Stress corrosion cracking materials affecting

All the above modes of fracture are affected by the environment around the crack tip. This behaviour is typified by the phenomenon of stress-corrosion cracking where a crack, which is subjected to a subcritical stress concentration, will grow in a corrosive environment when /f, the critical stress concentration for stress-corrosion cracking). Therefore, to predict accurately the occurrence of cracking and crack growth rate, not only the materials properties are required but also information on the immediate environmental conditions. 

Heat treatment may also affect the extent and distribution of internal stresses. These may be eliminated by appropriate annealing treatments which can remove susceptibility to stress-corrosion cracking. This must be explored in any studies of the performance of materials in environments where stress-corrosion cracking is a hazard. In particular cases, stress-relief annealing treatments may result in the appearance of new phases which, while eliminating the stress-corrosion effects, will induce another type of path of attack. This possibility must be kept in mind in assessing the overall benefits of heat treatments applied primarily for stress relief. 

If the material is susceptible to stress corrosion cracking (i.e., environmentally affected cracking under sustained loads), a contribution from this mechanism (for applications such as power plant equipment) must be incorporated, and is treated as an additive term. As such ... 

There are some differences in the behavior of alloys due to the variations in caustic composition among the three cell processes. These differences occur mostly in lower-grade applications using materials less robust than nickel. Monel, for example, is subject to liquid-metal cracking by mercury and its salts. Stainless steels seem to be equally affected by diaphragm- and mercury-cell caustic, but if the caustic is consumed in some application, the residual chloride from diaphragm-cell NaOH can cause stress corrosion cracking [146]. 

The non-electrochemical techniques include direct immersion of materials samples in the test fluid in either the laboratory or plant. These s lmples sometimes have an artificial crevice generated with a serrated washer. They may be welded to determine the effects of welds and weld heat affected zones. Real-time information can be obtained using electrical resistance probes. Heat transfer effects can be evaluated by having a test sample that is exposed to the corrodent on one side and the other side heated or cooled. Stressed samples are used to evaluate stress corrosion cracking tendencies [33]. 

Improved reactor coolant system materials to reduce the chance of reactor coolant system cracking, which can lead to reactor coolant system leakage and associated safety challenges and cleanup/repair operation radiation exposures. A specific example of this improvement is the elimination of Inconel 600, to prevent stress corrosion cracking affecting the reactor coolant system pressure boundary. 

Coupons may be used to determine the average fluid corrosivity by measurement of weight loss (See Figure 8.1). Susceptibility to pitting, bimetallic corrosion, stress corrosion cracking, crevice corrosion, corrosion in weldments or heat affected zones (HAZ), hydrogen embrittlement, scaling, erosion, and cavitation may also be determined. The method facilitates an assessment of the corrosivity of an environment with respect to the specific material of construction of that part of the plant. 

Select materials resistant to intergranular corrosion and stress corrosion cracking, where residual and induced stresses could affect the safe function of the equipment. 

Severe loss of ductility of a metal (or alloy) loss of load carrying capacity of a metal or alloy the severe loss of ductility or toughness or both, of a material, usually a metal or alloy. Many forms of embrittlement can lead to brittle fracture and many can occur during thermal treatment or elevated-temperature service (thermally induced embrittlement). Some of these forms of embrittlement, which affect steels, include blue brittleness, 885 °F (475 °C) embrittlement, quench-age embrittlement, sigma-phase embrittlement, strain-age embrittlement, temper embrittlement, tempered martensite embrittlement, and thermal embrittlement. In addition, steels and other metals and alloys can be embrittled by environmental conditions (environmentally assisted embrittlement). Forms of environmental embrittlement include acid embrittlement, caustic embrittlement, corrosion embrittlement, creep-rupture embrittlement, hydrogen embrittlement, bquid metal embrittlement, neutron embrittlement, solder embrittlement, sobd metal embrittlement, and stress-corrosion cracking. 

The type of corrosive environment responsible for brittle fracture of suspension composite insulators was established. A series of FTIR experiments was performed to identify chemical functionalities formed during the degradation process of composite insulators affected by brittle fracture. It was shown that the brittle fracture process was caused by the formation of nitric acid either outside or inside an insulator leading to stress corrosion cracking of the glass/polymer composite rod material. Nitrate was detected on the composite fracture surfaces inside a 115 kV suspension composite insulator which failed in service by brittle fracture. 17 refs. 

Mechanical Facton, Environments that promote metal dissolution can be considered more damaging if stresses are involved (see the discussion on stress-corrosion cracking in Chapter 7). In such circumstances, materials can fail catastrophically and unexpectedly. Safety and health can be significantly affected. 

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