Pitting corrosion of copper tubes for fire sprinkler system

•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.