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54 AUGUST 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 8 MATERIALS SELECTION & DESIGN H Previous studies of hydrogen perme- ation suggest that deformation asso- ciated with uniaxial tensile stress af- fects this behavior. However, few studies have focused on hydrogen permeation behavior during a slow strain rate test (SSRT). In order to clarify elastic and plastic deformation effects on hydrogen permeation, measurements were made by a Devana than-Stachurski double cell during SSRT. The results show that the background current density increases in the elastic deformation range dur- ing SSRT. The hydrogen permeation current increases slowly in the elastic deformation range and decreases quickly in the plastic range due to the trapping effect by dislocations formed during plastic deformation. Competing mechanisms—disloca- tion trapping and dislocation trans- port of hydrogen—affect the hydro- gen permeation current. Hydrogen absorbed by carbon steel (CS) has a devastating effect on its strength and ductility, resulting in a high risk of brittle failure, such as hydrogen-induced cracking and sulfide stress cracking. 1-4 Hence entry of hyd ro gen i nto st e el f rom a qu e o u s solutions has been widely studied. 5-9 Typically, the hydrogen permeation behavior of steel has been electrochemi- cally measured using the Devanathan-Sta- churski (D-S) cell. 5 This method has been successfully used by plating the hydrogen exit side of the steel membrane with Pd or Ni. The thin layer of coating on the steel surface improves the hydrogen oxidation, which ensures a stable hydrogen perme- ation current. 10-12 Many studies have been undertaken to measure the hydrogen permeation current for various metallic materials under tensile stress within their plastic range. 4,8-9 Those studies suggest that two competing effects (enhanced trapping and enhanced trans- port by dislocation) can both play a role when metals are deformed, with either one or the other being dominant under particu- lar conditions. For a steel membrane under externally applied stress, some researchers believe that the reliability of the hydrogen permeation test greatly depends on the sta- bility of the thin Pd coating layer, since the stability of that layer changes with the strength and elongation level of the steel substrate. Kurkela, et al. 9 measured the hydrogen permeation current for a Cr-Mo steel (yield strength [YS] = 496 MPa) within its plastic range using the conventional Pd coating method and permeation test proce- dure. They reported current spikes due to the disruption of the Pd coating layer by the plastic strain. Although this study reported valuable information about the effect of applied stress on hydrogen transport, it did not clearly explain whether the decrease in the permeation current under plastic load was due to dislocations trapping the hydro- Effect of Stress on Hydrogen Permeation for X70 Carbon Steel in Seawater Chuanbo Zheng and Cheng Wang, School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu Province, China