Just buying a skin, not buying the whole expansion joint, but also raising the expansion amount? This thing is just a piece of cloth and a few layers of rubber. Alas, it is so simple that there will be no pipeline leakage after half a year of installation. Today, let's make it clear-skin procurement, whether the expansion amount is a matter.
Figure out two things first
The skin, the soft connection part of the non-metallic expansion joint (fabric fiber expansion joint), is responsible for absorbing the thermal expansion, contraction and vibration of the pipe. The amount of expansion is not just asked to quote a number-it directly determines whether the skin will be torn or squeezed into a ball in high temperatures. For example: the pipe is heated and elongated by 1cm. If the skin does not leave enough margin, it will either crack or be pressed out of wrinkles. This is not a "probable" thing, but a real physical deformation.
How exactly does the expansion amount come from? The maximum values of axial, transverse and angular displacements will be given in the pipeline stress calculation report. You get that number, which is the core input of the skin design. The supplier should choose the number of fabric layers, the thickness of the sealing film, and even the amount of pre-compression according to it. Not mentioning it? That can only be done according to the general-purpose type. Whether it can handle the displacement depends on luck.
How ruthless are the consequences of not mentioning the amount of expansion?
Take the desulfurization flue gas pipeline as an example. The flue gas temperature fluctuates greatly, and the measured displacement can move by tens of millimeters. You buy the skin in standard size, it looks like it fits when you install it, and the edges of the skin start tearing after a few months of operation, or it leaks at the connecting bolts. The labor cost of changing the skin is more expensive than the skin itself, let alone the downtime loss-a production line is stopped for half a day, and hundreds of thousands are gone.
Two days ago, I met a machine repairman in a cement factory. They used the outlet pipe of the vertical millRectangular non-metallic expansion jointThe expansion amount was not mentioned at the time of purchase, and as a result, the skin bulged and torn within half a year of operation. After removing it, it shows that the inner temperature-resistant layer is completely cracked, and the sealing layer is directly exposed to 350℃ smoke. Do you think it can be bad? Later, it was replaced with our special skin, and the amount of pre-compression was added. There was no problem for five years.
Conversely, not all working conditions have to be mentioned
For example, the displacement of the dust removal pipeline at normal temperature and low pressure is so small that it can be ignored. Or the pipe has been used with metal corrugated expansion joints (such asUniversal corrugated expansion joint) absorbs most of the displacement, and the skin only acts as a seal-in this scenario, increasing the expansion amount is of little significance.
Then how to judge whether to mention it or not? The key is to look at three things: the medium temperature, the direction of the pipe, and the layout of the fixed bracket. If the temperature exceeds 150℃, the pipeline tends to bend sharply, or the spacing between brackets exceeds the standard, there is a high probability that it needs to be mentioned. You just take out the pipe stress calculation report and find the maximum displacement value-that's the amount of expansion you want to give. If you don't have a report yourself, ask the design institute or let the manufacturer's technology help you calculate it. Don't pat your head.
Then how to mention it? Don't come up and throw a number
How much is the axial displacement, how much is the lateral displacement, how much is the angular displacement. The skin is a multi-layer composite structure-temperature resistant layer, sealing layer, reinforcing layer-each with a different tensile allowance. The supplier should design the length and lamination of the skin according to the total displacement. For example, a vertical mill outlet pipeline in the cement industry, with a temperature of 350℃ and an axial expansion of 30mm, we have provided it to our customersRectangular non-metallic expansion jointThe skin has increased the amount of pre-compression, and it has been used for five years without any problems.
Some purchasing charts save trouble, only writing "displacement 30mm", but no direction. As a result, the supplier designed it in the axial direction, but the actual pipe swung laterally, and the skin was torn as well. Therefore, it is necessary to divide the direction, and it is best to attach a simplified diagram of pipeline layout.
Finally, a list for the purchasing veterans
When inquiring about the skin, in addition to the diameter size, medium temperature and pressure, be sure to write "expansion amount"-specific value and direction, and it is best to attach a simplified diagram of pipeline layout. If you are not sure, ask the manufacturer's technology directly, and don't pat your head yourself. The skin doesn't seem to be the core piece, but when it breaks down, the whole system will have to stop. Increasing the amount of inflation is not a trouble, but a lot of money.
And guess what? Some old purchasers told me that they never mentioned the expansion amount when buying skin before. If it was bad, it would be bad. Anyway, it was cheap. Later, I calculated the account: one downtime loss + labor replacement fee is enough to buy ten skins. Since then, they have honestly written out the expansion amount every time they inquire. So, you have to mention it when you need to mention it, and don't save those few minutes of communication time.