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Contents of the “Three Inspections and Four Determinations” in the petrochemical industry: I. Contents of the “Three Inspections and Four Determinations”: The construction unit or the general contractor organizes the design, production, and construction teams to carry out the “Three Inspections and Four Determinations” work. Three checks: check for missing items in the design, check for unfinished work, and check for potential quality issues in the project. Four fixations: For the identified problems, assign tasks, designate personnel, set timelines, and determine measures. II. Principles to be followed in “three inspections and four determinations” (1) The three inspections must be thorough. A thorough and meticulous inspection is carried out on the quality of installation for each design drawing, each process technology plan, each control scheme, as well as for every piece of equipment, pipeline, valve, instrument, etc., with records being kept in a categorized manner. (2) The work of establishing the four parameters must be accurate; the technical supervisor responsible for production preparation, together with the design and construction teams, shall evaluate each of the identified issues one by one. Any items that affect startup, normal production, or safe production must be added or modified. For projects that are merely optional and can be added on top of what’s already there, they should not be included at all, in order to ensure project progress and keep costs under control. For projects that require addition or modification, especially those involving significant issues (including equipment openings, additions or changes to control schemes, alterations to the process flow, and additions or removals of pipelines with a diameter of 150 millimeters or more), thorough evaluation is necessary, and approval must be obtained from the technical support and design teams. It must be done; the tasks assigned need to be accurate. III. Specific contents (taking pressure pipelines as an example) 1. Inspection of as-built documents As-built documents refer to the final drawing and documentation related to the design, procurement, and construction of a plant (unit); they mainly consist of three categories: design as-built documents, procurement as-built documents, and construction as-built documents. 1.1 Design completion documents: The inspection of design completion documents focuses on whether the design documents are complete, whether the design solutions meet the production requirements, and whether there are sufficient and practical safety protection measures included in the design. Only after confirming that these aspects meet the driving requirements can one drive; otherwise, corrective actions must be taken. Years of production experience have shown that the following issues are common problems and should be given special attention during inspections. 1.1.1 Design omissions: Large-scale design omissions occur very rarely, but design gaps that affect or hinder production operations are more likely to happen. Once the construction of the production unit is completed, especially after the operators have carried out thorough preparations for operation, design omissions can be easily identified. These problems mainly manifest in the following aspects ； a. Omission of necessary isolation valves, cross-connections, vent points, and drain points, etc. A production facility often uses thousands of valves, and most of these valves are used to shut off or open pipelines, especially those involved in switching operations, as valve closing or opening is frequently carried out during normal production. If such a valve is missed, the operation cannot proceed. The inlet and outlet pipes of the cooling equipment, pumps, and other components in the system often come equipped with connecting lines (such as bypass lines, warm pump lines, minimum flow lines, etc.). If these smaller-diameter connecting lines are omitted, it will affect normal operational processes. Installing venting facilities at the high points of pipelines and drainage facilities at their low points is a basic principle in pipeline design; if there are no such facilities at the high points or low points, the medium will accumulate at those locations when the unit stops operating. If the medium is toxic, it can cause poisoning in operators or maintenance personnel. If the medium is flammable and explosive, it may catch fire or explode due to hot work. When there is no vent at the highest point of the pipeline, and if the medium inside the pipeline is a liquid, it can cause gas blockage in the pipeline during normal operation. If this gas blockage occurs at the pump inlet, it can lead to pump cavitation. When there is no drainage at the lowest point of the pipeline, it may cause freezing and other issues in the pipeline. All these issues will affect the production operations of the device (unit). The aforementioned problems are the most common ones. Before operation, a thorough inspection must be conducted to ensure that it meets the requirements of production operations. b. Operators cannot reach the operating and observation points, or there is a lack of necessary operating platforms. For manually operated valves, field instrument components (such as pressure gauges, level indicators, etc.), safety valves, spring hangers, and other piping components, operators must perform periodic or occasional on-site operations or observations during the production process. Such pipeline components should be placed in a location where operators can access them, or appropriate operating platforms should be provided; otherwise, it will affect normal production operations. Similarly, for the operation and maintenance points that need to be accessed during shutdowns, it should also be checked whether they can meet the requirements for such operations and maintenance. In fact, in many production facilities, it is common for individual operation points or observation points to be too high to access. c. Lack of necessary operating instructions: For some of the following situations, the design documents should provide the necessary operating requirements or instructions: the operation and maintenance requirements for special valves such as pneumatic or electric valves that are the responsibility of the piping department ； Operation procedures for the sampling system ； Positioning requirements for spring hangers and supports ； Installation requirements for expansion joints ； Thermal tightening requirements for high-temperature flange seals ； Requirements for pipeline purging, nitrogen blanketing (when required by the process engineering team), alkali washing, etc., during shutdowns ； Wait. In the aforementioned situations, the absence of necessary instructions and requirements can affect the normal production operations of the equipment, and may even compromise the safety and reliability of pressure pipelines. For example, in the case of pipelines for hydrocracking reaction effluents, austenitic stainless steel (usually material 321) is generally chosen based on the conditions of the medium. However, such pipelines are prone to stress corrosion cracking when shut down due to a sulfurous acid environment; therefore, specific protective measures are required in the process – the pipelines should be sealed with nitrogen or cleaned with alkali immediately after pressure is released, otherwise the material is likely to be damaged. 1.1.2 Incomplete design documents. The issue of incomplete design documents often occurs during design modifications and changes. During the construction of installations, design modifications and changes often occur due to reasons such as procurement issues, construction problems, and errors in the design itself. When design modifications and changes occur, the documents detailing such modifications and changes shall be included as part of the design documents in the as-built design documentation, while also being marked in the original design documents. In the design and completion documents of some installations, markings indicating revisions and the preservation of revised documents are often omitted. As a result, there is no reference point for any future modifications to the installations, leading to discrepancies between the actual equipment and the drawings. 1.1.3 The safety protection measures of the device do not meet the requirements of relevant standards and local regulations. Pipeline design engineers are well aware that the design of the device must comply with applicable fire safety standards, explosion prevention regulations, environmental protection requirements, as well as local labor safety laws and regulations. These norms and regulations cover a wide range of areas; implementing them is a very complex task, and they can sometimes be easily overlooked. For example, issues regarding the explosion-proof distance from leak points such as flanges and valves to electrical distribution rooms and central control rooms; the distance between the fire-extinguishing steam distribution system and the fire points; and the requirement to install emergency showers and eye wash stations near carbon disulfide systems. However, the aforementioned standards and regulations are generally mandatory and must not be violated. When reviewing design documents, it is necessary to check whether these specifications and regulations have been implemented. When checking design documents, each item should be checked in accordance with specifications and regulations. In addition, GB50160 “Code for Fire Protection Design of Petrochemical Enterprises” also stipulates three levels of safety measures: first, preventing secondary hazards caused by a primary hazard; second, minimizing the extent and severity of such secondary hazards should they occur; and third, facilitating timely rescue operations and safe evacuation after secondary hazards have taken place. During inspections, should any issues violating standards and regulations be identified—such as the failure to implement necessary protective measures or the improper setup of such measures—corrective actions must be promptly recommended. 1.2 Inspection of procurement completion documents The inspection of procurement completion documents mainly involves checking whether they are complete and consistent with the design documents, etc., as well as verifying whether the procurement change documents and documentation accompanying the products are all present. 1.2.1 The procurement documents should include corresponding technical documentation related to the procurement. Complete procurement documents serve as valid evidence for ensuring product quality and, ultimately, the safe operation of pressure pipelines. By reviewing the procurement documents, especially the technical specifications, one can gain insight into the quality assurance measures for the procured products and identify any potential quality risks, thereby taking effective preventive measures. For example, does the procurement technical document clearly specify the delivery status of the product materials? Does it also clearly specify the chemical composition, mechanical properties, non-destructive testing requirements, etc., of the product materials? If there are no requirements regarding these aspects in the procurement documents, or even no corresponding procurement technical documents, the product must be carefully evaluated, or its reliability must be confirmed through appropriate inspections and tests. Otherwise, the product should be replaced or necessary corrective measures taken. 1.2.2 Procurement documents shall be consistent with design documents. It is a mandatory principle that procurement documents must be consistent with design documents. If procurement documents that do not conform to the design are obtained, they should be submitted to the designers for review to confirm their reliability; otherwise, the product should be replaced or necessary corrective actions taken. For example, it is generally feasible to replace pipes with a small wall thickness with those having a larger wall thickness. However, for large-diameter high-temperature pipes, especially when they are connected to sensitive equipment, a designer should be consulted to perform a static stress analysis and verify that all mechanical parameters meet the requirements. If spring supports are installed on the pipeline, it is also necessary to conduct a load verification of these spring supports and determine whether it is required to replace them or adjust their parameters. 1.2.3 Procurement change documents (procurement substitution forms) must be approved by designers. Procurement substitution forms are technical documents usually proposed by procurement personnel and signed off on by designers. They differ from the original procurement documents specified in the design; however, they should still be considered a part of the design documentation. If the procurement change document does not have the signature of the designer, it should be submitted to the designer for review to confirm its feasibility. It should be noted that procurement changes often occur as a last resort when sources of supply cannot be found or the manufacturing timeline cannot be guaranteed; therefore, substitute products are not the most suitable options, and sometimes they come with additional conditions. For example, when using ultra-low carbon austenitic stainless steel to replace low-carbon or high-carbon austenitic stainless steel at temperatures exceeding 500°C, in addition to verifying its strength, its creep rate must be closely monitored during operation. Once the creep exceeds a certain limit, the material should no longer be used; otherwise, accidents may occur. Since creep failure occurs over a very long period of time, it does not occur at the initial stage of operation. Therefore, it is acceptable to use readily available ultra-low-carbon austenitic stainless steel as a temporary substitute for low-carbon or high-carbon austenitic stainless steel for short-term emergency use. For these conditional design changes, a register should be maintained, and they should be monitored in accordance with the attached requirements. 1.2.4 The documents accompanying the product should be complete and properly preserved. In addition to standard documents such as the product certificate of conformity, these documents should also include detailed product descriptions as well as instructions for operating and maintaining the product. Product description documents serve as crucial reference materials for subsequent redesign, procurement changes, replacements, and maintenance. For example, for products that contain wear parts, when replacing those parts, they should be ordered in accordance with the requirements of the original parts; otherwise, it may affect the product’s performance. The product operation and maintenance manual is an important document to ensure the proper use of the product. Operators must carry out operations and maintenance in accordance with the requirements outlined in this manual; otherwise, it may affect the product’s performance or even cause damage to the product. Therefore, the documentation included with the product is an important part of the procurement documents; if it is missing, it should be requested from the manufacturer. 1.3 As-built documents for construction: The as-built documents that need to be inspected mainly include the following: a. Installation records of critical pipelines; b. Welding records of pipelines; c. Records of non-destructive testing and hardness testing of welds; d. Records of strength and tightness tests of the pipeline system; e. Records of pipeline system purging; f. Records of pipeline insulation work; g. Records of pipeline anti-corrosion work; h. Records of safety valve adjustment tests and inspection records of critical valves; i. Records of design and procurement changes; j. Other construction documents; k. As-built drawings. 2. The inspection focuses on whether these documents meet the requirements specified in the design documents and relevant standards. 2.1 Inspection of installation records for critical pipelines Critical pipelines refer mainly to high-pressure pipelines that are bent on-site, large-diameter pipelines and fittings that are welded on-site, pipelines that have thermal and wear-resistant linings applied to them on-site, pipelines connected to sensitive equipment, and pipelines that require cold tightening. When high-pressure pipes are bent on-site, the quality of the bent pipes is relatively poor due to the unfavorable working conditions at the site and inadequate equipment. Additionally, since the bending process is accompanied by a reduction in wall thickness at the bent section, the elbow becomes the weakest point in the entire pipeline. A proper bending process and comprehensive inspection and testing procedures are important means to ensure the reliability of bent elbows. By examining the bending process parameters and relevant inspection and test records, it is possible to assess the reliability of high-pressure pipe elbows. By the same logic, for large-diameter pipes and fittings welded on-site, their quality can be assessed by examining their manufacturing and inspection records; if necessary, measures such as adding more inspection items or increasing the number of inspections can be taken to enhance their reliability. The on-site installation of heat-insulating and wear-resistant linings on pipes is a complex construction task that is prone to various problems. The quality of the insulation and wear-resistant lining installation not only affects the normal operation of the equipment, but can also directly threaten the safety of the pipes themselves. For example, if the lining comes off during operation of the equipment, it not only contaminates the medium, but may also cause the pipe wall temperature to rise, thereby damaging the metal material. The inspection items shall be based on the design documents, and all specifications shall adhere to the requirements set out in the design. Pipes connected to sensitive equipment are subject to strict regulations in the commonly used pipeline construction standards. Taking SH3501 \"Code for Construction and Acceptance of Pipelines for Highly Toxic and Flammable Media in Petrochemical Industries\" as an example, it requires that after the construction of the pipelines and supports is completed, the flange bolts on the equipment connections be removed, and the parallel deviation, radial displacement, and spacing of the flanges be checked in their free state; these values must not exceed certain limits (the specific numbers are provided separately). The purpose of this regulation is to minimize the additional torque exerted by the pipes on the connected equipment, thereby ensuring that the pipes do not interfere with the proper operation of the equipment. A similar incident occurred with a certain device: the pipeline with a diameter of DN1200 exerted excessive force on the connected exhaust fan, causing the fan’s casing to deform and the blades of the rotor to wear out. This led to abnormal operation of the fan and resulted in significant losses. Therefore, checking the pipeline installation records of sensitive equipment and confirming that they meet standard requirements is an important task to ensure the proper operation of the equipment, as well as the entire system. The purpose of pipe cold straining is to transfer all or part of the deformation of the pipe in its hot state to the cold state, thereby reducing the stresses in the pipe system under hot conditions as well as the additional forces exerted on the connected equipment (including forces and bending moments). The cold tightening position and amount for the pipes are determined through precise calculations by the designers. If the construction work is not carried out in accordance with the design requirements, or if those requirements are not fully met, unexpected consequences may arise, which could even affect the proper functioning of the pipes or the connected equipment. If the cold tightening method is not performed properly, it can easily lead to false impressions, preventing the cold tightening from achieving the desired effect. In fact, this phenomenon occurs quite frequently. Therefore, prior to commencement of work, it is necessary to verify details such as the method used for pipe cold tightening and the magnitude of the cold tightening value, and to evaluate the effectiveness of the cold tightening. 2.2 Inspection of welding and non-destructive testing records for pipes There are many factors affecting welding quality. Besides the skill level of operators and environmental conditions, these factors also include the selection of welding materials, choice of welding parameters, selection of preheating and post-weld heat treatment methods, hardness testing, and non-destructive testing. The inspection of welding documents focuses on verifying whether they are prepared in accordance with the design documents and relevant standards, and whether there are any potential quality issues. If the records are incomplete, or if the work was not carried out in accordance with the design requirements or specifications, or if the number of inspections and tests performed does not meet the requirements set by the design or specifications, or if the criteria for non-destructive testing do not conform to the requirements of the design specifications, and so on. Once these issues are identified, relevant technical personnel should be organized to conduct a review, and appropriate corrective actions should be taken. It is not permissible to drive when it cannot be confirmed whether it is reliable. Before examining these items, it is necessary to review the welding procedure qualification records, welder training records, and welder qualification certification documents, adhering to the principle of meeting the relevant requirements. 2.3 Inspection of records for strength and tightness tests of pipeline systems: The strength and tightness tests of pipeline systems are the final comprehensive inspection tests carried out before the plant is put into operation. These tests assess the pressure resistance and tightness of the pipelines and their components; pipelines that fail these tests in terms of pressure resistance or tightness cannot be brought online. The relevant construction standards specify requirements for the pressure testing and leak tightness testing of pipelines. A strength test is a testing method that involves filling the completed pipeline system with a high-pressure liquid (usually water), which can subject the mechanical stresses in the pipeline material to levels close to the yield limit, in order to evaluate the strength and tightness of the pipeline and its components. When it is not possible to conduct strength tests on pipes due to structural or support constraints, 100% radiographic inspection of the pipe welds can be used as a substitute for the strength test. However, this approach increases the inspection costs. Moreover, radiographic inspection can only determine the integrity of the welds and any defects present, but it cannot assess the integrity of flanges and threaded connections in the piping system, nor the stability of the materials (since pipes and valves have already undergone strength tests during manufacturing). Therefore, for pipes for which 100% radiographic inspection is used as a substitute for strength testing, it is necessary to monitor their operation at the beginning of operation; should any abnormalities occur, immediate action must be taken, or the system should be shut down for repairs. The tightness test involves filling a pipeline that has passed the strength test with gas (the gas pressure is generally at the design pressure). Given that gas leaks more easily than liquids, this method is used to check the tightness of the pipe welds, various detachable joints, sealing pairs, etc. . In engineering, there are many pipelines that should not or even must not undergo hydrostatic tests and airtightness tests; examples include large-diameter low-pressure gas pipelines and pipelines with thermal-insulating and wear-resistant linings. For these pipes, inspectors should pay close attention to their handling methods to ensure that no potential hazards are left behind. For example, in the case of large-diameter gas pipelines, they are generally welded to the connected equipment; therefore, it is possible to pre-fabricate them to a certain extent before connecting them to the equipment. The pre-fabricated sections are then subjected to hydraulic strength tests. Once these tests pass, the pipelines are welded to the equipment, and the resulting welds are inspected using 100% radiographic testing (which allows for accurate detection of defects in the welds as well as their integrity). Pipelines that pass this inspection can serve as a substitute for pressure testing. For pipelines equipped with thermal-insulating and wear-resistant linings, since the portion responsible for providing strength and ensuring sealing is primarily the outer metal pipe, a pressure test must be conducted on the metal pipe section prior to lining installation. Only after the pressure test is passed can the thermal-insulating and wear-resistant lining be applied; furthermore, 100% radiographic inspection must be performed on all welds at the end. 2.4 Inspection of pipeline flushing records: Any contaminants left inside the pipes during construction must be removed prior to startup. For different pipelines, the purging media and methods used are different. Most pipelines are purged with steam, as steam not only has pressure but also temperature. It can effectively remove ordinary free-standing contaminants, as well as most adhered contaminants (such as oil, oxides, etc.). Pipelines that cannot be purged with steam (such as those with thermal-insulating and wear-resistant linings) shall be purged with air. Pipelines that require a high level of cleanliness need to undergo special cleaning in addition to regular purging. For example, in the lubrication oil pipelines of pumps, if solid contaminants remain within these pipelines, even if the particles are very small, they can cause damage to the moving parts of the pump. To this end, in addition to using conventional media to wash away free particles and loosely attached dirt, such pipes should also be acid- or alkali-washed to remove more firmly adhered substances such as oxides. For the inlet pipes of reciprocating pumps and compressors, in addition to regular purging, acid or alkali cleaning is also required to prevent oxide particles in the pipes from entering the highly precise piston cylinders of the pumps and compressors and causing damage. In addition to alkaline washing, the lubricating oil pipelines made of stainless steel (including other stainless steel pipes) must also undergo acid washing and passivation treatment, so as to form a passive film on their surfaces and prevent them from oxidizing and rusting again. Appropriate and qualified pipeline purging records are also one of the conditions to ensure the proper operation of the equipment. By checking the pipeline system purging records, one can understand the status of pipeline purging. 2.5 Inspection of records for pipeline insulation and anti-corrosion work: Pipeline insulation includes heat retention, cold retention, and heat protection. The quality of pipeline insulation generally does not pose a direct threat to the safety of pressure pipelines, but it does cause heat loss from the pipelines. Sometimes, significant temperature drops or the solidification/freezing of the fluid can affect the proper operation of the equipment. The quality of pipeline insulation also affects the amount of cold loss from the pipelines; since cold energy is more expensive than heat energy, this leads to greater economic losses. The quality of heat protection for pipes affects the safety of production operators, as it may cause them to get burned. The inspection of pipeline insulation construction records focuses on whether they meet the requirements of the design documents or relevant standards. Similar to thermal insulation, anti-corrosion measures for pipelines generally do not pose an immediate threat to the safety of pressure pipelines; in other words, they won’t jeopardize their safety in the short term. However, if the quality of anti-corrosion treatment is poor, especially in the case of buried pipes, over time the metal pipes will be damaged as a result of corrosion caused by the atmosphere or soil. Therefore, it is crucial to focus on inspecting the anti-corrosion construction of buried pipelines. 2.6 Inspection of safety valve adjustment test records and inspection records for key valves. Safety valves are protective components in pipelines; when the pressure in the pipeline rises suddenly due to accidental factors and exceeds a certain level, the safety valve opens automatically to release the excess pressure, thereby protecting the equipment and pipelines. If the calibration data of the safety valve does not match the design data, it will result in the safety valve losing its functionality. Therefore, safety valves must be adjusted and tested before installation. Key valves, such as those designed for high temperatures and pressures, can impair the proper operation of the equipment if they do not close properly, suffer from severe leakage, or have materials that do not meet the design requirements. This can lead to environmental contamination, and in severe cases, damage that endangers safe production. Therefore, it is necessary to conduct a systematic review of the key valves before installation. The inspection status can be understood by checking the records. 2.7 Inspection of records for design and procurement changes Design and procurement change documents are supplementary to the design files and serve as the basis for construction; therefore, the construction party should also maintain complete records. Checking the construction contractor’s records of design and procurement changes mainly involves verifying whether they correspond to the design completion documents and procurement completion documents. 2.8 Inspection of other construction documents, such as those related to the installation of supports and hangers (especially spring-type supports and hangers), documents concerning the heating of outer pipes and sleeves, records of flange bolt pre-tightening data (particularly for large-diameter pipes operating under high temperature and pressure), and installation records of bellows compensators. If the installation load on the spring hanger does not meet the design requirements, or if the suspender of the spring hanger is not properly tensioned, etc., the spring hanger will fail to function as intended. This may result in a portion of the forces acting on the piping system being transferred to the connected equipment, causing the equipment to be subjected to excessive stress; alternatively, it may directly cause the stress within the piping system to exceed its allowable limits. While checking the records related to this aspect, it is also necessary to go to the installation site to carefully inspect the actual installation conditions. The relevant design or construction specifications set out specific requirements for the heating of external pipes or casings, and by checking their construction records, it can be determined whether these requirements were met in accordance with the design specifications or relevant standards. The key points to be checked are: for pipelines transporting heat-sensitive media or stainless steel pipelines, if external tracing is used for heating, there must be non-metallic insulation blocks to separate the tracing pipe from the pipeline being traced ； For detachable pipe connections such as those with flanges or threads, the tracing pipe should also have detachable flanges ； For pipeline accessories such as valves, flanges, and instrument connections, the external heat tracing tubes should be properly bent and wrapped, etc. For flanges operating under high temperatures (T≥250°C), high pressures (P≥6.0 MPa), and large diameters (DN≥150 mm), a specified bolt preload must be established and ensured using special or dedicated tools (such as torque wrenches). Under normal circumstances, high-pressure pipelines require a high bolt sealing force, and relying on touch and experience is no longer sufficient; therefore, special tools should be used for pre-tightening, with the relevant measurements being recorded. The installation of bellows compensators is similar to that of spring supports and hangers; if not installed properly, they cannot fulfill their intended function, and in severe cases, insufficient compensation can lead to damage to the piping system. For example, the position of the tie rods in a constrained compensator or the location of its hinge structure should be installed in accordance with the design drawings, and it must not prevent the compensator from deforming ； The protective rods used during transportation should be removed after the compensator has been installed. Wait. All installations that affect the safety of pressure pipelines should be clearly documented, or on-site inspections should be conducted to verify whether they have been installed correctly. 2.9 Inspection of as-built drawings The as-built drawings are the actual record documents that describe the final installation state of the pipelines. They serve as systematic technical documents for checking whether the pipelines meet the design requirements and relevant standards and regulations; they are the basis for collecting and documenting pipeline data, and they also provide essential information for future modifications to the installation. The as-built drawings shall be complete, clear, and accurate. 3. On-site inspection: It can be said that on-site inspection and the inspection of completion documents are carried out in parallel, but they are also different from each other. The inspection of as-built documents involves checking for any issues documented in writing during the design, procurement, and construction phases. Meanwhile, on-site inspections should not only involve a visual verification of the issues recorded in writing, but also the detection of any new errors that arise during actual construction despite the written records being correct. Therefore, it can be said that on-site inspection is the continuation and extension of the inspection of as-built documents. Generally, the problems mentioned in the as-built documents definitely exist on site, while problems that are not shown on the drawings or in the construction records may also occur on site. Therefore, on-site problem inspection is sometimes more direct and important than checking problems in drawings or records. On-site inspections can be divided into three categories: design and construction omissions, unfinished work, and construction quality. 3.1 Omissions in design and construction Omissions in design and construction can occur in various aspects. Based on the author’s experience and knowledge, the problems that occur most frequently are as follows: a. Omissions of valves, jumpers, vents at high points, drains at low points, etc ； b. Operating and measuring indication points are too high to be operated on or observed, especially the on-site indication components of instruments ； c. Lack of ladders or insufficient number of ladders, making routine inspections inconvenient ； d. Insufficient supports and hangers, resulting in pipe deflection exceeding standard requirements or instability of the pipes ； e. Beams, columns, etc. of pipelines or structures obstruct the operating passageways ； f. There is a lack of necessary operating and maintenance space for equipment, pumps and machines, special instrument components (such as thermocouples, instrument cabinets, flow meters, etc.), valves, etc.; or the available space is too small, making operation and maintenance inconvenient. 3.2 Uncompleted Works The inspection of uncompleted works applies to intermediate inspections or inspections of installations that are put into operation in phases. For the work involved in this startup, it must be confirmed that it has been completed and does not affect the normal startup. For units that are put into operation in phases, the portions not included in this startup should be isolated, and it must be confirmed that they have no mutual interference. However, some of the following items do not constitute unfinished work: a. Insulation at flanges and valves. During the startup and heating process, it is necessary to check for leaks at detachable connections such as flanges and valves, as well as to tighten the bolts; therefore, local insulation should be applied after startup ； b. Covers for trench installations, covers for valve chambers, etc. The same principle applies; cover it again once driving is normal ； c. Temporary scaffolding or platforms used for thermal tightening of flanges. The same principle applies; remove it only after driving is normal again. 3.3 Construction quality: Construction quality can manifest in various aspects, therefore a comprehensive inspection is necessary. Based on the author’s experience, inspections should be focused on the following aspects: 3.3.1 Pipes and their components. Common problems in this area include: a. Directional valves being installed in the wrong orientation. Directional valves include check valves, globe valves, safety valves, angle valves, and most steam traps. If these valves are installed in the wrong direction, it can be very dangerous; therefore, this must be corrected before starting up the system ； b. The position and status of blind flanges (especially figure-8 blind flanges) are incorrect; they should be adjusted in a timely manner in conjunction with operations ； c. The valves, flanges, bolts, etc., are of the incorrect type. Different types of valves have their own characteristics. If the valve installed in practice does not match the design, it can have adverse effects on operation, and in severe cases, it may lead to accidents. Different flange types have distinct applicable conditions; for example, butt weld flanges cannot be used in place of slip weld flanges under harsh conditions, otherwise the sealing performance will not be guaranteed. Different bolts also have different applicable conditions; single-headed bolts cannot be used in place of double-headed bolts under harsh conditions, as this will likewise fail to ensure the sealing performance of the flange seal assembly. In addition, it is also necessary to check whether the number of bolts is sufficient, whether the bolt diameters and exposure lengths are uniform, and whether they meet the standard requirements ； d. The material and pressure rating of the pipes and their components do not meet the design requirements. This is a relatively serious construction error; once it occurs, there is a high likelihood of accidents happening. It is possible to determine whether the requirements of the design are met by checking the material markings on the pipes and fittings, the markings on the flanges and bolts, as well as the nameplates on valves and small piping equipment ； e. The installation condition of the bellows expansion joint is incorrect, and the transportation safety rod has not been removed. Under normal circumstances, for constrained expansion joints, the position of their links or hinges matches the direction of their displacement compensation; any error in this regard can lead to serious accidents, so it is necessary to verify this before starting operation. The transportation safety rod is used solely for protecting bellows expansion joints during transportation; if it is not removed when the unit is put into operation, it will hinder the compensatory deformation of the expansion joints. Therefore, it should be removed before the unit starts up. 3.3.2 Supports and hangers: Common problems in this area include: a. Incorrect type of supports and hangers. For example, converting guide brackets into ordinary load-bearing brackets (i.e., omitting the guide clips), welding sliding pipe supports to the support beams to turn them into fixed pipe supports, installing fixed brackets as ordinary load-bearing brackets (i.e., not using fixing bolts), and so on. An incorrect installation of the support type is a serious error; in mild cases, it can lead to excessive stress on the piping system itself, excessive forces on the equipment connections, and excessive thrust on the pipe racks and supports. In severe cases, it can directly cause damage to the pipes themselves, the supports, and the anchoring facilities, as well as damage to the connected equipment ； b. The installation status of the supports and hangers is incorrect. For example, the height of load-bearing supports is insufficient, causing the pipes to become unsupported in their installed position; the hangers’ rods are loose, so the pipes fail to bear any load in their installed state; the installation load or position of spring supports and hangers does not meet the design requirements, etc. All these problems can render the bracket ineffective or prevent it from performing its intended function; in severe cases, they can also cause damage to the tube or the connected equipment ； c. The material and specifications of the supports and hangers are incorrect. In terms of materials, problems most often occur with those components that are in direct contact with pipes or equipment (i.e., pipe attachments and components fixed to the equipment); these materials tend to be of poor quality, thereby affecting the stability of the corresponding equipment or pipe materials (as described in detail in Chapter 8). Under normal circumstances, the support and hanger components that are directly connected to pipes and equipment should be made of the same material as the corresponding equipment or pipes, or of a similar material. The specifications of the components used for supports and hangers should not be lower than those specified in the design drawings; otherwise, the strength of the supports themselves may be insufficient, leading to failure and thereby threatening the safety of the pipelines ； d. Temporary supports and hangers are welded arbitrarily. In fact, there are many pipelines for which on-site welding is not allowed, such as those at risk of stress corrosion cracking, high-pressure thick-walled pipelines, and other pipelines that require post-weld heat treatment. If temporary supports and hangers are welded, their weld points can cause a decline in the performance of the pipeline material. Once such issues are detected during inspection, relevant personnel should be organized to conduct an assessment, or appropriate measures should be taken to eliminate their impact. 3.3.3 Welding: Common problems in this area include: a. The visual quality of the welds on pipes and their components exceeds the specified standards. These are mainly manifested as excessive weld metal, incomplete filling, undercutting, weld beads, and spatter on the base material (especially in the case of alloyed base materials), and so on. These defects in the welds can affect the performance of the welded joint, thereby compromising the safety of the pipeline ； B. The welds of the pipe supports and hangers are unqualified. It is mainly manifested in: insufficient weld length (in some cases it is even spot welding), insufficient height of the fillet welds, weld penetration in thinner support and hanger components, and so on. These welding defects can affect the strength of the supports and hangers themselves. Thus threatening the safety of pressure pipelines ； c. The steel structure welds of the platform ladders and structures are substandard. It mainly manifests as: insufficient weld length ； Thinner components are welded through, platforms between hot and cold equipment, or between equipment and frames, or between equipment at different temperatures are welded together, and so on. Although these defects do not directly pose a threat to the safety of pressure pipelines, they directly endanger personal safety; therefore, they should also be corrected once discovered. 3.3.4 Insulation and corrosion protection: Common construction problems related to pipeline insulation and corrosion protection are failure to follow the design or standard requirements, or failure to adhere to the construction procedures, which in turn affects subsequent inspections. It mainly manifests in the following aspects: A. The insulation thickness does not meet the design requirements; B. The insulation protective layer is not properly sealed, resulting in the insulation layer absorbing water and becoming damaged; C. Valves and hot oil pumps on insulated pipes are not insulated (unless otherwise specified in the design); D. Insulation work is carried out prior to the hydrostatic test of the pipes ； Or, insulation work was carried out on detachable joints such as flanges and threads prior to hydrostatic testing, airtightness testing, or commissioning. E: Rust removal was not performed in accordance with design or standard requirements; the paint thickness did not meet the standards or design specifications, resulting in the anti-corrosion coating beginning to peel off before commissioning. F: Paint was applied to the welds prior to performing non-destructive surface testing, making it impossible to conduct inspections on the weld surfaces. 4. Documentation, labeling, and data collection: In accordance with the requirements of the “Regulations on the Safety Management and Supervision of Pressure Pipelines”, entities utilizing pressure pipelines shall compile records and documentation regarding the pressure pipelines in operation. This is regarded as a fundamental task for ensuring the safe management of pressure pipelines. In fact, it is highly necessary to keep records of operating pressure pipelines; the pipeline records can be used to promptly document the design and procurement processes of such pipelines ； Data related to various stages such as construction, operation, and maintenance, pipeline conditions, and problems that have occurred. Therefore, before operation, it is necessary to create a register of the pressure pipelines contained in each device or unit; simultaneously, mark the measurement points that require close monitoring and collect initial data. 4.1 Documentation The pressure pipeline files shall include at least the following information: pipeline number, start and end points, medium (including various corrosive media along with their concentrations or partial pressures), operating temperature, operating pressure, and design temperature ； Design pressure, main pipe diameter, pipe material, pipe grade (including nominal pressure and wall thickness grade), pipe category, insulation requirements, heat treatment requirements, pipe grade number, date of commissioning of regulated pipes, record of relevant matters, etc. 4.1.1 Pipeline number and starting/ending points of the pipeline: It should be consistent with the design documents so as to correspond to the process flow and actual site conditions. Based on the devices connected to it, one can determine the possible operating dynamics of the pipeline. For example, pipes connected to reciprocating compressors or reciprocating pumps may experience vibration problems ； Pipes connected to pressure swing adsorption tanks may be prone to low-cycle fatigue failure ； Pipelines connected to heavy equipment may be affected by uneven settlement ； Wait ； Based on the operating conditions of the pipeline, targeted marking and monitoring can be carried out selectively. 4.1.2 Medium and operating conditions The medium transported in the pipeline and its operating conditions (operating temperature and operating pressure) are important criteria for determining whether monitoring should be focused on, and they also serve as the main basis for classifying pressure pipelines. Pipelines with high medium hazard, as well as those operating at high pressures or temperatures, are those prone to accidents or that can cause significant damage in the event of an accident; therefore, they should be subject to focused inspection and monitoring. For example ； For pipelines carrying highly toxic substances, a leak can cause severe pollution and even put the safety of people in the surrounding area at risk; therefore, the requirements for their sealing reliability are much higher than those for pipelines carrying ordinary substances ； For high-temperature pipelines, a series of changes occur during operation ； If significant deformation and displacement occur, it can lead to creep and stress relaxation in the pipes and their components, among other things. Closely monitoring these changes is an important condition for ensuring the safe operation of pipelines ； High-pressure pipelines have high energy storage capacity ； Once an accident occurs, its consequences can be severe. Therefore, high-pressure pipelines are also a key focus for monitoring. 4.1.3 Pressure pipeline categories The pressure pipeline categories are code identifiers corresponding to the medium transported by the pipeline and its operating conditions. According to the requirements of the regulations on safety supervision of pressure pipelines, the contents and requirements for safety inspections vary depending on the type of pressure pipeline. Therefore, the classification of pressure pipelines is an important indicator of the safety monitoring level during pipeline operation. 4.1.4 Pipe classification. Pipe classification is a set of parameters—including the materials used, pressure rating, wall thickness grade, corrosion allowance, structural type, and applicable standards—for various components of a pipeline. These parameters are determined based on factors such as the properties of the medium being transported, its pressure, and temperature. Pipe classification serves as a comprehensive description of the attributes of pipe components and constitutes a crucial basis for reliability analysis, strength calculations, and service life assessment of pressure pipelines. Based on the pipe class number, data describing the relevant properties of each component in the pipe can be found in the corresponding class table. 4.1.5 Material of the pipe body and heat treatment requirements: The material of the pipe body and the heat treatment requirements are among the important parameters that characterize a pipe, and they are also part of the specifications defined for the pipe grade. However, different materials exhibit significant variations in performance; especially when combined with various medium environments, they show different forms of failure. For example, chromium-molybdenum alloy steel is prone to delayed cracking ； Carbon steel and stainless steel operating in wet hydrogen sulfide environments are prone to stress corrosion cracking ； Austenitic stainless steels operating in H2+H2S media are prone to polysulfate stress corrosion cracking ； Wait. Special failure modes arising from these materials themselves or when combined with sensitive media should be closely monitored and carefully prevented. In the pressure pipeline records, the main materials of the pipeline are listed separately to facilitate monitoring by operators. 4.1.6 Insulation and corrosion protection requirements for pipes: Under normal circumstances, the service life of insulation materials and corrosion protection materials used in pipes is relatively short; keeping records of these materials and their respective service lifespans facilitates their timely replacement. 4.1.7 Date of commissioning of regulated pipelines As mentioned in Chapter 3, most of the pipelines in petrochemical production facilities operate in corrosive environments. Whether the pipeline material suffers from uniform corrosion or localized corrosion, hydrogen damage, or fatigue and creep failure, it is all related to the service life of the pipeline. As the service time of pipelines increases, their stability tends to deteriorate. Therefore, the date on which the regulated pipeline is put into operation becomes an important parameter for assessing its lifespan. 4.1.8 Record of Events As mentioned earlier, the records of various events that occur at different stages of a pressure pipeline can be aptly referred to as the pipeline’s “medical record.” These records document various incidents that may have an adverse effect on the pipeline’s stability, such as material changes, welding rework, flange leaks, valve replacements, results of hydrostatic testing, data on the pipeline’s thermal displacement, data on the settlement of related equipment foundations, and the appearance of microcracks. Such records provide an important basis for assessing the pipeline’s stability and determining its service life. 5. Identification and Data Collection: The identification of pipelines can be divided into two main categories: conventional identification and special identification. Conventional markings are specifically stipulated in certain specifications, such as SHJ43 “Surface Colors and Markings for Equipment and Piping in Petrochemical Enterprises”. Under normal circumstances, the standard markings on pipes should at least indicate the pipeline number, the name of the medium, and the flow direction of the medium. Special markings are indicators applied selectively to certain weak points, hazardous locations, typical points where instability may occur in pressurized pipes under thermal conditions (such as creep and fatigue), key corrosion detection points, important non-destructive testing points, and other points requiring special inspection, based on the characteristics of each pressure pipe. When selecting the aforementioned typical points, priority should be given to the following locations on pressure pipelines: spring support and hanger points, points with significant thermal displacement, areas suffering from severe corrosion, points where coupon corrosion tests are required, typical points on vibrating pipelines, high-pressure flange joints, the elevation of foundations for heavy equipment, and any other points that are deemed necessary to be marked and recorded. For users of pressure pipelines, one of the means of safety management is to establish monitoring points and mark those areas that affect the safety of the pipelines, and to carry out closer surveillance during operation. After identifying the monitoring points, they should be recorded, and initial (pre-construction) data should be collected. 5.1 Spring support and hanger points: The installation load, installation position, working load, and working position of spring supports and hangers are determined based on the operating conditions. When the installation load and installation position are ensured during construction, it is necessary to check whether the operating load and operating position under normal operation meet the design requirements, thereby assessing the accuracy of the design calculations or determining the stability of the pipeline. Therefore, the locations in the pipeline where spring supports are installed should be specifically numbered, illustrated if necessary, marked on site, and their initial condition data recorded. 5.2 Points with Large Thermal Displacement The points with large thermal displacement referred to here are those where significant displacement of the pipeline may affect adjacent pipelines, or where the thermal displacement of the pipeline is hindered by adjacent structures and buildings, or where substantial additional forces are exerted on sensitive equipment, among other things. For example: Pipes on the pipe rack experience significant lateral displacement, which affects the adjacent pipes ； The pipes on the pipe rack undergo significant axial displacement, causing the pipe supports to slide off the crossbeams ； Pipes located near beams and columns may have their thermal displacement hindered by the beams and columns due to significant lateral displacement; this can also cause the thermal expansion to be transferred to supports or equipment at the other end ； Pipes connected to sensitive equipment experience excessive displacement, which causes additional forces to be exerted by the pipes on the equipment; this in turn prevents the equipment from functioning properly or leads to its damage. All of the aforementioned issues should be duly considered by designers. However, for pipes that are not calculated precisely or where there are calculation errors, these problems are likely to occur, often leading to rather serious consequences. For pipelines operating at temperatures exceeding the creep temperature of their materials, selecting appropriate points and monitoring their displacement values can help determine the creep behavior of the pipelines ； 5.3 Points with severe corrosion or where corrosion coupon tests are required As discussed in Chapter 3, in design, the corrosion in many corrosive environments is difficult to describe quantitatively. For example, it is sometimes difficult to obtain accurate values for the composition of the corrosive agents in each area of the device, as well as their respective concentrations and partial pressures. Not only is it hard to get data on the concentrations and partial pressures of these corrosive agents, but it is also difficult to obtain corrosion-related data for specific materials (such as the rate of uniform corrosion); at least currently, there are not many experimental data available in China that can serve as a basis for such information. During the operation of the equipment, for areas prone to severe corrosion, the corrosion coupon test can be employed to obtain actual corrosion data or to observe the true form of corrosion, thereby enabling an accurate assessment of the service life of the pressure pipelines. Corrosion coupon test sites should be selected in representative and easily accessible locations, and the coupons should be removed regularly to collect corrosion data, analyze it, and assess the progress of corrosion and its impact on pipeline stability. Before the equipment is put into operation, the planned corrosion coupon test points should be registered, labeled, and their initial data recorded. 5.4 Typical points on vibrating pipes For pipes subject to mechanical vibration or those where vibration is likely to occur, several typical points can be selected based on their layout characteristics (such as elbows, branch points, locations with concentrated loads, areas near vibrating equipment, etc.), recorded, and marked for measurement and documentation during operation. Based on the results of the measurement records, it is possible to determine whether the pipe’s amplitude exceeds the limit or to calculate its fatigue life. 5.5 High-pressure flange joints: For high-pressure thick-walled pipes, especially those under high temperature and pressure, their high stiffness often results in a significant additional external force being applied to the flange joints on these pipes. As described in Chapter 3, when the flange is subjected to a large additional force from the pipeline, it is prone to leakage. In addition to performing seal checks using flanges for these points, it is also necessary to systematically label them on site and keep records of them. Their sealing condition should be regularly monitored during operation to ensure the safe functioning of the pressure pipelines. 5.5 Elevation of heavy equipment foundations: For relatively heavy equipment such as hydrogenation reactors, their foundations may gradually sink over time, especially in coastal areas with soft soil; this phenomenon of foundation sinking is quite common for heavy equipment. As is well known, once the pipes are installed, additional displacement occurs in the connected pipes due to the sinking of heavy equipment (foundations) relative to pipe bridges or other lighter equipment. If this additional displacement is large, it can lead to a loss of strength in the pipeline. In such cases, a method of initial pre-compression is generally employed during the design phase to ensure that it settles into place before the pipes are installed. However, as a plant operator, it is necessary to consciously record the settlement data of the equipment and promptly analyze its impact on the stability of the pipes. Before operation, the foundation of the equipment to be monitored should be labeled and initial data recorded.