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Acid washing plan for the pipeline of the compressor unit in the methane gas liquefaction plant I. Overview This project involves a 2×50×104/m3/D methane gas liquefaction plant for the XX Fertilizer Project of XX Group; it was designed by Beijing Huafu Engineering Co., Ltd. and installed by the Tukou Project Department of China National Chemical Engineering Corporation No. 4 Construction Co., Ltd. The project includes a total of six reciprocating compressor units and two mixed refrigerant compressor units. The lubrication oil stations associated with these eight compressors supply oil to the units via stainless steel pipelines. To ensure the quality of the oil supplied to the compressor unit, it is necessary to keep the pipes clean. In accordance with the design specifications and construction standards, the oil supply pipes of the compressor unit must be acid-washed before the unit is put into operation; only after the acid-washing process is completed successfully can the pipes be reinstalled. According to the requirements of Quality Work Contact Sheet No. “HNRO-143” issued by the Petrochemical Quality Supervision Station: “Oil pipelines fabricated and installed on-site shall undergo acid washing and passivation treatment.” ； If the pipes supplied with the equipment have been pickled prior to leaving the factory, pickling may be omitted after the pickling effect is confirmed by all relevant parties. ” The carbon steel pipes that came with the compressor unit were not treated in any way. At the request of the client and due to our strict requirements regarding installation quality, it was decided to carry out acid washing on these pipes to ensure optimal installation quality. During construction, removable flanges should be installed based on the conditions on site. For sections of pipelines that are long and have many bends, the pipelines should be numbered during installation and recorded, with the numbers also marked on the flanges. For the acid cleaning of oil pipelines in this project, both tank immersion and pouring methods are used, while carbon steel pipelines are treated using a circulating acid cleaning method. II. Basis for Preparation 1. Code for Construction and Acceptance of Industrial Metal Piping Projects GB50235 2. Code for Construction and Acceptance of Piping Projects for Toxic and Flammable Media in Petrochemical Industries SH3501 3. Construction Technology Standards for Steel Piping Projects in Petrochemical Industries SHT3507 4. Code for Construction and Acceptance of Chemical Machinery Installation Projects (General Provisions) HGJ203 5. Quality Inspection and Evaluation Standards for Petrochemical Equipment Installation Projects SHJ 514 6. Code for Construction and Acceptance of Chemical Cleaning of Petrochemical Equipment and Piping SH/T 3547 7. Documentation and drawings provided by the equipment manufacturer III. Construction Preparation 3.1 Preparation of Materials and Tools 3.1.1 The temporary connection materials used for chemical pickling should be selected based on the operating pressure and temperature of the pickling system, as well as the corrosivity requirements of the pickling solution. 3.1.2 Containers used to hold pickling solutions should be made of stainless steel or other corrosion-resistant materials. 3.1.3 When cyclic acid washing is used, corrosion-resistant pumps should be selected, and their flow rate and head must meet the requirements of acid washing; the maximum flow rate of the circulation pump is calculated using formula (1). Image.....................(1) Where: Q---maximum circulating flow rate, m3/h. Fmax---the largest cross-sectional area for flow within each circulating component, m3. V---the maximum recommended circulating flow velocity, m/s; a value of 0.2m/s to 0.5m/s is suitable. 3.1.4 The performance parameters of the pickling solution shall comply with the corresponding product standards and remain valid within their shelf life. Medicines and their solutions should be stored in dedicated cabinets, classified, and warning signs should be placed. 3.1.5 Acid cleaning should be carried out using clean water such as industrial water or deionized water. The chloride ion content in the water used for pickling austenitic stainless steel shall not exceed 50 mg/L. 3.2 Operating Conditions 3.2.1 The location for the pickling operation should be determined based on the progress of equipment and pipeline installation as well as the requirements of the construction layout; the roads at the pickling site must be smooth and unobstructed. 3.2.2 The water, steam, gas, and waste discharge pipelines required for the pickling process should be connected. 3.2.3 Necessary communication facilities shall be provided, and lighting shall be available for night operations. 3.2.4 A perimeter fence and warning signs should be installed in the pickling area. 3.2.5 For pipelines and equipment subjected to cyclic acid cleaning, this should be carried out after installation and pressure testing are completed. Process equipment, instruments, and meters that cannot be cleaned with acid should be isolated or protected, and the isolation valves should be labeled. 3.2.6 Pipelines subjected to immersion pickling should be reasonably segmented. 3.2.7 During the pickling process, the power supply for pickling must not be interrupted. 3.3 Site preparation and tool preparation a) On the open area on the south side of the first floor of the compressor building, one pickling tank and one neutralization tank shall be installed, along with two DN25 washing water pipes ； One pickling pump. The selection of the pickling site should be coordinated with the owner and supervisor to facilitate the discharge of the pickling solution ； b) Construct an operating platform on the groove ； c) Check whether the numbering records of the oil pipes match the actual markings, then remove the pipe sections and transport them to the pickling site ； Prepare gauze, plastic sheeting, etc. for sealing, as well as acid-resistant suits, acid-resistant gloves, protective goggles, etc. d) Prepare an appropriate amount of solvent based on the dimensions of the beams. e) For the pickling of stainless steel pipes, prepare the pickling solution and determine the soaking time as shown in the table below: Table 1: Pickling Solution Preparation Table for Stainless Steel Pipes. Solution Name, Concentration (%), Temperature (°C), Time (min): Pickling Solution – Nitric Acid (HN03), 8, Room temperature, 15; Water (H2O), remainder. Neutralizing Solution – Sodium Carbonate (Na2C03), 5, Room temperature, 5–10. f) For the pickling of carbon steel pipes, prepare the pickling solution and determine the circulation time as shown in the table below: Table 2: Pickling Solution Preparation Table for Carbon Steel Pipes. Solution Name, Concentration (%), Temperature (°C), Time (h): Pickling Solution – Hydrochloric Acid (HCL), 7, 40–55, 3; Water (H2O), remainder. Neutralizing Solution – Sodium Carbonate (Na2C03), 5, Room temperature, 2.5. IV. Pipe Pickling Process 4.1 Pickling of Stainless Steel Pipes. The pipe pickling procedure is as follows: pickling → washing with water → neutralization → washing with water → drying → oiling → protective coating → reinstallation. a) Prepare the pickling solution and neutralizing solution in the two tanks according to their respective formula proportions. When preparing the solution, first add the calculated amount of clean water to the tank according to the desired volume, and then gradually add the specified amounts of nitric acid and sodium carbonate. When adding the solvents, it should be done through a funnel, with gentle stirring to prevent any splashing of the solvents. b) The pipes are transported to the pickling site, where the pipe sections are placed in the pickling tank appropriately depending on the size of the tank. They are left to soak for 15 minutes; after that, they are taken out and rinsed with water. Then, they are placed in the neutralization tank to soak for another 10 minutes, after which they are taken out and rinsed with water once more. c) The flushed pipe sections should be blown clean with compressed air to ensure they are free of debris; after drying, the inner walls of the pipes should be oiled, then covered with gauze or plastic sheeting, and promptly transported to their original locations for oil pipeline assembly. d) After pickling and before oiling the pipes, the quality is checked by visual inspection and pH test strips; the inner wall of the pipe should have a metallic luster, and the pH test strip should indicate a neutral or slightly alkaline value to be considered acceptable. 4.2 Pickling of carbon steel pipelines: Construction preparation → Installation of temporary pipelines → Inspection of the pickling process → Water flushing → Pickling → Water flushing → Neutralization treatment → Drying → Removal of temporary pipelines → Restoration of the pipeline system → Handover for operation or sealing for protection. 4.2.1 Based on the pickling process diagram, the cleaning system must meet the following requirements: a) The flow rate of the circulation pump must comply with specifications; the circulation pump and other rotating machinery must operate without any abnormalities. A filter screen with a pore size of less than 5 mm must be installed at the inlet of the circulation pump or at the outlet of the cleaning tank. b) The locations of venting and drain points must be correct; the pickling solution within the pickling pipelines must completely fill the pipes, come into contact with the inner walls of the system, and maintain a sufficient flow rate. c) The layout of temporary pipelines should be reasonable, with supports added as necessary for reinforcement and fixation; d) The elevation and liquid level of the pickling tank must meet the suction height requirements of the circulation pump. 4.2.2 After water flushing, prepare an acid cleaning solution according to the formula for cyclic acid cleaning; the operating temperature and acid cleaning time must meet the specified requirements. During the pickling process, a monitoring tube section or indicator piece should be installed. During the pickling process, the acid concentration, iron ion concentration, or the concentration of other major metals should be measured every 0.5 hours, and the duration of a single pickling session should not exceed 12 hours. 4.2.3 During the pickling process, the liquid flow rate should be controlled at 0.2 m/s to 0.5 m/s, and the fluid pressure should not exceed the design pressure. 4.2.4 The pickling process is completed after one hour of recycling once the iron ions in the pickling solution have stabilized and the acid concentration has stabilized; thereafter, the monitoring section or indicator strip is removed, weighed, and the corrosion rate is calculated in accordance with the provisions of Appendix D of the specifications. 4.2.5 After pickling is completed, the pickling solution should be neutralized to meet the specified standards before being discharged. After the pickling solution has been completely drained, clean water is poured in to flush the pipes with water until the pH level reaches a weakly acidic value of 4-4.5. 4.2.6 After the water flushing is complete, an alkaline substance is added to neutralize the acidity; the pump is then started to circulate the fluid, and a sample taken at the end of the circulation loop should show a pH value of 8-9.5. 4.2.7 The fluid can be discharged once neutralization is achieved. Blow the pipeline until all residual liquid is removed. Purging should be carried out using clean compressed air or industrial nitrogen that has been degreased and dehydrated. 4.2.8 Remove temporary facilities, reinstall them, and inspect to confirm. 4.2.9 After reset, it should be sealed promptly; when protected with nitrogen gas, the pressure of the nitrogen gas should be between 0.07 MPa and 0.1 MPa. V. Quality assurance measures 5.1 The surface of the pipes to be cleaned must be clean, free from surface rust, and without signs of over-washing that result in the formation of large metal crystals; moreover, a complete passivation layer must be present. 5.2 The quality of the passivation film on carbon steel can be tested using an acidic copper sulfate drop test; the testing method is specified in Table F attached to standard SH/T 3547-2011. The time it takes for the drip solution to change from blue to red must be at least 5 seconds to be considered acceptable. 5.3 The quality of the passivation film on austenitic stainless steel can be tested using an acidic potassium ferrocyanide test solution; the testing method is specified in Table F attached to standard SH/T 3547-2011. It is considered satisfactory if no more than 8 small blue dots appear within 10 minutes in the area covered by the drip solution. 5.4 For formulas used for the first time, they should be verified before cleaning and application. The corrosion rate and amount of corrosion in the pipes of the cleaning system shall not exceed the values shown in Table 1. Table 1 Corrosion rate and corrosion volume indicators. Material category: Corrosion rate in g/(m3·h), Corrosion volume in g/m3. Carbon steel: 6, 72; Stainless steel: 2, 24, 5.5. The cleaning quality is considered satisfactory if it meets one of the following requirements: A) Visually, no residue is present on the cleaned metal surface ； B) For those tested by scale removal rate or cleaning efficiency, they shall meet the requirements of Table 2 ； C) When using the spot-check method to determine the cleaning efficiency, for a 100 cm2 cleaned surface, the average number of residual dirt spots with a diameter of 5 mm to 10 mm across three samples should be less than 1; or the average number of residual dirt spots with a diameter of 5 mm or less across three samples should be less than 3, to be considered satisfactory. D) If the volume method is used to determine the scale removal rate, the specific steps are as follows: a) Use distilled water and a measuring cylinder to accurately measure the volumes V1 and V2 of the monitoring tube before and after cleaning ； b) Based on the known inner diameter D of the clean monitoring tube (measured using a vernier caliper), first calculate the volume V0 of the clean monitoring tube using the following formula, and then determine the scale removal rate ； Image Image In the formula: N---descaling rate, % ； V0---Volume of the pure monitoring tube, mL; D---Inner diameter of the pure monitoring tube, mm ； L---Length of the pure monitoring tube, mm ； V1---Volume of the monitoring tube before cleaning, mL ； V2---Volume of the monitoring tube after cleaning, mL ； Table 2: Indicators of scale removal efficiency and cleaning efficiency. Scale type, Scale removal efficiency, Cleaning efficiency: Carbonate scale – 90%, 95%; Sulfate scale and silicate scale – 85%, 80%; Rust scale – 95%, 95%; Oil scale – 95%, 95%; Other types of scale – 85%, 80%. VI. HSE measures: The safety measures for chemical cleaning shall comply with the relevant provisions of the “Safety Technical Regulations for Petrochemical Construction” and the “Guidelines for Chemical Cleaning”. 6.1 Before cleaning, the relevant personnel must learn the safety operating procedures, be familiar with the properties of the cleaning agents used, and know the emergency measures for burns. To avoid accidental operations, personnel involved in chemical cleaning should wear special markings, and those not related to the cleaning process must not stay at the cleaning site. 6.2 Fire-fighting equipment must be available at the cleaning site; fire hoses must remain unobstructed. Signs such as “Be careful”, “No smoking”, “Toxic and dangerous”, and “Do not approach” should be posted on site, and safety awareness campaigns must be carried out. 6.3 The safety inspection of the chemical cleaning system shall meet the following requirements: 6.3.1 Instruments and pipelines that are not related to cleaning shall be isolated ； 6.3.2 Temporarily installed pipes shall be in accordance with the cleaning system diagram and approved by technical personnel ； 6.3.3 Escalators, openings, trench covers, and scaffolding that affect safety must be properly handled ； 6.4 All pipes in the cleaning system shall have reliable welding, and all valves, flanges, and pump gaskets shall be airtight. When cleaning the pump gasket, acid-resistant gasket material should be used. A splash guard should be installed to prevent the cleaning fluid from splashing around. In addition, rubber mats, plastic sheets, clamps, and wire should be available to seal any leaks that may occur. 6.5 A water source should be available near the cleaning pumps, sampling points, and testing stations, connected by rubber hoses for use in flushing in case of leaks in valves or pipes. 6.6 During chemical cleaning, no other work shall be performed on the cleaning system; in particular, open flame operations are strictly prohibited. 6.7 Personnel who have direct contact with chemicals and maintenance workers should wear protective clothing, rubber boots, rubber aprons, rubber gloves, masks, and protective glasses or gas masks to prevent burns caused by splashes of acids and bases. 6.8 The cleaning area should be equipped with 5 L of 0.2% boric acid, 5 L of 2%–3% NaCO3, 5 L of 0.5% NaHCO3, 5 L of 2% ammonia solution, and 5 L of lime water. Medical personnel should be on duty during the cleaning process, and first-aid supplies for acid and alkali burns should also be available. 6.9 Operators shall not wear glass glasses or use glassware. 6.10 When unloading acid, it is strictly prohibited to repair joints and tighten bolts on the upper or lower part of the tank truck. 6.11 When lifting and transporting acid and alkali tanks, as well as preparing acid and alkali solutions, special tools shall be used. When lifting and transporting glass or ceramic tanks, the bottom should not be raised too high off the ground. 6.12 If acid or alkaline solutions spill or leak onto the work area, they should be immediately washed with water or neutralized using a dilute alkaline solution to counteract the acid solution. When opening the lids, caps, or stoppers of containers holding hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, etc. It is strictly prohibited for the bottle mouth to be directed at a person. 6.13 The dilution of concentrated acid shall comply with the following requirements: 1. Special tools should be used to take the acid; it is strictly prohibited to use a rubber hose and mouth to create suction ； 2. When opening the lids or stoppers of acid-containing containers, operators should stand on the upwind side. In the laboratory, operations should be carried out inside a fume hood ； 3. Remove the lid (plug) of the acid-containing container; it is strictly prohibited to use a metal hammer for this purpose. If a wooden hammer is used, do not apply excessive force ； 4. When diluting concentrated acid, it should be added to water slowly while stirring to prevent a rapid increase in temperature. It is strictly prohibited to add water to concentrated acid ； 5. After removing the acid, the lid of the container should be closed tightly, and the container, as well as any utensils and residual acid on the floor, should be rinsed thoroughly with water. 6.14 Acids, bases, and their solutions should be stored in dedicated areas, and contact with organic substances, oxidizers, degreasers, etc. is strictly prohibited. 6.15 Acid and alkali operations should be carried out outdoors or in an outdoor work shed. 6.16 In acid and alkali work areas, a certain amount of dilute acid and dilute alkali solutions should be prepared to enable workers to rinse, soak, and neutralize the areas affected by acid or alkali burns at any time. The on-site treatment methods for acid and alkali burns are as follows: A. Nitric acid 1. If it splashes onto the skin, rinse the area with plenty of clean water ； 2. Improve ventilation to allow the poisoned person to breathe fresh air or oxygen. 3. Take the person to the hospital for treatment. B. Hydrochloric acid: 1. The affected area can be rinsed thoroughly with water, followed by application of a 5% sodium bicarbonate ointment ； 2. Those with acute or chronic poisoning should be taken to the hospital for treatment ； 3. The mouth, eyes, and nose should be rinsed with a 2% sodium bicarbonate solution or normal saline. 5.17 Containers that have held acids or bases must not be left lying around carelessly. Waste liquid should be treated in accordance with the relevant regulations of industrial \"three wastes\" discharge standards. VII. Materials for pickling: 320 kg of nitric acid, 500 kg of hydrochloric acid, 276.52 kg of sodium carbonate, 18 pairs of latex gloves, 18 protective masks, 6 pairs of safety glasses, 1 air compressor, 1 scale, 3 plastic funnels, 2 kg of wire size 8#, 20 meters of rubber hose 11/2”, 26.5 m2 of Q235 steel plates with a thickness of 4 mm, 1 circulation pump, 10 T of clean water, several pieces of clean cotton cloth, and several H-test strips.