Gordon B.M.,Structural Integrity Associates
Corrosion | Year: 2013
Corrosion is a major service life-limiting mechanism for both pressurized water reactors (PWR) and boiling water reactors (BWR). While most of the corrosion research emphasis in the nuclear corrosion community has been focused on environmentally assisted cracking (EAC) of austenitic stainless steels and nickel-based alloys and weld metals, in particular stress corrosion cracking (SCC), there are other corrosion phenomena that seriously affect plant life extension that cannot be ignored. This paper presents three other important corrosion areas, i.e., general corrosion of the light water reactor (LWR) containments, flow-accelerated corrosion of carbon steel piping systems, and the corrosion of buried piping. © 2013, NACE International.
Wood P.,Structural Integrity Associates
NACE - International Corrosion Conference Series | Year: 2014
Power plants contain a complex network of buried piping composed of various materials, primarily metals, all electrically connected via a copper grounding grid. While the effects of mixed metal couples are a topic of discussion, little has been done to examine and document their measured impact in an installed plant environment. This paper will present an analysis of an extensive amount of native (static) copper/copper sulfate reference cell (CSE) potential data obtained from buried structure surveys at nineteen (19) nuclear plants, most with existing cathodic protection (CP) systems but several without CP systems. By integrating CSE potential data with detailed positional information from digitized drawings for piping, buildings, and grounding systems, a map of the native potential landscape in a nuclear power plant with respect to the buried mixed metal piping environment is developed. Statistical analyses of the distribution of native potentials will be discussed, along with implications of these analyses for the actual impact of mixed metals. Suggestions for further examination of the effects of mixed metals in a plant environment will also be presented. The perspectives discussed in this paper have implications for nuclear power plant operators, especially those pursuing License Renewal under the guidance of LR-ISG-2011-03, "Final License Renewal Interim Staff Guidance", for NUREG-1801, Revision 2 ("The GALL Report"), Aging Management Program XI.M411. © 2014 by NACE International.
Wright I.G.,Oak Ridge National Laboratory |
Dooley R.B.,Structural Integrity Associates
International Materials Reviews | Year: 2010
The focus of this review is the state of knowledge of the oxidation behaviour in steam of alloys with potential for use as pressure parts in steam boilers. The rate of oxide growth on steam-touched surfaces and the characteristics of that oxide are of increasing interest as the quest for improvements in cycle efficiency leads to progressively higher operating temperatures and pressures. The consequences of increased rate of growth of these oxides are of concern because of implications for tube overheating and oxide exfoliation. Mitigation of such problems requires a mechanistic understanding of the influences of alloy composition and microstructure, and especially of the evolution with time of specific scale structures. Similarly, the relative effects of factors such as time, temperature and operating parameters must be understood. The oxidation behaviour of the class of ferritic steels that forms the bulk of the heat transfer surface in steam boilers is of particular importance since alloys in the range 9-12%Cr (% in alloy compositions signifies weight percentage, unless indicated otherwise) are close to a transition from oxidation behaviour based on relatively thick Fe-based scales to the formation of much thinner, Cr-rich oxides. For austenitic steels protective behaviour in steam depends critically on the rapid development of a continuous Cr-rich oxide layer, otherwise oxide growth rates similar to the ferritic steels may result. Understanding the interplay among compositional and microstructural requirements for strengthening and oxidation resistance, and their influence on the rate and mode of scale evolution is key to the most effective application of these alloys. The oxidation behaviour of high-temperature Ni-based alloys in steam has received relatively little attention, but the broad range of alloying additions considered, compared to austenitic steels, has the potential to contribute in different ways to the scale morphologies and oxidation behaviour. Underlying these interests is the apparently significant contribution to oxide growth in steam from inward transport of oxidant species that likely involve hydrogen. The particular species involved and their roles in the oxidation process are expected to exert a large influence on the oxide morphologies developed, while the fate of any hydrogen released in the alloy is a further topic of particular interest. © 2010 Institute of Materials, Minerals and Mining and ASM International.
Sommerville D.,Structural Integrity Associates
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2013
Recent industry communications have identified issues pertaining to incorrectly calculated recirculation line break acoustic loads or structural evaluations that need to include, but have previously excluded, the recirculation line break acoustic loads. Various organizations have studied the recirculation line break event and have developed methodologies to calculate the decompression loads caused by this event on various boiling water reactor internal components. In general, loads are calculated in a plant specific and operating condition specific manner. Once these loads are available then the necessary structural evaluations can be performed. With the various flexibility options that an operating boiling water reactor can be licensed for it can become difficult to know when the recirculation line break acoustic loads must be updated and subsequently, which structural evaluations must be updated as well. In this paper a simple extension of an existing, benchmarked, acoustic loads methodology is suggested in which a bounding set of input parameters is evaluated in order to predict acoustic loads that will bound all flexibility options that are currently implemented at operating plants. The objective of this approach is to save the utilities time and money by enabling a single iteration of loads calculation and structural analysis. This approach is shown to produce loads that are approximately a factor of 1.5 larger than those predicted using typical operating parameters. Copyright © 2013 by ASME.
Gordon B.M.,Structural Integrity Associates
JOM | Year: 2013
Serious corrosion problems have plagued the light water reactor (LWR) industry for decades. The complex corrosion mechanisms involved and the development of practical engineering solutions for their mitigation will be discussed in this article. After a brief overview of the basic designs of the boiling water reactor (BWR) and pressurized water reactor (PWR), emphasis will be placed on the general corrosion of LWR containments, flow-accelerated corrosion of carbon steel components, intergranular stress corrosion cracking (IGSCC) in BWRs, primary water stress corrosion cracking (PWSCC) in PWRs, and irradiation-assisted stress corrosion cracking (IASCC) in both systems. Finally, the corrosion future of both plants will be discussed as plants extend their period of operation for an additional 20 to 40 years. © 2013 TMS.