Abstract: A system for detecting faults in the wall of a high-temperature pressure vessel, such as a fuel gasifier. The wall comprises an outer metallic shell having an inner refractory lining, together with cooling tubes extending along the refractory lining. In order to detect a fault, such as a rupture in a cooling tube and resultant melting of the refractory in the vicinity of the fault, one or more electrical conductors are embedded in the refractory and connected at their opposite ends to an external energizing circuit such that when the refractory melts, so also will the conductor, thereby breaking the circuit to indicate the existence of the fault.