The 3-phase separator is an instrumented vessel that separates well effluent into three phases—oil, gas, and water—for well testing. It was developed for land fracturing flowback and well test operations. The 3-phase separator is built in compliance with ASME Section VIII, Division 1 and NACE MR0175 for H2S environments. Multiple pressure safety valves contain and direct flow to a designed safe area in the event of vessel overpressurization. Bypass valves, a unique offering from M-I SWACO in a three-phase separator unit, enable operators to move effluent into containment areas for maintenance without shutting in the well or risking exposure to chemicals.