Linearly concentrating solution favors efficient and precise determination of critical pitting chloride concentration

• A new method to measure critical pitting chloride concentration (CPCC) is proposed. • Linearly increasing Cl concentration is realized via a pump with drip rate of μL/min. • CPCC of CoCrFeNiAl x alloys vary with concentrating rate of Cl ions. • High concentrating rate of Cl ions contributes to the acidification of metastable pit. • Linear Cl concentrating achieves remarkable high precision and efficiency. The critical pitting chloride concentration (CPCC) is an essential parameter for the safe service of structural alloys that sensitive to pitting corrosion. Precise lacking and time-consuming frustrates the traditional method (multiple tests), i.e., applies various solutions with different concentrations and then gradually approaches the real CPCC. Herein, a novel method (single test) was proposed to efficiently and precisely positioning CPCC, i.e., linearly increasing chloride concentration that realized by a peristaltic pump with a high precision drip rate of μL/min. Moreover, a non-linear sensitivity of CPCC to concentrating rate of chloride ion was revealed on CoCrFeNiAl x alloys and the possible mechanism is discussed.