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.