As per the normal cold cutting practice, contractor crew who were assigned for re-routing existing flow lines, identified, line walked and marked ‘C” on a flowline at cut points using red paint. They also marked red “C” on adjacent Long Term Closed (LTC) flow line based on the verbal confirmation that it is hydrocarbon free. This was done to save time as this line was scheduled for cut on following day. At the time of cold cut, additional red marking on the LTC line caused confusion resulting erroneous cutting of the wrong sequence line.