Cleaning, Passivation and Disinfection of Purified Water Pipes

1. The treatment (cleaning, passivation, disinfection) of the purified water system storage tank and stainless steel pipes is divided into purified water circulation pre-rinsing → lye circulation cleaning → purified water rinsing → passivation → re-rinsing with purified water → discharge → disinfection.

2. During the cleaning, passivation and disinfection of the pipes, the ultraviolet lamp, the filter medium of the sterile filter and the breather shall not be installed.

① Purified water circulation pre-rinsing:

‐ Start the water production system. When about 500L of purified water is injected into the purified water tank, start the purified water pump for circulation. After 15 minutes, open the water valves at each usage point, circulate and discharge at the same time. When the purified water in the purified water tank drops to the low level, close the purified water pump, fully open the emptying valve of the purified water tank and the valves at each usage point, drain all the accumulated water in the purified water tank and the pipes, and then close all the water valves on the purified water tank and the purified water pipes.

② Lye cleaning:

‐ Start the water production system to produce purified water (the produced purified water shall not be injected into the purified water tank). Inject about 250L of purified water into the cleaning tank, add 2.5 kg of NaOH (chemical pure), stir evenly to make a 1% NaOH solution, and transport it to the purified water storage tank with the cleaning pump. Repeat the preparation of 1% NaOH solution according to the above preparation method, and then transport it to the purified water storage tank through the cleaning pump. At this time, the volume of 1% NaOH cleaning solution in the purified water storage tank shall be 500L.

‐ Turn on the purified water pump to circulate the 1% NaOH cleaning solution in the purified water tank and the delivery pipeline for 2 hours. Open the valves at each usage point on the purified water pipeline and discharge for about 3 minutes to clean the valve parts. Fully open the emptying valve of the purified water tank and all the valves at each usage point to drain all the cleaning solution in the purified water tank and the pipes.

‐ After the cleaning solution is completely discharged, close the purified water tank and the valves at each water usage point, and prepare for purified water rinsing.

③ Purified water rinsing:

‐Start the water production system, inject the secondary reverse osmosis fresh water into both the cleaning tank for preparing lye and the purified water tank at the same time, and transport the purified water in the cleaning tank to the purified water tank through the cleaning pump to clean the cleaning tank.

‐When the purified water in the purified water tank reaches the middle level, start the purified water pump to circulate and rinse the storage tank and pipes for 30 minutes. Then open all the water valves at each usage point of the purified water delivery pipeline simultaneously and keep them half-open to rinse the valve parts with purified water for 3 minutes. Close the purified water pump, open the blowdown valve of the purified water storage tank and the valves at each usage point for emptying.

‐After emptying, continue to prepare purified water and perform circulating rinsing and discharge of the storage tank and pipes according to the above rinsing method until the pH and conductivity of the influent water of the purified water storage tank are consistent with those of the purified water storage tank, as well as the total supply and total return pH and conductivity.

‐After rinsing, fully open the purified water tank and all the valves at each usage point for emptying. After emptying, close all the usage valves of the purified water tank and pipes, and prepare for passivation.

④ Passivation:

‐Prepare a nitric acid preparation tank and a water pump, connect the pipeline to the spray ball at the top of the purified water tank, and connect the secondary reverse osmosis fresh water to the acid preparation tank.

‐Start the water production system to produce purified water into the acid preparation tank (strictly prohibit purified water from entering the purified water tank). Add nitric acid (chemical pure) to prepare 500L of 8% acid solution, start the water pump, and transport all the acid solution to the purified water tank.

‐Turn on the purified water pump to circulate the 8% acid solution in the purified water tank and the delivery pipeline for 2 hours, and passivate the inner surface of the purified water tank with the nitric acid solution through the action of the spray ball at the top of the purified water tank.

‐Within the 2-hour circulation of the acid solution in the purified water pipeline, half-open the valves at each usage point on the purified water pipeline and discharge for about 10 minutes to passivate the valve parts (when passivating the valve parts, use a container to hold the nitric acid solution, and then pour it back into the acid preparation tank and transport it to the purified water tank in a timely manner).

‐After the circulation time is over, close the purified water pump, fully open the emptying valve of the purified water tank and all the valves at each usage point to drain all the passivation solution in the purified water tank and the pipes.

‐Start the water production system to produce purified water into the purified water tank to about the middle level. Turn on the purified water pump to circulate and rinse the storage tank and pipes for 30 minutes. Then open all the water valves at each usage point of the purified water delivery pipeline simultaneously and keep them half-open to rinse the valve parts with purified water for 3 minutes. Close the purified water pump, open the blowdown valve of the purified water storage tank and the valves at each usage point for emptying.

‐After emptying, continue to prepare purified water and perform circulating rinsing and discharge of the storage tank and pipes according to the above rinsing method until the pH and conductivity of the influent water of the purified water storage tank are consistent with those of the purified water storage tank, as well as the total supply and total return pH and conductivity.

‐After rinsing, fully open the purified water tank and all the valves at each usage point for emptying. After draining the accumulated water in the purified water tank and pipes, close all the valves of the purified water tank and pipes, and prepare for disinfection.

⑤ Disinfection:

‐Preparation of 3% hydrogen peroxide: Start the water production system to produce purified water into the cleaning tank (strictly prohibit entering the purified water tank). Inject 250L of purified water, add 50L of 30% hydrogen peroxide into the cleaning tank to prepare a 6% hydrogen peroxide solution, and transport it to the purified water storage tank through the cleaning pump. After transportation, inject 200L of purified water into the cleaning tank again and transport it to the purified water storage tank, so that the concentration of hydrogen peroxide in the purified water storage tank is 3% and the volume is 500L.

‐Disinfection: Turn on the purified water pump to circulate the 3% hydrogen peroxide disinfectant in the purified water tank and pipes for 30 minutes, and perform circulating disinfection on the inner wall of the storage tank through the spray ball.

‐Discharge of disinfectant: After the circulation of 3% hydrogen peroxide, open the valves at each usage point of purified water and keep them half-open to disinfect the valve parts with the disinfectant until the disinfectant is completely discharged. (If the disinfectant cannot be completely discharged, close the purified water pump and open the blowdown valve of the purified water storage tank to drain the disinfectant completely).

‐Final rinsing with purified water: Start the water production system to prepare purified water into the purified water storage tank to the middle level. Turn on the purified water pump to circulate and rinse the storage tank and pipes for 30 minutes, then open the blowdown valve of the purified water storage tank and all the usage valves for emptying.

‐After emptying, continue to prepare purified water and transport it to the middle level of the purified water storage tank. Perform circulating rinsing and discharge of the storage tank and pipes according to the above rinsing method until the pH and conductivity of the secondary reverse osmosis fresh water, purified water storage tank, total supply and total return meet the standard requirements.