Abstract: In the thermodynamic evaluation Y was selected as a typical heavy rare earth metal for reducing the detrmental effects of tramp elements in the petroleum pipe steel. The possibilities of reactions between Y and tramp elements such as Sn, Sb, As, etc. after deoxidation and desulphurization were estimated by calculating the Gibbs free energies of formation. The equilibrium content of Y for eliminating the detrimental effects of tramp elements in the steel was recommended from the results of thermodynamic calculation.