Comprehensive nuclear materials 5 04 corrosion and stress corrosion cracking of ni base alloys

Comprehensive nuclear materials 5 04 corrosion and stress corrosion cracking of ni base alloys Comprehensive nuclear materials 5 04 corrosion and stress corrosion cracking of ni base alloys Comprehensive nuclear materials 5 04 corrosion and stress corrosion cracking of ni base alloys Comprehensive nuclear materials 5 04 corrosion and stress corrosion cracking of ni base alloys Comprehensive nuclear materials 5 04 corrosion and stress corrosion cracking of ni base alloys Comprehensive nuclear materials 5 04 corrosion and stress corrosion cracking of ni base alloys

5.04 Corrosion and Stress Corrosion Cracking of Ni-Base Alloys S Fyfitch AREVA NP Inc., Lynchburg, VA, USA ß 2012 Elsevier Ltd All rights reserved 5.04.1 Introduction 70 5.04.2 5.04.2.1 5.04.2.2 5.04.2.3 5.04.3 5.04.3.1 5.04.3.2 5.04.3.3 5.04.3.4 5.04.4 5.04.4.1 5.04.4.1.1 5.04.4.1.2 5.04.4.1.3 5.04.4.1.4 5.04.4.2 5.04.4.3 5.04.4.4 5.04.4.4.1 5.04.4.4.2 5.04.4.4.3 5.04.4.4.4 5.04.4.4.5 5.04.4.5 5.04.4.5.1 5.04.4.5.2 5.04.4.5.3 5.04.4.5.4 5.04.4.5.5 5.04.4.6 5.04.4.7 5.04.5 References Ni-Base Alloy Use in PWRS/BWRS Wrought Ni–Cr–Fe Alloys Age-Hardenable Ni-Base Alloys Ni-Base Welding Alloys General Corrosion Water Chemistry Flow Rates Crevices Mitigation Stress Corrosion Cracking Environmental Conditions Temperature Water chemistry Sulfur intrusions Electrochemical potential Flow Rates Crevices Material Susceptibility Factors Heat treatment Microstructure Grain size Chemical composition Product form Stress Operating stress Residual stress Surface effects Weld geometry Stress relief annealing Irradiation Mitigation Outlook 70 70 72 73 73 75 75 75 75 75 77 77 77 80 81 81 82 82 82 83 84 84 85 85 86 86 87 87 87 88 90 90 90 Abbreviations ASME ASTM B&PV BWR CEDM CMTRs American Society of Mechanical Engineers American Society for Testing and Materials Boiler and Pressure Vessel Boiling water reactors Control element drive mechanism Certified material test reports CRDM ECP EPRI GMAW GTAW HAZ IASCC Control rod drive mechanism Electrochemical potential Electric Power Research Institute Gas-metal-arc welding Gas-tungsten-arc welding Heat-affected zone Irradiation-assisted stress corrosion cracking 69 70 Corrosion and Stress Corrosion Cracking of Ni-Base Alloys IGSCC INCO LM LWR MSE NRC PWR PWSCC RCS RUBs SAW SCC SEM SMAW TT Intergranular stress corrosion cracking International Nickel Company Light microscopy Light water reactor Mechanical surface enhancement Nuclear Regulatory Commission Pressurized water reactors Primary water stress corrosion cracking Reactor coolant system Reverse U-bends Submerged-arc welding Stress corrosion cracking Scanning electron microscope Shielded-metal-arc welding Thermal treatment 5.04.1 Introduction Nickel–chromium–iron alloys (i.e., nickel-base alloys) are widely used in the power industry in both fossil (e.g., coal and gas) power stations and light water reactor (LWR) nuclear power stations (i.e., pressurized and boiling water reactors (PWRs and BWRs)) As a result, the service behavior of these alloys has been extensively studied,1 especially their susceptibility to corrosion and stress-induced corrosion phenomena The power industry is concerned with the occurrence of such failure phenomena because of their effect on the safety and availability of equipment Corrosion and, in particular, stress corrosion failures are not new The power industry is well acquainted with stress corrosion cracking (SCC) of stainless steel in BWR piping and nickel-base alloys in PWR steam Table generators and its effect on equipment availability.2 SCC of these austenitic alloys has been known for more than 50 years 5.04.2 Ni-Base Alloy Use in PWRS/ BWRS 5.04.2.1 Wrought Ni–Cr–Fe Alloys The wrought nickel-base alloys that are typically used for nuclear applications are Alloy 600 and, more recently, Alloy 690, which contain approximately twice the chromium content These materials are used primarily for their inherent resistance to general corrosion (i.e., oxidation resistance), strength at elevated temperatures, and a coefficient of thermal expansion very close to carbon and low-alloy steels The typical chemical composition and mechanical properties of these alloys are summarized in Tables and 2, respectively Both Alloy 600 and Alloy 690 are non-agehardenable, austenitic solid-solution strengthened materials No precipitation reaction is possible with either alloy to increase strength; however, strength can be increased by cold-working the material They are normally used in the annealed condition; however, a low-temperature heat treatment, or ‘thermal treatment’ (TT), is also generally used with these alloys, which tends to improve the resistance to SCC in primary water chemistry conditions, which is typically known as primary water SCC (PWSCC) (see later sections of this chapter) This improvement is clearly shown to be more pronounced, at least for Alloy 600 material, in crack initiation testing.3 Chemical composition of wrought nickel-base alloys used in nuclear applications Alloying element Alloy 690 Alloy 600 Alloy X-750 Alloy 718 Alloy 800 Ni ỵ Co C Mn Fe S Si Mo Cu Cr Ti Al P Nb ỵ Ta Others 58.0 0.04 max 0.5 max 7.0–11.0 0.015 max 0.50 max – 0.50 max 28.0–31.0 – – – – 72.0 0.15 max 1.00 max 6.00–10.00 0.015 max 0.50 max – 0.50 max 14.0–17.0 – – – – 70.0 0.08 max 1.00 max 5.0–9.0 0.01 max 0.50 max – 0.50 max 14.0–17.0 2.25 – 2.75 0.40–1.0 – 0.70–1.20 50.0–55.0 0.08 max 0.36 max Bal 0.015 max 0.35 max 2.8–3.3 0.30 max 17.0–21.0 0.65–1.15 0.20–0.80 0.015 max 4.75–5.50 B 0.006 max 32–35 0.03 max 0.4–1.0 Bal – 0.30–0.70 –