The main steps of chemical cleaning

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The main steps of chemical pipeline cleaning: Pre-washing with clean water – Acid washing to remove rust – Water rinsing – Degreasing – Passivation pre-coating – Water rinsing – Restoration to the original state – Inspection and acceptance. 1. Pre-washing: The purpose of pre-washing is to rinse away any residual mechanical impurities and other contaminants inside the pipeline. (2) It is to check whether the cleaning system is unobstructed. Continue rinsing in a cycle 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 scale, welding oxides, and other impurities from newly installed 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 drain 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, and then an appropriate amount of surfactants and other additives are added to perform cyclic cleaning of the pipes; the process continues until no oil residues remain, as determined by visual inspection or by using test strips. 5. Passivation: The purpose of passivation is to take anti-corrosion measures to prevent secondary rust formation 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 specific 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 weld 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 coupon measurement: The average metal corrosion rate is less than 6 g/m2·h for carbon steel ； Stainless steel 4 g/m2.h.