Fatigue stress corrosion cracking

Temperature is an important parameter for safety. At extreme temperatures, tlie risk of metal fatigue, stress corrosion cracking, and vessel rupture increases dramatically. 

All metals will corrode under certain conditions. Internal corrosion is caused by galvanic corrosion, pitting, corrosion fatigue, stress corrosion cracking, stray currents, etc. 

Corrosion, stress Corrosion fatigue, stress-corrosion cracking... 

Structural failure may occur when the overall structural cross-section cannot support the applied load or, when the critical flaw size ac is exceeded by preexisting discontinuity or by reaching the critical crack size through fatigue, stress corrosion cracking or creep mechanisms. Using fracture mechanics the stress at a crack tip can be calculated by a stress-intensity parameter K as,... 

Structural materials that are direcdy exposed, such as in cabinets, housings, and heat sinks, are fabricated fix>m materials such as steels, stainless steels, brass, zinc, aluminum, and other metals and alloys with appropriate prof>erties. The types of corrosion encountered in these structures depend on the environment and material as would be exp>ected. Both uniform and localized corrosion can be important when cosmetic corrosion is of concern. In structural applications, crevice corrosion, corrosion fatigue, stress corrosion cracking (SCC), galvanic corrosion, and intergranular corrosion causing reduction in mechanical properties are important. 

Mechanical forces (e.g., tensile or compressive forces) will usually have minimal effects on the general corrosion of metals and compressive stresses even reduce the susceptibility of metals to crack. In fact, shot peening is often used to reduce the susceptibility of metallic materials to fatigue, stress corrosion cracking (SCC), and other forms of cracking. However, a combination of tensile stresses and a specific corrosive environment is one of the most important causes of catastrophic cracking of metal structures. 

Which is the most common cause of corrosion damage, corrosion fatigue, stress corrosion cracking or pitting corrosion ... 

Several tests are not related to any particular part of the corrosion process, but involve only a specific test specimen that responds to corrosion by complete failure. These tests are used in the measurement of certain forms of corrosion involving factors such as stress. Examples are corrosion fatigue, stress corrosion cracking, and hydrogen embrittlement In designing such corrosion tests, the variety of test specimens parallels the number of apphcations. 

Pitting corrosion may occur generaHy over an entire aHoy surface or be localized in a specific area. The latter is the more serious circumstance. Such attack occurs usuaHy at surfaces on which incomplete protective films exist or at external surface contaminants such as dirt. PotentiaHy serious types of corrosion that have clearly defined causes include stress—corrosion cracking, deaHoying, and corrosion fatigue (27—34). 

Most cracking problems in cooling water systems result from one of two distinct cracking mechanisms stress-corrosion cracking (SCC) or corrosion fatigue. 

Intergranular corrosion-fatigue cracks in copper may he difficult to differentiate from stress-corrosion cracking. The longitudinal orientation of the cracks revealed that the cyclic stresses were induced by fluctuations in internal pressure. 

General description. In incomplete fusion, complete melting and fusion between the base metal and the weld metal or between individual weld beads does not occur (Fig. 15.8). Incomplete fusion that produces crevices or notches at surfaces can combine with environmental factors to induce corrosion fatigue (Chap. 10), stress-corrosion cracking (Chap. 9), or crevice corrosion (Chap. 2). See Fig. 15.9. 

Figure 15.18 Examples of crack patterns due to stress-corrosion cracking and corrosion fatigue in butt welds. (Reprinted with permission from Helmut Thielsch, Defects and Failures in Pressure Vessels and Piping, New York, Van Nostrand Reinhold, 1965.)...

Slides Corroded automobiles, fences, roofs stress-corrosion cracks, corrosion-fatigue cracks, pitting corrosion. 

Corrosion fatigue, therefore, is a special case of stress-corrosion cracking and fatigue failure. Figure 4-451 shows an example of pipe failures due to corrosion fatigue. Corrosion fatigue can be prevented or reduced by ... 

Cracking mechanisms in which corrosion is implicated include stress corrosion cracking, corrosion fatigue, hydrogen-induced cracking and liquid metal embrittlement. Purely mechanical forms of cracking such as brittle failure are not considered here. 

The presence of stress raisers, including sharp comers and imperfect welds, produces locally high stress levels. These should be avoided where possible or taken into account when designing the materials for use in environments in which they are susceptible to stress corrosion cracking or corrosion fatigue. 

D ye penetration inspection. This is a simple technique, requiring a minimum of operator training. In the hands of a skilled operator, it is capable of detecting fine cracks such as chloride stress corrosion cracks in austenitic stainless steels and fatigue cracks. 

Erosion —corrosion, fretting corrosion, impingement attack, cavitation damage stress corrosion cracking, hydrogen cracking, corrosion fatigue... 

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