Comparison of flow regimes on biocorrosion of steel pipe weldments: Fluid characterization and pitting analysis.

Pitting corrosion in microalloyed steel and its welded joints occur in fabricated structures, such as pipelines for oil and gas transport, which are exposed to corrosive environments. Although the formation of the pits consumes only a relatively small mass of material, the role of the pits as defect sites for crack initiation and continuing corrosion can be substantial. Furthermore, in natural and industrial environments where microorganisms are widely distributed, pitting corrosion is aggravated by the release of many reactive microbial metabolites. This is a report of a 28-day study aimed at the microbiologically influenced corrosion of joint welds by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) exposed to laminar and turbulent flows. The characterization of the planktonic microbial community indicated that laminar flow created an anoxic environment promoting the dominance of anaerobic microorganisms, in particular sulfate reducing bacteria (SRB). Both types of welded joints showed similar pit densities in the base metal (BM), heat-affected zone (HAZ) and weld metal (WM), nevertheless the pit depth was higher in the HAZ than the BM and WM. On the other hand, turbulent flow retained dissolved oxygen content, ensuring the presence of aerobic microorganisms, but there was no inhibition of SRB growth. Although the pit depth was low in both types of welded joints, the pit density was exacerbated in only one HAZ of each welded joint due to WM reinforcement height, while the other HAZ showed low pit density. This study demonstrates that turbulent flow can reduce the biocorrosion of non-welded areas but can aggravate welded joints biocorrosion. Image 1 • Biocorrosion of joints welded by gas tungsten arc welding and shielded metal arc welding were investigated. • The type of fluid flow regiment influenced the planktonic microbial community. • Planktonic sulfate reducing bacteria number was not affected by turbulent flow. • Pitting corrosion was more severe in the heat-affected zone, regardless of the welding process and flow regime. • Turbulent flow promoted a differentiated distribution of pits in the welded joints. [ABSTRACT FROM AUTHOR]