Hydrogen Blending in Natural Gas Pipelines

Blend Composition

H₂ blend fraction (vol.) 20%

Pipeline pressure 45 bar

Flow speed 6 m/s

Pipe material

Live Readouts

Wobbe Index— MJ/m³

Energy density vs pure CH₄— %

Embrittlement risk—

How it works

Blending hydrogen into a natural-gas (mostly methane, CH₄) pipeline is a real decarbonisation strategy: existing steel networks can carry a limited fraction of H₂ without new infrastructure. Two properties change immediately with the blend fraction x (volume share of H₂):

LHV_blend = x·LHV_H2 + (1−x)·LHV_CH4
  LHV_H2 ≈ 10.8 MJ/m³,  LHV_CH4 ≈ 35.8 MJ/m³

ρ_blend = x·ρ_H2 + (1−x)·ρ_CH4
  ρ_H2 ≈ 0.0899 kg/m³, ρ_CH4 ≈ 0.717 kg/m³

Wobbe Index = LHV_blend / √(ρ_blend / ρ_air)

The Wobbe Index is what actually matters for downstream burners — it predicts the heat delivered through a fixed orifice, so appliances are only rated for a narrow Wobbe band. Because H₂ carries roughly a third of methane's volumetric energy, blending lowers both the Wobbe Index and the delivered energy density even though volumetric flow stays the same.

The embrittlement-risk readout is a simplified, illustrative model of a real material-science effect: atomic hydrogen diffuses into steel under pressure and reduces its fracture toughness. Industry guidance commonly treats ~20% H₂ by volume as a rough ceiling for unmodified steel pipelines at typical distribution pressures — risk here scales with blend fraction × pressure, and drops sharply for hydrogen-rated composite/polymer pipe, which is far less susceptible.

H₂ blend fraction — volumetric share of hydrogen injected at the T-junction; recolors the particle stream and recomputes every readout.
Pipeline pressure — higher pressure drives more hydrogen into the pipe wall, raising embrittlement risk for the same blend fraction.
Flow speed — visual/model transport speed of gas through the network (m/s equivalent).
Pipe material — carbon steel is the incumbent, cost-effective choice but embrittlement-limited; composite/polymer pipe tolerates far higher blends at the cost of new infrastructure.

Natural gas (CH₄) Hydrogen (H₂)

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