Pitting resistance evaluation of ternary Ni-Cr-Mo alloys in flue gas environment

Abstract

After the appearance of pitting corrosion, the corrosion rate reaches very high values, which leads to a deterioration in the quality of the product in a short time. It may happen that the pitting does not continue its penetrating effect: if there are no necessary conditions for its growth, a pitting of greater activity is not formed, which will absorb all the current supplied from the area surrounding the cathode. Results of potenciodynamic investigations of four Ni‐base alloys are presented. The tests were conducted in 1 percent sulphuric acid, containing 0.2 percent chlorides at temperature 353K. Gravimetric test, performed in the same conditions, revealed excellent properties of alloy signed A3. Pitting corrosion of alloy A4 at the test conditions after long exposure at 353K was observed and was confirmed by the applied tests. The multiple anodic polarization (MAP) method is proposed to control alloys’ susceptibility to pitting corrosion.