Deep corrosion analysis
Introduction
Stress corrosion cracking (SCBT) is a phenomenon that occurs in some materials, in which the formation of cracks occurs in a corrosive environment when they are subjected to mechanical stress. It can cause unexpected and sudden failure in ductile metals or alloys normally subjected to mechanical stress, especially at elevated temperatures. It is a highly chemically specific process, since for certain alloys a slight exposure to potentially non-aggressive chemical environments is sufficient. The chemical environment that causes ACBT for a given alloy is often one that is only slightly corrosive to the metal. Therefore, metal parts with severe stress corrosion cracking may appear shiny and shiny, while they are full of microscopic cracks. This factor makes it common for ACBT to go unnoticed before failure occurs. It often progresses rapidly and is more common among alloys than pure metals. The specific environment is of crucial importance, and only very small concentrations of certain highly active chemicals are needed to produce catastrophic cracking, often leading to devastating and unexpected failure.[1].
Stresses may be the result of stress overload in the cracked areas, due to stress concentration, or they may be caused by the type of assembly or residual manufacturing stress (as in the case of cold working). Residual stresses can be relieved by annealing or other surface treatments. Unexpected and premature failures of chemical process equipment, for example due to stress corrosion, constitute a serious risk to the safety of personnel, operational facilities and the environment. By reducing the reliability of these types of equipment, these failures also negatively affect productivity and profitability.
Mechanisms
Contenido
La corrosión bajo tensión afecta principalmente a metales y a aleaciones metálicas. Un efecto comparable, también conocido como agrietamiento por tensión ambiental"), también afecta a otros materiales como polímeros, cerámica y vidrio.
Metals
Lower pH and lower applied reduction potential facilitate hydrogen evolution and enrichment during the ACBT process, thus increasing its intensity.[2].
• - Certain austenitic stainless steels and aluminum alloys crack in the presence of chlorides. This limits the usefulness of austenitic stainless steel to contain water with a chloride content greater than a few parts per million at temperatures above 50 degrees Celsius (122 °F).