The proposal requests 2-day access to ENGIN-X instrument for gathering diffraction data from 20 samples made of two high-temperature steels (10CrMoVNbN and TP316H). The samples have been taken from a set of interrupted high-temperature variable-stress creep tests and have a defined deformation history. The obtained diffraction patterns will be analysed using the CMWP method which evaluates the peak broadening characteristics of diffraction peaks for determination of dislocation density. The derived dislocation density values will be employed to understand the responsible mechanism for the repeated occurrence of fast creep stage during stress varying creep loading conditions (i.e. primary creep persistency, PCP). The observations will be used for examination of the reliability of our proposed PCP mechanism and effectiveness verification of our developed dislocation-based model.