When do stainless steel pipe need passivation? Conventionally, when the stainless steel pipe is corroded after the welding process and subjected to strong pollution, it must be passivated. The preferred passivation method is as follows.
In the case of stainless steel pipe sections with straight pipes and without branch pipes and hand-operated stainless steel pipes and fittings, they may be treated on site in the workshop using a passivating paste. The specific method is to weld the welded stainless steel pipes or armored parts. The polishing is done in advance. The polishing tool is a stainless steel polishing brush or a chuck-type page wheel. This can remove the oxides that remain on the surface of the stainless steel pipe and the surrounding oxide, restore the original color of the stainless steel pipe, and then use the brush for the passivation paste. Evenly smear on the surface to be treated, according to the appropriate ambient temperature, to determine the passivation time, usually the ambient temperature is less than 28 ° -35 ° for 1 hour, the ambient temperature of 15 ° -27 ° 2 hours, low It is 3-4 hours at 15°.
After the passivation time is reached, it is not possible to use pure water to flush directly, because the passivation paste is a strong acid, which will not only damage the surrounding construction sites, but more seriously cause the pollution of the water environment. The correct way is to use a clean rag or other tools similar to rags to wipe off the passivation paste first, then rinse with water. And while flushing, use a scouring pad to wipe the passivation point until it is confirmed that there is no residue of the passivation paste, and the weld and the other parts of the stainless steel pipe are bright. Passivated stainless steel pipes and armored parts are measured with a passivation thickness gauge, for example, readings above 60 are considered acceptable. It should be noted that since the passivation paste is a strong acid, it is a truly dangerous product. It must not only be kept by special personnel, but must be handled by the user. The operator must be aware of the requirements for passivation and ventilation when using it. Meet the corresponding passivation conditions.
Stainless steel pipes should also be inspected for quality after passivation. Chemical inspections can destroy the passivation film of stainless steel pipes, so they are usually tested on a sample plate. There are two methods, one of which is copper sulfate titration test, using 8g CuS04 + 500mLH20 +2 ~ 3mLH2S04 solution dropped onto the surface of stainless steel pipe samples to ensure that the wet state, such as precipitation does not appear within 6 minutes is qualified. The second is the titration test of potassium ferricyanide, which can use 2mLHCl+1mLH2S04+1gK3Fe(CN)6+97mLH20 solution to drop on the surface of the stainless steel pipe sample. The quality of the passivation film can be identified by the number of blue spots and the length of time. High and low.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)