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Validating hydrogen embrittlement models for steel tanks

By Paul Grad |

Hydrogen is transported in steel tanks and pipelines. However, H2 causes embrittlement of steels by accumulating at microstructures called dislocations and at the boundaries between the individual crystals of which the steel is composed. The accumulation of hydrogen weakens the steel along those features, leading to embrittlement that could allow the steel to fracture easily. Measuring the precise location of hydrogen atoms in steel has been challenging. Previous methods, such as thermal desorption spectroscopy, could identify hydrogen trapping, but could not easily identify the relative contributions of different microstructures.

Now, an important improvement in the safe production, storage and transportation of hydrogen has been found by a team from the University of Sydney (Sydney, Australia; sydney.edu.au), CITIC Metal Co. (Beijing, China), University of Science and Technology Beijing (China), Microscopy Solutions Pty (Caulfield North, Australia), and Shanghai Jiao Tong Univesity (Shanghai, China), led by Sydney University professor Julie Cairney. The team used cryo-transfer atom probe tomography to observe hydrogen at specific microstructures in steels. Direct observation of hydrogen at carbon-rich dislocations and grain boundaries provides validation of embrittlement models.

The team also found that clusters of niobium carbide within the steel trap hydrogen so that it cannot easily move to the dislocations and crystal boundaries to cause embrittlement. Hydrogen observed at an incoherent interface between niobium carbides and the surrounding steel provides direct evidence that that these incoherent boundaries can act as trapping sites. This information is vital for designing steels that can resist embrittlement, says Cairney.

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