Why do non-metallic compensators need regular maintenance? Structural characteristics and working environment determine its vulnerability
Non-metallic compensator, also called non-metallic expansion joint or fabric fiber expansion joint, mainly absorbs heat displacement, vibration and noise reduction in pipeline system. It consists of a flexible fabric layer, insulation layer, sealing layer and metal frame. This structure is inherently "tender" than metal bellows-the fabric layer is afraid of high temperature aging, acid and alkali corrosion, and mechanical scratching. What about the work environment? Desulfurization flue gas, hot air pipeline, cement kiln tail... are all working conditions with high temperature, dust and corrosive media. If you think about it, it would be strange if you were burned by smoke and fire every day.
Two days ago, I met the equipment supervisor of a cement factory.Rectangular non-metallic expansion jointIt took two years to leave it alone. As a result, the smoke was directly sprayed out, and the production line stopped for three days. Replacing a compensator itself is not expensive, but the loss of downtime is hundreds of thousands a day. So don't wait for a leak to remember, regular maintenance is about spending a small amount to save a lot of money.
Daily inspection: see, listen and touch, find problems in three steps
You don't need any sophisticated instruments for daily inspections, just use your eyes, ears and hands well.
look
Stand at a safe distance and glance at the whole first. See if the fabric layers are bulging, cracking, delaminating? Is there any rust or deformation in the metal frame? Pay special attention to welds and connecting bolts – usually the first thing that goes wrong is a loose bolt, resulting in a loose seal. Also, see if the deflector (if any) has any signs of wear and tear from the media. You can flip through our previous articles for the specific function of the guide tube, which will not be expanded here.
Listen
A normal non-metallic compensator runs with little to no sound. If you hear a "hiss" of air leakage, or a "click" of metal friction, it is 80% because the seal is broken or the frame is misaligned. Note when listening: Is it in a position with large displacement? For example, near the elbow and next to the fixed bracket.
Touch
After the machine is stopped (or with insulated gloves), touch the surface temperature of the fabric layer with your hand. If the local temperature is significantly higher than the surrounding temperature, it means that the internal insulation may collapse or break, and the heat is transferred directly to the external surface. Don't be careless at this time, the high temperature will accelerate the aging of the fabric, and it won't take long to leak.
Practical maintenance: cleaning, tightening and anti-corrosion, one cannot be missed
What to do after finding a minor problem? Three steps: clean, fasten, and prevent corrosion.
Cleaning: Use a soft brush or compressed air to clean up dust and scale on the surface of the compensator. It is strictly forbidden to scrape with a hard metal blade-once the fabric layer is scratched, it is the future leak point. If the medium is viscous (such as desulfurization slurry), rinse it with clean water and dry it before subsequent treatment.
fastening: Check all connecting bolts and tie rod nuts. Note: How to adjust the expansion joint tie rod nut? It's not that the tighter you screw it, the better. The function of the tie rod is to limit the excessive displacement and at the same time ensure the design compensation amount. If you tighten too tightly, it limits the normal displacement, and the pipe stress will transfer to the weak link. Standard practice: Pre-tighten to the design value and then lock the loose nut. You can refer to the manufacturer's installation instructions, or the Q&A of "The Function of Expansion Joint Tie Rod" we wrote before.
antisepticMetal frames, especially carbon steel, rust quickly in wet or corrosive environments. Find the corrosion spot, polish and remove rust first, and then apply temperature-resistant anti-corrosion paint twice. Pay attention to avoid the fabric layer, the lacquer will swell and harden when it touches the fabric, which is not worth the loss. For stainless steel frames (such asDesulfurization flue gas baffle doorMatching compensator), check pitting and stress corrosion cracks, if they appear, it will be a big trouble.
How to deal with common faults? Leakage, deformation, aging, right seat
Leakage, deformation, aging. It is handled differently.
leak: Confirm the leak location first. If it is on the fabric layer, the small hole can be temporarily treated with a special patch of repair glue (be careful to be temperature and pressure resistant). Don't mend the big tear, just change the components. If the leak is at the connection of the metal frame to the pipe, check that the seal gasket is damaged or that the flange surface is flat. Don't screw the bolts when you come up-if they are uneven, they won't seal them even if they break them.
deformation: Bulging of the fabric layer of the non-metallic compensator, usually due to collapse of the internal insulation, or the operating temperature exceeding the design value. At this time, you have to stop the machine and open it to check the insulation. Don't think about patching, the internal structure is broken and the external fabric won't last long. In addition, the deformation of the frame (such as the corner of the rectangular compensator tilting) is generally caused by excessive pipe thrust or installation deviation, so it is necessary to recalculate the pipe stress and adjust the bracket.
Aging: The fabric layer has a large area of cracking, hardening and loss of elasticity. Don't hesitate to change it directly. Aging compensators have a sharp decrease in strength and may burst at any time. To judge the degree of aging, you can pinch the edge of the fabric with your hand-if it breaks when pinched, it is "osteoporosis".
From the beginning of installation, it determines the ease of later maintenance
This view may be a little counter-intuitive, but the fact is: if you don't install it correctly, the maintenance behind you will exhaust you. There was a chemical factory before,Non-metallic compensatorIt was installed very close downstream of the pipe elbow, and as a result, the compensator was subjected to additional bending moment during operation, and six were replaced in three years. Normal installation considerations include:
- Ensure that the pipes on both sides of the compensator are coaxial and the deviation is within the allowable range (refer to the model and size table of the expansion joint).
- The installation direction should be correct: Pay attention to whether the medium flow direction is consistent with the direction of the arrow of the expansion joint, and the insulation layer will be blown askew if it is reversed.
- Temporary supports to be removed: Tie rods or supports may be installed for the convenience of transportation when leaving the factory, which must be removed after installation, otherwise the compensator will not work.
- Pre-stretching (or pre-compression): If it is cold installation, the compensator should be pre-adjusted according to the ambient temperature. See the design drawings for specific values. If it is not adjusted, the compensator will bear additional tensile stress when the temperature is low in winter.
Think about it, these details are done in place, and the post-maintenance workload is directly halved. Didn't do it? Then just wait to wipe your ass every few months.
When is it time to get a new one? Don't cause trouble just to save money
Many bosses think that "continue to use it if it can still be used", but the non-metallic compensator not only decreases in performance at the end of its life, but also may suddenly burst. Then when do you have to change?
First, achieve the designed service life.According to the national standard for non-metallic expansion joints (JB/T 12235-2015), the service life under normal working conditions is generally 3-5 years. If it is overrun, it is recommended to do regular water or air pressure tests, but don't expect it to last long.
Second, irreparable damage occurs.For example, large-area ablation of fabric layer, serious deformation of metal frame, cracking of weld seam, etc. Don't think about welding and repairing-once the structural integrity of the non-metallic compensator is destroyed, the reliability after repair is greatly reduced.
Third, there is no cure for leakage.Patched more than three times and still leaking? Don't worry about it, get a new one. The indirect cost of leak repair per shutdown is much higher than the cost of replacement. Don't count this account? Ask the cement factory in front.
By the way, when replacing a new one, it is recommended to check the pipe bracket and adjacent equipment (such as flue gas baffle door, electric plug-in insulation door, etc.) simultaneously. Often, the old compensator is broken because the pipe displacement exceeds the standard, and the root problem is not solved, so the new one dies early.
Don't wait for the smoke to remember. Look, listen, touch regularly, tighten what should be tight, clear what should be cleared, and change what should be changed. The non-metallic compensator is actually quite solid-as long as you have given it "due care".