Find out how the outer skin is broken
The outer skin of large non-metallic compensators is damaged for the same reasons: aging, mechanical scratches and media corrosion. But which one is specific, directly determines how you fix it later. For example, if high-temperature flue gas runs in the flue gas pipeline for a long time, coupled with the erosion of acidic gases (such as SO₂ and H₂S), the skin will gradually become brittle and hard, and fine cracks will appear on the surface-this is called aging damage. If pulverized coal or particulate material is transported in the pipeline, high-speed scour will partially wear the skin, forming small holes or strip-like scratches-this is mechanical damage. There is also chemical corrosion, such as the wet flue gas behind the desulfurization tower. The pH value of the condensate is low, the skin is soaked, and the surface is blistered and delaminated.
Are there any curls around the edges? Did it change color? Is the interior insulation cotton exposed?If the skin has become brittle as a whole and drops slag when touched, it is of little significance to repair it. It is more cost-effective to directly replace the whole non-metallic expansion joint (fabric fiber expansion joint) or rectangular non-metallic expansion joint. Repairs are only valuable if they are localized piercings or scratches.
What preparation work can't be saved before patching?
Safety comes first. Shutdown, pressure relief, power failure – these three steps are the bottom line. Non-metallic compensators are usually used in the environment of high temperature, dust and corrosive media. If the knife is moved without relieving pressure, an accident may occur. After the pressure relief is completed, wait for the pipeline temperature to drop to the ambient temperature (generally lower than 40℃), and then use a blade to clean all the dust accumulation, loose fibers and residual glue layer in the damaged area to expose the fresh substrate surface. The surface should be dry without water stains or oil stains.
In terms of materials, the commonly used accessories in our station are fluororubber cloth, silicone cloth and stainless steel wire mesh, which can be selected according to the same color and material of the original skin. If we can get a sample of the old skin on site,Be sure to measure the total thickness and number of layers。 The outer skin of non-metallic expansion joints is usually a multi-layer composite structure, such as the outermost layer is fluororubber cloth, sandwiched with aluminum silicate fiber cotton in the middle, and the inner layer is reinforced with stainless steel wire mesh. If the thickness is poor, the strength of making up is not enough, and it is easy to tear twice in the later stage.
Hands-on repair, divided into three common situations
Small area perforation (less than 50mm in diameter)
Cut a piece of composite material 30-50mm larger than the damaged area, and stick one layer inside and outside. The inner patch is attached to the inside of the pipe (sticking through the opening), and the outer patch is covered on the outside. High-temperature vulcanized glue is used for adhesive, and epoxy resin glue can be used if it is not available on the spot, but attention should be paid to the curing time. After the patch is attached, press the edge with mechanical strips (such as stainless steel flat strips), fix them with bolts, and apply a layer of sealant on the back of the strips in advance. Pay attention to the ambient temperature: when it is lower than 5℃, the adhesive effect will be discounted, so you have to preheat the repair area to above 15℃ with a hot air gun in advance.
Large area tear
If the tear length exceeds 200mm, or there are multiple tears, the double-sided patch will not be enough. It is necessary to cut a brand new skin, an area larger than the damaged area,Lap width at least 100mm。 Note: The non-metallic compensator is a multi-layer structure. Each layer should be staggered, and the overlap seams of all layers should not be stacked together, which will create weak points. When cutting a new skin, stick it layer by layer according to the lamination order of the original skin-first stick the inner fiber layer, then stick the middle insulation layer, and finally stick the outer fluororubber cloth. Each layer is compacted with a roller to drain air bubbles. Finally, tighten with strips and bolts, and control the spacing of strips at 150-200mm. Don't forget to apply high temperature resistant sealant on the back of the strip and around the bolt holes to prevent air leakage.
Edge breakage
Broken edges are easiest to fix. The compensator presses the skin tightly on the metal flange by the pressing bar. If the edge is broken, the old pressing bar is directly removed, the damaged section is cut off, a new skin is replaced and inserted again, and then the pressing bar is used to screw the bolts. During operation, pay attention to the new skin to leave sufficient flange length, at least 50mm, the press strip should be evenly pressed, and the torque should be according to the recommended value given by the manufacturer (generally, the torque of M12 bolts is 50-70N·m).
Don't be in a hurry to turn it on after replenishing
After the repair work is finished, do an airtightness check first: get some soapy water and spray it on the repair area and the gap between the strips, turn on the low-pressure air source (or blow it with compressed air) to see if there is any bubbling. Conditionally, do a low-pressure airtight test, control the pressure at about 1.2 times of the design pressure, and hold the pressure for 10 minutes without dropping the pressure. Check the torque of the strip bolt again-the torque attenuation is the main cause of later leakage, especially the thermal expansion and contraction under high temperature conditions can easily lead to bolt loosening.
Finally,Record repair location, date, material model used on equipment ledger。 Focus on this patch area the next time you shut down for maintenance, because the life of patches is usually only 60% to 80% of the original skin. Don't expect to do it once and for all.
When should I just replace it with a new one?
Patching is not a panacea. If the following occurs, don't hesitate to replace it with a brand-new non-metallic compensator or rectangular non-metallic expansion joint:
- The whole skin has reticular cracks, which feel brittle and breaks as soon as it is broken-indicating that the substrate has aged in an all-round way, and it will break if it is repaired here and there.
- The internal insulation cotton layer has rotted to black slag, or it absorbs water seriously-the failure of the insulation layer will cause the skin to be directly exposed to high temperatures, and the life will be shortened.
- There are more than three leakage points, and the spacing is less than 500mm-this porous state indicates that the skin has been fatigued in a large area and cannot be repaired.
The non-metallic expansion joints (fabric fiber expansion joints) and rectangular non-metallic expansion joints in our station are shipped from the factory according to JB/T 12235-2015 standard, and the warranty period and life are much more reliable than those of repair parts. Don't save hundreds of dollars, and you lose tens of thousands at a time when you shut down. Do you think that's true?