First, don't do it yet: shutdown, safety briefing and tool list, if you don't, you can get big things
Hey, I know you are in a hurry. The power plant is shut down for a few days, and I can't wait to rush up and work immediately. But listen to my advice: stop first and make the safety disclosure thorough. If something happens to this thing, it's no joke.
In the first step, you must get the Thermal Machinery Work Ticket to confirm that the boiler has been shut down, the flue temperature has dropped below 50℃, and the internal carbon monoxide concentration is qualified. Don't believe the nonsense of 'it doesn't feel hot anymore'. Hold a temperature measuring gun against the weld joint and measure it. By the way, there may be dust and sulfide in the flue, so it has to be forced to ventilate for more than half an hour. People who enter should fasten safety ropes, and people standing outside should watch.
In the second step, you have to make a full list of tools: a gas gun, an angle grinder, a welder, a hand hoist, a crowbar, a level rule, a torque wrench, and — don't laugh — a big tub of soapy water (for later leak detection). In addition, the newly bought expansion joint must be unboxed and checked in advance to see if the model on the nameplate and the design drawings are correct.
Tips: A lot of power plant accidents are caused by 'I thought it was down'. Always hang the' No Operation'sign and go to the DCS in person to verify that the valve is completely closed. The security briefing should be signed and photographed. Don't be lazy.
Second, how to dismantle the old expansion joint? Remember to "loosen before cutting" and don't deform the flue
Okay, it's time to dismantle the old parts. Guess what is the most common mistake? Gas cut when you come up. As a result, after cutting, it was found that the flue opening collapsed, and the seam could not be aligned during welding.
Xiansong— — All tie rod nuts should be withdrawn little by little, and do not screw them off directly. If there is a preload screw (such asLarge tie rod expansion jointThat kind), first loosen the nut to expose the thread buckle by 5mm, so that the expansion joint springs back naturally. This step is to release residual stress and prevent sudden collapse and injury to people.
Posterior cut— — Confirm that the stress is released, and then use gas cutting to cut along the welds on both sides of the old expansion joint. The cut is at least 10 mm away from the original flue wall, which is convenient for subsequent grinding. Remember: The cutting sequence is from the middle to both sides, cut in pieces, cut one piece and hang another piece away. Don't cut it all at once, otherwise the flue will 'collapse'.
attention: The weight of the cut old expansion joint is not small. When hoisting, you should estimate the center of gravity, and don't hit the flue flange.
Third, don't step on the pit when selecting the new expansion joint: metal or non-metal? This site has ready-made plans
That brings us to the crucial choice-do you use metal or non-metal? Many people come up and ask 'which one is durable'. In fact, it depends on the working conditions.
If the flue medium temperature exceeds 400℃ and there is corrosive flue gas (such as wet flue gas after desulfurization), I suggest you read this site directlyCorrugated expansion joint for power station industryOrHigh temperature axial expansion jointThey are metal, temperature and pressure resistant, but pay attention to the choice of 316L or 254SMO for bellows material, so don't be fooled by the low price. If the temperature is low (Non-metallic expansion joint (fabric fiber expansion joint)More cost-effective, it is light in weight, easy to install, and has a good vibration absorption effect. By the way, if the flue is rectangular, be sure to chooseRectangular non-metallic expansion jointDon't make do with the round ones.
Also, don't just look at the expansion joint itself, the matchingFlue gas baffle doorAndDesulfurization flue gas baffle doorWe have to check them all. Many power plants leak in less than half a year after replacing the expansion joint, which is caused by the inadequate seal of the baffle door.
Tips: This site hasMetal rectangular expansion jointAndRound Flap Door (Double Seal)Detailed parameter table, directly report to you the working temperature, pressure and displacement, and our customer service can recommend ready-made scheme to you. Don't do it for yourself.
4. The three most critical details during installation: centering, welding and adjustment of tie rod nuts
Started loading new pieces. This step is wrong, and the front is all in vain. There are three details you are staring at:
1. Alignment.After the new expansion joint is hoisted, check whether the two flange surfaces are parallel and coaxial with a level ruler and wire hammer. Adjust the gasket if the deviation exceeds 2 mm. Don't tighten the bolts hard, it will tear the bellows or fabric fibers.
2. Welding.Before welding, the grooves on both sides of the expansion joint are grinded clean to expose the metallic luster. Segmental jump welding method is adopted, the length of each welding bead does not exceed 50mm, and the next bead is welded after heat dissipation. Don't weld continuously, thermal stress can deform the bellows. Cool naturally after welding, don't water to cool. By the way, if it is a non-metallic expansion joint, the welding part is a metal frame, and the weld should be smoothed before installing a fabric skin.
3. Tie rod nut adjustment.This is a step that many people don't understand. Once installed in place, adjust the tie rod nut according to the designed pre-tension or pre-compression amount. How exactly to adjust? It is clearly written in the question and answer of this site-first loosen all nuts, measure the actual free length of the expansion joint, and then turn the nut to make the length equal to the designed installation length. When adjusting, twist diagonally alternately to ensure uniform force. After adjustment, screw the locking nut to death to prevent it from loosening during operation.
V. Acceptance trial operation: You can judge whether the installation is installed with naked eyes and ears
Once installed, don't rush to seal the door. Try these local methods:
macroscopic method— — Brush soapy water on the outside of the weld, and blow it from the inside of the flue with compressed air (the pressure is about 0.05MPa) to see if there are any bubbles coming out. If there are bubbles, it is leakage, repair welding. Non-metallic expansion joints are simpler. Check the pressure plate bolts around the skin one by one to see if the sealing strip has been squeezed out.
Ear method-After the unit is started, listen to the sound near the expansion joint. If there is a "hissing" air leak sound, or a "banging" impact sound, it means there is a displacement jam. Take out your mobile phone and record a video, and slow down to see if the bellows expands and contracts evenly with the temperature change. If you retract while extending, it is that the tie rod is not adjusted in place.
After 24 hours of operation, stop the furnace and review the flange bolt torque once, and make up for tightening if it is loose. It's called a post-temper inspection, from experience.
6. Routine maintenance tips: When should I change it? Don't wait until you miss it
'How long will this stuff last?' To be honest, it depends on the working conditions. Generally, the design life of metal expansion joints is 80,000-100,000 cycles, but the flue gas in actual power plants contains sulfur and dust, so it has to be checked once every 3-5 years. Non-metallic expansion joint skin life is about 3 years, but if you buy one with anti-corrosion coatingRubber PTFE compensatorThe life span can reach 5 years.
How do you judge that it's time to change? Three signals:
① There are cracks, pitting or bulging visible to the naked eye on the surface of the bellows;
② The skin surface of the non-metallic expansion joint is hard and cracked, or the pressure plate bolts are seriously corroded;
③ The flue vibration is bigger than before, or you can smell the smoke during the inspection.
Don't wait for a leak before replacing。 After leakage, it not only affects the desulfurization efficiency, but also may cause the flue collapse. It is recommended that every time you overhaul, take a bright flashlight to illuminate the inside of the expansion joint, focusing on the peaks and troughs. If you find that the thinning exceeds the original thickness by 30%, replace it directly, don't hesitate.
Okay, these 6 steps you digest. Next time you change the flue expansion joint, go in this order, and basically you won't roll over. If you are really worried, send us the working condition parameters directly. This site has a complete set ofCorrugated expansion joint for power station industryAndNon-metallic expansion joint (fabric fiber expansion joint)In stock, and can be matched for youElectric plug-in insulation doorOrManual plug-in insulation doorIt's very worry-free.