Essay About Importance Of Scc And Influence Of Key Controlling Variables

Explain the Importance of Scc and the Influence of Key Controlling Variables
KEY LEARNING OBJECTIVESGive a short concise explanation for any three of terms in consult task sheet.Explain the importance of SCC and the influence of key controlling variables.Stress corrosion cracking (SCC) is the progressive cracking, which is made up by the interaction between tensile stress and corrosive environment. In fact, this is a dangerous form of corrosion because of its insidiously damaged inside the material. This impairment is not an obviously visible inspection and it can bring about the mechanical fast displacement and destructive failure of components and structures.There are several accidents that are resulted from stress corrosion cracking such as the explosion of boilers, the wrecking of power stations and oil refineries, or the separation of high-pressure gas transmission pipes. Therefore, it is important to understand and minimize the risk of SCC by avoiding mechanical tensile stress concentration or selecting appropriate materials.[pic 1]It is proven that the occurrence of SCC depends on the simultaneous presence of three conditions including: a susceptible material, a critical environment and some component of tensile stress.Although SCC is not an unavoidable progress and we can detect the particular situation in which the combinations of metal and environment are subject to the problem, however, as the demand of using materials more efficiently by increasing working stresses and cheaper materials, there is a wide range of such combinations. The table below shows some combinations of metal and environment that SCC is most commonly associated with.MaterialEnvironmentConcentrationTemperatureCarbon steelHydroxidesNitratesCarbonate/BicarbonateLiquid ammoniaCO/ CO2/ H2OAerated waterHighModerateLow—HighModerateModerateLowLowVery highStainless steelThiosulphate or polythionateLowLowCopper alloys (excluding Cu-Ni)N2O4 high ammoniacal solutions and other nitrogenous-LowLow Aluminum alloysTitanium alloysChloridesChloridesLowHighLowLow