A cutting torch does not melt steel pipe. It burns it. Oxy-fuel cutting is a controlled combustion reaction. The preheat flame, typically oxy-acetylene or oxy-propane, raises the pipe wall to its kindling temperature of roughly 870 to 980 °C, where carbon steel glows bright orange. A central jet of high-purity oxygen is then released, and the iron oxidises faster than the surrounding wall can conduct heat away. That oxidation supplies nearly all of the energy needed to sever the wall. The flame simply keeps the reaction front alive. For the reaction to sustain itself, the metal must satisfy four conditions: • Kindling temperature must sit below the melting point of the base metal • The oxide must melt at a lower temperature than the metal, so it flows out of the kerf as slag • Oxidation must release enough heat to propagate through the full wall thickness • Thermal conductivity must be low enough that the reaction zone is not quenched Carbon and low-alloy steels pass every test. St...