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ABSTRACT Titanium alloy degradation modes are reviewed in relation to their performance in the repository environments. General corrosion, localized corrosion, stress corrosion cracking, hydrogen induced cracking, microbially influenced corrosion, and radiation-assisted corrosion of Ti alloys are considered. With respect to the Ti Grade 7 drip shields used in the repository at Yucca Mountain, general corrosion, hydrogen induced cracking, and radiation-assisted corrosion will not lead to failure within the 10,000 year regulatory period; stress corrosion cracking (in the absence of disruptive events) is of no consequence to barrier performance; and localized corrosion and microbially influenced corrosion are not expected to occur. To facilitate the discussion, Ti Grades 2, 5, 7, 9, 11, 12, 16, 17, 18, and 24 are included in this review. INTRODUCTION The Nuclear Waste Policy Act of 1982 as amended in 1987 designated Yucca Mountain in Nevada as the potential site to be characterized for high-level nuclear waste (HLW) disposal [1]. Long-term containment of the waste and subsequent slow release of radionuclides from the Engineered Barrier System (EBS) into the geosphere will rely on a system of natural and engineered barriers including a robust waste containment design. The waste package (WP) design during the Viability Assessment (VA) phase of the Yucca Mountain Project [2] used an all-metallic, dual-barrier waste container utilizing a thick outer corrosion-allowance metal barrier (A516 carbon steel) over a thinner inner container made of a suitable corrosion-resistant alloy [2]. During the Site Recommendation (SR) phase of the Project, the container design was modified to the current configuration with a highly corrosion resistant Ni-based Alloy 22 cylindrical barrier surrounding a 316 stainless steel inner structural container [3]. The waste package was to be covered by a self-supported mailbox-shaped drip shield (DS) composed predominantly of Ti Grade 7 with Ti Grade 24 structural support members [3]. The Ti drip shield provided defense in depth, because the WP and DS do not have common failure modes, lending a further margin of safety to repository design. The current design concept is schematically shown, with illustration of the mailbox-shaped drip shield, in Figure 1 [4. The minimum target lifetime for containment of HLW without exceeding a regulatory specified individual dose rate at the site boundary is 10,000 years [4]. Over the years, numerous studies have been performed to evaluate the susceptibility to stress corrosion cracking, general, localized, galvanic and microbially influenced corrosion for Alloy 22 [5, 6, 7, 8, 9, 10, 11, 12] and Ti Grade 7 [6, 7, 13, 14, 15]. The purpose of this work is to review the corrosion performance of Ti Grade 7 and other relevant titanium alloys for the current WP design under the repository environmental conditions. The review will concentrate on potential corrosion processes possible in aqueous environments at Yucca Mountain. A brief review of the background of titanium alloys, hydrogen absorption and the properties of passive film on titanium alloys will be given as the basis of the discussion. Next, the key corrosion processes that could occur will be addressed individually. Finally, the expected corrosion performance of these alloys under the specific environmental conditions anticipated at Yucca Mountain will be considered.
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- Water & Waste Management > Solid Waste Management (1.00)
- Materials > Metals & Mining > Titanium (1.00)
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Hydrogen Induced Cracking of Titanium Alloys in Environments Anticipated in Yucca Mountain Nuclear Waste Repository
Hua, Fred (Bechtel SAIC Company LLC) | De, Gopal C. (Bechtel SAIC Company LLC) | Gordon, Gerald M. (Bechtel SAIC Company LLC) | Pasupathi, V. (Bechtel SAIC Company LLC) | Mon, Kevin (Framatome Cogema Fuels) | Shoesmith, David W. (University of Western Ontario)
ABSTRACT This paper presents a review hydrogen-induced cracking (HIC) of Ti Grade 7 and other relevant titanium alloys under nuclear waste repository environmental conditions, with a primary emphasis on the corrosion processes possible in aqueous environments at Yucca Mountain. The current understanding of hydrogen absorption and the role of passive film on titanium alloys is presented. The key corrosion processes that could occur are addressed individually. Finally, the models developed to assess the hydrogen concentration in the drip shield due to passive general corrosion and galvanic coupling to less noble metals under repository conditions is described. To facilitate the discussion, Ti Grades 2, 5, 7, 9, 11, 12, 16, 17, 18, and 24 are included in this review. It can be concluded that under repository conditions, HIC of titanium alloys will not occur because there will not be sufficient hydrogen in the metal even after 10,000 years of emplacement. Based on the many assumptions adopted this assessment can be considered very conservative. INTRODUCTION The Nuclear Waste Policy Act of 1982 (as amended in 1987) designated Yucca Mountain in Nevada as the potential site to be characterized for high-level nuclear waste (HLW) disposal.[1] Longterm containment of waste and subsequent slow release of radionuclides into the geosphere will rely on a system of natural and engineered barriers including a robust waste containment design. The waste package (WP) design consists of a highly corrosion resistant Ni-based Alloy 22 cylindrical barrier surrounding a 316 stainless steel inner structural vessel.[2] The waste package is covered by a mailboxshaped drip shield (DS) composed predominantly of Ti Grade 7 with Ti Grade 24 structural support members.[2] The Ti Grade 7 drip shield provides defense in depth, because the WP and DS do not have common failure modes, lending a further safety margin to the repository design. The minimum target lifetime for containment of HLW, without exceeding a regulatory specified individual dose rate at the site boundary, is 10,000 years.[2] Over the years, numerous studies have been performed to evaluate the susceptibility to stress corrosion cracking, general, localized, galvanic and microbially influenced corrosion for Alloy 22 [3, 4, 5, 6, 7, 8, 9, 10, 11] and Ti Grade 7.[4, 5, 11, 12, 13] The purpose of this paper is to review hydrogen induced cracking (HIC) of Ti Grade 7 and other relevant titanium alloys under repository environmental conditions. The review will concentrate on the corrosion processes possible in aqueous environments at Yucca Mountain. A brief review of hydrogen absorption and the properties of the passive film on titanium alloys is presented. The key corrosion processes that could occur will be addressed individually. Finally, the models developed to predict the rate of hydrogen absorption into the alloy due to passive general corrosion and galvanic coupling to less noble metal under repository conditions are described.
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- Health, Safety, Environment & Sustainability > Environment (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT The Nuclear Waste Policy Act of 1982 as amended in 1987 designated Yucca Mountain as the site to be characterized for high-level nuclear waste (HLW) disposal.1 Long-term containment of the waste and the subsequent slow release of radionuclides from the engineered barrier system (EBS) into the geosphere will rely on a system of natural and engineered barriers, including a robust waste containment design. During the site recommendation (SR) phase of the Project, a container design using a highly corrosion-resistant Ni-based Alloy 22 (UNS N06022)(1) cylindrical barrier surrounding a Type 316 (UNS S31600) stainless steel inner structural container was adopted.2 The waste package is covered by a self-supported mailbox-shaped drip shield (DS) composed predominantly of Ti Grade 7 (UNS R52600) with Ti Grade 24 (UNS R56405) structural support members.2 The Ti drip shield protects the waste package against rock fall and limits the contact of the waste form to dripping water. The minimum target for the isolation of HLW without exceeding a regulatory specified individual dose rate at the site boundary is 10,000 years.3 Numerous studies have been performed to evaluate the susceptibility to stress corrosion cracking, general, localized, galvanic, and microbiologically influenced corrosion for Alloy 224-11 and Ti Grade 7.5-6,12-14 The purpose of this work was to review the corrosion performance of Ti Grade 7 and other relevant Ti alloys under repository conditions. A brief review of the background of Ti alloys, hydrogen absorption, and the properties of passive film on Ti alloys will be
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- Health, Safety, Environment & Sustainability > Environment > Waste management (0.88)
ABSTRACT Corrosion tests were run concurrently at Location A and Location B to determine the effects of ferric ion [Fe(III)] content on inhibiting general corrosion of titanium Grades 2 (UNS R50400), 7 (UNS R52400), 12 (UNS R53400), 16 (UNS R52402), 27 (UNS R52254), and 28 (UNS R56323) in hydrochloric acid (HC1) solutions at 66-282°C. Tests were conducted at Location A with 1,000 and 10,000 ppm Fe(III) additions to boiling HCI solutions to establish 5 mpy isocorrosion diagrams as an extension of previous work (~). Location A tests also assessed the effects of higher temperatures (282°C) on the corrosion performance of titanium Grades 2 and 7 in HCI solutions with 10,000 ppm Fe(III) additions. Location B tests were performed to evaluate the corrosion resistance in 66°C, 82°C, and boiling HC1 solutions at concentrations up to 35 wt.% and Fe(III) additions up to 28,000 ppm. The comprehensive alloy corrosion database developed is applicable to many chemical process streams such as hydrometallurgical acid ore leaching (2), acid cleaning of deep wells and other chemical processes involving Fe(III) and other multivalent metal ions. BACKGROUND Titanium and titanium alloys show limited corrosion resistance in uninhibited reducing acid media such as hydrochloric (HCI), phosphoric (H3PO4) and sulfuric (H2SO4) acids. However, the presence of process additives and/or contaminants (oxidizing species) can dramatically enhance the range of applications for these alloys. The presence of oxidizing species such as ferric Fe(III), nickelous Ni(II), cupric Cu(II), and other multivalent metal cations can inhibit general corrosion of titanium in reducing acids (1-3). These multivalent metal cations, other oxidizing anions, and oxidizing organic compounds reduce or mitigate corrosion by acting as cathodic depolarizers to shift metal potential in the noble (positive) direction. This, in turn, helps stabilize and maintain the passivity of titanium's oxide film in reducing acids (1-3). The presence of such oxidizing species can permit titanium to be effectively used in process streams and cleaning applications where a strong reducing acid is required. Hydrometallurgical acid ore leaching (2) and acid cleaning of deep wells are just two examples of applications where titanium alloys are used successfully because of the presence of multivalent metal ions. Without these oxidizing species present, titanium would exhibit severe corrosion. Another advantage of having oxidizing species present is the elimination of hydrogen absorption. Since the oxidizing species are reduced (i.e., acceptance of electrons lost from corrosion of the titanium) instead of hydronium (oxonium) ions, hydrogen pickup is controlled, thereby enabling titanium to be used in a hot reducing acid environment where a finite corrosion rate is exhibited. It should be cautioned, however, that crevice corrosion can be aggravated in hot acid halide media by the presence of oxidizing species, the discussion of which is beyond the scope of this paper. The corrosion tests described here were run concurrently at Location A and Location B to determine the effectiveness of Fe(III) additions in inhibiting titanium corrosion in HCI solutions and the effects of temperature on corrosion. Previous data showed that higher temperatures require more Fe(III) to be added to maintain corrosion resistance at useful levels. To better understand the effects of Fe(III) on corrosion resistance in sub-boiling, boiling, and higher temperatures, RMI Titanium Company (Location A) and DuPont (Location B) chose to evaluate numerous commercial titanium alloys in a wide range of HCI solutions with Fe(III) additions. Location A Tests The Location A tests sought to
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT Titanium Grade 38 (Ti-4Al-2.5V) has good cold-workability and exhibits relatively high ductility similar to Titanium Grade 9 (Ti-3Al-2.5V), but has strength properties approaching that of Titanium Grade 5 (Ti-6Al-4V). Grade 38, which was originally developed for industrial and armor applications, has higher strength than most other titanium grades and can be used in higher temperature applications up to 600 °F. Results of crevice corrosion, U-bend, and general corrosion tests in various different media are discussed in this paper. These tests were conducted in order to better understand how Grade 38 compares to common titanium alloys. The alloys included in this comparison were: ASTM Grade 2 Titanium, UNS R50400 ASTM Grade 5 Titanium, UNS R56400 ASTM Grade 9 Titanium, UNS R56320 ASTM Grade 12 Titanium, UNS R53400 ASTM Grade 38 Titanium, UNS R54250 The unique combination of high strength, ductility, formability, workability, and corrosion resistance gives Grade 38 versatility in a wide variety of applications. INTRODUCTION The ATI 425 titanium alloy, to be referred to as Grade 38, a proprietary alloy, was originally developed in the late 1990â??s by Dr. Kosaka for hot-rolled armor plate. The alloy was intended as a lower cost formulation which could utilize recycle streams with higher oxygen and iron contents.1, 2 The increased iron is used as a beta stabilizer and allows for the replacement of some of the higher priced vanadium.303E Table 1 shows the normal alloy chemistry of Grade 38 as well as other common titanium grades. TABLE 1 NORMAL ALLOY CHEMISTRY OF COMMON TITANIUM GRADES (available in full paper) It was discovered during preparation of plate samples for ballistics testing, that Grade 38 had very good hot workability. This allowed a more lenient window for processing than necessary for Grade 5. Grade 38 flowed easier in forging and rolling, was less prone to surface cracking, and required less surface conditioning for subsequent working than did Grade 5. It was also discovered that Grade 38 had the ability to be cold worked similar to Grade 9, even with oxygen levels higher than that of Grade 9. 4 All forms of Grade 38 tested showed mechanical properties similar to Grade 5 but had the added advantage of being easier to form. Table 2 shows the mechanical properties of Grade 38 as compared to other common titanium grades. 1 TABLE 2 MECHANICAL PROPERTIES OF COMMON TITANIUM GRADES (available in full paper) During initial alloy development, it was understood that armor plate could potentially be exposed to chlorides in a marine environment. One concern was the higher iron content and its effect in the presence of these chlorides. Initial seawater and hot salt cracking tests were performed and Grade 38 showed results similar to Grade 5. No further testing was deemed necessary as the only applications at that time were for amphibious vehicles, shipboard applications, and the potential to be used in some aircraft components. 4
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