What are the general steps for pre-coating circulating cooling water?

Currently, pre-coating in circulating water systems is mainly applied to carbon steel, with zinc salts and polyphosphates being the chemicals used. The addition concentrations of the two are 1:4. Our addition procedure is as follows: zinc salts are added first, followed by polyphosphates after half an hour; after another hour, pH, total phosphorus, and calcium hardness are measured. Ensure the pH is controlled at 6-7; once stable, hang the test strips. During the pre-coating process, acid 6-7 must be added in a timely manner; the pre-coating time is generally sufficient at 24 hours. Additionally, I’ve always had a question: are there any good pre-coating agents for heat exchangers made of stainless steel and copper? I hope fellow sailors can tell me.

1.1 Purpose of cleaning and pre-coating: To clean the newly installed circulating water system, removing grease from the inside of the new pipes as well as any rust that formed during the system’s construction； After cleaning is complete, a pre-coating is applied to the entire system, forming a protective layer on the pipes and heat exchangers to prevent corrosion and lay the foundation for the proper operation of the system. 1.2 Cleaning steps: A. Check that all mechanical equipment is functioning properly, and remove any dirt, debris, and other waste from the collection tank. B. Install a filter screen with about 18 mesh at the water inlet (before the circulation pump) to prevent wood and plastic debris from entering the pipes. C. Fill the collection tank with clean water and circulate it to flush out as much sediment as possible from the system pipes, then empty and clean the bottom of the tank. D. Inject clean water, hang in the bypass old test piece, add a pretreatment cleaner at a concentration of 1000 ppm (based on the minimum retained water volume), and circulate for about 48 hours; stop the cleaning process once the effect before and after cleaning of the test piece is observed. E. Since a large amount of foam is generated during cleaning, the defoamer must be added in separate batches, at a dosage of approximately 100 kg. F. After cleaning is complete, replace the water in the system until the turbidity of the water drops to 20PPM. Approximately 48 hours of displacement. 1.3 Pre-coating step: A. After completion of the displacement, add a pretreatment pre-coating agent at 1000 ppm (based on the minimum retained water amount), and place a new test piece in the bypass. B. Adjust the pH to 6-7, maintain this dosage, and run the cycle for over 48 hours to carry out pre-coating; due to losses caused by splashing, the chemical must be replenished to the recommended amount. (The system can now operate under load.) ) C. Clean the filter screen when necessary. D. Inspect the bypass test piece; once a colored halo appears in the light, proceed with the pre-coating process ； When the dosage is gradually restored to the normal controlled level through replacement, 1.3 Pre-coating step: A. After completion of the replacement process, add a pretreatment pre-coating agent at a concentration of 1000 ppm (based on the minimum retained water amount), and place it in a new test piece in the bypass system. B. Adjust the pH to 6-7, maintain this dosage, and run the cycle for over 48 hours to carry out pre-coating; due to losses caused by splashing, the chemical must be replenished to the recommended amount. (The system can now operate under load.) ) C. Clean the filter screen when necessary. D. Inspect the bypass test piece; once a colored halo appears in the light, proceed with the pre-coating process ； Once the dosage is gradually restored to the normal control level through replacement (total phosphorus at 2-8 ppm), routine maintenance and operation management are initiated. 1.4 Statistics on chemicals used for cleaning and pre-coating: (based on a minimum water volume of 1500 tons) 1.4 Statistics on chemicals used for cleaning and pre-coating: (based on a minimum water volume of ** tons) 1. Pretreatment cleaner – Amount to be added: **m3×1000ppm÷1000 = **kg; Method of addition: added in one go to the cooling tank. 2. High-efficiency defoamer – The amount required for the cooling water system is approximately 100 kg; Method of addition: added in several batches to the cooling tank to eliminate foam. 3. Pretreatment pre-coating agent – Amount to be added: **m3×1000ppm÷1000 = **kg; Method of addition: added in one go to the cooling tank

The pre-coating effect and the location where the test pieces are placed are both very important!