Why do stainless steel flanges sometimes rust?

Stainless steel flanges also rust under certain conditions, mainly due to a variety of factors that destroy the extremely thin and strong chromium-rich oxide film (protective film) formed on their surface. The following are some of the main reasons for stainless steel flange rust:

Surface contamination:

The oil, dust, acid, alkali, salt, etc. attached to the surface of the stainless steel flange will be converted into corrosive media under certain conditions, and chemical corrosion will occur with some parts of the flange, resulting in rust.

Surface scratches:

Various scratches will damage the passivation film on the surface of the stainless steel flange, reduce its protective ability, and make the flange more likely to react with chemical media, resulting in chemical corrosion and rust.

Incomplete cleaning:

If the cleaning after pickling passivation is not clean, it will lead to residual liquid retention and direct corrosion of stainless steel flange.

Carbon steel pollution:

Contact with carbon steel parts may cause scratches and corrosive media formed by galvanic reaction, resulting in galvanic corrosion.

Welding effects:

Physical defects (such as edge biting, pores, cracks, etc.) and chemical defects (such as coarse crystals, chromium-poor grain boundaries, segregation, etc.) in the welding zone will form a galvanic battery with the corrosive medium, resulting in electrochemical corrosion.

Material defects:

The chemical defects of stainless steel flange materials (such as uneven composition, containing S, P impurities, etc.) and surface physical defects (such as loose, sand holes, cracks, etc.) are conducive to the formation of galvanic cells and electrochemical corrosion of corrosive media.

Electrochemical corrosion:

If the surface of the stainless steel flange contains dust or alien metal particles containing other metal elements, in the humid air, the condensed water between the attachment and the stainless steel will connect the two into a microbattery, causing an electrochemical reaction and destroying the protective film.

Organic juice corrosion:

The organic juice attached to the surface of the stainless steel flange (such as melons and vegetables, noodle soup, sputum, etc.) will form an organic acid in the presence of water and oxygen and corrode the metal surface for a long time.

Corrosive gases and liquids:

In an environment with high chloride ion content and serious air pollution, or in an environment containing acids, alkalis and salts, stainless steel flanges are prone to corrosion. For example, due to the oxidation of seawater in seaside areas, stainless steel flanges are easy to form rust.

Improper maintenance and maintenance:

If the stainless steel flange is not properly maintained and maintained during use, such as not timely removal of dirt and corrosive media on the surface, or mechanical damage during use, it may lead to rust.

In order to ensure the anti-rust performance of stainless steel flanges, it is necessary to pay attention to maintenance and maintenance during use to avoid damage caused by the above factors. At the same time, when selecting stainless steel flanges, the appropriate materials and specifications should also be selected according to the specific use environment and requirements.