Internal corrosion failure behavior and preventive measures for crude oil gathering and transportation pipelines with seasonal blending shutdowns

Objective Seasonal blending shutdowns provide an effective solution for optimized operation, energy conservation and carbon reduction, and refined management of crude oil gathering and transportation systems. However, the complex physical properties of fluid media and varying operational conditions elevate the failure rate of water-blended pipelines, especially in characteristic segments with specific laying dip angles that are critical for corrosion failure. In contrast to other oil return and water injection pipelines with stable operational conditions, water-blended pipelines experience significantly reduced service cycles. Additionally, failures are more prevalent in winter, impacting the operation of gathering and transportation systems and resulting in higher overall costs for maintenance and replacement.

Methods This study focused on the internal corrosion prevention of pipelines with seasonal blending shutdowns. Based on the analysis on the medium characteristics of corroded pipeline segments and products, the corrosion failure behaviors in characteristic segments during both water-blended operation and operation with blending shutdown were studied and compared through numerical simulation. In addition, the corrosion prevention and control countermeasures including clear water displacement and compressed air purging for pipelines with seasonal blending shutdowns were put forward and evaluated.

Results Electrochemical corrosion and erosion collaboratively contribute to the internal corrosion behavior of water-blended pipelines, resulting in the formation of Fe₂O₃, FeS, CaCO₃, MgCO₃, CaSiO₃, MgSiO₃, and SiO₂. During operation with seasonal blending shutdowns, corrosion failure characteristics become more pronounced due to the influence of liquid accumulation volume and duration in pipeline segments of corrosion features. Both clear water displacement and compressed air purging effectively inhibited corrosion failure in water-blended pipelines during blending shutdowns. Under identical operational conditions, clear water displacement could reduce the maximum corrosion rate by an average of 85％, while compressed air purging could decrease corrosion depth by an average of 65％.

Conclusion Considering the effectiveness of the preventive measures and the operability of gathering and transportation facilities, clear water displacement is the more applicable and promising option for engineering applications. Therefore, the preference is given to clear water displacement for pipelines with seasonal blending shutdowns, providing a basis and method for the integrity management and safe, efficient operation of crude oil gathering and transportation systems in oilfields.