Why do you need a non-metallic compensator for drainage systems? — — Pits of metal, filled with non-metal
Drainage pipes, especially sewage and circulating water systems, often carry corrosive components-chloride ions, acids, bases, salts, and even oil pollution. Metal compensators (such as universal corrugated expansion joints) are like a bath in a salt tank in this environment, and rust and perforation are only a matter of time. You paid a lot for stainless steel? 316L also pits when it encounters high concentration of chloride ions. This is why drainage structures are increasingly inclined to use non-metallic compensators.
Non-metallic expansion joints (fabric fiber expansion joints) rely on acid-and alkali-resistant fabric layers and anticorrosive diaphragms to completely separate corrosive media from structures. Strictly speaking, both things in our station are applicable: non-metallic expansion joints (fabric fiber expansion joints) for round pipes and rectangular non-metallic expansion joints for square pipes. Choosing the wrong shape? You have to smash the wall when installing it.
What is so special about the so-called "drainage structure"? — Not just any non-metallic compensator
The temperature is not high (generally below 100 ℃), and the pressure is not fierce. However, there are three pits: large fluctuation of water pressure, limited installation space, and sometimes sharing ground dynamic loads. Two days ago, in a sewage treatment plant project, an ordinary rubber compensator was installed on the buried pipeline. As a result, the compensator was directly deformed when the earth was backfilled.
- Flange seal: Drainage pipes are often low pressure, but seepage is troublesome. The flange connection has to be thickened with gaskets, and the bolts have to be torqued. Don't expect a wrench to die.
- Guide tube material: If there is a guide tube in the design, use scour-resistant materials. The sand and hard particles in the sewage are washed out for a long time, and the ordinary carbon steel guide tube will wear out in half a year. The specific function of the expansion joint guide tube is to protect the corrugation from being directly impacted by the medium, but the material selection is not equal to white installation.
- External pressure protection: For buried or semi-buried pipelines, an outer sheath or compensator shell should be added, otherwise the fabric layer will be directly squeezed when the backfill soil is pressed.
When it comes to low-pressure drainage scenarios, rubber compensators and rubber PTFE compensators can make do, but the rubber ages quickly – you go and see it three years later and the surface is cracked like a dried riverbed. Non-metallic expansion joints of fabric fibers last more than twice as long.
Three parameters that are most prone to rollover during model selection: compensation amount, pressure class and media composition
Many people buy compensators and only stare at the caliber, but when they install them, they find that the displacement is not enough-the compensator is pulled apart as soon as the pipe expands and contracts thermally. Although the compensation capacity of non-metallic compensator is greater than that of metal, it depends on the corrugation deformation of fabric. The actual allowable axial, transverse and angular displacements must be checked according to the manufacturer's parameter table, so don't guess by experience. And guess what? Some customers take the compensation amount of the general-purpose corrugated expansion joint of DN500 to set the non-metallic one, which is 30% different.
In terms of pressure, although the working pressure of the drainage system is low (0.1-0.3MPa), the water hammer can rush to 0.6MPa instantaneously. It is recommended to consider 1.5 times the working pressure margin when selecting, that is to say, the design pressure is 0.25MPa, and you should choose at least 0.4MPa specification. Don't save those hundreds of dollars. If it explodes, it will wait for production to be stopped for maintenance.
The composition of the media should not be vague. The corrosiveness of oil-containing wastewater and chlorine-containing wastewater to fabric fibers is very different. The polytetrafluoroethylene fabric is used, but ordinary rubber is chosen, which will be scrapped in a few months. For example, in the wastewater pipeline of a chemical plant, the chloride ion concentration is 3000ppm, and PTFE coating layer is selected with non-metallic expansion joint (fabric fiber expansion joint). Now it is still intact after four years of use.
Are there any tricks for installation and maintenance? — Don't underestimate those rods and bolts
Referring to the contents of "How to Adjust the Tie Rod Nut of Expansion Joint" and "Correct Installation Method of Large Tie Rod Expansion Joint" in our station, the non-metallic compensator of drainage structure also needs to be pre-stretched or pre-compressed-according to the design displacement direction. The tie rod is a fixture during transportation and installation, but must be loosened before commissioning. A customer forgot to loosen the tie rod after installing it. After running for half a year, the compensator didn't move, and the pipe forced the bracket to be crooked.
Check the fabric surface every six months for blistering, delamination, and flange bolts for loosening. Don't believe the "put it on and leave it alone" nonsense. A sewage treatment plant used our rectangular non-metallic expansion joint, and it didn't do any maintenance for three years. As a result, the corrugated layer wore and leaked-in fact, it was done by taking a look every six months, and it had to wait until it exploded before repairing it. The maintenance cost was enough to buy three new ones.
Also, the installation direction arrow cannot be reversed. The direction of the arrow of the expansion joint refers to the flow direction of the medium. If the guide tube is installed in reverse, it becomes a pocket water, and the pressure loss increases exponentially.
Is the non-metallic compensator worth it compared to the metal expansion joint? — It will be clear if you settle the accounts
Metal expansion joints (such as general-purpose corrugated expansion joints) tend to last only 2-3 years in drainage systems. A DN500 metal compensator costs about 1,500 yuan, and it costs 1,000 yuan to add materials manually once, with a total cost of 4,500 yuan in three years. However, a non-metallic compensator with the same specification has a unit price of 2,800 yuan and a life span of 5-8 years. The annual cost is less than 500 yuan. Moreover, the weight of non-metal is only 1/3 of that of metal, so the installation does not require heavy lifting, and the forklift can do it. Especially for large-diameter drainage pipes-metal compensators above DN1200 should be customized, and the price doubles for a long cycle. However, non-metal large-diameter compensators are mature products with much faster delivery. Of course, if you have to choose the metal option of large-diameter, thick-walled expansion joints, you have to triple your budget.
So don't just look at the price tag. Although the unit price of non-metallic compensator is slightly higher, the comprehensive cost is lower.
To summarize in one sentence
Selecting non-metal compensator for drainage structure depends on the fabric material, compensation ability, seal design and installation details. Don't be superstitious about imports-non-metallic expansion joints (fabric fiber expansion joints) of domestic first-line brands can fully meet the drainage requirements, provided that they are customized according to working conditions. If you are not sure, send the pipeline parameters directly to the technical department to help you match the most suitable model, so as to avoid the trouble of selecting and rolling over.