Farid Vakili Tahami - Associate professor, Department of mechanical engineering, Tabriz University
Seyyed Saeed Sharifi - MSc. student, Department of mechanical engineering, Tabriz University
Peyman Majnoun - MSc. student, Department of mechanical engineering, Tabriz University
Afshin Abbasi - MSc. student, Department of mechanical engineering, Tabriz University

Due to the vast application of pressure vessels in different industrial fields such as gas and petrochemical plants and power generation, investigating their mechanical behavior is one of the major concerns in recent studies. These vessels usually operate at high temperature under internal pressure and axial rotation; therefore,their creep behavior should be studied. However, due to the nonlinear form of the creep constitutive equations,the numerical solution methods require sufficient and advanced software and hardware facilities. Hence, in most of the industrial standard codes such as R5, approximate procedures, which are based on reference stress method (RSM), are used. Consequently, the estimation of the reference stress is a priory for using these codes.Calculating reference stress in structures which are subjected to combined loadings is also a complicatedprocess. For this purpose a method is proposed to obtain the reference stress value for vessels which are subjected to combined internal pressure and axial rotation in order to predict their creep life. Based on the Finite Element Model (Abaqus) the precision of the analytical solutions in determining the value of referencestress is verified by an acceptable maximum error of 10 percent. Then the optimum design of pressure vesselsis performed by the purpose of maximizing the creep life and satisfying the strength criterion by using the reference stress. For instance a diagram of design parameters is prepared for a rotating cylindrical pressure vessel made of INCONEL 718 material at the operating temperature of 760 degree centigrade, which will be useful for designers.

Optimum design, Creep, Reference Stress Method (RSM), Cylindrical Pressure Vessel, Creep Life