Corrosion is usually imagined as surface erosion — material dissolving layer by layer, measurable by weight loss. But molten-salt corrosion in metals can thread through grain boundaries in a single dimension, bridging both sides of a containment wall while consuming almost no material.
This “wormhole” corrosion travels along grain boundaries — the interfaces between crystal grains in a metal — creating a connected path from one surface to the other. The penetration rate per unit of corroded mass is extraordinarily high because the attack is localized to boundaries just nanometers wide. A container can be breached by corrosion that a standard mass-loss measurement would classify as negligible.
The failure mode matters for next-generation molten salt nuclear reactors, which depend on metal containment resisting hot, chemically aggressive salt for decades. Traditional corrosion monitoring — weighing coupons, measuring thickness — would not detect a wormhole penetration until after the breach. The damage is structurally catastrophic but volumetrically trivial.
The engineering insight: the most dangerous corrosion is not the kind that consumes the most material but the kind that finds the thinnest continuous path. A crack needs only to connect, not to widen. The topology of the damage matters more than its volume — a lesson that extends to any system where failure is about connectivity, not magnitude.