Stress corrosion cracking (SCC) is the unexpected sudden failure of normally ductile metals subjected to a constant tensile stress in a corrosive environment, especially at elevated temperature. This type of corrosion often progresses rapidly. Ductility is the physical property of being capable of sustaining large plastic deformations without fracture (in metals, such as being drawn into a wire). ... Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. ... Corrosion is deterioration of intrinsic properties in a material due to reactions with its environment. ... Corrosion is deterioration of intrinsic properties in a material due to reactions with its environment. ...

The stresses can be the result of the service loads, or can be caused by the type of assembly or residual stresses from fabrication (eg. cold working); the residual stresses can be relieved by annealing. Residual stresses are stresses that remain after the original cause of the stresses has been removed. ... Annealing, in metallurgy and materials science, is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. ...

Certain austenitic stainless steels and aluminium alloys crack in the presence of chlorides, mild steel cracks in the present of alkali (boiler cracking) and copper alloys crack in ammoniacal solutions (season cracking). This limits the usefulness of stainless steel for containing water with higher than few ppm content of chlorides at temperatures above 50 °C. Worse still, high-tensile structural steels crack in an unexpectedly brittle manner in a whole variety of aqueous environments, especially chloride. With the possible exception of the latter, which is a special example of hydrogen cracking, all the others display the phenomenon of subcritical crack growth, i.e. small surface flaws propagate (usually smoothly) under conditions where fracture mechanics predicts that failure should not occur. That is, in the presence of a corrodent, cracks develop and propagate well below K_Ic. In fact, the subcritical value of the stress intensity, designated as K_Iscc, may be less than 1% of K_Ic, as the following table shows: The 630 foot high, stainless-clad (type 304) Gateway Arch defines St. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... An alloy is a combination, either in solution or compound, of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. ... The chloride ion is formed when the element chlorine picks up one electron to form an anion (negatively-charged ion) Cl−. The salts of hydrochloric acid HCl contain chloride ions and are also called chlorides. ... The old Steel cable of a colliery winding tower Steel is sometimes described as a sea of electrons. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Atomic mass 63. ... Ammonia is a compound of nitrogen and hydrogen with the formula NH3. ... Hydrogen embrittlement is the process by which various metals, most importantly steel, become brittle and crack following exposure to hydrogen. ... Structural failure refers to loss of the load-carying capacity of a component or member within the structure or of the structure itself. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

The subcritical nature of propagation may be attributed to the chemical energy released as the crack propagates. That is, In chemistry, a chemical bond is the force which holds together atoms in molecules or crystals. ...

elastic energy released + chemical energy = surface energy + deformation energy

The crack initiates at K_Iscc and thereafter propagates at a rate governed by the slowest process, which most of the time is the rate at which corrosive ions can diffuse to the crack tip. As the crack advances so K rises (because crack length appears in the calculation of stress intensity). Finally it reaches K_Ic , whereupon fast fracture ensues and the component fails. One of the practical difficulties with SCC is its unexpected nature. Stainless steels, for example, are employed because under most conditions they are 'passive', i.e. effectively inert. Very often one finds a single crack has propagated while the rest of the metal surface stays apparently unaffected. The 630 foot high, stainless-clad (type 304) Gateway Arch defines St. ...

See also

• Fracture mechanics
• Environmental stress cracking

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External links

• Stress corrosion cracking of aluminum alloys