Step 1: Figure out what type of expansion joint you have on your hand – non-metallic expansion joint or metal?
A few days ago, a customer called in a hurry, saying that the expansion joint on their flue had leaked after less than a year of use, and asked me if there was something wrong with the quality. I asked him to take a picture and come over and see, tsk, he bought itNon-metallic expansion joint (fabric fiber expansion joint)As a result, the installation position is next to a high-temperature pipe without heat insulation, and the surface temperature has already exceeded the design upper limit. Who do you think you can blame for this?
So, I want to extendFlue skin expansion joint lifeThe first step is to figure out what kind of thing you have. It is not to look at the appearance pattern, but to look at the core material and working principle.
- Non-metallic expansion joint: It mainly uses flexible materials such as fabric fiber, rubber and polytetrafluoroethylene, and absorbs displacement by elastic deformation of the skin itself. Like the one in our stationRectangular non-metallic expansion joint、rubber compensator、PTFE compensatorAll fall into this category. It has the advantages of no pressure and good corrosion resistance, but it is afraid of high temperature and sharp objects. Usually used in medium and low pressure flue, desulfurization system and other places.
- Metal expansion joint: likeUniversal corrugated expansion joint、High temperature axial expansion joint、Corrugated expansion joint for power station industryIt is compensated by the deformation of the metal bellows. It has high strength and high temperature resistance, but is afraid of chloride ion corrosion and fatigue. It is often used in main steam pipelines and high-temperature flue gas pipelines.
Non-metals are afraid of burning, metals are afraid of corrosion。 If you find that the medium temperature at the installation position exceeds 200℃, you must choose metal; If the working medium contains sulfur and chlorine, the non-metallic skin is more robust. Make the wrong type, and the life span is cut in half directly. Is this the truth?
Step 2: Do these 3 things well before installation, and the life will be doubled directly (attached with the installation pit avoidance list)
Two days ago, I met an installer, and he himself said, "We never read the instructions when installing expansion joints. Anyway, it's done if we tighten them without leaking." I shook my head after listening to it-the installation was not standard, and the back was full of pits.
Let me tell you three key actions that have at least doubled their lifespan:
1. Check the amount of cold tightening or pre-stretching
Whether metallic or non-metallic, there are usually pre-stretched or pre-compressed amounts available at the factory. Such asUniversal corrugated expansion jointBefore installation, it is necessary to calculate the compensation amount according to the design temperature, and lock it with a tie rod or limit nut on site. You must not foolishly screw the tie rod nut directly to death, you have to leave room for adjustment. How exactly to adjust? Look at the question and answer on "How to adjust the expansion joint tie rod nut" in the station.
2. Check the direction of the tube
Many expansion joints have a guide tube inside, such asCorrugated expansion joint for power station industryOne end of the guide tube is a bell mouth, which must be directed in the direction of the medium flow. Installation backwards will cause the media to flush the bellows and double the corrosion rate. This detail is particularly easy to overlook, but you can see it as soon as you take apart the flange.
3. Avoid stress concentration points
During installation, the pipes on both sides of the expansion joint must be strictly aligned, and the opposite mouths cannot be forcibly pulled. EspeciallyNon-metallic expansion jointThe skin is soft, and deadlifting will cause the skin to twist and wrinkle, and it will crack in less than three months. It is best to install limit bolts at the flange connection, and then tighten them after fixing them.
Attachment: Installation pit avoidance list (print it out and post it on the wall)
- Check whether the model is consistent with the design, especially looking at the material, nominal pressure and compensation amount
- Confirm that all transport supports and limits have been removed (many people forget to remove!)
- Clean the sealing surface of the flange, and the gasket must be temperature-resistant and corrosion-resistant (PTFE coated gasket is best)
- Tighten the bolts in diagonal order for 2-3 times, and the torque value shall refer to the standard
- Insulate heat after water pressure or air pressure test. Do not wrap heat insulation material directly on the expansion joint
Step 3: Where to look for daily inspections? Tell you the 3 most problematic areas
What's the use of a patrol inspection? I'm telling you,Flue skin expansion joint lifeThe length often depends on whether you can find the signs in advance. Three of the most problematic areas, you can just take two minutes a day to scan:
Part 1: Joint of weld and flange
The connection between the bellows and the end pipe of the metal expansion joint is a weak area, especiallyLarge diameter thick wall expansion jointThus, the welding heat-affected zone is prone to generating micro-cracks. If you take a flashlight to shine on it, if you see thin lines of rust or exudation, it is probably leaking. For non-metallic expansion joints, see if there is bulging or delamination at the flange holder.
Part 2: Skin surface (especially folded area)
If the fabric fiber layer of non-metallic expansion joint appears fluffy, discolored and hardened, it indicates that it is aged. The most fearful thing is that the particles with sparks in the flue will burn through the skin directly. You touch the surface temperature. If the local temperature is abnormally high, quickly stop the furnace for inspection. There used to be a power plant that just didn't pay attention, and as a result, the flue spark burned a hole in the skin, which almost caused an accident.
Part 3: Guide tube and dust accumulation inside
Many people don't watch this, but it is very critical. Such asDesulfurization flue gas baffle doorThe nearby expansion joint, the flue gas is liquid and ash, and the guide tube is easy to scale or block. Once the deflector is deformed, the media will flush the bellows. You stick an endoscope through the manhole and take a look, or regularly disassemble the flange to clean the dust. If there is more dust, the lifespan will immediately decrease.
Step 4: How to judge when the lifespan is close? Change these signals as soon as they appear
Exactly how many years do expansion joints last? The answer is-it depends on the working conditions. Normal non-metallic expansion joints are normal for 3-5 years in a non-corrosive flue gas environment below 150℃; The metal expansion joint is on the main steam pipeline of the power station, and the design life is generally 8-10 years. But don't wait for this number. If any of the following signals appear, don't hesitate to arrange for a replacement immediately:
- Air leak, smoke leak, liquid leak: This one is the most direct. Take a piece of paper near the flange or weld, and the paper is blown away.
- Obvious deformation or abnormal noise: Bulging, denting, or "crunching" rubbing sounds in the metal bellows during operation indicate fatigue cracks inside.
- Local hardening and cracking of skin: The surface of non-metallic expansion joints is hard and brittle, and even crumbles when pressed by hand. Don't think about repairing them, just change them.
- The amount of compensation is clearly insufficient: If you observe the pipe support or expansion joint tie rod, if you find that the displacement has exceeded the design limit, or the expansion joint has been straightened and compressed to the end, it means that it has long been unable to compensate.
Don't hold on just to save money。 An expansion joint burst, causing the whole pipeline to shut down, and the loss may be dozens of times that of replacing it with a new one. You do the math.
Step 5: Don't rush to dismantle it if it is broken. Try these two low-cost repair methods first
Don't rush to place an order to buy a new one. Some minor problems can be saved by yourself. Let me share two practical experiences:
Method 1: Non-metallic skin is partially damaged-patch
If the damaged area is less than the size of a palm, and the inner sealing film is not damaged, you can use a fabric fiber cloth of the same material, with high-temperature resistant silicone or special repair glue, and stick a patch on it. Before operation, be sure to clean up the damaged area and polish it roughly, so that the glue can stick. After sticking it, press it with a heavy object for 24 hours before resuming use. However, this method is only suitable for low-pressure, low-temperature flues, and you have to check the patch weekly for warping. If the damage exceeds 30% of the area, replace it, don't stick it hard.
Method 2: Tiny cracks of metal bellows repaired by argon arc welding (limited to low pressure occasions)
ForUniversal corrugated expansion jointIf you have an argon arc welding machine on hand, you can polish the grooves at both ends of the cracks and repair them with welding wires of the same material. After welding, do a penetration test to confirm that there is no leakage before reassembling. Note: This method is only suitable for the pressure below 0.5MPa and the temperature below 400℃. Moreover, the welding heat-affected zone may reduce the fatigue resistance of the base metal, which belongs to "life extension with illness". It can last for half a year to one year at most, and then it must be replaced.
Alas, at the end of the day, restoration is just an emergency measure. Want to radically extendFlue skin expansion joint lifeSelecting the right type, standardizing the installation, and inspecting on time are indispensable. If you follow these five steps, you can use it for five or eight years. If you are still unsure, feel free to flip through the questions and answers related to expansion joints in our station, which is more reliable than asking anyone.