the length of the guide tube to ensure that it can fit in the pipe.
tie rodWhat? It mainly plays a limiting role to prevent the expansion joint from excessively stretching or compressing. Customers in our FAQ askHow to adjust the tie rod nut of expansion joint, the answer is very simple-the tie rod will be pre-adjusted to a certain position when leaving the factory, and you have to readjust it according to the actual compensation amount during on-site installation. If the length of the tie rod exceeds the flange surface, then the installation space you have reserved will not be enough. Therefore, when ordering, you should make it clear to the manufacturer: the distance between the fixed brackets at both ends of the pipe, so that the length of the tie rod can match.
Step 4: Calculate the compensation amount according to the working condition and calibrate the installation length in reverse direction
This step is technical work, but don't be afraid, I'll dismantle it.
Expansion = linear expansion coefficient × pipe length × temperature difference。 The expansion coefficient of carbon steel pipeline is about 0.012mm/m·℃, and that of stainless steel is 0.016. For example: a 20-meter-long carbon steel flue, rising from normal temperature of 20°C to 300°C, with a temperature difference of 280°C, expansion =0.012×20×280=67.2mm. Which means that this pipe will stretch 67mm.
How to determine the installation length of the expansion joint? The general practice is to reserve half of the compensation amount for the expansion joint when it is cold. For example, in this working condition, the expansion joint needs to absorb 67mm compression, so the installation length is 33.5mm more than the free length (the nominal length of the manufacturer), so that it just retracts into its original position in the hot state. Reverse calibration means: you calculate the compensation amount first, and then push back the installation length, instead of blindly installing it according to the reserved position of the pipeline.
Reminder:Don't forget to consider pressure thrust! In the high-temperature and high-pressure flue, the bellows will bear the thrust generated by the internal pressure, which will make the expansion joint additionally compress, you have to count it in. Usually our stationsStraight pipe pressure balanced expansion jointIt is to offset this kind of thrust, and it is preferred when selecting the model.
Step 5: These Size Adjustment Techniques Can Rescue Emergencies During Site Installation
Armchair is over, and when you arrive at the scene, you will find that theory never keeps up with change. The pipeline is misaligned, the flange is corroded, and the bolt holes are not aligned... What should I do?
- Misalignment adjustment:If the flange surface deviation is within 3mm, you can useMetal hoseTransitionally, its flexibility absorbs small misalignments. We haveMetal hose size comparison tableJust choose a suitable diameter.
- Wrong screw hole:Don't think about reaming on site, it will weaken the flange strength. The correct way is to addeccentric flange gasketOr find a manufacturer to customize non-standard flanges.
- Not enough space:If the length of the expansion joint is exceeded, remove a section of pipe? Too much trouble. Try usingSleeve type pipe expansion joint, it is retractable by itself, and the mounting length can be adjusted within a certain range.
- Tie rod interference:Loosen the tie rod nut to the limit and re-tighten after installation. We have a question in our FAQDo you need to remove the screw of the expansion jointThe answer is: the transport screw must be disassembled, and the tie rod does not need to be disassembled, but it needs to be adjusted.
All dimensions must be confirmed with the manufacturer before installation, especially for non-standard items. You don't want to put on and remove iron bumps that are hundreds of pounds bigger, do you? Tsk, that scene, the labor cost alone is enough for you to drink a pot.
Hopefully, through these five steps, you canFlue expansion joint mounting dimensionsThat's a good deal. If you still have any questions, go directly to our website aboutMetal rectangular expansion jointOrNational standard for non-metallic expansion jointsThere is a detailed table of parameters.