Abstract The Factory Acceptance Test (FAT) for ITER components should be complied with the RCC-MR 2007 code and French regulations of nuclear pressure equipment (ESPN) to assure quality of nuclear pressure equipment. The procedure of FAT for lower port has been set to that visual test, pressure test, baking, vacuum leak test, and final dimensional inspection. Especially, the baking is critical cleaning method to satisfy required vacuum condition. The baking condition should be satisfied with both the given ramp-up/down condition, which is 5 °C/hr, and the temperature difference of the object within 40 °C, simultaneously. The air heating and circulating furnace has been specially designed to apply convective heating and cooling method. In this study, using the mock-up of the lower port stub extension, convective baking test is performed with the maximum holding temperature of 220 °C during 24 h. As a result, the maximum temperature difference of the mock-up is appeared 15.4 °C at the ramp-down condition. Using the measured result, transient thermo-structural analysis is performed. The maximum stress of 85.8 MPa is occurred, and this is reasonable stress intensity comparing to the allowable stress 195 MPa. It is proven that applying convective baking is feasible for the baking of lower port FAT.