Hydrogen Content and Charpy Toughness of Pipeline Steels with Different Hydrogen Charging Processes

Hydrogen embrittlementHydrogen embrittlement of pipeline steelsPipeline steel has become a major design concern for the transportation of pure hydrogen gasHydrogen gas or hydrogen blends using pipeline, especially at high design stresses. Quantification of the effects requires measurement of hydrogen contentHydrogen content in test samples and suitable test controls to simulate the practical service conditions. In this work, the total hydrogen contentHydrogen content in pipeline steelsPipeline steel pre-charged using electrolytic and gaseous methods was measured using the inert gas fusion (LECO) analysis. The analysis results showed that an average of approximately 0.2 ppm hydrogen existed in the as-received X65 steelSteel specimens without either electrolytic or gaseous hydrogen chargingHydrogen charging. The electrolytic pre-charging in 0.1 M NaOH solution with 150 mg/L As2O3 was effective to introduce hydrogen into the X65 steelSteel, and the highest total hydrogen contentHydrogen content of 1.4 ppm was achieved at a charging current density of 2.5 mA/cm2 and charging time of one hour. The highest total hydrogen contentHydrogen content achieved by the gaseous charging technique in pure H2 at 10.3 MPa pressure at room temperatureTemperature for 15 days was 0.4 ppm. Pd surface coatingCoating promoted hydrogen absorption into the steelSteel and led to almost doubled total hydrogen contentsHydrogen content for both charging techniques. Ex-situEx-situ Charpy testsCharpy test of electrolytically pre-charged X65 specimens at room temperatureTemperature showed approximately maximum 20% reduction in Charpy absorbed energy (CVN) compared to uncharged specimens. The discrepancy in the pre-charging time needed to reach the saturation effect (i.e., one hour for LECO vs. five hours for Charpy) can be attributed to the different sample geometry and dimensions for the LECO and Charpy testsCharpy test.