Pipe marking has a major role in the safety of facility workers. Pipe marking quickly communicates essential information to everyone in a facility, improving overall workplace safety and productivity. Unmarked pipes are a danger to both people and property. In fact, marking mistake are found in pipe identification during the installation. The aim of this research is to investigate the root cause of this problem happen due to avoid accidents, injuries and damage to equipment can be caused by not knowing what is flowing through the pipes. Root Cause Analysis (RCA) was used to identify the problem. In this research, the 5-whys tools was used to investigations marking mistake during piping installation. Based on results, there is a relationship between three main section, i.e. owner, QC of contactor, and Painting section of contractor which caused marking mistake. The root cause of the problem arePainting section assumed that RFI for marking number not required again based on previous piping project and Checking marking of installation number is not mention in the final checklist. To avoid this problem occurred in the future, recommendations of problem solving should be apply by all of section.

Keywords : Marking Mistake, Piping, RCA, 5-Whys.