Where exactly are grey tube metal expansion joints used? Firstly, the working conditions of ash-removing pipeline are discussed and then the type selection is discussed
Ash pipe metal expansion joint sounds like equipment, but in fact, it is a compensator, which is specially used in pneumatic conveying pipelines such as ash removal in power plants and dust removal in steel mills. To put it bluntly, this thing is to withstand the thermal expansion, contraction and vibration displacement of the pipe, so as to prevent the pipe from breaking itself.
But if you come up and ask, "How much is the metal expansion joint of gray pipe per meter?" Then I can't answer it. Because the working conditions are different, the price difference can be several times. The medium of ash pipeline is fly ash and abrasive particles, the temperature may run up to two or three hundred degrees, and the flow rate is fast-under this working condition, the inside of the expansion joint is polished by sandpaper every second. Without first figuring out the pressure, temperature, medium concentration and pipeline direction, the selection is blind.
Two days ago, a customer took an old expansion joint and asked why it leaked. When disassembled, there is a big hole in the bellows, the inner wall is smooth, and the guide tube has long been worn out. The mixing ratio of gray gas in his pipeline is high, and the flow rate is high, so ordinary expansion joints naturally can't stand it.
Structure is a little worse and life is twice worse: How to match bellows, guide tubes and wear-resistant liners
Bellows, deflectors, wear liners. The bellows is responsible for absorbing displacement, and the material is either 304, 316L, or heat-resistant alloy; The guide tube is blocked in front of the inner wall of the bellows, so that the medium flows along, and don't directly flush the bellows; Wear-resistant lining is the last line of defense, especially in high-wear areas, where wear-resistant steel plates or even ceramic liners are required.
Someone made the deflector a little thinner in order to save money. What was the result? After half a year of wear, the bellows is directly exposed to the ash powder, and it can't even survive for a year. Don't save this money. This station has corrugated expansion joints for power station industry and metal corrugated expansion joints for cement industry. The guide tubes and wear-resistant liners of these products are designed separately. When selecting the type, we must make the wear margin clear, especially the expansion joint near the elbow and downstream of the valve, where the flow field is chaotic and the wear is much more serious than that of the straight pipe section.
How to calculate the displacement amount? Don't let the expansion joints hold pressure in the pipe system
Gray tube metal expansion energy saving absorbs how much displacement, not you pat your head to set. How long is the pipeline, how big is the temperature difference, how much is the expansion coefficient, whether there is a fixed bracket in the middle, and how to turn the pipeline-only when these data are gathered together can the real thermal displacement be calculated.
What happens if you miscalculate? If the displacement is large, the bellows is easy to become unstable and the folds are torn; Given small, pipe stress is transferred to equipment, pump and elbow suffering first. More commonly, some people try to save trouble, mix axial, lateral and angular displacements together, and just multiply them by a coefficient and report them to the manufacturer. How can that work? The distribution of composite displacement on each bellows is completely different, and the displacement quantities in three directions must be listed separately when selecting the type.
In addition, the expansion joint is not used to harness the pressure. How to eliminate system stress? Piping and supporting hangers. The expansion joint is only responsible for displacement compensation, not for absorbing internal pressure thrust. If you leave out the fixing bracket, no matter how thick the expansion joint is, it will be useless.
More pits to install and maintain than you think: tie rods, nuts and guide brackets
After the grey pipe metal expansion joint arrives, don't rush to weld it. When leaving the factory, the tie rod and nut are adjusted to the installation length. Many people don't care and install it directly. When the pipeline was tested, it was discovered that the bellows had been pulled over and the cracks had come out.
First, the locking nut on the pull rod must be loosened, otherwise the expansion joint can't move, which is equivalent to white installation; Second, when welding, use a wet cloth or steel plate to block the bellows, splash and burn the surface, and the fatigue life will be directly discounted; Third, the spacing of the guide brackets should be according to the design. If the pipe is too far, it will become laterally unstable and the bellows will be twisted. Guess what, most of the field problems, are from these three pits.
There is also one that is easily overlooked-maintenance. Gray tube metal expansion joint for half a year, it is best to check the wear of the guide tube. You don't have to remove it, you can see it by shining a flashlight through the end. If the guide tube is partially worn out, repair welding or replace it as soon as possible. Don't wait for the bellows to be perforated before worrying.
Abrasion and perforation, bellows cracking: Failure investigation and countermeasures of grey pipe expansion joint
The failed metal expansion joint of gray pipe is broken in two kinds at most: one is wear and perforation, and the other is fatigue cracking of corrugated pipe. The wear perforations are concentrated on the backflow surface of the guide tube and bellows, because the ash powder forms a vortex in the bellows trough and repeatedly washes. The cracking of bellows is mostly caused by excessive displacement or too much vibration, and the crack extends along the wave root, which is not easy to see with the naked eye, so penetration detection is necessary.
When checking, first measure the actual displacement of the expansion joint and the design displacement ratio, and then check whether the pipe support and hanger are loose. If the wear rate is found to be too fast, the guide tube can be thickened or lined with a ceramic sheet. The general corrugated expansion joints and high-temperature axial expansion joints of this station also have wear-resistant modification schemes, which do not have to be non-metallic to resist wear.
Expansion joints are the "weak link" in the pipeline system, deliberately designed to be consumable. Don't expect it to last a lifetime, but you can use its life to the design value by reasonable selection and standardized installation. If you really wait until the bellows bursts and dust scurries around, the loss will not be the money of an expansion joint.