PSI - Issue 54

Margo Cauwels et al. / Procedia Structural Integrity 54 (2024) 233–240 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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of the DCPD current. The same charging condition was used for the in-situ charging and the pre-charging. The SENT test was stopped when the force dropped down to 80% of the maximal value achieved during the test. Specimens were then cleaned, heat tinted in a 200°C oven for 2h, and broken in liquid nitrogen in order to inspect the crack growth. Two air tests were carried out, as well as one test for each hydrogen charged condition. Hydrogen content was determined using representative 10 x 10 x 10 mm 3 samples taken from the middle section of the pipeline, in a G8 Galileo infrared furnace at 900°C and connected to a thermal conductivity detector (TCD). A hydrogen content of 0.42 ± 0.04 wppm was found after 48h of pre-charging, resulting from 3 samples measured at this charging time.

Fig. 1. SEM images of the mid-thickness microstructure (a) on the L plane, showing a segregation band in the center and (b) on the S plane.

Fig. 2. Schematic representation of the LS SENT specimen.

3. Results and Discussion 3.1. Mechanical data

Fig. 3 plots the normalized load over the initial cross-section versus the crack mouth opening displacement (CMOD) of the different tested specimens. While the ex-situ hydrogen charged case reaches similar tensile loads compared to the uncharged reference condition, this is not the case for the in-situ tested specimen, where a significant reduction is observed. This corresponds to a decrease in calculated fracture toughness for the in-situ tested specimen compared to the uncharged specimens. Note also the sudden drop towards the end for one of the uncharged specimens, probably resulting from a sudden delamination event in that specimen.