High strength carbon steel wire roads have been widely used in armor cables for offshore oil drilling plants. However, the materials can undergo some corrosions and hydrogen related damages such as hydrogen induced cracking (HIC) and sulfide stress cracking (SSC). In particular, it has been reported that HIC is highly influenced by content of MnS containing inside the steels. However, effects of sulfur content on the corrosion of carbon steel wire rod have scarcely been reported systematically. In this study, the effects of sulfur and propagation of corrosion in carbon steel wire rod were investigated in sour solutions with various pH.

 The carbon steel wire rods containing various sulfur content were used. All electrochemical tests were conducted using three-electrode system with a saturated calomel electrode (SCE) as the reference electrode and a Pt wire as the counter electrode. In addition, acetic acid based solution containing 95% CO₂ and 5% H₂S were used to adjust pH in the range of 2.5-6.5 at the room temperature for corrosion tests. Before testing, the carbon steel wire words were polished by abrasive papers and then washed with ethanol, and deionized water. The overall corrosion behaviors and corrosion rate of the samples were analyzed using potentiodynamic tests. In addition, the HIC characteristic of the steels was investigated by immersing the samples in the solution followed by observing the crack propagation inside the samples. Surface morphologies of the samples after tests were also observed by optical microscope (OM) and scanning electron microscope (SEM).

 The corrosion current densities (i_corr) of carbon steel increased with the increasing in sulfur contents in the steels. Further, from the polarization curves, it is observed that cathodic current density increased with sulfur content in steels. It is noticeable that the anodic current density rarely changes. This result indicates that the cathodic hydrogen evolution process on the surface of the steels was promoted by S content inside the steels. In addition, the samples without applied stress showed the internal macro-cracks in cross sections in pH 2.5~5.1, while only small micro-cracks were found in solution pH 5.1~6.5. The length of crack increased with increasing sulfur content except in the solution with pH 5.1~6.5. In particular, the micro-cracks by HIC appeared to initiate around inclusions. Some tracing of the cracks will be shown in this presentation.