Braze heater assembly and method

摘要

An improved heater assembly and method for applying a brazing heat across a selected longitudinal section of a tube is disclosed herein. The heater assembly generally comprises a heater mandrel having an electrical resistance heating element coiled thereabout, and a support mandrel for supporting and centering this heating element. The heater mandrel further includes a means for directing a flow of inert gas in the space between the coiled heating element and the inner walls of the tube being brazed in order to purge this space of ambient atmospheric oxygen and prevent the heater mandrel from oxidizing. The support mandrel includes a centering means in the form of two roller assemblies, each of which has three spring-loaded rollers equidistantly spaced 120 DEG around its diameter. In the method of the invention, the heater mandrel is inserted into the tube and slid across the longitudinal section to be brazed. The heater then applies a brazing heat while a purging flow of inert gas is directed in the annular space between the coiled heating element and the inner walls of the tube. After the brazing operation has been completed, the flow of purge gas may be increased to cool down the heater assembly. The heater assembly is particularly useful for brazing reinforcing sleeves across sections of corrosion-damaged heat exchange tubes in nuclear steam generators.