A system and method for performing hydrothermal treatment includes reactor vessel formed with a pressure bearing wall surrounding a reactor chamber. A liner protects the wall from exposure to temperature extremes, corrosives and salt deposits. The liner is formed with three layers: a non-porous, corrosion resistant primary layer; a porous layer; and a non-porous, secondary layer. The porous layer is sealed between the primary layer and the secondary layer. The liner is positioned in the reactor chamber with the secondary layer facing the pressure bearing wall of the reactor chamber and the primary layer facing the reactor chamber. Connectors extend through the wall of the reactor vessel and the secondary layer to allow a fluid to be pumped through the porous layer to maintain the temperature of the liner. The connectors also allow for sampling of the fluid within the porous layer to detect leaks in the primary layer.