Let's be clear first: what is the "wet method" working condition, and why does it make ordinary expansion joints have a headache?
Wet desulfurization, at present, the mainstream is limestone-gypsum method. The flue gas from this process is pitifully low-usually 60-80℃, near saturated humidity, and full of a mixture of acidic droplets (sulfuric acid, sulfurous acid) and gypsum slurry. To put it bluntly, it is a harsh environment of "acid fog + mud".
This condition is a disaster for the metal expansion joint. Pitting corrosion, stress corrosion cracking, find your door in minutes. The stainless steel bellows you spend a lot of money on may leak in less than a year. Therefore, the industry generally turns to non-metallic expansion joints (fabric fibers, rubber) as the mainstream choice. But here's the question: Can any non-metallic expansion joint be installed?
Of course not. In wet working conditions, non-metallic expansion joints have to bear not only corrosion, but also dust accumulation, condensate water and frequent displacement fatigue. If you choose the wrong material, it will be powdered in half a year; The structural design is wrong, and it will get stuck in one year. Let's talk about it one by one.
The real advantage of non-metallic expansion joints in wet scenarios is not just "not afraid of corrosion"
Many people think that non-metallic expansion joints are powerful in anti-corrosion. In fact, what is more important is that they have strong ability to resist fatigue and absorb multi-directional displacement. For example, in our product lineNon-metallic expansion joint (fabric fiber expansion joint)Andrubber compensatorAnd can simultaneously cope with axial expansion and contraction and lateral deflection. The direction of the inlet and outlet pipeline of the desulfurization tower is complicated, and the thermal displacement is often not a simple straight line. It is difficult for the metal expansion joint to handle the displacement in multiple directions at the same time, but the non-metal fabric layer can easily absorb it. Moreover, the weight is light, the requirement for the bracket is low, and the installation cost is greatly saved.
But there is a big pit-if the material is not selected correctly, it will be wasted in half a year. You said you wanted to buy an ordinary silicone cloth cheaply and try to soak it in an acidic droplet at 60℃ for three months? Soak it straight away. Therefore, knowing the word "non-metal" is far from enough, and we have to dig deeper.
The first level of selection: How to pick the skin material? Don't just focus on "temperature resistance"
The temperature of wet flue gas is low, only 60~80℃, and general rubber can carry it. However, acidic dew point corrosion is an invisible killer-once the smoke condenses on the skin surface, forming dilute sulfuric acid, ordinary rubber immediately expands and cracks. Viton rubber (FKM), polytetrafluoroethylene (PTFE) liners are the base configuration. We have them in our stationRubber PTFE compensatorIt is specifically aimed at this working condition: the inner polytetrafluoroethylene film is acid-resistant and non-adhesive, and the acid drops up and slides away directly.
In addition, the outer layer should be protected from ultraviolet rays and mechanical damage. Some on-site pipes are laid out in the open air, and ultraviolet rays can brittle the rubber layer in a few months. The skin structure has at least four layers: corrosion resistant layer (contact with smoke), insulation layer (prevent condensation), reinforcement layer (pressure-bearing) and outer protective layer (prevent environmental aging). With one less layer, the lifespan is compromised.
In the structural design, the cooperation of rectangular non-metal expansion joint and circular baffle door is the key
Desulfurization flue is mostly rectangular large cross-section, in our productsRectangular non-metallic expansion jointThat's what it does. However, many problems on the spot are because the interface between the expansion joint and the baffle door is not handled properly. For example, you are matchedDesulfurization flue gas baffle doorOrDouble-sealed single-axis circular baffle doorThe compensation amount of the expansion joint is not reserved enough, and the compensation amount of the expansion joint is directly dead during high-temperature expansion. There are also deflectors-which must extend to the inward side of the media flow. Do you know why? If it is not extended in, the gypsum slurry in the flue gas rushes directly into the wave gap of the expansion joint, slowly hardens, and the ash accumulates thicker and thicker, and finally the ripples are stuck.
In addition, the drain outlet must be added. Wet pipeline condensate more, not draining liquid will corrode the frame. Some design drawings save trouble without opening a drainage hole, and the bottom of the expansion joint rust through after half a year's operation.
In installation and routine maintenance, 80% of faults are in the details
The tie rod nut is installed in the reverse direction. We wrote specifically beforeHow to adjust the tie rod nut of expansion jointThe locking surface of the nut must face the expansion joint body, otherwise it will be loosened after a few vibrations, losing the limiting effect, and the excessive amplitude displacement will directly tear the skin.
Shipped unreinforced and the skin was pressed out of permanent folds. In order to save freight, some manufacturers stack and transport the expansion joints. As a result, the skin has been creased at the site-this kind of gap is the easiest to hide acid, and it will quickly corrode and penetrate.
What is the key point of inspection under wet working conditions? Look at the surface of the skin for any maculae with acid oozing. That's a sign that the inner layer is leaking, and once it is found, it must be shut down for replacement. In addition, if the pipeline is out of operation for a long time (for example, the maintenance period exceeds two weeks), it is necessary to manually drain water regularly, otherwise the gypsum slurry will harden in the folds of the expansion joint, and the thermal stress will directly crack the hard block when driving. And guess what? I have seen a power plant that stopped the furnace for a month without draining water. On the day of resumption, the expansion joint burst, and the whole flue emitted white smoke.
Finally, let me say something that is easily overlooked: the national standard JB/T 12235-2015 has clear provisions on non-metallic expansion joints
The national standard JB/T 12235-2015 specifies the technical requirements, test methods and inspection rules of non-metallic expansion joints in detail. Such as flange width, bolt hole spacing tolerance, bond strength between skin layers. However, in order to reduce the price, some small factories narrow the flange by 5mm. During installation, the bolt holes don't match, and the workers forcibly pull the flange through the bolts-the result? The skin was ripped out of internal injuries, and the first inspection leaked air.
Made exactly according to national standardsRectangular non-metallic expansion jointThe import and export of the desulfurization tower of a power plant in Shandong has been running continuously for three years without changing; However, a low-priced product leaked in one year. After shutting down and changing it once, it burned 150,000 electricity bills, plus labor and material costs, which was enough to buy three qualified products. So budget is not an issue, the question is whether you can survive a major overhaul cycle-the downtime loss of replacing an expansion joint is enough to buy three qualified products. Listen to my advice, the national standard is not a decoration, but the bottom line of life-saving.