Abstract
The work carried out by the operators shows that it is possible to integrate a significant volume of hydrogen into the gas mix with limited infrastructure adaptation costs (up to about 6% hydrogen in the short term and up to 20% by 2030) with modest modifications to the pipeline network.
Two hydrogen charging methods are used to study hydrogen embrittlement (HE): i) gaseous pressurized hydrogen and ii) in-situ electrochemical charging. The electrochemical charging method is classically used because of its most straightforward implementation. However, its representativity with respect to the embrittlement mechanisms under gas remains an important question. In this study, both methodologies were compared. First, a horizontal tensile test machine has been developed to perform toughness tests under in-situ electrochemical charging. Toughness tests using compact tension (CT) specimens on a “vintage” line pipe steel have been performed under different conditions: in air as a reference, in pressurized hydrogen, and under in-situ electrochemical charging conditions. In order to make strain rate sufficiently slow, the rate of crack mouth opening displacement was chosen as 2 x 10-5 mm/s (corresponding to Κ = 8.5 x 10-3 MPa m1/2 s-1). A strong HE effect is observed on J-Δa crack curves for both hydrogen charging methods. The SEM observation of the fracture surfaces showed similar quasi-cleavage fracture. Cumulative desorbed hydrogen content was measured by thermal desorption spectrometry (TDS) analysis. For gaseous pressurized method, the effect of plasticity is evaluated using flat tensile specimens mechanically loaded under 85 bar pressure for two strain rate conditions (10-4 s-1 and 10-5 s-1). Significantly more hydrogen is observed for a mechanically loaded sample (12% plastic deformation) compared to a non-deformed sample. No effect of strain rate is observed. Finally, the amount of