This study aims at developing on-site techniques to evaluate the sensitization of stainless steels. Sensitization and mechanical properties of clad metals in hot-rolled clad steel plates, STS 316 steel plate and carbon steel (A516), are investigated at the specific conditions of post heat treatment and welds which are multiple-layers-thick or are repeated for repair. Sectioned weldments and external surfaces are investigated to reveal the degree of sensitization by evaluating Micro Vickers hardness test, tensile test and etching. The results are compared with those of EPR tests. As test conditions, clad steel plates are butt-welded by FCAW + SMAW, and heat treatments are conducted at a temperature of $625^{circ}C$ for 80, 160, 320, 640 and 1280 minutes, using the time of heat treatment as a variable. The change of corrosion resistance is also evaluated for these specimens. As the heat treatment time increases in case of carbon steel (A516), the annealing effect causes the tensile strength to decrease. The micro-hardness gradually increased, and decreased after 640 min. Elongation and contraction of the area also increased gradually. After oxalic acid etch tests and EPR tests on STS316, clad metal shows STEP structure with no sensitization. It can be concluded that there is no effect on the corrosion resistance of clad metals by use of the test results on multi-layered and repair welds.