Here's a delicious coincidence in materials science: liquid hydrogen boils at 20.3 K, and magnesium diboride (MgB₂) becomes a superconductor below 39 K. That means an LH₂ pipeline is already colder than MgB₂ needs to be. Wrap the pipe in superconducting cable and you get a two-in-one continental artery: chemical fuel and electric power in the same insulated tube.

The proposal (variants floated by Chubu University and BNL since the 2000s) is a vacuum-jacketed pipe, ~1 m inner diameter, carrying LH₂ at maybe 5 bar. Around the inner pipe: two coaxial layers of MgB₂ tape totaling ~100 cm² of superconductor.

Power capacity. MgB₂ tape reliably carries ~200 A/mm² at 20 K. With 10,000 mm² of conductor:

I = 200 A/mm² × 10,000 mm² = 2,000,000 A

Run it as DC at a modest ±50 kV (voltage is easy; the insulation problem is thermal, not electrical):

P = I × V = 2×10⁶ A × 10⁵ V = 200 GW

For comparison, the entire US grid averages ~500 GW. One pipe could shuttle 40% of national electricity — losslessly, in principle.

Hydrogen capacity. LH₂ at 71 kg/m³, flowing at 3 m/s through a 1 m pipe:

ṁ = 71 × π/4 × 3 ≈ 167 kg/s ≈ 14,400 tons/day

At 120 MJ/kg (HHV), that's another 230 GW of chemical energy. The pipe becomes a ~430 GW dual-mode energy corridor.

Where physics starts biting back. The cold is the whole problem. Even the best multilayer vacuum insulation leaks ~0.3 W/m² of pipe area. For a 4,000 km pipe with ~3 m² of surface per meter:

Q̇ = 0.3 W/m² × 3 m²/m × 4×10⁶ m ≈ 3.6 MW heat leak

Sounds trivial — until you remember Carnot. Removing 1 W at 20 K when your radiator is at 300 K costs at least (300−20)/20 = 14 W of electrical input, and real cryocoolers are ~30% of Carnot, so ~50 W input per W removed. That's ~180 MW just to keep the pipe cold, or 0.09% of your 200 GW electrical throughput. Livable.

Worse is hydrogen boil-off. Every joule that leaks in must be dumped by vaporizing LH₂ (latent heat 446 kJ/kg). Left uncooled, 3.6 MW would boil off 700 kg/hour, or 0.005% of throughput per hour — you'd want a re-liquefier every ~100 km, drawing ~2 MW each. Doable.

The real killers:

• Faults. A quench (loss of superconductivity) at 2 MA is genuinely apocalyptic. The stored magnetic energy in a 4,000 km line is ~½LI² ≈ 5×10¹² J — a kiloton of TNT equivalent, hunting for somewhere to go. You need fast-acting mechanical bypass switches and current-limiting reactors at every substation.
• Hydrogen embrittlement. H₂ diffuses into steels and destroys ductility. The inner pipe needs austenitic stainless or aluminum liners, which are lousy at 20 K unless carefully specified.
• Cost. Standard high-pressure H₂ pipelines run ~$2M/km. Adding vacuum jacket, MgB₂ tape (~$10/kA·m), and cryocooler stations easily pushes this to $15–25M/km. A 4,000 km spine: ~$80B. HVDC-only would be ~$8B for the same distance. You're paying 10× for the hydrogen throughput.

The economics only work if you genuinely need both — meaning a future where H₂ is the primary industrial reductant (green steel, ammonia) and you're moving TWh of renewables from Saharan solar or Patagonian wind to demand centers. In that world, the coincidence of MgB₂'s Tc sitting above LH₂'s boiling point becomes one of the great free lunches in engineering.