Maintenance and Repair Procedures for Shell-and-Tube Heat Exchangers [2019 Edition]

Thread Content

This post was last edited by shijiazhuang on 2023-12-27 at 13:21. Maintenance and Repair Procedures for Shell-and-Tube Heat Exchangers 1 Scope 1.1 Subject matter: Maintenance and Repair Procedures for Shell-and-Tube Heat Exchangers. These procedures specify the maintenance intervals and tasks for shell-and-tube heat exchangers, as well as the repair processes and quality standards, testing and acceptance procedures, maintenance practices, and troubleshooting methods. 1.2 Scope of Application 1.2.1 These regulations apply to the shell and tube heat exchangers commonly used in petrochemical plants. They are applicable to petrochemical steel fixed-plate, floating-head, U-tube type and other shell and tube heat exchangers, as well as kettle-type reboilers, with a design pressure of less than 35 MPa. Heat exchangers with special requirements shall follow their respective special maintenance and repair procedures. 1.2.2 In addition to complying with these procedures, the maintenance and repair of shell-and-tube heat exchangers shall also conform to the requirements of the design documents. 1.2.3 The maintenance of pressure components shall comply with SHS 01004, \"Code for Maintenance and Inspection of Pressure Vessels\". 2 Normative reference documents The provisions in the following documents become provisions of this standard through reference to it. For dated reference documents, all subsequent amendment sheets (excluding corrigenda) or revised editions do not apply to this procedure. However, parties agreeing to comply with this procedure are encouraged to consider whether the latest versions of these documents can be utilized. For reference documents without a date, the latest version applies to these specifications. Law of the People’s Republic of China on the Safety of Special Equipment; Regulations on the Supervision of Safety of Special Equipment, TSG 08; Rules for the Use and Management of Special Equipment, TSG 21; Technical Regulations for the Safety Supervision of Fixed Pressure Vessels, GB 50461; Code for Acceptance of Construction Quality of Static Equipment Installation Projects in the Petrochemical Industry, GB 50484; Technical Specifications for Construction Safety in Petrochemical Engineering Projects, GB 50645; Code for Acceptance of Construction Quality of Insulation Works in Petrochemical Projects, GB/T 150.1–4 Pressure Vessels; GB/T 151 Heat Exchangers; GB/T 3098.8 Mechanical Properties of Fasteners – Bolted Joint Parts for Use at Temperatures from -200°C to +700°C; GB/T 19066.3 Technical Requirements for Flexible Graphite Metal Wave Tooth Composite Gaskets; GB/T 29463 Gaskets for Shell-and-Tube Heat Exchangers; NB/T 47015 Welding Procedures for Pressure Vessels; NB/T 47027 Fasteners for Pressure Vessel Flanges; HG/T 20583 Design Specifications for Steel Chemical Containers; JGJ 46 Technical Specifications for Safe Temporary Electricity Use at Construction Sites; SH/T 3074 Steel Pressure Vessels in the Petrochemical Industry; SH/T 3536 Construction Specifications for Lifting Operations in Petrochemical Projects; SH/T 3555 Technical Specifications for the Safe Erection of Steel Scaffolding in Petrochemical Projects; SH/T 3430 Flexible Graphite Wave Tooth Composite Gaskets for Shell-and-Tube Heat Exchangers in the Petrochemical Industry; SH/T 3503 Specifications for Technical Documents Related to the Handover of Petrochemical Engineering Projects; SH/T 3540 Construction and Acceptance Specifications for Composite Coatings on Tubes of Steel Heat Exchange Equipment; SHS 01004 Maintenance Procedures for Pressure Vessels; SHS 01033 Maintenance Procedures for the Insulation of Equipment and Pipelines; SHS 01034 Maintenance Procedures for Coatings on Equipment and Pipelines. 3 Maintenance Periods and Contents 3.1 Maintenance Periods In accordance with the requirements of TSG 21 “Technical Regulations for the Safety Supervision of Fixed Pressure Vessels”, and taking into account the long-term operation of the facilities as well as the operating condition of the equipment, the maintenance period for shell-and-tube heat exchangers is determined to be generally 36–72 months. 3.2 Maintenance contents
3.2.1 Items requiring rework identified during monthly inspections, annual inspections, and periodic inspections of pressure vessels. 3.2.2 Remove the insulation layer, install blind flanges, and remove the inlet and outlet pipelines and valves. 3.2.3 Core extraction, cleaning of tube bundles and shells, and tube boxes. 3.2.4 Treatment of tube bundle welds and flared joints, as well as single-tube repair, plugging, or replacement. 3.2.5 Inspect and repair the tube box and its internal accessories, floating head covers, hook rings, external head covers, connecting pipes, etc., as well as their sealing surfaces; replace gaskets, packing, etc. 3.2.6 Inspect or replace some bolts and nuts. 3.2.7 Inspect and maintain the lining (composite or surfacing layer). 3.2.8 Inspect and repair supports, brackets, and foundations. 3.2.9 Inspect, repair, and calibrate safety and instrumentation accessories. 3.2.10 Replace the tube bundle or shell. 3.2.11 Check the integrity of the grounding. 3.2.12 Remove blind plates and install pipeline valves. 3.2.13 Pressure testing, airtightness testing. 3.2.14 Repair or replacement of insulation layers and anti-corrosion layers. 4 Maintenance Procedures and Quality Standards 4.1 Preparation before Maintenance 4.1.1 Understand the operating condition of the equipment, prepare, approve, and issue maintenance plans; gather all the drawings, technical documents, and relevant maintenance records required for the work. Develop maintenance plans (including welding and lifting procedures) or maintenance operation instructions. The property owner and the maintenance contractor shall carry out a mutual briefing regarding the maintenance tasks in accordance with the regulations, and keep records of this briefing. 4.1.2 Prepare the necessary maintenance tools, testing fixtures, tooling, lifting equipment, etc. For bundles requiring high-pressure water jet cleaning, prepare the jet cleaning machinery and site. 4.1.3 Prepare the spare parts, components, and materials required for maintenance, and check to verify that their dimensions and materials meet the technical requirements. 4.1.4 The units responsible for maintenance work must possess the necessary qualifications and experience; moreover, the maintenance personnel must be familiar with the maintenance plans or work instructions. Welders and riggers must hold certificates and pass the owner’s skills test before they can perform maintenance work. 4.1.5 Verification of pre-maintenance conditions. 4.1.5.1 Cut off the feed to the heat exchanger and drain it; replace the internal medium and clean it thoroughly. 4.1.5.2 Check to confirm that all types of work permits have been issued in accordance with regulations. Special note: The samples taken for fire hazard, poisoning prevention, and suffocation prevention analyses must be representative; if necessary, sample collectors should wear long-circuit air respirators to enter confined spaces to collect samples. 4.1.5.3 For heat exchangers prone to the formation of FeS media, in order to prevent the spontaneous combustion of FeS, chemical cleaning should be preferred; alternatively, the unit can be disassembled and subjected to jet cleaning as soon as possible. Take measures to ensure that the environment is not polluted. 4.1.5.4 Verify that the power used for maintenance and lighting meets relevant standards and specifications. 4.2 Inspection Contents 4.2.1 Conduct a visual inspection of the shell, tube bundle, and components for corrosion, cracks, deformation, etc. When necessary, use surface testing as well as eddy current and ultrasonic testing. In cases where there are grooves, scratches, or severe surface corrosion caused by mechanical effects, corrosion, or erosion, a detailed inspection and verification should be carried out. 4.2.2 Conduct random thickness inspections on the nozzles, cylinders, tube bundles, tube boxes, and end caps; those that do not meet the requirements specified in the original design documents shall be replaced. 4.2.3 Check whether the anti-corrosion coating is aged or peeled off. 4.2.4 Inspect for lining corrosion, bulging, folding, and cracks. 4.2.5 Check the sealing surfaces and gaskets for scratches, grooves, corrosion, etc. 4.2.6 Check for any damage to the fasteners; high-pressure bolts and nuts should be cleaned and inspected one by one, and non-destructive testing should be carried out if necessary. 4.2.7 Check whether the foundation has settlement, tilting, damage, or cracks, and whether its foot bolts, shims, etc. are loose or damaged. 4.3 Maintenance quality standards
4.3.1 During the operations of extracting and installing the heat exchanger tube bundle, as well as transportation and lifting, bare steel wires shall not be used for direct binding; padding plates must be placed at the binding points. When moving and lifting the pipe bundle, it should be placed on specialized support structures to avoid damaging the bundle. 4.3.2 The scale on the inner and outer surfaces of the tube bundle shall be thoroughly removed. 4.3.3 When there are partitions in the tube box and floating head, their gaskets shall be integrally machined and must not have any defects that could affect sealing. 4.3.4 Leakage plugging in tube bundles: Within the same tube pass, the number of plugged tubes generally should not exceed 10% of the total number of tubes; however, within the allowable limits set by process specifications, this number may be appropriately increased. 4.3.5 The replaced parts shall meet the relevant technical requirements, come with material quality certificates, and be retested if necessary. 4.3.6 Replacement of heat exchange tubes: 4.3.6.1 The tube surface shall be free from defects such as cracks, folds, dents, and double walls; if necessary, each tube shall undergo a pressure test. 4.3.6.2 There shall be no butt welds in the straight pipe section of at least 50 mm length within the bent section of the U-tube; the misalignment at the joint shall not exceed 15% of the pipe wall thickness and shall not be greater than 0.5 mm. 4.3.6.3 When expansion jointing is used for joining tubes to tube sheets, the hardness of the tubes must be tested. Generally, it is required that the hardness of the tubes be 30 HB lower than that of the tube sheet. If the hardness of the tubes is higher than or close to that of the tube sheet, both ends of the tubes must be annealed; the length of the annealed portion should be 80–100 mm longer than the thickness of the tube sheet. 4.3.6.4 Both ends of the tube and the holes in the tube sheet must be clean, free from grease or other contaminants, and must not have any longitudinal or spiral scratches or other defects that could affect the tightness of the expansion joint. 4.3.6.5 Both ends of the pipe shall extend beyond the tube sheet, with a length that meets the design requirements. 4.3.6.6 Hydraulic expansion is preferred for expanding tubes into tube sheets; each expansion joint shall not be re-expanded more than twice. 4.3.6.7 When pipes and tube sheets are welded together, the cut surface of the pipes must be smooth, free of burrs, irregularities, cracks, or delaminations. Additionally, the welding area must not contain any impurities such as slag, iron oxide, or oil residues that could affect the quality of the weld. 4.3.7 The overall replacement of the tube bundle shall be carried out in accordance with GB/T 151 \"Heat Exchangers\" or the requirements of the design drawings. 4.3.8 The repair of pressure-bearing components such as shells shall be carried out in accordance with the requirements of SHS 01004, \"Code for Maintenance and Overhaul of Pressure Vessels\". 4.3.9 The replacement of sealing gaskets shall be carried out in accordance with the design requirements. If the selected gaskets differ from those specified in the original design, approval from the design unit must be obtained; gaskets with proven track records of successful use should be employed. The hardness of the metal ring gasket should be 15–20 HB lower than that of the flange surface; given the high pressures in hydrogenation units, the gasket’s hardness is required to be 30 HB lower than that of the flange surface. 4.3.10 When the bolts and nuts of the heat exchanger need to be replaced, they should be of the same type as specified in the original design or have the same material; Table 1 can be referred to for selection. The bolts should be replaced symmetrically and evenly distributed. 4.3.11 When removing the bolts, loosen each nut by half a turn or less in the first round, to prevent a few bolts from experiencing excessive stress, which could lead to yield deformation and failure, or residual pressure leakage causing damage. 4.3.12 When tightening the bolts of the heat exchanger, it is generally necessary to follow the sequence shown in Figure 1, and appropriate thread lubricant or anti-seize agent should be applied. 4.3.13 The load applied during the initial tightening of the bolts should not be too high; it is advisable to keep it at no more than 15% of the final bolt preload. After the initial cross-tightening, turn the bolts clockwise by one full turn, aiming for a preload of 40% of the final value. Then turn them counter-clockwise by one full turn, reaching a preload of 70% of the final value. Finally, turn them clockwise again to reach 100% of the preload. Lastly, check and make minor adjustments to ensure that the preload on each bolt is even. 4.3.14 Torque wrenches should be used when tightening bolts, while hydraulic wrenches or hydraulic stretchers should be used for bolts with larger diameters. 4.3.15 After the bolts are tightened, the equipment is allowed to warm up for a certain period of time; once the temperature of the bolts stops changing, their torque is checked and readjusted, and thermal tightening may be performed if necessary. 4.3.16 For heat exchange equipment equipped with internal anti-corrosion coatings, a macroscopic inspection of the coating on the heat exchanger shall be carried out; the coating surface should be smooth and even, with uniform color, and free from defects such as pores, drooping, sagging, or incomplete coating. When inspected under a 5–10x magnifying glass, a coating without any micro-pores is considered qualified ； The coating should be fully cured ； During lifting, installation, maintenance, and cleaning, the anti-corrosion coating must not be damaged. 4.3.17 The quality standards for the maintenance and repair of the insulation layers and anti-corrosion coatings of heat exchange equipment shall be in accordance with SHS 01033 \"Procedures for the Maintenance and Repair of Equipment and Pipelines\" and SHS 01034 \"Procedures for the Maintenance and Repair of Coatings on Equipment and Pipelines\", respectively. 5 Testing and Acceptance 5.1 Testing 5.1.1 The maintenance records must be complete and accurate, and signed off by both the construction party and the user party. 5.1.2 The construction unit and the user unit confirm that it is qualified and that the necessary testing conditions are available. 5.1.3 Pressure test: 5.1.3.1 Two pressure gauges shall be used for the pressure test; these gauges must be calibrated in advance, with an accuracy of not less than grade 1.6. Their range should be 1.5 to 3 times the test pressure, and the diameter of the dial should be at least 100 mm. 5.1.3.2 For design documents based on a pressure difference approach, it is necessary to ensure that the test pressure difference specified in the design documents is applied, with testing being carried out simultaneously in both the tube side and the shell side. 5.1.3.3 Fill the container with the pressure testing liquid at a temperature of not less than 5°C or as specified in the design documents. Remove all gas from the container, and only after the wall temperature of the container matches that of the liquid and it is confirmed that there are no leaks at the connection points, can the pressure be increased gradually. 5.1.3.4 The test medium shall be clean water or other liquids; for testing austenitic stainless steel equipment, the chloride ion content in the water should be limited to no more than 25 mg/L. 5.1.3.5 The test pressure value shall be the greater of the following two values: a) Hydrostatic test pressure value; b) Pneumatic test pressure value. Where: — Test pressure value for the pressure resistance test, in MPa ； —Maximum operating pressure of the tube side or shell side, MPa ； —The allowable stress of the material at the test temperature, in MPa, shall be selected in accordance with GB/T 150. —The allowable stress of the material at operating temperature, in MPa, shall be selected in accordance with GB/T 150. c) The value for the airtightness leak test shall be the maximum operating pressure of the equipment. 5.1.3.6 During the pressure test, the pressure should be gradually increased to the specified value and maintained at this level for no less than 10 minutes. Thereafter, it should be reduced to the maximum operating pressure and held at this level for no less than 30 minutes. A thorough inspection must be conducted; the test is considered successful if there are no cracks, leaks, residual deformations, or abnormal noises. In case of leaks or other issues, conduct tests after addressing them. 5.1.3.7 After completing the liquid test, all liquid must be drained; if necessary, use compressed air to dry the interior. 5.1.3.8 The medium used for pressure testing heat exchange equipment shall be dry and clean air, nitrogen, or other inert gases, with the gas temperature being no lower than 15°C or in accordance with the requirements specified in the design documents. 5.1.3.9 During the gas pressure testing, the pressure is increased slowly to 10% of the specified value; this pressure is maintained for 10 minutes. After a successful initial inspection, the pressure is further increased slowly to 50% of the specified value. If no issues are detected, the pressure is then increased in steps of 10% of the test pressure until it reaches the specified value. The pressure is held at this level for 10 minutes, after which it is reduced to the maximum operating pressure. This new pressure level must be maintained for at least 30 minutes. A test using soapy water or another leak-detection fluid shows no leaks, ruptures, residual deformation, or abnormal noises, indicating that the test is successful. In case of leaks or other issues, conduct tests after addressing them. 5.1.3.10 Sequence and requirements for pressure testing: a) Pressure testing of the shell in the fixed tube sheet type: Inspect the joints where the shell, heat exchange tubes are connected to the tube sheet, as well as related areas. Piping pressure test: Inspect the pipe box and related areas. b) U-tube heat exchangers, kettle reboilers (with U-tube bundles), and stuffing box heat exchangers. Shell-side pressure testing (using a test pressure ring): Inspect the shell, tube sheet, heat exchange tubes, and their connections to the tube sheet. Piping pressure test: Inspect the relevant parts of the pipe box. c) For floating-head heat exchangers and kettle-type reboilers (with floating-head tube bundles), pressure testing of the tube-to-tube sheet joints is carried out using test pressure rings and special tools for floating heads. For kettle-type reboilers, a special housing for pressure testing the tube-to-tube sheet joints is also required, in order to inspect the connections between the heat exchange tubes and the tube sheet as well as related areas. Shell pressure test: Inspect the shell, floating head cover, and related parts. Shell side pressure testing: Inspect the shell, the joints between the heat exchange tubes and the tube sheet, as well as related areas. d) Pressure testing of heat exchanger tube ends based on pressure difference: Inspect the relevant parts of the tube box. Piping and shell side step-by-step pressure testing: Inspect the shell, tube bank, and related areas. Appropriate control measures for pressure difference must be in place to ensure that the pressure difference does not exceed limits during the pressurization and depressurization processes during testing. e) When the test pressure of the tube side is higher than that of the shell side, the test pressure value shall be determined in accordance with the specifications in the drawings, or by a method agreed upon by both the production and construction parties. 5.2 Acceptance 5.2.1 After the equipment has been in operation for one week, all relevant indicators should meet the technical requirements or be sufficient to satisfy production needs. 5.2.2 The equipment’s anti-corrosion and insulation measures are intact, meeting the required standards. 5.2.3 Submit the following technical documents: 5.2.3.1 Change orders for design changes and material substitutions, quality certificates for material properties, and component qualification certificates ； 5.2.3.2 Maintenance Records ； 5.2.3.3 Weld quality inspection (including visual inspection and non-destructive testing, etc.) report ； 5.2.3.4 Test records: Fill in the records of the pressure resistance and leakage tests for heat exchange equipment in accordance with SH/T 3503 \"Regulations on Technical Documents for Project Handover in Petrochemical Construction Projects\". 6 Maintenance and Fault Handling 6.1 Routine Maintenance 6.1.1 When performing steam purging of the device system, it is necessary to avoid purging cold-exchange equipment that has coatings as much as possible. If it is unavoidable from a process perspective, the temperature of the purging steam must be strictly controlled to not exceed 200°C in order to prevent damage to the coatings. 6.1.2 During the start-up and shutdown of the unit, the heat exchanger should be heated and cooled slowly to avoid excessive pressure differences and thermal shock; moreover, when shutting down, the principle of \"heat first, then cold\" should be followed, that is, the hot medium should be removed first, followed by the cold medium ； At the start of operation, follow the principle of \"cool first, then heat\", that is, introduce the cold medium first and then the hot medium; in special cases, proceed according to the specific process requirements. 6.1.3 Before commissioning, it shall be confirmed that the system is unobstructed for heat exchangers, to prevent overpressure on one side of the tube sheet. 6.1.4 Carefully monitor the operating parameters of the equipment; it is strictly prohibited to allow temperatures, pressures, or liquid levels to exceed specified limits. For heat exchangers designed with a pressure difference, this specified pressure difference must not be exceeded during operation. 6.1.5 Operators shall strictly follow the equipment operation procedures, and conduct regular inspections of the heat exchange equipment to check the stability of the foundation supports and for any leaks in the equipment. 6.1.6 The temperature and pressure drop of the fluids in the tube and shell sides should be checked regularly to analyze any leaks or scaling in the heat exchanger. When the pressure drop increases and the heat transfer coefficient decreases beyond a certain value, effective cleaning methods should be selected based on the medium and the structure of the heat exchanger. 6.1.7 The changes in heat exchanger vibration should be checked regularly. 6.1.8 When cold exchange equipment with anti-corrosion coatings is in operation, the temperature must be strictly controlled to prevent damage to the coatings. 6.1.9 Keep the insulation layer intact. 6.2 Common Faults and Troubleshooting Methods The common functional faults of shell-and-tube heat exchangers and their corresponding troubleshooting methods are shown in Table 2. Table 1: Selection Table for Bolts and Nuts
Steel type for bolts | Steel type for nuts | Operating temperature range/°C
2010 | 15–20 to 350 | 3520 | 250 to 350
40Mn | 40Mn | 450 to 400 | 40MnV | 40Cr
30CrMoA | 40Mn | 45–10 to 400 | 35CrMoA | 100 to 500
35CrMoA | 40Mn | 45–10 to 400 | 30CrMoA, 35CrMoA | 70 to 500
35CrMoVA | 35CrMoA, 35CrMoVA | 20 to 425 | 25Cr2MoVA | 30CrMoA, 35CrMo | 20 to 500
25Cr2MoVA | 25Cr2MoVA | 20 to 550 | 40CrNiMoA | 35CrMoA, 40CrNiMoA | 50 to 350
S45110 (1Cr5Mo) | S45110 (1Cr5Mo) | –20 to 600 | S42020 | 0 to 400
S30408 | S30408 | –253 to 700 | S31008 | S31008 | –253 to 800
S31608 | S31608 | –253 to 700 | S32168 | S32168 | –253 to 700

Table 2: Common Functional Failures of Shell-and-Tube Heat Exchangers and Their Solutions
Serial number | Function | Functional failure | Failure mode | Consequences | Countermeasures and maintenance tasks | Maintenance cycle/months
1 | Heat exchange between two cold and hot media; processing capacity meets design requirements and product quality is satisfactory | Mixing of the two media (internal leakage) | Corrosion and cracking of heat exchange tubes | Poor heat exchange efficiency; contamination of the media | Replace or plug the tubes as appropriate |
Cracking at the expansion joints (welds) between heat exchange tubes and tube sheets | Poor heat exchange efficiency; contamination of the media | Re-expand, weld again, or plug the tubes as appropriate |
In floating-head heat exchangers: Leakage at the floating-head flange seals | Poor heat exchange efficiency; contamination of the media | Tighten bolts or replace them, as well as replace gaskets as appropriate |
Cracking and leakage in the heat exchanger tube sheet | Poor heat exchange efficiency; contamination of the media | Weld again or replace the tube bundle as appropriate |
2 | Heat exchange between two cold and hot media; product quality is satisfactory and there is no environmental pollution. At the flange, the sealing gasket does not provide sufficient pressure resistance, it is corroded or deteriorated, resulting in inadequate heat transfer performance; the product quality is substandard, and medium leakage causes environmental pollution. The bolts need to be tightened, and the gasket may need to be replaced depending on the situation. If the bolt strength is insufficient, they are loose or corroded, heat transfer performance is inadequate, product quality is substandard, and medium leakage causes environmental pollution; the bolt material should be upgraded, and the bolts may need to be tightened or replaced as appropriate. If the flange lacks rigidity or there are defects in the sealing surface, heat transfer performance is inadequate, product quality is substandard, and medium leakage causes environmental pollution; the flange may need to be replaced or the sealing surface repaired, depending on the situation. If the flanges are not parallel or misaligned, heat transfer performance is inadequate, product quality is substandard, and medium leakage causes environmental pollution; the flanges may need to be re-welded or replaced, depending on the situation. If the quality of the gasket is poor, heat transfer performance is inadequate, product quality is substandard, and medium leakage causes environmental pollution; the gasket may need to be replaced, depending on the situation. Table 2: Common functional faults of shell-and-tube heat exchangers and their treatment methods (continued) Serial number, Functional fault, Fault mode, Consequences, Strategies for dealing with the fault and maintenance tasks, Maintenance cycle/month: 3. Heat exchange between two cold and hot media; the processing capacity meets design requirements and the product quality is satisfactory. Poor heat transfer performance due to scaling on the heat exchange tubes; processing capacity does not meet design requirements. Chemical cleaning or jet cleaning, depending on the situation. Poor water quality, excessive oil and microorganisms also lead to poor heat transfer performance and insufficient processing capacity. It is necessary to improve the filtration and purification of the circulating water, depending on the situation. Short-circuiting of the partition plates results in poor heat transfer performance and insufficient processing capacity. The partition plates need to be repaired or replaced, depending on the situation. 4. Heat transfer efficiency and processing capacity meet design requirements, but the pressure drop exceeds the allowable value. The filter is ineffective, resulting in poor heat transfer performance and insufficient processing capacity. The filter needs to be cleaned or replaced, depending on the situation. Scaling inside and outside the shell and heat exchange tubes leads to poor heat transfer performance and insufficient processing capacity. Jet cleaning, chemical cleaning or online cleaning may be required, depending on the situation. 5. The heat exchanger facilitates heat exchange between two cold and hot media. Severe vibration caused by resonance due to the frequency of the medium can lead to equipment failure and leakage, causing environmental pollution. It is possible to adjust the flow rate or the natural frequency of the tube bundle, depending on the situation. Resonance caused by vibrations in external pipes can also lead to severe equipment failure and leakage, causing environmental pollution. It is necessary to reinforce the pipes to reduce vibrations, depending on the situation. Appendix A (Informational appendix): Record sheet for pressure resistance and leakage tests of shell-and-tube heat exchangers. SH/T3503-J340. Project name:, Organization:, Equipment name, Equipment location code, Product number, Equipment model, Operating medium – Tube side:, Shell side:, Design pressure – Tube side: MPa, Shell side: MPa. Design temperature – Tube side: °C, Shell side: °C. Pressure gauge serial number, Pressure gauge accuracy class, Date of pressure gauge calibration, Pressure gauge range in MPa. Temperature of test medium in °C, Ambient temperature in °C. Chloride content in mg/L in the water used for testing austenitic stainless steel equipment. Test procedure: Test type, Test location, Test medium, Medium temperature/°C, Test pressure/MPa, Holding time/min, Test date, Equipment management department/Supervising unit, Test results, Production facility construction unit, Inspectors. Pressure resistance test, Leakage test. Additional tests:. Appendix B (Informational appendix): Quality control confirmation form for maintenance of shell-and-tube heat exchangers. Name of maintenance task:, Organization:. Serial number, Inspection item, Inspection standard, Control level, Inspection result, Construction unit, Production facility equipment management department, Inspection time. 1. Disassembly and assembly of the heat exchanger. For removing the core from a shell-and-tube heat exchanger, core removal machinery should be used. C. When lifting the tube bundle of the heat exchanger, steel wires or other sharp lifting devices should not be used to tie the tube bundle directly. When installing the tube bundle, it must be supported on a tube sheet or support plate. C 2: The inner and outer surfaces of the tube bundle in the heat exchanger should be cleaned to remove any scale; the equipment should appear in its original color. B 3: The sequence and requirements for checking for leaks comply with relevant standards and specifications. B 4: Plugging of tubes within the same tube side – the number of tubes that need to be plugged should generally not exceed 10% of the total number of tubes; with the approval of the client, this percentage can be increased slightly. The taper of the pipe plug should be between 3° and 5°; the material of the plug should be the same as that of the heat exchange tubes. B 5 Sealing surfaces: All flange sealing surfaces must be cleaned thoroughly, with no defects present. C 6 Pressure testing: During pressure testing, the pressure should be increased slowly to the specified level, and the pressure should be maintained for at least 30 minutes. No cracks, leaks, or residual deformation are allowed; in such cases, the test is considered successful. A or B (A applies to critical equipment). 7 Draining: Any water remaining inside the heat exchanger after pressure testing must be removed; if necessary, it should be dried out. B 8 Tightening: Tightening must comply with GB 50461 “Code for Acceptance of Construction Quality of Static Equipment Installation Projects in Petrochemical Industries”. B Control level description: Grade A: Inspection and confirmation by professionals from the construction unit, production facility, and equipment management department, followed by signature. Grade B: Signed after inspection and confirmation by the construction unit and professionals from the production facility. Level C: Signed after inspection and confirmation by professionals from the construction unit. Additionally: if there is a supervisor, the supervisor’s responsibilities are authorized by Party A.