# Flow-Dependent Corrosion Behavior and Surface Degradation of X70 Pipeline Steel in Seawater Containing Pseudomonas aeruginosa

## TL;DR

This study examines how water flow and bacteria affect the corrosion of X70 steel in seawater, revealing that bacteria change how flow influences corrosion.

## Contribution

The novel contribution is identifying how Pseudomonas aeruginosa modifies the relationship between flow velocity and corrosion in X70 steel.

## Key findings

- Under sterile conditions, higher flow velocities increase corrosion severity due to enhanced mass transfer.
- P. aeruginosa presence leads to non-monotonic corrosion behavior with moderate flow velocities promoting localized pitting.
- High flow velocities reduce microbial influence by removing corrosion products and surface layers.

## Abstract

The corrosion behavior of pipeline steels in marine environments is strongly affected by hydrodynamic conditions and microbial activity, yet their coupled influence remains insufficiently understood. In this study, the corrosion behavior of X70 pipeline steel was systematically investigated in flowing artificial seawater over a velocity range of 0–1.5 m/s, under both sterile conditions and in the presence of Pseudomonas aeruginosa. Corrosion weight loss measurements, electrochemical techniques, and surface characterization were employed to evaluate flow-dependent corrosion evolution. The results show that flow velocity plays a dominant role in regulating corrosion behavior. Under sterile conditions, increasing flow velocity enhances mass transfer and surface renewal, leading to progressively increased corrosion severity. In the presence of P. aeruginosa, corrosion behavior exhibits a non-monotonic dependence on flow velocity. Lower flow velocities are associated with reduced corrosion rates and relatively uniform surface degradation, whereas moderate flow velocities promote localized corrosion and increased pitting severity. At higher flow velocities, strong hydrodynamic effects suppress the retention of corrosion products and microbe-associated surface layers, resulting in corrosion behavior primarily controlled by fluid flow. Overall, the results indicate that microbial presence modifies the flow–corrosion relationship of X70 steel by altering interfacial conditions under low-to-moderate flow regimes.