Evaluation of mechanical properties in hydrogen-exposed pipeline steels by using instrumented indentation technique

Abstract

To prepare the up-coming era of so-called `hydrogen economy`, many researches focused on the related topics are actively conducted all round the world. With a viewpoint of industrial field applications, one of the important topics being studied is hydrogen transmission (more specifically, `hydrogen pipeline`). Pipeline is conceivably the most economic way to consistently and safely transport a large amount of hydrogen over a long distance, which may be strongly requested in hydrogen economy era. So, the development of advanced high-pressure hydrogen pipelines is highly desirable. As a good starting point for the purpose, one might wonder whether conventional API pipeline steels (designed for oil and natural gas transmission) can be used as the hydrogen pipeline materials or not. To answer the question, here we performed a series of micro-/nano-indentations on the hydrogen-charged API X65 and X70 steels. By comparing the indentation results with those from tensile tests and microstructural observations, the hydrogen effects on the mechanical behavior in the API steels are systematically analyzed and discussed.