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Rapid implementation was possible by teaching a harmonized, and field-approved concept for infection protection and treatment. Realistic simulated scenarios and field-experienced trainers allowed transfer of knowledge as well as reassurance. Additional recommendations are further conversion of the training into a permanent program and, in the case of a crisis, interlocking of training with operational planning to allow rapid escalation and adaptation. Also, the concepts for training and interventions should be harmonized and developed further for additional challenges like airborne transmission and application of intensive-care medicine.

Two types of flow-driven wear phenomena are a frequent source of failures in Heat Recovery Steam Generators (HRSGs): Flow-Accelerated Corrosion (FAC) and Liquid-Droplet Impingement (LDI). The two mechanisms combined are also known by an older term, erosion-corrosion. This better describes what can be viewed as a continuum of mechanisms, driven by chemistry and/or fluid velocity, which lead to wear and consequent thinning of pipe walls. One common failure location in the HRSG is in Low Pressure (LP) Evaporator circuits, both in regions with two-phase and with single-phase flow conditions. Replacement and/or redesign of the LP Evaporator system is often required. Water chemistry is known to be a key factor in determining the risk of FAC; it can be modified if required during operation to potentially affect wear rates. Another key factor, determined at the design stage, is the chrome content of the steel. The emphasis here is on evaluating other design factors, particularly local process conditions throughout the LP Evaporator circuit, that affect susceptibility to FAC and LDI. LP systems today often are designed to operate at very low pressures (< 3 barg, 45 psi) with the goal of extracting the last practical amount of thermal energy from gas turbine exhaust gas. Furthermore, many combined cycle power plants (such as those in combined power and desalinization service) have variable loads that lead to wide variations in LP operating pressures. The overall bulk fluid circulation in natural circulation LP Evaporators of several different HRSG designs is evaluated over a range of operating conditions. These circulation calculations are sensitive to small changes in heat transfer and load conditions at low pressures, due to the high void fraction in the two-phase region. An accurate estimation of void fraction is therefore required to determine local process conditions (flow velocities and flow regimes) in this region. The limitations of some of the common methods for estimating void fractions, such as asymptotic values for high void fractions at low pressures, are considered. The evaporator process conditions determined by modeling are used as inputs to assess the potential for wear by FAC and/or LDI using several established methods (Kastner, Sanchez-Caldera). The results are compared with case studies from field investigations to assess if wall thinning encountered in actual HRSG service can be correlated with certain design factors.

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.

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