This paper presents key lessons learned from hundreds of field missions for assessing the condition of HRSGs at sites around the world. These involved field inspections, root cause of failure analyses and performance assessments on HRSGs of nearly every design, fuel type and operating mode. Statistics on degradation and failure risk areas are presented. Analysis techniques used in both preparing for field work and in assessing field examination results are also discussed. Trends in the evolution of the principal damage mechanisms over the years are examined, and predictions of future problem areas are considered with a view to guiding asset management actions. The impact on HRSG integrity of changes in unit designs, such as the move to flexible operation in response to the increasing contribution from renewables, is also assessed, and likely future trends are outlined. The use of qualitative and quantitative risk-based methods is also discussed and compared to the use of condition-based inspection methods as a basis for a fleet wide management strategy. A case study including a large IPP with several generating assets in its portfolio is presented and the most cost-effective method with respect to current corporate strategy is discussed. Recommendations for fleet management strategies are made.