How many stumbles has the metal compensator stumbled on the heating line?
Having worked in plumbing repair for more than a dozen years, I've seen too many cases of being pitted and cried by a metal compensator. Corrosion, stress fatigue, and limited installation-how much these three mountains pressure Party A to change parts every year. Especially in heating pipelines, dissolved oxygen and chloride ions in the medium are really rude to stainless steel bellows. Last year, a central heating station in the north, 26 metal corrugated expansion joints, used less than three heating seasons, and the weld began to leak. After removing it, the inner wall is pitted in a large area, and some of them have already penetrated. The cost of changing a set is more than 80,000 yuan, and it has to stop heating for three days. Residents' complaint calls explode. And that's just a visible loss.
More covert is stress fatigue. The heating pipeline starts and stops frequently, and the alternating heat and cold leads to cyclic fatigue of metal bellows, and the fatigue life is not accurate at all. Some projects use general-purpose corrugated expansion joints in order to save money. As a result, the pipeline tends to be slightly deflected, and the lateral displacement and angular displacement are superimposed, and it will crack in two or three years. You say it was wrong or not?
What is the structure of non-metallic compensator (fabric fiber expansion joint)?
To put it bluntly, non-metallic expansion joints (fabric fiber expansion joints) are multilayer composite "soft armor". Typical structure from the inside to the outside: silica gel cloth is used as the main sealing layer, and the maximum temperature resistance can reach 300℃ (short time); Intermediate fluororubber or polytetrafluoroethylene film, specially to prevent acid and alkali corrosion; The outer layer is insulation cotton (ceramic fiber or glass fiber cotton), and then a layer of silicone cloth for protection. The lamination process is very particular-each layer is hot pressed at high temperature with special adhesive, not simply stacked together. The pressure resistance depends on the number of layers and fiber strength, and the four-layer structure of conventional heating line (≤1.6MPa) is sufficient.
Such a soft thing, won't it bulge when the pressure is high? There is a key here-non-metallic compensators rely on the weave density of fibers and the thickness of coatings to bear pressure, not on the elastic deformation of metal corrugations. Its displacement ability is much stronger than that of metal parts, it can absorb axial, transverse and angular displacements, and there is no metal fatigue problem. In other words, the pipe "gasps" and it moves with it, not competing.
Select three knives: temperature, pressure and displacement
Instead of just looking at the parameter table, you have to combine the pipe direction and media properties. For example: steam heating pipes and non-metallic compensators for hot water heating pipes are simply not the same way. The temperature of the steam pipe is high (often exceeding 150℃), and the wet steam contains condensed water, which causes erosion and wear to the fabric layer. At this time, you have to choose the thickened type lined with fluororubber, and the guide tube must be made of stainless steel 316L, otherwise it will be worn out in half a year. The temperature of the hot water pipeline is low (generally ≤95℃), but the pressure fluctuates greatly, so we should focus on the fatigue life of the fiber layer. The calculation of displacement is more headache-not simply counting the thermal expansion coefficient of the pipe, but also counting the position of the fixed bracket and the force arm at the turn of the pipe. Two days ago, a customer took the drawings and asked us to help select the model. Good guy, the pipeline has three 90-degree bends with a valve in the middle. It went directly to the non-metallic compensator without calculating the lateral displacement. As a result, it was torn within two months of installation. Therefore, to select this knife, you have to find experienced manufacturers to cooperate, and don't pat your head.
The Three Details That Are Most Prone to Rollover When Installing
Direction of the guide tube. The function of the guide tube is to guide the flow direction of the medium and protect the inner wall, and the direction of the arrow must follow the flow direction of the medium. Install backwards? The inner wall was directly subjected to the erosion, and its lifespan decreased sharply. Refer to the article "Specific Function of Expansion Joint Guide Tube" in the Q&A of our station, which contains a physical picture, which is clear at a glance.
Do you want to remove the tie rod nut? Many masters try to save trouble, and they are welded with tie rod nuts. Alas, this nut is a fixture to prevent deformation during transportation and installation, and the pipeline must be loosened before it is put into operation, otherwise the compensator will be locked and will not be able to expand and contract freely. How to adjust it specifically? Our other question and answer "How to adjust the tie rod nut of the expansion joint" is very clear. There are three steps: first symmetrically loosen half a circle, then measure the pre-stretching amount, and finally adjust it in place. Don't wait for it to leak before crying.
Fixed bracket spacing. There must be firm fixing brackets at both ends of the non-metallic compensator, and the spacing is according to the size given by the manufacturer. If the spacing is large, the self-weight of the pipeline will deform the compensator; The spacing is small, and the amount of compensation is not enough. This pit is most common, I have seen a site where the fixed brackets are spaced one meter more than the design value, and as a result the compensator body bulges like a balloon.
After three or five years of use, when should the non-metallic compensator be replaced?
Do-it-yourself inspection is three steps. The first step is to see if there are bulges in the fabric layer. Bulging means that the internal fibers are broken or delaminated, the pressure bearing capacity is reduced and must be replaced. The second step is whether the flange sealing surface seeps water. Slight water seepage may be loose bolts, tighten them and have a look; If the seepage continues, it means that the sealing surface is aging or the flange is deformed, so you have to replace the gasket or even the whole. The third step is to measure the attenuation of the compensation amount. Simple method: In the shutdown state, draw a mark on the compensator body, then let the pipe go through a complete thermal cycle, and come back to see the mark position change. If the actual displacement is smaller than the design value by more than 30%, it means that the internal structure has been damaged and should be replaced.
The national standard of non-metallic compensator is JB/T 12235-2015, which stipulates the service life judgment standard. Under normal working conditions, the design life of 8-10 years is no problem. However, if the medium contains corrosive gases (for example, if the heating pipeline is filled with softened water but chloride ions remain), or it runs at overtemperature for a long time, it may have to be replaced in three to five years. Don't worry about the money. If the pipeline collapses late, it will lose a lot.
In the final analysis, the heating pipeline selects non-metallic compensator, which is designed to save maintenance, corrosion resistance and absorb multi-directional displacement
The price is a little more expensive than the metal ones? Tsk, calculate the account: a set of metal corrugated expansion joints is two or three thousand, and non-metallic ones may be four or five thousand, but metal ones are changed every three years, and non-metallic ones don't have to be moved for ten years. In ten years, the cost of materials alone will be saved by half, not counting the loss of heating and labor costs. Moreover, the corrosion resistance of non-metals is natural-silicone cloth, fluororubber, PTFE, which is afraid of water and chlorine? There is no way to corrupt it. The multi-directional displacement absorption capacity is not to be compared. Metal bellows can only absorb axial or transverse one, and non-metallic ones can absorb one pot end.
So, if you choose the right non-metallic compensator for heating lines, you can really save ten years of worry. The premise is that don't be sloppy in the selection, don't be lazy in the installation, and take a look regularly. Do all three, and it is the most reliable soft joint in your plumbing system.