CORROSION OF ALLOY 22 AND TITANIUM ALLOYS 

UNDER SEEPAGE WATER DRIPPING CONDITION 

Prepared for 

U.S. Nuclear Regulatory Commission 

Contract NRC–02–07–006 

Prepared by 

Hundal Jung1

Xihua He1

Tae Ahn2

Todd Mintz1

Roberto Pabalan1

1

Center for Nuclear Waste Regulatory Analyses 

San Antonio, Texas 

2

U.S. Nuclear Regulatory Commission 

Washington, DC 

September 2011
ii

ABSTRACT 

This report documents the results of a previously unpublished set of experiments that evaluated 

the corrosion behavior of Alloy 22 and titanium alloys (Grades 7 and 29) under seepage water 

dripping conditions at controlled temperature and relative humidity. Tests were conducted 

inside a chamber with controlled temperature and relative humidity. The simulated seepage 

water was dripped on the test specimens at rates of 65 or 80 mL/day [2.20 or 2.71 oz/day] 

depending on the test temperature. Three batches of tests were conducted for Alloy 22: a first 

batch at 80 °C [176 °F] and 85 percent relative humidity, a second batch at 95 °C [203 °F] and 

75 percent relative humidity, and a third batch at 60 °C [140 °F] and 95 percent relative 

humidity. The first two batches of tests were conducted for titanium alloys. After testing, the 

posttest specimens were examined with an optical microscope and salt deposits were analyzed 

in terms of chemical composition and crystal structure. Finally, after cleaning the posttest 

specimens, weight loss was measured to calculate corrosion rates of Alloy 22 and 

titanium alloys. 

In all of the tested conditions for Alloy 22, white deposits were observed on the posttest 

specimens. In the first batch of tests, the surfaces of the posttest specimens exhibited 

several corrosion pits along with many small sized pits ranged about 1 to 10 μm 

[3.94 × 10−5

 to 3.94 × 10−4 in] after 35 days of the dripping test. After 185 days of testing, 

however, the pits appeared to be shallow and there was no clear evidence of pit propagation. 

The corrosion rate decreased with test duration, and the rate measured after 185 days’ 

exposure was 25 nm/yr [9.84 × 10−7

 in/yr]. In the second batch at 95 °C [203 °F], pits were also 

present on the specimen surface. However, with time, the corrosion rate decreased. At the low 

temperature of 60 °C [140 °F] and the relative humidity of 95 percent, the corrosion rate 

decreased with time and was 24 nm/yr [9.45 × 10−7

 in] after 60 days of testing. There was no 

evidence of pit propagation. Under the seepage water dripping condition, Alloy 22 exhibited a 

temperature-dependent corrosion rate, which was commonly observed in the immersion tests. 

The corrosion rates obtained from the dripping tests in this study were close to the rates 

obtained from the immersion tests in the literature. Results of the salt chemistry analyses 

through thermodynamic calculations and analysis tools indicate that the major composition was 

calcium carbonate and other several compositions were also precipitated, including magnesium 

carbonate, sodium (calcium) sulfate, sodium chloride, and silica. 

For Titanium Grades 7 and 29 materials, the first batch of tests at 80 °C [176 °F] and 85 percent 

relative humidity for 181 days showed that the corrosion rates of the specimens subjected to 

dripping were in the range of 20–50 nm/yr [7.9 × 10−7

–2.0 × 10−6 in/yr], similar to the rates 

reported in the literature obtained from immersed conditions in similar water chemistry. No 

clear difference was observed between Titanium Grades 7 and 29. The front side surface 

subjected to direct dripping corroded more than the back side that was not subjected to 

direct dripping. The second batch of tests at 95 °C [203 °F] and 75 percent relative 

humidity for 64 days showed that the corrosion rates for Titanium Grades 7 and 29 under 

dripping were 130–380 nm/yr [5.12 × 10−6

–1.50 × 10−5 in/yr] and 260–530 nm/yr 

[1.02 × 10−5

–2.09 × 10−5 in/yr], respectively; higher than what was measured from the first batch 

of tests. The higher corrosion rates could be caused by the shorter test duration and higher test 

temperature. No localized corrosion was observed on either titanium alloys from the two 

batches of tests. 
iii

CONTENTS 

Section Page 

ABSTRACT ................................................................................................................................... ii 

FIGURES ..................................................................................................................................... iv 

TABLES ........................................................................................................................................ v 

ACKNOWLEDGMENTS .............................................................................................................. vii 

1 INTRODUCTION ................................................................................................................ 1-1

1.1 Background Information ............................................................................................ 1-1

1.2 Objective and Organization of the Report ................................................................. 1-3

2 EXPERIMENTAL DETAILS ................................................................................................ 2-1

2.1 Materials .................................................................................................................... 2-1

2.1.1 Alloy 22 Sheet ................................................................................................ 2-1

2.1.2 Titanium Alloys .............................................................................................. 2-1

2.2 Test Procedures ........................................................................................................ 2-1

2.2.1 Test Procedures for Alloy 22 ......................................................................... 2-4

2.2.2 Test Procedures for Titanium Alloys .............................................................. 2-6

3 RESULTS AND DISCUSSION ........................................................................................... 3-1

3.1 Alloy 22 Dripping Test ............................................................................................... 3-1

3.1.1 First Batch of Tests at 80 °C [176 °F] and Relative Humidity of 

85 Percent ..................................................................................................... 3-1

3.1.2 Second Batch of Tests at 95 °C [203 °F] and Relative Humidity of 

75 Percent ..................................................................................................... 3-5

3.1.3 Third Batch of Tests At 60 °C [140 °F] and Relative Humidity of 

95 Percent ..................................................................................................... 3-9

3.1.4 Salt Chemistry Analysis ................................................................................. 3-9

3.2 Titanium Alloys Dripping Test ................................................................................. 3-15

3.2.1 First Batch of Tests at Temperature of 80 °C and Relative Humidity of 

85 Percent ................................................................................................... 3-15

3.2.2 Second Batch of Tests at Temperature of 95 °C [203 °F] and Relative 

Humidity of 75 Percent ................................................................................ 3-22

4 CONCLUSIONS .................................................................................................................. 4-1

5 REFERENCES ................................................................................................................... 5-1
iv 

FIGURES 

Figure Page 

1-1 Range Modeled of Waste Package Temperature Versus Time in the 

Yucca Mountain Performance Assessment ................................................................... 1-2 

1-2 Range Modeled of Relative Humidity Versus Time in the Yucca Mountain 

Performance Assessment .............................................................................................. 1-2 

2-1 (a) Titanium Grade 7 and (b) Titanium Grade 29 Specimens Machined From 

 Original Plate or Pipe Sections ..................................................................................... 2-2 

2-2 Microstructure of (a) Titanium Grade 7 and (b) Titanium Grade 29 Specimens ............ 2-2 

2-3 Experimental Setup for Dripping Test ............................................................................ 2-3 

2-4 Weight Losses of the Corroded Test Specimens Resulting From Repetitive 

 Cleaning Cycles in an ASTM HCl Solution .................................................................... 2-5 

3-1 Photos of Pre- and Posttest Surfaces of Alloy 22 Tested at 80 °C [176 °F] and 

85 Percent Relative Humidity ......................................................................................... 3-2 

3-2 Optical Micrographs of Alloy 22 Surfaces Tested at 80 °C [176 °F] and 85 Percent 

Relative Humidity ........................................................................................................... 3-3 

3-3 Surface Topography of Alloy 22 Specimen After 35 Days Dripped at 

 80 °C [176 °F] and 85 Percent Relative Humidity: ......................................................... 3-4 

3-4 Surface Topography of Alloy 22 Specimen After 185 Days Dripped at 

 80 °C [176 °F] and 85 Percent Relative Humidity .......................................................... 3-6 

3-5 Photos of Posttest Surfaces of Alloy 22 After 33 Days Dripped at 

 95 °C [203 °F] and 75 Percent Relative Humidity .......................................................... 3-8 

3-6 Optical Micrographs of Alloy 22 Surfaces Tested at 95 °C [203 °F] and 75 Percent 

Relative Humidity. .......................................................................................................... 3-8 

3-7 Photos of Posttest Surfaces of Alloy 22 After 60 Days Dripped at 60 °C [140 °F] 

 and 95 Percent Relative Humidity ................................................................................ 3-11 

3-8 Optical Micrographs of Alloy 22 Surfaces Tested at 60 °C [140 °F] and 95 Percent 

Relative Humidity. ........................................................................................................ 3-11 

3-9 Corrosion Rate of Alloy 22 as a Function of Time Tested at Temperatures of 

 95, 80, and 60 °C [203, 176, and 140 °F] ..................................................................... 3-12 

3-10 X-Ray Diffraction Spectroscopy of Salts Deposited on Alloy 22 Specimen After 

32 Days Dripped at 60 °C [140 °F] and 95 Percent Relative Humidity ........................ 3-13 

3-11 X-Ray Diffraction Spectroscopy of Salts Deposited on Alloy 22 Specimen After 

185 Days Dripped at 80 °C [176 °F] and 85 Percent Relative Humidity. ..................... 3-14 

3-12 X-Ray Diffraction Spectroscopy of Salts Deposited on Alloy 22 Specimen After 

67 Days Dripped at 95 °C [203 °F] and 75 Percent Relative Humidity. ....................... 3-14 

3-13 First Batch of Posttest Titanium Grades 7 and 29 Specimens at Temperature 

 of 80 °C [176 °F] and Relative Humidity of 85 Percent ................................................ 3-16 

3-14 Energy-Dispersive X-Ray Spectroscopy of the White Deposits on the First Batch 

 of Posttest Titanium Grades 7 and 29 Specimens. ...................................................... 3-16 

3-15 Energy-Dispersive X-Ray Spectroscopy of the First Batch of Posttest Titanium 

 Grades 7 and 29 Specimen Surface Without Visible Deposits .................................... 3-17 

3-16 Optical Photos of the First Batch Posttest Specimens After Being Cleaned With 

 HCl Solution ................................................................................................................. 3-18 
v 

FIGURES (continued) 

Figure Page 

3-17 Surface of the Third HCl Cleaned Posttest Titanium Specimens Showing 

 That the Dripping Side Was Corroded Uniformly ......................................................... 3-19 

3-18 Optical Photographs of Specimens After First HNO3 Solution Cleaning 

 Showing That Most of the Corrosion Products Were Cleaned ..................................... 3-21 

3-19 Optical Photographs of Second HNO3-Cleaned Tested and Untested 

 Specimens Showing That the Dripping Tested Specimens Had Similar Features ....... 3-22 

3-20 Second Batch of Posttest (a) Titanium Grade 7 and (b) Titanium Grade 29 

 Specimens at Temperature of 95 °C [203 °F] and Relative Humidity of 75 Percent .... 3-23 
vi 

TABLES 

Table Page 

2-1 Chemical Composition of Mill-Annealed Alloy 22 (in Weight Percent) ........................... 2-2 

2-2 Chemical Composition of Titanium Grades 7 and 29 (in Weight Percent) .................... 2-3 

2-3 Chemical Composition of Simulated Seepage Water in This Study ............................... 2-4 

2-4 Test Matrix of Alloy 22 Dripping Tests .......................................................................... 2-5 

3-1 Corrosion Rates of Alloy 22 Dripped at 80 °C [176 °F] and 

 85 Percent Relative Humidity ......................................................................................... 3-7 

3-2 Corrosion Rates of Alloy 22 Dripped at 95 °C [203 °F] and 

 75 Percent Relative Humidity ......................................................................................... 3-9 

3-3 Corrosion Rates of Alloy 22 Dripped at 60 °C [140 °F] and 

 95 Percent Relative Humidity ....................................................................................... 3-11 

3-4 Solution Composition Before and After Evaporation .................................................... 3-12 

3-5 EDS Elemental Composition of Salt Deposit on Alloy 22 Specimen ............................ 3-13 

3-6 First Batch Sample Weight Before and After Test at Temperature of 

 80 °C [176 °F] and Relative Humidity of 85 Percent .................................................... 3-21 

3-7 Second Batch Sample Weight Before and After Test at Temperature of 

 95 °C [203 °F] and Relative Humidity of 75 Percent .................................................... 3-24 
vii 

ACKNOWLEDGMENTS 

This report describes work performed by the Center for Nuclear Waste Regulatory Analyses 

(CNWRA®) and its contractors for the U.S. Nuclear Regulatory Commission (USNRC) under 

Contract No. NRC–02–07–006. The activities reported here were performed on behalf of the 

USNRC Office of Nuclear Material Safety and Safeguards, Division of High-Level Waste 

Repository Safety and Safeguards, Division of High-Level Waste Repository Safety. This report 

is an independent product of the CNWRA and does not necessarily reflect the view or regulatory 

position of the USNRC. 

The authors gratefully acknowledge L. Yang for his technical review, K. Axler for his 

programmatic review, L. Mulverhill for her editorial review, and A. Ramos for his administrative 

support. H. Basagaoglu, C. Manepally, and K. Das are also acknowledged for their advice and 

fruitful discussion on environmental conditions for the test in this study. Special thanks to 

B. Derby, G. Bird, and G. Norman for their assistance in conducting experiments in this study. 

QUALITY OF DATA, ANALYSES, AND CODE DEVELOPMENT 

DATA: All CNWRA-generated original data contained in this report meet the quality assurance 

requirements described in the Geosciences and Engineering Division Quality Assurance 

Manual. Sources for other data should be consulted for determining the level of quality for 

those data. All data and calculations related to this report have been recorded in CNWRA 

Scientific Notebook 899 (Jung, et al., 2011) for Alloy 22 and Scientific Notebook 1024E 

(He, 2011) for titanium alloys. 

ANALYSES AND CODES: The computer software OLI Analyzer Studio Version 3 code 

(Gerbino, 2006; OLI Systems, Inc., 2010) was used for the analyses contained in this report. 

This software is commercial software controlled under the CNWRA quality assurance procedure 

Technical Operating Procedure (TOP)–18. 

References 

Gerbino, A. “A Guide for Using the OLI Analyzers.” Morris Plains, New Jersey: 

OLI Systems, Inc. 2006. 

He, X. “Corrosion Tests of Titanium Alloys and Borated Stainless Steel.” 

Scientific Notebook No. 1024E. San Antonio, Texas: CNWRA. pp. 1–68. 2011. 

Jung, H., B. Derby, and G. Bird. “Seepage Water Dripping Test for Alloy 22 in the Repository 

Relevant Environments.” Scientific Notebook No. 899. San Antonio, Texas: CNWRA. 

pp. 1–107. 2011. 

OLI Systems, Inc. “A Guide to Using OLI Analyzer Studio Version 3.1.” 

Morris Plains, New Jersey: OLI Systems, Inc. 2010.
1-1

1 INTRODUCTION 

This report is part of the knowledge management activities for the U.S. Nuclear Regulatory 

Commission high-level waste repository safety program. The report provides previously 

undocumented results from recent corrosion tests that used weight loss measurements and 

surface analysis to evaluate the corrosion behaviors of Alloy 22 and titanium alloys under 

seepage water dripping conditions. The corrosion experiments were conducted by dripping 

simulated seepage water in three batches with varying temperature and relative humidity: a first 

batch at 80 °C [176 °F] and 85 percent relative humidity, a second batch at 95 °C [203 °F] and 

75 percent relative humidity, and a third batch at 60 °C [140 °F] and 95 percent relative 

humidity. The corrosion rates of Alloy 22 and titanium alloys were estimated by measuring 

weight loss of the posttest specimens. The surface of the specimen was examined with an 

optical microscope, and the salts deposited on the specimen were also analyzed using energy 

dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD). 

1.1 Background Information 

Alloy 22 (Ni−22Cr−13Mo−3W−4Fe) and titanium alloys (Grade 7 and 29) have been candidates 

for the waste package outer container and drip shield materials, respectively, in the proposed 

Yucca Mountain repository (Sandia National Laboratories, 2007a,b). These materials have also 

been studied in various disposal programs around the world as reference waste package 

materials in various geological settings due to their high corrosion resistance (Kursten et al., 

2004). The high corrosion resistances of Alloy 22 and titanium alloys are attributed in part to the 

presence of passive films that protect against fast corrosion. In the event of deterioration or loss 

of passivity of these alloys, they can fail by fast corrosion. Therefore, it is important to 

determine the long-term corrosion rate and susceptibility to localized corrosion of these alloys 

under various service conditions. 

Most corrosion data on these alloys used in the disposal program were obtained from 

immersion experiments to develop the model abstraction for general corrosion rate and 

susceptibility to localized corrosion. In an unsaturated disposal environment, however, the 

corrosion conditions may include dripping seepage water contacting the waste package 

containers (Sandia National Laboratories, 2007a). In addition, the container temperatures 

would be higher than ambient values due to radioactive decay. Therefore, it is expected that 

salt deposits can form on surfaces by seepage water evaporation. 

Environmental Conditions of Temperature, Relative Humidity, and Water Dripping Rate in 

This Study 

Figures 1-1 and 1-2 show the modeled ranges of temperature and relative humidity versus time 

for all waste packages in the proposed Yucca Mountain repository, accounting for uncertainty of 

host-rock thermal conductivity and percolation flux (Sandia National Laboratories, 2008a). 

During the first 10,000 years, the waste package temperatures could have a wide range, from a 

peak of 203 °C [398 °F] to room temperature. In the time period of 1,500 and 10,000 years, 

there is a possibility that one or a few drip shields could fail by seismic impact, allowing seepage 

water to contact the waste package (Sandia National Laboratories, 2008a). During this period, 

the average temperature could range from about 95 to 60 °C [203 to 140 °F] and the average 

relative humidity could range from approximately 75 to 95 percent. These ranges of modeled 

temperature and relative humidity were selected for the experimental conditions in this study. 
1-2

Figure 1-1. Range of Modeled Waste Package Temperature Versus Time in the 

Yucca Mountain Performance Assessment (Sandia National Laboratories, 2008a)

Figure 1-2. Range Modeled of Relative Humidity Versus Time in the Yucca Mountain 

Performance Assessment (Sandia National Laboratories, 2008a)
1-3

The water dripping rates for the dripping tests in this study were selected based on the modeled 

seepage water flow rates as a function of repository time (Sandia National Laboratories, 2008b) 

and adjusted to have a focused flow to the test specimen because the seepage water dripping 

will not be uniform (i.e., not evenly distributed onto either the drip shield surface from the drift 

wall or the waste package surface from the breached areas of the drip shield). Lin, et al. (2003) 

calculated the dripping rate of seepage water to the waste package when the flow was focused 

through the breached area of the drip shield. They found that the dripping rates could increase 

100 to 10,000 times, depending on the size of the focused area. Therefore, in this study, the 

dripping rate was also adjusted to be either 65 or 80 mL/day [2.20 or 2.71 oz/day], depending 

on the test temperature. Scaling from the surface area of 0.002 m2

 [3.10 in2] of the Alloy 22 test 

sample to the surface area of 33 m2

 [51,150 in2] of one waste package, these rates are 

equivalent to 360,000 to 482,000 kg/yr [7.94 × 105

 to 1.06 × 106 lb/yr] with a focusing factor of 

~1,100. In the literature, the dripping rates used for Alloy 22 were about 30 mL/day [1.01

oz/day] of simulated concentrated water (Ashida, et al., 2008) or 200 mL/day [6.76 oz/day] of 

simulated seepage water (Dunn, et al., 2006). The rates in this study fall between these two 

rates, which is a good range to compare the test results with the literature results. 

Dripping Water Droplet Size

The volume (mass) of water droplets in the experiments was initially estimated by a mass 

balance between gravitational force and capillary force by surface tension. Assuming a 

spherical water drop, the gravitational energy per unit volume from the mass of half of a 

spherical water droplet is 

ρ × g × R [erg/cm3

] (1-1) 

where ρ is density of water {e.g., 1 g/cm3

 [3.56 × 10−2 lb/in3] for pure water, varying with 

dissolved species}; g is gravitational force {980 cm/sec2 [385.8 in/sec2

]}; and R is the radius of 

the droplet. The surface energy per unit volume due to surface tension of the droplet is 

2 × γm/R [erg/cm3

] (1-2) 

where γm is specific surface energy of the drop e.g., ~100 erg/cm2

 [645.2 erg/in2] for pure 

water, varying with dissolved species and substrates. By equating these two terms, R is 

calculated to be ~0.45 cm [0.177 in]. If the drop is bigger than this size, it will flow on 

the waste package surface or on the drift wall surface. The mass of half of a spherical droplet 

is 0.19 g [6.7 × 10−3

 oz]. 

This value was different from the actual measured mass of one water droplet. The measured 

mass of a water droplet in this study was about 0.075 g [2.65 × 10−3

 oz]. This actual measured 

mass was used to adjust the water dripping frequency to be either 65 or 80 mL/day [2.20 or 2.71 

oz/day] in this study. This is presumably due to the complex, nonspherical nature of a water 

drop, affected by aqueous water chemistry or temperature, or by the gravitational force on the 

necking of the drop. The total volume of the half sphere may not drop completely, because a 

portion of the droplet water will remain on the rock surface. 

1.2 Objective and Organization of the Report 

The objective of this report is to document the results of recent corrosion tests that used weight 

loss measurements and surface analysis to evaluate the corrosion behavior of Alloy 22 and 

titanium alloys under seepage water dripping conditions. The corrosion tests were conducted to 
1-4

assess the persistence of the passive film and to measure the corrosion rate. The persistence 

of the passive film was assessed by determining susceptibility to localized corrosion 

(primarily pitting), and the corrosion rate was determined by weight loss measurement. Note 

that this report presents preliminary results; longer term corrosion tests are warranted for 

conclusive results. 

This report consists of four chapters: introduction, experimental details, results and discussion, 

and conclusions. This chapter briefly describes the corrosion behaviors of Alloy 22 and titanium 

alloys. Environmental conditions including temperature, relative humidity, and seepage water 

dripping rates under seepage water dripping conditions in a repository are also discussed in this 

chapter. Experimental conditions in this study are provided in Chapter 2, including details of 

test samples, test solutions, and test procedures. Relative humidity, water droplet size, and 

frequency of dripping were controlled, in addition to temperature and seepage water chemistry. 

The values of these variables used in the test are detailed in Chapter 2. Results of experiments 

and analyses are discussed in Chapter 3, including surface and salt analyses, weight loss 

measurements, and corrosion rate calculations. Chapter 4 presents the study conclusions. 
2-1

2 EXPERIMENTAL DETAILS 

2.1 Materials 

2.1.1 Alloy 22 Sheet 

The samples used for the tests were disk-shaped Alloy 22 sheet metal. The chemical 

composition of the Alloy 22 (HT 2277–9–3119) samples is shown in Table 2-1. The samples 

had a diameter of 5.08 cm [2.0 in] and a thickness of 0.0635 cm [0.025 in]. The specimens 

were polished using up to a 2,000-grit sandpaper and 2,000 diamond paste for final finish, 

rinsed and ultrasonically cleaned in deionized water and acetone, and dried. 

2.1.2 Titanium Alloys 

Titanium Grades 7 and 29 coupons with approximate dimensions of 4 × 4 × 0.6 cm3

[1.6 × 1.6 × 0.2 in3

] were used in the dripping tests. The Titanium Grade 7 specimens were 

sectioned from the middle of a 1.27-cm [0.5-in]-thick Titanium Grade 7 plate as schematically 

shown in Figure 2-1(a). Because of the unavailability of Titanium Grade 29 plate, the Titanium 

Grade 29 specimen was machined from the wall of a seamless extruded pipe {40 cm [16 in] 

outer diameter and 1.4-cm [0.57-in] wall thickness} obtained from Titanium Metals Corporation 

as shown in Figure 2-1(b). The Titanium Grade 7 is in mill-annealed condition with single 

α-phase conforming to ASTM B265 (ASTM International, 2008). The Titanium Grade 29 pipe is 

in the β-transformed (final processed above the β-transus temperature) plus subsequently 

annealed condition conforming to ASTM B861 (ASTM International, 2010). The microstructures 

of the two materials are shown in Figure 2-2. The chemical composition of the titanium 

specimens used in this study is shown in Table 2-2. The specimens were polished with 

120-, 240-, 320-, 400-, 600-, 1,000-, 2,000-grit sandpaper and 2,000 diamond paste, and 

1-μm alumina suspension for final finish; rinsed and ultrasonically cleaned in deionized water 

and acetone; and dried. 

2.2 Test Procedures 

The dripping corrosion tests of Alloy 22 and titanium alloys were conducted inside a chamber 

with a controlled temperature and relative humidity as shown in Figure 2-3. Each test specimen 

was set on a 3.4 cm [1.3 in] outer diameter polytetrafluoroethylene (PTFE) cylinder spacer. The 

PTFE cylinders with the test specimens were placed inside a PTFE tray in the chamber. The 

top of the dripping tubes was located about 10 cm [3.94 in] above the test specimen. The 

dripping water is simulated seepage water with the chemical composition shown in Table 2-3. 

Dunn, et al. (2006) used the same composition to represent neutral-type seepage waters in 

experiments to evaluate the effect of environmental conditions on the performance of the 

Alloy 22 waste package material. The water was pumped from a reservoir outside of the 

chamber through PTFE tubing into the chamber and allowed to drip on the test specimens. The 

temperature and relative humidity were controlled and maintained constant through the testing 

periods. The temperature and relative humidity near the test specimens were monitored by 

using additional measurement probes from the outside. The probes of the thermocouple and 

humidity gauge were extended to be located close to the test specimens. Because the 

temperature and humidity sensors were located at the edge of the ceiling inside the chamber, it 

was necessary to confirm the actual temperature and relative humidity to which the test 

specimens located on the floor inside the chamber were directly exposed. 
2-2

Table 2-1. Chemical Composition of Mill-Annealed Alloy 22 (in Weight Percent) 

Ni* Cr* Mo* W* Fe* Co* Si* Al* Mn* V* P* S* C* 

Bal† 21.62 12.98 2.86 3.56 1.29 0.03 0.22 0.29 0.01 0.008 0.0005 0.004

*Ni—nitrogen; Cr—chromium; Mo—molybdenum; W—tungsten; Fe—iron; Co—cobalt; Si—silicon; 

 Al—aluminum; Mn—manganese; V—vanadium; P—phosphorous; S—sulfur; C—carbon 

†Bal—balance

 

 (a) (b) 

Figure 2-1. (a) Titanium Grade 7 and (b) Titanium Grade 29 Specimens Machined From 

Original Plate or Pipe Sections 

(a) Titanium Grade 7 (b) Titanium Grade 29 

Figure 2-2. Microstructure of (a) Titanium Grade 7 and (b) Titanium Grade 29 Specimens 

Titanium Grade 7 specimen 

Titanium Grade 29 specimen 
2-3

Table 2-2. Chemical Composition of Titanium Grades 7 and Grade 29 

(in Weight Percent) 

Material Ti* Pd* Fe* C* N* O* H* Al* V* Ru* 

Titanium Grade 7 

Heat CN2775 Bal. 0.16 0.08 0.01 0.01 0.13 0.001 NA NA NA 

Titanium Grade 29 

Heat 00192DB Bal. NA 0.19 0.04 0.006 0.109 0.0021 5.62 4.16 0.10 

*Ti—titanium, Pd—palladium, Fe—iron, C—carbon, N—nitrogen, O—oxygen, H—hydrogen, 

 Al—aluminum, V—vanadium, Ru—ruthenium 

 

Figure 2-3. Experimental Setup For Dripping Test

PTFE Tray

PTFE Spacer

Temperature and Humidity Control Chamber

Dripping Lines

Test Sample

Reference Sample
2-4

Table 2-3. Chemical Composition of Simulated Seepage Water in This Study 

Ion Na+ K+ Mg2+ Ca2+ Cl− SO4

2−

 NO3

−

 HCO3

−

 CO3

2−

mol/L (M) 1.5 × 10−2 1.7 × 10−4 4.9 × 10−4 9.9 × 10−4 7.7 × 10−4 7.0 × 10−3 1.5 × 10−3 1.7 × 10−3 1.7 × 10−5

The posttest specimens were observed under optical microscope for pitting or other possible 

corrosion features. Surface deposits and/or surface oxides on the posttest specimens were 

analyzed with EDS and XRD. Weight loss measurement was used to measure the corrosion 

rates of Alloy 22 and titanium alloys. 

2.2.1 Test Procedures for Alloy 22 

In all of the tested conditions for Alloy 22, white deposits were observed on the surface of 

posttest specimens. After carefully removing and collecting the surface deposits, the specimens 

were first rinsed with deionized water and then chemically cleaned multiple times in an HCl 

solution {150 mL [5.1 oz] diluted to 1,000 mL [34 oz] deionized water} in accordance with the 

procedures recommended in ASTM G1–03 (ASTM International, 2003). The specimens were 

immersed and agitated for 2 minutes at room temperature. Then, the specimens were 

ultrasonically cleaned in acetone and dried. Before measuring the weight loss of the posttest 

specimens, the cleaned surface was observed by optical microscope to confirm the absence of 

any remaining deposits on the surface. The weight change was measured using a 

microbalance with a precision of ± 2.5 × 10−5

 g [8.82 × 10−7 oz]. Figure 2-4 shows a typical plot 

for weight loss measurements as a function of the number of cleanings. The four test 

specimens were exposed at 80 °C [176 °F] and 85 percent relative humidity for 35 days. Most 

of the weight loss plateaued after two or three cycles of cleaning. Therefore, the weight losses 

after the third cycle of cleaning were used to calculate the corrosion rate in accordance with the 

equation defined in ASTM G1–03 (ASTM International, 2003). 

Table 2-4 shows the test matrix of Alloy 22 including three batches of temperature and humidity: 

a first batch at 80 °C [176 °F] and 85 percent relative humidity, a second batch at 95 °C [203 °F] 

and 75 percent relative humidity, and a third batch at 60 °C [140 °F] and 95 percent relative 

humidity. The table also provides information on the test duration and sample identification 

number for each batch. The water dripping rates for each set were selected and adjusted to be 

a focused flow equivalent to the test specimen size, as discussed in Chapter 1. The droplet size 

was also discussed in Chapter 1. 

To evaluate the depth of pitting, four specimens were analyzed with a laser profilometer. These 

included two Alloy 22 samples held at 80 °C [176 °F] for 35 days (specimens A and B) and 

another two samples held at the same temperature for 185 days (specimens G and H). The 

laser profilometer is a noncontact, fully automatic imaging system with a depth resolution 

(z-axis of the machine) of 0.5 μm [1.97 × 10−5

 in] and lateral surface resolution of 1 μm 

[3.94 × 10−5

 in] (x- and y-axes). The laser profilometer uses a laser-optical displacement sensor 

and signal conditioning electronics to measure the vertical distance on a material. The laser 

used is a helium-neon laser operating a wavelength of 632.8 nm. The sensor uses the optical 
2-5

Figure 2-4. Weight Losses of the Corroded Test Specimens Resulting From Repetitive 

Cleaning Cycles in an ASTM HCl Solution (ASTM International, 2003). The Weight Loss 

After the Third Cycle of Cleaning Was Used in the Weight Loss Analysis. 

Table 2-4. Test Matrix of Alloy 22 Dripping Tests 

Temperature and 

Relative Humidity 

Water Dripping 

Rate Test Duration 

Specimen 

Identification 

80 °C [176 °F] and 

85 Percent Relative 

Humidity 

80 mL/day 

[2.71 oz/day] 35 Days A, B, C, and D 

70 Days E and F 

185 Days G and H 

95 °C [203 °F] and 

75 Percent Relative 

Humidity 

65 mL/day 

[2.20 oz/day] 33 Days I and J 

67 Days K and L 

60 °C [140 °F] and 

95 Percent Relative 

Humidity 

80 mL/day 

[2.71 oz/day] 32 Days M, N, O, and P 

60 Days Q and R 

triangulation principle where a visible, modulated point of light is projected onto the sample 

surface. The diffusive part of the reflection of this point of light is focused onto a charged, 

coupled device array. The intensity of the beam provides information about the vertical 

distance. Laser scans of surface morphology were conducted for all four samples. The scan 

lateral resolution was set at 5 μm [1.97 × 10−4

 in]. The scan of the pit was initiated and ended 

on the surface of the samples that were only degraded by general corrosion. 

0.00000

0.00005

0.00010

0.00015

0.00020

0.00025

0.00030

0.00035

0.00040

before 1 2 3 4 5 6 7 8

Specimen A Specimen B

Specimen C Specimen D

Number of Cleaning Cycles

Weight Loss (g)
2-6

2.2.2 Test Procedures for Titanium Alloys 

As schematically shown in Figure 2-3, dripping tests of titanium alloys were conducted 

inside the same chamber with the same setup as for Alloy 22. Each titanium coupon was 

set on a 3.4 cm [1.3 in] outer diameter PTFE cylinder with one 4 × 4-cm [1.6 × 1.6-in] side 

subject to dripping. For the first batch of tests at 80 °C [176 °F] and relative humidity of 

85 percent with a test duration of 181 days, 2 coupons for each material were subject to 

dripping. The dripping rate was approximately 80 mL/day [2.7 oz/day] as shown in Table 2-4. 

The droplet size was discussed in Chapter 1. For the second batch of tests at 95 °C [203 °F] 

and relative humidity of 75 percent with a test duration of 64 days, 3 coupons for each material 

were used for dripping. The dripping water is simulated seepage water, which is the same as 

that for Alloy 22. For each batch of tests, one additional coupon for each material without 

dripping was set in the chamber under the same temperature and relative humidity as the 

reference specimen for comparison. 

Weight loss measurement was used to measure the corrosion rate. After testing, the coupons 

were rinsed with deionized water, ultrasonically cleaned, dried, and weighed. The coupons 

were observed under microscope for pitting or other possible corrosion features. Surface 

deposits and surface oxides were analyzed with EDS. Afterwards the coupons were chemically 

cleaned multiple times using cleaning procedures in ASTM G1–03 (ASTM International, 2003) 

as a guidance. ASTM G1–03 (ASTM International, 2003) did not recommend a solution recipe 

to clean titanium. The recipe used in this work was obtained from that used in the literature for 

Titanium Grade 7 (Bechtel SAIC Company LLC, 2004). The coupons were cleaned for 

2 minutes at room temperature in the solution prepared by diluting 150 mL [5.07 oz] of 

concentrated HCl acid (37.0 percent HCl of specific gravity of 1.19) with deionized water to 

1,000 mL [33.8 oz] of solution. During each cleaning, one new coupon without any corrosion 

testing, but with the same surface finish as the test specimen, was cleaned as a control 

specimen along with the corroded specimen. After each cleaning, the specimen was 

ultrasonically cleaned in deionized water, then dried and weighed.
3-1

3 RESULTS AND DISCUSSION 

This section summarizes and discusses the results of experiments and analyses of Alloy 22 

and titanium alloys including weight loss measurements and corrosion surface morphologies. 

In addition, salt deposits formed on the posttest specimens were characterized in terms of 

chemical composition and crystal structure using EDS and XRD. 

3.1 Alloy 22 Dripping Test 

Three batches of Alloy 22 dripping tests were conducted: a first batch at 80 °C [176 °F] and 

85 percent relative humidity, a second batch at 95 °C [203 °F] and 75 percent relative humidity, 

and a third batch at 60 °C [140 °F] and 95 percent relative humidity. 

3.1.1 First Batch of Tests at 80 °C [176 °F] and Relative Humidity of 85 Percent 

Figure 3-1 shows the optical photos of the posttest specimens after 35, 70, and 185 days of the 

dripping tests at 80 °C [176 °F] and relative humidity of 85 percent. Most of the surface areas 

on the front upper side subjected to water dripping were covered with white salt deposits. The 

white deposits were also observed on the lower side, particularly the outside area of the PTFE 

spacer covered inner area as seen in Figure 3-1(f). 

Optical Microscopy 

After removing the salt deposits, followed by sample cleaning with HCl solutions, the specimens 

were examined with an optical microscope. Figure 3-2 shows typical morphologies of the 

corroded surface of Alloy 22. After 35 days of the dripping test, as shown in Figure 3-2(a), 

corrosion pits were observed throughout the area exposed to the dripping water. Many small 

sized pits ranged about 1 to 10 μm [3.94 × 10−5

 to 3.94 × 10−4 in] were also present. With 

dripping for 70 days, as shown in Figure 3-2(b), the surface exhibited similar pits in terms of pit 

size and popularity. However, pitting appeared to a lesser extent, indicating no growth of 

nucleated pits. After longer term tests (185 days) the pits appeared to be smaller and shallow. 

There was no clear evidence of pit propagation. Ashida, et al. (2008) also observed salt deposit 

formation and localized corrosion (i.e., pitting and intergranular corrosion) on the Alloy 22 

surface after 40 days’ dripping of saturated concentrated water at 90 °C [194 °F]. However, the 

microsized pits were not stable and did not grow deep. A similar observation was reported on 

Alloy 22 tested in saturated acidic water at 80 °C [176 °F] (Badwe, et al., 2006). 

Surface Topography

The pits were further analyzed by using a laser profilometer to estimate the pit depth. 

Figure 3-3(a) shows the typical pit morphology of the corroded surface of Alloy 22 after 

35 days’ exposure to dripping conditions. As can be seen from both the three-dimensional (3-D) 

and two-dimensional (2-D) profiles in Figure 3-3(b,c) the pit has a width of roughly 150 μm 

[5.91 × 10−3

 in], with a depth of roughly 40 μm [1.58 × 10−3 in]. These results are similar to 

those observed from the optical microscopy. Figures 3-4(a) shows the typical pit morphology of 

the corroded surface of Alloy 22 after 185 days’ exposure to the dripping water. Figure 3-3(a) 

and 3-4(a) are taken at the same magnification. As can be seen from Figure 3-4(a), the pit 

morphology is not much different from that after 35 days. Figure 3-4(b,c) shows the 2-D and 

3-D profiles for the 185-day exposed pit. The pit width is roughly 125 μm [4.92 × 10−3

 in], with a 
3-2

(a) (b) 

(c) (d) 

(e) (f) 

Figure 3-1. Photos of Pre- and Posttest Surfaces of Alloy 22 Tested at 80 °C [176 °F] 

and 85 Percent Relative Humidity: (a) Before Corrosion Test, (b) Chamber Inside 

During Dripping, (c) After 35 Days Dripped, (d) After 70 Days Dripped, (e) After 

185 Days Dripped (Upper Side), and (f) After 185 Days Dripped (Lower Side) 
3-3

(a) 

(b) (c) 

Figure 3-2. Optical Micrographs of Alloy 22 Surfaces Tested at 80 °C [176 °F] and 85 Percent 

Relative Humidity: (a) After 35 Days Dripped, (b) After 70 Days Dripped, and (c) After 

185 Days Dripped 

depth roughly 30 μm [1.18 × 10−3

 in]. Similar to the results observed from the optical 

microscopy, there was no evidence of pit propagation. 

Corrosion Rate as a Function Time

Corrosion rates of Alloy 22 specimens were calculated using Eq. (3-1) per ASTM G1–03 

(ASTM International, 2003), and results are listed in Table 3-1. 

 Corrosion Rate [nm/yr] = (8.76 × 1010 × ∆w) / (ρ × A × t) (3-1) 

where ∆w id weight loss (g), ρ is Alloy 22 density {8.69 g/cm3

 [0.31 lb/in3]}, A is exposed surface 

area {32.47 cm2

 [5.03 in2]}, and t is exposed time (hours). The exposed surface of 32.47 cm2

[5.03 in−2

] is the sum of the areas including the front side surface of 20.27 cm2 [3.14 in2], the 

edge area of 1.01 cm2

 [0.16 in2], and the wetted back side surface of 11.19 cm2 [1.73 in2]. 
3-4

(a) 

(b) 

Figure 3-3. Surface Topography of Alloy 22 Specimen After 35 Days Dripped 

at 80 °C [176 °F] and 85 Percent Relative Humidity: (a) Optical Micrograph, 

(b) 3-D Laser Scan Profiles of the Pit Area, and (c) 2-D Profiles 

Note: The Square Box in (a) Indicates the Laser Scanning Area. 

The Units in (b) and (c) Indicate x-, y-, z-axes Are Micrometer. 
3-5

(c) 

Figure 3-3 (continued). Surface Topography of Alloy 22 Specimen After 35 Days 

Dripped at 80 °C [176 °F] and 85 Percent Relative Humidity: (a) Optical Micrograph, 

(b) 3-D Laser Scan Profiles of the Pit Area, and (c) 2-D Profiles 

Note: The Square Box in (a) Indicates the Laser Scanning Area. 

The Units in (b) and (c) Indicate x-, y-, z-axes Are Micrometer. 

Because a part of the back side surface, except the areas inside the PTFE cylinder spacer, was 

wetted with the dripped water as seen in Figure 3-1(f), this wetted surface area of 11.19 cm2

[1.73 in2

] was included in the exposed surface area. 

As seen in Table 3-1, all samples exhibited weight loss and the amount of loss increased 

with test time. After 35 days, corrosion rate ranged from 78 to 96 nm/yr [3.07 × 10−6

 to 

3.78 × 10−6 in/yr] and the average rate was 85 nm/yr [3.35 × 10−7

 in/yr] with the standard 

deviation of 7.98 nm/yr [3.14 × 10−7

 in/yr]. This initially high corrosion rate is most likely due to 

the pit formation, resulting in large weight loss. However, corrosion rates gradually 

decreased with time. After 185 days of testing, Alloy 22 had an average corrosion rate of 

25 nm/yr [9.84 × 10−7

 in/yr]. Considering relatively shallow pits on the Alloy 22 surface after 

185 days as demonstrated by surface topography, it is likely that existed pits could repassivate 

and no more pit propagation could occur. A decrease of Alloy 22 corrosion rate was generally 

observed as shown in Figure 1-1, and this was mainly due to the presence of the protective 

passive film formed on the Alloy 22 surface that inhibited fast metal dissolution. 

3.1.2 Second Batch of Tests at 95 °C [203 °F] and Relative Humidity of 75 Percent 

Figure 3-5 shows the posttest Alloy 22 specimens after 33 days of testing at 95 °C [203 °F] and 

relative humidity of 75 percent. Similar to the observations on Alloy 22 from the first batch, 

white deposits were also present on the specimens. By removing the deposits, as seen in 

Figure 3-6(a), the Alloy 22 surface exhibited several corrosion areas with tiny pits. Any changes 
3-6

(a) 

(b) 

Figure 3-4. Surface Topography of Alloy 22 Specimen After 185 Days Dripped at 

80 °C [176 °F] and 85 Percent Relative Humidity: (a) Optical Micrograph, (b) 3-D 

Laser Scan Profiles of the Pit Area, and (c) 2-D Profiles 

Note: The Square Box in (a) Indicates the Laser Scanning Area. 

The Units in (b) and (c) Indicates x-, y-, z-axes Are Micrometer. 
3-7

(c) 

Figure 3-4 (continued). Surface Topography of Alloy 22 Specimen After 185 Days 

Dripped at 80 °C [176 °F] and 85 Percent Relative Humidity: (a) Optical Micrograph, 

(b) 3-D Laser Scan Profiles of the Pit Area, and (c) 2-D Profiles 

Note: The Square Box in (a) Indicates the Laser Scanning Area. 

The Units in (b) and (c) Indicates x-, y-, z-axes Are Micrometer. 

Table 3-1. Corrosion Rates of Alloy 22 Dripped at 80 °C [176 °F] and 85 Percent 

Relative Humidity 

Specimen 

Identification 

(Dripping 

Duration) 

Initial 

Weight 

(g) 

Weight Loss

(g) 

Corrosion 

Rate 

(nm/yr)* 

Average Corrosion Rate ±

Standard Deviation 

(nm/yr)* 

A (35 Days) 10.96570 0.00021 78 

85 ± 7.98 B (35 Days) 10.99504 0.00026 96 

C (35 Days) 11.01710 0.00022 81 

D (35 Days) 11.08025 0.00023 85 

E (70 Days) 10.84316 0.00031 57 61 ± 5.23 F (70 Days) 10.98447 0.00035 61 

G (185 Days) 10.95778 0.00034 24 

25 ± 1.48 

H (185 Days) 10.96577 0.00037 26 

*1 nm/yr = 3.94 × 10−8 in/yr
3-8

(a) (b) 

Figure 3-5. Photos of Posttest Surfaces of Alloy 22 After 33 Days Dripped at 95 °C 

[203 °F] and 75 Percent Relative Humidity for (a) Specimen I and (b) Specimen J

(a) (b) 

Figure 3-6. Optical Micrographs of Alloy 22 Surfaces Tested at 95 °C [203 °F] and 

75 Percent Relative Humidity: (a) After 33 Days Dripped and (b) After 67 Days Dripped 

in pit size and populations were not appreciable with of test time increased up to 67 days as 

shown in Figure 3-5(b), indicating no pit growth. Compared to the pits observed at a lower 

temperature of 80 °C [176 °F] from the first batch, interestingly, the size of pits at 95 °C [203 °F] 

was smaller. 

Table 3-2 lists the calculation results of corrosion rates with weight losses after either 33 or 

67 days of testing. The corrosion rate of 90 nm/yr [3.54 × 10−6

 in/yr] for the 33-day tests 

decreased to 68 nm [2.68 × 10−6 in/yr] after 67 days of dripping. This decrease in corrosion 

rate with time is consistent with the tendency from the first batch; however, the corrosion rates 

at 95 °C [203 °F] were slightly higher those at 80 °C [176 °F], which could be due to the higher 

test temperature. 
3-9

Table 3-2. Corrosion Rates of Alloy 22 Dripped at 95 °C [203 °F] and 75 Percent 

Relative Humidity 

Specimen 

Identification 

(Dripping 

Duration) 

Initial 

Weight 

(g) 

Weight 

Loss 

(g) 

Corrosion Rate 

(nm/yr)* 

Average Corrosion Rate ±

Standard Deviation 

(nm/yr)* 

I (33 Days) 10.25711 0.00020 78 90 ± 16.63 J (33 Days) 10.62251 0.00026 102 

K (67 Days) 9.67790 0.00025 48 68 ± 27.30 L (67 Days) 10.55815 0.00045 87 

*1 nm/yr = 3.94 × 10−8 in/yr 

3.1.3 Third Batch of Tests at 60 °C [140 °F] and Relative Humidity of 95 Percent 

The third batch of tests was conducted at 60 °C [140 °F] and 95 percent relative humidity. 

Similar to the posttest specimens from the previous two batches, there was salt deposition on 

the Alloy 22 surface (see Figure 3-7). Salts were not strongly adhered to the specimen surface, 

while salts formed at both 80 and 95 °C [176 and 203 °F] were tightly adhered to the surface. 

Micrographs on the Alloy 22 surface after 32 days of testing revealed several corrosion pit areas 

along with many tiny pits as shown in Figure 3-8(a). The maximum size of the pits observed 

was about 10 μm [3.94 × 10−4

 in] in width. After 60 days of testing, the pits tended to decrease 

in terms of size and amount, indicating repassivation of the pits. Consistent with the previous 

batches, with time, the corrosion rate decreased and reached the average rate of 24 nm/yr 

[9.45 × 10−7

 in/yr] after 60 days of testing as shown in Table 3-3. 

Figure 3-9 presents a comparison of the corrosion rates at temperatures of 60, 80, and 95 °C 

[140, 176, and 203 °F] as a function of time. As seen in the comparison, the corrosion rate 

was dependent on the test temperature in a dripped water environment. As the temperature 

increased, the corrosion rate increased. Compared to the corrosion rates of Alloy 22 in the 

literature (Sandia National Laboratories, 2007a), the range of corrosion rates measured at 80 

and 95 °C [176 and 203 °F] under the simulated seepage water dripping condition in this study 

is close to the corrosion rates of Alloy 22 measured in an immersed condition at 90 °C [194 °F]. 

Note that the solutions used in the literature above were highly concentrated simulated water 

(e.g., saturated acidic water, saturated concentrated water, and basic saturated water). This 

result can also be valid within the test condition in this study in terms of range of temperature, 

humidity, and dripping rate. 

3.1.4 Salt Chemistry Analysis 

Thermodynamic Simulation of Solution Evaporation

Thermodynamic calculation was conducted using the OLI Analyzer Studio Version 3 code 

(Gerbino, 2006; OLI Systems, Inc., 2010) to determine the water chemistry and the salts that 

would result from evaporation of dripping water. Using the code’s Mixed-Solvent Electrolyte 

chemistry option allows for simulation of aqueous chemical systems for temperatures up to 

300 °C [572 °F], pressures up to 1,500 bar, and concentrations ranging from dilute conditions to 

pure molten salts or pure acids. Thermodynamic properties calculated with this software have 

been shown to agree very well with experimental data (e.g., Gruszkiewicz, et al., 2007). Of key 

interest was the concentration of aggressive species, such as chloride, and corrosion-inhibiting 
3-10

species, such as nitrate. The chemical composition of the aqueous solution used in the Alloy 22 

dripping tests was used as input in the evaporation simulation. This initially dilute water was 

evaporated to equilibrium using OLI Analyzer Studio at the following temperature and relative 

humidity conditions: (i) 60 °C [140 °F] and 95 percent relative humidity; (ii) 80 °C [176 °F] and 

85 percent relative humidity; and (iii) 90 °C [203 °F] and 75 percent relative humidity. The 

compositions before and after evaporation are shown in Table 3-4. The OLI Analyzer Studio 

simulation indicated that the salts calcium carbonate, magnesium carbonate, sodium sulfate, 

and sodium–calcium sulfate would precipitate due to solution evaporation. 

The calculated nitrate-to-chloride molar ratio of the evaporated solutions did not change from 

the initial value of 1.95. This value is a factor of 20 higher than the 0.1 value considered 

necessary to inhibit localized corrosion of Alloy 22 (Dunn, et al., 2003), which would imply 

Alloy 22 localized corrosion is not expected. However, the thermodynamic simulations 

assumed equilibrium conditions and therefore do not replicate the dynamic processes occurring 

in a corrosion test under dripping conditions. For example, evaporation on the Alloy 22 surface 

under dripping conditions could vary spatially and temporally. Transient processes could enable 

the less soluble sodium chloride to precipitate and the more soluble nitrate salts to remain 

dissolved in and flow with the transient solution. These processes would make the salts 

deposited on the Alloy 22 surface have nitrate-to-chloride ratios less than 0.1 and make the 

Alloy 22 material susceptible to localized corrosion. As discussed in the following section, EDS 

data suggest the presence of sodium chloride in the salt deposit but in amounts less than the 

detection limit of XRD analysis. Other dynamic processes of small water volume, temperature 

fluctuation, and mechanical (or chemical) impingement by water droplet may also affect the 

validity of the equilibrium thermodynamic simulation. 

Salt Deposit Analysis

The chemical composition of the salts deposited on the Alloy 22 specimen was analyzed using 

EDS and XRD analysis. EDS was used to determine the elemental composition of the 

corrosion products, whereas XRD analysis was used to determine the structure and phases 

present. EDS analysis was carried out using a Noran Voyager M3105 system. XRD analysis 

was carried out using a Siemens Kristalloflex 805 with a D500 goniometer. The salts present in 

the corrosion products were identified by comparing the XRD spectroscopy of the samples with 

reference spectroscopy of different salts in a database. Note that XRD analysis has a detection 

limit of about 5 weight percent. 

The EDS result is shown in Table 3-5, and the XRD data are shown in Figures 3-10 to 12. The 

XRD data indicate that the salts are dominantly calcium carbonate. Minor amounts of calcium 

sulfate, magnesium phosphate, calcium silicate carbonate, and magnesium silicate also could 

be present. The XRD result is consistent with the EDS data that show calcium and magnesium 

as the dominant elements in the salt deposit. Based on the EDS results, sodium chloride and 

sodium sulfate also could be present in the salt deposit but in amounts less than the detection 

limit of the XRD method. For comparison, OLI Analyzer Studio evaporation simulation indicated 

the possible formation of calcium carbonate, magnesium carbonate, sodium sulfate, and 

sodium-calcium sulfate. 
3-11

(a) (b) 

Figure 3-7. Photos of Posttest Surfaces of Alloy 22 After 60 Days Dripped at 60 °C 

[140 °F] and 95 Percent Relative Humidity for (a) Specimen Q and (b) Specimen R 

(a) (b) 

Figure 3-8. Optical Micrographs of Alloy 22 Surfaces Tested at 60 °C [140 °F] and 

95 Percent Relative Humidity: (a) After 32 Days Dripped and (b) After 60 Days Dripped 

Table 3-3. Corrosion Rates of Alloy 22 Dripped at 60 °C [140 °F] and 95 Percent 

Relative Humidity 

Specimen 

Identification 

(Dripping 

Duration) 

Initial 

Weight 

(g) 

Weight 

Loss 

(g) 

Corrosion Rate 

(nm/yr)* 

Average Corrosion 

Rate ± Standard 

Deviation 

(nm/yr)* 

M (32 Days) 10.59580 0.00011 45 

41 ± 12.20 N (32 Days) 10.20020 0.00007 29 

O (32 Days) 10.56262 0.00008 34 

P (32 Days) 10.47481 0.00014 57 

Q (60 Days) 10.23063 0.00013 28 24 ± 6.10 R (60 Days) 9.74089 0.00009 19 

*1 nm/yr = 3.94 × 10−8 in/yr
3-12

Figure 3-9. Corrosion Rate of Alloy 22 as a Function of Time Tested at 

Temperatures of 95, 80, and 60 °C [203, 176, and 140 °F] 

Table 3-4. Solution Composition Before and After Evaporation 

Ionic 

Component 

Concentration 

Before 

Evaporation* 

(molarity) 

Concentration 

After Evaporation 

at 60 °C [140 °F] 

and 95 Percent 

Relative 

Humidity† 

(molarity) 

Concentration 

After Evaporation 

at 80 °C [176 °F] 

and 85 Percent 

Relative 

Humidity† 

(molarity) 

Concentration 

After Evaporation 

at 95 °C [203 °F] 

and 75 Percent 

Relative 

Humidity† 

(molarity) 

Na+ 1.50 × 10−02 5.38 × 10+00 5.64 × 10+00 6.98 × 10+00

K+ 1.70 × 10−04 2.00 × 10−01 3.24 × 10−01 5.03 × 10−01

Mg2+ 4.90 × 10−04 6.13 × 10−02 1.71 × 10−02 6.15 × 10−03

Ca2+ 9.90 × 10−04 8.49 × 10−04 4.40 × 10−04 3.14 × 10−04

Cl− 7.70 × 10−04 9.07 × 10−01 1.47 × 10+00 2.28 × 10+00

SO4

2− 7.00 × 10−03 1.51 × 10+00 8.33 × 10−01 3.88 × 10−01

NO3

− 1.50 × 10−03 1.77 × 10+00 2.86 × 10+00 4.44 × 10+00

CO3

2− 1.70 × 10−03 3.45 × 10−04 2.79 × 10−04 1.55 × 10−04

HCO3

− 1.70 × 10−05 1.70 × 10−02 9.80 × 10−03 5.23 × 10−03

pH — 7.70 7.62 7.47 

NO3

−

/Cl−

ratio 1.95 1.95 1.95 1.95 

*Charge balanced using OLI Analyzer Studio 

†Salts present after evaporation: CaCO3, MgCO3, Na2SO4, and Na2Ca(SO4)2

10

30

50

70

90

110

20 40 60 80 100 120 140 160 180 200

Corrosion Rate (nm/yr)

Exposure Time (Days)

95 °C

80 °C

60 °C
3-13

Table 3-5. EDS Elemental Composition of Salt Deposit on Alloy 22 Specimen After 

185 Days Dripped at 80 °C [176 °F] and 85 Percent Relative Humidity 

Element Weight Percent 

Na 0.45 

Mg 2.68 

Al 0.09 

Si 0.71 

P 0.16 

S 0.60 

Cl 1.45 

Ca 93.86 

Total 100.00 

Figure 3-10. X-Ray Diffraction Spectroscopy of Salts Deposited on Alloy 22 

Specimen After 32 Days Dripped at 60 °C [140 °F] and 95 Percent Relative Humidity. 

Also Shown Are the Reference Spectroscopy of Salts That Best Match the Salt 

Deposit Spectroscopy. 
3-14

Figure 3-11. X-Ray Diffraction Spectroscopy of Salts Deposited on Alloy 22 Specimen 

After 185 Days Dripped at 80 °C [176 °F] and 85 Percent Relative Humidity. Also Shown 

Are the Reference Spectroscopy of Salts That Best Match the Salt Deposit Spectroscopy. 

Figure 3-12. X-Ray Diffraction Spectroscopy of Salts Deposited on Alloy 22 Specimen After 

67 Days Dripped at 95 °C [203 °F] and 75 Percent Relative Humidity. Also Shown Are the 

Reference Spectroscopy of Salts That Best Match the Salt Deposit Spectroscopy. 
3-15

3.2 Titanium Alloys Dripping Test 

3.2.1 First Batch of Tests at Temperature of 80 °C and Relative Humidity of 

85 Percent 

The first batch of tests was terminated after 181 days. Figure 3-13 shows the Titanium 

Grades 7 and 29 specimens after 6 months of testing at 80 °C [176 °F] and 85 percent relative 

humidity. The front side subjected to dripping was covered with a layer of white deposits. The 

back side, outside of the PTFE spacer covered area, was also covered with white deposits, but 

to a lesser extent. The white deposits were strongly adhered to the specimens, and they were 

not able to be removed by ultrasonic cleaning in deionized water. For both titanium Grades 7 

and 29, the EDS in Figure 3-14 shows that the white deposits consist of calcium, carbon, 

oxygen, silicon, sulfur, aluminum, and magnesium. The higher concentration of calcium, 

carbon, and oxygen suggests that the white deposit is primarily CaCO3, deposited from 

evaporation of the dripping water. Sulfur and magnesium came from the dripping water. Silicon 

and aluminum are likely from residual deposits from the specimen surface preparation process 

before the test or from trace elements in the chemicals used to prepare the dripping solution. 

No titanium or aluminum and vanadium were detected on the white deposits of Titanium Grade 

7 or Grade 29 specimens, suggesting that the titanium corrosion product dissolved into the 

deposits was under the EDS detection limits. 

The EDS in Figure 3-15 of the surface without deposits shows that there is a very small amount 

of carbon, magnesium, aluminum, silicon, and calcium deposited on the surface, but the main 

composition is the same as the original specimen without testing. For Titanium Grade 7, the 

palladium on the surface was not detectable by EDS. The specimen for comparison without 

being subjected to dripping shows a thin, multicolored corrosion layer (yellow, violet, and blue) 

likely because of optical interference colors caused by varying oxide film thickness. 

All the specimens were chemically cleaned with HCl solution three times. Right after immersing 

the specimen in HCl solution, the white deposits dissolved and generated gas, which supports 

the previous assumption that the white deposits are primarily CaCO3. Figure 3-16 shows the 

optical photos of the first HCl-cleaned specimens. Photos show that thick oxide still remained 

on the surface, and the weight difference summarized in Table 3-6 still showed weight gain after 

the test. After the third cleaning with HCl, the specimens were examined under the microscope 

with higher magnification, which showed consistently (as in Figure 3-17) that there is more 

general corrosion on the side subjected to dripping as evidenced by a smoother surface 

compared to more evident polishing scratches at the back side. Table 3-6 shows that the 

Titanium Grade 7 control specimen had negligible weight change, which suggests that the HCl 

solution cleaning does not dissolve the base metal. However, the Titanium Grade 29 specimen 

showed some weight loss, suggesting the dissolution of the base metal in HCl solution. 

Because of the consistent weight gain after cleaning with HCl solution three times, the specimen 

was further cleaned in boiling 10 percent HNO3 solution for 5 minutes per Covington and Schutz 

(1981). After the first cleaning with HNO3, the specimens showed obvious weight loss 

compared to the specimen before the test, and the thick oxide shown in Figure 3-16 was 

cleaned away as shown in Figure 3-18. However, the Titanium Grade 7 control specimen also 

showed weight loss of about 0.2 mg [7 × 10−6

 oz], which suggests that the HNO3 solution slightly 

dissolved some base metals in addition to the corrosion products. Compared to Titanium Grade 

7, the Titanium Grade 29 control specimen showed minimal weight change. All the specimens 

were further cleaned with HNO3 solution, and showed very little weight change. 
3-16

Specimens Subject to Dripping 

Front Side Back Side 

Reference Specimens Without Dripping 

Figure 3-13. First Batch of Posttest Titanium Grades 7 and 29 Specimens at Temperature 

of 80 °C [176 °F] and Relative Humidity of 85 Percent. The specimen Size Was 

Approximately 4 × 4 × 0.6 cm3

 [1.6 × 1.6 × 0.2 in3].

Figure 3-14. Energy-Dispersive X-Ray Spectroscopy of the White Deposits on the First 

Batch of Posttest Titanium Grades 7 and 29 Specimens Showing That the White Deposits 

Consist of Calcium, Carbon, Oxygen, Silicon, Sulfur, Aluminum, and Magnesium

4 cm 
3-17

Figure 3-15. Energy-Dispersive X-Ray Spectroscopy of the First Batch of Posttest 

Titanium Grades 7 and 29 Specimen Surface Without Visible Deposits Showing the 

Main Constituent to be Elemental Titanium for Titanium Grade 7 and Titanium, 

Aluminum, and Vanadium for Titanium Grade 29. 

After the removal of white deposits with HCl solution, the specimens were examined with a 

microscope along with the control specimen. For the tested specimens, there were some 

localized features protruding on the surface that persisted through the cleaning process. Similar 

features were shown on the control specimens. Figure 3-19 showed several examples of the 

localized features. Because both the tested and untested specimens showed similar features 

and these features were protruding from the surface, these features are not pits or any other 

localized corrosion form generated from the dripping process since they are features of the 

material in the as-received condition. They are considered to be artifacts of the manufacturing 

process or from the surface preparing process.
3-18

Figure 3-16. Optical Photos of the First Batch Posttest Specimens After Being 

Cleaned With HCl Solution Showing That All the White Deposits Were Cleaned, 

But the Thick Oxide Remained 

Because further HNO3 cleaning led to metal dissolution indicated by the control specimen, the 

weight loss to calculate the corrosion rate was determined from the weight difference of the 

specimen before the test and the first HNO3 cleaning. The weight loss was not corrected by 

cleaning as recommended by ASTM G1–03 (ASTM International, 2003), although some weight 

loss was observed on the control specimens for the following reasons: 

• The oxide film on the tested specimen was aged and thickened in the humidity chamber, 

while the oxide film on the control specimen was fresh and thin, possibly resulting in 

more dissolution of the control specimen in HCl. A simple correction by adding the 

weight loss from the control specimen to the weight loss of tested specimen may 

underestimate the actual weight loss of the test specimen. 

• The corrosion rate calculated from weight loss without correction is more conservative. 

The corrosion rate was calculated using Eq (3-1). For the specimens subject to dripping, the 

surface area is the entire surface area excluding the area covered by the PTFE cylinder. The 

material densities used for the calculation are 4.5 g/cm3

 [0.16 lb/in3] for Titanium Grade 7 and 

4.4 g/cm3 [0.16 lb/in3

] for Titanium Grade 29. For the specimens subjected to dripping, the 

corrosion rates were in the range of 20–50 nm/yr [7.9 × 10−7

–2.0 × 10−6 in/yr], similar to what 

has been observed in literature data (Sandia National Laboratories, 2007b). 
3-19

Ti 7-1 Front Side Subject to Dripping Ti 7-1 Back Side 

Ti 7-2 Front Side Subject to Dripping Ti 7-2 Back Side 

Ti 7-3 (Not Dripped Specimen) Front Side Ti 7-3 Back Side 

Figure 3-17. Surface of the Third HCl Cleaned Posttest Titanium Specimens Showing 

That the Dripping Side Was Corroded Uniformly and the Polishing Scratches Were 

Smoothed Out. However, There Was Less General Corrosion at the Back Side as 

Evidenced by the Polishing Scratches (Scale Bar Is Not Available, Because of the 

Limitation of the System).
3-20

Ti 29-1 Front Side Subject to Dripping Ti 29-1 Back Side 

Ti 29-2 Front Side Subject to Dripping Ti 29-2 Back Side 

Ti 29-3 ( Not Dripped Specimen) Front Side Ti 29-3 Back Side 

Figure 3-17 (continued). Surface of the Third HCl Cleaned Posttest Titanium Specimens 

Showing That the Dripping Side Was Corroded Uniformly and the Polishing Scratches 

Were Smoothed Out. However, There Was Less General Corrosion at the Back Side as 

Evidenced by the Polishing Scratches (Scale Bar Is Not Available, Because of the 

Limitation of the System). 
3-21

Table 3-6. First Batch Sample Weight Before and After Test at Temperature of 80 °C 

[176 °F] and Relative Humidity of 85 Percent 

Sample 

Identification 

Ti 7-1 Ti 7-2 Ti 7-3 

Without 

Dripping 

Ti 7-4 

(Control) 

Ti 29-1 Ti 29-2 Ti 29-3 

Without 

Dripping 

Ti 29-4 

Subject to Dripping Subject to Dripping (Control) 

Initial 

weight, g 43.85001 42.33159 43.11402 42.58403 52.63078 53.48684 53.57979 34.33493 

Posttest 

weight before 

acid 

cleaning, g 

44.05787 42.57674 43.11535 N/A 52.83661 53.68799 53.57991 N/A 

Weight gain 

after test, g 0.20786 0.24515 0.00133 N/A 0.20583 0.20115 0.00012 N/A 

First HCl 

cleaning 43.85039 42.33199 43.11437 42.58402 52.63115 53.48718 53.57983 34.33492 

Second HCl 

cleaning 43.85037 42.33199 43.11429 42.58403 52.63113 53.48712 53.57982 34.33502 

Third HCl 

cleaning 43.85021 42.33188 43.11428 42.58403 52.63099 53.48697 53.57986 34.33475 

First HNO3

cleaning 43.84963 42.33132 43.11335 42.58380 52.63055 53.48649 53.57963 34.33472 

Second 

HNO3

cleaning 

43.84965 42.33135 43.11329 42.58370 52.63046 53.48629 53.57954 34.33449 

Weight 

loss, g 0.00038 0.00027 0.00067 N/A 0.00023 0.00035 0.00016 N/A 

Corrosion 

rate, nm/yr 49.5 35.9 69.9 N/A 28.7 43.7 15.9 N/A 

Titanium Grade 7 Front Side Titanium Grade 7 Back Side 

Titanium Grade 29 Front Side Titanium Grade 29 Back Side 

Figure 3-18. Optical Photographs of Specimens After First HNO3 Solution Cleaning 

Showing That Most of the Corrosion Products Were Cleaned 
3-22

Ti 7-1 Front Side Subject to Dripping 

 

Ti 7-4 Untested Specimen 

Ti 29-1 Front Side Subject to Dripping Ti 29-4 Untested Specimen 

Figure 3-19. Optical Photographs of Second HNO3-Cleaned Tested and Untested 

Specimens Showing That the Dripping Test Specimens Had Similar Features as the 

Untested Control Specimens. The Imperfections Shown on the Posttested Specimens 

Likely Existed Before the Test and Did Not Result From the Corrosion Process. 

The Titanium Grade 7 specimen without dripping showed the highest corrosion rate, and the 

surface was covered by a colored surface film. This could be due to the relatively unstable 

environment near the edge of the humidity chamber. 

3.2.2 Second Batch of Tests at Temperature of 95 °C [203 °F] and Relative 

Humidity of 75 Percent 

The second batch of tests was terminated after 64 days. Figure 3-20 shows the posttest 

specimens. The specimens subject to dripping were covered with white deposits. EDS shows 

that the chemical composition is similar to that from the first batch of tests. The specimens 

without dripping showed some stains on the surface. Table 3-7 summarizes the weights before 

and after the test, the weight loss, and corrosion rates. All the specimens showed weight gain 

after the test because of the deposits and scales formed on the surface. After the first HCl 

cleaning, all the specimens subject to dripping still showed weight gain compared to the original 
3-23

Subject to Dripping Subject to Dripping 

Without Dripping Without Dripping 

(a) Titanium Grade 7 (b) Titanium Grade 29 

Figure 3-20. Second Batch of Posttest (a) Titanium Grade 7 and (b) Titanium 

Grade 29 Specimens at Temperature of 95 °C [203 °F] and Relative Humidity 

of 75 Percent 

weight; the specimens without dripping showed weight loss. The control specimen also showed 

minor weight loss. All the specimens were examined under a microscope. No localized 

corrosion was observed. After the second HCl cleaning all the specimens showed weight loss 

compared to the original weight. It appears that the scales from the second batch of tests were 

easier to clean, possibly because of the shorter test duration. The control specimen also 

showed weight loss, possibly resulting from the dissolution of fresh oxide film on the surface 

compared to the aged surface film on the tested specimens. Because the control specimen 

consistently showed weight loss, the weight loss of the tested specimens was calculated based 

on the weight after the second HCl cleaning. This was compared to the original weight without 

correcting it from cleaning for reasons stated in Section 3.2.1. The corrosion rates were 

calculated based on Eq. (3-1) and shown in Table 3-7. The corrosion rates for Titanium 

Grades 7 and 29 under dripping were 130–380 nm/yr [5.12 × 10−6

–1.50 × 10−5 in/yr] 

and 260–530 nm/yr [1.02 × 10−5

–2.09 × 10−5 in/yr], respectively, higher than what was 

measured from the first batch of tests. The higher corrosion rates could be caused by the 

shorter test duration and higher test temperature. 
Table 3-7. Second Batch Sample Weight Before and After Tests at Temperature of 95 °C [20

Relative Humidity of 75 Percent 

Samples 

Titanium Grade 7 Titanium Grade 29 

Subject to Dripping 

Without 

Dripping 

Control 

Specimen Subject to Dripping 

Wit

Drip

Initial weight, g 42.97176 42.36883 42.63832 42.62994 41.01415 53.31863 33.63283 34.32682 34.1Posttest weight before acid cleaning, g 

43.02630 42.40567 42.73694 42.63050 N/A 53.34756 33.66642 34.43903 34.1

Weight gain after test, g 

0.05454 0.03684 0.09862 0.00056 N/A 0.02893 0.03359 0.11221 0.00

First HCl cleaning 42.97266 42.37071 42.63862 42.62974 41.01387 53.31882 33.63344 34.32722 34.1Second HCl cleaning 

42.97075 42.36847 42.63741 42.62832 41.01251 53.31715 33.63197 34.32613 34.1

Weight loss, g 0.00101 0.00036 0.00091 0.00162 N/A 0.00148 0.00086 0.00069 0.00Corrosion rate, nm/yr 372 133 336 473 N/A 521 333 267 755 

3-24 
4-1 

4 CONCLUSIONS 

In this report, the corrosion behavior of Alloy 22 and Titanium Grades 7 and 29 was evaluated 

under seepage water dripping conditions. Three batches of dripping tests were conducted on 

Alloy 22 and two batches of tests were conducted on Titanium Grades 7 and 29. The following 

are the main conclusions from this study. 

Corrosion of Alloy 22 

• In the first batch of tests at 80 °C [176 °F] and 85 percent relative humidity, the surfaces 

of the posttest specimens exhibited several corrosion pits along with many small sized 

pits. After 185 days of testing, the pits appeared to be shallow and there was no clear 

evidence of pit propagation. The corrosion rate decreased with test duration, and the 

measured rate was 25 nm/yr [9.84 × 10−7

 in] after 185 days’ exposure. 

• In the second batch at 95 °C [203 °F] and 75 percent relative humidity, pits were also 

present on the specimen surface. However, with time, the corrosion rate decreased. At 

a low temperature of 60 °C [140 °F] and relative humidity of 95 percent in the third batch 

test, the corrosion rate decreased with time and reached 24 nm/yr [9.45 × 10−7

 in] after 

60 days of testing. There was no evidence of pit propagation. 

• Under the seepage water dripping condition, Alloy 22 exhibited a 

temperature-dependent corrosion rate, which was commonly observed in 

the immersion tests. The corrosion rates obtained from the dripping tests in this 

study were close to the rates obtained from immersion tests in the literature. 

• Results of the salt chemistry analyses through thermodynamic calculations and analysis 

tools indicate that major composition was calcium carbonate; several other compositions 

were possibly precipitated, including magnesium carbonate, sodium (calcium) sulfate, 

sodium chloride, and silica. 

Corrosion of Titanium Alloys 

• The first batch of tests at 80 °C [176 °F] and 85 percent relative humidity for 181 days 

showed that the corrosion rates of the specimens subjected to dripping were in the 

range of 20–50 nm/yr [7.9 × 10−7

–2.0 × 10−6 in/yr], similar to data obtained in immersion 

tests in the literature. No clear difference was observed between Titanium Grades 7 and 

29. The front side subjected to direct dripping corroded more than the back side that 

was not subjected to direct dripping. 

• The second batch of tests at 95 °C [203 °F] and 75 percent relative humidity for 

64 days showed that the corrosion rates for Titanium Grades 7 and 29 under 

dripping were 130–380 nm/yr [5.12 × 10−6

–1.50 × 10−5 in/yr] and 260–530 nm/yr 

[1.02 × 10−5

–2.09 × 10−5 in/yr], respectively, higher than what was measured from the 

first batch of tests. The higher corrosion rates could be caused by the shorter test 

duration and higher test temperature. 

• No localized corrosion was observed on either material from the two batches of tests. 
5-1 

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