Excessive creep strain design check with simulations based on material properties from material standards

Abstract

The possibility of doing the Excessive Creep Strain Design Check (ECS-DC) according to EN 13445–3 Annexe B based on simulations was investigated. As a constitutive law for creep, Norton’s law and, as an alternative, a hyperbolic sine law were considered. Creep strain limits given in material standards are the basis for the parameters of these creep laws. A check for reversal creep ensures that repeated primary creep does not occur. The application of this method on a nozzle in a spherical shell shows the calculation of the parameters of the constitutive law and possibilities of damage determination. The geometry is analysed both at constant temperature and with uniform materialas well as with non-uniform material and temperature variations. The focus of the paper is the conservative creep damage determination for design calculations. Therefore, the use of safety factors is included, and appropriate values are discussed.