Autoclave tests were performed to determine the amount of hydrogen absorbed by two casing and tubing steel grades, a OCTG grade comparable to the API grade L80 (Steel A) and a high strength sour gas resistant steel grade (Steel B), under high hydrogen partial pressures up to 1000 bar and high temperatures up to 200 °C. Steel samples were charged with pressurized pure hydrogen gas for different times to obtain the saturation concentration of hydrogen under these conditions as well as the relationship between hydrogen uptake and charging time.
Furthermore, electrochemical permeation experiments were conducted. Those were done in an electrochemical double cell as first proposed by Devanathan and Stachursky. Data gathered by these measurements were used to calculate the effective diffusion coefficient of the tested material. Additionally, the effective diffusion coefficient was determined by fitting Fick’s second law to hydrogen charging data. By comparing both diffusion coefficients it seems likely that the hydrogen absorption process is not controlled by diffusion under the applied conditions.
The results of the charging experiments showed that even though Steel B is the higher strength steel grade the amount of hydrogen the material absorbed was similar to the lower strength Steel A. Furthermore, it was found that the sample geometry as well as the surface finish and roughness of the samples severely affected the amount of hydrogen the material absorbed.