Creep Relaxation Behavior of High-Energy Piping

Abstract

The analysis of the elastic stresses in high-energy piping systems is a routine calculation in the power and petrochemical industries. The American Society of Mechanical Engineers (ASME) B31.1 Power Piping Code was developed for safe design and construction of pressure piping. Postconstruction issues, such as stress relaxation effects and selection of maximum expected creep damage locations, are not addressed in the Code. It has been expensive and time consuming to evaluate creep relaxation stresses in high energy piping systems, such as main steam and hot reheat piping. After prolonged operation of high-energy piping systems at elevated temperatures, it is very difficult to evaluate the redistribution of stresses due to dead weight, pressure, external loading, and thermal loading. The evaluation of stress relaxation and redistribution is especially important when nonideal conditions, such as bottomed-out or topped-out hangers, exist in piping systems. This paper uses three-dimensional four-node quadrilateral shell elements in the ABAQUS finite element code to evaluate the time for relaxation and the nominal relaxation stress values for a portion of a typical high-energy piping system subject to an ideally loaded hanger or to an overloaded hanger. The stress relaxation results are evaluated to suggest an approximation using elastic stress analysis results. [S0094-9930(00)01304-4]