A Comparative Investigation of the Effect of Microstructure and Crystallographic Data on Stress-Oriented Hydrogen Induced Cracking Susceptibility of API 5L X70 Pipeline Steel

In this research, stress-oriented hydrogen induced cracking (SOHIC) test was carried out on a 50 mm thickness of commercial API 5L X70 steel plate. The evolution microscopic features such as phase, boundary, interface, grain, and crystallographic data analyzed before after SOHIC, in order to comprehend the effect orientation SOHIC propagation. Chemical composition previous thermomechanical processing even finish rolling temperature cooling rate determine ferrite matrix microstructure. A recrystallized ultrafine grain with about 3–5% degenerated pearlite dispersed microstructure characterized, called as-received specimen. average lattice strain dislocation density calculated first using multiple Gaussian peak-fitting method from XRD pattern. Electrochemically charged combination mixed H2S-CO2 solution, constant injection, external loading were applied tensile specimen, simulate H2S CO2 environment. results show that local misorientation Taylor factor analyses predicted possibility crack nucleation especially at boundaries interfaces. Moreover, propagation occurred along mid-thickness cross section plate ferritic boundaries, pearlitic colonies, ferrite-cementite propagated distorted {110} {001} grains, indicating strong gradient towards boundaries. analysis patterns tested specimen by estimated 68% increment micro-deformation approximately 170% increase density.