Page 101 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

ENVIRONMENTALLY INDUCED CRACKING (EIC) 79

7J2 (A) 50×
Figure 1.22 SOHIC in plate steel exposed to sour gas. (Figure originally published in Ref-
erence 104. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and
Petroleum. www.cim.org.)

excess hydrogen is picked up during melting or welding. Some examples of SSC are:
shatter cracks, flakes, and fisheyes found in steel forgings, weldments, and castings.
High-temperature high-pressure exposure to hydrogen is encountered usually in
steels used in petrochemical plants that handle hydrogen and hydrogen–hydrocarbon
∘
streams at high pressure (21 Mpa or 3 ksi) and temperatures as high as 540 C. This
type of hydrogen damage is irreversible while HE is often reversible and occurs
∘
below 200 C. The absorbed hydrogen reacts with carbides present in steel and forms
methane bubbles along the grain boundaries. The methane bubbles grow and cause
fissures. Fissures occur at grain boundaries and are accompanied by decarburization.
Copper alloys containing small amounts of cuprous oxide are susceptible to hydrogen
attack, leading to significant void formation (4).

Cu O + H → 2Cu + H O
2
2
2
Hydrogen gas exposure may also cause titanium embrittlement (96).

1.8.10.12 Other Types of Hydrogen Attack Hydrogen trapping, microperforation,
and degradation in flow properties have been observed (4). Liquid metal-induced
embrittlement (LMIE) is the catastrophic brittle failure of a normally ductile metal
when coated with a thin film of liquid metal and then stressed in tension (110).
Solid-metal-induced embrittlement occurs below the melting temperature of the solid
in certain liquid metal environments (LMIE couples). The severity of the embrittle-
ment increases with temperature with sharp increase in severity at the melting point
of the embrittler (4).

1.8.10.13 Mechanisms of EIC . EIC extends over a wide range from brittle frac-
ture to electrochemical process, and the underlying mechanisms are complex.