Stress-corrosion cracking corrodent concentration

Stress corrosion cracking A process of cracking which occurs by the action of a corrodent and a stress. Stress concentration factor It is the ratio of greatest stress in the region of a notch or discontinuity to the corresponding nominal stress. 

This denotes a type of stress corrosion cracking encountered in steel exposed to high concentration of hydroxide at a temperature of200-250°C. Caustic cracking of steel is sometimes called as caustic embrittlement (Fig. 11.16). It is a special type of stress corrosion cracking that occurs in boilers. The tube cracks under the influence of stress and high concentration of hydroxide which causes it to corrode. There are two conditions which must be satisfied ... 

No common industrial metal is immune to corrosion fatigue since some reduction of the metal s resistance to cyclic stressing is observed if the metal is corroded, even mildly, by the environment in which the stressing occurs. Corrosion fatigue produces fine-to-broad cracks with little or no branching. They are typically filled with dense corrosion product. The cracks may occur singly but commonly appear as families of parallel cracks (Fig. 10.2). They are frequently associated with pits, grooves, or other forms of stress concentrators. Like other forms of... 

H2S can cause corrosion of stainless steels such as 316 and 410 stainless in the form of sulfide stress cracking. (Other factors, such as pH, chloride concentration, and temperature also affect the potential for steel cracking.) Copper alloys corrode rapidly in H2S service. An industry value that has been developed is NACE MR-01, 2003, from the National Association of Corrosion Engineers. In the gas phase, a stream is sour if the H2S partial pressure exceeds 0.05 psia. If a single phase hquid is in equilibrium with a gas phase, where the gas phase H2S partial pressure exceeds 0.05 psia, then that hquid is also considered to be sour. If the liquid is not in equihbrium with the gas phase, then the liquid is considered sour, if this bubble point gas phase H2S partial pressure exceeds 0.05 psia. The presence of water is not required for a gas and/or hquid to be considered to be sour, nor is there a minimum pressure to avoid designating a gas or hquid as sour. 

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