Recent activities in ISIJ HLP research committee corrosion working group: Proposal of pH buffer test solution for fitness-for-purpose HIC evaluations

Abstract

The HLP (High-strength Line Pipe) Research Committee in the Iron and Steel Institute of Japan (ISIJ) has investigated the major issues of line pipes from the viewpoints of corrosion and fracture. Fitness-For- Purpose (FFP) evaluations for Hydrogen Induced Cracking (HIC) have been the subject of considerable study in recent years. FFP is the idea that appropriate materials are chosen depending on the severity of the use environment. Therefore, it is possible that the applicable range of material strength and the flexibility of manufacturing can be expanded by establishing the FFP evaluation approach. This paper reviews the recent activities of the HLP Corrosion Working Group during the past few years. The current status of the conventional HIC test method and FFP HIC evaluation methods were overviewed. Based on the results of a variety of experiments, the HLP Research Committee proposed a HIC test solution for FFP evaluations in the NACE Task Group. The proposed solution is a highly concentrated acetate buffer solution that is 5%NaCl+0.93N - (CH3COOH+CH3COONa), and is expected to be adopted as the optional solution in NACE TM0284. The solution displayed an excellent pH buffering capacity during a long-term HIC test in comparison with the conventional HIC test solutions. The corrosion rate and hydrogen permeation behavior of the steel specimen in the solution were similar to those in the conventional solutions.