The flue expansion joint is leaking air, or it looks deformed? Don't rush to get started and dismantle it, maybe the more you repair it, the worse it gets. This article is specifically written for you-every step tells you exactly how to do it, just follow it, and don't waste money.
Step 1: Don't be in a hurry to remove it, find out what type of expansion joint you have
Is this thing in front of you metal or non-metal? This is a mistake, and the rest is all for nothing. Metallic ones are commonly corrugated, such asCorrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement IndustryOr the kind of squareMetal rectangular expansion joint。 Nonmetallic, usuallyRectangular non-metallic expansion jointOrNon-metallic expansion joint (fabric fiber expansion joint)It feels like cloth. How to distinguish? Simple: take a magnet and suck it, the metal one can suck it; The non-metallic ones are fabric or rubber composite at first glance. And the ones with tie rods, mostly metal. If you are still unsure, flip through the equipment nameplate or the previous purchase order. It is clearly written on it. Don't guess by your feeling-two days ago, a customer forced non-metallic ones as metallic ones. As a result, the welding gun caught fire. Do you think it was wrong?
Step 2: Safety first, shutdown and pressure relief!
This step is life-saving! There may also be high-temperature flue gas in the flue, or residual corrosive gases (such as acid gases after desulfurization). You must wait until the system is completely cooled, emptied, and ventilated before you can do it. How to operate it? Turn off the heat source, open the release valve, and let the pressure in the pipe drop to zero. Then test it with a gas detector to confirm that there are no flammable or harmful gas residues. Don't forget to hang a "under overhaul" sign on the operation switch-don't say I'm long-winded. Some people really think it's troublesome to do it directly, and as a result, they get a big blister. Safety, if you save one step, the hospital may charge you 2,000 yuan more.
Step 3: How to fix the metal expansion joint?
Local crack of bellows, falling off of guide tube and aging of flange gasket. Let's talk about cracks first-if it's just a small surface crack, you can sand it clean with an angle grinder and then repair welding. But pay attention! The wall of the bellows is very thin, and the ordinary welding heat is directly deformed. It is necessary to use stainless steel welding electrode of the same material, adjust the current, and adopt jump welding method (weld for a section, stop for a while, and wait for cooling). If the crack is in the trough, or has already penetrated several layers-then don't bother, just replace it with a new one. Recommended BuyUniversal corrugated expansion jointOrHigh temperature axial expansion jointJust select according to your working condition and temperature.
What should I do if the deflector falls off? Check, if only the screws are loose, just tighten them; If it has fallen and is stuck in the pipe, remove the flange and refix it. Refer to the "Specific Function of Expansion Joint Guide Tube" written in our previous Q&A. This thing is mainly to protect the bellows from being washed by high-speed airflow. If it falls off, it must be put back.
Also, don't forget to check the tie rod nuts. The tie rod of many metal expansion joints is used to limit the displacement, and the nut will loosen over time. How to adjust? Refer to the question and answer "How to adjust the tie rod nut of the expansion joint"-first loosen the nut, let the expansion joint reset naturally, and then preload it again according to the designed displacement. Generally, it is screwed to about 80% of the design value, leaving some margin. And guess what? Many air leakage problems are actually that the tie rod is not adjusted properly, resulting in the bellows being overstretched and cracked.
Step 4: The repair routine of non-metallic expansion joints (fabric fibers) is different
Such expansion joints (such asRectangular non-metallic expansion joint) It is easiest to wear out at corners, or be corroded by acid and alkali to make a hole. If the damaged area is not large-for example, less than a slap-you can buy silicone cloth or fluorine tape of the same material, then apply high-temperature sealant, and stick two layers inside and outside like a patch. Attention! When sticking, ensure that the surface is clean and dry, compact and exhaust, and then wait for the glue to be completely cured before turning on. Generally, it takes 6 hours in summer and more than 12 hours in winter. Don't worry, the glue turns on before it dries thoroughly, and it collapses when it blows.
If the damaged area exceeds 30%, or the whole ring is aging and brittle, and it breaks when pinched-then don't make it up, and it won't last long. Buy spare parts directlyNon-metallic expansion joint (fabric fiber expansion joint)To replace. When dismantling the old ring belt, take a photo with your mobile phone and write down the original number of layers (single or multi-layer) and the specifications of the beading bolts (M10 or M12). After the new ring belt is installed, tighten the bolts symmetrically-first twist the diagonal corners, and then gradually apply force to prevent deviation. Many people will ignore this step. As a result, after installing it, it is loose and tight, and it leaks again.
Step 5: How to accept after repair?
Don't rush to put it into use immediately after it is repaired. Do static inspection first: see if the weld seam has any leakage and wrinkles, and whether the bolt tightening torque is uniform. Then brush with soapy water on the weld and flange interface, and introduce compressed air at 80% of the design pressure to see if there is any bubbling. If it is bubbling, it means it is still leaking, and it has to be reprocessed.
Okay, okay? Get the system back up and running. But remember: heat up and pressure up slowly! The flue expansion joint is most afraid of rapid cooling and heating, and the heating speed is controlled at no more than 5℃ per minute. At the same time, observe the amount of displacement of the expansion joint-see if the expansion and contraction are within the allowable range. If you find that the displacement is abnormally large or stuck, stop the machine quickly and check whether the pipe support and hanger are stuck by sundries. This problem is often overlooked, but a lot of deformation air leaks are caused by it.
Tip: How to extend the life of flue expansion joint at ordinary times?
Pay more attention to whether the guide tube has fallen off at ordinary times (refer to the question and answer "Specific function of the guide tube of expansion joint"). Clean up ash regularly-especially the ash in the trough of metal bellows, which will scale over time and affect expansion and contraction. Also, don't let acidic condensate soak the bellows for a long time. If there is condensate in the working condition, consider installing a drain valve or doing heat insulation and tracking under the expansion joint. If the operating temperature exceeds 400℃ during model selection, preference will be givenHigh temperature axial expansion joint； If the smoke is strongly corrosive, usePTFE-lined hoseOrPTFE compensatorMore reliable. Alas, in the final analysis, choosing the right product in the early stage is a hundred times worry-free than repairing it in the later stage. Is this the reason?