The MIMA-2 International Conference was held on-line for three days between 11 and 13.October-2022. This was the second in the series of on-line conferences organised by ETD Consulting concerning Materials, Inspection, Monitoring and Assessment, with a total of 26 presentations contained in five sessions relating to
High Temperature Materials Issues (Session 1)
Plant Life Assessment (Session 2)
Plant Inspection and Maintenance (Session 3)
Component Damage and Failure (Session 4)
Power Plant Flexibility Issues (Session 5)
In addition, four additional presentations were made in a final Plenary Session (Session 6).
Following a Rapporteur overview summary of the MIMA-2 conference proceedings, the MHT MIMA-2 Special Issue contains 7 papers based on presentations made during the course of this conference. Importantly, papers originating from four of the main sessions are included [an eighth paper based on a third session presentation was published in Materials at High Temperatures, 2023, 40(1), 88-98]. For example, the first session, which was concerned with High Temperature Materials Issues, mainly (but not exclusively) covered developments associated with 9Cr-3W-3Co-VNbBN (alternatively referred to as MARBN).
The MARBN steel was originally developed in Japan by a group headed by Fujio Abe, who has continued to be active in studying the metallurgy of this alloy, and a number of other associated advanced martensitic steels. It was therefore appropriate that the first presentation in the first session of the conference was by Dr Abe, and that the 9Cr-3W-3Co-VNbBN alloy played an integral part in the first paper in this Special Issue. In fact, Dr Abe’s paper is more generally concerned with The role of inclusions on the degradation in creep life and rupture ductility of ferritic power plant steels and, more specifically, considers the role of BN, AlN and MnS particles on degradation of the creep properties of 9 to 12%Cr martensitic steels and a 1%Cr bainitic steel at temperatures in the range 550 to 700°C.
A second paper from the first session concerns Experience of P93 manifold welding under fabrication conditions, and was by de-Smet, Tang & Bok (of Siemens Energy Heat Transfer Technology). While MARBN is an ASME Code Case variant of P93 (or 9Cr-3W-3Co), the presented evidence indicates that further optimisation of the heat treatment and welding procedures are required in order to attain the required impact toughness properties for weldments of the more generic grade of this steel.
The second session was concerned with Plant Life Assessment, with the contribution of Professor Nonaka (of Tohoku University) from the Plenary Session representing the Japanese perspective on this topic. Entitled Activities to advance residual life evaluation techniques for highly aged power plant, Professor Nonaka’s paper concerns the wide ranging activities of a Japanese Materials Sciences Society Working Group and recent developments in techniques being adopted for the life assessment of very old power generation units.
Two papers based on presentations from the third session (Plant Inspection and Maintenance) are included. The first by Pascal Decoussemaeker (of GE Power, Switzerland) is concerned with Risk-based life management for steam turbines and generators, and considers the necessary important details of an asset management program to ensure reliable operation over the commercial life of, in particular, steam power plant.
The third session presentation of Adam Wojcik (Matelect, UK) et al formed the basis of A review of the factors affecting the use of electrical potential drop (EPD) for creep life monitoring. Direct current (DC) and alternating current (AC) variants of electrical potential drop instrumentation have been widely used for identifying and monitoring sub-critical crack growth in the laboratory and in plant in a variety of engineering materials for over 50 years. The novelty of the work described in the Wojcik et al paper is the successful development of a unit combining both DC and AC EPD instrumentation to give advance warning of the evolution of creep damage in power plant components. The research represented the outcome of work conducted as part of an ETD-led industry-sponsored project.
A third paper from the third session was inadvertently published in a previous issue of Materials at High Temperatures (i.e. 2023, 40(1), 88-98) instead of this Special Issue. This paper, by Wu, Wang, Zhao & Liang (of Xi’an Jiaotong University, China) presented a detailed and informed review of High temperature corrosion data and mechanisms for T122, Super 304 H and HR3C after 15 years in a 1000 MW ultra-supercritical power plant. While information concerning hot flue gas and steam-side corrosion is comprehensively described, it is acknowledged that the detail is to some extent power plant specific, depending on the respective times and temperatures of operation and the number of operating cycle start/stops experienced by the heat exchanger pipework under investigation.
Two papers included in this Special Issue originated from presentations made in Session 5 (Power Plant Flexibility Issues). Stuart Holdsworth reviews the approaches which have been (and can be) adopted for verifying the effectiveness of assessment procedures used to predict high temperature component integrity in turbines required for flexible operation. In the past, when there was a long period during which power plant operating conditions and the adopted materials of construction remained unchanged, the effectiveness-verification of structural integrity assessment procedures could rely on feedback from service experience. More recently, as the rate of change in turbine operating conditions and the materials adopted (to compensate for these changes) has increased, the effectiveness-verification of new (and refined) assessment procedures has had to increasingly rely on the results of component feature-specimen testing.
Finally, from Session 5, Rolf Sandström’s paper considers Cavitation during creep-fatigue loading. His latest work develops mechanical formulations which go beyond previous creep cavitation models to represent creep-fatigue damage accumulation, in particular, in 1Cr0.5Mo steel. Creep-fatigue interaction is considered in terms of the influence of pre-creep exposure on LCF properties, as well as a consequence of LCF cycles without and with hold times. Both diffusion and strain-controlled cavity growth are analysed, with growth being assumed to be unconstrained. Mid-life cycle creep-fatigue stress-strain hysteresis loops for 1Cr0.5Mo at 535°C are reasonably predicted.