The all-clear: If you feed hydrogen into the existing gas network, this affects the lines less than feared, as tests have now shown. Accordingly, the metals commonly used for pipes and industrial plants show no signs of increased hydrogen embrittlement even under stress. Mixing hydrogen with natural gas or using the gas lines for hydrogen transport is therefore feasible, according to the researchers.
Hydrogen is an important pillar of the future energy supply. Via electrolysis, it can serve as an energy store for excess solar or wind power. If electricity is needed again later, the hydrogen can be converted into electricity again using fuel cells. Hydrogen can also be used directly for heating, in industrial processes or for chemical reactions. However, this assumes that the gas can be transported to the place of use.
The problem of embrittlement
The existing natural gas network has long been considered the distribution network of choice: The lines for it exist in most cities and many industrial plants. The first technologies for the simple separation of the two gases at the destination have also already been developed. The problem, however, is that if hydrogen diffuses into the metal, this can lead to corrosion and embrittlement of the material. Atomic hydrogen is stored in the structural lattice of the material and reacts at impurities to form molecular hydrogen.
This storage of H2 leads to internal stresses in the grid and to an increase in pressure, which can lead to micro-cracks in the material. Metals are particularly susceptible to such embrittlement when they are deformed under mechanical pressure or tensile load, when certain chemicals such as hydrogen sulfide are used and at elevated temperatures. In the German natural gas network, only a maximum of ten percent hydrogen has been added to date.
All clear for common materials
Researchers working with Martin Bonnet from the Technical University of Cologne have now investigated in more detail how great the risk of corrosion is and how hydrogen affects the material of common industrial plants. To do this, they exposed nine typical materials, including structural steels and copper, to gas mixtures with hydrogen contents between zero and 100 percent. In order to test the behavior of the materials even under load, all materials were also subjected to constant tensile forces and thus stretching over a day.
The result: “We could not find any hydrogen embrittlement in the materials used,” reports Bonnet. “The natural gas-hydrogen mixture is not critical for structural steels that are used in pipes and fittings under H2 pressure. A conversion to hydrogen admixture is therefore possible without any negative effects on metallic materials. ”Transporting hydrogen via existing lines should therefore be harmless in most cases.
In addition, the team investigated how strongly hydrogen attacks the metals when the system is heated up to 920 degrees. The result here: “At elevated temperatures, the diffusion speed of the hydrogen in the metal grid increases, so that the hydrogen is stimulated to diffuse out of the metal grid,” reports Bonnet.
Source: Technical University of Cologne