[ materials ]
Figure 1
Material properties
Environmental conditions
Hydrogen Embrittlement
Mechanical stress characteristics
Although the diagram in Figure 1 is qualitative , it can still serve as a guide to identify variables that must be considered when assessing the risk for hydrogen embrittlement . In the material properties space , variables such as material strength , alloy-element composition , and metallurgical features can all affect the potential for hydrogen embrittlement . One prevailing trend across all classes of metals is that higher-strength alloys are more prone to hydrogen embrittlement than lowerstrength alloys . In the context of Figure 1 , this means that hydrogen embrittlement can be activated in higher-strength alloys for more combinations of environmental conditions and mechanical stress characteristics compared to lower-strength alloys . A practical extension of this concept is that managing hydrogen embrittlement by modifying environmental conditions or mechanical stress characteristics may be less effective for hydrogen containment components fabricated from higher-strength alloys . One example of a higher-strength alloy that can be encountered in components employed for hydrogen containment is 17-4 PH stainless steel . There are documented cases of components fabricated from 17-4 PH stainless steel that have failed in gaseous hydrogen service . 1
In the mechanical stress characteristics space in Figure 1 , one important consideration is the time-variation of mechanical stresses on metals in hydrogen containment components . Specifically , the activation of hydrogen embrittlement can depend on whether the applied mechanical stress is constant or whether it repeatedly cycles between maximum and minimum levels . For example , as mentioned previously , lower-strength alloys tend to be more resistant to hydrogen embrittlement than higher-strength alloys . However , this trend is most consistent when applied mechanical stresses are constant . Certain lower-strength alloys may not exhibit hydrogen embrittlement under constant mechanical stress , but when the same alloys are subjected to cyclic mechanical stress , then hydrogen embrittlement may be promoted . In addition to the time-variation of mechanical stresses , the absolute magnitudes of mechanical stresses can dictate the activation of hydrogen embrittlement . In particular , geometric discontinuities in containment components can give rise to elevated mechanical stresses , and in turn these sites promote the formation of hydrogen embrittlement-related cracks . A real-world case study of how mechanical
Hydrogen Tech World | Issue 9 | April 2023 23