Where is this hurdle? — — What practical problems have been solved by adding drainage holes and flanging?
Two days ago, a customer engaged in a desulfurization project complained to me, saying that the non-metallic expansion joint on their flue took less than half a year, and water began to seep inside, and condensed acid dropped out of the joint. As soon as I heard it, I knew what the problem was: ordinary fabric fiber expansion joints had no drainage design, and the water vapor in the smoke condensed and accumulated at the bottom, soaking the skin and insulation layer. It was strange that it didn't rotten over time. The flanged non-metallic compensator with drainage holes, to put it bluntly, is to do the two things of "preventing water accumulation" and "preventing air leakage" together. The drainage hole is installed at the lowest point at the bottom, specifically to allow the condensed water to flow away; The flange is to make the compensator port into a flange-type flange structure, which is directly bolted with the pipe flange, thus saving the trouble of matching another pressure plate. These two designs look simple, but in the working conditions of power plant desulfurization and cement kiln tail, who uses it knows.
The drainage hole is not just a hole-the location, hole diameter, and anti-plugging all have to be counted
Many people think that the drainage hole is to drill a hole in the bottom of the compensator. As a result, after installing it, either the hole is too small and the drainage is not smooth, or the hole is too big to leak the medium all over the floor. According to the recommended practice in JB/T 12235-2015 "Non-metallic Expansion Joint" standard, the diameter of the drainage hole is generally between DN15 and DN25, and it should be matched with a stainless steel drainage valve or wire plug, tightened at ordinary times, and opened when drainage is needed. More critical is the location of the hole-it must be located at the lowest point of the compensator, and it must be arranged along the pipe axis direction. Why? Because the non-metallic expansion joint will deflect when absorbing heat displacement, if the hole is opened on the side, the displacement will bury the drainage hole to a high place, which is equal to opening for nothing. In addition, for dusty media (such as flue gas in cement industry), a filter or sewage outlet must be installed, otherwise the plaster will block the hole and still accumulate water.
The wider the flange is not the better – the core of the connecting seal is the "pinch area."
The flanging of the flanged non-metallic compensator is usually made of multi-layer composite of the same material (silicone cloth, fluororubber cloth or polytetrafluoroethylene film), and the thickness is between 3-8mm. On the side where it touches the pipe flange, the surface will be treated with anti-slip treatment-some are pressed with fine lines, others are stuck with a thin rubber pad. The difference from ordinary flange connection is that the width of flange directly determines whether the bolt compression force can be transmitted evenly. According to experience, the flange width should be at least 15-20mm longer than the center distance of the flange bolt hole, so as to ensure that the preload force is not concentrated at the root of the bolt. We have done a comparative test: under the same pressure of 0.2MPa, the leakage of the compensator with a flange width of 40mm is less than one third of that of 25mm. Those who want to save trouble and buy narrow flanged products will leak immediately as soon as the flange end face warps during actual operation.
Don't just look at size when selecting a model-media temperature and displacement are the dead lines
The customer reported the pipe diameter and said to make a DN1000 non-metallic compensator with flanged drainage holes. As a result, we asked the medium temperature and axial displacement, but we couldn't answer it. The upper temperature resistance limit of non-metallic expansion joints depends on the skin material-silicone cloth resists 150℃, fluororubber cloth resists 200℃, and PTFE film can reach 250℃. Beyond this temperature, the cuffs will charcoal and become brittle. The amount of displacement determines the number of layers of fabric and the spacing of reinforcing ribs. For example, for a compensator used in the flue of a power station, the axial displacement requires ±50mm and the transverse displacement is ±30mm. The skin must have a four-layer structure (silica gel cloth + glass fiber cloth + polytetrafluoroethylene film + stainless steel wire mesh), and the stainless steel wire mesh lining should be clamped inside the flange, otherwise the flange will be torn when stretched frequently, and it is useless to install drainage holes.
One of the most overlooked things when installing: drain hole orientation and pre-stretching
We have seen too many installation accidents in our factory. Some workers install the flanged non-metallic compensator with drainage holes backwards, and the drainage holes face upward. As a result, they do not drain water and only receive water; Some people found that the flange bolts could not be screwed after installation, because the compensator was not pre-stretched. When the non-metallic compensator leaves the factory, a pre-compression amount is usually set according to the working temperature. When installing, this pre-compression should be adjusted to the design value before it can be installed. Specific operation: First fix the flange at one end, stretch the compensator to the marked installation length with a tie rod or bolt, and then lock the other end. What about the drain hole? Remember to make sure that it is oriented at the lowest point of the pipe before installation, and leave room for the drain valve to operate. Some site space is limited, and the drain valve handle can't be turned, so it has to be replaced with a side-row type with a hose to lead to the trench.
Maintenance? Don't wait until water seeps to remember the drain hole-it is recommended to check it every two weeks
The life of non-metallic compensators is usually 5-8 years, but versions with drain holes tend to fail early because the drain valve is corroded or clog with debris. It is recommended to open the drain valve to drain water every two weeks to see the color and pH of the liquid coming out. If it is the clean flue gas after desulfurization, the pH of the condensed water is usually 2-4, indicating that there is a risk of acid corrosion-at this time, it is necessary to check whether the inner layer of the flange is corroded and foamed by acid. In addition, if the flange surface is cracked or hardened, it means that the material is aging and must be replaced. We have a cement customer who insists on discharging sewage every month and measuring the surface temperature distribution with infrared thermal imaging camera every quarter. Their compensators have not been flanged for seven years. Tsk, that's the maintenance gap.