Point corrosion test, point corrosion, also known as small hole corrosion, is a form of corrosion, which is concentrated in a small range of metal surface and penetrates into metal or even perforation. Self-passivating metals, such as stainless steel, aluminum and aluminum alloys, often undergo pitting corrosion in chloride-containing media. Pitting corrosion also occurs in carbon steel in many chloride-containing media. The main characteristics of pitting corrosion are three aspects as follows: (1) pitting is mostly born on metal or metal surface with passivating film on the surface (such as tin, copper and nickel on the surface of carbon steel). When some points on these membranes are destroyed, the metal matrix and the undamaged area under the damaged area are activated - passivation corrosion battery, the passivation surface is the cathode and the area is much larger than the activated area, and the corrosion develops into the small hole in the depth. (2) Pitting occurs in a medium containing special ions, such as stainless steel is particularly sensitive to halogen ions, and the sequence of action is Cl-> Br-> I-. (3) pitting usually occurs above a certain critical potential, called a pitting potential or a breakdown potential, and stops below a potential, and this potential is called a protective potential or a re passivation potential. When the potential is larger than the pitting potential, pitting occurs quickly and develops. The pitting corrosion that has occurred between the pitting potential and the protective potential continues to develop, but does not produce a new etching hole. The pitting corrosion does not occur when the potential is below the protective potential, that is, no new pitting is produced, and some of the holes will be passivate no longer. Point corrosion test standard and method test method test standard stainless steel pitting potential measurement method ASTM G48 method A stainless steel trichloride corrosion test method GB/T 17897 stainless steel corrosion test method for iron chloride JIS G 0578-2000 point corrosion test sample requirements for stainless steel pitting potential measurement method sample Requirements: There are two parallel planes, and one of them has an area of at least 1cm2, 3PCS. Sample requirements for spot corrosion test of stainless steel ferric chloride: (30-40) mm * 20MM * (1.5-5) mm