Hydrogen

Advanced technology needs advanced materials

Hydrogen is rapidly becoming a key element in the energy transition towards Net Zero.

But as governments, institutions and commercial organisations throughout the world pour billions into R&D and early-stage production, fundamental issues and risks regarding the materials utilised in both gaseous and liquid hydrogen production, storage, transportation and utilisation are being overlooked.

N'GENIUS H2 Series

What should we be concerned about?

What should we be concerned about?

Conventional 316L grades are being considered as potential benchmark grades for use in hydrogen applications. However, such conventional grades do not have single-phase austenitic microstructures and they contain a percentage of the ferrite phase.

Furthermore, the austenite phase in conventional 316L grades is meta-stable and can transform to martensite phases because of their chemical compositions, material processing, mechanical straining, the amount and rate of deformation or sub-zero and cryogenic temperature changes.

Why is this an issue?

Both ferrite and martensite phases in conventional austenitic stainless steels are more susceptible to hydrogen embrittlement since such secondary phases can enhance hydrogen uptake.

This is a fundamental and serious issue which needs to be fully discussed and appreciated by all interested parties throughout the hydrogen storage and transportation industry.

Fortunately, this problem is starting to be acknowledged by certain standards committees, as seen in the ASME B31.12 Hydrogen Piping & Pipelines standard.

ASME B31.12 Hydrogen Piping & Pipelines

A-2.4 Austenitic Stainless. Austenitic stainless steels generally provide the best performance of any structural metal in hydrogen gas service.

Hydrogen embrittlement in single-phase austenitic stainless steels has been primarily correlated with two metallurgical variables: alloy composition and the presence of secondary phases, such as ferrite and martensite.

Ferrite can be present in austenitic stainless steels as a result of material processing, while martensite can be induced by mechanical straining. Both ferrite and strain-induced martensite render austenitic stainless steels more vulnerable to hydrogen embrittlement. The ferrite and martensite can be intrinsically more susceptible to hydrogen-assisted fracture than the austenite matrix. Additionally, ferrite and martensite can enhance hydrogen uptake in the steels.

Alloy composition is perhaps the most important metallurgical variable governing hydrogen embrittlement in single-phase austenitic stainless steels […]. As an austenite stabilizer, higher nickel content, in particular, correlates well with resistance to hydrogen embrittlement. Data seems to indicate that more-stable austenitic stainless steels are preferable for hydrogen gas service.

Hydrogen Pipeline Feasibility Study

Hydrogen Pipeline Feasibility Study

In addition to giving a more stable single-phase austenitic microstructure which is essential for the hydrogen storage and transportation industries, the N'GENIUS H2 SeriesTM also offers other direct advantages when compared to conventional austenitic grades.

N'GENIUS 316LM4N H2™ Alloy Types and Variants have significantly higher minimum mechanical strength properties than conventional 316L grades, enabling higher allowable design stresses to be utilised where applicable.

Alloy Type Tensile Strength
(min)		 Yield Strength
(min)		 PREn
(min)
N'GENIUS 316LM4N H2™ 700 MPa 380 MPa ≥37.5
Conventional 316L 485 MPa 170 MPa ≥24

To illustrate this further, a feasibility study has been undertaken for a current hydrogen project at the conceptual design stage. For a 600lb system based on ASME design code B31.12 for Hydrogen Piping and Pipelines, significant wall thickness reductions and weight savings can be achieved if N'GENIUS 316LM4N H2™ is specified compared to conventional 316L grades.

* For illustrative purposes
NB OD
(mm)		 Calculated Wall Thickness
(mm)		 Weight
(Kg/m)
316L N'GENIUS
316LM4N H2™		 316L N'GENIUS
316LM4N H2™
4" 114.3 5.6 2.5 9.0 6.8
6" 168.3 7.9 3.6 30.3 13.9
12" 323.9 15.8 7.0 119.1 54.8
16" 406.4 19.8 8.8 187.4 86.2
30" 762.0 37.1 16.6 659.0 303.1

Furthermore, the minimum Pitting Resistance Equivalent values of N'GENIUS 316LM4N H2™ Alloy Types and Variants are significantly higher than in conventional 316L stainless steel.

Significant benefits for Engineering Design Teams

Significant benefits for Engineering Design Teams

The N'GENIUS H2 SeriesTM provides the following performance benefits to engineering design teams:

  • Unique combination of mechanical and corrosion resistance properties
  • Higher mechanical strength properties compared to conventional austenitic stainless steels for high pressure service and improved safety
  • Higher allowable design stresses
  • Reduced wall thicknesses can lead to weight savings, reduced transport costs and reduced fabrication time which leads to an overall reduction in construction and project costs
  • Opportunity to increase flow-rate with larger Inside Diameter (ID) without changing Outside Diameter (OD)
  • Excellent ductility due to a more stable single-phase austenitic microstructure
  • Excellent toughness at sub-zero temperatures for gaseous hydrogen and cryogenic temperatures for liquid hydrogen
  • Superior resistance to Hydrogen Embrittlement due to a more stable single-phase austenitic microstructure
  • Superior resistance to Localised Corrosion (Pitting and Crevice Corrosion)
  • Superior resistance to Stress Corrosion Cracking (SSCC and Chloride SCC) in a wide range of service conditions and process environments
  • Superior resistance to General Corrosion even in low pH acid environments
  • Increased safety can be built into system design.

Design Characteristics of the N'GENIUS H2 Series

N'GENIUS H2 SeriesTM Alloys to be considered for hydrogen applications.

The following N'GENIUS H2 SeriesTM of High Strength Austenitic Stainless Steels are extremely well suited for both gaseous and liquid hydrogen applications:

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The N'GENIUS Series™ of High Strength Austenitic Stainless Steels, or products made using the N'GENIUS Series™, can only be manufactured by Approved Licensed Manufacturers.

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