AbstractDebottlenecking and estimating fouling in a clarifier piping system for the expansion of an existing chemical manufacturing facility in the U.S. Gulf Coast was analyzed and modified. The existing clarifier piping system fitting data was gathered for the real-world operation from the field. This data was used in the Applied Flow Technology (AFT) Fathom, a program used to study hydraulic systems. The hydraulic results with and without recommended piping modifications along with changing piping roughness factors were also analyzed. The two piping roughness factor cases tested were roughness of 0.152 mm and fouling of 25.4 mm. The AFT Fathom results showed that without piping modifications and specifying fouling of 25.4 mm, required flow cannot be established due to insufficient driving force for liquid movement. The measured field flow data confirmed that the reduced clarifier capacity was due to high pressure losses in the hydraulic system. Also, it was found that the existing clarifier nozzle was inadequately designed originally, and replacing the nozzle showed an increase in the clarifier capacity due to reduced entrainment of the air. These modifications were further adapted in the plant expansion and operations were validated using the actual plant data. The plant data matched closely with the estimated capacities of the clarifiers. AFT Fathom hydraulic software was effective in predicting a fouling severity in the clarifier piping system and debottlenecking of the clarifier capacity was done. The conclusions derived from this study can be used all over the world where clarifiers are utilized.