Why are the overall dimensions of non-metallic compensators not randomly marked? Understand what factors constrain it first
Two days ago, I met a customer who was engaged in desulfurization flue. He asked me with the drawings, "The diameter of my pipe is 2m ×2m. Can you give me an 800×800 non-metallic compensator?" I laughed on the spot-brother, if the overall dimensions of non-metallic compensators can be determined with such a pat on the head, how can there be so many accidents that can't be installed on the spot?
Frankly speaking, the dimensions of non-metallic compensators (that is, we often call non-metallic expansion joints, including rectangular non-metallic expansion joints and fabric fiber expansion joints) are never randomly marked. It is subject to three hard conditions:Pipe interface size, displacement compensation requirements, and installation space constraints。 If your tube is square, the compensator has to be square-round tube with circle, square tube with rectangle, this is the iron rule. However, it is far from enough for the light tube mouth to match, and it has to be calculated how big the thermal displacement is. For example, the temperature of the flue gas pipe rises from normal temperature to 400℃, and the pipe elongation per meter is about 4-5mm. The effective length of your compensator has to eat this amount.
And the pressure? Different positive pressure and negative pressure, the number of layers and structure of compensator are different. Under high-pressure conditions, the multilayer structure is more resistant to pressure, but the external dimensions will become thicker. To put it bluntly, these constraints are a systematic project. Don't expect to fool things with a universal size.
Rectangular or circular? Applicable scenarios with different shapes and dimensions-from rectangular non-metallic expansion joints to fabric fiber expansion joints
Rectangles and circles。 More than 90% of rectangular non-metallic expansion joints (that is, rectangular non-metallic expansion joints) are used in rectangular pipes such as desulfurization, dust removal and flue. Why? Because the flue itself is square, you have to change it to a circular shape and then connect the compensator, and add two reducing segments, which will double the cost and have a large pressure loss. The outer dimensions of rectangular non-metallic expansion joints are usually expressed as length × width × height, such as 2000mm ×1500mm ×300mm. This 300mm is the axial length, which determines how much displacement it can absorb.
What about the round? Generally used in boiler outlet, fan inlet and outlet such places. The non-metallic expansion joints (fabric fiber expansion joints) in the product line are often round, and the outer dimensions are diameter and length. Let me tell you a trick: when the diameter of the air duct exceeds 1000mm, give priority to non-metallic ones, because the cost of enlarging the diameter of metal bellows is too high, and it is easy to sag due to its own weight.
There's another scenario – guess what? The operating temperature of the pipeline exceeds 800℃? Then you have to use non-metallic ones. The metal compensator has to burn and deform at this temperature, while the expansion joint of ceramic fiber fabric holds steadily. However, once the temperature is high, the insulation layer has to be thickened, the thickness in the external dimensions will increase, and the installation space has to be sufficient.
What are the core parameters hidden behind the form factor? Length, width, wave height, number of layers, one must not be less
Many people only look at the interface size and think that "it can be matched with the flange". Tsk, this kind of thinking is most likely to go wrong. There are at least four core parameters behind the overall dimensions of non-metallic compensators. If you count one less, the equipment may be wasted when installed:
- Effective length (axial length): Directly determines the axial compensation amount of the compensator. The longer the length, the greater the displacement that can be absorbed, but too long will destabilize. For example, for the same length of 200mm, the scheme is completely different for 20mm axial displacement and 40mm axial displacement.
- Width/Diameter: Corresponds to the size of the pipe, but pay attention to whether it has a guide tube. With a guide tube, the internal airflow flushing path should avoid the fabric layer, and the inner diameter in the outer dimension should be slightly larger than the inner diameter of the pipe.
- Wave height (or arch height): This is a parameter unique to non-metallic expansion joints. The arching height of the fabric fiber layer determines the lateral deflection and angular displacement it can withstand. The wave height was not enough, and a slight twist ripped the fabric.
- Number of layersComprises a temperature resistant layer, a sealing layer and a heat insulating layer. The more layers, the better the pressure resistance and insulation, but the overall thickness on the form factor will become thicker. For example, there are usually three layers in high temperature conditions: aluminum silicate fiber cotton (insulation) + polytetrafluoroethylene film (sealing) + stainless steel wire mesh (reinforcement).
When the wave is big, the effective length has to be adjusted; The number of layers has been added, and the installation space has to be recalculated. Where is there a reason to place an order just by looking at an interface size?
What does the size have to do with the installation space? Field Survey Pit Avoidance Guide
I've seen too many people fall into the "measurement" step. You think you can just measure the flange spacing on site and do it? Wrong. Let me tell you a few real pits:
Distance difference between cold and hot states is not measured。 The difference between the length of the pipeline during installation and operation at normal temperature directly determines the amount of pre-compression when the compensator is installed. You measure a cold size, and as a result, the tube is elongated during operation, the compensator is pulled to the bottom limit, and the life is directly halved. Correct practice: Understand the design thermal displacement direction and value, measure the cold nozzle spacing on site, and then calculate the installation length.
Ignore the perpendicularity of the flange surface。 If the pipe flange is installed crooked, the compensator is hard screwed on, the bolt stress is uneven, and the skin leaks quickly. When measuring, check the verticality and horizontality of the flange surface with a level ruler. If the deviation exceeds 1.5mm/m, it must be corrected.
No room for access。 The skin of the non-metal expansion joint may need to be replaced. If you install it against the wall, not even a wrench will fit in either side, and you will have to remove the whole pipe once you change it. For on-site measurement, at least 300mm operating space should be reserved around. This is not determined by the size of the compensator, but you have to take the surroundings into account when you size it.
Common myth: Bigger form factor is better? Wrong! Don't step on these thunders in model selection
The larger the external dimension, the stronger the compensation ability。 Those who say this are basically laypeople. The compensation ability mainly depends on the effective length and structural design, not on the cross section. You make a 2m ×2m compensator, but the length is only 100mm, and the axial compensation amount is not as good as that of 1m ×1m with a length of 300mm. Blind target large size, instead increase wind resistance and cost.
The more layers, the safer。 Not necessarily. The number of layers increases, the thickness becomes larger, and if the installation space is not changed, the activity space of the compensator is compressed. Moreover, the voltage resistance of multilayer structures can be achieved with more economical solutions, such as thickening at key layers rather than layering them over each other. The national standard JB/T 12235-2015 for non-metallic compensators has specific requirements for the number of layers and materials, so just follow them.
The length of the rectangular compensator is equal to the spacing of the pipes。 This one is the deadliest. Compensator installation usually requires pre-compression or pre-stretching, and the installation length is not equal to the product free length. You place an order according to the flange spacing without looking at the drawings, and the processing will either not fit or crush it to death. Again: measuring and designing dimensions are two different things.
Non-Metal Compensator vs Metal Compensator: The Design Logic of Form Dimensions is Completely Different
If you have used metal corrugated expansion joints and looked at non-metal compensators, the design logic is simply two worlds. The metal is deformed by bellows, and the external dimension is mainly determined by wave number and wave distance. Moreover, the metal structure is limited by pressure fatigue life, so it can't be lengthened casually. What about non-metallic ones? By flexible deformation of the fabric skin, the design freedom of "wave height" and "length" in the external dimensions is much greater, but it is limited by temperature, corrosion and aging. For example, metal compensators can be used in high-temperature steam pipelines (such as corrugated expansion joints used in power station industry), but non-metallic ones can't bear high-pressure steam, so non-metallic compensators are basically invisible on steam pipelines.
Non-metallic compensators have no resilience。 The metal bellows has an elastic recovery, so the metal compensator itself resists the thrust generated by internal pressure. The non-metallic fabric layer is soft and restrained entirely by the frame and tie rod. Therefore, the "frame thickness" in the outer dimension of the non-metallic compensator is much larger than that of the metal, otherwise it cannot withstand the pressure. If you take the size of the metal compensator to set the non-metal one when selecting the model, you will certainly be frustrated.
The dimensions of non-metallic compensators are not determined by patting the head. They are connected with the diameter of pipes, displacement, temperature and pressure, installation space and convenience of maintenance. Understand the relationship between these parameters, and you can avoid 80% of the selection pits.