Metal flexible joint and expansion joint, don't be stupid to distinguish
Many people run to our website and ask "How much is the metal soft joint expansion joint per meter". But if you ask him whether there is a large displacement or a large vibration in the pipe, he is often stunned. These two words are not the same thing at all in engineering.
The core task of metal hose is flexible connection and vibration reduction, such as pump port and compressor inlet and outlet, which is just suitable for high-frequency vibration. As for the corrugated expansion joint, the core task is to absorb heat displacement-the steam pipe heats up by tens of degrees and the pipe extends by several centimeters, depending on it. You take the metal hose to absorb the large displacement, and the bellows quickly cracks through fatigue; Take the expansion joint to reduce vibration, and the stiffness is too great, so the effect is very poor. It's not that you can't use it in combination, but the premise is to find out what your working conditions are mainly.
Three numbers are uncertain, and the rest is all for nothing
Nominal diameter, design pressure, design temperature. These three numbers directly determine the number of layers, wall thickness and material of the bellows.
Take an example. Under high temperature conditions, the strength of ordinary 304 stainless steel drops severely above 400℃, so temperature-resistant alloys have to be considered. If your media is corrosive, it is more troublesome-conventional metal bellows can't handle it, so you have to be lined with PTFE hoses or PTFE compensators. Two days ago, a customer of a chemical plant, whose medium was dilute sulfuric acid and the temperature was 80℃, took the selection table of the general corrugated expansion joint and asked us if we could do it. I told him directly that you have to look at the PTFE or PTFE compensator in this working condition. The material of the bellows is wrong, and it will leak in less than half a year.
Select type by displacement form: axial, transverse, angular
This link is the easiest to confuse people. In the axial type, there are general corrugated expansion joint, external pressure single axial expansion joint and directly buried (fully buried) expansion joint; The transverse type has a double hinge transverse type expansion joint; There are also straight pipe pressure balance type and curved pipe pressure balance type, which are specially used to deal with scenarios with high internal pressure and thrust.
Each structure corresponds to a typical working condition. For example, for directly buried pipelines, directly buried (fully buried) expansion joints are used, and there is no need to set an inspection well; On high-pressure pipelines, the internal pressure thrust is frightening, and the ordinary expansion joint fixed bracket can't hold it at all, so it is necessary to balance the thrust with straight pipe pressure balance type. Don't be too complicated. If you choose the wrong one, the life will be short, and the pipeline will crack. Before, there was a customer who used an ordinary axial type on the steam pipeline. As a result, the pressure was high, and the bellows was pushed out of the bulge by internal pressure, which was wasted in two months. Later, it was replaced with external pressure single axial type, and the problem was solved.
More pits for installation than for selection
The tie rods and screws on the expansion joints are used for adjustment when they leave the factory, not for transportation and fixation. I have to say this three times. Someone forgot to dismantle the limit screw, and as a result, the displacement was all stuck on the pipeline, and the expansion joint was useless. And guess what? The elbow of the pipe was directly pulled and cracked, and it came to us to compensate, saying that the product quality was not good. When disassembled, the limit screw remained intact.
Someone else asked how to adjust the expansion joint tie rod nut. This should be according to the design pre-deformation amount, and cannot be twisted casually. The pre-deformation is to make the expansion joint have a reverse pre-offset in the cold state and just return to zero in the isothermal state. If you twist it randomly, or lock the tie rod to use it as a fixed bracket, the expansion joint will be wasted. In addition, the direction of the installation arrow must be consistent with the flow direction of the medium, and the direction of the guide tube should not be reversed, otherwise the medium will directly wash the bellows and wear it out quickly.
Industry Differences: No Universal Models, Only Matching Conditions
Different industries are too different to use. Corrugated expansion joints are commonly used in power plants, which are used on smoke ducts with flue gas baffle doors and circular baffle doors. The temperature is high, the flue section is large, and the requirements for tightness and temperature resistance are very strict. In cement factories, in high-temperature dust environment, metal corrugated expansion joints or non-metallic expansion joints (fabric fiber expansion joints) in cement industry are used to absorb large displacements-non-metals have good flexibility, large compensation and dust wear resistance. Because of the strong corrosion of desulfurization medium, we have to choose desulfurization flue gas baffle door and PTFE-lined products, but ordinary carbon steel can't do it at all.
So don't keep thinking about finding "universal models". For the same nominal diameter, the number of corrugations is different, and the compensation amount can be different by a large section; The material is one grade worse, and the price is twice the difference. This is not a matter of the quality of the product itself, but of the details of the selection.
Practical advice: Leave the work condition to the engineer
If you research the model yourself, it is easy to fall into the parameter trap. The same nominal diameter, the number of corrugations is different, and the compensation amount is different by a large section; With the same compensation amount, the stiffness data is different, and the forces of pipeline bearings are very different. The stiffness is too large, and the thermal displacement cannot be absorbed; The stiffness is too small, and the pipe is prone to instability.
Send the working condition parameters and site diagram to the manufacturer, and let the engineer help you choose. You only need to provide the information of medium, temperature, pressure, caliber, displacement direction and connection mode. By the way, ask for the stiffness data, which is related to the design load of the fixed bracket. The design life and actual life of metal soft joint expansion joint are often different in the selection details-the number of bellows layers is thick, which has high cost but long life; Choose thin, save money but can't use it. Let a professional settle this account.