First, find out one thing first: the deformation of non-metallic expansion joints and the deformation of metal expansion joints are not the same thing at all
The deformation of metal expansion joint is mostly corrugation fatigue cracking, and the crack can be seen at a glance. The deformation of non-metallic expansion joints (fabric fiber expansion joints) tends to begin at the skin, insulation, and frame joints. The bulging, twisting and local depression you see may be caused by excessive temperature, abnormal pressure, misalignment of installation, or media corrosion that destroys the fiber layer. Only by distinguishing the nature of deformation can we decide whether to replace or repair it. Don't rush to dismantle the deformation as soon as you see it. Ask yourself first: Is this deformation a matter of the surface of the skin, or is the internal structure completed?
2. The three most common deformation sites
Inadequate thermal displacement absorption, negative pressure deflation and excessive angular displacement-these three situations account for more than 90%. Many engineers regard non-metallic expansion joints as "soft connections", thinking that they can be installed casually. In fact, when the rectangular non-metallic expansion joint and the circular non-metallic expansion joint absorb the lateral displacement and the angular displacement, the skin force distribution is completely different. For example, if the non-metallic expansion joint on the flue gas pipe is not aligned during installation, one side will be stretched and the other side will be wrinkled during operation. After a long time, the fiber layer will be delaminated, and the surface will only be "deformed", and the inside will have lost its sealing ability. If you take it apart, it will be a rotten mess.
Third, don't rush to replace a new one, first calculate whether the deformation is still within the design range
The national standard JB/T 12235-2015 for non-metallic expansion joints clearly stipulates the displacement compensation amount, but many people at the site don't look at the design parameters, but directly judge with the naked eye. Alas, isn't this digging a hole for yourself? I met a cement factory customer, and the surface of the non-metallic expansion joint looked more than ten millimeters crooked. As a result, when I checked the original design, the allowed radial displacement was ±25mm, which did not exceed the limit at all. On the other hand, the expansion joint at the entrance of the desulfurization tower of some power plants looks fine, but it actually exceeds 80% of the rated displacement, and the internal fibers of the skin are broken. Therefore, the first step to judge the deformation is to dig out the design drawings and factory inspection records, measure the actual displacement and calculate the proportion. What about that? Take a ruler and measure it. Don't just look.
4. If it is confirmed that the deformation exceeds the limit, it depends on whether to change the skin or the whole
The structure of non-metallic expansion joints is generally composed of skin, thermal insulation cotton, stainless steel wire mesh and frame. In many cases, the frame is not broken, but the skin is aging. At this time, replacing the skin alone can solve the problem, and the cost is only about one-third of the overall replacement. However, it should be noted that if the deformation is caused by the falling off of the guide tube or the collapse of the internal heat insulation layer, just changing the skin is a cure for the symptoms but not the root cause. Take a look inside with an endoscope before disassembling. Don't skip this step. Besides, when replacing, it must be done according to the original laminated structure. The skin material, number of layers and thickness are one layer different, and the life is twice the difference. The materials you save will be doubled back from the maintenance fee in the end.
5. Deformation is not a unique problem of non-metallic expansion joint, but its failure mode is different from that of rubber compensator and metal expansion joint
The deformation of rubber compensator is mostly aging and sticky, the deformation of metal expansion joint is the plastic yield of bellows, while the deformation of non-metal expansion joint is often the loosening of fiber layer and suture fracture. Therefore, the treatment method is completely different: the rubber compensator can only be replaced as a whole, the metal expansion joint can be corrected by pre-deformation, and the non-metal expansion joint gives priority to local repair. This is why many power stations and cement plants will prepare several different types of compensators at the same time, just to respond quickly to different working conditions. You say, if you use all the same, don't stare when something goes wrong?
6. The last hard suggestion
Record each deformation, take photos, measure the size, and record the operating temperature. Don't be too troublesome. With more deformation data accumulated, you can summarize the laws of your own system. For example, the non-metallic expansion joint in a certain position will shift to the same side by a few millimeters every winter, which is mostly because the pipeline is not cold and tight; For example, if there is a local bulge after three months of operation, and the position is fixed, it is necessary to check whether the sealing wind pressure of the baffle door fluctuates. The data is more reliable than experience, especially in occasions where flue gas baffle doors and desulfurization systems are highly corrosive and have large temperature fluctuations. Recording the deformation trend in advance can save a lot of unplanned shutdown losses. Don't wait until it blows up to remember to ask, it will be too late.