Find out what you have in your hand first: round welded non-metallic compensator vs metal expansion joint
Can this thing replace metal? Alas, materials and structure are completely different things. Circular welding non-metallic compensator (that is, the non-metallic expansion joint and fabric fiber expansion joint mentioned in our station) uses composite layers of silicone cloth and fluororubber as circular belts, which rely on flexibility to compensate for displacement. Circular welding type refers to welding short pipes at both ends, which are directly welded to the pipeline. Note-it does not absorb axial thrust, which is very different from metal bellows. If you confuse the position of the guide bracket when installing it, something will go wrong later.
You have to do three things before installation: check the model, check the appearance, and remove the screw or not?
Don't rush to weld. Look at the product nameplate first to confirm whether the caliber and compensation amount are consistent with the design drawings. Is the non-metal ring strip broken or wrinkled? The tie rod nut is locked out of the factory to protect shipping. The tie rod nut must be loosened before installation-how to loosen it? Refer to the question and answer of "Does the screw of the expansion joint need to be removed" in our station. If it is not loose, the ring belt will explode directly as soon as the temperature rises after welding. How much looser is that? Look at the amount of compensation, and generally set aside half of the design displacement. Don't twist by feel, measure with a caliper.
The welding link is the easiest to roll over
The short tube wall thickness of circular welding non-metallic compensator is usually thinner than that of pipe, and the welding electrode is not selected correctly, and it will be worn as soon as it is burned. It is recommended to use DC welding machine, low current, multi-layer welding. After welding, it must be cooled. Don't rush to water the loop-the temperature resistance of the loop is only a few hundred degrees, and it will crack when quenched. Also, the welding sequence is particular: first welding the fixed end, then welding the free end, and finally welding the middle. Why? Prevent thermal expansion from pulling the non-metallic ring tape askew. Think about it, if you weld the middle first, as soon as the two ends shrink, the loop tape will directly wrinkle into a rag.
Finished installation does not mean finished, the tie rod and guide bracket still have to be adjusted
Circular non-metallic compensators generally only absorb axial displacement, and lateral displacement depends on the guide bracket of the pipeline itself. The function of the tie rod is not to bear pressure, but to prevent over-stretching-see the article "The Function of the Expansion Joint Tie Rod" for details. Adjustment method: Twist the nut with a wrench, so that the clearance at both ends of the pull rod is symmetrical. Don't be thick on one side and thin on the other. By the way, how to determine the distance of the guide bracket? Look up the table according to the pipe diameter. We mentioned the influence of the guide tube on the flow direction of the medium in the "Specific Function of the Expansion Joint Guide Tube". The direction of the guide tube must be consistent with the flow direction of the medium. Is it installed backwards? Later cases will tell you the consequences.
How do you judge that it is time to change after it is put into operation?
Non-metallic compensators are most afraid of corrosive media and ash accumulation. In those working conditions in cement industry and desulfurization flue, the aging of the ring belt is easy to harden and crack from the outer surface. Regularly light the interior with a flashlight to see if there are any piercings. Don't think about repairing it if it leaks-the non-metallic band can't be welded and repaired, so it can only be replaced as a whole. The life span is generally 3 to 5 years, which is shorter than that of metal, but the cost is low and the installation is convenient. If you find it troublesome to change it, refer to the "desulfurization flue gas baffle door" and "circular baffle door (double seal)" of our station, which can prolong the life. And guess what? Many power plants are so equipped, and they haven't changed the ring belt for 8 years.
Finally, let's talk about a practical case
Last month, a power plant customer installed a circular welding non-metallic compensator at the outlet of the induced draft fan, and it leaked less than half a year after installation. In the past, the problem was that the guide tube was installed backwards, and the high-temperature flue gas directly washed the inner wall of the ring belt. In addition, the position of the guide bracket was not welded correctly, and the pipe displacement tore the ring belt. After replacing the new parts, it was reinstalled according to our JB/T 12235 standard. Now it has been running for one and a half years without any accident. So, don't underestimate those nuts and brackets. Details are the real skill. Understand "How to use circular welding non-metallic compensator?" Actually, there are two points: First, don't use it as a metal part, and second, the installation sequence and tie rod adjustment must be strict.