A thermowell-thermocouple assembly for installation in a refractory-lined process vessel has an expansion joint for compensating for expansion, contraction and movement of the refractory. Examples of expansion joints include unsupported bellows, bellows that have a support sleeve around the bellows, a sliding, hexagonal coupling with crimping to hold the sliding tubes together, a pin-and-slot coupling and a spring-loaded, pin-and-slot sliding connection. The thermocouple-thermowell assembly can include a metal, a ceramic material, a refractory brick and/or a conical-shaped tip at a distal end, which can be or which can become fixed to the refractory.