Step 1: Find out what kind of expansion joint you have on your hand before checking
Don't come up and do it. Is this thing in front of you metal or non-metal? Is it round or square? Is it with or without a tie rod? This determines that the focus of your later examination is completely different. For example, if you are a power plant boiler flue, there is a high probability that you will useCorrugated expansion joint for power station industryOrNon-metallic expansion joint (fabric fiber expansion joint)； If it is a pipeline in the cement industry, it may encounterMetal Corrugated Expansion Joints in Cement Industry。 Look at the nameplate first. Is it on the nameplate? Then it depends on the shape-the metal bellows can be recognized at a glance, with circles of ripples; The non-metallic ones are fabric bands, which are soft to the touch. Look at whether there are pull rods, guide rings and limiting devices. These structures determine the inspection method. Get the wrong type, and the rest is all in vain.
Step 2: Appearance inspection-don't miss cracks, deformation and corrosion
This step is the most intuitive, but it is also the easiest to see the flowers. You walk around the expansion joint and keep your eyes on three places:
●Bellows body: Is there a crack? Are there any bulges? Especially in the trough position, stress corrosion cracks are most likely to occur. Shine it with a flashlight. Don't touch it with your hands. It's hot. If you find a crack, don't hesitate to report it directly. Cracks are no joke. Smoke leaking out not only pollutes, but may also burn people.
●Metal site: Is there any rust in the flange, receiver, and tie rod? If the corrosion is more than 1mm deep, you have to be vigilant. Two days ago I met a customer from their factoryDesulfurization flue gas baffle doorThe expansion joint beside it, because of corrosion and perforation, leaked in the middle of the night and alarmed.
●Non-metallic band: If yesNon-metallic expansion jointFocus on whether the ring belt is delaminated, blistered and damaged. The fabric will be hard and brittle after aging, and will shatter when pinched.
Tips: Don't just look at the surface, sometimes the cracks are very fine, and you have to use a magnifying glass or penetration detection to find them. But for daily inspection, you just have a flashlight. If you really find anything suspicious, put on the equipment.
Step 3: Displacement check-whether the tie rod, guide ring and limit device are stuck
The function of the expansion joint is to absorb the thermal displacement of the pipe. If your tie rod is loose and the guide ring is stuck, the displacement is all stuck in the bellows, and it will soon crack fatigue.
How to check? It's simple.
1. Inspectiontie rod: Twist the nut with your hand to see if it is loose? PressHow to adjust the tie rod nut of expansion jointExperience, the preload force should be within the range specified by the manufacturer. Tighten when loose, but don't screw to death-leave a gap for thermal expansion. If the nut has rusted to death, spray some rust remover and move again.
2. Inspectionguide ringAndlimiting device: This thing is very common in metal expansion joints. Do you see if there are any wear marks on the inner wall of the guide ring? A scratch indicates that the bellows rubs against the deflector during lateral displacement, which is dangerous. If the limiting device is stuck, the bellows will lose lateral protection.
3. Inspectiondisplacement amount: Take a tape measure to measure the distance between the flanges at both ends of the expansion joint, and compare the initial length during installation. If the difference exceeds the design allowable range (this data is available in the factory data), it means that there may be a problem with the pipe support and hanger.
Hey, don't bother. This step can detect 80% of the problems ahead of time. Many factory diagrams are skipped directly to save trouble, and as a result, the bellows are bent like twists.
Step 4: Seal Inspection-Non-metal Ring Belt and Metal Hose Leakage
Flue leakage is the most annoying. How to check the seal?
● ForNon-metallic expansion jointYou take a piece of tissue paper and make a circle along the pressing surface of the loop band and flange. If the paper can be blown, it means there is an air leak. Or directly use the back of your hand close to the seam and feel if there is any airflow. Windy is leaking.
● ForMetal expansion jointFocus on the weld connecting the bellows and the end pipe, andMetal hoseAt the joint. Spray the weld with soapy water to see if there are bubbles. If there are bubbles, repair the welding quickly and don't delay it.
● Another isrubber compensatorOrPTFE compensatorAir leakage typically occurs at the flange gasket. You might as well see if the tightness of the flange bolts is even? Tighten diagonally, not one end tight and the other loose.
Note: If it is during maintenance, do air tightness test if conditions permit. No conditions? Then use the above earth method, it will work as well.
Step 5: Internal Inspection (If Conditional) -Deflector and Bellows Wear Degree
This step needs to be shut down and disassembled, and not every inspection can be done. But when it comes to overhauls or annual overhauls, it must be done.
After you disassemble the expansion joint, focus onguide tube。 Remember, the deflector is designed to protect the bellows from being washed by high-speed smoke. If the guide tube has been worn out and fallen off, the bellows will be directly exposed to the smoke, and its life will be sharply reduced. I've seen one beforeLarge diameter thick wall expansion jointThe guide tube was worn to a thin layer of skin, and the owner thought it was normal-isn't this laying a mine for himself?
Look at the inside of the bellows again: are there any wear, scratches and pitting? Especially if there is any dust accumulation? Excessive dust accumulation will affect the free expansion and contraction of the bellows. Take a flashlight and clean up any dust. If you find that the wall thickness of the bellows is thinned by more than 20% of the design value, change it directly, don't hesitate.
In addition, checkPTFE-lined hoseDid the inner lining come off? Once the PTFE layer is damaged, the corrosive medium will corrode the metal mesh, and the whole hose will be scrapped quickly.
Bonus Reminder: When should I change? Don't hold on to these signals
After talking about so many inspection methods, let me give you a final reminder-which signals appear to indicate that the expansion joint should be retired?
●crack: If penetrating cracks appear at any position, change them directly. Don't think that welding can be used. Welding will change the heat treatment state of the bellows, and the stress concentration will be more serious.
●deformation: The bellows appears obvious twist, depression and bulge, indicating that plastic deformation has occurred and the compensation ability is zero.
●leak: When the seal fails, air leaks and liquid leaks, and the plug can't be blocked.
●Over-limit displacement: The measured displacement exceeds the design value by more than 20%, and the pipe support cannot be found, which indicates that the expansion joint has been fatigued.
●USEFUL LIFE: According toService life of expansion jointIndustry experience, metal expansion joints generally 8-10 years, non-metal 3-5 years. Even if it is not broken at the end of the year, it is recommended that you do a comprehensive test. Don't feel bad about those few dollars. Once it explodes, the downtime loss is more than ten times more expensive than replacing an expansion joint.
Well, follow these 5 steps, and you will know the state of the flue expansion joint. Checking this matter depends on careful and common sense, just don't be lazy.