Environmental Engineering Reference
In-Depth Information
Figure 8.2
Ductility loss of austenitic stainless steels in high-pressure hydrogen [21].
strophic cracking of high-strength steels in hydrogen sulfide environments,
known as sulfide stress cracking, is a special case of HSC.
The cracking of the embrittled metal is caused by static external stresses, trans-
formation stresses (e.g., as a result of welding), internal stresses, cold working,
and hardening. In the absence of a sharp initial crack, the hydrogen-induced frac-
ture often initiates at subsurface sites where triaxial stress is highest. If a sharp
crack is already present, as in the case of a fatigue or stress corrosion crack or
a surface defect, the hydrogen cracking may initiate at the tip of the preexisting
crack. High hydrogen concentration ahead of the crack tip then helps the subcriti-
cal crack to grow. The source of hydrogen for HSC may be gaseous hydrogen
or the hydrogen generated in thermal processing, electrolysis, or corrosion. A
total hydrogen content of as low as 0.1-10 ppm is sufficient to induce cracking.
However, local concentrations of hydrogen are substantially greater than average
bulk values.
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