PSI - Issue 79

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

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1.3. A solution of 2gr of red phosphorous P4 in 40 ml of carbon disulfide (CS2) was added to the electrolyte to induce the hydrogen absorption into the steel. The steel plate was connected as the cathode, while a graphite bar was connected as the anode. The steel plates were charged at 20 mA/cm2 to obtain similar H-crack damage with comparable kinetics. The CC experiments were conducted for 30 days or until no HIC growth was detected, whichever occurred first. The unexposed side of the plate was ultrasonically inspected by manual scanning to detect HIC nucleation and growth. The 50% drop of the gain signal criterion was used to determine the location of the edge of the HIC cracks, with ±1.0 mm of crack detection sensitivity.

Table 1. Chemical composition of the studied pipeline steels (Wt. %).

Type

Specimen

C Si

Mn P+S+Al

Cr

Mo+Ni

V+Ti+Nb Co+W+Cu

X70-1 X70-2

0.165 0.329 1.630 0.027 0.126 0.088 0.173 0.342 1.540 0.022 0.137 0.089 0.155 0.282 1.620 0.016 0.052 0.041 0.209 0.340 1.040 0.033 0.142 0.092 0.258 0.380 1.070 0.034 0.112 0.103 0.157 0.279 0.860 0.037 0.024 0.013

0.105 0.110 0.040 0.041 0.040 0.037

0.153 0.079 0.063 0.097 0.113 0.262

NG

X80 X46 X52 X56

OG

Table 2. Tensile mechanical properties of tensile mechanical properties. Steel grades Type UTS (MPa) Elongation (%) X70-1 NG 640 27 X70-2 620 27 X80 755 20 X46 OG 435 22 X52 460 21 X56 490 19

The hydrogen permeation tests were conducted according to the ISO 17081 standard [14] on 2 mm side cube blocks extracted from uncharged steel plates. The test was done in a modified Devanathan-Stachurski electrochemical cell, with solutions of 11 ml of sul furic acid (H₂SO₄) and 3 g/L of ammonium thiocyanate (NH₄SCN) in 1000 ml of distilled water in the charging cell, and 6 g of sodium hydroxide (NaOH) in 1000 ml of distilled water in the oxidation cell.

Fig. 1. Experimental setup for cathodic charging. 2.3 Microstructural characterization, hydrogen microprint technique and EBSD

The metallographic specimens were prepared by mechanical polished up to a mirror like finish, cleaned ultrasonically, and etched with Nital. Optical microstructural analysis was performed using an Olympus GX51