Corrosion types stress

When an alloy fails by a distinct crack, you might suspect stress-conosion cracking as the cause. Cracking will occur when there is a combination of corrosion and stress (either externally applied or internally applied by residual stress). It m.ay be either intergranular or trans-granular, depending on the alloy and the type of corrosion. 

In our concluding remarks we can emphasize that depending on the nature of interactions between the components that constitute the medium and the solid, as well as on a combination of external conditions, one may observe the effects of various types and intensity. These include the facilitation of plastic flow of solids, or, alternatively, brittle fracture due to the action of lowered stresses mechanochemical phenomena in the zone of contact mechanically activated corrosion (the stress corrosion) the processes that are close to the spontaneous dispersion (the so-called quasi-spontaneous dispersion), and the true spontaneous dispersion, leading to the formation of thermodynamically stable lyophilic system. A great variety of types of interactions that exist between the stressed solids and the medium in contact with it requires careful and thorough examination of conditions under which... 

Single-component corrosion types, important for heat exchanger design and operation, are as follows (1) uniform attack corrosion, (2) galvanic corrosion, (3) pitting corrosion, (4) stress corrosion cracking, (5) erosion corrosion, (6) deposit corrosion, and (7) selective leaching [153],... 

Standard austenitic stainless steels such as type 316 (18 Cr 10 Ni 3 Mo) have useful if limited resistance, to acids and reasonable resistance to pitting corrosion. Type 304 (18 Cr. 10 Ni) stainless steel has a good resistance to nitric acid. Austenitic stainless steels have relatively low strength, poor antierosion and abrasion properties and do not possess the ability to resist stress corrosion cracking. 

FYom the multitude of intricate corrosion processes in the presence of mechanical action (friction, erosion, vibration, cavitation, fretting and so on) it is justified to touch upon corrosion types joined under a single failure mode induced by mechanical stresses. These are the stresses that govern the corrosion wear rate of metals during friction. Such processes are usually called corrosion stress-induced cracking in the case that the mechanical action is effective only in one definite direction, or otherwise termed corrosion fatigue in the case that compressive and tensile stresses alternate within cycles. In spite of the differences between the appearance of these corrosion types, they have much in common, e.g. fundamental mechanisms, the causes, and they overlap to a certain degree [19]. 

For each aTToy, experiments Have been done in which specimens were exposed unstressed, to solutions that can cause cracking, under a variety of conditions. If broken in air immediately after removal from the solution, specimens exhibited a low value of Zf and fracture surfaces characteristic of stress corrosion cracking. If lapse of time occurs between removal from solution and stressing, specimens exhibited increased values of Sf and decreased amounts of stress corrosion-type fracture with increasing length of lapse of time. This behavior is characteristic of hydrogen embrittlement fracture and has been interpreted as such for the four types of alloys described. These are simple but very clear experiments. 

One of the most important forms of stress corrosion that concerns the nuclear industry is chloride stress corrosion. Chloride stress corrosion is a type of intergranular corrosion and occurs in austenitic stainless steel under tensile stress in the presence of oxygen, chloride ions, and high temperature. 

If these phenomena relate to other independent factors such as stress, etc. the result is accelerated corrosion with more complications. However, the phenomena in real life must be generally complicated and from the viewpoint, they may be universal corrosion types. Also for such corrosion, the basics and fundamentals of corrosion could be applied to the phenomena to solve technical and scientific problems. 

If susceptibility to specific types of corrosion is of interest, specialized sample configurations can be used. If the corrosion performance of the material in seawater is completely unknown, at a minimum it should be evaluated for general corrosion and pitting, galvanic corrosion, crevice corrosion, and stress corrosion. 

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. 

Uniform surface corrosion, i.e. corrosion at a nearly uniform corrosion rate over the entire surface, is usually less problematic from an operational point of view. This factor can be taken into account in the structural element design in the form of an anticorrosive additive and can be controlled in many structural elements by means of regular wall thickness measurements, e.g. by ultrasonic means. Much more difficult problems result from local corrosion types such as pitting corrosion and stress corrosion cracking (SCC). The corrosion types are difficult to control and can rapidly lead to failure of structural elements after only a low level of mass loss. Damage from such corrosion types are rarely predictable and not only cause considerable losses in economic terms but also entail risks to safety and environmental protection. This applies in particular to system elements that must function under pressure. 

Many corrosion phenomena are related to the formation of a barrier-type film on metal surfaces. In most cases this is an oxide or a hydroxide layer. Phosphate layers are important as well, especially as a primer for organic coatings. Under certain conditions, these passivating layers may be destroyed locally, which leads to special corrosion phenomena like pitting corrosion, crevice corrosion, and stress corrosion cracking. Although passivity is discussed in detail in Chap. 3 of this Volume, an introduction is given in order to understand these localized corrosion phenomena. 

Other forms of corrosion such as crevice corrosion and stress corrosion may also occur. They can be prevented by selecting alloys that are suitable for this type of environment, by specific protections and by appropriate design avoiding recesses and dead areas. 

Corrosion fatigue is a type of failure (cracking) which occurs when a metal component is subjected to cyclic stress in a corrosive medium. In many cases, relatively mild environments (e.g., atmospheric moisture) can greatly enhance fatigue cracking without producing visible corrosion. 

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