LYCOS RETRIEVER 
Corrosion: Stress Corrosion
built 280 days ago
Corrosion treatment chemicals available from GE for use in chemicals production and hydrocarbon refining include neutralizers, filmers, and non-nitrogen-based corrosion inhibitors. These chemical programs prevent or mitigate damage from galvanic (two-metal) corrosion, under-deposit corrosion, pitting, intergranular corrosion and stress corrosion. In addition, specialized GE products are available that provide dual capability, addressing two or more of the following functions: filming, neutralizing, dispersing, scavenging and inhibiting.
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Stress Corrosion is yet another form of corrosion, as it's name implies, occurs when a metal is under heavy stress. This is a combination of crevice corrosion cells combined with heavy loading. It most often occurs on sailboat rigging and power boat propeller shafts. Old style swage fittings on sail boat rigging combines both stress and corrosion cells from entrapped water within the swaged cable. It ... occurs at mast rigging attachments where water is entrapped between the mast and bolt-on parts, or even getting under welded parts. See photo below.
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Stress corrosion cracking and hydrogen embrittlement are corrosion-related phenomena associated with the presence of a tensile stress. Stress corrosion cracking results from a combination of stress and specific environmental conditions so that localized corrosion initiates cracks that propagate in the presence of stress. Mild steels are susceptible to stress corrosion cracking in environments containing hydroxyl ions (OH−; often called caustic cracking) or nitrate ions (NO3−). Austenitic stainless steels are susceptible in the presence of chloride ions (Cl−) and hydroxyl ions (OH−). Other alloys that are susceptible under specific conditions include certain brasses, aluminum and titanium alloys. Hydrogen embrittlement is caused by the entry of hydrogen atoms into a metal or alloy, resulting in a loss of ductility or cracking if the stress level is sufficiently high.
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Rust is a type of corrosion you are probably familiar with, but corrosion comes in various forms. General or uniform corrosion is when the entire metal corrodes at an even rate. Stress corrosion usually happens to a metal with good corrosion resistance, but it is under stress and in an unfriendly environment, which causes cracks to form in the metal. It is in these cracks where the corrosion forms. Pitting corrosion, which ... occurs on metals with good corrosion resistance, occurs when the natural protection of the metal breaks down in small areas and tiny pits of corrosion form.
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Unlike many other forms of corrosion where corrosion occurs over long periods of time, environmental cracking can occur very rapidly. Because it is unanticipated, it can be catastrophic. Environmental cracking is the brittle failure of an otherwise ductile material caused by the combined action of corrosion and tensile stress. It can be identified by tight cracks that are at right angles to the direction of maximum tensile stress. Types of environmental cracking include stress corrosion cracking (SCC), hydrogen-induced cracking (HIC), liquid metal embrittlement (LME), and corrosion fatigue (CF).
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Stress corrosion cracking is where the internal stresses (residual stresses) vary across a section so that when they are loaded with additional outside forces, the grain boundaries at the surface start to break. When a part (sheet, extrusion, etc) is quenched and the outside layer cools too quickly, tension stresses are set up on the outside and compression stresses in the middle. This is sometimes taken care of by stretching or shot peening.
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Stress Corrosion