How to judge that non-metallic compensator should be replaced
How to replace a non-metallic compensator? In fact, before asking this question, one thing has to be clear-whether it should be replaced or not. Blind replacement not only wastes money, but also may dismantle the originally stable system.
Non-metallic compensators (often called fabric fiber expansion joints) work in high-temperature flue gas and corrosive media for a long time, and the loop belt is a loss part. When you inspect, focus on these places:crack。 If the surface of silicone rubber coating or fluororubber is cracked and the depth exceeds half of the thickness of the coating, it will basically reach its life;Aging。 Press the surface of the loop band with your hand, and the rebound is slow, hard and brittle, indicating that the material has lost its elasticity;deformation。 Use a ruler to lean on the flange surface. If the ring belt is wrinkled and the local bulge exceeds 10mm, it must be treated;leak。 This is the most direct-there is smoke running out during operation, or obvious wear and penetrating damage can be seen after shutdown. Don't hesitate to arrange replacement directly.
If the internal guide tube of the compensator falls off, or the external stainless steel wire mesh is damaged, resulting in the exposure of the fiber layer, even if the surface looks okay, it is recommended to replace it as soon as possible. This kind of damage will accelerate the overall failure of the ring belt, which won't last long.
Preparation before replacement: Don't rush to do it
How to change a non-metallic compensator? The premise is that security measures are in place. This thing is mostly used in places with harsh working conditions such as smoke duct, desulfurization system and cement kiln tail of power plants. The medium is either high temperature or corrosive gas. In the flue above 200℃, do you dismantle it directly? That's not work, it's life-threatening.
The first step is to stop the machine and relieve pressure. Reduce system pressure to zero and temperature to ambient temperature. Don't save this step-some pipes have dead ends, and the dust accumulation inside is still slowly storing heat. I have seen more than once that the surface can't be seen but the internal temperature is still very high. In the second step, use blind plates or baffle doors to separate the pipes on both sides. Speaking of this, the circular baffle door (double seal) in our station is designed for this kind of maintenance scenario. After locking, it can ensure zero leakage, and the later operation is safe. The third step, padlock, hanging tag and gas detection, is completed according to the factory's LOTO process.
Check spare parts at the same time. The specifications and parameters of non-metallic expansion joints are different for each item-diameter, pressure, temperature, displacement, flange hole distance, which must be compared one by one. Don't think you can pretend just by looking at it. Last year, a customer took a short 50mm rectangular non-metallic expansion joint to the site, but the hole position didn't match. Finally, it was reworked, and the construction period was delayed for three days.
Practical details of old compensator removal
When disassembling, the first thing is to draw the installation positioning line with a marker on the outer ring of the flange, and measure the diagonal size. There is no cost to this step, but it saves you a lot of adjustment time when you reinstall it.
There is no technical content in bolt removal, but pay attention to protecting the flange surface. This is especially true when cutting-some welds join structures that need to be fired, and make sure there are no combustible around before cutting. When hoisting, use a sling or soft rope, and the wire rope directly strangled on the loop belt will crush the fabric fibers. You're dismantling old pieces, but the equipment and plumbing next to it are still good.
Flange surface cleaning is a link that many people ignore. After the old compensator is removed, the flange surface is covered with aging cement, rust residue and old gasket residue. Use an angle grinder with a steel wire wheel to polish it clean until the metallic luster is exposed. If the flange surface is uneven, it will still leak if a new non-metallic compensator is installed.
Critical steps for new compensator installation
When installing new pieces, alignment is the most error-prone step. The alignment of the flange holes is not complete, and the centerline of the compensator must coincide with the centerline of the pipe. How to check? Take four points evenly on the circumference of the flange, and measure the distance to the pipe wall, so long as the deviation does not exceed ±3mm.
Then there is pre-compression/pre-stretching. When the non-metallic compensator leaves the factory, the manufacturer presets an installation length based on the design displacement. You can work according to the drawing-how many millimeters are marked on the drawing for pre-compression, and you can adjust the tie rod nut to how much. Here's an easy mistake: thinking that pre-compression is just pressing a little. No, the amount of pre-compression directly affects the displacement compensation range during operation. Too much pressure, insufficient positive displacement; Less pressure, not enough reverse displacement. Specifically, how to adjust the tie rod nut? Our technical department has specially written an instruction on how to adjust the tie rod nut of the expansion joint, which contains detailed data of torque and adjustment sequence.
The first pass is all put on, and the torque is screwed to 30%; The 2nd pass is screwed to 70% in diagonal order; Third pass again in order to 100%. The four corner bolts are tightened one last time. Such a simple process can avoid local leakage caused by warping of the flange surface.
Acceptance after reinstallation: Don't rush to turn on the machine
After installation, the final step in how to replace the non-metallic compensator is verification. Direct power supply to power on? That won't work.
Do the tightness test first. Brush with soapy water on the flange joint surface and the ring belt surface, pressurize the pipe to 1.25 times the design pressure, and stabilize the pressure for 30 minutes. If there are bubbles coming out, it is the leakage point, so mark, relieve pressure and treat it immediately. No air bubbles indicate that the seal is qualified.
Confirm the displacement compensation effect again. This is particularly important for non-metallic compensators, whose fabric fiber bands require some room to move to absorb thermal displacement. You check whether there is enough space on both sides of the compensator, and watch for abnormal bulging or stretching on the surface of the loop belt while running. If conditions permit, record a set of data for each cold state and hot state: temperature, pressure, and displacement. This data is back to the draft of the device file.
Finally, write the replacement date, reason for replacement, model of new compensator, pre-compression amount during installation, and torque value of fastening bolts into the operation record. I don't remember it now, but I can't find it if I want to check it the next time I overhaul it.
It is difficult to replace the non-metallic compensator, but it must not be careless. Each step has stringent process requirements, and which step is skipped will end up being exposed in the run. If you encounter specific problems on the spot, such as uncertain ring belt selection and special installation conditions, go directly to the manufacturer for technical confirmation, which is more reliable than thinking about it yourself.