Corrosion fatigue crack stress concentration

It is often difficult to conduct laboratory tests in which both the environmental and stressing conditions approximate to those encountered in service. This applies particularly to the corrosive conditions, since it is necessary to find a means of applying cyclic stresses that will also permit maintenance around the stressed areas of a corrosive environment in which the factors that influence the initiation and growth of corrosion fatigue cracks may be controlled. Among these factors are electrolyte species and concentration, temperature, pressure, pH, flow rate, dissolved oxygen content and potential (free corrosion potential or applied). [Pg.1052]

Stress increases corrosion attack and must be controlled through proper design and use of equipment, as well as by reduction of enviromnental corrosives. For example, corrosion pits concentrate stress and are prime initiation points for corrosion fatigue cracks, which are the major cause of drill pipe failure. It is easily understood that corrosion problems become more critical as well depth increases, because among other things, high temperature becomes one of the more critical problems faced in many deep drilling projects. [Pg.160]

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... [Pg.227]

Undue static or cyclic stressing and other features which give rise to stress concentrations should be avoided as these may lead to premature failure by stress-corrosion cracking or corrosion fatigue. [Pg.68]

Determination of residual stress of a failed component is one of the most important steps in failure analysis. The determination of residual stress is useful when failed components experience stress concentration, overload, distortion or the formation of cracks in the absence of applied loads, subjected to corrosive environments as in stress corrosion, mechanical or thermal fatigue due to cyclic loading, or when faults in processing such as shot peening, grinding, milling and improper heat treatment such as stress relief, induction hardening, thermal strains, exposure temperature are involved. [Pg.161]

CF cracks are always initiated at the surface, unless there are near-surface defects that act as stress concentration sites and facilitate subsurface crack initiation. Crack initiation takes place independently of fatigue limit in air as it can be decreased or eliminated through the increase of dissolution rates at anodic sites. Localized corrosion such as pitting favors fatigue crack initiation through stress concentration and a local acidic environment. The two main mechanisms of CF are anodic slip dissolution and HE (80). [Pg.64]

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