Weldments knife-line attack

Henthorne , in considering the corrosion testing of weldments, points out that the test will also give high rates due to (a) end-grain attack, which is particularly prevalent in resulphurised or heavily cold-worked material and (d) dissolution of Ti(C, N) such as occurs in Type S2J weldments and leads to knife-line attack. Since most service conditions do not cause attack on the alloy in these conditions the test can be misleading. 

Corrosion resistance of aluminum alloys. Researchers have shown that aluminum alloys, both welded and unwelded, have good resistance to uninhibited HN03 (both red and white) up to 50°C. Above this temperature, most aluminum alloys exhibit knife-line attack (a very thin region of corrosion) adjacent to the welds. In inhibited fuming HNO3 containing at least 0.1% hydrofluoric acid (HF), no knife-line attack was observed for any commercial aluminum alloy or weldment even at 70°C (160°F). 

Other parts of the weldment (Ref 2,3). A very selective knife-line corrosive attack can result fixxm this immersed service. 

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