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55 NACE INTERNATIONAL: VOL. 56, NO. 8 MATERIALS PERFORMANCE AUGUST 2017 gen, or a combined effect with a reduced rate of hydrogen oxidation due to disrup- tion of the Pd layer. Brass and Chene 13 con- ducted a permeation test without Pd depo- sition and repor t ed an extrem ely low permeation current because of low hydro- gen oxidation. Sung Jin Kim 12 developed a modified hydrogen permeation technique. Instead of coating the Pd layer on the hydro- gen exit side of the specimen before loading, the loading was performed prior to coating the specimen with Pd. By changing the sequence of the Pd coating and loading, the deformation problem of the soft Pd coating layer can be completely eliminated. Studies of uniaxial tensile stress defor- mation effects have been more common than those focused on hydrogen perme- ation behavior during the slow strain rate test (SSRT). In this study, a D-S cell was used to measure the hydrogen permeation current during the whole elastic and plastic deformation by SSRT. The effect of a Ni coating layer deformation on background current density (CD) was observed, and the effects of deformation on hydrogen perme- ation behavior of pipeline steel were inves- tigated in simulated seawater. Experimental Method Materials and Specimens The material used for the study was a commercial pipeline steel (API 5L, Grade X70 CS) with a chemical composition of 0.18 wt% C, 1.2 wt% Mn, 0.018 wt% P, and 0.014 wt% S. Its YS σ and ultimate tensile strength σ b were 398 and 406 MPa, respec- tively. Cylindrical specimens (10 mm in diameter, 50 mm in height, and 0.5-mm thickness) were used as working electrodes, with the inside surface of the specimens coated with a thin layer of Ni. The outer, central part of the cylindrical specimens was used as the working (hydrogen entry) si d e. A s o lution c ont ainin g 250 g L –1 nickel(II) sulfate hexahydrate (NiSO 4 ·6H 2 O), 45 g L –1 nickel(II) chloride hexahydrate (NiCl 2 ·6H 2 O), and 40 g L –1 boric acid (H 3 BO 3 ) was used to electroplate nickel at a CD of 3 mA cm –2 , for a coating time of 3 min. Pre- vious studies confirm that a Ni-plated sur- FIGURE 2 Typical variation in background current of the specimen with different loading values in the elastic deformation range. FIGURE 1 The experimental setup. face provides advantages over a Pd-plated surface 14 for the hydrogen exit side of the cell (inner portion of the specimen). Before th e test, th e specim ens were carefully cleaned with alcohol and acetone using an ultrasonic bath, and then dried with cold air. Experimental Setup Figure 1 shows the experimental setup. The inside of the specimen was used as the exit side of the hydrogen permeation cell and filled with 0.1 mol L –1 sodium hydrox- ide (NaOH). The counter electrode was comprised of Pt, and the reference elec- trode was made of Ir. Before the test, the inside of the specimen was potentiostati- cally polarized at 50 mV vs. the Ir electrode in NaOH for more than 24 h until the remaining CD was <0.1 µA cm –2 . The tem- perature of the chamber was thermostati- cally controlled at 298 °K (77 °F [25 °C]). The test solution was artificial seawater. It has been previously established that hydro- gen permeation behavior is directly related to the strain rate. At high strain rates, a