Pitting corrosion alloy composition

For materials like stainless steels, the mechanisms are quite different. Corrosion resistance in stainless steels is provided by a passive film that acts as a barrier between the alloy and the water. The passive film is a continuous, non-porous and insoluble film, which, if broken under normal conditions, is self-healing. Due to these characteristics, the uniform corrosion of stainless steels is usually very low and the major risk is pitting corrosion. The pitting corrosion risk of stainless steels is influenced not only ly the composition of the alloy and by water quality but also by service conditions, quality of the material and quality of the installation (fitting, soldering conditions, etc.). 

Duplex alloys with a composition around Fe-26Cr-6.5 Ni-3Mo with low carbon and nitrogen have been found to be resistant to chloride SCC, pitting corrosion, and IGC in the as-welded condition (48). 

Effects of Alloy Composition on Pitting Corrosion Inhibition of Pitting Corrosion Crevice Corrosion... 

These measurements lead, in particular, to an understanding that there is a critical solution composition that must be maintained within the pit, and if this does not occur then the pit will die. As a consequence, there is an important effect of the kinetics of active dissolution of the alloy within this critical solution. Measurements of the characteristics of metastable pits, coupled with studies of the dissolution kinetics of steel within the aggressive solutions that characterize the local pit environment, have provided an explanation as to why certain alloy additions (specifically Mo) act to inhibit pitting corrosion by making the maintenance of metastable pits more difficult. Other important effects include those of salt films, which... 

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