How bad is the ash leaking conveyor working condition? — — Why non-metallic expansion joints are the first choice
The ash leakage conveyor, the environment is really bad. The heat, the dust, and the corrosive gas that poured out from time to time, the metal parts inside were like a melting furnace. We have seen many customers. At first, the metal expansion joint was cheap, but it leaked within half a year-either the weld cracked or the bellows wore out. Why? Metal is afraid of fatigue, stress concentration, and even more afraid of high-speed scour of dust particles. Non-metallic expansion joints are different. They use fabric fibers and rubber composite layers, which are naturally able to "overcome rigidity with softness". It not only absorbs heat displacement, but also eats vibration and noise, and most importantly, it is not afraid of dust accumulation. Ash falls on the fabric, and it falls off with the deformation. Instead, the dust accumulated in the metal bellows will jam the ripples, resulting in failure. Therefore, veterans in this business directly ask "non-metallic expansion joints" at the beginning, which is the truth.
Three major pits in type selection: temperature, pressure and medium (with actual cases)
Choosing non-metallic expansion joints looks simple, but there are many pits. Pit 1: Temperature. Many working conditions are nominal to 300℃, but in actual operation, the instantaneous temperature can reach 400℃. If the fabric fiber layer is only coated with ordinary silica gel, it will be directly burned through. We changed it for a cement factory before, and they used a standard non-metallic expansion joint, but it smoked in two months. Later, it was replaced with high-temperature resistant type, with ceramic fiber felt on the inner layer and fluororubber coating on the outer layer, which stabilized. Pit 2: Pressure. Don't think that non-metallic expansion joints can only run low voltage. Some positive pressure conveying systems, the pressure is dry to 0.3MPa, if you take the conventional type to top, the bulge is a matter of time. When selecting the model, we must look at the design pressure, match the stiffener and the restraint ring structure, like oursNon-metallic expansion joint (fabric fiber expansion joint)There is an enhanced version for medium and high voltage. Pit 3: Medium. Flue gases containing sulfur and chlorine can corrode both fabrics and metal flanges. A customer didn't pay attention and used an ordinary stainless steel flange, which was rusted out in half a year. You must choose duplex stainless steel or coat with anti-corrosion layer, and the inner layer is lined with PTFE. Refer to ourPTFE compensatorThe lining ideas can be carried. In short, don't just look at the parameter table when selecting a model, and explain the actual working conditions clearly, so that the manufacturer can match it.
Installation is not in place, no matter how good an expansion joint is, it is useless-key operating details
Install this matter, talk about it too much is all tears. I have seen too many scenes: the expansion joint is crooked, the direction of the guide tube is reversed, and even the transportation bolts are turned on without removing. There's a power plant, and the installerExpansion joint tie rod nutIt was screwed too hard, and as a result, the pipe couldn't pull at all when it expanded thermally, directly tearing the flange. Correct approach: First, the transport fixtures must be removed before installation (that is, those temporary screws, don't keep them as permanent parts). Second, adjust the tie rod nut to reserve the pre-stretching amount or compression amount required by the design. For details, refer toHow to adjust the tie rod nut of expansion jointThat article. Third, the direction of the guide tube must be consistent with the flow direction of the medium, otherwise vortex and wear will easily occur. Fourth, when the flange is connected, it is symmetrically tightened with a torque wrench. Don't screw one side to death and loosen the other side, which will leak ash. Fifth, if there is a vibration source on site, it is recommended to install limiting devices on both sides of the expansion joint to prevent excessive displacement. When these steps are done, the lifespan is at least doubled.
Don't be in a hurry to change dust if it leaks. Check these five places first
Ash leakage is common, but don't tear it down as soon as it leaks. Check in order first:
- Check flange sealing surface-The most common ash leakage spot. See if the seal gasket is aged or displaced, and re-tightening the bolts can often solve it.
- Check the fabric layer for damage— — There are not a few scratches during transportation or installation. Small holes can be temporarily plugged with repair glue, and large holes must be replaced.
- Check rod/restraint— — The length of the tie rod is wrong, or the limit block falls off, which will cause the expansion joint to be overstretched and torn.
- Check the guide tube— — If the guide tube is worn out, the medium will directly wash the bellows, causing local leakage. refer toSpecific Function of Expansion Joint Guide Tube, it protects the bellows, but it will wear itself.
- Check the dust accumulation in the pipe— — Some non-metallic expansion joints accumulate too much dust inside, which cracks the fabric when drying and shrinking. The seal can often be restored after cleaning up the accumulated dust.
Check all five places, and most of the ash leakage problems can be located. If you can't consider replacing it again, don't waste your money.
Compared with metal expansion joints, what are the advantages and disadvantages of non-metal?
Metal expansion joints (e.g.Universal corrugated expansion joint、High temperature axial expansion joint) Strong pressure resistance, can be used in high-pressure steam and oil pipelines, and has a long life-provided that the working conditions are clean and corrosion-free. However, in the "dirty and messy" environment of ash leaking conveyor, the metal bellows is prone to fatigue fracture, and once dust accumulates, the compensation ability will be greatly reduced. Non-metallic expansion joints have good flexibility, can absorb multi-directional displacement, save installation space, and only a fraction of the weight of metal. The disadvantages are also obvious: low pressure resistance (generally not more than 0.5MPa), not resistant to piercing by sharp objects, and the fabric will age under long-term high temperature. So which one to choose? Depends on the working conditions. Dust, large temperature fluctuation, low pressure, decisive non-metal; High pressure, clean medium, long life requirement, metal. In some cases, the two are used together, such as installing one at each end of the pipe, and the effect is also good.
Routine maintenance is done correctly, and life is doubled (with checklist)
Maintenance is not complicated, but it is important to persist. Here's a practical checklist for you:
- Once a month: Visually inspect the fabric layer for cracks, bulging and discoloration; Whether the tightening moment of the flange bolts is uniform.
- Quarterly: Clean up the dust accumulated inside and outside the expansion joint, especially the folds; Measure the tie rod nut position and record if there is any offset.
- Semi-annually: Check the wear of the guide tube. If the wear exceeds 1/2 of the thickness, it is recommended to replace it; Scan the surface temperature with a thermal imager to verify that there are no abnormal hot spots.
- Once per year: Comprehensive shutdown inspection, replacement of aging sealing gasket; Pressure testing is recommended if the expansion joint has been in service for more than 3 years.
Two days ago, I met an old customer. It took five years to change the non-metallic expansion joints in their factory. The secret is to insist on cleaning dust every quarter and changing gaskets every six months. Do you say this is a big investment? Not big. However, the downtime loss and replacement cost saved are enough to buy several pieces of equipment. So don't be lazy, maintain it in place, and the non-metallic expansion joint can carry it for you for several years.