Chemical cleaning of storage and transportation systems

In my opinion, it is necessary to clean oil pipelines and storage tanks. I would appreciate it if experts could provide relevant regulations or actual cases

I just found some information; I hope it will be useful to you. In the past, it was believed that newly installed chemical processing equipment did not require chemical cleaning before being put into operation. However, practice has shown that such cleaning is essential for improving production efficiency and preventing dirt from affecting production. Therefore, before putting newly installed chemical equipment into operation, pre-commissioning cleaning is carried out. The chemical production process involves various chemical raw materials and the use of catalysts. The purity requirements for certain raw materials and catalysts are extremely high; therefore, high standards are imposed on the cleanliness of the equipment and pipelines used in the production process. The presence of any impurities can lead to catalyst poisoning, the occurrence of side reactions, and even the disruption of the entire manufacturing process. Furthermore, some of the equipment and accessories in the device require high precision or are highly sensitive to contaminants; as a result, the presence of any mechanical contaminants can very likely damage the quality of these precision components and affect normal production. During the manufacturing, transportation, storage, and installation of the equipment and pipelines for any new installation, dirt such as rolling scales, oil sludge, welding slag, surface residues, and various oxides inevitably forms. Therefore, it is necessary to clean these installations before they are put into operation in order to remove all such contaminants and bring them to the required level of cleanliness, thus creating favorable conditions for normal production. 2. Preparation before cleaning: Before cleaning, components in the equipment or device to be cleaned that are susceptible to damage from the cleaning solution, such as control valves and flow meters, should be removed. Additionally, the filter elements (nets) and the valve elements of check valves must also be taken out. Temporary short pipes, bypasses, or blind flanges are also used to ensure that no leaks occur during the cleaning process, that other components are not damaged, and that the equipment being cleaned is separated from equipment and pipelines that are not being cleaned. And prepare the required engineering materials such as water, electricity, steam, nitrogen, and air; the nitrogen to be used must have a purity of over 99%, be dry and oil-free, with its pressure maintained at 0.2–0.6 MPa. 3. Cleaning procedures and process conditions (1) Cleaning method: Depending on the specific conditions of the equipment, either immersion cyclic cleaning or spray cleaning can be used. When using a soaking cycle for cleaning, a circulation process with liquid inlet at a low point and high point for ammonia return can be employed. Vent holes are also provided at the high points to prevent air blockages that could prevent the cleaning solution from filling the system. When using spray cleaning, a process with liquid inlet at the high point and return flow at the low point can be adopted. The nitrogen pipelines used in both processes can be installed at high points, with low-point drain points provided to remove any residual liquid. (2) Cleaning procedures and chemicals used: The general cleaning process includes system water pressure leak testing (water flushing), degreasing, water flushing, acid washing, rinsing, washing out, neutralization and passivation, followed by inspection and manual treatment. The following explains each process. The purpose of hydraulic leak testing (water flushing) is to check for leaks in temporary systems, while simultaneously removing dust, sediment, detached metal oxides, slag, and other loose contaminants that can be easily removed from the system. When testing for leaks, water should first be injected at a high point and discharged at a low point, in order to remove debris and maintain balance between inflow and outflow. The flushing flow rate is generally greater than 0.15 m/s, and it can be switched back and forth if necessary. Rinse until the effluent appears transparent to the naked eye with no particles visible. Next, fill the system with water, close the outlet valve, and increase the pressure to 0.4–1.0 MPa. Check for leaks at all welds, valves, flanges, short pipes, and other connections, and repair any leaks found. Once everything is satisfactory, drain the water used for flushing from the system, then fill it with hot water heated to 60–70°C. Finally, inspect the system by hand to ensure there are no dead corners, air blocks that could cause flow interruptions, or any other issues. The purpose of degreasing and cleaning is to remove oils such as machine oil, graphite grease, oil coatings, and rust-inhibiting oils from the system, in order to ensure uniform pickling. The formula for a degreasing cleaner suitable for materials such as carbon steel and stainless steel is: 0.5%–2.5% sodium hydroxide ； Soda ash 0.5%～2.5% ； Sodium phosphate 0.5%～2.5% ； Water glass (Na2SiO3) 0.5%～2.5% ； Surfactant: 0.05%–1.0%. The surfactants can be wetting agents such as JFC, polyether F68, sodium alkylbenzene sulfonate, or emulsifiers such as OP-10. The degreasing cleaner formula suitable for non-ferrous metals such as aluminum is: trisodium phosphate at 0.5%–2.0% ； Sodium silicate 0.5%～2.0% ； Sodium tripolyphosphate 0.5%～2.0% ； Surfactant: 0.05%–1.0%. The procedure involves draining the rinsing water from the system, filling it with preheated water and circulating it for heating, then adding a degreasing cleaning solution and maintaining the temperature at 80°C ± 5°C. Check the alkalinity, oil content, and temperature 1–2 times every 3 minutes. Degreasing can be completed once the alkalinity and oil content of the system degreasing solution are roughly in balance, and all dirt on the monitoring section has been removed; thereafter, nitrogen is used to flush out the degreased liquid. The purpose of washing after degreasing is to remove the residual alkaline cleaning agents in the system, and to dislodge any remaining impurities from the surface so that they can be carried away. After the degreasing liquid is forced out using nitrogen, warm water is promptly injected for rinsing, and the pH value and turbidity are monitored every 10 minutes until the system reaches a neutral or slightly alkaline condition. The water rinsing can be stopped once the pH value stabilizes and the turbidity meets the required standards; generally, this rinsing process lasts around 3 to 5 hours. The purpose of pickling is to use a chemical reaction between acid and metal oxides to convert them into soluble substances, thereby removing them. The formula for the pickling cleaning solution suitable for carbon steel is: (9) 6%–10% hydrochloric acid, and 0.2%–0.25% of the corrosion inhibitor Lan—826. (b) Hydrochloric acid 6%～10%, hydrofluoric acid 0.2%～1%, corrosion inhibitor: Lan—826 0.25%～0.3%. The formula for the pickling cleaning solution suitable for stainless steel and carbon steel–stainless steel composite materials is: (a) 5%～1.0% nitric acid, 0.5%～10% hydrofluoric acid, and 0.25%～0.30% corrosion inhibitor Lan-826 ； (b) Hydrofluoric acid 1%～2%, corrosion inhibitor Lan—826 0.20%～0.25% ； (c) Citric acid 2%–3%, ammonia water (to adjust pH to 3.5–4.0), corrosion inhibitor Lan—826 0.1%–0.2%. The pickling method involves using nitrogen to remove the rinsing water, then pumping the prepared pickling solution into the system. When cleaning fluid returns, evacuation and drainage checks are used to verify that the system is filled with the pickling solution; once this is confirmed, the pump is used for cyclic cleaning, with the direction of flow being changed periodically. During the circulation process, sewage discharge and venting are carried out at regular intervals to prevent air blockages and clogging of the drain lines, which could affect the cleaning efficiency. Check the acid concentration and pH value 1–2 times every 30 minutes, check the concentrations of iron ions and copper ions once, and monitor the corrosion rate at all times. The acid cleaning process is complete when the concentration of the cleaning solution stops decreasing, the concentration of metal ions remains essentially stable, and the fouling in the monitored section has been completely removed, revealing the true color of the metal. The acyl washing process takes about 4 to 8 hours. Rinsing with water after pickling is intended to remove residual pickling solution and solid particles that have fallen out of the system, to facilitate rinsing and passivation. The method involves using nitrogen to purge the pickling solution, and performing an open-circuit cleaning of the entire system with large amounts of water. The various drain valves of the system are rotated continuously to remove debris and residual liquids accumulated inside the short tubes. During the flushing process, the pH value is measured every 10 mm, and flushing is stopped once the pH value approaches neutrality. The purpose of rinsing is to use ammonium citrate to chelate the iron ions remaining in the system and remove the floating rust formed during water washing, thereby reducing the total concentration of iron ions in the system to ensure effective passivation later on. The rinse solution formula is: 0.2%–0.5% citric acid, adjusted to pH 3.5–4.0 with ammonia water, and 0.1%–0.2% of the corrosion inhibitor Lan-826. Pump this rinsing solution into the system, maintain the rinsing temperature at 80°C ± 5°C, and control the pH at 3.5–4.0. Check the pH value and temperature every lmin. The concentration of the rinsing solution and the iron ion concentration are measured every 20 minutes. The rinsing process can be terminated once the concentration of the rinsing solution and the total iron ions reach equilibrium; the rinsing time is approximately 2–3 hours. The purpose of the neutralization and passivation steps is to remove any residual acid, while passivation serves to prevent the metal surface, which is in an activated state after acid cleaning, from oxidizing again and forming secondary rust. The passivation solution formula is: 1%–2% sodium nitrite, 0.5%–1.0% soda ash; ammonia water is used to adjust the pH value. After rinsing, if the iron ion concentration in the solution is less than 500 mg/kg, the pH can be adjusted to 9–10 using ammonia water, followed by the addition of a passivation solution for passivation treatment. If the iron ion content is greater than 500 mg/kg, the rinsing solution should be replaced so that the iron ion content in the solution is less than 50 mg/kg, after which ammonia and a passivation solution should be added. The passivation temperature should be maintained between 40 and 60°C. During the passivation process, it is necessary to continuously vent air from high points and drain liquid from low points in order to eliminate air blocks and avoid dead zones, thus ensuring effective passivation. During the passivation process, the pH value and temperature are measured every 30 mm. The passivation time is generally 4 to 6 hours. The purpose of the manual processing step is to conduct a final inspection of the equipment after cleaning, and to carry out manual repairs in those areas where local passivation has been damaged and rust has formed.

Bro Bin, I’m here to help you out, and at the same time I want to learn from you*.