Experimental Investigation of Hydrogen Assisted Cracking in Micro Alloyed High Strength Line Pipe Steels

This research focuses on conducting experimental investigations into hydrogen-assisted cracking in micro-alloyed high-strength line pipe steels (API5LX80), with the aim of understanding the negative impact of corrosion affecting the physical and mechanical characteristics of API5LX80 steel. Initially, fracture and failure analyses were performed on various sections of the API5LX80 steel, including the base material, heat-affected zone, and weld. These analyses involved microstructural studies, as well as various tests such as hardness, CTOD, and J-R. The heat-affected zone was found to have a finer grain structure and higher hardness compared to the weld and parent materials. Moreover, the presence of impurities (such as inclusions and porosity) in the welded zone reduced its fracture toughness. Fracture micro-mechanisms observed in the weld area included river lines, quasi-cleavage fracture, and microstructure cracks induced by environmental factors, all of which contributed to decreased toughness. Fractography was utilized to determine the cause and type of fractures, as well as the potential location and nature of flaws that contributed to the fractures. Non-destructive testing using dye reentrant was also conducted to identify surface-breaking flaws in all closely examined materials, specifically focusing on crack-initiated materials from various locations. Meanwhile, fracture and failure analyses were employed to investigate how the presence of hydrogen affected the toughness behavior of steels in pipelines. Additionally, the weld regions exhibited 53% less ductility compared to the base metal. Fractographic examination of fractured tensile and CTOD specimens from the weld region revealed the failure mechanism, which showed reduced energy absorption capacity and consequently diminished fracture toughness. The experimental investigations carried out in this study establish an empirical foundation for the widespread adoption of upgraded materials and safety systems, as well as a method for assessing the resilience and safety of active pipelines.