Types and definitions of corrosion in the stainless steel pipe

In many industrial applications, stainless steel can provide satisfactory corrosion resistance. According to the experience of use, in addition to mechanical failure, the corrosion of stainless steel mainly manifests in a serious form of corrosion of stainless steel is localized corrosion (i.e., stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue, and crevice corrosion). Failure cases caused by this local corrosion account for almost half of the failure cases. In fact, many failure accidents can be avoided through reasonable material selection.

Stress Corrosion Cracking (SCC): A general term that refers to the mutual failure of stress-bearing alloys due to the expansion of strong cracks in corrosive environments. Stress corrosion cracking has a brittle fracture morphology, but it can also occur in ductile materials. The necessary conditions for stress corrosion cracking to occur are the presence of tensile stress (whether it is residual stress applied stress, or both) and a specific corrosive medium. The formation and expansion of the pattern are roughly perpendicular to the direction of tensile stress. This stress value that causes stress corrosion cracking is much smaller than the stress value required for the material to fracture in the absence of corrosive media. Microscopically, cracks that pass through grains are called transgranular cracks, while cracks that expand along grain boundaries are called intergranular cracks. When stress corrosion cracking expands to its depth (here, on the section of the material that bears the load The stress reaches its fracture stress in air), the material breaks according to normal cracks (in ductile materials, usually through the aggregation of microscopic defects). Therefore, the cross-section of a part that fails due to stress corrosion cracking will contain areas characteristic of stress corrosion cracking as well as "dimple" areas associated with the aggregation of micro defects.

Pitting corrosion: is a localized form of corrosion that results in corrosion.

Intergranular corrosion: The intergranular boundaries are the disorderly interlocking boundaries between grains with different crystallographic orientations. Therefore, they are favorable conditions for the segregation of various solute elements in steel or the precipitation of metal compounds (such as carbides and δ phases). District city. Therefore, it is not surprising that in some corrosive media, the grain boundaries may be corroded first. This type of corrosion is called intergranular corrosion, and most metals and alloys may exhibit intergranular corrosion in certain corrosive media.

Crevice corrosion: It is a form of localized corrosion that may occur in crevices where the solution stagnates or in shielded surfaces. Such gaps can form at metal-to-metal or metal-to-nonmetal joints, such as where rivets, bolts, gaskets, valve seats, loose surface deposits, and marine growth meet.

General corrosion: A term used to describe corrosion that occurs in a relatively even manner over the entire alloy surface. When comprehensive corrosion occurs, the material gradually becomes thinner due to corrosion, or even the material fails due to corrosion. Stainless steel may show general corrosion in strong acids and alkalis. Failure due to general corrosion is less of a concern because it can usually be predicted by a simple immersion test or by reviewing the corrosion literature.