Hydrogen influence on crack propagation and stress-strain evolution of alloy 718

Abstract

Nickel base alloys such as 718 are used for many applications in the drilling, completion and production segments in the Oil and Gas Industry. The alloy selection is based on high strength levels while exhibiting resistance to embrittle-ment and environmental cracking. Hydrogen embritdement can be a limiting factor to applications and this investigation was undertaken to better understand the mechanisms and characteristics of hydrogen in 718. Saluted hydrogen into metal could be presented in different conditions: diffuse-active and trapped by different defects and structure elements. Fatigue was used in current work as a tool for (1) the generation of structure defects and (2) hydrogen effects on crack growth. The following items were studied: (I) hydrogen solubility into different versions of 718 alloy; (2) effects of increased surface and volume defects density on hydrogen solubility; (3) hydrogen effects on stress-strain evolution; and (4) effects of hydrogen at different locations within the structure on crack growth rate. The specifics of each type of hydrogen location within the structure on crack propagation including diffusion-active and trapped by different defects and structure elements were discovered and presented.