The R5 procedures provide a comprehensive methodology for the assessment of structures operating within the high temperature creep regime. This includes advice on the modifications required to the basic procedure to account for weldments in creep–fatigue crack initiation assessments. The current approach is based on the use of a Fatigue Strength Reduction Factor (FSRF) which has a value according to the particular class of welded joint. The FSRF affects the calculation of creep and fatigue damage. However, the current approach can be excessively conservative for as-welded weldments which are the main type of weldments in plant. The new approach separates the FSRF into two components which are as follows: • the geometric strain enhancement due to the material mismatch effect between parent material and weld metal and the overall weldment geometry (if applicable), which is called the Weld Strain Enhancement Factor (WSEF), and; • the fatigue endurance 1 1 The term ‘endurance’ refers to the number of cycles to crack initiation. reduction effect due to the presence of small imperfections (e.g. inclusions, porosity, etc.) in the weldment constituent materials, which is called the Weld Endurance Reduction (WER). The WSEF is used to determine the stress at the start of a dwell or hold period and, because it has a lower value than the FSRF (due to the removal of the WER), results in less conservative calculations of creep damage compared to the current procedure, which uses the full FSRF. For fatigue damage predictions, the modified route is broadly similar to the current route, since the combination of the WER and the WSEF in the modified route corresponds to the FSRF used in the current route. This paper also includes some details of the validation analysis to demonstrate improved life predictions, plus sensitivity analyses examining the influence of salient material properties on the life predictions.