•Thermogravimetry technique has been used to identify the kinetics of oxidation.•Oxide scale of HAZs was found in more spalling and cracking than that of Weld metal.•The non-presence of Cr oxide in inner-scale of HAZs, leads to inner diffusion of oxygen to metal.•The parabolic-growth rate was investigated in oxidized regions of weldment. Overheating is the main concern in steam generating system because of the deposition of oxalates on the water side resultant of high-temperature which creates localized spallation/cracking in normally protective oxide scale, leads to catastrophic failures. This research article, therefore, focused on oxidation kinetics, oxide cracking of HAZs and weld-metal of Shielded Metal Arc (SMA) weldment in T22 steel after exposure to thermal-cyclic conditions at 900 °C in air. Thermogravimetry method was applied to examine the kinetics-of oxidation. The scale thickness on HAZs was merely higher than weld-metal because the formation of higher extent of surface cracks, and non-availability of Cr-in inner-scale as confirmed by EDX, provides the easy diffusion path for ionic-transport. Oxide-scale of these regions of weldment obeys the parabolic-kinetics.