Hydrogen diffusion was studied in API grade X70 pipeline steel, simulated coarse grained heat affected zone (HAZ) and weld metal of type HBQ Coreweld using the electrochemical permeation technique. Hydrogen diffusion measurements were carried out at 25°C, 50°C and 70°C. The results were similar for all three metals with the average values of effective diffusion coefficient at 25°C ranging from 1.26 × 1CT~7 to 1.22 ×10~6cm~2/s. The values decreased in the order: HBQ Coreweld metal > X70 grade steel > simulated HAZ. The metals showed similar response to increased temperature with respect to the diffusion coefficient. The simulated HAZ showed the highest values for the sub-surface hydrogen concentration, and the value did not vary significantly as a function of temperature for any of the materials. The number of reversible trapping sites was in the order of 1019 sites/cm3. The values of their binding energy varied from 34 to 41 kJ/mol.
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