July 15-20, 2018
Notch sensitivity effects under environmentally-assisted cracking (EAC) conditions have been recently quantified considering the tolerance to short cracks that may start at their tips and become non-propagating after growing for a while, a behavior that depends on the stress gradients ahead of the notch tips and on the basic material resistances to crack initiation (SEAC) and propagation (KIEAC) inside an aggressive medium under static loadings. Such properties are time-independent, so they can be directly compared with the notch gradient-affected stress intensity factors of the short cracks that depart from notch tips. This model can provide a powerful alternative design tool for the pass/non-pass criterion traditionally used to deal with such mechanical-chemical problems, since it properly considers and quantifies the stress analysis issues that affect them. This model has been validated by proper tests under liquid metal embrittlement conditions, and it can be used to propose a defect-tolerant design criterion under EAC conditions that includes the unavoidable notch effects always present in actual structural components.
This paper objective is to experimentally verify the proposed model predictions under other EAC mechanisms. Among them, hydrogen embrittlement (HE) is a most important one, since many catastrophic failures have been associated to it. Due to its practical importance, two different sources of hydrogen are used in this work to understand the HE short crack behavior: (1) sulfide stress corrosion (SSC) on super martensitic stainless steel in salt water with high amounts of H2S, which produces hydrogen by a corrosive process; and (2) cathodic protection (CP) on a high strength steel in salt water, which produces hydrogen by electrolysis. In both cases, the hydrogen diffusion is slow, due to the martensitic microstructures, although high amounts of hardly-measurable hydrogen may be present around the cracking region. Since the driving force for short cracks can be associated to the stress gradient ahead of the crack tip, the SSC and CP short cracks behavior can be predicted by the same set of procedures previously qualified under liquid metal embrittlement conditions, and with under some SSC tests made with carbon steels. Moreover, a third EAC mechanism is studied in this work as well, chloride-induced cracking in austenitic stainless steels, using a boiling solution of MgCl2.
JTP Castro, RV Landin, IN Viçosa, GR Altoé, and RRC Saúde, "Short crack tolerance under EAC conditions" in "Stress-Assisted Corrosion Damage V", A.K. Vasudevan, ONR (retired) Ronald M. Latanision, Exponent, Inc. N. J. Henry Holroyd, Luxfer Eds, ECI Symposium Series, (2018). http://dc.engconfintl.org/sacd_v/22