PSI - Issue 79

Jorge Luis González-Velázquez et al. / Procedia Structural Integrity 79 (2026) 526–533

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Fig. 2. Microstructure of OG pipeline steels. (a) API X46 (b) API X52 and (c) API X56 pipeline steels. Optical microscopy, bright field, etched Nital 3.

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Fig. 3. Crack contours of pipeline steel plates cathodically charged for 30 days at 20 mA/cm 2 . A) X46 OG, b) X56 OG, c) X70-1 NG, d) X70-2 NG. Fig. 4 shows the HIC kinetics. It is observed that in both steel NG and OG groups, the stage of individual HIC growth occurred at similar rates, ranging from 0.25 cm 2 /h to 0.35 cm 2 /h, but after the nucleation of individual cracks ceased and the growth was mostly by crack interconnection, the crack growth rate decreased below 0.75 cm 2 /h to finally became near zero after 500 hours of CC. Plots of HIC kinetics with respect to the H-solubility ( C app ) and density of reversible traps (  RT ) are shown in Fig 5. It is observed that the crack growth rate in Stage I does not correlate well with C app , but if the correlation is done separately for each steel type, the correlation is greatly improved. On the other hand, the HIC kinetics correlated very well with the  RT for both OG and NG steels.