Crevice Corrosion mild steel

Wastage was caused by crevice corrosion, accelerated by the difference in tube and tube sheet metallurgies. The brass tube, being more noble, was cathodically protected by corrosion of the surrounding mild steel tube sheet. However, the galvanic effect was secondary to the primary cause of failure, namely, crevice corrosion. 

It is appropriate to consider first the crevice corrosion of mild steel in oxygenated neutral sodium chloride, and then to consider systems in which the metal is readily passivated. Initially, the whole surface will be in contact with a solution containing oxygen so that attack, with oxygen reduction providing the cathodic process, occurs on both the freely exposed surface and the surface within the crevice (Fig. 1.50). However, whereas the freely exposed surface will be accessible to dissolved oxygen by convection and diffusion, access of oxygen to the solution within the crevice can occur only... 

The control of corrosion in pharmaceutical product processes is largely managed through the use of stainless steel. Rust-free surfaces and cleanliness issues to prevent product contamination have been the primary corrosion concerns. Resistance to mildly aggressive cleaning solutions and saline solutions and the potential for under deposit or crevice corrosion present the most severe service conditions. The high standards of cleanliness necessary for pharmaceutical processes favor the mitigation of corrosion. 

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