Objectives of the project include: Enable the use of high strength steel hydrogen pipelines, as significant cost savings can result by implementing high strength steels as compared to lower strength pipes. Demonstrate that girth welds in high-strength steel pipe exhibit fatigue performance similar to lower-strength steels in high-pressure hydrogen gas. Identify pathways for developing high-strength pipeline steels by establishing the relationship between microstructure constituents and hydrogen-accelerated fatigue crack growth (HA-FCG)
One of the most efficient methods for supplying gaseous hydrogen long distances is by using steel pipelines. However, steel pipelines exhibit accelerated fatigue crack growth rates in gaseous hydrogen relative to air. Despite conventional expectations that higher strength steels would be more susceptible to hydrogen embrittlement, recent testing on a variety of pipeline steel grades has shown a notable independence between strength and hydrogen assisted fatigue crack growth rate. It is thought that microstructure may play a more defining role than strength in determining the hydrogen susceptibility. Among the many factors that could affect hydrogen accelerated fatigue crack growth rates, this study was conducted with an emphasis on orientation dependence. The orientation dependence of toughness in hot rolled steels is a well-researched area; however, few studies have been conducted to reveal the relationship between fatigue crack growth rate in hydrogen and orientation. In this work, fatigue crack growth rates were measured in hydrogen for high strength steel pipeline with different orientations. A significant reduction in fatigue crack growth rates were measured when cracks propagated perpendicular to the rolling direction. A detailed microstructural investigation was performed, in an effort to understand the orientation dependence of fatigue crack growth rate performance of pipeline steels in hydrogen environments.