I’ve attached my own compilation titled “Inspection of Pressure Relief Towers”; I hope experts can offer their guidance

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I’m a equipment technician at Sinopec; I lack experience. During the major overhaul of the plant in 2016, I compiled a document titled “Maintenance of the Vacuum Distillation Column”, which also includes the maintenance procedures and materials required for the overhaul. I hope that all experts here can offer me some guidance. Maintenance Procedures for Packed Towers 1.1 Description: The packed towers in the atmospheric and vacuum distillation unit of Refinery Division II include the vacuum tower 101-C-400 and the sweetening tower for vacuum overhead gas 101-C-410. Tower C410 is a randomly packed tower with a relatively simple structure. The following specific maintenance steps are described primarily using the vacuum tower C400 as an example; the maintenance of the sweetening tower 101-C-410 can be carried out by referring to the procedures for the vacuum tower. 1.2 Preparations before maintenance 1.2.1 Based on various factors such as the operation performance of the vacuum tower during the previous cycle, the properties of the process media, past maintenance records, and the maintenance experiences of similar vacuum towers in other companies, it is determined what types, quantities, materials, and models of internal components are required. 1.2.3 Approximately 10 months in advance, communicate with the original manufacturer of the internal components to determine the types, quantities, materials, and models required. Apply for material codes and submit a major maintenance plan. 1.2.4 After the spare parts are delivered to the company, their model and material should be carefully checked. Together with the manufacturer, as well as the various teams responsible for procurement and maintenance, an inspection should be carried out to confirm that everything is in order. Once verified, the parts should be stored properly according to the manufacturer’s instructions. Before maintenance work begins, it is essential to communicate closely with the maintenance team; the parts should be delivered to the site about 3 days before the maintenance starts. Storage at the site must meet the manufacturer’s requirements – the parts should be placed on a raised surface, covered with tarpaulins, and proper protective measures taken. 1.2.5 After the unit is shut down, the residual medium inside the vacuum distillation tower must be drained. The tower should be vented, and after laboratory analysis confirms that the conditions are suitable, a permit for working in a confined space must be obtained before maintenance personnel can be allowed to enter the tower. 1.2.6 After obtaining the permit for work in a confined space, enter the decompression tower and arrange for a construction crew qualified to erect scaffolding to do so. Only after the scaffolding has been inspected and found satisfactory, and after appropriate signage has been posted, may it be put into use. 1.2.7 Since the components inside the vacuum distillation tower are generally covered by patent technology, it is necessary to communicate with the manufacturer prior to entering the tower for inspection. Efforts should be made to have the manufacturer send technical personnel to provide on-site guidance for tasks such as inspecting, removing, transporting, and installing these components, in order to ensure the quality of their installation. 1.3 Internal inspections 1.3.1 Internal inspections should involve joint inspections by relevant specialists such as those in process management, equipment operation, safety, and manufacturing; personnel must wear appropriate protective clothing and carry specialized tools, especially hydrogen sulfide detectors, flashlights, and communication devices. A designated person should be assigned to take notes, and after the inspection, a written report should be prepared and signed before being filed. 1.3.2 During inspections, particular attention should be paid to those parts of the internal components that are not scheduled for replacement. If maintenance is required, a plan should be submitted as soon as possible for procurement or advance funding; proper records must also be kept to prevent any omissions. The installation of the tower internals should be carried out after the tower has passed the pressure test and has been cleaned thoroughly ； During the installation of internal components, construction must be carried out strictly in accordance with the technical requirements specified in the drawings to ensure compliance with process specifications. 1.3.4 Before installing the internal components, the installation surface inside the tower should be cleaned to remove contaminants such as oil, weld slag, rust, sediment, and burrs from its surface. The tower must have strict fire prevention measures as well as safety measures for personnel. 1.3.5 An inspection of the air quality inside the tower must be conducted before it is put into use; special attention should be paid to new towers that were sealed with nitrogen at the time of manufacture, as well as to renovated old towers. 1.3.6 On-site pre-assembly of tower internals: The interior components to be installed must be numbered for easy installation. Internals that are installed in sections must be pre-assembled on-site prior to installation. During pre-assembly, the components should be assembled outside the tower according to the assembly drawings. 1.4 Maintenance of internal components 1.4.1 Installation of packing: (a) Tools: tape measure, chalk, hemp rope, scissors, wire cutters, and hand grinder. (b) Before installing the packing, the welds on the shell must be inspected; the protrusion height inside the tower should be less than 3 mm. Otherwise, it must be ground down to meet the requirements ； Additionally, check whether there are any damages on the wall of the inspector; if any issues are found that do not meet the requirements, the construction workers should be asked to address them promptly. (c) Measure whether the elevation of each section of packing and internal components matches the actual height within the tower. Otherwise, please guide the installers on-site to handle it. (d) When lifting the filler, it should be placed in a special container. It is strictly prohibited to lift the filler by directly tying it with ropes. (e) After unpacking, the packing should be assembled into discs outside the tower according to the block diagram and packing labels; once verified, it should be hoisted onto the tower in accordance with the sequence numbers. During this process, it is strictly prohibited for the packing sheets to deform or for any foreign materials to enter the packing blocks ； Upon noticing the above situations, corrective measures should be taken promptly. (f) The packing is tied with brown rope according to its serial number and then fed into the tower through the manhole. (g) Starting from the upper surface supported by the packing, marks shall be made on the tower wall every 1 meter, with the distance in meters indicated, so as to keep track of the height tolerance of the packing layer at all times. During installation, constant attention should be paid to whether there are any damages on the tower walls; if any damages are found, installation must be stopped immediately and the issue addressed promptly. (h) The relative orientation of the first layer of packing and the packing support is shown in the drawings. Each packing piece should be placed in the tower in order of sequence number. Before the packing block is in place, the ends should be shaped using a filling tool to match the tower wall. The packing blocks should be packed as tightly as possible, with no gaps left between them. After each piece is in place, use the filler filling tool to adjust the tightness in various areas so that the tightness is uniform throughout. Then remove the wire and packing tape (if any), and press everything firmly together to ensure tight contact between the upper and lower layers of the filler. No debris shall be introduced during the installation of the packing; wires and other packaging materials must not remain inside the tower. (i) Each layer of packing blocks should be filled toward the center of the tower from both sides of the tower wall simultaneously. Generally, when installing the last packing block, the remaining gap will be smaller than the width of the packing block; in such cases, a packing installation aid must be used. It is strictly prohibited to use feet to kick or a narrow stick to push down on the packing, as this may cause the packing to deform or get damaged. (j) During the installation of the packing, the installer should handle it gently to minimize damage to it. (k) During installation, if work cannot be carried out due to special circumstances, it shall be handled in accordance with the instructions of the on-site supervisor. (l) In cases where it is difficult to install the packing due to issues such as significant deviations in the roundness of the tower body, sheet removal and trimming should be carried out under the guidance of on-site installation personnel. Installation personnel must not remove sheets on their own initiative to ensure the quality of the installation. (m) After each tray of packing is installed, it must be approved by the on-site supervisor before the installation of the next tray of packing can proceed. (n) Installers should not always stand in the middle of the tower cross-section, as this can lead to a situation where the area around the edges is higher while the center is lower (forming a ‘bottom of a pot’ shape). (o) During the installation of the flow barrier ring, it must be placed in position as required. Installation usually starts from one end and goes to the other. 1.4.2 Installation of the adapter (a) The adapter should be straight, with positioning marks on all relevant components; it must not exhibit any significant twisting or deformation, nor any local welding defects. (b) Install the connections, ensuring that all of them are at the same level. (c) After tightening the beam (if any), the connecting plates, and the U-bolts with bolts and nuts, turn the first nut back 180 degrees (half a turn) and secure it with the second nut. (d) After connecting at the flange, all bolts and nuts should be tightened to ensure a seal. (e) After welding the various supports to the tower, it is necessary to ensure that they are all on the same horizontal level. (f) The connection should be straight; after installation, the allowable deviation in the levelness of each distribution pipe is as follows: for the reduced-medium return distribution pipes, the allowable deviation in levelness ≤ 6 mm ； The deviation in the horizontal alignment of the return distribution pipe after reduction to the first level shall be ≤6 mm ； The horizontal deviation of the reflux distribution pipe in Unit 2 is ≤8mm ； The horizontality deviation of the return distribution pipe in Substation 3 is ≤8mm ； The horizontal deviation of the washing oil distribution pipe installation shall be ≤8mm ； The horizontality deviation of the quench oil distribution pipe shall be ≤5mm ； The deviation from horizontal alignment for the installation of the stripping steam distribution pipe shall be ≤5mm. 1.4.3 Installation of trough-type liquid distributors: (a) This component should be straight and free of obvious twisting, deformation, or local welding defects. (b) Before the various components are taken to the tower on site, they should be pre-assembled; once approved, positioning marks should be applied to the relevant parts. (c) Before installing the trough-type liquid distributor, it is necessary to check whether all the distribution holes on the distributor are unobstructed. After installation, dust, welding slag, and other debris should be removed. (d) During installation, place the secondary groove (auxiliary groove) on the packing gland or the ladder beam of the packing gland, and position it according to the spacing specified in the drawings. Install the reference beam, adjust its levelness (using a level), and weld the positioning tube to the arc plate. Tighten all fasteners securing the stiffening beam to the tower components (such as supports or connecting plates). (e) Install the channel steel beams (if any), and adjust their levelness (using a level). Tighten all fasteners securing the stiffening beam to the tower components (such as supports or connecting plates). (f) Tighten the fastening bolts at the secondary groove (branch groove) and the channel steel beam, and adjust the levelness of the secondary groove during tightening to secure it. If there are no channel steel beams, after adjusting the levelness of the secondary channel, the positioning tube is welded and fixed to the arc plate at the tower wall. (g) Install the primary tank and tighten the bolts that connect the primary tank to the secondary tank. (h) After the connecting plates on the secondary tank are tightened with bolts and nuts, they are welded to the tower wall on site. (i) There shall be no bundled leakage at the joints of the primary tank after assembly, but dripping is permitted (dripping is defined as 4 drops or less in 1 second). (j) Check that all fasteners are tightened ； Remove all debris from the tank to ensure that all distribution holes remain unobstructed. (k) After installation, the trough-type liquid distributor should be adjusted to be level; the deviation in levelness for trough-type liquid distributors (1) and (2) shall be ≤5mm ； The deviation from horizontal installation of trough-type liquid distributors (III), (IV), and (V) shall be ≤6mm. 1.4.4 Supply and installation of the packing compression ring (a) Finished product, assembled on-site according to the construction drawings. (b) This component shall be pre-assembled before being installed in the tower. After pre-assembly is completed, positioning marks are made on the relevant components. This component should be neat and free from distortion. (c) The length direction of the compression ring grid blocks shall be determined as per the drawings; unless otherwise specified, the direction of the compression ring bars shall form an angle of 45–90° with the length direction of the filler plates. (d) Adjust the levelness of the compression ring (using a level); when adjusting, press down on the packing, and do not lift the compression ring upward. Tighten all fasteners. (e) Connect the ladder beam (if any) to the supports, adjust it to level and fix it; then bolt together the compression ring grid blocks as well as the grid and the ladder beam. (f) Install the compression beam (if any) and tighten all fasteners. (g) After assembly, the packing should be compressed, and the upper surface of the compression beam should be at the same level. The horizontal deviation for the installation of packing ring (1) shall be ≤6 mm, while the horizontal deviation for the installation of packing rings (2)–(4) shall be ≤8 mm. 1.4.5 Supply and installation of truss beams (a) Finished products; the entire truss beam is installed in the tower. (b) The fabrication and installation of this component shall comply with the requirements of GB50205-95 “Code for Construction and Acceptance of Steel Structure Engineering”. (c) This component must be straight; there shall be no twisting or deformation. (d) After the beam is in place, screw the bolts into the nuts on both supports of the beam to adjust its level, and fill the space between the beam and the supports with stainless steel plates. (e) After tightening the beam and connecting plate with bolts and nuts, turn the first nut back two turns, and then secure it with the second nut. (f) Ensure that after all beams are installed in place, their upper surfaces are on the same plane, with a levelness deviation of ≤6mm. (g) The installation elevation of this component is based on the upper surface of the beam. 1.4.6 Supply and installation of packing supports (a) Finished products, assembled on-site according to the construction drawings. (b) This component shall be pre-assembled before being installed in the tower. After pre-assembly is completed, positioning marks are made on the relevant components. This component should be neat and free from distortion. (c) Install the beams and support grid blocks, making sure that the grid blocks are placed in the direction specified in the drawings and not stacked arbitrarily. (d) Tighten all fasteners. (e) Weld the limit plates continuously to the support bars, beam reinforcement plates, and arc plates as required by the drawings, to ensure the proper positioning of the grid. After assembly, it is necessary to ensure that the upper surface of the support is level, with the horizontal deviation of the packing support installation being ≤6 mm. 1.4.7 Supply and installation of the oil collection tank (a) Supply of individual components (after the welded parts of the oil collection tank are installed, the components that still need to be installed include liquid baffles, support ribs, tie rods, etc.) ； (b) After the oil collection tank is installed, a leak test must be conducted on-site. (c) All welds not specified on the drawings shall be continuously welded; the weld leg height shall be equal to the thickness of the thinner of the two parts being joined, and slag removal shall be carried out after welding. (d) Some of the support gussets need to be welded on-site to the blocking plates according to their actual positioning and the liquid barrier plates ； (e) The tie rods need to be connected to both the truss beam and the fuel tank after the truss beam is installed ； (f) Tighten all fasteners. (g) The oil collection tank shall be manufactured and inspected in accordance with SH/T 3088-2012 \"Technical Specifications for Petrochemical Trays\". All are positioned using the upper surface of the support ring as a reference. (h) After the oil collection tank is installed, dust, slag, and other debris should be removed. (i) Oil collection tank leak testing: 1) Temporarily seal the weep holes and discharge ports on the bottom plate, and fill the oil collection tank with water. The guaranteed water level is maintained at a certain height below the upper opening of the oil collection tank’s overflow pipe. 2) Fill with water and keep it for a while; observe from below the oil collection tank to check for any leakage points (leakage is indicated by streams of liquid escaping), and identify and record the locations of all leakage points. After releasing water, weld or seal the leak point, then refill the system with water to locate the leak again; repeat this process until no leak point is found. 3) Fill to the designed maximum liquid level (or 50 mm above the upper edge of the vent pipe), and maintain for 20 minutes; the liquid level shall not drop by more than 25 mm. 1.4.8 Supply and installation of trays (a) Welding and assembly on site in accordance with the construction drawings. (b) Manufacture and acceptance shall be carried out in accordance with SH/T 3088-2012 \"Technical Specifications for Petrochemical Trays\". (c) The surface of the tray should be cleaned of oil, rust, and other contaminants before installation. (d) The tray spacing is based on the upper surface of the tray support ring. (e) The local flatness tolerance over a chord length of 300 mm on the upper surface of the support ring (support plate) after welding it to the tower wall is 1 mm. The tolerance for the levelness of the upper surface of the entire support ring (support plate) is 6 mm, and the spacing tolerance between adjacent support rings (support plates) must not exceed ±3 mm. (f) The support rings and connecting plates shall be welded to the tower wall in accordance with the drawing requirements to ensure a tight fit. (g) The deviation between the center line of the channel steel beam and the center of the tower’s cross-section at that point shall not exceed 2 mm. For the positioning of the auxiliary beams, the deviation between the centerlines of two adjacent auxiliary beams shall not exceed 2 mm, and the distance between the centerlines of any two auxiliary beams shall not exceed 5 mm. (h) After the main beams and secondary beams are installed, their upper surfaces shall be on the same horizontal level as the upper surface of the support ring (support plate), with a tolerance for the levelness of this plane being 6 mm. (i) When installing the tray plates and channel plates, make sure that the larger end of the fixed valve faces the liquid receiving tray side, while the smaller end faces the liquid dropping tray side. (j) After the tray is installed, the allowable tolerance for the distance between two adjacent trays in the same layer is ±3 mm, while the allowable tolerance for the distance between any two trays is ±6 mm. The tolerance for the levelness of the tray surface across its entire area is 9 mm. (k) After the liquid receiving tray, liquid dropping plate and tower body are assembled, the tolerance for the outlet weir is ±3mm, and the tolerance for the bottom gap is ±3mm. (l) The auxiliary beams are connected to the channel steel beams via connection plates, which are welded to the channel steel beams in a continuous manner on both sides at the site. (m) On-site, the liquid dropping plate and the liquid receiving tray are fixed by spot welding with gusset plates, and the nuts are tightened on-site before being secured with spot welding. (n) Tighten all fasteners. 1.5 After installation, conduct inspections. 1.5.1 Manufacturing and acceptance shall be carried out in accordance with SH/T 3088-2012 \"Technical Specifications for Petrochemical Trays\". 1.5.2 Check whether the welding level of the support ring (support plate) meets the requirements; the support ring (support plate) shall not warp upward or downward after welding. 1.5.3 Check whether the upper surface of the support ring (support plate) is flat, whether the butt welds are smoothed, and whether the slag is removed completely. After all the internal components of the tower have been installed, clean again the oil collection tank, the trough-type liquid distributor, and the surface of the packing of any debris such as tools, weld slag, fasteners, gloves, etc. This debris can affect the proper operation of the tower; once it has been removed, the tower can be prepared for a pressure testing with water.