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The effects of surface condition on localized corrosion were evaluated quantitatively using electrochemical analysis and corrosion simulation. Carbonaceous residue, copper chloride, and deposit were investigated as surface conditions that affect localized corrosion. Electrochemical acceleration via the potentiostatic polarization method showed that the three surface conditions induced localized corrosion on the copper and pitting factor increased in the sequence of deposits, copper chloride, and carbonaceous residue. Furthermore, corrosion simulation revealed that the galvanic corrosion current density increased with a decrease in the surface coverage and density of chloride residue. [Display omitted] • Four surface conditions were obtained from either as-received or used copper tube. • Corrosion behavior according to the surface conditions was investigated. • Carboxylic acid was the most influential factor on localized corrosion of copper. • Galvanic current increased with decreasing coverage and density of chloride residue. [ABSTRACT FROM AUTHOR]

In this study, pitting corrosion in copper pipe used for sprinkler according to dissolved oxygen (DO) concentration was investigated through failure analyses, flow visualization test, DO consumption rate analysis, electrochemical tests, surface analyses, and corrosion simulation test. As a result of the failure analysis, all 10 leaks were due to pitting corrosion, and 8 leaks occurred in the branch pipe at the end of sprinkler system. As a result of flow visualization test, there were air pockets occupying 20% of the maximum total volume at the end of the branch pipe due to pressure drops. DO consumption rate analysis showed that air pocket acted as the oxygen source to maintain high DO concentration. As a result of electrochemical tests, surface analyses, and corrosion simulation, the corrosion rate of the higher DO concentration is about 10 times higher than that of lower DO concentration due to the increased oxygen reduction reaction. Through these results, it was confirmed that an air pocket was formed at the end of the pipe in the sprinkler system, and this air pocket became an oxygen source and accelerated galvanic corrosion between inside and outside of the pit during pitting propagation. This can be used as a guideline to prevent water leakage for pitting corrosion on copper pipe. [Display omitted] • Oxygen concentration cell formed in the pit is the cause of pitting propagation. • A decrease in oxygen concentration reduces the rate of copper corrosion. • Depletion of oxygen outside the pit reduces pitting propagation. • Air pockets formed at the end of the branch pipes act as an oxygen source. • Air pockets delay oxygen depletion and increase pitting corrosion. [ABSTRACT FROM AUTHOR]

The effect of benzotriazole on the corrosion prevention of electroless nickel–immersion gold (ENIG)-treated copper in 3.5 wt% sodium chloride solution was investigated using electrochemical tests, qualitative and quantitative surface analyses, and density functional theory calculations. Benzotriazole showed high corrosion inhibiting efficiency of approximately 90% or more for both copper and nickel, which are components of ENIG-treated copper. Furthermore, adding benzotriazole suppressed more than half of galvanic corrosion between nickel and gold, previously identified as the cause of corrosion of ENIG-treated copper. By chemisorption of its nitrogen atoms on the copper and nickel surfaces, benzotriazole effectively inhibited corrosion of ENIG-treated copper. The corrosion and corrosion inhibition mechanisms of ENIG-treated copper specimens were investigated using scanning electron microscopy with energy-dispersive X-ray spectroscopy after immersion testing of ENIG-treated copper specimens. • The corrosion protection effect of benzotriazole on ENIG-treated copper is studied. • Benzotriazole shows high corrosion inhibiting efficiency on both copper and nickel. • Benzotriazole effectively inhibits the galvanic corrosion between nickel and gold. • Benzotriazole inhibits corrosion by chemisorption on copper and nickel surfaces. • Benzotriazole effectively inhibits corrosion of ENIG-treated copper. [ABSTRACT FROM AUTHOR]

• Total 20 copper tubes for the fire sprinkler system were investigated. • Carbonaceous residue and deposit induced pitting corrosion in failure analyses. • Carbonaceous residue with chloride were detected in the as-received copper tube. • Carbonaceous residue with chloride induced pitting corrosion in electrochemical test. • Pitting corrosion of copper occurred in the presence of sufficient oxygen. Failure analyses with 10 leaked and 10 non-leaked Cu tubes for a fire sprinkler system were conducted to understand the cause of pitting corrosion. Water analysis revealed that the water in the leaked tubes was more corrosive than that in the non-leaked tubes. Surface analysis revealed that the leakage due to the pitting corrosion occurred with carbonaceous residue and deposits in the presence of trapped air in the tube. Furthermore, the chloric residue in the as-received Cu tube induced localized corrosion on the Cu. [ABSTRACT FROM AUTHOR]

Carbonaceous residues on copper pipes during the manufacturing process are known to be one of the main causes of pitting corrosion on copper pipes. This study examined the corrosion-inhibiting effect of benzotriazole (BTA) on C12200 copper pipes with carbonaceous film in synthetic tap water. In the absence of BTA, localized corrosion mechanisms due to galvanic corrosion, crevice corrosion, and oxygen-concentration cell were proposed in the boundary part of the carbonaceous film on the copper through X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) analyses. Electrochemical tests showed that BTA inhibits corrosion by forming Cu−BTA complexes on all over the copper surface where carbonaceous film is present. BTA mitigates galvanic corrosion and crevice corrosion at the boundary of the carbonaceous film and suppresses the formation of oxygen-concentration cells through the formation of a Cu−BTA complex. [ABSTRACT FROM AUTHOR]