A collaborative research team from from the Shenyang National Laboratory for Materials Science, the Institute of Metal Research, Chinese Academy of Sciences (IMR, CAS), and Nanyang Technological University in Singapore has made a significant breakthrough in understanding a complex threat to energy infrastructure. They have systematically revealed the dual and dynamic role that sulfate-reducing bacteria (SRB) play in both accelerating and later partially mitigating the corrosion and cracking of high-strength steel pipelines used for transporting oil, gas, and hydrogen.
Microbiologically influenced corrosion, particularly from SRB, is a major challenge for pipelines buried in soil or submerged in seawater. These microbes can significantly shorten a pipeline's lifespan, but the detailed interplay between their biological activity, chemical corrosion, and mechanical failure has been poorly understood.
The study, published in Acta Materialia, focused on X80 high-strength pipeline steel. Researchers found that SRB activity has a time-dependent dual effect. In the early stages, SRB significantly accelerate the initiation of stress corrosion cracking by promoting localized metal dissolution and by facilitating the generation and uptake of hydrogen into the steel, which embrittles the material.
However, as corrosion progresses, SRB metabolism leads to the formation of a unique biogenic film rich in iron sulfide (FeS) on the steel surface. This film exhibits a surprising protective property. Electrochemical tests showed that this FeS film acts as a barrier to hydrogen, substantially reducing the amount of hydrogen that can enter and diffuse through the steel. This inhibitory effect was further confirmed by theoretical calculations.
This critical finding means that under certain conditions, such as when cathodic protection is applied to the pipeline, the FeS film can shift the dominant cracking mechanism. It reduces the contribution of hydrogen embrittlement, making the corrosion process slower and more localized. This new understanding of the microbial film's "dual role" provides a more complete scientific basis for assessing the long-term safety of pipelines and for designing smarter corrosion protection strategies in microbial environments.
Microbial corrosion behavior of X80 steel: (a) corrosion rate; (b) statistical analysis of pit depth; (c) SEM morphology of the deepest pit and its corresponding 3D surface profile. (Image by IMR)
Hydrogen permeation behavior of X80 steel covered by microbiological corrosion product film: (a) hydrogen permeation current density–time curves under −1.1 V vs. SCE cathodic polarization; (b) effective hydrogen diffusion coefficient (D_eff); (c) apparent hydrogen concentration (C_app). (Image by IMR)
Stress corrosion cracking susceptibility test results for X80 steel covered by microbiological corrosion product film: (a, c) stress–strain curves and SCC susceptibility of X80 steel without cathodic protection; (b, d) stress–strain curves and SCC susceptibility of X80 steel under −1.1 V vs. SCE cathodic protection. (Image by IMR)
Schematic diagram illustrating the mechanism of biogenic FeS film in regulating stress corrosion cracking of X80 steel in an SRB environment.(Image by IMR)
