Comparison of Preheat Predictive Methods

Abstract

Four methods of preheat temperature prediction were compared for structural steels, from a mild steel and a TS780 grade steel with carbon contents between 0.034% and 0.234% C. The BS method and the CEN method predict almost the same preheat temperatures except for the carbon-reduced steels. The prediction by the AWS hydrogen-control method and the CE _T method are conservative for mild steels and C-Mn steels. All the methods predict the same preheat temperatures for the TS780MPa steel with 0.11% C. However, only the CEN method can properly predict necessary preheat temperatures for the Cu-precipitated steel grade TS780MPa. Necessary preheat temperatures for very low carbon line-pipe steel grade API X80 is preferably predicted by the AWS hydrogen-control method and CEN method. Significant discrepancy in the prediction by these methods solely stems from a difference of carbon equivalency employed. All the preheat predictive methods are intended for avoiding HAZ cold cracking. It is necessary to consider the likelihood of weld metal cold cracking in determining the necessary preheating temperature when welding high strength steels with improved weldability.