In a major gas-oil separation plant (GOSP) in Saudi Arabia, a major flare header suffered from severe internal corrosion. Upon analyzing the scale and sludge that was found accumulated in the line, a significant proportion of elemental sulfur was identified. This indicated that in addition to hydrogen sulfide and water (which were expected to be present in the line), significant amount of oxygen was also present. An investigation was conducted to identify the source of this oxygen and to eliminate it. Other critical factors that impacted the internal corrosion were also identified. The line was not properly sloped to drain accumulated moisture. Knock-out boot levels were often high and not regularly drained. In addition, purge gas was not operated at rates adequate to sweep any accumulated liquids. All of these factors combined led to an accelerated deterioration of the header.