The preferential weld corrosion has been a major problems historically and remain a significant concern for industry. The term preferential weld describes selective attack of the weld itself rather than parent plate plate but is sometimes used in a somewhat loose way to describe corrosion of other features of a weldment for example the heat affected zone (HAZ).The origin of preferential attack is usually combination of more active weld material (the weld will tend to be more susceptible o corrosion than the parent material if in isolation) together with galvanic coupling to the parent material, The influence of the coupling is accentuated by the poor area ratio, i.e a small anodic weld and large cathodic based material. The key features of preferential weld corrosion,have been reviewed by Turnbull(1982) elsewhere.
Lundin (1967), drew the following conclusion from a detailed investigation. In the welding of C- Mn steels , the silicon are the most anodic and unkilled steels are the most anodic and the unklled steels with the silicon content are the most cathodic. Of the weld metals,the normal basic coated electrodes exhibit the anodic potential and the acid types the most cathodic,while the potentials
for the weld metal from rutile electrodes are placed in an intermediate position.
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