Once the nonmetallic compensator (that is, we often call the fabric fiber expansion joint) bulges, collapses or twists, many people's first reaction is to remove it and replace it with a new one. Wait a minute – deformed ≠ scrapped. Find out what kind of deformation it is first, and then decide whether to repair or replace it, which can save thousands of shutdown losses and spare parts costs. Today, let's get this out of the way.
Look at the form first, then look for the cause
Bulging, collapse, twisting, localized wear. The bulge is mostly caused by gas expansion inside the fabric fiber layer or damage to the inner lining; Collapse is mostly caused by negative pressure suction or condensate corrosion, which causes the fiber to lose elasticity; The twist is probably due to the misalignment of the pipeline during installation and the shear force of the compensator; Localized wear is common in particle-containing scouring of media. And guess what? Deformations that occur in the same location may have completely different causes. For example, the non-metallic compensator behind the desulfurization flue gas baffle door has been exposed to acidic condensate for a long time, and the fiber layer begins to eat away from the inside. The outside appears to be only slightly collapsed, but when it is disassembled, it is already layered inside. You just change your skin at this time? It's useless, we have to do it with the drainage device and the anti-corrosion coating.
Temperature overruns and pressure fluctuations: the number one killer
The design temperature resistance of non-metallic expansion joints is generally engraved on nameplates, but the local heat radiation or flue gas flow rate changes are often neglected in actual working conditions. Two days ago, I met a cement factory customer. The measured temperature in the pipeline was 50℃ higher than the design value, and the skin was directly carbonized and deformed-the surface felt like a charred biscuit. What about that? Check the heat source and insulation first, and don't dismantle the compensator as soon as it comes up. After lowering the local temperature and restoring the heat insulation layer, as long as the fiber is not broken, adjust the limit bolt (refer to the adjustment method of the expansion joint tie rod nut), so that the compensator can restore part of the pre-compression amount, and it can last for a while. The same is true for pressure fluctuations, especially near the position of electric plug-in type isolation door or manual plug-in type isolation door. The impact at the moment of valve opening and closing may make the compensator bulge instantly. Priority is given to checking the system pressure relief and valve action logic rather than hardening the compensator itself.
Installation deviation: a fault that is slowly worn out
When the pipe is matched, if the flanges at both ends are not in a straight line, the non-metallic compensator will be forcibly pulled to bear the shear force. This deformation is not visible to the naked eye in its early stages-it feels normal when you glance at it during your inspection. But after a few months of operation, one side of the compensator will appear with dense folds, like the wrinkles on the face of an old lady. Why? Because of the long-term uneven stress of the fabric fiber layer, local fatigue. The solution is simple: Readjust the pipe support to release the stress. Don't reinforce the frame of the compensator, it will only transfer the stress to a weaker place.
Corrosion and ash accumulation: comprehensive treatment of chronic diseases
Rubber compensator and rubber PTFE compensator are very common in chemical industry and desulfurization scenes. Rubber is corrosion resistant, but rubber PTFE compensator is easy to age and deform at high temperature. The materials of the two are different, and the processing logic is also different. If the rubber compensator bulges, it is likely that the oil or solvent in the medium penetrates into it and swells the rubber. At this time, you measure its hardness. If it becomes obviously soft, you have to change it. If the rubber PTFE compensator ages and hardens, and the surface cracks, it has to be replaced. However, there is an exception: if the non-metallic compensator behind the desulfurization flue gas baffle door collapses and deforms but is not broken, you can first check whether the drainage device is blocked, clean up the dust by the way, and then adjust the limit bolt to observe the operation.
What conditions can be "conservatively treated"?
If it is slightly bulged and not damaged, it can be saved in this way: the first step is to shut down for cooling and pressure relief; In the second step, gently poke the bulge with a screwdriver. If you feel that there is gas released inside (the fiber layer is just bulging, not tearing), you can adjust the tie rod nut to let the compensator restore a little pre-compression; The third step is to reduce the operation parameters of the system, such as lowering the temperature by 10℃ and the pressure by 0.05MPa, and running for 24 hours for observation. The bulge disappeared? Then keep using it, and arrange regular inspections. Remember: Nonmetallic compensators are different from metallic expansion joints in that their flexibility depends on the fiber layer, which must be replaced once the fibers break or delaminate. If you touch the deformed area with your hand, if it feels loose and baggy like linen, it means that the fiber has broken. Don't hesitate, according to JB/T 12235-2015 standard, continuing operation at this time will only accelerate the fatigue failure of the whole pipeline system-whether it is corrugated expansion joint or straight pipe pressure balance expansion joint, adjacent equipment may suffer.
What circumstances must be shut down for replacement?
Leaked, delaminated, metal frames and pipes detached. For example, the non-metallic compensator on the vacuum pipeline of the air-cooled island of a power plant began to leak after deformation, and the inspector didn't take it seriously. As a result, a month later, the adjacent transverse expansion joint of the compound hinge also cracked. Because after the compensator failed, no one absorbed the thermal displacement of the pipe, and all of it was pushed to the nearby equipment. You must pay attention to two points when replacing: First, the selection should match the original design-rectangular non-metal expansion joint or round fabric fiber expansion joint? The dimensions and interface flanges must be consistent; Second, don't use brute force to force the counter when installing, first adjust the pipe support and then install the compensator. And guess what? Many people try to save trouble. As soon as the new compensator is installed, the bolts are tightened, and as a result, the torsional stress is brought back to the compensator, which is wasting money.
What if the non-metallic compensator is deformed? To put it bluntly, there are three steps: first judge the form and cause, and adjust the limit bolts and working conditions if you can save them; If you can't save it, replace it strictly according to the standard, and repair the installation deviation and corrosion source together. Don't be lazy, and don't mess around. If you use the compensator right, it will last five years, but if you use it wrong, it will be wasted for three months.