[ materials ]
stresses can govern the activation of hydrogen embrittlement is the spate of failures that occurred in steel hydrogen transport cylinders throughout Western Europe in the 1970s . Two prominent factors that contributed to these hydrogen embrittlement-related failures were cyclic mechanical stresses resulting from filling / discharging operations and localized mechanical stress concentration at the base of the cylinders . 2
The final space in Figure 1 is environmental conditions , and here two of the primary variables influencing the activation of hydrogen embrittlement are gas pressure and temperature . As hydrogen gas pressure increases , hydrogen ingress into metals becomes more extensive so the potential for hydrogen embrittlement is enhanced concomitantly . Such enhanced hydrogen embrittlement susceptibility does not continue indefinitely as gas pressure increases since the severity of hydrogen-induced material degradation reaches a limit . Regarding temperature , the potential for hydrogen embrittlement is typically highest at near-ambient conditions . As temperature decreases , hydrogen diffusion becomes slower , which can limit the extent of hydrogen penetration into metals . At higher temperature , although hydrogen diffusion is accelerated , there is less interaction between hydrogen and metallurgical defects . As a result , at both lower and higher temperatures , hydrogen-induced material degradation is less severe .
The high-level view encapsulated in Figure 1 can guide various approaches for assessing the risk of hydrogen embrittlement in hydrogen containment systems . In some scenarios , simply identifying key variables associated with a hydrogen containment component may be sufficient to assess the risk of hydrogen embrittlement . For example , a component fabricated from lower-strength steel and
About the author
Dr . Brian Somerday is currently a Materials Engineering Consultant with Somerday Consulting , LLC ., a member of the Hydrogen Safety Panel , and routinely supports activities at the Center for Hydrogen Safety . He has 25 years of experience in mechanical metallurgy with a focus on environmental effects on fracture and fatigue of structural alloys . Brian has published extensively on the topic of hydrogen-assisted fracture and fatigue in structural alloys , including co-authoring the Technical Reference for Hydrogen Compatibility of Materials ( www . sandia . gov / matlsTechRef /) and co-editing the two-volume set Gaseous Hydrogen Embrittlement of Materials in Energy
Technologies ( Woodhead Publishing , 2012 ).
subjected to constant mechanical stresses at typical design levels is unlikely to suffer hydrogen embrittlement .
Another way the concepts in Figure 1 can be helpful is when the successful field experience of hydrogen containment systems serves as a reference for evaluating the hydrogen embrittlement potential in other systems considered for hydrogen service . Here , the guidance from Figure 1 is to determine whether the three variable types associated with the system in question may enhance the potential for hydrogen embrittlement relative to the system with successful field experience . For example , assume the two systems are identical in the material properties and environmental conditions spaces , but the system with successful field experience was only subjected to constant mechanical stresses while the system in question is expected to experience cyclic mechanical stresses . In this case , the successful field experience cannot provide confidence that the system in question is safe from hydrogen embrittlement .
24 Hydrogen Tech World | Issue 9 | April 2023