January 2014 

NASA/CR2014-218158 

 

Multilayer Pressure Vessel Materials 

Testing and Analysis 

Phase 2 

Carl F. Popelar, and Joseph W.Cardinal 

Southwest Research Institute, San Antonio, Texas 
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January 2014 

NASA/CR2014-218158 

 

Multilayer Pressure Vessel Materials 

Testing and Analysis 

Phase 2 

Carl F. Popelar, and Joseph W.Cardinal 

Southwest Research Institute, San Antonio, Texas 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

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iv

LIST OF REVISED PAGES 

Multilayer Pressure Vessel Materials 

Testing and Analysis (Phase 2) 

SwRI Project 18.17633 

Table One 

Revision Number Issue Date 

Final Report August 30, 2013 

Revision 01 September 13, 2013 

Issue dates for the original document and all subsequent changes are given in Table One. Table 

Two lists all pages affected by the latest revision or by any previously issued revision. Pages not 

listed in Table Two are the same as issued with the original document 

Table Two 

Revision 

No. 

Page 

No. Description 

01 1 Section 1.0  paragraph 2  revised 

01 2 Section 2.0  paragraph 3  last sentence revised; 

Section 2.0  paragraph 5  last sentence revised 

01 7 Section 3.1.1  paragraph 2  revised 

01 8 Table 3-2 revised 

01 11 last sentence on page revised 

01 13 Section 3.1.4  paragraph 2 – last two sentences revised 

01 19 Table 3-9  revised 

01 23 Table 3-13  revised 

01 34 Table 4-1 – column heading revised 

01 43 Section 5.4  Item a – sentence added to end (including footnote 4) 

Section 5.4  Item c – last sentence revised 

01 44 Section 6.1  Item c – sentence added to end 

01 45 Section 6.2  Item b – sentence added to end 

01 46 Section 6.3  Item d added 

01 49 Appendix A now begins on page 49 due to revisions made in body of report 

01 51-52 new flysheet and test certificate added 

01 53 table revised to add footnote “c” (formerly page 49 in orig report) 

01 112 table revised and footnote added (formerly page 108 in orig report) 

01 125 flysheet revised and footnote added (formerly page 121 orig report) 
v

Table Two (Continued) 

Revision 

No. 

Page 

No. Description 

01 183 Appendix B now begins on page 183 

01 185-186 new flysheet and test certificate added 

01 191 new certification sheet added 

01 297 table revised (formerly page 289 in orig report) 

 
vi

TABLE OF CONTENTS 

1.0 INTRODUCTION.............................................................................................................. 9

2.0 PRESSURE VESSEL AND MATERIALS ................................................................... 10

3.0 MATERIAL CHARACTERIZATION AND ANALYSIS .......................................... 14

3.1 AO Smith 1146a Shell Material Characterization.......................................................... 14

3.1.1 Basic Tensile and Hardness Properties ................................................................... 15

3.1.2 Charpy V-Notch Testing ......................................................................................... 17

3.1.3 Fracture Toughness Testing .................................................................................... 20

3.1.4 Fatigue Crack Growth Testing ................................................................................ 21

3.2 A-225, Gr. B Head Characterization .............................................................................. 25

3.2.1 Basic Tensile Properties .......................................................................................... 26

3.2.2 Charpy V-Notch Testing ......................................................................................... 27

3.2.3 Fracture Toughness Testing .................................................................................... 29

3.2.4 Fatigue Crack Growth Testing ................................................................................ 31

4.0 FATIGUE CRACK GROWTH MODELING .............................................................. 36

4.1 Fatigue Crack Growth Rate Modeling Background ....................................................... 36

4.2 NASGRO Equation Fits for the AO Smith 1146a Shell Material.................................. 37

4.3 NASGRO Equation Fits for the A-225 Gr. B Head Material ........................................ 38

4.4 Comparison of NASGRO Equation Fits to the Barsom Equation ................................. 38

4.5 NASGRO Equation Fits for the Head-to-Shell Weld and HAZ Materials .................... 43

4.6 Comparison of NASGRO Equation Fits for Base Metal and Weld Materials ............... 43

4.7 Re-Evaluation of the FCG Analysis of the Notch in the Outer Shell ............................ 43

5.0 SUMMARY AND CONCLUSIONS .............................................................................. 49

5.1 Vessel Construction........................................................................................................ 49

5.2 AO Smith 1146a Shell Material Characterization.......................................................... 49

5.3 A-225 Gr. B Head Material Characterization ................................................................ 50

5.4 Fatigue Crack Growth Modeling.................................................................................... 50

6.0 RECOMMENDATIONS ................................................................................................. 52

6.1 AO Smith 1146a Shell Material ..................................................................................... 52

6.2 A-225 Gr. B Head Material ............................................................................................ 53

6.3 Fatigue Crack Growth Modeling.................................................................................... 53

7.0 REFERENCES ................................................................................................................. 54

Appendix A: AO SMITH 1146a SHELL MATERIAL CHARACTERIZATION 

RESULTS ............................................................................................................ 55

Appendix B: A-225 Gr. B HEAD MATERIAL CHARACTERIZATION RESULTS ..... 179

 
vii

LIST OF TABLES 

Table 2-1. Chemical Composition of Head and Outer Shell Materials [1] ............................... 13

Table 3-1. AO Smith 1146a Shell Material Test Matrix ........................................................... 16

Table 3-2. AO Smith 1146a Outer Shell Tensile Properties ..................................................... 16

Table 3-3. AO Smith 1146a Inner and Outer Shell Hardness Results ...................................... 17

Table 3-4. AO Smith 1146a Shell Charpy V-Notch Results ..................................................... 19

Table 3-5. AO Smith 1146a Shell Weld Charpy V-Notch Results ........................................... 20

Table 3-6. AO Smith 1146a Shell Fracture Toughness Results ................................................ 21

Table 3-7. AO Smith 1146a Shell FCG Testing ....................................................................... 22

Table 3-8. A-225 Gr. B Head Material Test Matrix .................................................................. 26

Table 3-9. A-225 Gr. B Head Tensile Properties ...................................................................... 27

Table 3-10. A-225 Gr. B Head Charpy V-Notch Results ........................................................... 28

Table 3-11. A-225 Gr. B Head Weld Charpy V-Notch Results .................................................. 29

Table 3-12. A-225 Gr. B Head Weld Fracture Toughness Results ............................................. 30

Table 3-13. A-225 Gr. B Head FCG Testing .............................................................................. 31

Table 4-1. NASGRO Equation Parameters Obtained for the Shell and Head Materials .......... 42

Table 4-2. NASGRO Equation Parameters Obtained for the Head-to-Shell Weld and 

HAZ Materials ......................................................................................................... 45

Table 4-3. Comparison of Results of FCG Analyses between Phase 1 and Phase 2 (Phase 1 

Kc = 90 ksi√in., Phase 2 Kc = 170 ksi√in.) ............................................................. 48

 
viii

LIST OF FIGURES 

Figure 2-1. Nameplate from AO Smith Multilayer Pressure Vessel (MV50466-8) ................... 11

Figure 2-2. As-Received Layered Pressure Vessel at SwRI Fabrication Shop .......................... 11

Figure 2-3. Outer Layer Seam Weld and Penetration into Inner Layer ...................................... 12

Figure 2-4. Cross-section of Head-Body Interface ..................................................................... 12

Figure 3-1. Vessel, Material and Specimen Orientations ........................................................... 15

Figure 3-2. AO Smith 1146a Charpy V-Notch Results .............................................................. 18

Figure 3-3. AO Smith 1146a Seam Weld and HAZ Charpy V-Notch Results .......................... 20

Figure 3-4. AO Smith 1146a Inner Shell FCG Behavior in L-T Orientation ............................. 23

Figure 3-5. AO Smith 1146a Shell FCG Behavior at RT ........................................................... 24

Figure 3-6. AO Smith 1146a Shell FCG Behavior ..................................................................... 25

Figure 3-7. A-225 Gr. B Head Charpy V-Notch Results ........................................................... 28

Figure 3-8. A-225 Gr. B Head Weld and HAZ Charpy V-Notch Results .................................. 29

Figure 3-9. A-225 Gr. B FCG Behavior ..................................................................................... 32

Figure 3-10. A-225 Gr. B FCG Behavior as a Function of Temperature ..................................... 33

Figure 3-11. Schematic of Head Weld FCG Specimen Extraction .............................................. 34

Figure 3-12. Inner Head Weld and HAZ FCG Behavior .............................................................. 35

Figure 4-1. Schematic of Fatigue Crack Growth Behavior Illustrating the Three Regions of 

Fatigue Crack Growth .............................................................................................. 37

Figure 4-2. NASGRO Equation Fit for AO Smith 1146a Shell at Room Temperature ............. 39

Figure 4-3. NASGRO Equation Fit for AO Smith 1146a Shell at -20oF ................................... 39

Figure 4-4. NASGRO Equation Fit for A-225 Gr B Head at Room Temperature ..................... 40

Figure 4-5. NASGRO Equation Fit for A-225 Gr B Head at -20oF ........................................... 40

Figure 4-6. Comparison of NASGRO Equation Fits to Barsom Equation at R = 0.15 and 

Room Temperature .................................................................................................. 41

Figure 4-7. NASGRO Equation Fit for Head-to-Shell Weld Material at Room Temperature ... 44

Figure 4-8. NASGRO Equation Fit for Head-to-Shell HAZ Material at Room Temperature ... 44

Figure 4-9. Comparison of NASGRO Equation Fits at R = 0.15 for Base Metal and Weld 

Materials .................................................................................................................. 46

Figure 4-10. NASGRO Input Screen for NASGRO Equation for AOS 1146a Shell Material 

(RT) .......................................................................................................................... 47

Figure 4-11. NASGRO Input Screen for Barsom Equation ......................................................... 47
9

1.0 INTRODUCTION

The National Aeronautics and Space Administration (NASA) owns and operates several hundred 

multilayer pressure vessels, some of which are more than fifty years old. While available 

construction records show that generally good design, fabrication, and inspection processes were 

followed, these vessels are “non-Code” vessels and actual records do not exist for many of these 

vessels. In addition, the materials used typically correspond to a proprietary manufacturer’s 

specification, not an ASME or ASTM material grade. Furthermore, due to their age and 

operating history, it is possible that cracks have developed over time and could provide a 

potential failure mechanism during future operation. Therefore, a mechanical characterization of 

these pressure vessel materials is necessary in order to ensure their safe future operation. 

To provide NASA with a suite of materials strength, fracture toughness and crack growth rate 

test results for use in remaining life calculations for the vessels described above, Southwest 

Research Institute® (SwRI®) was contracted in two phases to obtain relevant material property 

data from a representative vessel. An initial characterization of the strength, fracture and fatigue 

crack growth properties was performed in Phase 1. The Phase 1 effort also included a 

fractographic evaluation of an induced flaw that was subjected to cyclic pressure in an attempt 

by Digital Wave Corporation to use modal acoustic emissions to monitor fatigue crack growth. 

Fracture mechanics and fatigue crack growth analyses of this flaw were also performed with the 

NASGRO® software using the data generated in the Phase 1 effort to demonstrate the ability to 

perform remaining safe service life assessments on similar vessels. 

Based on the results and recommendations of Phase 1, a more extensive material property 

characterization effort was developed in this Phase 2 effort. This Phase 2 characterization 

included additional strength, fracture and fatigue crack growth of the multilayer vessel and head 

materials. In addition, some more limited characterization of the welds and heat affected zones 

(HAZs) were performed. 
10

2.0 PRESSURE VESSEL AND MATERIALS

The multilayer pressure vessel provided by NASA was manufactured by AO Smith in 1959 

(serial number MV50466-8) and the name plate is shown in Figure 2-1. The vessel was not 

ASME Code stamped. The vessel was nominally 36.25 inches in outside diameter and 

approximately 7 feet 4 inches long (see Figure 2-2). 

The body of the vessel was constructed from twelve layers (shells), with the inner (first) layer 

3/8-inch thick and the remaining eleven layers each 1/4-inch thick for a total nominal wall 

thickness of 3.125 inches. The shells are fabricated from AO Smith 1146a, a proprietary, nonASME material specification. During Phase 1, the shell material was found to meet the 

requirements of ASTM A-299 and A-225, Grade C (see Table 2-1). 

Successive layers were formed into shells such that the inner diameter closely matched the outer 

diameter of the previous shell. With the exception of the outer-most layer, seam welds were 

ground flush with the shell diameter. The seam welds were staggered from shell to shell and 

seam welds penetrated into the inner shell about 25-30% of the shell thickness (see Figure 2-3). 

All layers but the inner-most contained periodic arrays of weep holes, providing a leak path 

should the inner layer rupture or otherwise develop a leak. 

Monolithic, hemi-spherical heads, nominally 2.5 inches thick, were girth welded to the layered 

vessel body to form the pressure vessel. A cross-section of the head-vessel body interface is 

shown in Figure 2-4. The heads were fabricated from A-225, Gr. B, a standard ASTM material 

(see Table 2-1). 

As described in the Phase 1 report [1], the multilayer AO Smith pressure vessel was sent to SwRI 

and sectioned for material testing using facilities at the SwRI Fabrication Shop in the Structural 

Engineering Department. The Phase 1 effort used only a portion of the vessel material with a 

larger number of additional samples having been excised for the Phase 2 efforts. A considerable 

amount of the vessel heads and shell remain and are being retained in storage at SwRI. These 

remnants could be used to provide additional material for future studies on this type of vessel. 
11

Figure 2-1. Nameplate from AO Smith Multilayer Pressure Vessel (MV50466-8) 

Figure 2-2. As-Received Layered Pressure Vessel at SwRI Fabrication Shop 

 
12

Figure 2-3. Outer Layer Seam Weld and Penetration into Inner Layer 

Figure 2-4. Cross-section of Head-Body Interface 

 
13

Table 2-1. Chemical Composition of Head and Outer Shell Materials [1] 

Material 

Composition, wt.% 

C Mn P S Si Ni Cr Mo Cu V Al 

Head 0.16 1.40 0.033 0.028 0.20 0.20 0.19 0.02 0.02 NM1 <0.01 

Outer 

Shell 0.21 1.36 0.025 0.018 0.26 0.53 0.07 0.01 0.04 NM1 0.05 

AISI 

1513

0.10-

0.16 1.1-1.4 0.040 max 

0.050 

max       

AISI 

1522

0.18-

0.24 1.1-1.4 0.040 max 

0.050 

max       

AISI 

1524

0.19-

0.25 

1.35-

1.65 

0.040 

max 

0.050 

max       

ASTM A225 Gr. C20.25 

 max 

1.72 

 max 

0.035 

max 

0.035 

max 

0.13-

0.45 

0.37-

0.73    0.11-0.20 

ASTM A2992

0.28 

 max 

0.84-

1.52 

0.035 

max 

0.035 

max 

0.13-

0.45      

ASTM A225 Gr. B3

0.20 

 max 

1.45 

 max 

0.04 

 max 

0.05 

max 

0.15-

0.30 

0.09-

0.14 

AO Smith 

1146a 

0.18-

0.25 

1.10-

1.50 

0.04 

 max 

0.05 

max 

0.20-

0.35 

0.40-

0.70 

0.13-

0.18 

1

 Not measured 

2

 1999 vintage ASTM specification 

3

 1956 vintage ASTM specification 

 
14

3.0 MATERIAL CHARACTERIZATION AND ANALYSIS

Based on the results of Phase 1, a more extensive material property characterization effort was 

developed in this Phase 2 effort. The characterization included strength, fracture and fatigue 

crack growth of the multilayer vessel and head materials. In addition, some more limited 

characterization of the welds and heat affected zones (HAZs) was performed. This section 

provides the material characterization results for the multilayer pressure vessel materials. 

3.1 AO Smith 1146a Shell Material Characterization 

The test matrix for the AO Smith 1146a shell material characterization is shown in Table 3-1 and 

includes hardness, tensile, Charpy V-notch (CVN), fracture toughness and fatigue crack growth 

(FCG) testing. It should be noted that a test matrix was originally developed with the assumption 

that all shell layers had the same material orientation. However, as testing and characterization 

progressed, it became apparent that the inner and outer shells likely had different orientations. 

Both the inner and outer shells were subjected to a metallurgical polish and light etch in order to 

confirm the rolling (longitudinal) orientation of the shell plate material. The material rolling (L) 

direction of the outer shell was oriented in the longitudinal (L) direction of the vessel while the 

material rolling direction of the inner shell was oriented in the circumferential (C) direction of 

the vessel.1

A schematic of the specimen and material orientations is shown in Figure 3-1. Material 

orientations are shown in black while vessel orientations are shown in white. As previously 

noted, there is a difference in orientation of the inner and outer layers of the shell. The CVN, 

toughness and FCG specimens use a standard orientation scheme in which the first designates the 

direction of the applied load and the second designates the direction of crack growth. Using this 

schematic, specimen orientation with respect to the vessel can be mapped to the more relevant 

material orientation. 

The difference in inner and outer shell material orientation was discovered midway through 

execution of the original test matrix and the remaining shell testing was re-prioritized in light of 

this finding. The test matrix shown in Table 3-1 represents the actual test matrix that was 

performed. 

 

1

 As appropriate, distinctions between material and pressure vessel orientations are maintained throughout this 

report. Material orientations are relative to the plate directions and correspond to longitudinal (L), transverse (T) 

and short-transverse (ST). Vessel orientations are relative to the pressure vessel and correspond to the vessel 

longitudinal (L), hoop/circumferential (C) and radial (R) directions. 
15

(a) CVN 

(b) Toughness and FCG 

Figure 3-1. Vessel, Material and Specimen Orientations 

(12-layer shell illustrated with 4 layers) 

3.1.1 Basic Tensile and Hardness Properties 

Tensile testing was performed according to ASTM E8 [2] on the AO Smith 1146a outer shell 

material. Tensile specimens were removed from the outer shell in the vessel circumferential (C) 

direction, which is the primary outer shell loading direction. This orientation corresponds to the 

rolling (L) direction of the outer shell. Tensile testing was performed at room temperature (RT) 

in Phase 1 [1] and at -20o

F during this Phase 2 effort. 

The results of the tensile testing are presented in Table 3-2 for the 1146a shell material. By way 

of reference, the tensile properties are compared to data available in a NASA Tech Memo [3]. 

The room-temperature properties of the 1146a outer shell material are in reasonable agreement 

with the reference data (no reference data was available at -20o

F) but demonstrate a slight 

increase in strength and a slight reduction in elongation at failure. While the source of the 

reference material is unclear, testing on both these Phase 1 and 2 activities was performed on 

material extracted from the actual pressure vessel described in Section 2. The slight differences 

in shell properties may be the result of the forming process in creating the multilayered body of 

the vessel. 

head

shell

L-R

C-L

L-C

C-L L-C

T

ST

L

T

ST

L

L

ST

T

L

R

C

head

shell

L-R

L-C

C-L

L-C

C-L

T

ST

L

T

ST

L

L

ST

T

L

R

C
16

Table 3-1. AO Smith 1146a Shell Material Test Matrix 

Material Orientation Test Notes/Comments RT 0 o

F -20 oF 

AO Smith 

1146a 

Layered 

Shell 

Outer 

L-T 

(vessel L-C) Toughness none Toughness Secondary loading orientation 

T-L 

(vessel C-L) 

Hardness 

Tensile 

CVN

FCG 

none 

Tensile 

CVN

Primary loading and weak material 

orientation; some CVN, toughness and 

FCG testing performed in Phase 1

T-ST 

(vessel L-R) --- --- --- Primary loading and weak material orientation, but thickness limits testing 

Inner 

L-T 

(vessel C-L) 

Hardness 

CVN

Toughness 

FCG 

CVN

CVN

Toughness 

FCG

Primary loading orientation

T-L 

(vessel L-C) CVN CVN CVN Weak material orientation but secondary loading orientation 

T-ST 

(vessel L-R) --- --- --- Primary loading and weak material orientation, but thickness limits testing 

Outer 

Seam 

HAZ 

T-L 

(vessel C-L) CVN CVN CVN Primary loading and weak material orientation 

T-ST 

(vessel C-R) --- --- --- Primary loading and weak material orientation, but thickness limits testing 

Outer 

Seam 

Weld 

T-L 

(vessel C-L) CVN CVN CVN Primary loading and weak material orientation 

T-ST 

(vessel C-R) --- --- --- Primary loading and weak material orientation, but thickness limits testing 

Table 3-2. AO Smith 1146a Outer Shell Tensile Properties 

ID Temp 

 ( oF) 

Yield (ksi) UTS (ksi) Elongation (%) 

Test Ref [3] Test Ref [3] Test Ref [3]

1 

RT*

86.1 

75.0 

118.7 

101.3

23.0 

31 

2 79.3 119.4 24.0 

3 81.3 119.2 23.0 

Ave 82.2 119.1 23.3 

1 

-20oF 

89.1 121.7 20.0 

2 92.6 122.2 25.0 

3 91.1 121.7 23.0 

Ave 90.9 121.9 22.7 

* From ref [1].

As previously mentioned, during the course of the shell characterization, unanticipated 

differences in properties were found between the inner and outer shells, which were ultimately 

attributed to differences in material orientation with respect to the vessel. In addition, hardness 

testing was performed on both the inner and outer shell. Vickers hardness measurements were 
17

performed on the metallurgical samples (in the vessel C-L plane) used to determine shell 

orientation. 

The results of the hardness testing are provided in Table 3-3. The Vickers hardness results 

correspond to relative low hardness – high Rockwell B or very low Rockwell C – but do indicate 

a significant difference in hardness between the inner and outer shells. As hardness is indicative 

of yield strength, it is likely that there is a difference in tensile behavior in the inner and outer 

shells. However, tensile testing was not performed on the inner shell material in this program. 

Table 3-3. AO Smith 1146a Inner and Outer Shell Hardness Results 

Material 

Vickers Hardness (HV) 

Test Ave 

Layered 

Shell 

Outer 

255 

265 

271 

271 

264 

265 

Inner

175 

172 

168 

170 

175 

173 

3.1.2 Charpy V-Notch Testing 

Charpy V-notch (CVN) testing was performed in keeping with ASTM E23 [4] on the AO Smith 

1146a inner and outer shell material. The limited thickness of shells required the use of sub-sized 

CVN specimens in the vessel C-L and L-C orientations2,3. As such, CVN specimens had a 2-mm 

notch in a 10-mm width but were only 5 mm thick instead of the standard 10-mm thickness. Note 

that sub-sized specimens are not suitable in the vessel L-R orientation as this would result in a 

significant reduction in the un-notched ligament and invalidate results scaling. 

A scaling factor [5, 6] was used to adjust the sub-size CVN data in order to facilitate comparison 

to available CVN values from standard 10-mm x 10-mm specimens. This scaling applies to subsized specimens of reduced thickness by simply scaling the measured sub-sized CVN energy by 

the ratio of the thickness reduction to the standard 10-mm thickness. However, the thinner 

specimens have reduced notch-tip constraint, which can result in increased CVN energy. As the 

correction does not account for changes in notch-tip constraint, the thickness-corrected CVN 

energy may be an overestimation. 

 

2

 The first direction corresponds to the loading direction and the second indicates the crack growth direction. 3

 The ASME B&PV Code (Section VIII, Div. 3, Article KM-2) allows the use of sub-size CVN specimens when 

material size or shape precludes the use of full-size CVN specimens, and recommends appropriate scaling of results. 
18

A summary of the Charpy testing is presented in Table 3-4 for the 1146a shell material (complete 

CVN results for the shell material are presented in Appendix A). Given the sub-size nature of the 

CVN specimens, the results presented were scaled to represent a standard, full-size Charpy 

specimen. 

As indicated in Figure 3-2, the CVN of the AO Smith 1146a shell material is generally 

independent of temperature between RT and 0oF and shows a drop between 0 and -20oF. It 

should be noted that this testing was not designed to determine the ductile-to-brittle transition 

temperature and it is not clear that these data establish an upper/lower shelf. However, these data 

are consistent with a reported decrease in CVN with temperature between RT and -20oF for the 

1146a material, although a nil-ductility temperature was not reported in the NASA Tech 

Memo[3]. Unfortunately, however, the Tech Memo does not reference specimen orientation, 

which obfuscates comparisons with these results. 

Figure 3-2. AO Smith 1146a Charpy V-Notch Results 

 

0

10

20

30

40

50

60

70

80

-40 -20 0 20 40 60 80

CVN (ft-lbs)

T (oF)

Inner (L-T)

Inner (T-L)

Outer (T-L)
19

Based on the results of the inner shell, there is a significant dependence of CVN on material 

orientation. As expected, CVN is higher in the L-T orientation as crack growth is transverse to 

the rolling direction and principal grain orientation. There also appears to be some difference in 

CVN between the inner and outer shells. Recall that differences in hardness between the inner 

and outer shells were also reported (see Table 3-3), though the connection to CVN is unknown. 

Table 3-4. AO Smith 1146a Shell Charpy V-Notch Results 

Material Orientation 

Average CVN (ft-lbs)a

Notes/Comments

RT 0 oF -20 oF 

Outer 

L-T 

(vessel L-C) 

not 

tested 

not 

tested 

not 

tested 

Secondary loading; CVN deferred to 

inner shell 

T-L 

(vessel C-L) 

12 

15b not tested 

9 

7b Testing only to confirm Phase 1 results 

L-ST 

(vessel L-R) --- --- --- Not suitable to sub-size CVN in crack growth direction 

Inner 

L-T 

(vessel C-L) 72 62 60 Primary loading orientation

T-L 

(vessel L-C) 28 30 28 Weak material orientation

T-ST 

(vessel L-R) --- --- --- Not suitable to sub-size CVN in crack growth direction 

Ref [3] unknown 79 35 41 Reference CVN with unknown specimen 

orientation 

a Average based on three tests 

b Obtained during Phase 1, refer to reference [1] 

CVN testing was also performed on the HAZ and seam weld of the outer shell (see Table 3-5). 

The results in the HAZ are reasonably consistent with those of the base outer shell material (see 

Figure 3-3). The outer seam weld demonstrated significantly increased CVN toughness over the 

outer layer material. 
20

Figure 3-3. AO Smith 1146a Seam Weld and HAZ Charpy V-Notch Results 

Table 3-5. AO Smith 1146a Shell Weld Charpy V-Notch Results 

Material Orientation Average CVN (ft-lbs)* Notes/Comments

RT 0 oF -20 oF 

Seam HAZ 

(outer)

T-L 

(vessel C-L) 20 16 12 Weak material and primary loading orientation

L-ST 

(vessel L-R) --- --- --- Not suitable to sub-size CVN in crack growth direction

Seam Weld 

(outer)

vessel C-L 58 52 50 Primary loading and failure orientation 

vessel C-R --- --- --- Not suitable to sub-size CVN in crack 

growth direction

* Average based on three tests 

3.1.3 Fracture Toughness Testing 

Given the limited thickness of the shell material, determining a valid plane strain toughness was 

deemed unlikely. Initially, a K-R approach per ASTM E561 [7] was attempted to determine the 

plane stress toughness based on the apparent toughness results from Phase 1 [1]. Ultimately, 

however, valid plane stress toughness measurements could not be achieved due to insufficient 

remaining ligament which was not possible to resolve given the limited shell dimensions. As 

such, a limited amount of elastoplastic JIc toughness testing was performed per ASTM 

E1820 [8]. 

 

0

10

20

30

40

50

60

70

80

-40 -20 0 20 40 60 80

CVN (ft-lbs)

T (oF)

Inner (T-L)

Outer (T-L)

Outer HAZ (T-L)

Outer Weld
21

The results of the fracture toughness testing are summarized in Table 3-6 (complete toughness 

results for the shell material are presented in Appendix A). Unfortunately, not all of the testing 

resulted in meeting the strict validation conditions with ASTM E1820. The violations were 

typically associated with minor deviations in crack front planarity and growth. Thus, while 

strictly invalid, these results are believed to be representative of expected values. 

Table 3-6. AO Smith 1146a Shell Fracture Toughness Results 

Material Orientation

Toughness (ksi√in.) 

Notes/Comments

RT -20 oF 

Outer 

L-T 

(vessel L-C) 149a,b 163a

T-L 

(vessel C-L) 90c

 86c Invalid Kc results from Phase 1. Weak material 

and primary loading orientation. 

T-ST 

(vessel L-R) --- --- Primary failure orientation but not practical due to 

material limitations.

Inner 

L-T 

(vessel C-L) 170a 171a,b Primary vessel loading orientation. 

T-L 

(vessel L-C) not tested not tested Secondary loading; T-L toughness characterized on outer shell

T-ST 

(vessel L-R) --- --- Primary failure orientation but not practical due to material limitations.

Notes: 

a. Reported as K = √(J∙E/(1-X2

)) with E = 28.3 x106 psi and X = 0.3 

b. Strictly invalid per ASTM E1820 but believed to be representative 

c. Result invalid plane stress toughness per ASTM E561 due to insufficient remaining ligament 

3.1.4 Fatigue Crack Growth Testing 

Fatigue crack growth (FCG) testing was performed per ASTM E647 [9] on the AO Smith 1146a 

materials. Testing was performed using standard compact tension, C(T), specimens. Phase 2 

FCG testing was designed to target the upper range of the FCG da/dN-'K behavior by testing at 

high 'K. The strategy employed for this testing was to perform some testing at very high 'K, 

which would result in a very limited amount of valid FCG behavior. Other tests were designed to 

start lower on the da/dN-'K curve and develop data up to these higher 'K tests. Due to the low 

yield, high toughness nature of the shell material and limited specimen size, it was only possible 

to obtain FCG data up to approximately 50 ksi√in. at R = 0.15. A summary of the AO Smith 

1146a shell material FCG test conditions is shown in Table 3-7. 

Figure 3-4 shows the FCG behavior for the inner shell material in the L-T orientation for each R 

ratio as a function of temperature. Note that the FCG behavior exhibits negligible temperature 

dependence. A comparison of the FCG behavior between the inner shell in the L-T orientation 

and the outer shell in the T-L orientation is shown in Figure 3-5. Only slight differences are 

noted. 

A composite of the AO Smith 1146a shell material FCG behavior is shown in Figure 3-6. The 

minimal R-ratio dependence indicated by these data is typical of most steels. 
22

Table 3-7. AO Smith 1146a Shell FCG Testing 

Material Orientation

FCG Testing 

Notes/Comments

RT -20 oF 

Outer 

L-T 

(vessel L-C) not tested not tested L-T FCG behavior from outer shell 

T-L 

(vessel C-L) R = 0.7 not tested R = 0.15 at RT performed in Phase 1

T-ST 

(vessel L-R) --- --- Primary failure orientation but not practical due to material limitations

Inner 

L-T 

(vessel C-L) 

R = 0.15 

R = 0.7 

R = 0.15 

R = 0.7 Primary loading and weak material orientation 

T-L 

(vessel L-C) not tested not tested T-L FCG behavior from outer shell 

T-ST 

(vessel L-R) --- --- Primary failure orientation but not practical due to material limitations

 
23

(a) R = 0.15 

(b) R = 0.7 

Figure 3-4. AO Smith 1146a Inner Shell FCG Behavior in L-T Orientation 
24

(a) R = 0.15 

(b) R = 0.7 

Figure 3-5. AO Smith 1146a Shell FCG Behavior at RT 
25

(a) room temperature 

(b) -20oF 

Figure 3-6. AO Smith 1146a Shell FCG Behavior 

3.2 A-225, Gr. B Head Characterization 

The test matrix for the A-225 Gr. B head material characterization is shown in Table 3-8 and 

includes tensile, Charpy V-notch (CVN), fracture toughness and fatigue crack growth (FCG) 
26

testing. For consistency with the Phase 1 effort, all characterization of the head material was 

limited to the same head. Given the axisymmetric nature of the head, a metallurgical polish and 

light etch was used to determine the rolling direction of the head plate material in order to extract 

specimens with known material orientations. 

The angle between the head rolling direction and girth weld varies around the circumference of 

the head weld. Thus, a region of the head-vessel interface was specifically selected where the 

head rolling direction was parallel to the head girth weld for testing of the head HAZ (refer to 

Figure 3-1). 

Table 3-8. A-225 Gr. B Head Material Test Matrix 

Material Orientation 

Test 

Notes/Comments

RT 0 oF -20 oF 

A-225 

Gr. B 

Head 

Base 

Head 

Material 

vessel L-C CVN

FCG not tested CVN Phase 1 results but actual material orientation unknown

T-L 

(vessel L-C) 

CVN

Toughness 

FCG

CVN

CVN

Toughness 

FCG

Primary loading and weak 

material orientation

T-ST 

(vessel L-R) CVN CVN CVN Primary loading and weak 

material orientation

Outer 

HAZ 

T-L 

(vessel L-C) none none none

Characterization focused on inner 

HAZ to minimize material 

constraints

T-ST 

(vessel L-R) --- --- --- 

Primary loading orientation but not 

suitable for conventional 

specimens and testing

Inner 

HAZ 

T-L 

(vessel L-C) 

CVN

Toughness 

FCG

CVN CVN

Toughness 

Primary loading and weak 

material orientation

T-ST 

(vessel L-R) --- --- --- 

Primary loading orientation but not 

suitable for conventional 

specimens and testing

Weld 

vessel L-C 

CVN

Toughness 

FCG

CVN CVN

Toughness Primary loading orientation

vessel L-R --- --- --- 

Primary loading orientation but not 

suitable for conventional 

specimens and testing

3.2.1 Basic Tensile Properties 

Tensile testing was performed according to ASTM E8 [2] on the A-225, Gr. B head material. 

Tensile specimens were removed from the head circumferential (C) direction of the vessel, 

corresponding to the transverse (T) direction of the head material. Tensile testing was performed 

at room temperature (RT) in Phase 1 [1] and at -20o

F during this Phase 2 effort. 

The results of the tensile testing are presented in Table 3-9 for the A-225 Gr. B head material. By 

way of reference, the tensile properties are compared to data available in a NASA Tech Memo 
27

[3]. The room-temperature properties of the head material are in very good agreement with the 

reference data. No reference data was available at -20o

F. 

Table 3-9. A-225 Gr. B Head Tensile Properties 

ID Temp 

( oF) 

Yield (ksi) UTS (ksi) Elongation (%) 

Test Ref [3] Test Ref [3] Test Ref [3]

1 

RT*

53.1 

58.4 

80.0 

82.1

34.0 

34 

2 51.7 77.5 36.0 

3 52.7 80.4 33.0 

Ave 52.5 79.3 34.3 

1 

-20oF 

59.1 84.1 34.0 

2 57.7 82.7 34.0 

3 60.3 83.6 37.0 

Ave 59.0 83.5 35.0 

* From ref [1]. 

3.2.2 Charpy V-Notch Testing 

Charpy V-notch (CVN) testing was performed in keeping with ASTM E23 [4] on the A-225 

Gr. B head material and the head weld and associated HAZ. Testing was performed in the T-L 

and T-ST orientations, which are the weak material and primary loading orientations. CVN 

testing was only performed in the T-L orientation for the HAZ and the vessel L-C orientation for 

the weld. As CVN specimens for the HAZ and weld span into the layered portion of the vessel 

body, it was not reasonable to test the HAZ and weld with the notch in the radial direction. 

A summary of the CVN results are presented in Table 3-10 for the A-225 Gr. B head material 

(complete CVN results for the head material are presented in Appendix B). Figure 3-7 presents 

the CVN results for the head material in the T-L and T-ST orientations. While some difference is 

noted at 0o

F, very little difference is noted at RT and -20oF. 

However, a significant drop in CVN from RT to -20o

F is noted in the data. Although this testing 

was not designed to determine the ductile-to-brittle transition temperature, the data suggest that 

the transition temperature might be somewhat above 0o

F in the T-L orientation given the 

relatively low CVN toughness at 0 and -20oF. The transition temperature in the T-ST orientation 

appears to be near 0o

F as the CVN toughness at 0oF in the T-ST orientation is about mid-way 

between the toughness at RT and -20o

F, which, given its especially low toughness, is almost 

certainly on the lower shelf. These results are consistent with the reported decrease in CVN with 

temperature between RT and -20o

F. However, the reported nil-ductility temperature of -25oF is 

considerably lower than these data suggest [3]. Unfortunately, the Tech Memo does not 

reference specimen orientation, which obfuscates comparisons with these results. 
28

Figure 3-7. A-225 Gr. B Head Charpy V-Notch Results 

Table 3-10. A-225 Gr. B Head Charpy V-Notch Results 

Material Orientation Average CVN (ft-lbs)* Notes/Comments

RT 0 oF -20 oF 

A-225 

Gr. B 

Head 

T-L 

(vessel L-C) 90 17 10 Primary loading and weak material 

orientation

T-ST 

(vessel L-R) 98 46 5 Primary loading and weak material orientation

Ref [3] Unknown 41 25 20 Reference CVN with unknown 

specimen orientation

* Average based on three tests 

A summary of the CVN results of the head weld and HAZ are shown in Table 3-11. Note that the 

geometry of the head-shell interface inhibited testing of the outermost portion of the weld and 

HAZ. However, the CVN results of the inner HAZ are very consistent with the base A-225 head 

material (see Figure 3-8). The results of the head weld indicate a significant drop in CVN 

toughness between RT and 0o

F and no significant further reduction at -20oF, suggesting that the 

transition temperature may be greater than 0oF. 

0

20

40

60

80

100

120

-40 -20 0 20 40 60 80

CVN (ft-lbs)

T (oF)

Head (T-L)

Head (T-ST)
29

Figure 3-8. A-225 Gr. B Head Weld and HAZ Charpy V-Notch Results 

Table 3-11. A-225 Gr. B Head Weld Charpy V-Notch Results 

Material Orientation Average CVN (ft-lbs)* Notes/Comments

RT 0 oF -20 oF 

Outer HAZ

T-L 

(vessel L-C) --- --- --- Vessel construct inhibits testing in this orientation

T-ST 

(vessel L-R) --- --- --- Vessel construct inhibits testing in this orientation

Inner HAZ

T-L 

(vessel L-C) 90 23 8 Primary loading and weak material orientation

T-ST 

(vessel L-R) --- --- --- Vessel construct inhibits testing in this orientation

Weld 

vessel L-C 58 30 29 Primary loading orientation

vessel L-R --- --- --- Vessel construct inhibits testing in 

this orientation

* Average based on three tests 

3.2.3 Fracture Toughness Testing 

Based on the findings and recommendations of Phase 1 [1], elastoplastic JIc toughness testing 

was performed per ASTM E1820 [8]. The results of the fracture toughness testing are 

summarized in Table 3-12 (complete toughness results for the head material are presented in 

Appendix B). Because specimens from the weld and HAZ extended into the layered shell, testing 

was performed on the inner weld and HAZ, which eased specimen size constraints with the 

thicker inner shell. 

0

20

40

60

80

100

120

-40 -20 0 20 40 60 80

CVN (ft-lbs)

T (oF)

Head (T-L)

HAZ (T-L)

Weld
30

Unfortunately, as noted, not all testing resulted in valid JIc results. In some instances, unstable 

growth occurred prior to obtaining sufficient stable tearing to determine JIc. Nevertheless, in 

most instances, a valid JC result was obtained (though this measure does not strictly satisfy plane 

strain conditions). 

The fracture toughness results are very consistent with the CVN behavior. Like CVN, a noted 

drop in toughness was observed between RT and -20o

F. Similarly, the toughness behavior of the 

HAZ is similar to the base head material. While the weld toughness was lower than the HAZ at 

RT, it was comparable in toughness at -20oF. 

Table 3-12. A-225 Gr. B Head Weld Fracture Toughness Results 

Material Orientation Toughness (ksi√in.)aNotes/Comments 

RT -20 oF 

A-225 

Gr. B 

Head 

T-L 

(vessel L-C) 217 140b

T-ST 

(vessel L-R) --- --- Head thickness minimized ability to obtain valid result

Outer HAZ

T-L 

(vessel L-C) not tested not tested Inner HAZ tested; inner shell thickness eased specimen size constraints

T-ST 

(vessel L-R) --- --- Vessel construct inhibits testing in this orientation

Inner HAZ

T-L 

(vessel L-C) 197 93b

T-ST 

(vessel L-R) --- --- Vessel construct inhibits testing in this orientation

Weld 

vessel L-C 121c 97b

vessel L-R --- --- Vessel construct inhibits testing in this 

orientation

Notes: 

a. Reported as K = √(J∙E/(1-X2)) with E = 28.3 x106 psi and X = 0.3 

b. Invalid for JIc due to lack of stable tearing but valid Jc result 

c. Strictly invalid per ASTM E1820 but believed to be representative 
31

3.2.4 Fatigue Crack Growth Testing 

Fatigue crack growth (FCG) testing was performed per ASTM E647 [9] on the A-225 Gr. B head 

and the head weld and associated HAZ. A summary of the A-225 Gr. B head material FCG test 

conditions is shown in Table 3-13. 

As with FCG of the shell material, this Phase 2 FCG testing of the head material was also 

designed to target the upper range of the FCG da/dN-'K behavior by testing at high 'K. The 

same strategy was employed for this testing by performing some testing at very high 'K, which 

would result in a very limited amount of valid FCG behavior. Additional tests were designed to 

start lower on the da/dN-'K curve and develop data up to these higher 'K tests. Due to the low 

yield, high toughness nature of the head material and limited specimen size, it was only possible 

to obtain FCG data up to approximately 40 ksi√in. at R = 0.15. 

The FCG behavior of the A-225 Gr. B head material at RT and -20o

F is shown in Figure 3-9. The 

minimal R-ratio dependence indicated by these data is typical of most steels. A comparison of 

the RT and -20o

F behavior at each R ratio is shown in Figure 3-10, indicating negligible 

temperature dependence on the FCG behavior. 

Table 3-13. A-225 Gr. B Head FCG Testing 

Material Orientation FCG Testing Notes/Comments 

RT -20 oF 

A-225 

Gr. B 

Head 

T-L 

(vessel L-C) 

R = 0.1 

R = 0.7 

R = 0.1 

R = 0.15 

R = 0.7 

R = 0.15 at RT performed in Phase 1 

T-ST 

(vessel L-R) none none FCG of weld and HAZ prioritized over additional characterization of head FCG

Outer HAZ

T-L 

(vessel L-C) none none Inner HAZ tested; inner shell thickness eased specimen size constraints

T-ST 

(vessel L-R) --- --- Vessel construct inhibits testing in this orientation

Inner HAZ

T-L 

(vessel L-C) 

R = 0.15 

R = 0.7 none R ratio characterization prioritized over temperature

T-ST 

(vessel L-R) --- --- Vessel construct inhibits testing in this orientation

Weld 

vessel L-C R = 0.15 

R = 0.7 none R ratio characterization prioritized over temperature

vessel L-R --- --- Vessel construct inhibits testing in this 

orientation
32

(a) RT 

(b) -20oF 

Figure 3-9. A-225 Gr. B FCG Behavior 
33

(a) R = 0.1 

(b) R = 0.15 

(c) R = 0.7 

Figure 3-10. A-225 Gr. B FCG Behavior as a Function of Temperature 
34

Producing adequate FCG specimens from the head weld and HAZ was problematic. A schematic 

indicating FCG specimen extraction from the weld is shown in Figure 3-11 and is similar for 

FCG specimens extracted from the HAZ in the head. As individual shell layers are not joined 

together (except at their seam welds), the layers separated during specimen extraction, only 

being joined at the head weld. Thus, producing a viable specimen was difficult, especially for 

specimens extracted from the weld, which extended further into the layered shell. 

Because both specimen types extended into the layered shell, specimens were extracted from the 

inner weld and HAZ associated with the thicker inner shell. As a result, specimens only extended 

into two layers – extraction anywhere else would have resulted in specimens extending into three 

shell layers, further complicating specimen extraction and testing. 

Figure 3-11. Schematic of Head Weld FCG Specimen Extraction 

Fatigue crack growth testing of the head weld and HAZ was similarly challenging. Particularly at 

higher crack driving forces, crack growth tended to extend out-of-plane toward the layered 

shells. As such, the resulting valid FCG behavior was more limited, particularly for the higher Rratio of 0.7. 

The FCG behavior of the inner head weld and HAZ is shown in Figure 3-12. The same FCG 

testing strategy as that used for the base head material was employed by performing some testing 

at very high 'K, which would result in a very limited amount of valid FCG behavior, followed 

by additional testing designed to start lower on the da/dN-'K curve and develop data up to these 

higher 'K tests. However, out-of-plane growth limited the range of valid data. It should also be 

noted that the tensile properties of the base A-225 Gr. B head material were used to assess the 

validity of the weld and HAZ FCG data – obtaining tensile properties of the weld and HAZ will 

be challenging and was not performed as part of this Phase 2 effort. 

Head Weld Shell

ID

OD
35

(a) Inner Head Weld 

(b) Inner Head HAZ 

Figure 3-12. Inner Head Weld and HAZ FCG Behavior 

 

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1 10 100

da/dN (in/cyc)

'K (ksi √in)

R = 0.15

R = 0.7

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1 10 100

da/dN (in/cyc)

'K (ksi √in)

R = 0.15

R = 0.7
36

4.0 FATIGUE CRACK GROWTH MODELING

This section first provides a review of fatigue crack growth (FCG) data and how they are 

modeled using the NASGRO equation [10]. This is followed by a discussion of fits of the 

NASGRO equation to the data obtained in this effort. While the NASGRO software contains 

some data for these materials from the 1975 NASA Langley report [3], these legacy data sets are 

not as extensive as one would hope, exhibit considerable scatter, and are of questionable validity 

considering current testing methods [1] and hence, motivated the testing documented in this 

current effort. 

The limited sets of FCG data generated in the Phase 1 [1] were combined with the more 

extensive range of data generated in this Phase 2 effort and used to develop fits to the NASGRO 

equation as described below. 

4.1 Fatigue Crack Growth Rate Modeling Background 

Fatigue crack growth rate data are generally characterized on log-log plots of growth rate, da/dN

(in./cycle) versus stress intensity factor range, ΔK (ksiξin.). It is commonplace to consider FCG 

data to be divided into three regions as shown schematically in Figure 4-1. Region I is the fatigue 

“threshold” region where cracks propagate very slowly and the data usually exhibit a threshold 

(ΔKth) below which cracks do not propagate. Region II is the linear or steady-state region where 

the relationship between da/dN and ΔK is linear on a log-log plot. Region II is also commonly 

referred to as the Paris region after the power law equation [da/dN = C(ΔK)

n

] that has been used 

to model fatigue crack growth in this region for many years. Region III is the near instability 

region where rapid unstable crack growth occurs as fracture instability is approached. 

Crack growth rate calculations in NASGRO use a relationship called the NASGRO equation 

given by: 

 (4.1) 

where N is the number of applied fatigue cycles, a is the crack length, R is the stress ratio, 'K is 

the stress intensity factor range, and C, n, p, and q are empirically derived constants. The 

NASGRO equation is a “full-range” crack growth model in that it can represent all three crack 

growth regions as well as account for the dependence of FCG rate on the stress ratio. Closure is 

modeled using the Newman crack opening function, f. For additional detail on the NASGRO 

equation, the reader is referred to the documentation for the NASGRO software [10]. 

To fit the NASGRO equation to fatigue crack growth rate data, one generally needs multiple sets 

of data at different R values. In the Phase 1 effort, FCG rate data were obtained only at an R of 

0.15; Phase 2 testing at a higher R value (0.70) was conducted to determine the extent of the 

variation on da/dN as a function of R, and in addition, the effect of temperature (-20o

F) at both R 

values for both materials. Fits to the NASGRO equation for each material and for each 

temperature were obtained using the NASMAT module contained in the NASGRO software [10] 

da

dN

C f

R

K

K

K

K

K

n th

p

c

 q





§

©

 ̈ ·

1

 ̧ a

¬

« o

1⁄4

»

 §

©

 ̈ ·

1

 ̧

 §

©

 ̈ ·

1

 ̧

1

1

1

1

'

'

'

max
37

and are presented below. Note that only the “valid” FCG data were used in the NASGRO 

equation fits. 

One of the key features of the NASGRO equation is its ability to model closure and the variation 

in FCG rate data as a function of R which, in many materials, can be significant. However, for 

many steels, the variation in FCG data as a function of R is small and the testing performed 

herein confirmed this expectation. Therefore, because of the NASGRO equation’s use of the 

closure function, f, as described above, modeling a tight set of da/dN data with the NASGRO 

equation can become problematic. The strategy adopted herein was to focus the NASGRO 

equation fit on the low R data (i.e., R = 0.10 and 0.15) because the pressure cycling of the vessels 

is generally anticipated to be from zero or very low pressures to peak values and back again. 

Figure 4-1. Schematic of Fatigue Crack Growth Behavior Illustrating 

the Three Regions of Fatigue Crack Growth 

4.2 NASGRO Equation Fits for the AO Smith 1146a Shell Material 

The fit to the NASGRO equation for the AO Smith 1146a shell material at room temperature 

(RT) is shown in Figure 4-2. In this plot the Phase 1 data are the black circles (R = 0.15, t = 

0.236) and are the only data set that approach the threshold region. Figure 4-3 plots the 
38

NASGRO equation fit for AO Smith 1146a shell material at -20o

F. There were no data obtained 

in the threshold region at -20o

F and the “fit” in this region was based on what was obtained at RT 

in Figure 4-2. The principal difference, albeit slight, between these two fits is that the -20oF 

exhibit a somewhat shallower slope, n, than shown in the RT condition (2.57 versus 2.75). In 

general, the RT data/fit is slightly above the -20o

F data/fit and would be conservative choice to 

use in an analysis. The NASGRO equation parameters for the AO Smith 1146a shell material are 

summarized in Table 4-1. 

4.3 NASGRO Equation Fits for the A-225 Gr. B Head Material 

The fit to the NASGRO equation for the A-225 Gr B. head material at room temperature is 

shown in Figure 4-4. In this plot the Phase 1 data are represented by the pink “X” symbols” (R = 

0.15, t = 0.25) and are the only data set that approach the threshold region. Figure 4-5 plots the 

NASGRO equation fit for the A-225 Gr B. head material at -20o

F. There were no data obtained 

in the threshold region at -20o

F and the “fit” in this region was based on what was obtained at RT 

in Figure 4-4. For the head material at both conditions, the slopes of the data are about the same 

(2.75); again, the RT data/fit is slightly above the -20o

F data/fit and would be conservative 

choice to use in an analysis. The NASGRO equation parameters for the A-225 Gr. B head 

material are summarized in Table 4-1. 

4.4 Comparison of NASGRO Equation Fits to the Barsom Equation 

For fatigue crack growth in ferrite-pearlite steels, Barsom [11] developed an “upper bound” Paris 

equation that the Langley report recommended be used [3]: 

 da/dN = 3.6E-10 (ΔK)

3.0 (4.2) 

This relationship is shown plotted in Figure 4-6 for comparison against the head and shell 

NASGRO equation for R = 0.15 and RT. The Barsom equation matches the NASGRO equation 

at R = 0.15 quite well in the linear, Paris region. However, the Barsom equation should not be 

considered an upper bound over the full range of R or ΔK for these materials.
39

Figure 4-2. NASGRO Equation Fit for AO Smith 1146a Shell at Room Temperature 

Figure 4-3. NASGRO Equation Fit for AO Smith 1146a Shell at -20oF 
40

Figure 4-4. NASGRO Equation Fit for A-225 Gr B Head at Room Temperature 

Figure 4-5. NASGRO Equation Fit for A-225 Gr B Head at -20oF 

 
41

Figure 4-6. Comparison of NASGRO Equation Fits to Barsom Equation at R = 0.15 

and Room Temperature 

 
42

Table 4-1. NASGRO Equation Parameters Obtained for the Shell and Head Materials 

NASGRO 

Equation Parameters

Shell Head 

AO Smith 1146a Plate A-225 Gr. B Plate Notes (a)

RT -20oF RT -20oF 

Crack Growth:

C 2.00E-09 2.00E-09 1.50E-09 9.00E-10

n 2.75 2.57 2.75 2.756 

p 1.00 1.00 0.50 0.50 

q 1.00 1.00 1.00 1.00 

DK1 2.50 2.50 4.05 4.05 

Cth 1.00 1.00 0.00 0.00 

Cth- 0.10 0.10 0.10 0.10 (b) 

Alpha 2.50 2.50 2.50 2.50 

Smax/Sflow 0.30 0.30 0.30 0.30 (b) 

a0 0.0015 0.0015 0.0015 0.0015 (b) 

Kth(s)/Kth(l) 0.2 0.2 0.2 0.2 (b) 

Strength/Toughness: 

UTS (ksi) 119.1 121.9 79.3 84.1 

Yield (ksi) 82.2 90.9 52.5 59.1 

Kc (KIe, KIc) (ksi√in.) 170.0 163.0 201.0 201.0 (c) 

Ak 1.0 1.0 1.0 1.0 (c) 

Bk 0.0 0.0 0.0 0.0 (c) 

Notes: 

(a) Refer to Section 4.1 and the NASGRO manual [10] for details of the NASGRO equation and parameters. 

(b) These parameters are typical NASGRO equation default values. 

(c) The choice of Bk = 0.0 implies no dependence of toughness on thickness. In the absence of any other data, KIc

and KIe are assumed to be equal to the value of Kc obtained in this test program. Setting Bk = 0.0 is generally a 

conservative policy, with the rationale being that you need toughness data as a function of thickness in order to 

justify use of the NASGRO toughness relationship as a function of thickness (Eqn 2.14 in the NASGRO manual). 

If you are using a true value of KIc, then setting Bk = 0.0 forces Kc = KIc as a lower bound and is conservative. 

However, in this case, a “strictly valid” toughness value is not available, only a toughness for a given thickness. 

Therefore, to ensure the use of this value (only), Bk is set equal to zero and Kc = KIc = KIe. 

 
43

4.5 NASGRO Equation Fits for the Head-to-Shell Weld and HAZ Materials 

The fit to the NASGRO equation for the head-to-shell weld material at room temperature (RT) is 

shown in Figure 4-7 and the corresponding fit for the HAZ material is shown in Figure 4-8. 

There were no data obtained in the threshold region for these materials and the “fit” in this 

region was based on what was obtained at RT for the head in Figure 4-4. The NASGRO equation 

parameters for the weld and HAZ materials are summarized in Table 4-2. 

4.6 Comparison of NASGRO Equation Fits for Base Metal and Weld Materials 

The fits to the NASGRO equation for R = 0.15 at RT for the AO Smith 1146a shell, the A-225 

Gr. B head and the weld and HAZ are plotted together for comparison in Figure 4-9. The Barsom 

Equation is also shown for reference. This figure shows that the fatigue growth rates in the weld 

and HAZ are generally below that of the base metals up to a ΔK of about 50 ksi√in. For higher 

ΔKs the fits somewhat converge; however, recognize that there were not any valid FCG data in 

this range. Therefore, using the base metal FCG data would appear to be conservative when 

compared to the weld/HAZ data at least for the majority of the crack growth curve. 

4.7 Re-Evaluation of the FCG Analysis of the Notch in the Outer Shell 

In Phase 1 of this effort [1], the NASGRO software was used to perform fatigue crack growth 

analyses of the notch in the AO Smith 1146a outer shell material in an attempt to predict the 

crack growth behavior that occurred at this location during the cyclic pressure tests on the 

vessel [12]. These analyses were repeated herein using the new Phase 2 shell material properties 

(the NASGRO equation fit shown in Figure 4-2 and the parameters listed in Table 4-1). The key 

difference between the two analyses was that a fracture toughness of 90 ksi√in. was used in the 

Phase 1 analysis whereas the toughness of 170 ksi√in. obtained in Phase 2 for the shell was used 

herein (see Table 3-6). The NASGRO material data input screens for each of these Phase 2 

analyses are shown in Figures 4-10 and 4-11. 

Table 4-3 compares the results of the crack growth analyses from the Phase 1 effort (i.e., 

Table 7-1 from Ref. [1]) with analyses using the new Phase 2 shell NASGRO equation fit and 

the higher toughness value. Also shown is the Barsom equation analysis using the higher 

toughness of 170 ksi√in. In each case Kc = KIc = KIe = 170.0 ksi√in. There is essentially no 

practical difference in the crack growth life up until the surface crack transitions to a through 

crack. However, once the surface crack transitions to a through crack, the crack remains stable 

for much longer (because of the higher toughness now being used: 170 vs 90 ksi√in.). This is not 

unexpected. Using the lower toughness value of 90 ksi√in., once the part through crack 

transitions to a through crack, the computed K is such that not much or no life is computed after 

transition (Phase 1). But now that a much higher toughness (from Phase 2) is being used, the 

through crack is calculated to grow stably for quite a while longer. 

The failure analysis conducted in Phase 1 indicated that the crack from the notch grew through 

the thickness of the outer shell just before the testing was terminated [1]. The FCG analyses 

performed in Phase 2 indicate that after transition to a through crack, the crack in the shell would 

have continued to grow in a stable fashion as a through crack for many, many more cycles had 

the test continued. 
44

Figure 4-7. NASGRO Equation Fit for Head-to-Shell Weld Material at Room Temperature 

Figure 4-8. NASGRO Equation Fit for Head-to-Shell HAZ Material at Room Temperature 
45

Table 4-2. NASGRO Equation Parameters Obtained for the Head-to-Shell Weld and HAZ Materials 

NASGRO 

Equation Parameters

Head-to-Shell 

Room Temperature Notes (a)

Weld HAZ 

Crack Growth:

C 2.38E-10 1.61E-10

n 3.173 3.461 

p 1.00 1.00 

q 1.00 1.00 

DK1 4.0 4.0 

Cth 0.00 0.00 

Cth- 0.10 0.10 (b) 

Alpha 2.50 2.50 

Smax/Sflow 0.30 0.30 (b) 

a0 0.0015 0.0015 (b) 

Kth(s)/Kth(l) 0.2 0.2 (b) 

Strength/Toughness: 

UTS (ksi) 79.3 84.1 

Yield (ksi) 52.5 59.1 

Kc (KIe, KIc) (ksi√in.) 121.0 197.0 (c) 

Ak 1.0 1.0 (c) 

Bk 0.0 0.0 (c) 

Notes: 

(a) Refer to Section 4.1 and the NASGRO manual [10] for details of the NASGRO equation and parameters. 

(b) These parameters are typical NASGRO equation default values. 

(c) The choice of Bk = 0.0 implies no dependence of toughness on thickness. In the absence of any other data, KIc

and KIe are assumed to be equal to the value of Kc obtained in this test program. Setting Bk = 0.0 is generally a 

conservative policy, with the rationale being that you need toughness data as a function of thickness in order to 

justify use of the NASGRO toughness relationship as a function of thickness (Eqn 2.14 in the NASGRO manual). 

If you are using a true value of KIc, then setting Bk = 0.0 forces Kc = KIc as a lower bound and is conservative. 

However, in this case, a “strictly valid” toughness value is not available, only a toughness for a given thickness. 

Therefore, to ensure the use of this value (only), Bk is set equal to zero and Kc = KIc = KIe. 

 
46

Figure 4-9. Comparison of NASGRO Equation Fits at R = 0.15 for Base Metal and Weld Materials 

 
47

Figure 4-10. NASGRO Input Screen for NASGRO Equation for AOS 1146a Shell Material (RT) 

Figure 4-11. NASGRO Input Screen for Barsom Equation 
48

Table 4-3. Comparison of Results of FCG Analyses between Phase 1 and Phase 2 

(Phase 1 Kc = 90 ksi√in., Phase 2 Kc = 170 ksi√in.) 

 
49

5.0 SUMMARY AND CONCLUSIONS

NASA owns and operates several hundred multilayer pressure vessels, some of which are more 

than fifty years old. While available construction records show that generally good design, 

fabrication, and inspection processes were followed, these vessels are “non-Code” vessels and 

actual records do not exist for many of these vessels. To provide NASA with materials strength, 

fracture toughness and crack growth rate test results for use in remaining life calculations, a 

material property characterization effort has been performed in two phases. An initial 

characterization of the strength, fracture and fatigue crack growth properties was performed in 

Phase 1 [1], and, based on the results and recommendations of Phase 1, a more extensive 

material property characterization effort was developed in this Phase 2 effort. 

The following results summarize the culmination of the findings for the material characterization 

of both Phase 1 and 2. 

5.1 Vessel Construction 

a. The body of the vessel was constructed from twelve layers (shells), with the inner (first) layer 

3/8-inch thick and the remaining eleven layers each 1/4-inch thick for a total nominal wall 

thickness of 3.125 inches. The shells are fabricated from AO Smith 1146a, a proprietary, 

non-ASME material specification. During Phase 1, the shell material was found to satisfy the 

compositional requirements of ASTM A-299 and A-225, Gr. C. 

b. Successive layers were formed into shells such that the inner diameter closely matched the 

outer diameter of the previous shell. With the exception of the outer-most layer, seam welds 

were ground flush with the shell diameter. The seam welds were staggered from layer to 

layer and seam welds penetrated into the inner shell about 25-30% of the shell thickness. All 

layers but the inner-most contained periodic arrays of weep holes, providing a leak path 

should the inner layer rupture. 

c. The material orientations of the shells were different. The material rolling direction of the 

outer shell was oriented in the longitudinal direction of the vessel while the material rolling 

direction of the inner shell was oriented in the circumferential direction of the vessel. The 

orientation of the intermediate layers is unknown. 

d. Monolithic, hemi-spherical heads, nominally 2.5 inches thick, were girth welded to the 

layered vessel body to form the pressure vessel. The heads were fabricated from A-225, 

Gr. B, a standard ASTM material. 

5.2 AO Smith 1146a Shell Material Characterization 

a. Tensile properties of the outer shell are indicative of a modest strength steel and only slight 

differences in tensile properties between RT and -20o

F were noted. 

b. Hardness measurements indicated a significant difference in hardness between the inner and 

outer shells. This difference in hardness suggests a difference in tensile behavior between the 

inner and outer shells. 

c. Only a slight decrease in CVN toughness between RT and -20o

F was noted. However, there 

was a significant dependence on material orientation, with CVN toughness in the T-L 

orientation of nominally half that in the L-T orientation. 

d. There appears to be a difference in the CVN toughness between the inner and outer shell 

layers. 
50

e. The CVN toughness of the outer shell seam weld HAZ was consistent with the outer shell 

material. The outer shell seam weld CVN toughness was significantly greater than and 

demonstrated less temperature dependence than the outer shell material. 

f. Albeit based on very limited sample size, fracture toughness testing did not indicate any 

significant dependence of fracture toughness on temperature between RT and -20o

F for the 

shell material. Similar to CVN, a slight difference in toughness was noted between the inner 

and outer shell, though based on very limited test results. 

g. FCG characterization of the shell material focused on the upper range of the da/dN-'K 

behavior. Only a slight dependence on R ratio, typical of steels, was noted. 

h. Negligible dependence of FCG behavior on temperature between RT and -20o

F was noted. 

Similarly, only slight differences in FCG behavior between the outer shell in the T-L 

orientation and the inner shell in the L-T orientation were noted. Unfortunately, because FCG 

testing was performed with specimens of the same vessel orientation but not the same 

material orientation, no comparison between inner and outer shells with the same material 

orientation was possible. 

5.3 A-225 Gr. B Head Material Characterization 

a. Tensile properties of the A-225 Gr. B head material are indicative of a low-strength steel and 

only slight differences in tensile properties between RT and -20o

F were noted. 

b. A significant drop in CVN from RT to -20o

F was noted. Although this testing was not 

designed to determine the ductile-to-brittle transition temperature, the data suggest a 

transition temperature might be somewhat above 0o

F in the T-L orientation and near 0oF in 

the T-ST orientation. 

c. CVN results indicated only a slight dependence on orientation between the T-L and T-ST 

orientations for the A-225 head material. 

d. CVN results of the inner HAZ are very consistent with the base A-225 head material. The 

results of the head weld indicate a significant drop in CVN toughness between RT and 0o

F 

and no further reduction at -20o

F. 

e. The fracture toughness results for the A-225 Gr. B head material were consistent with the 

CVN behavior. A noted drop in toughness was observed between RT and -20oF. 

f. The fracture toughness behavior of the HAZ was similar to the base head material. While the 

weld toughness was lower than the HAZ and base head material at RT, it was comparable in 

toughness at -20o

F. 

g. The FCG behavior of the A-225 Gr. B head material at RT and -20o

F indicated minimal Rratio dependence, typical of most steels. Negligible temperature dependence on the FCG 

behavior was noted. 

h. Obtaining valid FCG behavior of the head weld and HAZ was challenging as specimens 

extended into the layered shell. Particularly at the higher crack driving forces, fatigue crack 

growth tended to occur out-of-plane toward the layered shell, which limited the extent of 

valid FCG behavior. 

5.4 Fatigue Crack Growth Modeling 

a. NASGRO equation fits were developed for the shell and head materials and represent the 

FCG behavior at room temperature and -20o

F. NASGRO equation fits were also developed 

for the head-to-shell weld and HAZ materials albeit only at room temperature. As discussed 

in Section 4.1, the fitting strategy adopted herein focused on representing the low R data 
51

(0.10, 0.15) as a priority and consequently this results in a conservative fit to the high R data 

(0.7) in some cases4

. 

b. As the main goal of the fatigue crack growth testing performed in this Phase 2 effort was to 

obtain data in the linear and upper regions of the FCG curve, the NASGRO equation fits for 

these materials in the threshold region must be considered approximate since they relied on 

only the limited amount of near-threshold data obtained in Phase 1. 

c. The Barsom equation recommended in the Langley report [3] does not provide an upper 

bound for the shell or head materials. However, it does serve as a good approximation for the 

low R fatigue crack growth rate behavior in the Paris region. 

d. The slopes (exponent, n) of the NASGRO equation fits to the weld and HAZ materials are 

larger (steeper) than those determined for the shell and head base metals. However, fatigue 

growth rates at R = 0.15 in the weld and HAZ are generally below those of the base metals 

up to a ΔK of about 50 ksi√in. 

e. The failure analysis conducted in Phase 1 indicated that the crack from the notch grew 

through the thickness of the outer shell just before the testing was terminated [1]. The FCG 

analyses performed in Phase 2 indicate that after transition to a through crack, the crack in 

the shell would have continued to grow in a stable fashion as a through crack for many, many 

more cycles had the test [12] continued. 

 

4

 NASGRO also has the capability to represent FCG data in tabular form instead of using the NASGRO equation 

and this feature can be used to overcome deficiencies in curve fitting. However, for these steels, there are not 

enough data (for multiple R values over a full range of ΔK) to use the tabular da/dN input approach. 
52

6.0 RECOMMENDATIONS

Based on the culmination of results during both Phase 1 and Phase 2 of the material 

characterization effort for the multilayer pressure vessel, the following summarize the 

recommendations for future material characterization. These recommendations for additional 

characterization should be prioritized in concert with specific fitness-for-service analyses of 

these pressure vessels. 

A considerable amount of pressure vessel shell and head material still remains from the sectioned 

vessel and is in storage at SwRI. While it cannot be retained indefinitely, these remnants can be 

used to extract samples for additional material testing as recommended below. 

6.1 AO Smith 1146a Shell Material 

With the apparent differences in some material properties between the inner and outer shells, 

chemical analysis should be performed on the inner shell to confirm its composition. 

a. Given differences in shell plate material orientation in the construction of the vessel and the 

noted differences in properties in the in-plane orientations, the full characterization of tensile, 

CVN and toughness properties in the L-T and T-L orientations of both the inner and outer 

shell should be completed. Similarly, FCG testing should be performed on the outer shell in 

the L-T orientation and on the inner shell in the T-L orientation to more definitively 

characterize the FCG behavior of each shell. 

b. Because only a limited number of valid fracture toughness results exist, additional toughness 

testing should be performed to develop a more statistically-robust measure of fracture 

toughness. Although obtaining valid toughness results will remain challenging given the 

material constraints, additional data will contribute to the robustness of the toughness that is 

currently based on very minimal sample sizes. 

c. Additional FCG testing designed specifically to capture the lower 'K, near-threshold 

behavior should be performed. If the previously mentioned additional FCG testing were to 

indicate no significant dependence on orientation or inner/outer shell, and due to the 

demonstrated lack of temperature dependence of the existing FCG behavior, this nearthreshold FCG characterization could be limited to a single orientation and shell (inner or 

outer). 

d. FCG characterization should be performed on the shell seam weld and HAZ. The properties 

of the seam weld are likely to be largely independent of shell material orientation and, as 

such, FCG characterization could be performed on either the inner or outer seam weld. 

However, properties of the HAZ are likely dependent on the base shell orientation. Thus, 

FCG characterization of the inner and outer seam weld HAZ should be considered. 

e. The HAZ in the shell at the head weld has not been characterized in either of the Phase 1 or 

Phase 2 efforts. Although the vessel construct inhibits characterization of this HAZ, similar 

characterization of the HAZ should be performed as material limitations allow. 

f. While the current material characterization has been limited to the AO Smith 1146a shell 

material extracted from a single vessel, layer-to-layer and vessel-to-vessel variation in 

material properties may exist. For example, some differences in mechanical behavior were 

noted between the inner and outer layers, which could be an indication of lot-to-lot 

variability. Variation in weld properties may also be significant as welding techniques may 
53

vary from person to person and/or with the size of the vessel. Thus, additional mechanical 

characterization, in keeping with the specific fitness-for-service analyses, should be 

performed on multiple layers from the same vessel and/or layers from multiple vessels. 

6.2 A-225 Gr. B Head Material 

a. Tensile properties should be determined for the head weld and HAZ. Although it is 

anticipated to have minimal impact, the validity of the weld and HAZ FCG behavior should 

be re-assessed with the actual tensile properties as opposed to the base head tensile properties 

used in this effort. 

b. Because only a limited number of valid fracture toughness results exist, additional toughness 

testing should be performed to develop a more statistically-robust measure of fracture 

toughness. Although obtaining valid toughness results will remain challenging given the 

material constraints, additional data will contribute to the robustness of the toughness that is 

currently based on very minimal sample sizes. 

c. As the T-ST orientation is a primary loading and weak material orientation, fracture 

toughness and FCG testing in this orientation should also be considered. 

d. Additional FCG testing designed specifically to capture the lower 'K, near-threshold 

behavior of the head, weld and HAZ should be performed. 

e. While the current material characterization has been limited to the A-225 Gr. B head material 

extracted from a single head, head-to-head and vessel-to-vessel variation in material 

properties may exist. Variation in weld properties may also be significant as welding 

techniques may vary from person to person and/or with the size of the vessel. Thus, 

additional mechanical characterization, in keeping with the specific fitness-for-service 

analyses, should be performed on both heads from the same vessel and/or heads from 

multiple vessels. 

6.3 Fatigue Crack Growth Modeling 

a. The material characterization data (tensile, fracture toughness and fatigue crack growth data) 

for these pressure vessel steels should be incorporated into the NASMAT database in 

NASGRO. 

b. The curve fits (NASGRO equation parameters) to the FCG data for these materials should be 

incorporated into the library of NASGRO equation curve fits in the NASFLA module of 

NASGRO. 

c. As warranted, the NASGRO equation fits should be reviewed and updated pending 

additional near-threshold FCG testing. 

d. As mentioned in conclusion 5.4.b and elsewhere, the NASGRO equation fits for these 

materials in the threshold region must be considered as approximate estimates since they 

were based on the trend from only a small amount of near-threshold data. If one is concerned 

about using the fits as presented in the threshold region, one could eliminate the threshold 

downturn by choosing to set the exponent “p” in the NASGRO equation to zero. This would 

extend the linear region of the fit backwards as a straight line, effectively eliminating the 

threshold behavior in the model. This would be a conservative approach; however, in many 

cases it could be overly conservative. 
54

7.0 REFERENCES

[1] J.W. Cardinal, C.F. Popelar and R.A. Page, “Multilayer Pressure Vessel Materials Testing 

and Analysis (Phase 1),” Final Report, Southwest Research Institute Project No. 18.17408, 

Rev. 1, October 2012. 

[2] ASTM E8, “Standard Test Methods for Tension Testing of Metallic Materials,” Vol. 03.01, 

ASTM International, West Conshohocken, PA, 2010. 

[3] C.M. Hudson, J.C. Newman, Jr., and P.E. Lewis, NASA Technical Memorandum, “An 

Investigation of Fracture Toughness, Fatigue Crack Growth, and Impact Properties of 

Three Pressure Vessel Steels,” NASA TM X-3316, NASA LaRC, Hampton, VA, 

December, 1975. 

[4] ASTM E23, “Standard Test Methods for Notched Bar Impact Testing of Metallic 

Materials,” Vol. 03.01, ASTM International, West Conshohocken, PA, 2010. 

[5] Towers, O., “Testing Sub Size Charpy Specimens – Parts 1, 2 and 3,” Metal Construction, 

March, April, and May, 1986. 

[6] API RP 579/ASME FFS-1, Fitness-For-Service, API Recommended Practice 579, Second 

Edition, American Petroleum Institute, Washington, DC, June 2007. 

[7] ASTM E561, “Standard Test Method for K-R Curve Determination,” Vol. 03.01, ASTM 

International, West Conshohocken, PA, 2010.

[8] ASTM E1820, “Standard Test Method for Measurement of Fracture Toughness,” Vol. 

03.01, ASTM International, West Conshohocken, PA, 2010. 

[9] ASTM E647, “Standard Test Method for Measurement of Fatigue Crack Growth Rates,” 

Vol. 03.01, ASTM International, West Conshohocken, PA, 2010. 

[10] NASGRO® Fracture Mechanics and Fatigue Crack Growth Analysis Software, Version 7.0, 

Southwest Research Institute and NASA Johnson Space Center, November 2012. 

[11] Barsom, J.M. and Rolfe, S.T., Fracture and Fatigue Control in Structures: Applications of 

Fracture Mechanics, Third Edition, ASTM, West Conshohocken, PA, 1999. 

[12] Ziola, S.M., “Cyclic Crack Growth Testing of an A.O. Smith Multilayer Pressure Vessel 

with Modal Acoustic Emission Monitoring and Data Assessment,” Final Report, Digital 

Wave Corporation, November 13, 2012. 
55 

APPENDIX A: AO SMITH 1146A SHELL MATERIAL

CHARACTERIZATION RESULTS

 
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APPENDIX B: A-225 GR. B HEAD MATERIAL 

CHARACTERIZATION RESULTS

 
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Multilayer Pressure Vessel Materials Testing and Analysis

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obtain relevant material property data from a representative vessel. An initial characterization of the strength, fracture and 

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limited characterization of the welds and heat affected zones (HAZs) were performed. This report describes Phase 2 of this 

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