Stress corrosion cracking environmental considerations

Moreover, lack of understanding of processing and heat-to-heat variations or the effects of trace alloying elements further limits the predictability of the onset or growth of stress corrosion cracks. Similar considerations can apply to environmental effects on high-temperature crack growth in gaseous environments. 

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. 

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