First, look at the symptoms first: What does the expansion joint deformation look like? Don't treat the normal as an exception
You stand next to the boiler and look up at the expansion joint in the flue and always think something is wrong. But to be honest, some "deformations" are actually normal thermal displacements, so don't panic when you see the bulge. So how do you tell the difference?
Look at the surface first.Normal expansion joints, whetherMetal rectangular expansion jointStillNon-metallic expansion joint (fabric fiber expansion joint)The corrugated or fabric surface should be smooth and continuous. If you find that a certain section of ripples has obviously collapsed, or the fabric layer is wrinkled and twisted, there is a high probability that it is really deformed.
Touch the connection again.Use your hands (wearing gloves!) to touch along the edge of the flange to feel the feeling of steps. Under normal circumstances, the flange and the pipe are flush. If there is a height difference, it means that the expansion joint has been displaced or twisted.
Finally, look at the deflector.If your home is installed with a guide tubeUniversal corrugated expansion jointPay attention to whether there is any abnormal noise during operation-the clicking metal friction sound is mostly due to the deviation of the guide tube, which is also a manifestation of deformation.
Don't putexpansion joint tie rodThe normal adjustment clearance is treated as a deformation. The tie rod originally has a margin of movement, which is designed to absorb displacement, not broken. If you can't tell, you can take a ruler to measure the original size when installed, and you will know by comparing it.
Second, tracing back to the source: the common causes of deformation, have you been recruited?
The expansion joint is not deformed for no reason. I have met several customers, and when they came up, they asked "can they be repaired?" When I asked about the working conditions, nine out of ten reasons were the following.
1. The tie rod nut was not loosened during installation.This one is the most pitiful. Many installers try to save trouble,The screw of the expansion joint needs to be removed(The locking screw for transportation should be removed or the tie rod nut should be loosened) But it was not removed and welded directly. As a result, when the pipeline is hot, the expansion joint has no expansion and contraction space, and it is forcibly squeezed and deformed. You say it was wrong or not?
2. The selection is not the right seat.The flue has a high temperature and a large pressure fluctuation, but you chose a low pressure onerubber compensatorOr not high temperature resistantPTFE compensator。 With a long time, it is a matter of time before the material ages, collapses and deforms.
3. Something is wrong with the pipe support.The stationary bracket or guide bracket of the flue is displaced, causing the expansion joint to be subjected to a lateral thrust that it should not be subjected to. If you don't believe me, check the bracket. It is probably loose or corroded.
4. The flue gas contains corrosive media.The flue gas after desulfurization contains acidic condensate, which will corrodeCorrugated expansion joint for power station industryThe metal bellows, after the wall thickness is thinned, is not strong enough, so it will naturally deflate.
Which one did you fall for? Don't worry, let's check it out step by step.
3. On-site inspection: judge the degree of deformation with naked eye and simple tools
A steel ruler, a vernier caliper, a marker. Oh yeah, and your eyes.
Step 1: Measure the corrugation spacing.Take a ruler and measure the distance between two adjacent peaks. Normally, the spacing should be even. If the spacing of a certain section suddenly becomes larger or smaller, it means that the place has been stretched or compressed. Note the maximum deviation value.
Step 2: Measure flange parallelism.Use a ruler against the flange face to see if the flanges on both sides are parallel. If a V-shaped angle occurs, it means that the expansion joint has been angularly displaced. This condition is more common inHigh temperature axial expansion joint, caused by uneven thermal expansion.
Step 3: Look at the pointer position.Some expansion joints come with displacement indicators (likeStraight pipe pressure balanced expansion jointIt's on it). See if the needle is out of the red cordon. Beyond? Don't hesitate, it's time to change.
Step 4: Listening to the sound to identify the position.Take a screwdriver as a stethoscope and put one end against the expansion joint housing and the other end against the ear. I heard a sharp hissing sound, probably a crack in the bellows and an air leak; When you hear the impact sound of "dong dong", it may be that the internal guide tube has fallen off.
After the test, record the data. Slight deformation (displacement within 10%) can still last for a while, but more than 20% is recommended to be treated immediately.
4. Selection and replacement: Select the right expansion joint according to the working conditions, don't buy the wrong model
Changing the expansion joint is not to buy radish and cabbage. If the parameters don't match, it will be useless to install it. You first prepare these information:
- Pipeline media: How high is the flue gas temperature? Is it corrosive? If it is wet flue gas after desulfurization, preference is givenDesulfurization flue gas baffle doorcomplementaryNon-metallic expansion jointOr with a corrosion-resistant liningPTFE-lined hose。
- displacement direction: Is it axial expansion and contraction, or horizontal and angular? If it is purely axial,External pressure single axial expansion jointOrUniversal corrugated expansion jointThat's enough. If you still have lateral displacement, you have to go upCompound hinge transverse expansion jointOrCurved tube pressure balance expansion joint。
- Installation space: Is there an obstacle next to the flue? Is the space large enough? If space is tight, you can considerSleeve type pipe expansion jointIt occupies a short length, but has a slightly worse sealing performance, which is suitable for low-pressure applications.
- Pressure rating: Generally, the boiler flue is slightly positive pressure or negative pressure, and 0.1MPa level is enough. However, if it is behind the booster fan, the pressure may reach 0.05~0.1MPa, it is recommended to chooseLarge diameter thick wall expansion jointA larger wall thickness is more resistant to deformation.
Attention! Don't buy by imagination. It is better to remove the old expansion joint and look at the model number on the nameplate. If you can't see the nameplate clearly, measure the outer diameter of the flange, the center distance of the bolt hole and the number of bolts. Send these data to our customer service, and we will help you match the most suitable one. If you are not sure, you can also refer to this siteModel and size of expansion jointQ&A.
5. Remove the old and replace it with the new: teach you the correct installation steps step by step
Before dismantling, stop the furnace, confirm that the pipeline has cooled to a safe temperature, and hang a warning sign of "Manned Working". Safety first, don't bother.
Step 1: Release pipe stress.If there is aexpansion joint tie rodFirst, loosen all the tie rod nuts, but can't be removed (to prevent sudden bounce and injury). Then use a jack or inverted chain to push the pipe up slightly, so that the expansion joint is no longer stressed.
Step 2: Remove the flange bolts.Remove diagonally with a suitable wrench, first remove the lower half, hold the expansion joint with temporary support, and then remove the other half. When disassembling, note that the flange surface may be stuck with old gaskets. Clean it with a blade, but don't scratch the flange sealing surface.
Step 3: Install the new expansion joint.When hoisting, the sling should be pocketed on the reinforcing ring or flange of the expansion joint, and never strangle it directly on the bellows-that will deform the bellows. Note the installation direction:The direction of the arrow of the expansion joint refers toMedia flow direction, don't pretend backwards.
Step 4: Adjust the pull rod.When a new expansion joint leaves the factory, the tie rod is usually locked in the minimum length position (shipped condition). You need to follow the design drawings, loosen the nut and adjust to the installation length. How to tune it? You can refer to this site'sHow to adjust the tie rod nut of expansion jointQ&A: First loosen the locking nut, then rotate the adjustment nut so that the length of the tie rod is equal to the size required by the drawing, and finally lock it. Note that after adjustment, it is necessary to ensure that the flanges on both sides are parallel and not crooked.
Step 5: Tighten the flange bolts.Use a torque wrench and tighten it in 3~4 times in the order of "crossing". The torque value is based on the recommended value of the gasket manufacturer- -Metal hoseThe torque of the flange gasket is generally 80~120N·m, and the torque of the soft connection section of the non-metallic expansion joint should be smaller to prevent crushing the fabric layer.
Step 6: Remove the transport locking piece.This step is so critical! Many accidents are caused by forgetting to tear them down. Remove all the welded limit plates or locking screws when leaving the factory, so that the expansion joint can expand and contract freely.
After installation, slowly raise the temperature for trial operation, and observe whether there is any abnormal displacement of the expansion joint. It is best to record the displacement once in the cold state and the hot state respectively, and reserve it for later comparison.
6. Prevention before it happens: What should we pay attention to in daily maintenance and inspection
With a new expansion joint, don't think it's once and for all. A good daily inspection can avoid 80% of accidental deformation.
Appearance inspection once a month.Focus on whether there are cracks, corrosion spots, dust and scale in the bellows. Especially there arerubber compensatorOrRubber PTFE compensatorParts, the rubber is easy to age, and it has to be replaced when it is hard or cracked.
Quarterly displacement checks.Use a ruler to measure the original installation length of the expansion joint and compare it with the current length. If it is found that the displacement exceeds 15% of the design value, it is necessary to check whether the pipe support has been displaced or the insulation layer has fallen off, resulting in uneven thermal expansion.
Clean up dust once every six months.The ash in the flue will adhere to the surface of the expansion joint, affecting heat dissipation and accelerating corrosion. You can sweep it with compressed air, don't scrape it with hard objects, so as not to damage the ripples.
Pay attention to the deflector status.If you use one with a guide tube at homeMetal Corrugated Expansion Joints in Cement IndustryOrCorrugated expansion joint for power station industryWhen the furnace is shut down for maintenance, use a flashlight to shine through the manhole to see if the guide tube is crooked and whether it has been washed out of the pit by the smoke. Once the guide tube is damaged, the high-temperature flue gas will be blown directly onto the bellows, and it will deform in minutes.
Don't wait until the expansion joint breaks and smoke leaks before replacing it in a hurry. Minor distortion is dealt with quickly, and the cost is much lower than an overhaul. If you pay more attention when you usually inspect, the equipment will cause you less trouble.
Hey, after saying so much, I actually want to tell you:Boiler flue expansion joint deformationIt's not terrible. As long as you follow the above steps to troubleshoot, select, replace and maintain, your flue system can fight for another ten years. If you still can't get it done, welcome to our website to flip through the product information, or directly find customer service, let's chat at any time.