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Given the complex and stringent requirements associated with the installation of oxygen pipelines, quality issues that arise during installation can easily lead to safety accidents. Defects such as inadequate degreasing or incomplete purging can result in fires and explosions when the oxygen pipelines are put into use, causing casualties. Therefore, each step of the oxygen pipeline installation process must be closely monitored. To strengthen the supervision and control of the construction and installation quality of oxygen pipelines, and to ensure that dedicated personnel within the company are responsible for carrying out inspections, these regulatory provisions are formulated. I. Organization of design documents 1. Based on the construction schematic diagram (axonometric view) of the oxygen pipeline, organize the design data such as the material of the pipelines (including fittings and valves), operating temperature, pressure, etc., as well as the design and construction instructions for the oxygen pipeline along with any special requirements. 2. Draw a simplified line diagram based on the construction line diagram (axonometric view) of the oxygen pipeline; the diagram should indicate the welds, flanges, instrument connections, etc., included in the pipeline, as well as the sequence numbers of each component, so that installation can be carried out in accordance with these sequence numbers. 3. The organizing work is carried out by technicians, who compile the information into tables, designate a supervisor for each pipeline, and submit them to the production department for record-keeping, to serve as a basis for future construction supervision and inspection. II. Supervision of the installation process: As the owner, ensuring the quality of each installation task is essential to guarantee the quality of oxygen pipeline construction and installation. Before each construction session, the inspector must be present; construction shall not proceed without the inspector’s presence. All inspection sheets, confirmation forms, imaging materials, and other records related to supervision work must be submitted to the Production Department for filing. 1. Inspection before installation: Before installing the oxygen pipelines, all pipes and pipeline accessories must be inspected. The specifications and technical parameters of all pipes and accessories should comply with the design requirements; it is strictly prohibited to change the material used or to substitute alternative materials. The surfaces of valves shall be free from defects such as sand adhesion, cracks, and pores; the outer surfaces of flanges, bolts, metal gaskets, etc. shall be smooth and free from defects such as pores, cracks, burrs, and dents. The inner walls of elbows, tees, etc., used in pipelines should be smooth. 2. Supervision of degreasing during installation: 1) Fittings and valves must be degreased before leaving the factory, and the degreasing records must be checked. Degreasing of pipes, pipe fittings, valves, etc. should be carried out again before installation; pressure testing of valves and calibration of safety valves also need to be completed prior to degreasing. After degreasing, pipes, pipe fittings, valves, etc. must have their open ends promptly sealed with plastic sheeting or tape to prevent secondary contamination. 2) When testing the valves under pressure, it is essential to strictly control the water quality (use grade-1 deionized water or tap water with a chloride ion concentration of less than 25 ppM). If the water is contaminated, degreasing testing must be conducted after pressurization to ensure it meets the requirements; in cases of severe contamination, the valves need to be sent to the manufacturer for disassembly and degreasing. 3) Before degreasing the pipes, preliminary preparation can be carried out; all openings in the main pipes and branch pipes prior to degreasing must be completed, the grooves must be properly ground free of burrs, and any slag or spatter on the welds must be removed. 4) For pipes and pipe fittings, the immersion method is preferred; before immersion, it is necessary to ensure that they are clean enough. The immersion time must meet the requirements specified for the degreasing agent. The immersion method should be used for all flanges, gaskets, and fasteners as well. 5) Pipes that have not been fully installed should be promptly sealed with plastic sheeting or tape. 6) The oil content in the organic solvent used for degreasing should not exceed 50 mg/L; the methods for testing oil content shall be followed. 7) After degreasing, the pipes should be dried (using clean, oil-free dry air or nitrogen) before installation. 3. Pipeline installation supervision: 1) Tools, measuring devices, instruments, etc., used for degreasing, inspection, and installation must be pre-degreased in accordance with the requirements for the parts to be degreased; those that have not been degreased shall not be used. Protective plastic sheets and the like should be oil-free. Check the conditions required for degreasing work: whether a shelter against rain, snow, and freezing has been set up, whether consumables such as plastic sheeting, tape, and degreasing cotton are ready, and whether testing equipment such as ultraviolet lamps (or test strips, pure camphor) is available. If the workers refuse to carry out the construction, video evidence should be taken promptly and reported, with a request for them to redo the work. 2) Verify that the pipeline is properly sealed after degreasing; if the seal is damaged, further degreasing of the pipe ends is required. If the inside of the pipe is contaminated, the entire pipe needs to be degreased again. Parts that have passed the degreasing test and those that have failed it, or those that have not been degreased at all, must be stored separately; mixing them is strictly prohibited. The inspector shall promptly leave behind visual records and conduct a verification before each installation; otherwise, the installation shall be halted. 3) If cutting on-site is required (pre-fabrication and degreasing are preferred), mechanical cutting or plasma cutting should be used, along with the creation of bevels; mechanical cutting is generally the preferred method, while other cutting methods are prohibited. 4) After cutting and beveling, checks for surface finish and cleanliness are carried out; the pipe ends must also be inspected. Only after manual cleaning to remove grease is successful can TIG welding be performed for the root pass and subsequent welding. In particular, there must be no cutting burrs. If workers fail to comply with these requirements, photographic evidence should be taken immediately and reported, with a request for rework. 5) For the short circuits welded to the oxygen pipeline, the same installation requirements as those for oxygen pipelines apply; welding of any carbon steel material is strictly prohibited. 6) During construction, properly protect the degreased and qualified pipes, fittings, and valves to prevent secondary contamination. 7) Support materials made of carbon steel must be effectively isolated. 8) Construct strictly in accordance with the pipeline construction drawings; no arbitrary changes are permitted. 9) During pipeline welding, strict control must be exercised over the misalignment of the weld joints; any misalignment detected requires rework. After welding each weld, promptly check (using an endoscope) whether the weld inside the tube is smooth. 10) Before flange connection, check that the valve passage, flange surfaces, and gaskets are free of defects, and ensure they have been cleaned and degreased on-site using solvents such as acetone or carbon tetrachloride to an acceptable standard. 11) For flange static bonding, it is necessary to check that the connecting materials are of suitable quality and properly tightened. III. Three Inspections and Four Determinations: Conduct inspections of the oxygen pipelines in strict accordance with the various confirmation forms for the three inspections and four determinations; submit the completed confirmation forms to the Production Department for archiving. IV. Hydrostatic Testing: The hydrostatic testing plan must be strictly followed, and those involved should have received training on this plan. Special attention should be paid to the following aspects: 1. Oil-free deionized water should be used for the hydrostatic testing of oxygen pipelines, and the water pumps must be oil-free. 2. Before pressure testing, valves, fittings, etc. that should not be tested together with the pipeline should be removed from it and temporary bypasses installed. Equipment that is not suitable for testing should be isolated using blind flanges, and all openings in the pipes must be sealed. 3. An exhaust valve should be installed at the highest point of the pipeline, while a drain valve should be installed at the lowest point. 4. The pressure gauge used for pressure testing is properly calibrated and has an appropriate range: 1.5–2 times the design pressure. 5. The pressure increase process should be slow; the rate of pressure rise needs to be controlled. Once the test pressure is reached, the welds, flanges, etc. should be inspected, and only if the test is successful can the water be discharged. V. Pipeline Purging: The purging plan must be strictly followed, and those involved should have received training on this plan. Special attention should be paid to the following aspects: 1. Steam purging: The steam used for purging should be clean, superheated steam. 2. Air (or nitrogen) purging: The air used for purging should be oil-free air (clean air free of oil and dust at the outlet of the air separation molecular sieve). 3. Before carrying out purging, check whether the pipeline supports and hangers are secure. All instrument ports, pressure sampling points, and instrument boxes on the oxygen pipeline must be purged simultaneously; process engineers should work in conjunction with instrument technicians to ensure thorough purging of the pipeline. The purging pressure should be controlled according to the design pressure of the pipeline to prevent overpressure and similar issues. VI. Supervision of chemical cleaning (including cleaning, degreasing, and passivation): Professional cleaning companies specialized in oxygen pipelines should be hired for chemical cleaning. The cleaning plan must be discussed and explained in detail with the supervisor, the construction party, and the professional cleaning company. All personnel involved must receive training on this plan. Special attention should be paid to the following aspects: 1. The cleaning process must be carried out step by step, with each step being verified as successful before moving on to the next one. 2. Flow meters, control valves, pressure gauges, temperature sensing elements, check valves, level gauges, and other components sensitive to cleaning fluids that are not compatible with the pipeline material shall be temporarily removed as required, and a removal confirmation form shall be filled out. 3. Install prominent process flow signs at the cleaning site, as well as clear cleaning indicators. 4. Strictly implement the methods and plans for chemical cleaning analysis and testing. 5. During cleaning, the person in charge of the instruments must also carry out degreasing and cleaning tasks on all instrument points, pressure tapping points, and pressure tapping pipes in the pipelines simultaneously. VII. Pipeline Drying: The drying plan must be strictly followed, and those involved should have received training on this plan. After the chemical cleaning of the pipelines is completed, the lines must be thoroughly purged and dried. Nitrogen or air (clean air free of oil and dust from the molecular sieve outlet of air separation units) should be used for this purpose, and the purging process must be carried out in strict accordance with the specified drying procedures. During purging, open the valves at all instrument points and pressure tapping points to ensure there are no dead zones in the pipeline during purging. VIII. Reinstallation of valves, fittings, and instruments: After the pipes have been chemically cleaned and dried, all temporary connections are removed, and the valves, fittings, and instruments are reinstalled. Before reinstallation, degreasing and drying must be completed successfully before installation can take place. IX. Airtightness: The airtightness plan must be strictly followed, and those involved should receive training on this plan*. Special attention should be paid to the following aspects: 1. Prepare a special confirmation form for airtightness; the airtightness testing process must be carried out strictly in accordance with this form, with thorough inspections of the flanges, welds, instrument connections, etc., as listed in the form. 2. The instrument shop should also carry out airtightness checks simultaneously, checking the instrument points on the pipelines and the instrument cabinets, and fill out confirmation forms for record-keeping. X. Inspection of static electricity grounding: Before putting the oxygen pipeline into use, a thorough inspection of its static electricity grounding system must be carried out; a detailed confirmation sheet should be prepared and filed for record-keeping. XI. Oxygen passivation: Passivation is carried out using oxygen introduced through the oxygen pipelines; the passivation plan must be strictly followed to ensure the required passivation time and thus achieve optimal passivation results. XII. Oxygen Introduction via Pipelines 1. Strictly follow the oxygen introduction plan and emergency response plans; those involved must receive training on these plans. 2. Oxygen supply through the oxygen pipeline can proceed only after signing to confirm all relevant conditions. 3. Thoroughly carry out all preparatory work for the accident plan before introducing oxygen.