In pressure vessel fabrication, cold formed carbon and alloy steels are required to have a subsequent heat treatment because of the loss of ductility and toughness from cold forming. The requirements for heat treatment are dependent on the materials, thickness, amount of cold forming and service condition. There are significant differences among the pressure vessel codes on the requirements for cold forming heat treatment. In this paper, the code requirements for cold forming heat treatment are reviewed for ASME Section VIII Divisions 1 and 2, EN 13445-4 and GB-150. The technical basis of forming strain calculations is discussed. Based on experimental data on the impact toughness as a function of forming strain, and fracture mechanics studies on cold formed components, improved guidelines are proposed on cold forming limits for heat treatment.