Hydrogen is 14 times lighter than air, non-toxic, colourless and odourless, and burns without residue with a colourless flame. It is gaseous down to -253 °C, after which it liquefies. It is a very reactive element that only occurs in a bound form, for example as a hydrogen molecule, in water with oxygen or in methane with carbon.

Hydrogen itself is energy intensive to produce. Worldwide annually, 30 million tonnes of “grey” hydrogen are produced from fossil fuels such as natural gas or oil, mostly by steam reforming. This is a process that converts water and methane into hydrogen and carbon dioxide (CO₂). And every tonne of hydrogen produces ten tonnes of CO₂.

Going green

The more climate-friendly alternative is “green” hydrogen, produced in a climate neutral manner from 100% renewable energies. The most common production process for green hydrogen is electrolysis of water where hydrogen is separated from the oxygen.

Hydrogen is an important raw material for the chemical and petrochemical industries

Hydrogen is an important raw material for the chemical and petrochemical industries to produce basic chemicals such as green ammonia or green methanol. More than half of hydrogen production is processed into ammonia for the manufacture of fertilisers. Hydrogen can also be used directly for building heating, industrial furnaces and in fuel cells to drive electric motors for transportation. It is so attractive because its only exhaust emission is water.

The specific properties of hydrogen place the highest demands on the materials used for its generation, cryogenic storage, transport and use of electrolysers, high-pressure compressors, tanks, valves, pipes and fittings. The high diffusibility of hydrogen requires reliable gas tightness of all components to avoid losses and mitigate the risk of explosion or fire due to escaping hydrogen.

Strength & resistance

With many metals, hydrogen atoms can penetrate the material (permeation) and significantly impair their mechanical properties. Even at a hydrogen concentration of a few ppm, in susceptible material, degradation can occur resulting in the formation of cracks and brittle fracture and therefore represents an unacceptable safety risk. Components made of nickel-containing stainless steel, on the other hand, permanently resist both permeation and degradation thanks to their microstructure. Thus, they prevent gradual escape of gas and protect the components from embrittlement, maintaining consistently high strength, ductility and homogeneity.

For components that come into contact with hydrogen, austenitic stainless steel Types 316L (UNS S31603) and 304L (S30403) are used as standard. Types 317LMN (S31726), 2205 (S32205) and 2507 (S32750) are tried and tested for particularly critical applications.

Looking forward to a sustainable future, ways and means of producing, using and distributing green hydrogen are being expanded around the world. Many grades of stainless steel will play a key role in the process, from start to finish.

Hydrogen colour coding

Hydrogen is an element that exists primarily in molecular forms such as water and organic compounds. Hydrogen gas can be produced from various sources or processes. To identify these different sources or processes the hydrogen is identified by a colour-code. 

The most significant are the following:

This article is adapted from an article by Ursula Herrling-Tusch on behalf of Warenzeichenverband Edelstahl Rostfrei e.V., https://www.wzv-rostfrei.de/

It was first published in our Nickel Magazine VOL 38-31, in April 2023.

_{Cover picture of this article: LINDE HYDROGEN CENTER UNTERSCHLEISSHEIM, GERMANY © LINDE PLC}