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Passivation purpose and method of stainless steel pipe for water supply

Usually the stainless steel pipe as the water supply pipeline before, in the process there will be a passivation process, its purpose is to protect the formation of chromium oxide coating on the inner wall of stainless steel pipe with smooth surface, so that it can resist high temperature of liquid on the surface of stainless steel may produce intergranular corrosion.
One of the commonly used formulations of passivation treatment is the use of purified water and chemical pure nitric acid to become 8% of the acid solution. Circulation at 49 to 52 degrees centigrade after 60 minutes. 8%, the role of nitric acid is mainly until the action of oxidant. The surface of stainless steel is oxidized to nitric oxide, so that it can achieve the purpose of passivation. The manufacturer is not usually stainless steel passivation, all processors to do. For the passivation water pipe, the stainless steel pipe must be polished both inside and outside, and the inner surface of the pipe must be passivated.
The whole passivation process of stainless steel pipes includes cleaning, passivation and disinfection. The main processes are deionized water circulation pre flushing, alkaline solution cycling cleaning, purified water washing, passivation, purified water washing, discharging and pure steam disinfection.
The first is the purified water flushing, a liquid storage tank and a water pump in advance and passivation of the water supply pipeline into a circulating passage, injecting deionized water at room temperature enough in the liquid storage tank, the use of pumps for circulation, open the drain valve in 15 minutes, while circulating emissions, the best put a meter.
The next is alkali cleaning, prepare sodium hydroxide, chemical reagent and add hot water to make 1% of the lye in advance, then use the pump to do the cycle. The time is no less than 30 minutes, then it will be discharged again.
Next is to rinse, add purified water to the liquid storage tank, start the pump and open the drain valve to discharge, until the electrical resistivity of each outlet is consistent with that of the water in the tank, and the emission time is longer than 30 minutes.
The following is the passivation procedure, can use the purified water and nitrate with chemical pure acid in a concentration of 8%, 60 minutes after the discharge cycle at 49 DEG -52 DEG C; using 3% or 20% hydrofluoric acid, nitric acid and 77% water purification solution, solution temperature control at 25-35 DEG C, cycling 10-20 minutes then discharge, finally through high pressure steam to flush the water supply pipeline to remove the dirt.
The flushing is divided into initial washing and final rinsing. The former is rinsed at room temperature, and the time is more than 5 minutes. The latter requires that the electrical resistivity of import and export ionic water should be consistent.
Source: China Stainless Steel Pipelines Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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