Why Do Recycling Water Pipes Have Headaches? Pain point after pain point
Anyone who has engaged in recycled water projects knows that this thing looks simple, but it actually has a lot of pits. Thermal expansion and contraction is the most basic-the water temperature in the north can reach 5℃ in winter, and it is almost 75℃ in summer. If the pipeline with a temperature difference of 70℃ doesn't choose the right compensator, it will be a matter of time before the weld cracks. Even more headache is corrosion. The concentration of chloride ions in circulating water is hundreds of ppm at every turn, and ordinary 304 stainless steel bellows will pitting and perforating in less than a year. Coupled with the limited space, many computer room pipes are arranged like spider webs. The universal corrugated expansion joint connected by traditional flanges can't be stuffed in at all, while the sleeve-type pipe expansion joint saves space, but the sealing ring ages quickly, and when there are too many impurities in the circulating water, the packing wears out quickly.
What about that? Plug-in metal expansion joints are specially designed to cure these problems. It is directly inserted into the pipe, without flange or welding, occupies a small area, and it is hassle-free to change. But then again, this thing is not a master key. If you choose the wrong parameters, it will leak in half a year. Not only will you spend money in vain, you will have to stop the machine for emergency repair, which will delay production.
What's the matter with plug-in structures? It's kind of like the direct burial type, but it's different
To put it bluntly, the plug-in expansion joint is to integrate the bellows and the pipe, one end is directly inserted into the inner wall of the pipe, and the medium is sealed by the gland and sealing packing. You go see what we have on the stationDirect buried (fully buried) type expansion jointThe structural logic is similar, but the directly buried type is mainly aimed at buried pipelines and bears external soil pressure; The plug-in type is more aimed at the working conditions of low pressure (0.6-1.6MPa) and large pipe diameter such as circulating water. What are the benefits? The axial compensation is large, and it can absorb a certain angular displacement-this is particularly practical where there are elbows in the direction of the pipe. TraditionalSleeve type pipe expansion jointAfter the sealing packing is worn, the whole section has to be removed and replaced. What about the plug-in type? The padding can be changed from the gland side, which is so much more convenient. Moreover, impurities such as sediment and rust in circulating water are easy to get stuck on the sealing surface. When the plug-in structure is overhauled, the gland is directly loosened, the old filler is taken out and replaced with a new one, and it takes half an hour to do it.
Don't just look at the caliber when selecting the model-the material and the guide tube are the vital gates
Many people choose plug-in expansion joints, and when they come up, they ask "What is the caliber?", thinking that if the pipe diameter is right, it will be done. Not even close. Although the circulating water pressure is not high, the temperature fluctuates greatly, so you have to calculate the axial compensation amount first. For example, a DN600 carbon steel pipe is 20 meters long, with a temperature difference of 70℃ and a thermal elongation of about 16mm. If there is still angular displacement in the pipeline, the actual compensation amount needs to be added to 20% margin. The amount of compensation is considered small, and the bellows will crack as soon as it is stretched, which is no joke.
Chloride corrosion. The circulating water system is often sterilized with sodium hypochlorite, and the chloride ion concentration easily reaches 500ppm. At this time, the material of corrugated pipe must be 316L or duplex steel. 316L performs okay at chloride concentrations below 1000ppm, over 1000ppm? Use 2205 duplex steel obediently, otherwise the pitting corrosion won't run. We have a customer who bought 304 material cheaply, and it leaked in less than a year. The labor cost of disassembling and assembling it once is more expensive than the expansion joint itself.
Deflector tube. Many people think that the diversion tube is expensive, or think that "the circulating water pressure is low and unnecessary". Wrong! The flow rate of circulating water is generally 2-3m/s. If the bellows is not protected by the guide tube, the high-speed water flow directly washes the corrugated surface, and the thinning speed is faster than you think. We wrote an articleSpecific Function of Expansion Joint Guide Tube, which explains in detail how the guide tube guides the flow beam to the direction of the tube wall to avoid vortex scour. In a word: the plug-in metal expansion joint must also be equipped with a guide tube, so don't save this money.
Installation is faster than expected-just insert it and tighten the gland? It's not that simple
Two days ago, a customer called and said that it would bulge as soon as it heated up after installing it. When asked, it turned out that the pipe incision was not polished, and the burrs scratched the sealing packing. It didn't look serious during installation, but it seeped as soon as it was pressurized. What's even more outrageous is that he locked the tie rod nut directly-according to the installation method of the general expansion joint! And guess what? After heating up, the pipeline is elongated, the bellows is jacked to death, and it is directly bulged and scrapped.
What's the right thing to do? First, the pipe cut must be polished smoothly with an angle grinder, don't be lazy. Second, leave an allowance for the insertion depth-because the pipe will also be thermally elongated after installation, and inserting too deep will push the bellows to death. Refer to our siteHow to adjust the tie rod nut of expansion jointKey points: First pre-tighten to 50% of the design displacement, and after the system runs to a stable temperature, fine-tune the nut to the design value. Third, if there are elbows or valves in the direction of the pipeline, it is recommended to install fixing brackets on both sides of the plug-in expansion joint, otherwise the thrust of the pipeline may pull the joint off.
What should I do if I leak after three or five years of use? Don't be in a hurry to change the whole machine
One of the biggest advantages of plug-in expansion joints is the ease of maintenance. Minor leakage? Just tighten the gland bolts. If the packing has aged and hardened, loosen the gland, remove the old packing and replace it with a new PTFE seal-we standRubber PTFE compensatorThe kind of sealing ring used can also be universal. The whole process does not require moving pipes or welding, and it can be done with a wrench. But if the bellows body is cracked, it is hopeless and can only be replaced with a new one. That's when you'll know why we haveMetal hoseThere are also various corrugated expansion joints-different failure modes correspond to different spare parts strategies.
Check what on a regular basis? Two key points: the wear condition of the deflector and the corrosion pit of the bellows. The sediment in the circulating water will grind out a groove at the outlet of the guide tube. If the depth is found to exceed 30% of the wall thickness, it will have to be replaced. Whenever pitting pits the size of needle tips appear on the bellows surface, the remaining life should be evaluated. I'm really not sure. Use an ultrasonic thickness gauge to probe it. The data speaks for itself.
Plug-in metal expansion joints are not fast-moving consumer goods. Choose the right model, install the right method, and do a good job of maintenance. You can use them for seven or eight years without pressure. However, if you jump any of the above pits during the selection-the material is wrong, the deflector is not equipped, and the locking rod is installed-it will be not only money, but also the time cost of shutting down production.