Pitting susceptibility of induction-quenched pipeline with microstructural heterogeneity

Abstract

Pitting corrosion was found to be the immature failure mechanism for a slurry pipe that has an internal surface hardened with induction-quenching technique. The metallographic examination shows that the microstructure of surface layer is a banded mixture of martensite, ferrite, and pearlite. The pits initiate preferably in the ferrite bands. Electrochemical measurements are conducted to evaluate the pitting susceptibility of each constituent. When the small amount of chloride is present, the breakdown potential of ferrite is lower than those of martensite and pearlite. The high likelihood of metastable pit initiation in ferrite is also demonstrated by the electrochemical noise records. The development of pits in ferrite in the mixed microstructure is further promoted by the galvanic effect when ferrite is coupled with pearlite or martensite. The passive film of steel is an n-type semiconductor. The Mott-Schottky measurements indicate that the passive film formed on the ferrite specimen contains more oxygen vacancies, suggesting that the lower breakdown resistance is likely due to a highly defective film structure. The high-to-low pitting susceptibility is ferrite [ martensite [ pearlite. The experimental observations of this study imply that a practical approach to improve the performance of tailing pipes is to eliminate the microstructural heterogeneity in the surface layer by modifying the induction-heating process.

pH Effect on Sulfur-Induced Passivity Degradation of Alloy 800 in Simulated Crevice Chemistries

“…Much experimental evidence has indicated the corrosion resistance of a passive film is related to its electronic properties. 22,23,47,48 Mott-Schottky plots were developed for passive Alloy 800 after passivation at corrosion potential for 24 hours in NC and AKC solutions at ambient temperature. When film formation potentials were −0.4 to 0 V SCE (Figure 6a), the passive film exhibited linear Mott-Schokky behavior, indicating that the capacitance response of the oxide is controlled by the band bending and can be described by the variation of the spacecharge capacitance under depletion conditions.…”

pH Effect on Sulfur-Induced Passivity Degradation of Alloy 800 in Simulated Crevice Chemistries

“…Hence, the electrochemical behavior of passive films is often interpreted in terms of its semiconductive nature. Much experimental evidence has indicated the corrosion resistance of a passive film is related to its electronic properties [11][12][13][14]. Mott-Schottky plots were developed for passive Alloy 800 after passivation at corrosion potential for 24 hours in NC and BC solutions at ambient temperature.…”

Effect of Heat Treatment on the Passive Film and Depassivation Behavior of Cr-Bearing Steel Reinforcement in an Alkaline Environment

“…Heat treatment can lead to a change in the microstructure of steels in terms of the carbides, grain size, and so on. Numerous works have observed a direct relationship between localized corrosion susceptibility and the presence of carbide phases in steel [11,12], since carbides with a noble electrochemical equilibrium potential accelerate galvanic corrosion and ferrite dissolution [13,14]. Even worse, carbides such as cementite can continuously aggravate galvanic corrosion during corrosion evolution processes due to the sustained accumulation of cementite on the steel surface, which can lead to an increase in the surface area ratio between the cathode and anode [12,15].…”