Environmental hydrogen embrittlement

Environmental hydrogen embrittlement means that the material was subjected to a hydrogen atmosphere, e.g., storage tanks. Absorbed and/or adsorbed hydrogen modifies the mechanical response of the material without necessarily forming a second phase. The effect occurs when the amount of hydrogen that is present, is more than the amount that is dissolved in the metal. The effect strongly depends on the stress imposed on the metal. It also maximizes at around room temperature. 

A materials test equipment has been developed in Japan within the WE-NET project to investigate the environmental hydrogen embrittlement of specimens in high-pressure hydrogen up to 10 MPa at different temperature levels between 20 K and 1500 K. Additions of various gaseous inhibitors have been examined as a preventive technique to arrest crack growth in the materials [129]. 

Environmental Hydrogen Embrittlement (EHE) and Stress Corrosion Cracking (SCC)... 

Owing to hydrogen embrittlement, the mechanical properties of metallic and nonmetal-lic materials of containment systems may degrade and fail resulting in leaks. Hydrogen embrittlement depends on many factors such as environmental temperature and pressure, purity of metal, concentration and exposure time to hydrogen, stress state, physical and mechanical properties, microstructure, surface conditions, and the nature of the crack front of material [23]. 

The previous sections provided general guidance on materials for hydrogen gas service and emphasized the metallurgical variables that influence hydrogen embrittlement. This section describes additional factors that impact hydrogen embrittlement, primarily environmental and mechanical-loading conditions. 

Aluminum alloys, particularly the high-strength compositions, are susceptible to environmental cracking, both in aqueous environments and in air as a function of relative humidity. This susceptibility is particularly sensitive to alloy composition and thermal treatment, which is shown by differences in the dependence of ductility on strain rate. Understanding these differences can contribute to identification of mechanisms of the strain-rate sensitivity. A summary of the influence of strain rate on the ductility of 2000-, 5000-, and 7000-series aluminum alloys in environments represented by 3% NaCl + 0.3% H202 is shown in Fig. 7.84 (Ref 121). The 7000 series shows susceptibility to hydrogen embrittlement at strain rates below 10 5 to 10-6 s 1. Although there is... 

R.N. Parkins, Environmental Aspects of Stress Corrosion Cracking in Low Strength Ferritic Steels, Stress Corrosion Cracking and Hydrogen Embrittlement of Iron Base Alloys NACE 5, R.W. Staehle, J. Hochman, R.O. McCright, and J.E. Slater, Ed., National Association of Corrosion Engineers, 1972, p 601-619... 

Wei, R. P., and Gao, M., Hydrogen Embrittlement and Environmentally Assisted Crack Growth, in Hydrogen Effects on Material Behavior, Neville R. 

Wei, R. P., and Gao, M., Hydrogen Embrittlement and Environmentally Assisted Crack Growth, Hydrogen Effects on Material Behavior, N. R. Moody and A. W. Thompson, eds.. The Mineral, Metals Materials Society, Warren-dale, PA (1990), 789-815. (D. Ressler, M. S. Thesis, Dept, of Mech. Eng g and Mechanics, Lehigh University, Bethlehem, PA, 1984.)... 

Hydrogen embrittlement is not a permanent condition. If cracking does not occur and the environmental conditions are changed so that no hydrogen is generated on the surface of the metal, the hydrogen can rediffuse from the steel, so that ductility is restored. 

On high-strength steel used in prestressed concrete (but not with common reinforcing steel) under very specific environmental, mechanical loading, metallurgical and electrochemical conditions, hydrogen embrittlement can occur, which may lead to brittle fracture of the material (Chapter 10). 

Microstructure can have a considerable effect on the susceptibihty of steels to hydrogen embrittlement [155]. Untempered martensite promotes environmental embrittlement, apparently due in large part to the brittle nature of the martensite plates [156, 157]. Grain refinement generally increases the resistance to cracking under a wide range of polarization and environmental conditions [158, 159]. 

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