Numerical Predictions of Mild-Steel Corrosion in a H 2 S Aqueous Environment Without Protective Product Layers Xiufeng Li,* Haijun Hu, ‡, * Guangxu Cheng,* Yun Li,* Wei Wu,* Yong Xia,** and Wei Wu* ABSTRACT The corrosion of mild carbon steel in a H 2 S aqueous envi- ronment without corrosion product layers is predicted using the computational fluid dynamics method. The Abe–Kondoh– Nagano low-Reynolds-number model is applied to predictions of hydrodynamics and mass transfer in a rotating cylinder electrode system. The flow domain in the system is modeled using three-dimensional geometries and meshed by grids with the first near-wall node at the position y + = 0.1. The azi- muthal velocity and mass transfer coefficient are predicted and validated with experimental data. User-defined functions based on the electrochemical model of H 2 S uniform corrosion are developed and interpreted with software. Corrosion rates of iron in dissolved H 2 S aqueous are predicted and compared with experimental data. Predicted corrosion rates are lower than experimental data with a relative error of 4% to 22%. The Abe–Kondoh–Nagano model shows credible and reliable per- formance in predicting the hydrodynamics, mass transfer, and H 2 S corrosion of a rotating cylinder electrode system. KEY WORDS: Abe–Kondoh–Nagano low-Reynolds-number model, corrosion rate, carbon steel, hydrogen sulfide, rotating cylinder electrode system, uniform corrosion INTRODUCTION The corrosion of carbon steel in a H 2 S aqueous en- vironment remains an important issue in the oil and gas industry because new developed gas and oil fields have large quantities of H 2 S, especially in China. 1 Many studies have investigated the corrosion mechanism and attempted to improve the prediction of the corrosion rate. 2-5,8-13 Several factors, such as the flow condi- tions, temperature, pH value, H 2 S pressure, and for- mation of iron sulfide, have been shown to control the corrosion process. Morris, et al., 2 investigated the electrochemical behavior of carbon steel in H 2 S solution under condi- tions of pH = 2 to 4 and H 2 S partial pressure of 0 atm to 1.0 atm (0 kPa to 101.325 kPa) using a rotating disk electrode cell. They found that the presence of H 2 S makes the reversible potential more negative. Cheng, et al., 3 claimed an acceleration effect of H 2 S on the anodic dissolution of iron in acid solutions, resulting from the high surface coverage of adsorbed H 2 S. Ma, et al., 4 studied the inhibition effect of H 2 S on iron corrosion. They found that H 2 S accelerates both anodic and cathodic reactions but inhibits iron corro- sion under conditions of C H2S < 0.04 mmol/dm 3 , pH = 3 to 5, and immersion time longer than 2 h. The inhibition effect is mainly attributed to FeS formation. Sun and Neši´ c 5 investigated the mechanism and kinetics of mild-steel corrosion in a H 2 S environment by conducting glass cell experiments. They con- cluded that mackinawite is the predominate type of iron sulfide. A thin inner mackinawite layer is Submitted for publication: January 15, 2016. Revised and accepted: February 15, 2017. Preprint available online: February 15, 2017, http://dx.doi.org/10.5006/2031. ‡ Corresponding author. E-mail: huhaijun@mail.xjtu.edu.cn. * Department of Process Equipment and Control Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China. ** The first Natural Gas Plant, PetroChina Changqing Oilfield Com- pany, Jingbian 718500, China. 786 ISSN 0010-9312 (print), 1938-159X (online) 17/000131/$5.00+$0.50/0 © 2017, NACE International CORROSION—JULY 2017 CORROSION SCIENCE SECTION