Page 100 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

78 INTRODUCTION AND FORMS OF CORROSION

(a)

112X 25KV WD:16MM S:00000 P:00003
200VM
MnS inclusion

(b)

Figure 1.21 Hydrogen-induced cracking: (a) centerline cracks and (b) blister crack. (Figure
originally published in Reference 104. Reproduced with permission of the Canadian Institute
of Mining, Metallurgy and Petroleum. www.cim.org.)

perpendicular to the stress and in the plane defined by nonmetallic inclusions
as depicted in Figure 1.22. SOHIC is a process by which SSC can propagate
in relatively low-strength steels (hardness <22HRC), which would otherwise be
considered resistant to SSC.
It is useful to note that there may be more than one cracking mode that can cause
a failure. The following four main environmental cracking modes can result when
steels are exposed to wet H S environments (108, 109).
2
1. Hydrogen blistering: blister formation, originating at nonmetallic inclusions.
2. HIC also known as SWC.
3. SOHIC.
4. SSC: cracking in high strength or hardness steels.

1.8.10.11 Precipitation of Internal Hydrogen During cooling of the melt, hydro-
gen precipitates in voids and discontinuities. Cracking because of precipitation of
internal hydrogen may be considered as a special case of blistering and occurs when