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1. Purpose: To standardize the maintenance management of equipment, eliminate equipment defects in a timely manner, ensure the safety of maintenance operations, improve the quality of maintenance, reduce maintenance costs, save time spent on maintenance, and guarantee the \"safe, stable, long-lasting, efficient, and optimal\" operation of the equipment, these regulations have been formulated. They specify the maintenance cycles and tasks, the standards for maintenance and quality control, procedures for testing and acceptance, as well as measures for maintenance and fault resolution. 2. Scope of application This plan is applicable to the maintenance and repair management of tower equipment. 3. Preparation of the basis for revisions 3.1 Maintenance and repair procedures for tower-type equipment SHS 01007—2004 3.2 Technical documents related to equipment drawings 4. Maintenance intervals and scope of repairs 4.1 Maintenance intervals The maintenance intervals are shown in the table below. Repair type: Maintenance cycle, in months; Maintenance time, in days. Minor repair: 24 days; 5 days. Medium repair: 48 days; 10 days. Major repair: 120 days; 32 days. 4.2 Preparatory work before maintenance: (1) Stop the operation of the tower equipment, relieve the pressure inside the tower, remove all materials remaining inside it, and then blow steam into the tower for cleaning. Open the large cover at the top of the tower (or the vapor-phase outlet at the top) for steaming, purging, displacement, and cooling. Then, open the access holes in the tower body from top to bottom. Prior to maintenance, appropriate fire prevention, explosion prevention, and toxicity prevention safety measures must be taken. It is necessary to thoroughly clean and purge all flammable or toxic substances inside the tower, as well as conduct chemical analyses of the gases within the equipment and in the surrounding area, so as to meet the requirements for safe maintenance. (2) Tower inspection: a. During each maintenance session, it is necessary to check whether all accessories (pressure gauges, safety valves and vent valves, thermometers, check valves, fire steam valves, etc.) are functioning properly and accurately. b. Inspect the tower for corrosion, deformation, reduced wall thickness, cracks, and the condition of welds in various areas; conduct ultrasonic thickness testing and physical/chemical analyses, and keep detailed records to serve as a basis for further research and improvement as well as for future maintenance. Upon inspection and evaluation, if it is determined that there is an impact on the design allowable strength, a hydrostatic test may be conducted; the relevant values can be found in the applicable regulations. c. Inspect the dirt inside the tower and the internal insulating material. (3) Inspection of tower internals. a. Inspect for coking, dirt, and blockages in all components of the trays; check for corrosion and deformation of the trays and supporting structures. b. Check whether the dimensions of various components on the tray (exit weir, liquid receiving tray, downcomer) comply with the drawings and standards. c. Check the tightness of various components such as trays and bubbling elements to ensure there is no loosening. (4) Check the deformation of the connection pipelines in various sections, and verify whether the seals at the connections are reliable. 4.3 Repair of Major Components 4.3.1 Tower Body (1) Repair of Cracks in the Tower Body Cracks in the tower body can generally be detected using kerosene and magnetic testing methods. The types of cracks include non-penetrating cracks, narrow penetrating cracks, and wide penetrating cracks. The repair methods are as follows: a. For non-penetrating cracks, if the depth of the crack is less than 10% of the wall thickness and not more than 1 mm, the crack can be ground away using a grinding wheel, ensuring a smooth transition with the metal surface. If the crack depth does not exceed 40% of the wall thickness, during repair a bevel can be cut within the depth of the crack, followed by welding repairs. However, it should be noted that small holes should be drilled at both ends of the crack to prevent its propagation. To repair long cracks, a segmented welding-back method should be used to reduce welding stress and deformation. If the crack depth has exceeded 40% of the wall thickness. A groove should be made throughout the wall thickness and repair welding should be performed, treating it as a narrow crack that penetrates the material. b. Penetrating narrow cracks: Cracks with a width of 15 mm or less are referred to as narrow cracks. Before performing patch welding, it is necessary to check whether there are crack stop holes at both ends; the diameter of these holes should be slightly larger than the width of the crack. If such holes are not present, they must be drilled first, after which a bevel should be created along the crack using a chisel or gas cutting. The shape of the groove should be determined based on the wall thickness of the equipment. When the wall thickness is less than 12–15 mm, a single-sided groove can be used ； When the wall thickness exceeds 12–15 mm, double-sided grooves should be used. During welding, cracks shorter than 100 mm can be welded in one pass. When repair-welding long cracks, care should be taken to compensate for shrinkage and reduce internal stresses. It is recommended to weld from both ends of the crack toward the middle, using multiple layers of welding. Except for areas with stress concentration, cracks and narrow penetrating cracks in various parts of the equipment (such as the shell, end caps, tube sheets, etc.) can be repaired by welding. c. Wide cracks that penetrate the structure: Cracks with a width of 15 mm or more are considered wide cracks, and they require repair by cutting out the steel plate containing the entire crack. Bevels are then created at the edges of the cut, after which a patch plate of the same size as the removed plate is welded in place. The length of the cut steel plate should be 50–100 mm greater than the length of the crack, and its width should be less than 250 mm, so as to prevent thermal interference between the two parallel welds when welding the patch plate. When welding repair plates, a symmetric segmented welding method from the center to the edges should be used, so as to avoid uneven gaps around the repair plate. A symmetric segmented welding method from the right end to the left end should be employed, as welding stresses cause uneven gaps around the patch plates, which will pose difficulties in the final welding process and affect the quality of the weld. The tower welds are inspected using X-rays, and the inspection length shall not be less than 15% of the total length of the tower welds. The repair welding of the above three types of cracks shall be carried out in accordance with the original equipment drawings and manufacturing specifications, or in compliance with JB/Z105 \"Welding Procedures for Steel Pressure Vessels\". (2) Repair of local deformation of the tower. Local deformation refers to phenomena such as local indentations or protrusions that appear on the equipment housing. Local deformation can reduce the reliability of the equipment. The main cause of local deformation is unreasonable design and operation. For carbon steel equipment, under conditions where the operating pressure is low, local deformation is not severe, and no cracks have occurred, static pressure or impact methods can be used to thermally correct the local deformation. Depending on the degree of deformation, the correction can be completed in one step ； It can also be completed multiple times. A layer of low-carbon steel can be welded onto the corrected wall surface to prevent further deformation there. If the local deformation of the equipment is severe, patch repair should be carried out. When the area to be cut is large and the wall thickness of the equipment is thin, support tools can be attached by spot welding at positions 500 mm above and below the area to be removed. The edge of the cut opening should be worked on to create a bevel for welding a patch plate. The supports can be removed after the patch plates have been welded and passed inspection. (3) Inspection and adjustment of the tower’s verticality: After the tower is in place, its verticality should be checked and adjusted. The common methods for checking verticality are the plumb line method and the theodolite method. The tilt of the tower body shall not exceed 36 mm, and the maximum deviation of the top of the tower from being vertical shall not exceed 30 mm. 4.3.2 Sprinkler Systems When maintaining sprinkler systems, the following points should be noted: (1) For tubular sprinklers and showerhead-type sprinklers, since liquid is sprayed through small holes, it is necessary to check during maintenance whether the size and spacing of these spray holes meet the requirements specified in the drawings. (2) For the overflow-type spraying device, the lower edge of its opening (the bottom of the teeth) should be on the same horizontal level, with a tolerance of 2 mm. (3) The allowable tolerances for the installation position of liquid distribution devices are shown in the table below. Allowable tolerances for the installation of liquid spraying and redistribution devices, in mm: Component name – Tolerance for levelness, Tolerance for centerline alignment, Tolerance for installation height. Disk-type sprayers: 4, 3, 3; Nozzle-type sprayers: Maximum deviation from the installation axis of 1, 3, 3; Overflow trays and channels: 2.2, 5, 10; Pagoda-type sprayers: Maximum deviation from the installation axis of 1, 3, 3. (5) Sprayers and other distribution devices must be installed firmly, with no swinging under operating conditions. (6) A spraying test should be conducted after maintenance. During the spraying test, the spraying within the cross-section of the tower should be even, and the nozzles must not be blocked. 4.3.3 Demisters The thickness of the wire mesh in small-sized demisters is determined based on process conditions; it generally ranges from 50 to 150 mm. The wire mesh must be laid flat, with the corrugation directions of adjacent layers offset by a certain angle from each other. It is then secured using support plates. The free cross-sectional area of the screen support grid should be greater than 90%, and the grid must remain horizontal during installation. Large demisters are modular in design, with demister frames placed on the support rings, and grills placed on top of them. When installing the demisting frames, work on both sides simultaneously; finally, push the middle frame in and secure it with flat steel strips. After the demisting frames are installed, tie stainless steel wires at regular intervals between the upper grating plates. The frames must be pressed tightly together to minimize gas short circuits. The main failures of demisters during use are clogging and mesh failure. It can be cleaned and replaced during maintenance. The installation center, elevation, and levelness of the defoamer shall comply with the design specifications. 4.3.4 Tray (1) Preparations and precautions before tray assembly. a. For parts that remain usable after maintenance, surface contaminants such as oil, weld spatter, rust, dirt, sand, and burrs should be removed. b. The new parts to be replaced should be checked to ensure they meet the requirements of the drawings. c. Before assembly, the tray plates, liquid distribution plates, crossbeams, etc. can be stored on site, but care must be taken to prevent deformation, damage, corrosion, etc.; the site should be kept clean. During assembly, handle all parts of the tray gently to prevent collisions, deformation, and dirtiness. d. When working on the tray, maintenance personnel must wear clean footwear and should stand on the crossbeams or planks that support the tray. e. One tray can accommodate 3 people. f. Protective measures should be taken for the sealing surfaces of manholes and manhole covers, as well as for the pipe openings at the bottom of the tower, to prevent damage or blockage. g. The plate assembly can be carried out in a horizontal or vertical configuration. The laying of bedding should be carried out after the levelness of the tower body and the verticality of the support rings meet the requirements (the allowable tolerance for the tower body levelness is 6 mm), and the tower body is able to rotate. Loose parts on the trays shall be assembled after the tower body is positioned. Erection should be carried out after the verticality of the tower and the levelness of the support rings have been adjusted to meet the requirements (the allowable tolerance for tower verticality is no more than 30 mm, and the allowable deviation for the levelness of the support rings is ≤5 mm). (2) Assembly of tray plates a. Assembly and adjustment of segmented tray plates: The distance between the support plates at both ends of the tray plate, as well as its length and width, must meet the specified requirements. The installation of the tray plates should be carried out by assembling them sequentially from both sides of the tower wall toward the center of the tower, after the liquid distribution plate and crossbeams have been securely fastened. After each layer of tray is assembled, the levelness of the tray is checked using a level. Once the levelness meets the specified requirements, the arrangement of the tray holes is inspected, as well as the distance between the tray holes and the beams, the dimensions of the joints between the trays and the beams or support rings, and the sealing filler, to ensure that all these aspects comply with the specifications in the drawings. b. After the tray is assembled, check whether the levelness of the overflow weir and its height meet the specified requirements; if not, adjustments must be made. c. After all the tray plates have been installed, inspections shall be carried out in accordance with the above items, and all kinds of debris on the tray plates and inside the tower shall be removed. After the final inspection, install the tray channel plates and manhole covers, seal them, and keep maintenance records. 4.3.5 internals of the packing tower (1) Installation and adjustment of the packing support structure. a. The filler support structure should be stable and secure after installation. b. The pore diameter and pore spacing of the packing support structure shall meet the design requirements, and the pores must not be blocked. c. The levelness of the packing support structure after installation (for regular packing) shall not exceed 4 mm. (2) Filling of the filler: a. Granular fillers (ring-shaped, saddle-shaped, etc.). During filling, it should be ensured that the filler is clean and free of sediment, oil, and dirt. For regularly arranged packing, it should be neatly and correctly arranged in layers against the tower wall ； For irregular arrangements, the wet method is commonly used for tall towers during loading, while the dry method is more often used for low towers. b. Screen corrugated packing: For the screen corrugated packing filled in layers, the direction of the corrugations on the lowest layer of packing plates should be perpendicular to the support grid plates; the direction of the corrugations on the remaining layers should form an angle of 30° (or 45°) with the tower axis. The inclination angles of the corrugations on adjacent layers should be opposite to each other and 90° apart. When filling the screen corrugated packing in sections, each layer is first filled along the perimeter near the tower wall, and then gradually filled toward the center of the tower; each piece is secured with special clamps, and it must be compressed tightly during filling. There should be no gap between the packing tray and the tower wall. The quality of the corrugated packing meets the standards. 4.4 Maintenance Quality Standards 4.4.1 Quality Standards for Tower Body Maintenance (1) The out-of-roundness e at the same cross-section of the tower body is allowed to be ≤22 mm; the allowable deviation in the outer circumference at the joints between tower segments is ±11 mm, and the unevenness of the end faces at these joints shall not exceed 2 mm. The allowable tolerance for the tower height is ±40 mm, and the allowable tolerance for the tower’s straightness is ≤35 mm. (Technical requirements on the drawings: The ellipticity of the tower body itself should be less than 11 mm, its bending degree should be less than 20 mm, and the vertical deviation in its installation should be less than 15 mm.) (2) Quality standards for tower installation: The allowable tolerances after the tower is installed are shown in the table below. Allowable tolerances for tower installation and maintenance: Inspection item – Allowable deviation; Ordinary towers connected to machinery: Centerline position – ±10, ±3; Elevation – ±5; Relative elevation – ±3; Verticality – not more than 30 mm. (3) Other aspects: The anti-corrosion coating on the tower body should have no blisters, cracks, or delamination. The insulation material of the tower meets the requirements of the drawings. The outer wall of the tower is painted and insulated in accordance with the provisions of HG1074-79 \"Code for Insulating Paints of Equipment Piping\". 4.4.2 Quality standards for the maintenance of internal components of the tower (1) Tray support rings: The allowable tolerance for the levelness of these support rings is ≤5mm. Local horizontal deviation of the upper surface over a chord length of 300 mm after welding the support ring to the tower wall