A correlation of sensitization with thermomechanical work accumulated in a weld heat affected zone of Type 304 pipe was investigated in conjunction of heat-to-heat difference, and of a welding simulation. Highly susceptible pipe heats for stress corrosion crackings were introduced primarily through inappropriate mill practices that left pre-existing grain boundary carbides or strained subsurface layers in pipes. These undesirable heats that may have a sufficient corrosion resistance in the as-received state, most rapidly lose the resistance after being exposed to weld heat cycles. A weld simulation study was made to evaluate the thermomechanical effect on sensitization development, and distinct differences from isothermal sensitizations were confirmed by microstructure observations and some corrosion tests. The thermomechanical work and the successive continuous cooling enhance sensitization significantly.