Wide Range Buffering Capacity of HLP Solution for Long-term HIC Testing under Mildly Sour Conditions

Hydrogen Induced Cracking (HIC) is a major issue of carbon steels for pipelines exposed to wet sour environments. For Fitness-for-Purpose (FFP) HIC evaluations which require a longer test duration than the conventional 96 h, Solution C was registered in NACE TM0284. However, because Solution C requires frequent pH adjustment using HCl and NaOH during HIC testing depending of the sour conditions, there is a strong need for a FFP testing solution with higher pH stability. The High-strength Line Pipe (HLP) Committee of The Iron and Steel Institute of Japan (ISIJ)⁽¹⁾ proposed a 5.0 wt% NaCl + 0.93N (CH₃COOH + CH₃COONa) solution (HLP solution). In this study, the pH stability of the HLP solution during HIC tests was investigated under a wide range of sour environments, and the effect of the solution volume for achieving higher pH stability without pH adjustment was also investigated. The results confirmed that the HLP solution is applicable to a wide range of pH and H₂S partial pressure conditions and requires less or no pH adjustment during the HIC test. Based on these advantages, the HLP solution is expected to enhance the use of high grade linepipe steels for mildly sour environment.