Abstract: A temperature detecting apparatus for pipes in refinery furnaces and the like comprises a thermocouple (2) which is supported in cantilevered fashion in the region of its detection end (2b) fastened to the outer surface of a pipe (5) which is located inside a furnace. The thermocouple is provided with a rod (2a) coming out of the furnace through an opening (3) formed in the furnace wall (4). Coaxial with the rod (2a) is a tubular protection element (10) which is secured along the rod, slidably and loosely passes through the opening (3) and extends as far as close to the pipe (5). Formed between the rod (2a) and tubular element (10) is an air space (2) through which air is sucked from the outside to the inside of the furnace by effect of the slight vacuum created in the furnace to cool the rod in order to prevent the thermocouple from being overheated due to the high temperature present in the furnace.