Influence of pH and Chloride Concentration on the Pitting and Crevice Corrosion Behavior of High-Alloy Stainless Steels

Abstract

Localized corrosion resistance (pitting and crevice corrosion) of two high-alloy stainless steels (superduplex and superaustenitic) was studied in solutions with chloride concentrations of 200, 400, 600, and 6,000 ppm at pH values ranging from 2 to 6.5. Critical temperatures for pitting and crevice corrosion were calculated for these test media using electrochemical techniques (continuous current). From results obtained for cyclic polarization, the critical pitting temperature (CPT) and critical crevice temperature (CCT) of these materials in the different test media were determined. Under the tested conditions, the resistance of these materials to localized corrosion was very high. Only in test conditions of higher aggressivity (6,000 ppm Cland pH 6.5), pitting or crevice corrosion was observed. In those cases, values of pitting potential (E pit ) and crevice potential (E cre ) showed little tendency to decrease with an increase in Clconcentration, temperature, and pH. Moreover, the CPT of these steels was determined in a ferric chloride (FeCl 3 ) medium, which corresponds to the standard ASTM G48 practice (Method A).

Passivation behaviour of stainless steel (UNS N-08028) in industrial or simplified phosphoric acid solutions at different temperatures

“…This mainly depends on the composition of the medium, especially the presence of chloride and sulphide ions that may accelerate anodic processes by altering passivity and thus enhancing the metal dissolution. This harmful effect was attributed to the adsorption of ions on the SS surface [4][5][6][7][8][9][10][11].…”

Corrosion Studies on Stainless Steel (FE6956) in Hydrochloric Acid Solution

“…However, the corrosion resistance of stainless steel is nevertheless better than most alloys. Various studies have been carried out to determine the corrosion behavior of stainless steel in acid and basic media as well as aqueous solutions contaminated with chloride (Cl − ) ions which is known to cause pitting and crevice corrosion on metal surface [13]. Pitting is simply a breakdown of the passive layer followed by localized corrosion that produces pits, which causes perforation of steel vessels or pipes.…”

Study on the Corrosion Behavior of Aqueous Extract of Thermal Insulation Materials to A3 Steel

“…Many efforts have been made to explain the pitting initiation of metal in chloride-containing solutions [21][22][23][24][25][26][27][28][29][30][31]. Cl -can destroy the passive film on the surface of A3 steel generated by corrosion, which making steel surface always in the activated state.…”