During operation of flowline pipe at Kondur Petroleum SA, damages are often occur likes external corrossion, pitting, and leaks. Improvements are often conducted through patching techniques. The objective of this study is to analyze the microstructure and mechanical properties of the patching result. This study used API 5L Grade B Schedule 80 pipe and by variation of patching with the flow conditions and without the flow condition of crude oil in it. Based on result and discussion it can be concluded that the presence of flow in patching forming a small grain microstructure, increases strength and hardness on the weld area, and there is initial crack in the weld metal. Patching without the flow condition have the best result and characteristic based on procedure, process, and welding result. However, patching still can be done with the flow conditions (online) because of differences in microstructure and mechanical properties are almost similar with patching without flow (offline) and initial crack that occur still conform with specified API 5L acceptance criteria.