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.
Conventional 304L and 316L grades were being widely considered as potential benchmark grades for use in Hydrogen applications. However, neither of these conventional grades have single-phase austenitic microstructures and they contain a percentage of the ferrite phase.
Furthermore, the austenite phase in these conventional 304L and 316L grades is meta-stable and can transform to martensite phases because of 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.
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 seem to indicate that more-stable austenitic stainless steels are preferable for hydrogen gas service.
Alloys within the N'GENIUS H2 SeriesTM have been specifically formulated and designed to adjust and balance their chemical composition in order to maintain a more stable, single-phase austenitic microstructure.
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 H2 316LM4N™ | 700 MPa | 380 MPa | ≥35 |
| 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 B32.12 for Hydrogen Piping and Pipelines, significant wall thickness reductions and weight savings can be achieved if N'GENIUS 316LM4N is specified compared to conventional 316L grades.
| NB | OD (mm) |
Calculated Wall Thickness (mm) |
Weight (Kg/m) |
||
|---|---|---|---|---|---|
| 316L | N'GENIUS H2 316LM4N™ |
316L | N'GENIUS H2 316LM4N™ |
||
| 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 H2 Series 316LM4N™ Alloy Types and Variants are significantly higher than in conventional 316L stainless steel.
The N'GENIUS H2 SeriesTM provides the following benefits to engineering design teams:
The following N'GENIUS H2 SeriesTM of High Strength Austenitic Stainless Steels are extremely well suited for gaseous and liquid hydrogen applications::
The N'GENIUS SeriesTM of High Strength Austenitic Stainless Steels, or products made using the N'GENIUS SeriesTM, can only be manufactured by Approved Licensed Manufacturers.