Maintenance methods and quality standards for reaction kettles

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Vessel body 1. Replacement conditions: After the reaction vessel has been in use for a certain period of time, it should be replaced if one of the following conditions occurs: 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 limits (e.g., serious structural defects that jeopardize safe operation ； The weld is unqualified ； When it cannot be repaired due to severe lack of weld penetration, cracks, etc. 2. Steel reactor vessel: 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 smoothed out using a grinding wheel, so as to achieve a smooth transition with the metal surface. If the crack depth does not exceed 40% of the wall thickness, a bevel can be created in the area of the crack 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 employed (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-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 penetrating narrow 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 hole should be drilled 3-5 mm outside each end of the crack. 4. Glass-lined reactor body: The glass lining is brittle and prone to damage, as well as having poor thermal stability. Care must be taken to protect the ceramic surface during maintenance; lifting should be carried out using hooks or ropes at designated points. Necessary cooling measures must be taken during welding. Depending on the extent of the damage, the following repair methods can be used respectively. a. Corrosion-resistant metal packing method. When micropores are found in the porcelain surface, plugs made of corrosion-resistant metal materials can be used to be inserted directly into those micropores. 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 inserts. c. Inorganic coating repair method. Clean the surface to be repaired; first remove rust using 15-20% dilute sulfuric acid, then neutralize it with a 10% sodium hydroxide solution. Rinse with water, wipe dry, blow dry with hot air, and finally apply an inorganic coating, allowing it to cure through slow heating. Coating weight ratio: pyroxene 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 in a diagonal direction; excessive force should not be used, nor should they be tightened all at once. 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 seam between the head and the adjacent cylinder section, shall be offset from each other. The distance between them shall be greater than three times the thickness of the cylinder wall, and not 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 in 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. Agitation device: a. When the agitator shaft is bent, it can generally be straightened using mechanical pressure methods. The straightness of the agitator shaft is 0.10 mm/m, and the straightness of the shaft diameter position is 0.04 mm/m. b. When wear occurs at the junction between the stirring shaft and the sealing packing, slight machining is required to round it out; if the wear amount exceeds 0.5 mm, surfacing followed by machining should be carried out to restore the dimensions specified in the drawings. Surface roughness 0.8. c. The agitator shall be replaced when its uniform corrosion exceeds 30% of its original thickness. d. Local corrosion, cracks, and deformation of the agitator shall be repaired by welding, reshaping, and straightening. When glass-lined mixers suffer damage such as corrosion or enamel loss, they should be repaired using the appropriate methods for glass lining repair. e. The axis of paddle, frame, and anchor agitators shall be perpendicular to the blades, with a perpendicularity of 4/1000 of the total length of the blades, and shall not exceed 5 mm. f. Turbine-type and impeller-type mixers with a rotational speed higher than 100 r/min shall undergo a static balance test. Balancing can be achieved using the deduplication method or the weighting method; the thickness removed or added shall not exceed 1/4 of the wall thickness, and the joints must have a smooth transition. When the rotational speed is less than 500 r/min, the unbalanced mass on the outer diameter of the impeller should not exceed 20 g. g. For turbine and propeller type mixers, the fit between the impeller hole and the mixing shaft journal is H7/k6, with a surface roughness of 1.6/0.8. h. Special tools should be used to remove rolling bearings; when installing them under heat, the oil temperature should be 140°C, and direct heating with a flame is strictly prohibited. i. When installing a rolling bearing at the lower end of the stirring shaft, its outer ring should not be compressed; a clearance of about 0.5–1.0 mm for axial thermal expansion and contraction must be left. j. The rolling elements of the rolling bearing and the raceway surfaces should be free from corrosion, pits, or spots, with smooth contact and no abnormal noises. The journal that fits into the inner bore of the rolling bearing is designated as K6, with a surface roughness of 0.8; the hole that fits into the outer ring of the rolling bearing is designated as K7, with a surface roughness of 1.6. Axial sealing device 1. Packing seal a. The fit between the packing gland and the packing box is H11/d11; the clearance between the gland hole and the shaft is 0.75–1.00 mm (for shaft diameters of 50–110 mm), while the clearance between the stirring shaft and the box is 0.60–1.00 mm (for shaft diameters of 50–110 mm). b. The gap between the filler gland and the end face of the housing should be equal, with an error not exceeding 0.3 mm. c. The material and specifications of the filler must be used correctly; its length should be appropriate. The overlaps between successive layers of filler should be evenly spaced in a circular pattern, with the cut edges at 30° to each other, and these edges should be smooth and aligned vertically. d. The filler must have an appropriate amount of compression allowance. e. Ensure the oil ring is in the correct position and that the oil flow is unobstructed. 2. Mechanical seal: a. The perpendicularity between the shaft and the sealing chamber is generally 0.05 mm; the coaxiality with respect to the sealing chamber is usually 0.5 mm. The radial runout is 1 mm, and the axial movement is also 1 mm. b. At the location where the mechanical seal is installed, the surface roughness of the shaft should be no less than 1.6. c. The sealing chamber must be kept clean; the roughness of the sealing surfaces of the moving and stationary rings should not be less than 0.2, and it should not leak when filled with water. d. The end pressure ratio should be adjusted appropriately to ensure good lubrication while minimizing leakage as much as possible. Bring the sealing surface into a semi-liquid friction state. e. The winding direction of the spring must be consistent with the operating direction of the shaft. f. The perpendicularity of the static ring end face to the axis shall not exceed 0.05 mm. g. In a properly installed mechanical seal, the rotating ring should open smoothly and reliably. h. When turning the shaft by hand, the seal rotates smoothly with no abnormal phenomena. i. For the airtightness test, it is considered successful if no continuous small bubbles are formed. Safety accessories such as safety valves, rupture discs, and pressure gauges shall be installed in accordance with the relevant regulations for pressure vessels. Level gauge: Before installation and use, the level gauge must undergo a hydrostatic pressure test at 1.5 times its nominal pressure. The level gauge should be stopped from use and repaired or replaced if any of the following conditions occur ； a. Exceeds the inspection period ； b. The glass plate (tube) has cracks or is broken ； c. Valve components stuck ； d. False levels frequently occur. Other instruments, signal interlocks, safety devices, etc., shall all be implemented in accordance with relevant regulations. Installation a. The allowable horizontal error for the installation of the kettle body is 1 mm/m. b. The allowable error for the installation elevation of the kettle body is ±5 mm; the allowable error for the positions of the meridians and parallels is ±5 mm when the diameter is less than 1 m ； When the diameter is greater than 1m, it is ±8mm. c. The distance between the material pressing tube, the thermometer sleeve, the heating coiled tube, and the mixer should be no less than 40 mm. d. The deflection between the two flanges should be less than 1 mm, and the distance between the flange surfaces should be less than 2 mm. Only one gasket is allowed to be used between the two flanges; it is not permissible to use additional gaskets in order to address an excessive distance between the flange surfaces. e. The flange sealing surface must be smooth. Free from defects such as mechanical damage, radial scratches, severe rust, weld scars, and material residues. The human access covers show no obvious defects such as deformation, rust, or cracks. f. The gasket must be installed correctly, with a thin layer of flake graphite coating applied to both surfaces of the gasket. g. The nut should rotate smoothly on the bolt without wobbling, and the threads must be clean. When tightening the flange, it is required to use a torque wrench to tighten it in two to three steps in a symmetrical and even manner; the tightening force must not be excessive, insufficient, or uneven. h. Bolts of different materials and specifications are not allowed to be used together on the same flange. i. Relevant regulations must be followed for bolts that require thermal tightening or cold tightening during the heating or cooling process.