The Hidden Danger in Europe's New Energy Networks

When the Tube opens its doors in Düsseldorf next year, one topic will be in particular focus: the safe handling of hydrogen. In this context, there is no way around hydrogen embrittlement, the Achilles' heel of hydrogen transport. In this phenomenon, known since the 19th century, cracks develop in steel and other materials through sustained contact with hydrogen – a massive danger for the safety and economic viability of the new H2 infrastructure. Understanding this effect is therefore of crucial importance for pipe manufacturers, plant engineers, network operators, and testing technicians.

A microscopic view of hydrogen embrittlement in Inconel. Image from Iannuzzi, Mariano & Barnoush, Afrooz & Johnsen, Roy. (2017): Materials and Corrosion Trends In Offshore and Subsea Oil and Gas Production.
Image: © General Electric

Technically speaking, hydrogen embrittlement refers to a change in mechanical properties caused by the penetration and storage of hydrogen in a metal lattice. The effect resembles material fatigue: cracks form that significantly limit the use of certain materials.

"This is due to the specific properties of hydrogen," explains Werner Hannig, Head of Quality & Development at stainless steel tube manufacturer Schoeller Werk GmbH & Co. KG, in an interview with the trade journal gwf Gas + Energie. "As the smallest atom, hydrogen can move in the interstitial sites of steel's crystal structure. At a standard pressure of 700 bar, as found in hydrogen tanks of fuel cell cars, it quickly becomes clear how relevant this issue is."

Hydrogen-induced cracks (HIC)
Image: © CEphoto, Uwe Aranas

The Mechanism of Hydrogen Embrittlement

The interaction between hydrogen and material is complex and can occur in various ways. Fundamentally, we distinguish between environmental embrittlement, where hydrogen from the environment penetrates the material. This typically occurs through corrosion processes. This type of embrittlement is particularly critical for pipelines that are in permanent contact with hydrogen. The second type is internal embrittlement, which occurs during the material's manufacturing or processing.

Whatever the cause, the process always follows a characteristic pattern. First, hydrogen is adsorbed on the metal surface. The prior transition from molecular to atomic hydrogen is crucial: only in the form of individual atoms can hydrogen penetrate the metal structure. After adsorption, hydrogen then diffuses inside the material to areas of high tensile stress – such as notches or material defects.

As a result, hydrogen atoms preferentially accumulate at grain boundaries, inclusions, and other defects or "trap sites." Once the hydrogen concentration reaches a critical level, the material fails and crack formation begins. At lower hydrogen concentrations, failure occurs only at higher critical stresses, while at very high concentrations, even low stresses are sufficient. What makes hydrogen embrittlement particularly insidious: the damage is initially completely invisible. Pressure, mechanical stress, and high temperatures accelerate hydrogen uptake and thus the damage process after the initial H2 entry, but this usually only becomes apparent after months or years – then catastrophically and without warning.

Distribution of hydrostatic stress in the notch region of a bend specimen at a stress intensity of 28 MPa√m. Tensile stresses are negative. Right: Hydrogen distribution after saturation
Image: © Ken Wackermann, Fraunhofer IWM

Not All Steels Are Equally Affected

While hydrogen embrittlement can affect many construction materials in principle, not all materials react with equal sensitivity. High-strength steels, titanium, and certain aluminum alloys are most susceptible. In steels, the microstructure plays a decisive role in their susceptibility.

"The microstructures delta ferrite and α'-martensite particularly absorb hydrogen when exposed," explains Werner Hannig from Schoeller. "Ferritic stainless steels consist of 100% ferrite phase, through which hydrogen atoms are absorbed very quickly. This leads to pronounced brittle fracture tendency under static or dynamic loading."

Particularly at risk are unalloyed and low-alloy steels as well as higher-strength steels with high martensite content and a yield strength above 800 MPa. In practice, this also affects high-strength bolts from strength class 10.9. The risk of embrittlement increases with increasing martensite content, as this microstructure is particularly susceptible to hydrogen storage. Especially with these materials, hydrogen embrittlement leads to sudden failure without prior warning signs.

Austenitic steels form an important exception. Their face-centered cubic lattice structure shows a significantly lower diffusion rate for hydrogen than the body-centered cubic structure of ferrite or martensite. "The diffusion coefficient of hydrogen in austenitic steels at room temperature averages about 5 x 10-15 m²/s, while in ferritic steels it is several orders of magnitude higher," explains Werner Hannig. This reduced hydrogen uptake makes austenitic steels preferred materials for hydrogen-carrying systems.

The alloy composition also plays an important role: while nickel reduces the critical delta ferrite content and thus the susceptibility to embrittlement, elements like chromium, molybdenum, or titanium increase the susceptibility to hydrogen uptake. Higher-alloyed austenitic stainless steels show the highest resistance – an important aspect for designers of hydrogen infrastructures.

Scanning electron microscope fracture surface images of hollow specimens after slow tensile testing with (left) 70 bar hydrogen filling and (right) in air. The effect of H2 embrittlement is clearly visible on the fracture surface on the left
Image: © Ken Wackermann, Fraunhofer IWM

Prevention and Monitoring – Keys to Safe Hydrogen Use

Therefore, preventing hydrogen embrittlement begins with material selection. Currently, steel-processing companies can refer to the U.S. standard SAE J2579, which defines clear criteria for the use of materials in hydrogen applications. The German Federal Ministry of Economics has also recognized the importance of uniform standards and commissioned a "Standardization Roadmap for Hydrogen Technologies." "Without standards, the interaction of the supply and value chain cannot function smoothly," emphasizes Werner Hannig.

Since the time between hydrogen uptake and damage often takes days or even months, prevention plays a key role. Various technical options are available for this.

Mechanical galvanizing instead of classical galvanization

Special surface coatings such as Dacromet or Geomet

Alternative joining technologies like laser or TIG welding

Adapted heat treatment processes with precise temperature control

According to Wackermann et al., targeted heat treatment has proven particularly effective. The so-called stress relief annealing at 200-230°C not only reduces critical residual stresses in the material but also tempers the highly distorted, freshly formed martensite. For high-strength steels, hydrogen baking is also essential, a process that removes dangerous diffusible hydrogen from the component.

Heat treatment is particularly important after galvanic processes. The temperature should be between 200°C and 230°C, with duration between 2 and 24 hours. It is crucial that the treatment occurs within four hours after galvanization – ideally even within the first hour.

Prevention also includes monitoring hydrogen-carrying systems. This is typically done through regular mechanical and technological material testing. Testers look for changes in ductility and possible reduction in uniform elongation and elongation at break. Standard ISO 15330 defines the standard procedure: components are exposed to a defined tensile stress for at least 48 hours and examined for crack formation.

Outlook: Hydrogen Needs New Standards

Given the numerous national hydrogen strategies that have been adopted around the globe for about five years, it's clear: the safe handling of the gas will become a key competency of the pipe and pipe processing industry in the coming years. This affects not only the planned development of a network of hydrogen pipelines and storage facilities but also numerous industrial applications – from heavy industry to mobility. Hydrogen embrittlement will remain a particular challenge, as it poses an enormous safety risk if not prevented.

Uniform international standards will play a central role. The "Standardization Roadmap for Hydrogen Technologies" initiated by the Federal Ministry of Economics is a first step, but there is still a long way to go before implementing the goals formulated therein. The industry needs clear guidelines for material selection, testing procedures, and maintenance intervals.

The wire & Tube 2026 will reflect this development: visitors can learn about the latest developments in materials technology, innovative testing methods, and forward-looking coating technologies. The exhibition's broad spectrum of offerings – from pipe materials and testing technology to complete system solutions – provides a thorough overview of the current state of the art.

For more information about wire & Tube 2026, visit www.tube.de

Sources

Wackermann, K., Schweizer, F., Pfeiffer, W.: Hydrogen Embrittlement of Metallic Materials: Adsorption, Diffusion and Material Properties. gwf Gas+Energie, 2-3/2019

Hannig, W.: Hydrogen Embrittlement in Stainless Steel Tubes: Standards and Specifications are Crucial. Interview. gwf Gas + Energie 01-02|2025

Bossard Group: Hydrogen Embrittlement. White Paper, Zug 2020

Federal Ministry for Economic Affairs and Climate Action (BMWK): Standardization Roadmap Hydrogen Technologies, Berlin 2024