Analysis of effect of flow condition on NH ₄HS corrosion

Effect of flow condition on NH ₄HS corrosion was studied by analysis of a corroded elbow sample and computational simulation. The thickness of corrosion products film formed on the inner surface of the elbow was measured and chemical composition of the film was analyzed using EPMA (Electron Probe Micro Analysis). In addition, flow pattern prediction and CFD (Computational Fluid Dynamics) analyses were employed. The center of the outer radius of the elbow was preferentially corroded in the sampled elbow. The film on the outer radius of the elbow was thinner than the inner radius and contained less sulfur than the inner radius. Based on three CFD models, it was found that the liquid volume fraction increased in the center of the outer radius of the elbow. Thus, corroded area was consistent with the area of high liquid volume fraction. Furthermore, a calculated wall shear stress on the outer radius was much higher than the inner radius from CFD results. Therefore, it was concluded that a protective iron sulfide film could not be formed on the outer radius due to a high wall shear stress.