A portion of a freight train derailed in South Baltimore early yesterday, causing a stretch of Patapsco Ave. to be temporarily closed as workers from CSX Transportation Inc. conducted repairs. The derailment occurred while train workers were connecting cars together as part of normal operations. The derailment involved four empty tankers and an empty flat-bed, which were repaired. Repairs to the track, which is only used for industrial and freight purposes, according to CSX, were continuing. No injuries were reported.