Corrosion and microstructural analysis data for AISI 316L and AISI 347H stainless steels after exposure to a supercritical water environment
This article presents corrosion data and microstructural analysis data of austenitic stainless steels AISI 316L and AISI 347H exposed to supercritical water (25 MPa, 550 °C) with 2000 ppb of dissolved oxygen. The corrosion tests lasted a total of 1200 h but were interrupted at 600 h to allow measurements to be made. The microstructural data have been collected in the grain interior and at grain boundaries of the bulk of the materials and at the superficial oxide layer developed during the corrosion exposure.
Corrosion and stress corrosion cracking in supercritical water
Abstract Supercritical water (SCW) has attracted increasing attention since SCW boiler power plants were implemented to increase the efficiency of fossil-based power plants. The SCW reactor (SCWR) design has been selected as one of the Generation IV reactor concepts because of its higher thermal efficiency and plant simplification as compared to current light water reactors (LWRs). Reactor operating conditions call for a core coolant temperature between 280 °C and 620 °C at a pressure of 25 MPa and maximum expected neutron damage levels to any replaceable or permanent core component of 15 dpa (thermal reactor design) and 100 dpa (fast reactor design). Irradiation-induced changes in microstructure (swelling, radiation-induced segregation (RIS), hardening, phase stability) and mechanical properties (strength, thermal and irradiation-induced creep, fatigue) are also major concerns. Throughout the core, corrosion, stress corrosion cracking, and the effect of irradiation on these degradation modes are critical issues. This paper reviews the current understanding of the response of candidate materials for SCWR systems, focusing on the corrosion and stress corrosion cracking response, and highlights the design trade-offs associated with certain alloy systems. Ferritic–martensitic steels generally have the best resistance to stress corrosion cracking, but suffer from the worst oxidation. Austenitic stainless steels and Ni-base alloys have better oxidation resistance but are more susceptible to stress corrosion cracking. The promise of grain boundary engineering and surface modification in addressing corrosion and stress corrosion cracking performance is discussed.
Importance of surface preparation for corrosion control in nuclear power stations
To enable nondestructive inspection, construction rules generally specify the final surface condition of components only in terms of limiting roughness values. However, the microgeometry is only one of many important surface characteristics. Failure to ensure overall cleanness of circuits (i.e., of all exposed surfaces) by taking certain precautions can have serious consequences. Furthermore, the presence of a heavily cold-worked surface layer, from machining or other causes, can completely modify its corrosion behavior in service. It has long been known that the oxidation resistance of stainless steels in steam or carbon dioxide (CO{sub 2}) at temperatures in the vicinity of 500 C is considerably improved by a cold-worked surface layer, which enhances Cr diffusion and promotes the formation of a tenacious and protective oxide scale. More recently, the effect of cold-worked surface layers on the susceptibility to stress corrosion cracking has been clearly revealed in components that have been subjected to strain during manufacture by tube bending, expansion operations, or even welding. Very high residual stresses can be induced in the skin region, and if the cold-worked layer is sufficiently thick, cracks can be initiated in a very short time. Based on the difference in the depth of cold work inducedmore » by various mechanical treatments, it has been possible to model this effect and to explain the wide scatter in the service behavior of certain pressurized water reactor components. It is essential to take these factors into account to predict correctly the service behavior of the components concerned, without which satisfactory plant maintenance planning is impossible.« less