Hot Bolting is the practice of removing and replacing or freeing and re-tightening bolts on live operating piping and equipment while the system is pressurized. It is potentially hazardous and the utmost caution needs to be exercised when planning and carrying it out. The hot bolting tools designed by Irgens Engineering AS aim to establish a safe barrier for flange connections during the hot bolting operation. Their application would extend the hot bolting operation, increase the safety and simplify the working process. Qualification of new hot bolting tools was carried out by the joint efforts of producer, operator and classification society. The paper addresses a part of the integrity assessment of the new hot bolting tools. The nonlinear finite element analyses were performed by ABAQUS for sequential loading during hot bolting operation under the temperature specified by operator and the nonlinear contact interactions between different components were taken into account in the analysis. In the present study, the structural integrity was investigated for 4″ class 1500 flange with ring gasket and class 150 flanges with IFG gasket of four different dimensions (1/2″, 1.5″, 3″, and 8″). The gasket stress and strain as well as contact pressure of the gasket were studied to investigate the possible leakage. The test was performed for 4″ class 1500 flange with ring gasket by Irgens Engineering AS, and the comparison between analysis and test results showed good agreement both for the gap between flange just outside ring gasket and the flange bolt force.