The main steps of chemical pipeline cleaning

Thread Content

Clean water pre-washing -- Acid cleaning for rust removal -- Water rinsing -- Degreasing cleaning -- Passivation pre-coating -- Water rinsing -- Restoration to original condition -- Inspection and acceptance. 1. Pre-washing: The purpose of pre-washing is to (1) remove residual mechanical impurities and other contaminants from within the pipes. (2) It is to check whether the cleaning system is unobstructed. Continue to wash in cycles until no impurities flow out and the water is clear. 2. Pickling for rust removal: The purpose of pickling is to remove various types of rust, rolling scales, welding oxides, and other impurities from newly constructed steam pipes. First, hang the corrosive test pieces in the chemical preparation tank. Based on the volume of the pipeline, calculate the amounts of pickling agents, additives, and corrosion inhibitors required. Prepare the corrosion inhibitor as an aqueous solution and introduce it into the system to be cleaned for circulation. Then, inject the acid and additives into the pipeline through the chemical preparation tank to carry out circulating cleaning. After 2 hours, measure the pH value, turbidity, and iron ion content of the cleaning solution every 30 minutes until the values stabilize. 3. Water flushing: After rust removal by pickling, promptly discharge the pickling waste liquid into the wastewater treatment tank for centralized treatment. Then, rinse cyclically with clean water until the pH value approaches neutrality. 4. Degreasing cleaning: The purpose of degreasing cleaning is to remove any residual oil in the pipes. A basic aqueous solution is prepared in the mixing tank, followed by the addition of an appropriate amount of surfactants and other additives to carry out cyclic cleaning of the pipes; this process continues until no oil stains remain, either through visual inspection or by using test strips. 5. Passivation: The purpose of passivation is to take anti-corrosion measures to prevent secondary rust from forming on the metal surface that has been activated following pickling. Polyphosphates and additives are used as passivators; this method is quite common, and the passivation effect (commonly known as phosphating) is also good at room temperature. Prepare the passivation solution in the mixing tank at a certain concentration, pump it into the pipes for cyclic passivation, with the process duration being controlled to over 24 hours. 6. Water flushing: After the pipes have been coated with the passivation film, the passivation solution is drained into the waste liquid tank for disposal, and the pipes are rinsed repeatedly with large amounts of clean water. Finally, the direction of flushing is reversed to wash from top to bottom, thereby removing mechanical impurities such as slag from outside the pipes. Until the water is clear and free of impurities. 7. Restore the original system: Remove and clean the temporary system, then restore the original system. 8. Inspection and acceptance: Inspection of rust removal and passivation effects: Rust removal rate of 99%; a dense passivation film is present, with no secondary rust formation on the surface, and no pitting or over-washing occurs ； Corrosion monitoring test strip measurement: The average metal corrosion rate is less than 6 g/m2·h for carbon steel ； Stainless steel 4 g/m2.h.