Corrosion of Weld Heat-Affected Zones Submersed in Seawater with Indigenous Microorganisms

Abstract

The corrosion behaviors of different weld heat-affected zones (HAZs) were investigated, comprising an API 5L X65 steel immersed in seawater with an abundant native microbial community. Before tests, HAZ physical simulations were performed at the peak temperatures of 700°C, 860°C, 1000°C, and 1350°C. Throughout 14 days of immersion, various planktonic bacterial groups associated with microbiologically in uenced corrosion were metabolically active in the seawater. Desulfovibrio members were present in a considerable number of OTUs. Scanning electron microscopy showed an intense microbial adhesion and corrosion product deposits in all HAZ sub-regions and the control base metal coupon (BM). The electrochemical tests revealed that the corrosion behavior of all HAZ sub-regions and BM were indistinguishable. However, topography analysis showed different behaviors of pitting corrosion. The results revealed that the pitting resistance of the microstructure composed of cementite grains (700°C HAZ) was superior to that of other HAZ sub-regions. On the other hand, the microstructure composed of martensite and austenite grains (860°C HAZ) exhibited the worst pitting resistance of the weld joint, leading to a maximum pit penetration of 2.3 times greater than that pit on the BM. The changes in the HAZ sub-region sensitivity to pitting corrosion were attributed to variations in the microstructural composition.

The Role of Metallurgical Features in the Microbially Influenced Corrosion of Carbon Steel: A Critical Review

“…Work on and reports of the MIC of carbon and low-alloy steel welds are definitely less comprehensive and less conclusive when compared to the work published on stainless-steel welds [84,85,108,[220][221][222][223][224][225][226][227]. In addition, a wide variety of test configurations have been used, making it very difficult to compare results or determine trends.…”

“…In addition, a wide variety of test configurations have been used, making it very difficult to compare results or determine trends. Test media range from natural seawater [220,221,225] to microbiological growth media containing SRB [222][223][224]226]. Various types of welded sample configurations have been used in research studies, including samples that encompass complete weld samples, i.e., the base metal, the HAZ, and the weld in one sample.…”

“…Although there are potential advantages to each of these different test configurations, it makes comparisons very challenging. The MIC test results are split roughly in half between those that indicate increased corrosion of weld regions [84,85,220,221,225] and those that show that the base metal has greater levels of pitting attack when compared to the HAZ and weld zone [222][223][224]226]. Tests on microbiological attachment also show mixed results, with some tests indicating increased microbial attachment in the weld zone [84,85,226], while others showed greater attachment on the base metal [221,223].…”