Maintenance methods and quality standards for reaction kettles

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Reactor Vessel 1. Conditions for replacement: After the reactor vessel has been in use for a certain period of time, it should be replaced if any of the following conditions occur: a. The uniform corrosion of the vessel wall thickness exceeds the minimum value specified in the design； b. The local corrosion of the kettle wall thickness exceeds the minimum value specified in the design, and the corroded area is more than 20% of the total area ； c. During the hydrostatic test, the equipment shows significant deformation or residual deformation exceeding the specified values ； d. When cracks occur in the reactor vessel or welds due to alkali embrittlement or severe intergranular corrosion and cannot be repaired ； e. When the damaged area of the porcelain surface exceeds 15% or when the damaged part cannot be repaired ； f. Defects exceeding standards (e.g., severe structural defects that endanger safe operation) ； The weld is unacceptable ； When it cannot be repaired due to severe lack of weld penetration, cracks, etc. 2. Steel kettle body: a. Local corrosion of the shell is repaired using arc surfacing; if the area of corrosion is large, patching is employed for repair. b. Unpenetrating cracks. If the crack depth is less than 10% of the wall thickness and not more than 1 mm, the crack can be ground flat using a grinding wheel, ensuring a smooth transition with the metal surface. If the crack depth does not exceed 40% of the wall thickness, a groove can be cut within that depth range for welding repair; however, small holes should be drilled at both ends of the crack to prevent it from spreading. For long cracks, the step-by-step desoldering method is used (welding from both ends of the crack toward the center in stages) to reduce welding stress and deformation. If the crack depth exceeds 40% of the wall thickness, it shall be treated as a through narrow crack. c. Narrow cracks that penetrate. Before welding repair, drill crack-stopping holes at both ends of the crack; the diameter of these holes should be slightly larger than the width of the crack, and grooves should be prepared as well. When the wall thickness is less than 12 mm, a V-shaped groove is used ； When the wall thickness is greater than 12 mm, an X-shaped groove is used. During welding, cracks shorter than 100 mm can be welded in one go ； When the crack is long, it is advisable to weld from both ends of the crack toward the center, avoiding circular motions, and to use multi-layer welding. Except for the areas with stress concentration, cracks and narrow penetrating cracks in all parts of the kettle body can be repaired by welding. d. Wide cracks that penetrate. Wide cracks should be repaired by patching. The length of the patch should be 50–100 mm greater than the length of the crack, and its width should be no less than 250 mm. The welded patch should be level with the surface of the main body, and its radius of curvature should be the same as that of the main body. e. Bulging of the stainless steel lining. When the lining is deformed over a large area and the ratio of the bulging height to the average diameter of the deformed area is less than 0.15, it is advisable to use the water pressurization method to restore the deformed lining. For shells or linings with a small deformation area, mechanical pressing can be used for repair, but care must be taken to prevent brittle fracture during the correction process. 3. Cast iron kettle body: Common defects in cast iron kettle bodies such as sand holes, cracks, pitting corrosion, or local corrosion are usually repaired using arc cold welding. When welding to repair, a crack-stopping through-hole should be drilled 3-5 mm outside each end of the crack. 4. Glass-lined reactor vessel: The glass lining is brittle and prone to damage, as well as having poor thermal stability. Care must be taken to protect the porcelain surface during maintenance; lifting should be carried out using hooks or ropes at designated points. Necessary cooling measures must be taken when welding. Depending on the degree of damage, the following repair methods can be used respectively. a. Corrosion-resistant metal packing method. When microholes are found in the porcelain surface, plugs made of corrosion-resistant metal materials can be used to be inserted directly into those holes. b. When the damage to the porcelain surface is relatively severe, it should be secured to the damaged surface using corrosion-resistant metal bolts and corrosion-resistant pads. c. Inorganic coating repair method. Clean the surface to be repaired first; use 15-20% dilute sulfuric acid to remove rust, then neutralize it with a 10% sodium hydroxide solution. After that, rinse with water, wipe dry, dry it with hot air, and finally apply an inorganic coating, allowing it to cure through slow heating. Coating weight ratio: pyroclastic rock powder: 100, fineness 80–100 mesh ； Sodium fluosilicate: 5, purity >95% ； Water glass: 95, specific gravity 1.48. d. Organic coating repair method. The steps are the same as those for repairing with inorganic coatings. Weight ratio of organic coatings: Epoxy resin: 100; dibutyl phthalate: 15; m-phenylenediamine: 12–14; graphite (or other fillers): 50–100. After coating, carry out heat treatment at a temperature of 80~100°C; the temperature should be increased slowly during heating. It can be used once it has fully cured. e. The number of fastening clamps on the glass-lined reactor body flange must be maintained at the specified standard and evenly distributed. The fastening clips must be tightened symmetrically and evenly along the diagonal direction; excessive force or one-time tightening is not allowed. 5. Quality standards for kettle body repair a. The welds should transition smoothly into the base material. b. The local root penetration depth of the weld shall not exceed 0.5 mm, and the length of the root penetration area shall not be greater than 100 mm. c. The welds shall be free from defects such as cracks, lack of penetration, lack of fusion, inclusions, and pores. d. The slag on the weld and the spatter on both sides should be removed completely. e. After repair, no cross welds shall be present; the longitudinal seams between adjacent cylinders, as well as the longitudinal seams between the end caps and adjacent cylinder sections, shall be offset from each other. The distance between them shall be greater than three times the thickness of the cylinder wall, and shall not be less than 100 mm. f. The repair of welds should not exceed two times. g. The correct type of welding rod should be selected; the welding rods and flux must be dried and used as needed. h. The reactor vessel after welding must undergo a hydraulic strength test. During the hydraulic strength test, the air inside the tank must be completely removed. Once the wall temperature of the tank is close to that of the liquid, the pressure should be increased slowly. The tank should be held at the test pressure for 10–30 minutes, after which the pressure should be reduced to the maximum operating pressure for inspection. The test is considered successful if there are no leaks, no visible abnormal deformations, and no unusual noises during the test. For kettle bodies with an out-of-band insulation layer or whose exterior cannot be observed, they must be held at the maximum operating pressure for at least 2 hours; they are considered qualified if the pressure does not drop and no abnormal noises are heard. i. The airtightness test for the reactor vessel, which is required to be conducted, should be carried out after the hydraulic test is successful; the temperature of the gas used for this test should be no lower than 5°C. Transmission: V-belt drive. a. When installing and aligning the pulleys, the parallelism between the axes of the two pulleys should be no more than 0.01a, and the axial displacement of the symmetrical planes of the pulley widths should be no more than 0.005a (where a is the actual center distance between the two pulleys, in mm). b. For the fit between the pulley hole and the shaft, H7/k6 is selected; the surface roughness is set at 1.6/0.8. c. The tension of the triangular belt should be even and moderate. d. The pulley hole should be replaced if it is cracked, or if there are notches in the pulley groove or severe wear on the groove surface. e. The V-belt is severely worn ； The belt is in contact with the bottom of the groove ； Belt aging ； crack ； The plastic distortion should be replaced. f. The V-belts on the same pulley should be replaced at the same time.