Concentrated chelants ( amines and other protecting chemicals) can attack magnetite, steam drum internals most susceptible. A surface under attack is free of deposits and corrosion products, it may be very smooth and coated with a glassy black like substance Horse shoe shaped contours with comet tails in the direction of the flow may be present. Alternately deep discrete isolated pits may occur depending on the flow and turbulence. The main concentrating mechanism is evaporation and hence DNB should be avoided. Careful watch on reserves and O2 prescience should be maintained.