Abstract
This review summarizes the thermodynamics of hydrogen (H2) in mixed gases of nitrogen (N2), methane (CH4) and natural gas, with a special focus on hydrogen fugacity. A compilation and interpretation of literature results for mechanical properties of steels as a function of hydrogen fugacity implies that test results obtained in gas mixtures and in pure hydrogen, both at the same fugacity, are equivalent. However, this needs to be verified experimentally. Among the test methods reviewed here, fatigue crack growth testing is the most sensitive method to measure hydrogen effects in pipeline steels followed by fracture toughness testing and tensile testing.
Highlights
Significant efforts are ongoing in the European Union and worldwide to defossilize private and industry sectors by reducing the emission of green house gases
This review summarizes the thermodynamics of hydrogen (H2) in mixed gases of nitrogen (N2), methane (CH4) and natural gas, with a special focus on hydrogen fugacity
It is further known that the deterioration of mechanical properties of steels increases with increasing hydrogen concentration inside the steel, which increases with increasing hydrogen gas pressure, more precisely hydrogen fugacity [2]
Summary
Significant efforts are ongoing in the European Union and worldwide to defossilize private and industry sectors by reducing the emission of green house gases. One important goal is to replace natural gas (NG) with hydrogen. This goal shall be reached stepwise by blending natural gas with increasing amounts of hydrogen (H2). It is well established that the mechanical properties of most metallic alloys including steels deteriorate under the influence of hydrogen. This effect is often referred to as ‘hydrogen embrittlement’. Several publications report the effect of hydrogen in NG-H2 gas blends upon the mechanical properties of steels, see e.g., [6,7]. It will be shown that the hydrogen fugacity can be used as a single parameter to describe hydrogen effects on steels independent of testing these in a gas blend or in pure hydrogen, and that testing in gas blends is not necessary to assess hydrogen effects on materials used in NG-H2 infrastructures
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