NUREG/CR-7226

Primary Water Stress 

Corrosion Cracking of 

High-Chromium, NickelBase Welds Near 

Dissimilar Metal Weld 

Interfaces 

 

Office of Nuclear Regulatory Research

NUREG/CR-7226

Primary Water Stress 

Corrosion Cracking of 

High-Chromium, NickelBase Welds Near 

Dissimilar Metal Weld 

Interfaces 

Office of Nuclear Regulatory Research

Manuscript Completed: February 2016 

Date Published: January 2018 

Prepared by: 

B. Alexandreanu, Y. Chen, K. Natesan, and W. J. Shack 

Argonne National Laboratory 

Argonne, IL 60439 

M. Audrain, NRC Project Manager

iii 

ABSTRACT 

The report summarizes the results of a testing program to evaluate the stress corrosion cracking 

(SCC) susceptibility at or near the interface between Alloy 52 and 152 weld metals and other 

weld or base metals. Alloys 52 and 152 are high-chromium weld metals used in reactor 

pressure vessel head penetration nozzles and as overlays, inlays, or onlays for dissimilar metal 

piping welds. Alloys 52 and 152 typically show very low SCC growth rates in laboratory testing 

and are not known to have cracked in service. Nevertheless questions remain as to whether 

the localized dilution of chromium content or the presence of microstructural features near the 

interface with the low-chromium weld metals Alloy 82 and 182, as in the case of a weld overlay 

(WOL), or with steel, as in the case of a head penetration nozzle, could affect the SCC 

response. For this study, SCC growth rates were measured on a WOL mockup with Alloy 52M 

(a compositional variant of Alloy 52) on Alloy 182 and on a butt weld mockup with Alloy 152 

joined to low-alloy steel (LAS). For the WOL mockup, tests were performed in which the crack 

growth direction was either from Alloy 182 directly into Alloy 52M or along their interface. In the 

butt weld mockup, measurements were made in the first layer of weld butter beads, within about 

1 mm of the interface with LAS. The tests on both mockups resulted in crack growth rates in 

Alloy 52M and 152 that are higher than have been previously reported for the weld metals, even 

though the dendrites were not favorably oriented for cracking. In the WOL mockup, crack 

branching along the interface was observed when the cracking direction was perpendicular to 

the interface. In the butt weld mockup, material compositional analyses taken along the crack 

path indicated that locations with the highest measured crack growth rates did not necessarily 

correlate with the lowest chromium content. This suggests that microstructural factors, in 

addition to the chromium content, could affect the SCC susceptibility near the interface. 

v 

FOREWORD 

This report describes a study sponsored by the NRC Office of Nuclear Regulatory Research 

(RES) to investigate the stress corrosion cracking (SCC) susceptibility at or near the interface 

between Alloy 52 and 152 weld metals and other weld or base metals. SCC of nickel-based 

weld metals, such as those used for reactor vessel head penetration nozzles and reactor 

coolant system nozzles, is a degradation mechanism that can affect the operational safety of 

pressurized water reactors (PWRs). For instance, through-wall cracking was detected in an 

Alloy 82 and 182 hot leg nozzle weld at the V.C. Summer plant in 2000. Alloys 52 and 152 are 

thought to be more resistant to SCC than Alloys 82 and 182 because of higher chromium 

content, and there is no operational experience of their cracking in service. In light of the 

positive service history and low crack growth rates measured in laboratory testing sponsored by 

the industry, utilities have submitted requests to the Office of Nuclear Reactor Regulation (NRR) 

for relief from the inspection requirements found in Title 10 of the Code of Federal Regulations, 

Section 50.55a, including a 10 year interval for volumetric examination of pressure vessel 

head nozzles. 

In the course of reviewing the relief requests and test results from industry-sponsored research, 

RES and NRR staff raised questions with respect to the potential for SCC susceptibility to be 

enhanced by localized dilution of chromium in the Alloy 52 and 152 weld metals near interfaces 

with other weld or base metals. These include interfaces with Alloys 82 and 182 in the case of 

weld overlays (WOLs), inlays, and onlays, or with stainless and low-alloy steel (LAS) in vessel 

head penetration nozzles and piping welds. For this study, SCC growth rates were measured 

on a WOL mockup with Alloy 52M (a compositional variant of Alloy 52) deposited on Alloy 182 

and on a butt weld mockup with Alloy 152 joined to LAS. For the WOL mockup, tests were 

performed in which the crack growth direction was both normal to and along the weld metal 

interfaces. In the butt weld mockup, measurements were made in the first layer of weld butter 

beads, within 1 mm of the interface with LAS. 

The tests on both mockups resulted in crack growth rates in Alloy 52M or 152 that were higher 

than have been reported in previous tests for the weld metals, and similar to those typically 

found in Alloys 82 and 182. In the WOL mockup, crack branching along the interface was 

observed even when the test was intended to propagate the crack perpendicular to the 

interface, suggesting high SCC susceptibility at the interface between the two welds. In the butt 

weld mockup, material compositional analyses taken along the crack path indicated that 

locations with the highest measured crack growth rate did not necessarily correlate with the 

lowest chromium content. This suggests that microstructural factors, in addition to the 

chromium content, could affect the SCC susceptibility near the interface. 

These data highlighted to both NRC and the industry the need for additional testing at weld 

interfaces to better understand the mechanistic basis for the reported behavior. The application 

of the test results to plant components is particularly challenging given the large number of 

potential variations in weld designs and configurations that are found in service. Nevertheless, 

such tests are ongoing and will continue to inform the evaluations by NRR to determine 

whether inspections for components with Alloy 52 and 152 welds provide a reasonable 

assurance of safety. 

vii 

TABLE OF CONTENTS 

ABSTRACT ................................................................................................................... iii 

FOREWORD ................................................................................................................... v 

TABLE OF CONTENTS ................................................................................................ vii 

LIST OF FIGURES ......................................................................................................... ix 

LIST OF TABLES ........................................................................................................ xix 

EXECUTIVE SUMMARY ............................................................................................. xxi 

ACKNOWLEDGMENTS ............................................................................................ xxiii 

ABBREVIATIONS AND ACRONYMS ........................................................................ xxv 

1 INTRODUCTION ........................................................................................................ 1 

2 EXPERIMENTAL SETUP AND METHODOLOGY ..................................................... 3 

2.1 Alloy 52M WOL ................................................................................................................. 3 

2.2 Alloy 690 to Alloy 533 Grade B Joint ................................................................................. 3 

2.2.1 Alloy 152 Weld Buttering ....................................................................................... 4 

2.2.2 Alloy 152 Butt Weld ............................................................................................... 5 

2.3 CT Specimens ................................................................................................................... 5 

2.4 PWSCC Test Facilities ...................................................................................................... 6 

2.5 CGR Test Methodology ..................................................................................................... 9 

2.6 Analysis of CGR Data ..................................................................................................... 11 

3 RESULTS ................................................................................................................. 17

3.1 SCC CGR Testing of Alloy 52M WOL ............................................................................. 17 

3.1.1 Specimen A52M-182-TS-3 .................................................................................. 17 

3.1.2 Specimen A52M-182-TS-1 .................................................................................. 36 

3.1.3 SCC Along the Alloy 52M-182 Interface, Specimen WOL-ST-1 ......................... 49 

3.1.4 SCC in Alloy 52M Near the Interface with Alloy 182, Specimen WOL-ST-2 ....... 65 

3.2 SCC CGR Testing of Alloy 152-LAS 1st Dilution Layer .................................................. 86 

3.2.1 SCC CGR Test on 1st layer Alloy 152 Weld Butter Specimen N152-LAS-1 ....... 86 

3.2.2 SCC CGR Test on 1st Layer Alloy 152 Weld Butter Specimen 

N152-LAS-11 ..................................................................................................... 105 

4 DISCUSSION .......................................................................................................... 127

4.1 SCC CGR Response of Alloy 52M WOL ...................................................................... 127 

4.2 1st Layer Alloy 152-LAS Cyclic and SCC CGR Response ........................................... 129 

4.3 Comparison of Cyclic and SCC CGR Responses in 1st Layer Alloy 

152-LAS and 1st Layer Alloy 52M-182 WOL ................................................................ 130 
viii 

4.4 The Effect of Local Cr Concentration and that of the Substrate on the 

Cyclic and SCC CGR Response of a Cr-Depleted 1st Layer High Cr Ni-Base 

Weldment ...................................................................................................................... 131 

5 CONCLUSIONS ..................................................................................................... 133

6 REFERENCES ....................................................................................................... 135
ix 

LIST OF FIGURES

Figure 2-1 (a) Conceptual schematic (units in inch), and (b) photograph of the 

resulting Alloy 52M-182 weld overlay. The continuous welded restraints 

used during the Alloy 52M WOL deposition are visible in the photograph. ............ 3 

Figure 2-2 Joint design, Alloy 690 to SA-533 Gr B. Units are in inch...................................... 4 

Figure 2-3 Configuration of the (a) 1-T and (b) 1⁄2-T CT specimens used for this study. 

Dimensions are in mm. ........................................................................................... 6 

Figure 2-4 Layout of the 2-liter SCC test system. .................................................................... 7 

Figure 2-5 Photograph of the specimen load train for the 2-liter autoclave ............................. 7 

Figure 2-6 Schematic diagram of the recirculating 2-liter autoclave system. ........................... 8 

Figure 2-7 Principle of crack length measurement by the DC potential method. ..................... 9 

Figure 2-8 CGRs in air and environment for Alloys 600, 690 and Ni-base welds as a 

function of predicted rates in air for Alloy 600 (data taken from Refs. 12, 

13, 20). ................................................................................................................. 13 

Figure 2-9 Cyclic CGRs for typical Ni-base weld tested in a PWR environment. 

Expected corrosion fatigue (Eq. 7, green) and SCC (Eq. 9, blue) curves 

are included. ......................................................................................................... 14 

Figure 2-10 (a) Cyclic CGR data for the Alloy 152 weld tested in primary water 

environment, and (b) Alloy 152 weld produced in a double-J geometry. .............. 15 

Figure 3-1 Photograph of the Alloy 52M-182 WOL. The SCC CGR test directions, TS 

and ST, are indicated in the figure. ....................................................................... 17 

Figure 3-2 Photograph of Alloy 52M-182 WOL specimen A52M-182-TS-3 prior to the 

SCC test. .............................................................................................................. 18 

Figure 3-3 Crack–length–vs.–time for specimen A52M-182-TS-3 in simulated PWR 

environment during test periods: (a) precracking-4, (b) 5-8, (c) 9-14, (d) 

15-19, (c) 18-23, (f) 24-25. (g) 24-79, (h) 80-89, (i) 90-98, and (j) 99-106. ........... 21 

Figure 3-4 The two side surfaces of Specimen A52M-182-TS-3. Crack advance is 

from left to right (a), and right to left (b). The green arrows show the 

interface between the two welds and the red arrows indicate the end of 

the test. ................................................................................................................. 25 

Figure 3-5 Interaction with the Alloy 52M interface (a) location A in Fig. 3-4a, crack 

propagation is from left to right, and (b) location B in Fig. 3-4b, crack 

propagation is from right to left. ............................................................................ 26 

 
x 

Figure 3-6 SCC interaction with the Alloy 52M WOL interface (location A in Fig. 3-4a): 

(a) overlap of SEM image and elemental map, and (b) Cr concentration 

(wt. %) at each location. Crack propagation is from left to right. Green 

arrows indicate the Alloy 52M-182 interface. ........................................................ 27 

Figure 3-7 SCC interaction with the Alloy 52M WOL interface (location B in Fig. 3-4b): 

(a) overlap of SEM image and Cr map, and (b) Cr concentration (wt. %) at 

each location. Crack propagation is from right to left. Green arrows 

indicate the Alloy 52M-182 interface. ................................................................... 28 

Figure 3-8 Fracture surfaces of Specimen A52M-182-TS-3. ................................................. 29 

Figure 3-9 Crack interaction with the Alloy 52M interface. Crack propagation is from 

left to right. The major crack directions are indicated. ......................................... 29 

Figure 3-10 The two halves of fractured specimen A52M-182-TS-3. ...................................... 30 

Figure 3-11 Fractured specimen A52M-182-TS-3 ................................................................... 30 

Figure 3-12 Fracture surface of Specimen A52M-182-TS-3 (a) photograph, and (b) 

SEM micrograph. Regions marked “A” and “B” represent the two most 

prominent regions of IG SCC propagation into the Alloy 52M WOL. Crack 

propagation is from bottom to top. ........................................................................ 31 

Figure 3-13 Crack transition across the Alloy 52M-182 interface at locations (a) A, and 

(b) in Fig. 3-12b. Crack advance is from bottom to top. ....................................... 32 

Figure 3-14 Fracture surface of specimen A52M-182-TS-3. The arrow indicates the 

beginning of transitioning to IG in Alloy 52M. Crack advance is from 

bottom to top. ........................................................................................................ 33 

Figure 3-15 Cyclic CGR data in PWR environment for (a) specimen A52M-182-TS-3 

and specimen A182-TS-1 of the same alloy tested previously (without 

WOL), (b) specimen A52M-182-TS-3 and Alloy 152 specimen A152-TS-4 

under similar loading, and Alloy 52 data from the literature [24, 25], (c) 

Comparison between Alloy 52M data obtained in the current test and Alloy 

52 data from the literature [24, 25], (d) Transitioning in Alloy 52M, periods 

78-93. ................................................................................................................... 34 

Figure 3-16 SCC CGR in Specimen A52M-182-TS-3 as a function of distance to the 

182/52M interface ................................................................................................. 36 

Figure 3-17 Photographs of the two sides of the 52M/182 weld overlay specimen 

A52M-182-TS-1. ................................................................................................... 36 

Figure 3-18 Crack–length–vs.–time for WOL specimen A52M-182-TS-1 in simulated 

PWR environment during test periods (a) precracking-2, (b) 3-5, (c) 6-11, 

(d) 12-19, (e) 20-21, (f) 22-25, (g) 26-27, (h) 28, (i) 30, (j) 31-32, (k) 33, 

and (l) 33-42. ........................................................................................................ 39 

 
xi 

Figure 3-19 (a, b) The two halves of fractured specimen A52M-182-TS-1. Crack 

advance is from bottom to top. (c,d) Same fracture surfaces 

photographed at an angle to show the cracking pattern at the interface. ............. 42 

Figure 3-20 Fracture surface of specimen A52M-182-TS-1. The interface is indicated 

by black arrows. Crack advance is from bottom to top. The units of the 

bottom and side rulers are mm. ............................................................................ 43 

Figure 3-21 Specimen A52M-182-TS-1: (a) first half of fracture surface, (b) detail at 

location 1, and (c) detail at location 2. Crack advance is from bottom 

to top. .................................................................................................................... 44

Figure 3-22 Specimen A52M-182-TS-1: (a) detail at location 3, and (b) detail at 

location 4 in Fig. 3-21a. Crack advance is from bottom to top. ............................. 45 

Figure 3-23 Specimen A52M-182-TS-1: (a) second half of fracture surface, (b) detail at 

location 1, and (c) detail at location 2. Crack advance is from bottom 

to top. .................................................................................................................... 46

Figure 3-24 Cyclic CGR data for Alloy 52M WOL specimen A52M-182-TS-1 in 

simulated PWR environment during (a) precracking and transitioning in 

Alloy 182, and (b) at the end of the test in Alloy 52M. The dotted blue line 

shows the “air line” for Alloy 52M obtained in the prior test. ................................. 47 

Figure 3-25 SCC CGR vs. distance for the two Alloy 52M-182 WOL specimens tested 

in the TS orientation. ............................................................................................ 48 

Figure 3-26 Specimens for SCC CGR testing of Alloy 52M-182 WOL in the ST 

orientation. ............................................................................................................ 49 

Figure 3-27 Notch area in specimen WOL-ST-1. P3 and P8 represent the approximate 

locations where SCC CGR measurements were made in Alloy 600 HAZ, 

and P19 represents the approximate location where the crack was to 

intersect the interface with the Alloy 52M WOL. ................................................... 50 

Figure 3-28 (a) Cyclic CGR data for the Alloy 600 (HAZ) region of specimen WOL-ST1 in simulated PWR environment; (b) SCC CGR data for the Alloy 600 

(HAZ) region of specimen WOL-ST-1 and MRP-55 disposition curve for 

Alloy 600 [11]. The data obtained prior to the first test period at constant 

load (3) is shown with dark blue symbols, and the data obtained prior to 

the second test period at constant load (8) is shown with light blue 

symbols). .............................................................................................................. 51 

Figure 3-29 Cyclic CGR data for the Alloy 182 region of specimen WOL-ST-1 in 

simulated PWR environment. ............................................................................... 52 

Figure 3-30 Crack–length–vs.–time for specimen WOL-ST-1 in simulated PWR 

environment during (a) precracking-2, (b) 3, (c) 4-7, (d) 8, (e) 9, (f) 10-18, 

and (g) 19. ............................................................................................................ 53 

 
xii 

Figure 3-31 Post-test specimen WOL-ST-1 seen from both sides: (a) side 1, and (b) 

side 2. The red arrows indicate the Alloy 52M WOL interface. Crack 

advance is from left to right. ................................................................................. 55 

Figure 3-32 Cross sections of specimen WOL-ST-1: (a) side 1, and (b) side 2. Blue 

arrows indicate the Alloy 600/182 interface and the red arrows indicate the 

Alloy 182-52M interface. Crack advance is from left to right. .............................. 57 

Figure 3-33 Micrographs on the cross section of specimen WOL-ST-1 on: side 1 taken 

at location (a) 1A, and (b) 1B in Fig. 3-32a, and side 2 taken at location 

(c) 2A and (d) 2B in Fig. 3-32b. Inserts show the local Cr concentrations 

(wt. %). Crack advance is from left to right. ......................................................... 58 

Figure 3-34 Fracture surface of specimen WOL-ST-1. Blue arrows indicate the Alloy 

600-Alloy 182 interface, green arrows indicate the Alloy 182-Alloy 52M 

interface, and the red arrows and line mark the end of the test. The 

locations of the two test periods in Alloy 600 (P3 and P8) and along the 

Alloy 52M-182 interface (P19) are indicated in the figure. Crack advance 

is from bottom to top ............................................................................................. 59 

Figure 3-35 Fracture surface of specimen WOL-ST-1. Blue arrows indicate the Alloy 

600-Alloy 182 interface, green arrows indicate the Alloy 182-Alloy 52M 

interface, and the red arrows and line mark the end of the test. Crack 

advance is from bottom to top. ............................................................................. 60 

Figure 3-36 Fracture surface of specimen WOL-ST-1 at location 1 in Fig. 3-35. The 

blue arrows designate the intersection with the Alloy 182 weld, and the 

white arrows show areas of TG obtained most likely during fast cycling in 

at the beginning of test period 9, Table 3-4. Crack advance is from bottom 

to top. .................................................................................................................... 61

Figure 3-37 Fracture surface of specimen WOL-ST-1 at location 2 in Fig. 3-35. The 

blue arrows indicate the onset of cracking in Alloy 182, and white arrows 

indicate the occasional TG fracture that occurred prior to transitioning into 

Alloy 52M. An early occurrence of IG is indicated with a green arrow. 

Crack advance is from bottom to top. ................................................................... 62 

Figure 3-38 Fracture surface of specimen WOL-ST-1 at location 3 in Fig. 3-35. The 

green arrows indicate the onset of IG along the interface. Crack advance 

is from bottom to top. ............................................................................................ 63 

Figure 3-39 Fracture surface of specimen WOL-ST-1 at (a) location 4, and 

(b) location 5 in Fig. 3-35. Crack advance is from bottom to top. . ...................... 64 

Figure 3-40 Fracture surface of specimen WOL-ST-1 at (a) locations 6 in Fig. 3-35, 

and (b) detail at the white arrow in (a). Crack advance is from bottom 

to top. .................................................................................................................... 64

Figure 3-41 Fracture surface of specimen WOL-ST-1 at (a) location 7, and 

(b) location 8 in Fig. 3-35. The red arrows indicate IG fracture mode at the 

end of the test. Crack advance is from bottom to top. ......................................... 65 
xiii 

Figure 3-42 Notch area in specimen WOL-ST-2. P16 and P33 represent the 

approximate locations where SCC CGR measurements were made in this 

specimen. ............................................................................................................. 65 

Figure 3-43 Cyclic CGRs for Alloy 52M specimen WOL-ST-2 in simulated PWR 

environment. Also included are Alloy 52 data from the literature [24, 25] 

obtained in air at room temperature and in PWR environment. ............................ 68 

Figure 3-44 Environmental enhancement of two control test conditions vs. calculated 

distance to the interface. Crack propagation is from right to left (see also 

Fig. 3-25 for guidance). ........................................................................................ 68 

Figure 3-45 Crack–length–vs.–time for Alloy 52M specimen WOL-ST-2 in simulated 

PWR environment during test periods (a) precracking, (b) 1-3, (c) 4-7, 

(d) 8-9, (e) 10-12, (f) 13-15, (g) 16, (h) 17-19, (i) 20-27, (j) 28-32, (k) 31, 

(l) 33, (m) detail in the first part of test period 33, (n) detail in the second 

part of test period 33, and (o) 34. ......................................................................... 69 

Figure 3-46 Notch area post-test in specimen WOL-ST-2 seen from both sides: 

(a) side 1, and (b) side 2. The red arrows indicate the WOL interface. 

Crack advance is from right to left. ....................................................................... 75 

Figure 3-47 Cross section of specimen WOL-ST-2: (a) side 1, and (b) side 2. Crack 

advance is from right to left. The red arrows indicate the WOL interface. ......... 76 

Figure 3-48 Crack tip region on the first side surface of specimen WOL-ST-2 (side 1, 

location 1A in Fig. 3-47a). Crack advance is from right to left. Cr 

concentration at select locations is indicated in the figure. The red arrows 

indicate the WOL interface. .................................................................................. 77 

Figure 3-49 Crack tip regions on the second side surface of specimen WOL-ST-2 

(side 2, location 2A in Fig. 3-47b). Crack advance is from right to left. Cr 

concentration at select locations is indicated in the figure. The red arrow 

indicates the WOL interface. ................................................................................ 78 

Figure 3-50 Cross section of specimen WOL-ST-2: taken in the middle of the 

specimen (side M). Crack advance is from right to left. The red arrows 

indicate the WOL interface. .................................................................................. 79 

Figure 3-51 Crack tip regions on the second side surface of specimen WOL-ST-2 

(side M, location A in Fig. 3-50). Crack advance is from right to left. Cr 

concentration at select locations is indicated in the figure. The red arrow 

indicates the WOL interface. ................................................................................ 80 

Figure 3-52 Fracture surface of specimen WOL-ST-2. The yellow arrows indicate the 

beginning of SCC growth, the red arrows show the end of the test, and the 

green arrows indicate the region where the crack would have intersected 

the interface. Crack advance is from bottom to top. ............................................. 82 

 
xiv 

Figure 3-53 (a) First half (right hand side of Fig. 3-52a) of the fracture surface of 

specimen WOL-ST-2 obtained under constant load in simulated primary 

water. (b) location 1, (c) location 2, and (d) location 3. Crack advance is 

from bottom to top. ............................................................................................... 83 

Figure 3-54 Fracture surface of specimen WOL-ST-2 at (a) location 4, and (b) location 

5 in Fig. 3-53a. The white arrow indicates an unbroken ligament. Crack 

advance is from bottom to top. ............................................................................. 84 

Figure 3-55 Second half (left hand side of Fig. 3-52a) of the fracture surface of 

specimen WOL-ST-2 obtained under constant load in simulated primary 

water. (b) location 1, and (c) location 2. Crack advance is from bottom 

to top. .................................................................................................................... 85

Figure 3-56 Fracture surface of specimen WOL-ST-2 at location 3 in Fig. 3-55a. Crack 

advance is from bottom to top. ............................................................................. 85 

Figure 3-57 Photograph of the Alloy 152 weld joining Alloy 690 and Alloy 533 LAS. 

SCC CGR test specimens were aligned in the 1st layer of Alloy 152 butter. ....... 86 

Figure 3-58 Specimen N152-LAS-1, overlapped images before and after the specimen 

notch was machined: (a) side 1, and (b) side 2. Units of the rulers are 

mm. ....................................................................................................................... 87 

Figure 3-59 Environmental enhancement of two control test conditions and SCC CGRs 

vs. distance from the specimen notch for Specimen N152-LAS-1. Test 

periods are indicated in the figure. ....................................................................... 89 

Figure 3-60 Crack–length–vs.–time for dilution specimen N152-LAS-1 in simulated 

PWR environment during test periods (a) precracking-2, (b) 3-4, (c) 5, (d) 

6, (e) 7-10, (f) 11-17, (g) 18, (h) 19-20, (i) 21, (j) 22-23, and (k) 24. ..................... 90 

Figure 3-61 The two sides of the dilution specimen N152-LAS-1 after testing in primary 

water: (a) side 1, and (b) side 2. The red arrows indicate the approximate 

location of the end of the test as determined on the fracture surface. Units 

of the side rulers are mm. ..................................................................................... 94 

Figure 3-62 (a) Cross section 1 of Specimen N152-LAS-1, (b) detail at location 1 in (a), 

and (c) detail at location 2 in (a). The local Cr concentration is shown in 

red. Crack advance is from left to right. ............................................................... 96 

Figure 3-63 (a) Cross section 2 of Specimen N152-LAS-1, (b) detail at location 1 in (a), 

and (c) detail at location 2 in (a). Crack advance is from left to right. ................. 97 

Figure 3-64 Fracture surface (A, Fig. 3-63) of specimen N152-LAS-1 tilted to show the 

final IG region. Two regions of interest, R1 and R2 are marked in the 

figure. Crack advance is from bottom to top. ....................................................... 98 

 
xv 

Figure 3-65 Region R1 on the fracture surface A of specimen N152-LAS-1 (Fig. 3-64). 

Blue arrows indicate the transition from LAS to Alloy 152, and two 

additional locations of interest: IG-1 (location 1) and the second 

intersection of the crack with the LAS interface (location 2), labelled LAS-i. 

Crack advance is from bottom to top. ................................................................... 99 

Figure 3-66 Fracture surface of specimen N152-LAS-1, locations: (a) 1, and (b) 2 in 

region R1, Fig. 3-65. Crack advance is from bottom to top. ............................... 100 

Figure 3-67 Region R2 on the fracture surface A of specimen N152-LAS-1 (Fig. 3-64). 

Blue arrows indicate the transition from LAS to Alloy 152, and two 

additional locations of interest: IG-1 (location 1) and the second 

intersection of the crack with the LAS interface (location 2), labelled LAS-i. 

Crack advance is from bottom to top. ................................................................. 101 

Figure 3-68 Fracture surface of specimen N152-LAS-1, locations: (a) 1, and (b) 2 in 

region R2, Fig. 3-67. Crack advance is from bottom to top. ............................... 102 

Figure 3-69 Fracture surface of N152-LAS-1, region IG-2 (Fig. 3-64): (a) first half of the 

fracture surface, (b) detail at location 1, and (c) detail at location 2.Crack 

advance is from bottom to top. ........................................................................... 103 

Figure 3-70. Fracture surface of N152-LAS-1, region IG-2 (Fig. 3-64): (a) second half of 

the fracture surface, (b) detail at location 3, and (c) detail at location 4. 

Crack advance is from bottom to top. ................................................................. 104 

Figure 3-71 Approximate locations of the CT specimen blanks for first layer and 

second layer weld butter SCC CGR testing. The specimen blank that will 

later become CT test specimen N152-LAS-11 is indicated in the figure. ........... 105 

Figure 3-72 The two sides of specimen N152-LAS-11 prior to the SSC test: (a) side 1, 

and (b) side 2. Alloy 152 is in the top half, and the LAS is in the bottom 

half of both pictures. ........................................................................................... 106 

Figure 3-73. Environmental enhancement of two control test conditions and SCC CGRs 

vs. distance from the specimen notch for Specimen N152-LAS-11. Test 

periods are indicated in the figure. ..................................................................... 108 

Figure 3-74 Crack–length–vs.–time for dilution specimen N152-LAS-11 in simulated 

PWR environment during test periods (a) precracking-2, (b) 3-5, (c) 6, 

(d) 7-9, (e) 10, (f) 11-13, (g) 14-15, (h) 16-27, and (i) 28. ................................... 108 

Figure 3-75 SEM images of the two sides of the dilution specimen N152-LAS-11 after 

the test: (a) side 1, and (b) side 2. Alloy 152 and the LAS are as marked 

in each picture. The red arrows mark the end of the test. ................................. 112 

Figure 3-76 (a) Side surface 2 of Specimen N152-LAS-11; Regions with low (b) and 

high (c) SCC CGRs as observed on the side surface “2” at locations 1 and 

3. Local Cr concentration (wt. %) measurements are indicated with red in 

each figure. Crack propagation is from left to right. ........................................... 113 
xvi 

Figure 3-77 “Swirls” appearing to slow down/arrest crack propagation observed on the 

side surface 2 in specimen N152-LAS-11 (locations 2 and 3 in Fig. 2-9b). 

Measured Cr concentration (wt. %) for each “swirl” is indicated with red in 

the figure. Crack propagation is from left to right. .............................................. 114 

Figure 3-78 Fracture surface of specimen N152-LAS-11. The red lateral arrows 

indicate the end of cyclic loading and the beginning of the final constant 

load test period. Measured Fe concentration (wt. %) for at several 

locations is indicated on a blue background in the figure. Crack advance 

is from bottom to top. .......................................................................................... 115 

Figure 3-79 Fracture surface of specimen N152-LAS-11. Crack advance is from 

bottom to top. ...................................................................................................... 116 

Figure 3-80 Fracture surface of specimen N152-LAS-11 at locations (a) 1, and (b) 2 in 

Fig. 2-3. Crack advance is from bottom to top. .................................................. 117 

Figure 3-81 Fracture surface of specimen N152-LAS-11 at location: (a) 3, and (b) 4b in 

Fig. 3-79. Crack advance is from bottom to top. ................................................ 118 

Figure 3-82 Fracture surface of specimen N152-LAS-11 at location 4a in Fig. 3-79. 

Crack advance is from bottom to top. ................................................................. 119 

Figure 3-83 Fracture surface of specimen N152-LAS-11 at location: (a) 5, and (b) 6 in 

Fig. 3-79. Crack advance is from bottom to top. ................................................ 120 

Figure 3-84 Fracture surface of specimen N152-LAS-11 at location: (a) 7, and (b) 8 in 

Fig. 3-79. Arrows indicate unbroken ligaments. Crack advance is from 

bottom to top. ...................................................................................................... 121 

Figure 3-85 (a) Fracture surface of specimen N152-LAS-11. Additional cross sections 

were obtained along directions “11” (a), and “22” (b). Red arrows are 

placed at the specimen notch and indicate the direction of propagation. 

Green arrows indicate the end of the test. .......................................................... 123 

Figure 3-86 SEM (a) and EBSD (b) map obtained on cross section “22” (Fig. 3-85) of 

Specimen N152-LAS-11. The yellow arrow points to a set of aligned 

boundaries that could plausibly explain the crack path in this test [28]. 

Crack propagation is from right to left. ................................................................ 124 

Figure 3-87 SEM (a) and EBSD (b) map obtained on side surface 2 (Figs. 3-75b and 

3-76) of Specimen N152-LAS-11. The blue arrows point to sets of aligned 

boundaries in the next weld bead [29]. Red arrows are placed at the 

specimen notch and indicate the direction of propagation. Green arrows 

indicate the end of the test. Crack propagation is from left to right.................... 125 

Figure 4-1 SCC CGRs in an Alloy 52M-182 overlay: (a) Schematic showing the test 

specimen orientations with respect to the Alloy 52M-182 WOL, and 

(b) SCC CGRs vs. distance to the Alloy 52M-182 interface. .............................. 127 
xvii 

Figure 4-2 SCC CGRs in the Alloy 52M-182 overlay: (a) along the Alloy 52-182 

interface in specimen WOL-ST-1, and (b) as a function of average Cr 

content in specimen WOL-ST-2. Also included are Alloy 152 data 

generated at ANL [22,23] and the MRP-115 disposition curve for 

Alloys 82/182 [1]. ................................................................................................ 128 

Figure 4-3 Environmental enhancement of two control test conditions and SCC CGRs 

vs. distance from the specimen notch for (a) N152-LAS-1, and (b) 

N152-LAS-11. Crack propagation is from left to right. ....................................... 129 

Figure 4-4 SCC CGRs in and 1st layer Alloy 152-LAS specimens. Also included are 

Alloy 152 data generated at ANL [22, 23] and the 75th percentile MRP-115 

disposition curve for Alloys 82/182 [1]. ............................................................... 130 

Figure 4-5 Environmental enhancement of two control test conditions and SCC CGRs 

vs. distance from the specimen notch for 1st layer (a) Alloy 52-182 

specimen WOL-ST-2, and (b) Alloy 152-LAS specimen N152-LAS-11. ............. 131 

Figure 4-6 SCC fracture modes the regions near the interface in (a) Alloy 152 – LAS, 

and (b) Alloy 52M WOL specimens tested in simulated primary water 

environment. SCC propagation is from bottom to top. ...................................... 131 

xix 

LIST OF TABLES 

Table 2-1 Chemical composition (wt.%) of Alloy 182 double-J weld and Alloy 

52M WOL ............................................................................................................... 3 

Table 2-2 Welding process and conditions for various weld passes used for 

fabricating the A152 butter ..................................................................................... 4 

Table 2-3 Chemical composition (wt.%) of Alloy 152 heat 720129 used to produce 

the 1st layer of buttering. ......................................................................................... 5 

Table 2-4 Welding process and conditions for various weld passes used for 

fabricating the A152 butt weld. ............................................................................... 5 

Table 3-1 Crack growth data for specimen A52M-182-TS-3 of Alloy 152 weld in PWR 

watera,b ................................................................................................................. 19 

Table 3-2 Summary of SCC CGR and cyclic (control cycle) data for specimen 

A52M-182-TS-3 .................................................................................................... 35 

Table 3-3 Crack growth data for WOL specimen A52M-182-TS-1 in PWR watera,b. ........... 38 

Table 3-4 Crack growth data for specimen WOL-ST-1 in PWR watera,b .............................. 51 

Table 3-5 Crack growth data for 52M specimen WOL-ST-2 in PWR watera,b ...................... 67 

Table 3-6 Crack growth data for dilution specimen N152-LAS-1 in PWR watera,b,c ............ 88 

Table 3-7 Crack growth data for Alloy 152 dilution specimen N152-LAS-11 in 

PWR watera,b,c ................................................................................................... 107 

xxi 

EXECUTIVE SUMMARY 

Nickel-base Alloy 690 and the associated weld Alloys 52 and 152 are typically used for nozzle 

penetrations in replacement heads for pressurized water reactor (PWR) vessels, because of 

their increased resistance to stress corrosion cracking (SCC) relative to Alloys 600, 82, and 182. 

This is attributed to a higher chromium content. In addition, many PWRs use Alloys 52 or 152 

as weld overlays (WOLs), inlays, or onlays to mitigate SCC on Alloy 82 or 182 dissimilar metal 

piping welds. However, questions remain about whether localized chromium dilution could 

increase the SCC susceptibility in Alloys 52 and 152 at or near interfaces with Alloys 82 and 

182, as in the case of a WOL, or with steel, as in the case of a head penetration nozzle. While 

Alloys 52 and 152 have generally shown very low SCC growth rates in laboratory testing, there 

has been limited prior testing on what is often referred to as the weld dilution zone. To address 

this knowledge gap, Argonne National Laboratory (ANL) fabricated two mockups, the testing of 

which is the subject of this report. The first was a WOL mockup with Alloy 52M (a compositional 

variant of Alloy 52) on Alloy 182. The second was a butt weld mockup with Alloy 152 joined to 

low-alloy steel (LAS). 

SCC testing on the Alloy 52M-182 WOL was conducted in two orientations, TS (weld interface is 

perpendicular to the crack growth direction) and ST (crack growth direction is parallel to the 

weld interface). In the orientation referred to as TS, the interface was perpendicular to the crack 

growth plane and the crack was grown from the Alloy 182 weld directly into the Alloy 52M 

overlay. The nominal chromium content in Alloy 182 is in the range of 13 to 17%, and in Alloy 

52M is in the range of 28 to 31.5%. Compositional analyses showed that the chromium content 

in Alloy 52M could be diluted to as low as 22 to 23 percent within 0.5 mm of the interface with 

Alloy 182. In the orientation referred to as ST, the crack growth plane was along the interface 

between Alloys 182 and 52M. For two specimens tested in the TS orientation, it was found that 

as cracks in Alloy 182 approached within 1 mm of the interface, the crack growth rates (CGRs) 

decreased by approximately one order of magnitude compared to those measured farther away. 

In both specimens, it was also observed that when cracks intersected the interface, they would 

branch such that one front would continue to grow straight into the Alloy 52M overlay, while 

other fronts would propagate along the interface between Alloys 52M and 182, even though this 

was not the intended growth direction. For the specimens with the ST orientation, relatively high 

CGRs were measured both along the interface between Alloys 182 and 52M and in the first 

layer of Alloy 52M weld beads next to the interface. The SCC CGRs along the interface 

between the two weld metals were found to be as high as the 75th percentile curve for Alloys 82 

and 182 reported in the Electric Power Research Institute Report, MRP-115, “Crack Growth 

Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Alloy 82, 182, and 

132 Welds” [1]. The SCC CGR in the first layer of Alloy 52M weld was a factor of two lower 

than the 75th percentile curve reported in MRP-115 [1], despite the fact that the crack 

propagation direction was perpendicular to the dendritic grains. This direction is expected to be 

less susceptible to crack growth. 

For the butt weld mockup, Alloy 152 butter and weld filler metal were joined to a piece of Alloy 

533-Grade B LAS that was recovered from the reactor pressure vessel lower head for the 

cancelled Midland nuclear power plant. Two specimens were aligned to place the crack growth 

plane in the first layer of weld beads, parallel to, and at a distance of approximately 1 mm from 

the interface with LAS. The nominal chromium content in Alloy 152 is in the range of 28 to 

31.5%, while LAS has essentially no chromium. Compositional analyses showed that the 

chromium content in Alloy 152 could be diluted to as low as 19 to 20 percent within 0.5 mm of 

the interface with LAS. The environmental enhancement of fatigue crack growth was found to 
xxii 

be a good predictor for the SCC response. Both fatigue and SCC CGR responses were similar 

to those observed in the first layer of weld beads in the Alloy 52M overlaid on Alloy 182. In both 

cases, in the most favorable orientations, the SCC CGRs were within a factor of two of the 

MRP-115 75th percentile curve [1]. Material compositional analyses taken along the crack path 

indicated that locations with the highest measured crack growth did not necessarily correlate 

with the lowest chromium content. This suggests that microstructural factors, in addition to the 

chromium content, could affect the SCC susceptibility near the interface. 
xxiii 

ACKNOWLEDGMENTS 

The authors thank E. Listwan and Z. Zheng and their contributions to the experimental effort, as 

well as the ANL Electron Microscopy Center. This work is sponsored by the Office of Nuclear 

Regulatory Research, U.S. Nuclear Regulatory Commission, under Contract 

NRC-HQ-60-16-T-0001; Program Manager: G. Oberson. 

xxv 

ABBREVIATIONS AND ACRONYMS 

ANL Argonne National Laboratory 

ASTM American Society for Testing and Materials 

B&W Babcock and Wilcox 

BPR Back Pressure Regulator 

BWR Boiling Water Reactor 

CGR Crack Growth Rate 

CL Constant Load 

CMTR Certified Material Test Report 

CRDM Control Rod Drive Mechanism 

CT Compact Tension 

DO Dissolved Oxygen 

ECP Electrochemical Potential 

EDX Energy Dispersive X-ray Spectroscopy 

EPRI MRP Electric Power Research Institute Materials Reliability Program 

GTAW Gas Tungsten Arc Welding 

HAZ Heat Affected Zone 

HX Heat Exchanger 

IG Intergranular 

LAS Low Alloy Steel 

LWR Light Water Reactor 

NRC Nuclear Regulatory Commission 

PNNL Pacific Northwest National Laboratory 

PPU Partial Periodic Unloading 

PWR Pressurized Water Reactor 

PWHT Post Weld Heat Treatment 

PWSCC Primary Water Stress Corrosion Cracking 

SCC Stress Corrosion Cracking 

SEM Scanning Electron Microscopy 

SMAW Shielded Metal Arc Welding 

SS Stainless Steel 

S Side 

T Transverse 

TC Thermocouple 

TG Transgranular 

WOL Weld Overlay 

WPS Weld Procedure Specification 

1 

1 INTRODUCTION 

Alloy 600, a nickel-based alloy, was used at the time of construction in light water reactors 

(LWRs), and has over the years proven to be susceptible to stress corrosion cracking (SCC). 

Such cracking was first observed in steam generator tubes, but it has also occurred in 

components such as instrument nozzles and heater thermal sleeves in the pressurizer and 

control-rod drive mechanism (CRDM) housings in reactor pressure vessel upper closure heads, 

as in the notable case of the Davis-Besse plant in 2002. In operating plants, the nickel-based 

weld Alloys 82 and 182 are used with Alloy 600, and are themselves also susceptible to SCC. 

Through-wall cracking was detected in an Alloy 82 and 182 hot leg nozzle weld at the V.C. 

Summer plant in 2000. Alloy 690, which has higher chromium (Cr) content than Alloy 600, has 

been widely used since the 1980s to replace Alloy 600 components in pressurized water 

reactors (PWRs), beginning with thin-walled steam generator tubes, and eventually including 

thick-section nozzle penetrations in reactor pressure vessel heads. This choice was made 

following numerous laboratory studies worldwide which established an excellent resistance to 

SCC in reactor coolant primary water for this alloy [2-4]. Alloys 52 and 152 are the higher Cr 

content nickel-based weld metals that are used for joining Alloy 690 components, and which are 

also used for overlays (WOLs), inlays, or onlays to mitigate the SCC susceptibility of Alloy 82 

and 182 welds. To date, there are no known cases of in-service SCC of Alloys 690, 52, 

and 152. 

Despite the increased resistance to SCC of Alloy 52 and 152 welds in laboratory tests and the 

positive service history, questions remain about whether localized Cr dilution could increase the 

SCC susceptibility in Alloys 52 and 152 at or near interfaces with Alloys 82 and 182, as in the 

case of a WOL, or with steel, as in the case of a dissimilar metal weld (DMW) or head 

penetration nozzle. There has been limited testing of what is referred to as the weld dilution 

zone. This zone may extend up to several hundred microns from the weld interface, To 

address this knowledge gap, Argonne National Laboratory (ANL) fabricated two mockups, the 

testing of which is the subject of this report. The first was a WOL mockup with Alloy 52M (a 

compositional variant of Alloy 52) on Alloy 182. The second was a butt weld mockup with 

Alloy 152 joined to low-alloy steel (LAS). 

Chapter 2 of this report describes the mockups used for testing, including the materials of 

fabrication, the schematic design of the welds, and the weld fabrication processes. It was 

intended that the materials and welding parameters should be representative of those used for 

actual welds used in service. Chapter 2 also discusses the SCC testing equipment and 

experimental approach. ANL generally followed well-established testing practices that have 

been employed for a number of years and were reported in previous ANL reports. Chapter 3 

provides the testing results for the WOL and butt weld mockups. The plots are provided to 

show the crack extension as a function of time, and photographs and micrographs are given to 

document the appearances of the fracture surfaces. The WOL was tested in two different 

orientation, the first of which involved crack growth from Alloy 182 into Alloy 52M, directly 

through the interface, which was aligned perpendicular to the crack growth plane. In the second 

orientation, crack growth was measured along the interface between Alloys 182 and 52M. For 

the butt weld mockup, the crack growth was measured in the first layer of Alloy 152 weld beads, 

parallel to, and less than 1 mm from the interface with LAS. Chapter 4 includes a discussion of 

the testing results, including compositional and microstructural factors that could affect the SCC 

response. Comparisons are made between Alloy 182 and LAS with respect to their effects on 

the adjoining Alloy 52 or 152 weld metal. Finally, Chapter 5 gives a summary of the main 

findings and conclusions. 

3 

2 EXPERIMENTAL SETUP AND METHODOLOGY 

This section describes the fabrication of the Alloy 52M and Alloy 152 weldments, the 

configuration of test specimens, and the CGR test apparatus and experimental approach. 

2.1 Alloy 52M WOL 

The Alloy 52M (Heat NX75W1TK) WOL (Figure 2-1) was deposited on top of an existing Alloy 

182 weld [5]. The chemical compositions of the two welds provided in Table 2-1 shows that the 

Cr concentrations for the two alloys were 29.98% and 14.35%, respectively. The Alloy 182 weld 

had been tested previously (without the overlay), and a set of both cyclic and SCC CGR data 

existed for this weld [6]. 

The Alloy 52M WOL was produced at ANL Central Shops using welding parameters prototypical 

of those used in the nuclear industry. The Alloy 52M deposit was made with 1/8”-dia. wire, 

current 158-160A, voltage 16V, travel speed 3.5-4 in./min, 99.99% Ar shield gas 22-26 ft3/hr 

(CFH), oscillation approximately 1⁄4”, and weave approximately 1⁄4”. 

(a) (b)

Figure 2-1 (a) Conceptual schematic (units in inch), and (b) photograph of the resulting 

Alloy 52M-182 weld overlay. The continuous welded restraints used during 

the Alloy 52M WOL deposition are visible in the photograph. 

Table 2-1 Chemical composition (wt.%) of Alloy 182 double-J weld and Alloy 52M WOL 

Alloy ID Analysis C Mn Fe S P Si Cu Ni Cr Ti Nb Co 

Alloy 182 double-J ANL 0.0415 7.095 6.005 0.008 0.06 0.53 0.03 65 14.35 0.43 1.585 0.03 

Alloy 52M CMTR 0.019 0.81 8.80 <0.0005 0.003 0.11 0.03 59.6 29.98 0.20 0.88 0.01 

2.2 Alloy 690 to Alloy 533 Grade B Joint 

This subsection documents the steps taken to produce a 3-inch thick butt weld for Alloy 690 

(Heat NX3297HK12) welded to SA-533 Gr B class 1 steel (Heat A5466-2 from the Midland 

reactor lower head [7]) buttered with Alloy 152 filler metal. The geometry of the joint is shown in 

Figure 2-2. The joint was designed with a straight edge on the Alloy 690 side to facilitate SCC 

Alloy 600

Alloy 182

1

Alloy 52M
4 

CGR testing of the Alloy 690 heat affected zone (HAZ) which was also of interest in the 

research program. The SMAW welding procedure was qualified to ASME Section IX by ANL 

Central Shops [5]. 

Figure 2-2 Joint design, Alloy 690 to SA-533 Gr B. Units are in inch. 

2.2.1 Alloy 152 Weld Buttering 

The LAS plate was machined with a bevel on one end. The beveled end was buttered with 

Alloy 152 F43 filler metal. A record was kept of the number and location of weld passes 

together with the heat code of the filler metal used, and the welding parameters that were used 

[5]. This record is shown in Table 2-2. After each layer, a liquid penetrant (LP) check was 

performed. After buttering, the LAS piece was stress relieved at 1150 ± 25oF for 3h. The 

chemical composition of the Alloy 152 filler heat 720129 that was used to produce the first layer 

of buttering is given in Table 2-3. 

Table 2-2 Welding process and conditions for various weld passes used for fabricating 

the A152 butter 

Weld 

Pass Process 

Filler 

Metal 

Filler 

Size, in. 

Heat 

Code 

Type 

Polarity 

Current, 

A 

Voltage, 

V 

Travel Speed, 

in./min 

Notes 

1 – 23 SMAW Alloy 152, 

EniCrFe-7 

1/8 720129 DCRP 97-102 21 – 23 5 Layer 1 

LP 

24-44 SMAW Alloy 152, 

EniCrFe-7 

5/32 146444 DCRP 113-117 25 – 26 5 Layer 2 

LP 

45-65 SMAW Alloy 152, 

EniCrFe-7 

5/32 146444 DCRP 113-117 25 – 26 5 Layer 3 

LP 

DCRP = direct current reverse polarity 
5 

Table 2-3 Chemical composition (wt.%) of Alloy 152 heat 720129 used to produce the 1st

layer of buttering. 

Alloy ID Analysis C Mn Fe S P Si Cu Ni Cr Ti Nb+Ta Co 

Alloy 152 CMTR 0.037 3.70 9.28 <0.001 <0.003 0.51 0.01 55.26 28.92 0.12 1.92 <0.01 

2.2.2 Alloy 152 Butt Weld 

The buttered LAS piece described in the previous sub-section was beveled on the buttered 

edge leaving 1⁄4” of Alloy 152 F43 weld material on the face, and a section of Alloy 690 plate was 

used to make the opposing part of the butt weld. A double bevel J-grove weld was produced 

according to the design shown in Figure 2-2, and the number and location of weld passes 

together with the heat code of the filler metal used, as well as the welding parameters are given 

in Table 2-2 [5]. The root pass of the weld and back grind was LP tested, and the final weld 

surface was also LP tested. The final weld was radiographed per ASME Section IX. 

Table 2-4 Welding process and conditions for various weld passes used for 

fabricating the A152 butt weld. 

Weld 

Pass Process 

Filler 

Metal 

Filler 

Size, in. 

Heat 

Code 

Type 

Polarity 

Current, 

A 

Voltage, 

V 

Travel 

Speed, 

in./min Notes 

1 – 8 SMAW Alloy 152, 

EniCrFe-7 

1/8 720129 DCRP 97-102 21 – 23 5 

9-14 SMAW Alloy 152, 

EniCrFe-7 

1/8 146444 DCRP 97-102 25 – 26 5 Root LP 

BG LP 

15-26 SMAW Alloy 152, 

EniCrFe-7 

5/32 146444 DCRP 113-117 25 – 26 5 Final LP 

27-76 SMAW Alloy 152, 

EniCrFe-7 

1/8 WCO4F6 DCRP 97-102 25 – 26 5 Final LP 

DCRP = direct current reverse polarity 

2.3 CT Specimens 

All CGR tests were conducted in simulated PWR environments at 320°C. The testing protocol 

was in accordance with ASTM E-647, “Standard Test Method for Measurement of Fatigue 

Crack Growth Rates,”[8] and ASTM E-1681, “Standard Test Method for Determining a 

Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials under 

Constant Load” [9]. Depending on the dimensions of the available materials, the tests were 

performed on either 1-T or 1⁄2-T compact tension (CT) specimens; the geometries of the CT 

specimens are shown in Figure 2-3. 

 
6 

(a) 

(b) 

Figure 2-3 Configuration of the (a) 1-T and (b) 1⁄2-T CT specimens used for this study. 

Dimensions are in mm. 

2.4 PWSCC Test Facilities 

The CGR tests were conducted in test facilities equipped with either 2 or 6-liter stainless steel 

(SS) autoclaves. Each system has a suite of calibrated instrumentation, including digitally 

controlled hydraulic loading and load cells, and an independent water loop to maintain a 

simulated PWR environment with water chemistry monitoring. The test systems are nearly 

identical except for the maximum load rating of the test frame and the volume of the autoclave 

vessel. A detailed description of the test system with the 2-liter autoclave is provided in 

this section. 

The 2-liter autoclave test facility allows test temperatures of up to 350C [662°F]. Figure 2-4 is a 

photograph showing the entire test system. The servo-hydraulic test frame consists of a load 

train, an autoclave support frame, and autoclave. The hydraulic actuator is mounted on bottom 

of the test frame, with the load train components located above it. The load cell is located at the 

bottom of the pull rod. An Instron Model 8800 system is used to control the load on the 

specimen. The test temperature is maintained by heater bands mounted on the autoclave body. 

LAY MARKS TO FALL

PERPENDICULAR TO CENTER

LINE OF RADIUS "M SURFACE" 

DETAIL 'C' DETAIL 'M'

40°

.025

.076 R

±2°

1.19 2.39

1.19 R

1.27

9.53

±0.25

±0.05

12.7

C

25.4

2.39

CENTERED

C

30.5 ±0.25

14.0 ±0.25

30.5 'C'

XXXXXX

SPECIMEN 

 I. D.

12.7

'M'

2 THRU HOLES

12.7 DIA.

+0.25

- 0.00

63.5 ±0.51

±0.25

12.7

2.26 DIA. DRILL 9.53 DP.

4-40 UNC-2B TAP 6.35 ± 0.51 DP.

ONE EA. ON TOP & BOTTOM FACE 

TOP FACE

±0.25

50.8

61.0 ±0.51 14.0 ±0.25

±0.25

14.00

14.00

6.60

6.60

1.60

CENTERED

6.00 DIA.

2 THRU HOLES

+.05

- .00 30.00

28.00

'M'

A .02

A .02

B

B .02

A .02

A .02

12.00

24.00

4.00

1.53 DIA

2 THRU HOLES

4.00

4.00

2.00

4.5

2.00

1.53 DIA. 2 HOLES 8.0 DEEP. 

XXX-X

SPECIMEN ID

C

C .02

C .02

9.0 A

.90 R

.90

DETAIL 'M'
7 

Figure 2-4 Layout of the 2-liter SCC test system. 

The autoclave support frame consists of a thick plate supported by four compression rods 

(Figure 2-5). The internal load frame that contains the test specimen consists of a top plate 

supported by three rods. The upper two-piece clevis assembly is fastened to the top plate of 

the internal load frame, and the lower piece clevis assembly is connected to the pull rod. The 

specimen to be tested is mounted between the clevises. The specimen and clevises are kept 

electrically insulated from the load train by using oxidized Zircaloy pins and mica washers to 

connect the clevises to the rest of the load train. Water is circulated through a port in the 

autoclave head, which serves both as inlet and outlet. A schematic diagram of the recirculating 

water system is shown in Figure 2-6. 

Figure 2-5 Photograph of the specimen load train for the 2-liter autoclave. 

 
8 

1. COVER GASS SUPPLY TANK 19. ACCUMULATOR

2. TWO-STAGE HIGH-PRESSURE REGULATOR 20. RUPTURE DISC 

3. FLASH ARRESTOR 21. HEAT EXCHANGER (HX) 

4. LOW-PRESSURE REGULATOR 22. DRAIN 

5. FLOW METER 23. SYSTEM BLEED PORT 

6. CHECK VALVE 24. HEAT EXCHANGER OUTLET TC 

7. COMPOUND VACUUM & PRESSURE GAUGE 25. AUTOCLAVE PREHEATER 

8. PRESSURE RELIEF VALVE 26. PREHEATER OUTLET TC 

9. VENT TO AIR & FLASH ARRESTOR 27. COMMERCIAL AUTOCLAVE 

10. FEEDWATER STORAGE TANK 28. THERMOWELL 

11. SPARGE TUBE 29. “BAL SEAL” RETAINER 

12. WATER SAMPLE PORT 30. ECP CELL 

13. FEEDWATER FILL PORT 31. AIR-COOLED COIL 

14. FEEDWATER TANK RECIRCULATION PUMP 32. WATER COOLED HEAT EXCHANGER 

15. SOLENOID VALVE 33. BACK-PRESSURE REGULATOR (BPR) INLET TC 

16. HIGH-PRESSURE PUMP 34. BPR 

17. PRESSURE TRANSDUCER 35. PH METER 

18. HIGH-PRESSURE GAUGE 36. CONDUCTIVITY METER

Figure 2-6 Schematic diagram of the recirculating 2-liter autoclave system. 

The simulated PWR feedwater contains 2 ppm Li as LiOH, 1000 ppm B as HBO3, ≈2 ppm 

dissolved hydrogen (≈23 cm3/kg), and less than 10 ppb dissolved oxygen (DO) [10]. Water is 

circulated at relatively low flow rates (15-25 mL/min). The test temperatures were 

320°C [608°F]. 

Crack extensions are monitored by the reversing-direct current (DC) potential difference 

method, Figure 2-7. In this method, a constant DC current is passed through the test specimen 

V9

1

3

2

4

7

6

V2

V1

5 V2

10

9

11

8 3

V3

V22

V4

V5 V6

V8

V7

12

13

15 14

25

20

19

18

17

16

6

6

22

27

28

29

30

31

32

33

V16

12

12 36

V18 V19

V17

26

23

24

V20

22

V21
9 

and the crack length is measured through the changes in the electrical voltage at the crack 

mouth. The electrical voltage measured across the crack mouth is related to the unbroken 

crack ligament resistance through the Ohm’s law. Thus, as the crack advances, the length of 

the unbroken ligament decreases and its resistance increases. In short, as the crack advances 

the voltage measured across the crack mouth increases. Figure 2-7 shows a typical 

configuration of a CT specimen instrumented for crack growth measurements by the DC 

potential method: the current leads are welded on the top and bottom surfaces of the specimen, 

and potential leads are welded on the front face of the specimen across the machined notch but 

on diagonal ends. Also, to compensate for the effects of changes in resistivity of the material 

with time, an internal reference bar of the same material being tested is installed in series, near 

the test specimen. The voltage readings across the reference bar are used to normalize 

potential drop measurements for the CT test specimen. The changes in potential drop 

measurements for the CT test specimen are transformed into crack advance data using 

correlations developed for the specimen geometry that is tested. In practice, voltage readings 

are taken successively as the current is reversed, and, typically, 800 voltage readings are 

needed to generate 1 crack advance data point, approximately every 4 min. with a resolution of 

approximately 1-2 μm [0.039-0.079 mils]. 

Figure 2-7 Principle of crack length measurement by the DC potential method. 

2.5 CGR Test Methodology 

A typical CGR test at ANL consists of three stages: in-situ precracking, transitioning to SCC, 

and the SCC growth stage. At the end of the test the specimen is broken open, and the fracture 

surface is examined. The objective of each stage will be highlighted next. 

The objective of precracking is to produce a sharp crack tip. This is typically achieved by 

fatigue cracking, using a triangular waveform at load ratio R = 0.31, frequency of ≈1 Hz, and 

maximum stress intensity factor (Kmax) of 20-25 MPa·m1/2 [18.2-22.8 ksi·in1/2]. Under rapid 

cyclic loading, the crack growth is dominated by mechanical fatigue; hence, the known fatigue 

behavior of the alloy being tested is expected to be reproduced. In turn, this step ensures that a 

straight crack front has been produced. 

After approximately 0.5-mm (20 mils) extension in fatigue, the transitioning stage is initiated. 

The purpose of this stage is to transition from the fatigue/transgranular (TG) fracture mode to an 

SCC/intergranular (IG) fracture mode. As such, cycling is continued under loading conditions 

expected to foster environmental effects. In general, environmental enhancement of cyclic rates 

 

1 Load ratio R = Kmin/Kmax
10 

is typically observed under loading conditions that would lead to CGRs between 10-11 and 

10-9 m/s in air. To generate these rates, the load ratio R is increased incrementally to 0.5-0.7,

and the loading waveform is changed to a slow/fast sawtooth with rise times of 30-1000 s and

an unload time of 12 s. Transitioning to an IG SCC fracture mode is assessed by analyzing the

cyclic response. The analysis, described in detail in the subsequent section, relies in principle

on superposition. Under cyclic loading, the measured CGR is the superposition of mechanical

fatigue, corrosion fatigue, and SCC components. Thus, a crack is considered “transitioned”

when the SCC component is non-zero, that is, the measured CGR is larger than the sum of the

fatigue and corrosion fatigue components. Once the crack is transitioned to IG SCC, the

specimen is set at constant load. By eliminating the mechanical fatigue and corrosion fatigue

components, constant load allows for the SCC CGR to be measured directly. However, as the

crack grows in an IG fracture mode, it typically follows the least resistant grain boundary path.

As such, crack branching develops, and that in turn results in unbroken/uncracked ligaments.

As described in the previous section, the DC potential method measures the potential drop 

across the unbroken ligament in the sample; hence, the ligaments formed during the preferential 

SCC path often confound the DC potential measurement by making the crack appear shorter 

than it is in reality. As a result, the crack advance measured on the fracture surface of the 

specimen at the end of the test is almost always longer than that measured in-situ. Therefore, a 

correction of the DC potential data is almost always needed after the test is completed, and the 

DC potential data is compared to the actual crack advance measured on the fracture surface. 

The downside of this approach is that in the case of SCC tests conducted under multiple 

conditions resulting in the same fracture mode, e.g., multiple stress intensity factors or multiple 

test temperatures, the fracture surface cannot be used to distinguish between the various test 

periods. Hence, in complex tests, there is almost always an uncertainty in correlating the test 

conditions to the resulting fracture surface. Nevertheless, the uncertainty regarding the amount 

of crack growth during a test period at constant load can be minimized by introducing cycling 

loading at the end of that test period. This cyclic loading is typically a well-known condition for 

which the CGR is known precisely. If ligaments form during constant load, the resulting CGR 

during this subsequent test period is typically higher than the known rate. This is the case for as 

long as ligaments are broken, then the CGR eventually settles to the known rate once that 

process is complete. The point at which the rate settles to the known rate can be conservatively 

interpreted to signal the actual extent of crack advance during the previous test period at 

constant load. This approach results in a conservative CGR as it does not take into account the 

growth due to cyclic loading. 

As an alternative to the purely constant loading described previously, some form of cycling or 

partial periodic unloading (PPU) is introduced during the constant load test period with the 

purpose of breaking the ligaments as they form, and allow for a more realistic SCC CGR to be 

measured in real time. As a guideline, the cycle/periodic unloading is chosen to be subtle 

enough not to advance the crack by itself, but aggressive enough to be effective at breaking the 

ligaments. These experimental challenges have been recognized in industry publications [1,11], 

and periodic unloading is, in fact, recommended [1]. Such conditions have been used to 

generate a portion of the database used for generating the industry disposition curves [1,11]. 

The data generated at ANL conform to these guidelines. In addition, for each test conducted at 

ANL, the fatigue behavior is confirmed at the beginning of the test during precracking; this way 

the contributions from fatigue during constant load with periodic unloading or cycling plus hold 

conditions are calculated with precision during each test. Nevertheless, to increase confidence 

in the results, the objective of each ANL test is to measure the SCC CGR under not just one, 

but under several loading conditions.
11 

There are two types of PPU used at ANL to supplement and/or confirm the SCC CGR 

determinations under constant load: “constant load with periodic unloading” and “cycle + hold”. 

They are in principle similar, in that the constant load is interrupted periodically (“hold” time) by a 

unload/reload cycle. However, the nature of the loading cycle is different in each case, hence a 

different approach is undertaken in the interpretation of the response. For constant load with 

periodic unloading, the cycle is essentially an aggressive fatigue cycle, e.g. R = 0.5, 12 s rise / 

12 s unload times. This type of cycling results by itself in a transgranular (TG) fracture mode. 

Hence, if the resulting fracture mode is verified at the end on the test to be intergranular (IG), 

then it is assumed that most of the growth occurred at constant load during the hold time. The 

actual hold time under constant load can be set to result in a fatigue CGR less than the SCC 

CGR to be measured; for Alloy 52/152 weldments hold times of minimum 2h have typically been 

used to result in a CGRair of approx. 5×10-12 m/s. By contrast, “cycle + hold” involves a gentle 

cycle, e.g. R = 0.5, 600 s rise / 12 s unload times. This type of cycle is used during transitioning 

from TG to IG, and by itself usually results in an IG fracture mode. Hence, under “cycle + hold” 

IG SCC growth occurs under both cyclic loading and constant load (hold). In this case, in order 

to calculate the SCC CGR component (SCC growth under constant load), the cyclic contribution 

to the total growth is subtracted. As before, hold times of minimum 2h have typically been used. 

A post-test examination of the specimen is always conducted. Typically, all specimens are 

examined microscopically at the fracture surface and sometimes in the cross section. For the 

cross section examination, the two side surfaces are ground to remove the side grooves. The 

cross sections are then polished and etched. They are examined by scanning electron 

microscopy (SEM) to verify the planarity of the crack front and to determine the extent of crack 

branching. Next, the specimens are fractured to expose the fracture surface obtained during 

the test. The fracture surface is examined by SEM to measure the crack extension and to 

determine the fracture mode(s). The crack length measurements obtained on the fracture 

surface are used to correct the data obtained in-situ by the DC potential method. As described 

in the previous paragraph, the DC potential method typically underestimates the full extent of 

the crack, particularly during IG cracking. Hence, during the correction stage, the DC potential 

data is adjusted to match the measurements obtained on the fracture surface. The known 

relationships between the loading conditions and the expected fracture mode are used to the 

extent possible to substantiate the correction approach. 

2.6 Analysis of CGR Data 

Under cyclic loading, the CGR (m/s) in the environment, env a , can be expressed as the 

superposition of the rate in air (i.e., mechanical fatigue) and the rates due to corrosion fatigue 

and SCC ( C F a and a SCC  , respectively), given in previous reports [12-14] as: 

APPENDIX B a aaa env ai  r CF SCC    . (1) 

The cyclic CGRs for Ni alloys and welds in air were determined from correlations developed 

earlier at Argonne [12-14]: 

APPENDIX A    2.2 4.1

air r r

da a / t C 1 0.82 R K / t

dN

                    , (2) 

where da/dN is the growth rate per cycle, tr is the rise time for the loading cycle, R is the load ratio 

(i.e., ratio of the minimum and maximum stress intensity factors Kmin/Kmax), K is Kmax – Kmin
12 

in Mpa m1/2, and the constant C depends on the material and temperature. For Alloy 600, the 

constant (CA600) is a third-order polynomial with respect to temperature T (°C) [12-14], 

APPENDIX B -14 -17 -18 2 -21 3 C = 4.835 10 + (1.622 10 )T - (1.490 10 )T + (4.355 10 )T A600    .(3)

In LWR coolant environments, the CGRs of Alloy 600 show frequency-dependent enhancement 

under cyclic loading conditions. In high-DO water [i.e., normal water chemistry in boiling water 

reactor (BWR)], the environmental enhancement of the growth rates does not appear to depend 

on the material composition (e.g., C content) or material heat treatment. In contrast, 

environmental enhancement of CGRs of Alloy 600 in low-DO water does seem to be strongly 

dependent on material conditions. In the literature [15-19], such variability has been attributed 

to thermomechanically controlled parameters, such as yield strength and grain boundary 

coverage of carbides, although the evidence for this dependence is more substantial for steam 

generator tubing than for structural components. 

For Alloy 690, the constant CA690 is given by a third-order polynomial of temperature T (°C), 

expressed as [12]: 

APPENDIX C -14 -16 -18 2 -21 3 C = 5.423 10 + (1.83 10 )T - (1.725 10 )T + (5.490 10 )T . A690    (4) 

For Ni-alloy welds, including Alloys 82/182 and 52/152, the constant CNi-weld is given by a fourthorder polynomial with respect to temperature T (°C), expressed as [20]: 

APPENDIX D 

-14 -17 -18 2

Ni-weld

-20 3 -23 4

C = 8.659 10 - (5.272 10 )T + (2.129 10 )T

- (1.965 10 )T + (6.038 10 )T

 

 

 (5)

In earlier ANL work, correlations were developed to estimate the enhancement of cyclic CGRs 

in LWR environments relative to the CGRs in air under the same loading conditions. In the 

absence of any significant contribution of SCC to growth rate, the cyclic CGRs for Alloy 600, 

either in the solution annealed (SA) condition or the SA plus thermally treated (TT) condition, in 

≈300 ppb DO water at 289°C are given by the expression [12]: 

APPENDIX E  0.33 7

env,A600 air,A600 air,A600 a a 4.4 10 a       . (6)

In low-DO environments (e.g., hydrogen water chemistry for the BWR or PWR environment) at 

320°C (608°F), some alloys show little enhancement, while others show enhancement 

comparable to that predicted by Eq. 6. The environmental enhancement of Alloy 690 [12, 13] 

was found to be almost always less that that predicted by Eq. 6. 

Similarly, correlations describing the cyclic CGRs of Ni-alloy welds (e.g., Alloys 182 and 82) 

have been developed [20, 21]. Under similar loading conditions, the CGRs of Ni-alloy welds are 

a factor of 2-3 higher than those of Alloy 600. The analysis indicated that the cyclic CGRs of Nialloy welds in PWR water are represented by the expression: 

APPENDIX F  0.78

env,Ni weld air,Ni weld air,Ni weld a a0.018 a       . (7)

Figure 2-8 summarizes the expected behaviors for cyclic rates in air and environment for Alloys 

600, 690 and Ni-base welds as described by Eqs. 2-7. All data is plotted as a function of the 

predicted behavior for Alloy 600 in air. 
13 

Figure 2-8 CGRs in air and environment for Alloys 600, 690 and Ni-base welds as a 

function of predicted rates in air for Alloy 600 (data taken from Refs. 12, 

13, 20). 

The SCC growth rate data for Alloy 600 and its weld metals have been reviewed in MRP-55 [11] 

and MRP-115 [1] to determine the effects of critical parameters such as stress intensity factor, 

temperature, material heat treatment, cold work, and water chemistry on growth rates. For Alloy 

600, the CGR (m/s) under SCC conditions is represented by the expression [11], 

APPENDIX G A600 th

ref

Q1 1 a exp (K K ) RT T

    

           

 , (8) 

where: Q = activation energy for crack growth (130 kJ/mol for Alloy 600) 

 R = universal gas constant (8.314×10-3 kJ/mol K) 

T = absolute operating temperature in units of K 

Tref = absolute reference temperature to normalize the CGR data (598 K) 

α = crack growth amplitude (2.67×10-12 at 325°C), 

K = crack tip stress intensity factor in units of MPa·m1/2, 

Kth = crack tip stress intensity factor threshold (9 MPa·m1/2), and 

β = exponent 1.16. 

The effect of K on the SCC growth rate for Ni-alloy welds in PWR environments has been 

represented by a modified [1] version of the above relationship. Unlike the CGR relationship for 

Alloy 600, the relationship for Ni-alloy welds has no threshold value for the stress intensity 

factor K, 

APPENDIX H Ni weld

ref

Q1 1 a exp K RT T

 

   

          

 , (9) 

10-11

10-10

10-9

10-8

10-7

10-11 10-10 10-9 10-8 10-7

CGR env 600 (NUREG-4667)

CGR air 690 (NUREG-6383)

CGR air weld (NUREG-6921)

CGR env weld (NUREG-6921)

CGRenv (m/s)

CGRair (m/s)

CGR env Ni-weld 

CGR env 600

CGR air 600

CGR air 690

CGR air Ni-weld
14 

where Q, R, T, and Tref are the same as in Eq. 8, the crack growth amplitude α is 1.5×10-12 at 

325°C, and exponent β is 1.6. Also, unlike Alloy 600, for which a reliable value for the activation 

energy for crack growth was determined, no such number is available for the Ni-weld alloys. 

Thus, for Ni-weld alloys, the activation energy is assumed to be the same as that for Alloy 600. 

Figure 2-9 illustrates how the superposition concept introduced earlier is used to analyze the 

cyclic CGR data generated in a SCC test on Alloy 182 weld. A typical test at ANL consists of 

three stages: in-situ precracking, transitioning to SCC, and the SCC growth stage. The 

precracking stage is dominated by mechanical fatigue, hence, in this stage of the test where 

CGR rates are typically larger than 10-9 m/s, the expectation is that the measured CGRs are 

close to those expected under the same loading conditions in air, air a (often called the “air line”), 

and is calculated using Eqs. 2 and 3. During the transitioning to IG SCC stage, cyclic loading is 

continued under loading conditions expected to induce environmental enhancement. The 

environmental enhancement is typically observed under loading conditions that lead to CGRs 

between 10-11 and 10-9 m/s in air, and the effect of the additional corrosion fatigue component 

is labeled air CF a a    in the figure. For a typical Ni-base weld, the corrosion fatigue behavior is 

expressed by Eq. 6. Finally, if an SCC component is also present, the specimen response is 

expected to follow the curve labeled aaa   air CF SCC   in the figure. For the purpose of the 

illustration shown in Figure 2-9, the a SCC  component was calculated using Eq. 9, and 

represents the SCC CGR of an alloy with a cracking susceptibility ranking at the 75th percentile. 

Figure 2-9 Cyclic CGRs for typical Ni-base weld tested in a PWR environment. Expected 

corrosion fatigue (Eq. 7, green) and SCC (Eq. 9, blue) curves are included. 

In the specific case of tests in the first weld layer described in this report, the dendritic grains are 

normal to the crack growth plane, hence, in most cases, IG SCC is likely to be off-plane, in an 

orientation that prevents the CGR from being measured by DC potential correctly. Therefore, in 

order to be able to measure SCC growth in the current tests, locations prone to IG SCC 

propagating in the test crack growth plane had to be identified prior to the SCC CGR 

determinations. This was accomplished by monitoring the cyclic response and comparing that 

with prior experience. Specifically, in these tests, the crack was advanced until an 

environmental enhancement of similar to that obtained in prior tests on Alloy 152 in which the 

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-12 10-11 10-10 10-9 10-8 10-7 10-6

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloy 182

Simulated PWR Water at 320°C 

K = 28 MPa·m1/2

air a

air CF SCC aaa    

air CF a a   
15 

direction of propagation was parallel to the dendritic grains. Of reference are tests conducted at 

ANL on an Alloy 152 weld that was produced in a symmetric, double-J geometry, as shown in 

Figure 2-10 [22, 23]. In those tests it was found that environmental enhancement peaks during 

cyclic with load ratios of R = 0.5, and rise time of 600s, and the resulting fracture mode is IG. 

Based on that experience, a similar level of environmental enhancement in the current tests will 

be interpreted as IG SCC propagation in a forward direction that can readily be measured by 

DC potential, and the specimen will be set at constant load. 

(a) (b) 

Figure 2-10 (a) Cyclic CGR data for the Alloy 152 weld tested in primary water 

environment, and (b) Alloy 152 weld produced in a double-J geometry.

10-12

10-11

10-10

10-9

10-8

10-7

10-12 10-11 10-10 10-9 10-8 10-7

A152-TS-2

A152-TS-4

A152-TS-5

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloy 152 Weld

Simulated PWR Water at 320°C 

Best Fit Curve for Alloy 182

CGRair + 0.018 (CGRair)

0.78

R = 0.3

R = 0.5

R = 0.7

17 

3 RESULTS 

This section presents the SCC CGR test data obtained on Alloys 52M WOL and 152 weld in the 

first layer configuration. The tests are presented in chronological order, as “lessons learned” 

from the early tests were used to inform the management of the subsequent tests. The 

specimens and areas to be tested were selected randomly in the regions of interest. As 

described previously, the microstructural evaluation, including Cr levels were determined along 

the actual SCC paths during the post-test examination of the specimens. 

3.1 SCC CGR Testing of Alloy 52M WOL 

SCC CGR testing on the Alloy 52M-182 WOL was conducted in two orientations, TS and ST 

(Fig. 3-1). Initially, the SCC CGR testing was conducted in the TS orientation on two specimens 

with the purpose of observing the behavior of the SCC crack propagating from Alloy 182 into the 

Alloy 52M WOL. The subsequent testing in the ST orientation was conducted to confirm the 

observations resulting from the initial (TS-oriented) tests. 

Figure 3-1 Photograph of the Alloy 52M-182 WOL. The SCC CGR test directions, TS and 

ST, are indicated in the figure. 

3.1.1 Specimen A52M-182-TS-3 

The first SCC CGR test involved specimen A52M-182-TS-3, shown in Fig. 3-2. The initial notch 

was measured on the lateral surfaces to be approximately 3.5 mm from the weld interface. The 

specimen was fatigue precracked and transitioned to SCC in Alloy 182. Then the crack was 

advanced toward the interface using gentle loading conditions to maintain the IG SCC fracture 

mode. Past the interface, the fast cycling resumed and the crack was advanced in Alloy 

52M where it was transitioned again. Finally, the test ended with fast cycling to mark the 

fracture surface. 
18 

Figure 3-2 Photograph of Alloy 52M-182 WOL specimen A52M-182-TS-3 prior to the 

SCC test. 

The testing conditions and resulting CGR data corrected as described in the previous section 

are given in Table 3-3; the portion on the test that took place in Alloy 182 is shaded with grey. 

The crack length and Kmax vs. time plots are shown in Fig. 3-2. 

The test was initiated with precracking in the environment, followed by IG transitioning steps 

(periods precracking-4, Table 3-1). As expected, transitioning in Alloy 182 occurred readily, with 

cyclic rates in excellent agreement with previous data on the same weld alloy. Next, the 

specimen was set at constant load approximately 1 mm from the interface with Alloy 52M. The 

initial SCC CGR response (period 5) was in agreement with the rates measured previously on 

this weld (1.4 and 1.7x10-10 m/s [6], shown on the plot in Figure 3-3b). Following an 

uncharacteristic slowing of the CGR (Figure 3-b), especially when compared to the known 

behavior (specimen A182-TS-1 was tested previously without the WOL), the immediate need 

was to straighten the crack front. Hence, a loading condition with well-known response was 

employed, sawtooth loading at R = 0.5, 1000s rise /12s down times, to advance the crack. 

Upon starting cycling (period 6), a “jump” in crack advance was observed immediately, 

suggesting that ligaments were being broken. Given the fact that in this type of test a precise 

measurement of the crack advance is essential, it was decided to continue the test with a 

succession of periods consisting of cycle (“control”), cycle + hold (C+H) and constant load with 

periodic unloading (CL + PU). These periods are marked in the plots shown in Fig. 3-3. By 

using superposition, SCC CGR components were calculated for all C+H conditions. The 

resulting rates were re-verified subsequently at CL + PU. The fracture surface will demonstrate 

that that all these loading conditions (periods 5-23, Table 3-1) maintained the IG fracture mode 

in both Alloys 182 and 52M. 

After reaching the interface (test periods 17-18, Fig. 3-3d) the gentle cyclic conditions were 

maintained for approximately 3000h. The post-test examination of the specimen – which will be 

presented later in this section – showed that at this stage, the crack front branched along the 

interface, in a direction perpendicular to the original direction of propagation, and into Alloy 52M 

along the original direction of propagation. 

Next, the crack was advanced in Alloy 52M (periods 24-72, Table 3-1). The response to fast 

cyclic conditions was inconsistent; the breaking of ligaments during the straightening of the 

crack front was also likely to play a role. A baseline fatigue response (“air line”) for Alloy 52M 

cyclic rates could not be established. In addition, the now fully-grown interface cracks relieved 
19 

the stress driving the main crack. Very likely, the CGRs measured at this stage were affected 

by the diminished stress intensity factor at the crack tip. 

Finally, the response to fast cycling stabilizes (periods 77-79), suggesting that the fracture 

surface has somewhat straightened. An “air line” for Alloy 52M could be established. The CGR 

response was overall much less than expected, perhaps due to the lower than calculated stress 

intensity factors. Nevertheless, the response was consistent and the known R-dependence 

(Fig. 2-10a) was reproduced. Test periods 80-96, Table 3-1, correspond to IG transitioning in 

Alloy 52M. Several SCC CGR determinations were made in Alloy 52M in test periods 94-98, 

however, given the abnormally low cyclic response preceding and subsequent to these 

measurements, the stress intensity factors are deemed highly unreliable. 

Table 3-1 Crack growth data for specimen A52M-182-TS-3 of Alloy 152 weld in 

PWR watera,b

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time, 

Down 

Time, 

Hold 

Time, Kmax, ∆K, CGRenv, 

Estimated 

CGRair, 

Crack 

Length, 

Period h C R s s s Mpa·m1/2 Mpa·m1/2 m/s m/s mm 

Pre a 53 320.6 0.29 2 2 21.4 15.2 3.02E-09 1.76E-08 12.079 

Pre b 69 320.4 0.29 50 50 21.5 15.3 2.69E-09 7.19E-10 12.158 

Pre c 75 321.1 0.29 2 2 23.1 16.4 5.42E-08 2.42E-08 12.683 

Pre d 76 321.0 0.29 5 5 23.2 16.5 3.75E-08 9.96E-09 12.780 

Pre e 78 321.1 0.29 2 2 23.8 16.9 8.53E-08 2.74E-08 12.941 

Pre f 93 320.8 0.29 50 50 24.5 17.4 5.88E-09 1.23E-09 13.144 

Pre g 94 320.7 0.29 2 2 25.2 17.9 9.79E-08 3.48E-08 13.351 

1 100 321.1 0.49 50 12 25.4 12.9 3.20E-09 6.29E-10 13.439 

2 120 320.5 0.50 300 12 25.8 12.9 9.62E-10 1.05E-10 13.501 

3 145 320.7 0.50 600 12 26.0 13.0 5.52E-10 5.45E-11 13.546 

4 189 320.5 0.50 1000 12 26.2 13.1 4.47E-10 3.38E-11 13.618 

5 723 320.9 1.00 0 0 26.7 0.0 1.30E-10 - 13.768 

6 746 320.6 0.50 1000 12 27.4 13.7 5.73E-10 4.04E-11 13.914 

7 1,055 320.5 0.50 12 12 7,200 27.4 13.7 7.51E-11 - 13.918 

8 1,078 320.5 0.50 1000 12 27.8 13.9 3.49E-10 4.34E-11 14.019 

9 1,107 320.7 0.50 1000 12 7,200 28.1 14.0 5.47E-11 5.49E-12 14.022 

10 1,439 320.0 0.50 12 12 7,200 28.4 14.2 5.30E-11 6.52E-12 14.082 

11 2,351 319.6 0.50 12 12 7,200 31.5 14.5 4.86E-11 - 14.250 

12 2,613 319.7 0.54 1000 12 32.4 14.9 1.98E-10 - 14.448 

13 2,908 319.8 0.54 1000 12 3,600 32.8 15.1 8.00E-11 1.48E-11 14.513 

14 3,959 320.4 0.54 12 12 7,200 33.5 15.4 3.24E-11 - 14.633 

15 4,131 320.7 0.54 1000 12 34.1 15.7 1.80E-10 8.10E-11 14.755 

16 4,374 320.4 0.54 1000 12 3,600 34.4 15.8 6.73E-11 1.82E-11 14.795 

17 5,062 321.7 0.54 12 12 7,200 34.7 15.9 2.69E-11 - 14.862 

18 5,306 321.3 0.54 1000 12 35.9 16.5 1.79E-10 1.00E-10 15.042 

19 5,494 321.9 0.54 1000 12 3,600 36.1 16.6 6.22E-11 2.24E-11 15.065 

20 5,974 322.2 0.54 12 12 7,200 36.3 16.7 2.44E-11 - 15.103 

21 6,223 322.5 0.54 1000 12 37.8 17.4 1.67E-10 1.25E-10 15.308 

22 6,553 322.7 0.54 1000 12 3600 38.0 17.5 4.77E-11 3.58E-11 15.340 

23 7,106 322.7 0.54 12 12 7200 38.2 17.6 1.83E-11 - 15.379 

24 7,415 323.0 0.54 1000 12 27.6 12.7 1.27E-11 3.51E-11 15.408 

25 8,117 323.2 0.54 1000 12 3600 27.8 12.8 6.62E-12 7.77E-12 15.416 

26 8,136 321.3 0.54 100 12 27.8 12.8 2.78E-10 3.52E-10 15.480 

27 8,160 321.4 0.54 100 12 27.9 12.8 1.47E-10 3.57E-10 15.496 

28 8,168 321.2 0.54 12 12 28.0 12.9 7.23E-10 3.01E-09 15.507 

29 8,184 321.3 0.54 100 12 28.0 12.9 1.24E-10 3.63E-10 15.512 

30 8,190 321.1 0.54 12 12 28.1 12.9 6.30E-08 3.04E-09 15.525 
20 

Table 3-1 (Cont.) 

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time, 

Down 

Time, 

Hold 

Time, Kmax, ∆K, CGRenv, 

Estimated 

CGRair, 

Crack 

Length, 

Period h C R s s s Mpa·m1/2 Mpa·m1/2 m/s m/s mm 

31 8,257 321.2 0.54 300 12 28.1 12.9 4.70E-11 1.22E-10 15.533 

32 8,263 321.3 0.54 12 12 28.2 13.0 4.63E-10 3.09E-09 15.540 

33 8,280 321.2 0.54 100 12 28.2 13.0 1.09E-10 3.71E-10 15.545 

34 8,288 321.5 0.54 12 12 27.3 12.5 4.90E-10 2.70E-09 15.353 

35 8,304 321.2 0.54 100 12 28.3 13.0 9.36E-11 3.75E-10 15.557 

36 8,315 321.3 0.54 12 12 28.3 13.0 5.43E-10 3.16E-09 15.569 

37 8,352 321.4 0.54 100 12 28.4 13.0 9.15E-11 3.82E-10 15.578 

38 8,360 321.4 0.54 12 12 28.4 13.1 5.79E-10 3.22E-09 15.585 

39 8,448 321.2 0.54 300 12 28.5 13.1 4.58E-11 1.29E-10 15.598 

40 8,450 321.4 0.54 12 12 28.6 13.1 5.85E-10 3.27E-09 15.607 

41 8,471 321.2 0.54 100 12 28.6 13.1 9.24E-11 3.93E-10 15.611 

42 8,480 321.3 0.54 12 12 28.6 13.1 6.25E-10 3.27E-09 15.622 

43 8,496 321.4 0.54 100 12 28.6 13.2 1.09E-10 3.96E-10 15.627 

44 8,505 321.3 0.54 12 12 28.7 13.2 6.08E-10 3.33E-09 15.638 

45 8,520 321.2 0.54 100 12 28.9 13.3 9.48E-11 4.09E-10 15.671 

46 8,528 321.3 0.54 12 12 28.8 13.2 6.78E-10 3.36E-09 15.652 

47 8,592 321.4 0.54 300 12 28.8 13.2 4.71E-11 1.35E-10 15.662 

48 8,600 321.5 0.54 12 12 28.9 13.3 7.27E-10 3.43E-09 15.673 

49 8,616 321.4 0.54 100 12 28.9 13.3 9.66E-11 4.12E-10 15.678 

50 8,619 321.1 0.30 5 5 28.8 20.2 4.91E-09 2.33E-08 15.722 

51 8,682 321.0 0.30 100 100 29.0 20.3 2.72E-10 1.20E-09 15.748 

52 8,686 321.0 0.30 10 10 29.2 20.4 2.50E-09 1.23E-08 15.775 

53 8,689 321.0 0.30 50 50 29.3 20.5 5.21E-09 2.50E-08 15.800 

54 8,708 321.1 0.30 50 50 29.3 20.5 3.47E-10 2.52E-09 15.805 

55 8,714 321.0 0.30 10 10 29.4 20.6 1.36E-09 1.27E-08 15.821 

56 8,734 321.1 0.30 50 50 29.5 20.6 2.85E-10 2.56E-09 15.828 

57 8,739 321.1 0.30 10 10 29.6 20.7 1.15E-09 1.30E-08 15.845 

58 8,756 321.1 0.30 50 50 29.6 20.7 2.92E-10 2.60E-09 15.845 

59 8,763 321.0 0.30 12 12 29.7 20.8 9.12E-10 1.10E-08 15.866 

60 8,778 321.0 0.30 50 50 29.7 20.8 3.45E-10 2.65E-09 15.873 

61 8,786 321.0 0.30 12 12 29.8 20.9 1.17E-09 1.12E-08 15.893 

62 8,874 321.0 0.30 100 100 30.0 21.0 3.04E-10 1.38E-09 15.925 

63 8,880 321.1 0.30 12 12 30.2 21.1 1.36E-09 1.17E-08 15.947 

64 8,949 321.1 0.30 50 50 30.5 21.4 4.58E-10 2.95E-09 16.006 

65 9,043 321.1 0.30 100 100 30.8 21.6 3.27E-10 1.53E-09 16.052 

66 9,050 321.2 0.30 50 50 30.9 21.7 5.48E-10 3.13E-09 16.068 

67 9,183 321.6 0.30 100 100 31.4 22.0 3.70E-10 1.68E-09 16.157 

68 9,192 321.4 0.30 2 2 32.4 22.7 1.01E-08 9.45E-08 16.303 

69 9,209 321.6 0.30 50 50 32.5 22.8 7.65E-10 3.85E-09 16.321 

70 9,216 321.9 0.30 2 2 33.3 23.3 9.70E-09 1.06E-07 16.450 

71 9,236 321.8 0.30 50 50 33.5 23.4 8.21E-10 4.36E-09 16.472 

72 9,242 321.7 0.30 2 2 33.8 23.7 1.03E-08 1.14E-07 16.521 

73 9,283 321.6 0.30 50 50 34.8 24.4 9.13E-10 5.10E-09 16.649 

74 9,287 321.5 0.30 2 2 32.8 23.0 3.53E-09 9.95E-08 16.709 

75 9,303 321.5 0.30 50 50 33.3 23.3 2.52E-10 4.25E-09 16.713 

76 9,312 321.6 0.30 2 2 33.4 23.4 4.65E-09 1.08E-07 16.787 

77 9,326 321.5 0.30 50 50 34.1 23.9 4.21E-10 4.69E-09 16.792 

78 9,336 321.6 0.30 2 2 34.3 24.0 5.86E-09 1.19E-07 16.881 

79 9,359 321.7 0.30 50 50 34.5 24.1 5.45E-10 4.91E-09 16.898 

80 9,383 321.7 0.50 100 12 34.6 17.3 1.91E-10 1.08E-09 16.930 

81 9,448 321.5 0.50 300 12 34.8 17.4 3.73E-11 3.64E-10 16.948 

82 9,545 321.7 0.50 600 12 34.8 17.4 5.16E-11 1.84E-10 16.965 

83 9,616 321.8 0.50 1000 12 34.9 17.4 3.31E-11 1.11E-10 16.974 

84 9,661 321.6 0.60 1000 12 35.2 14.1 1.44E-11 6.41E-11 16.977 

85 9,728 321.3 0.60 1000 12 35.2 14.1 1.18E-11 6.39E-11 17.020 

86 9,826 320.8 0.70 1000 12 35.2 10.6 2.72E-12 2.88E-11 17.022 

87 10,044 321.0 0.50 1000 12 35.4 17.7 2.68E-11 1.17E-10 17.048 

88 10,477 320.4 0.50 1000 12 7200 35.5 17.8 5.47E-12 1.43E-11 17.058 

89 10,549 320.4 0.50 300 12 36.1 18.0 1.08E-10 4.18E-10 17.119 
21 

Table 3-1 (Cont.) 

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time, 

Down 

Time, 

Hold 

Time, Kmax, ∆K, CGRenv, 

Estimated 

CGRair, 

Crack 

Length, 

Period h C R s s s Mpa·m1/2 Mpa·m1/2 m/s m/s mm 

90 10,740 320.0 0.50 600 12 36.3 18.1 3.71E-11 2.13E-10 17.145 

91 10,913 319.8 0.50 1000 12 36.3 18.2 2.10E-11 1.28E-10 17.155 

92 11,011 319.9 0.30 2300 12 39.4 27.6 1.03E-10 1.81E-10 17.192 

93 11,247 319.9 0.30 4600 12 39.8 27.9 5.12E-11 9.42E-11 17.235 

94 11,701 319.1 0.30 4600 12 7,200 40.1 28.1 2.44E-11 3.76E-11 17.269 

95 11,966 319.3 0.30 4600 12 14,400 40.2 28.2 1.53E-11 2.36E-11 17.285 

96 12,109 319.1 0.30 4600 12 28,800 40.3 28.2 8.72E-12 1.35E-11 17.289 

97 12,124 319.0 0.50 12 12 28,800 40.3 20.2 4.04E-12 6.77E-12 17.289 

98 12,241 319.4 1.00 0 0 40.2 0.0 5.37E-12 - 17.297 

99 12,246 319.2 0.50 12 12 40.7 20.4 2.14E-09 1.70E-08 17.346 

100 12,268 319.2 0.50 12 12 40.9 20.4 1.55E-09 1.72E-08 17.359 

101 10,350 319.2 0.50 20 20 40.9 20.5 9.17E-10 1.04E-08 17.364 

102 12,288 319.2 0.50 100 12 41.0 20.5 2.17E-10 2.10E-09 17.375 

103 12,292 319.2 0.50 12 12 41.2 20.6 9.62E-10 1.77E-08 17.388 

104 12,312 319.2 0.50 100 12 41.2 20.6 1.72E-10 2.14E-09 17.397 

105 12,316 319.2 0.50 12 12 41.3 20.7 9.03E-10 1.80E-08 17.405 

106 12,383 319.2 0.50 300 12 41.4 20.7 8.83E-11 7.27E-10 17.414 

a

 Simulated PWR water with 2 ppm Li, 1000 ppm B, and 2 ppm. DO<10 ppb. Conductivity was 213 μS/cm, and pH 6.4. b

 Data was corrected using fractography. 

Figure 3-3 Crack–length–vs.–time for specimen A52M-182-TS-3 in simulated PWR 

environment during test periods: (a) precracking-4, (b) 5-8, (c) 9-14, (d) 15-19, 

(c) 18-23, (f) 24-25. (g) 24-79, (h) 80-89, (i) 90-98, and (j) 99-106. 

11.60

12.00

12.40

12.80

13.20

13.60

14.00

10

20

30

40

50

60

40 60 80 100 120 140 160 180 200

Crack Length (mm)

Kmax (MPa m0.5)

Time (h)

Kmax

Crack Length

Alloy 52M/182 WOL

Specimen # A52M-182-TS-3

320°C, Simulated PWR Water

Pre c

Pre a

1 2 3

Pre b

Pre f

4
22 

Figure 3-3 (Cont.)

(b) 

(c) 

(d) 

13.50

13.60

13.70

13.80

13.90

14.00

14.10

10

20

30

40

50

60

200 400 600 800 1000 1200

Crack Length (mm)

Kmax (MPa m0.5)

Time (h)

Kmax

Crack Length

Alloy 52M/182 WOL

Specimen # A52M-182-TS-3

320°C, Simulated PWR Water

Period 5

average CGR 1.3 x 10–10 m/s

26.7 MPa m0.5

Constant load 

Period 7

7.5 x 10–11 m/s

27.4 MPa m0.5

Constant load with 

periodic unloading

6

C

1.7 x 10–10 m/s

7

C

8

C+H

A182-TS-1

1.7 x 10–10 m/s

13.90

14.00

14.10

14.20

14.30

14.40

14.50

14.60

14.70

20

40

60

80

100

1000 1500 2000 2500 3000 3500 4000

Crack Length (mm)

Kmax (MPa m0.5)

Time (h)

Kmax

Crack Length

Alloy 52M/182 WOL

Specimen # A52M-182-TS-3

320°C, Simulated PWR Water

Period 10

5.3 x 10–11 m/s

28.4 MPa m0.5

Constant load with 

periodic unloading

8 9 Period 11

4.9 x 10–11 m/s

31.5 MPa m0.5

Constant load with 

periodic unloading

12

C

1

C+H

Period 14

3.2 x 10–11 m/s

33.5 MPa m0.5

Constant load with 

periodic unloading

14.60

14.70

14.80

14.90

15.00

15.10

20

40

60

80

100

4000 4200 4400 4600 4800 5000 5200 5400 5600

Crack Length (mm)

Kmax (MPa m0.5)

Time (h)

Kmax

Crack Length

Alloy 52M/182 WOL

Specimen # A52M-182-TS-3

320°C, Simulated PWR Water

Period 17

2.7 x 10–11 m/s

34.7 MPa m0.5

Constant load with 

periodic unloading

15

C

16

C+H

52M/182 interface

18

C 19

C+H
23 

Figure 3-3 (Cont.) 

(h) 

(i) 

(j) 

16.80

16.85

16.90

16.95

17.00

17.05

17.10

17.15

17.20

10

20

30

40

50

60

9200 9400 9600 9800 10000 10200 10400 10600 10800

Crack Length (mm)

Kmax (MPa m0.5)

Time (h)

Kmax

Crack Length

Alloy 52M/182 WOL

Specimen # A52M-182-TS-3

320°C, Simulated PWR Water

80 81 82 83 84 85 86 87

17.00

17.05

17.10

17.15

17.20

17.25

17.30

17.35

17.40

10

20

30

40

50

60

10500 11000 11500 12000

Crack Length (mm)

Kmax (MPa m0.5)

Time (h)

Kmax

Crack Length

Alloy 52M/182 WOL

Specimen # A52M-182-TS-3

320°C, Simulated PWR Water

89 90 91 92

0.5

300/12

0.5

600/12

0.5

1000/12

0.3

2300/12

93

0.3

4600/12

0.3

4600/12

2h

94

95 96 98

0.3

4600/12

4h

0.3

4600/12

8h

Constant

Load

17.25

17.30

17.35

17.40

17.45

10

20

30

40

50

60

12200 12250 12300 12350 12400 12450 12500

Crack Length (mm)

Kmax (MPa m0.5)

Time (h)

Kmax

Crack Length

Alloy 52M/182 WOL

Specimen # A52M-182-TS-3

320°C, Simulated PWR Water

Periods 99-106
24 

The first step in the post-test examination of this specimen involved the two side surfaces. For 

this purpose, the sides of the specimen were ground to remove the side grooves, then polished, 

and etched. The SEM images of the two cross sections are shown in Fig. 3-4. As expected, 

the crack initiated in the Alloy 182 weld and propagated into the Alloy 52M interface. In each 

figure, several locations of interest are marked, however, the region of highest interest was the 

interaction of the crack with the Alloy 52M WOL interface. 

On the first cross section examined (Fig 3-4a), the crack started – as expected – as a fatigue 

crack and transitioned to SCC in Alloy 182. The first unusual behavior was observed at the 

interface with Alloy 52M (location A), where the crack changes direction and propagates along 

the interface. This behavior is shown with additional detail in Fig. 3-5a. The propagation along 

the interface is substantial, approximately 0.3 mm, then, the crack branches into Alloy 52M. 

The crack appearance suggests an IG fracture mode. 

On the second cross section examined (Fig 3-4b), the crack started in similar fashion, as a 

fatigue crack and was transitioned to SCC in Alloy 182. Crack branching was observed at 

location A in Alloy 182, however, crack branching is typical for a weld alloy. Nevertheless, the 

introduction of periodic unloading apparently minimized the effect of the ligaments ahead of the 

interface. Moreover, given that crack branching occurred despite the periodic unloading, it 

appears that perhaps a more aggressive periodic unloading would have been more appropriate 

for this type of test. 

The crack interaction with the Alloy 52M interface is similar to that observed on the first cross 

section (location B in Fig 3-4b). This behavior is shown with additional detail in Fig. 3-5b. Of 

interest is the crack that branches off the main crack front, and propagates in Alloy 52M near 

the interface, Fig. 3-5b. As with the crack observed on the first cross section, the growth is 

substantial, approximately 0.7 mm. The morphology seems IG, and it is possible for this 

particular crack to have propagated at a rate of the order 10-10 m/s since that amount of growth 

occurred over 2000-3000 h.
25 

Figure 3-4 The two side surfaces of Specimen A52M-182-TS-3. Crack advance is from left 

to right (a), and right to left (b). The green arrows show the interface between 

the two welds and the red arrows indicate the end of the test. (a) 

(b)
26 

(a) (b) 

Figure 3-5 Interaction with the Alloy 52M interface (a) location A in Fig. 3-4a, crack 

propagation is from left to right, and (b) location B in Fig. 3-4b, crack 

propagation is from right to left. 

In order to further examine the crack behavior at the interface and the paths of the branching 

cracks, additional images were obtained at the crack intersection with the interface. Then, SEM 

Energy Dispersive X-ray Spectroscopy (EDX) Cr concentration maps were obtained from the 

same regions. In these maps, the higher color intensity reflects a higher Cr concentration. 

Finally, the backscatter SEM images were overlapped onto the Cr maps. The results for the two 

regions where the crack interacts with the Alloy 52M WOL are shown in Figs. 3-6 and 3-7. It 

appears that in both cases, the crack impinging on the interface branches at the interface or 

after crossing the interface, and propagates in Cr-diluted Alloy 52M, in a direction parallel to the 

interface, in what appears to be an IG mode. The observations are substantiated by the 

individual Cr concentrations measured by SEM EDX at select locations along those cracks. 

Overall, the examination of the two cross sections revealed that the test progressed largely as 

expected, and the crack advanced from Alloy 182 into Alloy 52M; extensive cracking 

propagating in Alloy 52M in a direction along the interface between the two welds was 

also observed. 
27 

(a) 

(b) 

Figure 3-6 SCC interaction with the Alloy 52M WOL interface (location A in Fig. 3-4a): (a) 

overlap of SEM image and elemental map, and (b) Cr concentration (wt. %) at 

each location. Crack propagation is from left to right. Green arrows indicate 

the Alloy 52M-182 interface. 
28 

(a) 

(b) 

Figure 3-7 SCC interaction with the Alloy 52M WOL interface (location B in Fig. 3-4b): (a) 

overlap of SEM image and Cr map, and (b) Cr concentration (wt. %) at each 

location. Crack propagation is from right to left. Green arrows indicate the 

Alloy 52M-182 interface. 
29 

Next, the specimen was broken into two halves to examine the fracture surface. The two 

resulting fracture surfaces are shown in Fig. 3-8. The outcome demonstrates that cracking 

along the Alloy 52M-182 interface was more severe than was originally inferred from the 

examination of the two lateral cross sections. In fact, for the most part, it was the major crack in 

this specimen. The schematic shown in Fig. 3-9 will be used to describe the observed behavior. 

Figure 3-8 Fracture surfaces of Specimen A52M-182-TS-3. 

Figure 3-9 Crack interaction with the Alloy 52M interface. Crack propagation is from left 

to right. The major crack directions are indicated. 

Figure 3-9 shows the cross section of the test specimen with several crack propagation 

directions marked. Initially, the crack propagated along direction 1a towards the interface. Upon 

reaching the interface, the crack branched into three directions. While the crack partially 

continued along the forward direction 1b, cracking also developed parallel along the interface 

and into Alloy 52M along directions 2 and 3. Direction 2 turned out to be the most prominent. 

Post test, the specimen fractured primarily along this direction. 

 
30 

Figure 3-10 shows additional images of the two resulting specimen halves; the photos were 

oriented to match the crack directions illustrated in Fig. 3-9. The crack propagated as expected 

in Alloy 182 along the initial direction 1a, then branched at the interface. There is evidence for 

propagation along the original (forward) direction 1b, and along the interface in both directions 2 

and 3. As noted previously, propagation along direction 2 appeared to be the most severe. 

Figure 3-10 The two halves of fractured specimen A52M-182-TS-3. 

Figure 3-11 shows additional pictures taken at various angles to better illustrate the severity of 

the cracking. 

Figure 3-11 Fractured specimen A52M-182-TS-3. 
31 

For the CGR data analysis, the fracture surface shown on the left side of Fig. 3-8 was chosen 

because it was judged to possess the necessary details pertaining to propagation along the 

initial direction (direction 1 in Fig. 3-9). Such details are necessary for the correction and 

interpretation of the DC potential data. This fracture surface is shown in Fig. 3-12 both as a 

photograph and as an SEM micrograph. The relationship with respect to the two sides of the 

specimen discusses previously (Fig. 3-14) is indicated in each figure. Also, the interface 

between Alloys 182 and 52M is indicated by arrows. The fracture surfaces show that, as 

expected, the crack propagated from the initial notch, transitioned to an IG mode in Alloy 182 

after approximately 1.9 mm, and reached the interface located at 2.9 mm from the initial notch. 

This SCC front in Alloy 182 appears straight, suggesting that the crack reached the interface as 

a front rather than as individual “fingers”. 

(a) 

(b) 

Figure 3-12 Fracture surface of Specimen A52M-182-TS-3 (a) photograph, and (b) SEM 

micrograph. Regions marked “A” and “B” represent the two most prominent 

regions of IG SCC propagation into the Alloy 52M WOL. Crack propagation is 

from bottom to top. 
32 

Figure 3-12 also shows that upon reaching the interface, the crack apparently propagated in 

both the original direction and along the interface between the two welds. While a large portion 

of the fracture surface is unavailable due to the way this specimen fractured post-test, Fig. 3-12 

reveals that approximately 40% of the crack continued in the original direction in a finger-like 

manner, and maintained the IG fracture characteristics. Propagation at locations A and B in 

Fig. 3-12b was the most prominent. Figure 3-13 shows additional detail at the interface 

between the two welds at these locations. 

(a) (b)

Figure 3-13 Crack transition across the Alloy 52M-182 interface at locations (a) A, and (b) 

in Fig. 3-12b. Crack advance is from bottom to top. 

It is important to note that the amount of IG fracture observed in regions A and B in Fig. 3-12b is 

equivalent to an average growth of approximately 0.35 mm over the entire width of the 

specimen. For such cracking to develop over 3000h, the average SCC CGRs must have been 

approximately 3x10-11 m/s, and this is consistent with the CGRs measured in periods 19-23 by 

DC potential. It is also interesting to note that the maximum crack advance in region B is 

2.5 mm, corresponding to a maximum SCC CGR of approximately 2x10-10 m/s. 

A precise measurement of the entire extent of crack growth is impossible in this case because 

the surface needed for the correction of the DC potential data (direction 1b, Fig. 2-3) was not 

fully revealed after the specimen was fractured. However, the first side surfaces shown in 

Fig. 3-4 yielded total crack advance measurements of 5.9 mm on one side and 5.2 mm on the 

other. Given the crack morphology observed past the interface, an uneven crack front was to 

be expected. Thus, an average of the two side surface measurements was judged to give the 

best estimate for the full extent of crack advance. That would translate into a correction of 23% 

for the entire crack length. Nevertheless, the correction for the pre-interface part of the test is 

likely to be small when compared to that needed for the region tested after the interface cracks 

developed. As such, given the unevenness of the front, and assuming that the interface cracks 

had developed by the resumption of fast cycling, the decision was made to apply the entire 

correction from that point on. Therefore, the needed correction (factor 2.7) was applied to data 

points resulting from regions 0.35 mm past the interface (test period 26). It is interesting to note 

that transitioning in Alloy 52M (period 78) as found on the fracture surface (marked with an 

arrow in Fig. 3-31) occurs approximately 2.6 mm from the Alloy 52M-182 weld interface. As 

such, the good agreement between the expected fracture mode and the corrected crack length 

shown in Table 3-1 further substantiates the correction approach described previously. 
33 

Figure 3-14 Fracture surface of specimen A52M-182-TS-3. The arrow indicates the 

beginning of transitioning to IG in Alloy 52M. Crack advance is from bottom 

to top. 

The evolution of this test can also be inferred from the cyclic rates obtained at the various 

stages of the test, Fig. 3-15. In all figures, the CGRs measured in the environment are plotted 

vs. the predicted rates in air under the same loading conditions. The corrosion fatigue curves 

for Ni-weld alloys are also included. Initially, during test periods precracking–4, the cyclic data 

was in very good agreement with the data obtained previously on the same Alloy 182 weld, 

shown in Fig 3-15a. However, as noted previously, the environmental enhancement observed 

in the subsequent periods begins to diminish, shown in Fig. 3-15b. This figure includes both 

Alloy 182 data and Alloy 52M data (blue open symbols) from the current specimen, as well as 

the Alloy 152 data obtained at ANL previously under similar loading conditions (Fig. 2-10a), and 

Alloy 52 “air line” data from the literature [24-25]. The Alloy 52M data seem consistent with 

Alloy 152 (red symbols), and are higher than the Alloy 52 “air line”. The behavior suggests a 

high degree of environmental enhancement, and likely propagation in an IG mode. The 

subsequent data obtained during periods 24-77, shown in Fig. 3-15c, are inconsistent, most 

likely due to the breaking of ligaments during the overall straightening of the fracture surface. 

The overall response is lower than expected, perhaps due to a diminished stress intensity factor 

caused by crack branching at the interface. The baseline – the “air line” for Alloy 52M cyclic 

rates - cannot be established. By contrast, during test periods 78-93, shown in Fig. 3-15d, the 

response to fast cycling stabilizes, suggesting that the fracture surface has somewhat 

straightened. The “air line” for Alloy 52M was established. The cyclic response is much smaller 

than expected, perhaps due to the lower than measured stress intensity factors caused by crack 

branching at the interface. It is interesting to note that in order to match the behavior shown by 

the current specimen, Alloy 52 would have to be loaded at stress intensity factors about half of 

those shown in Table 3-1. Nevertheless, the specimen response is consistent, and the known 

R-dependence (Fig. 2-10a) was reproduced. The behavior over a range of load ratios 

R = 0.3-0.7 seems similar to that observed previously for Alloy 152. This data set also seems to 

indicate that the optimum loading for environmental enhancement is R = 0.5. Similar to Alloy 

152 (see Fig. 2-10a), one observes that by further increasing R to 0.6 the environmental 
34 

enhancement begins to diminish. When R is 0.7 and rise time is 1000s, the rate in the 

environment equals that in air, that is, the environmental enhancement appears to be lost. 

Interestingly, data obtained at R = 0.3 but with very long rise times (periods 92 and 93) exhibit 

the highest environmental enhancement. 

(a) (b)

(c) (d)

Figure 3-15 Cyclic CGR data in PWR environment for (a) specimen A52M-182-TS-3 and 

specimen A182-TS-1 of the same alloy tested previously (without WOL), (b) 

specimen A52M-182-TS-3 and Alloy 152 specimen A152-TS-4 under similar 

loading, and Alloy 52 data from the literature [24, 25], (c) Comparison between 

Alloy 52M data obtained in the current test and Alloy 52 data from the 

literature [24, 25], (d) Transitioning in Alloy 52M, periods 78-93. 

Table 3-2 provides a summary of the SCC CGR data resulting from this test. These data will be 

used to illustrate the CGR dependence on the distance to the 52M-182 interface. 

10-12

10-11

10-10

10-9

10-8

10-7

10-12 10-11 10-10 10-9 10-8 10-7

A52M-182-TS-3

A182-TS-1

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloy 182 Weld

Simulated PWR Water at 320°C 

Best Fit Curve for Alloy 182

CGRair + 0.018 (CGRair)

0.78

10-12

10-11

10-10

10-9

10-8

10-7

10-12 10-11 10-10 10-9 10-8 10-7

A52M-182-TS-3

A152

A52, PWR water (Dombrowski)

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloy 182 Weld

Simulated PWR Water at 320°C 

Best Fit Curve for Alloy 182

CGRair + 0.018 (CGRair)

0.78

18,21

Alloy 52 air line

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-12 10-11 10-10 10-9 10-8 10-7 10-6

A52M (A52-182-TS-3)

A52, 25C air (van Der Sluys)

A52, PWR water (Dombrowski)

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloys 52 and 52M Welds

Simulated PWR Water at 320°C 

Best Fit Curve for 

Alloy 182 in PWR env

CGRair + 0.018 (CGRair)

0.78

Alloy 52 air line

Alloy 52M WOL

air line

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-12 10-11 10-10 10-9 10-8 10-7 10-6

A52M (A52-182-TS-3)

A52, 25C air (van Der Sluys)

A52, PWR water (Dombrowski)

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloys 52 and 52M Welds

Simulated PWR Water at 320°C 

Best Fit Curve for 

Alloy 182 in PWR env

CGRair + 0.018 (CGRair)

0.78 Alloy 52 air line

Alloy 52M WOL

air line

92

93
35 

Table 3-2 Summary of SCC CGR and cyclic (control cycle) data for specimen 

A52M-182-TS-3 

Test period 

K 

(MPa·m1/2)

Distance to interface 

(mm)

SCC CGR 

(m/s)

Cyclic CGR 

(m/s) Method 

5 26.2 -1.214 1.30E-10 CL 

10 27.4 -0.914 7.51E-11 CL + PU 

11 31.5 -0.582 4.86E-11 CL + PU 

14 33.5 -0.199 3.24E-11 CL + PU 

17 34.7 0.030 2.69E-11 CL + PU 

20 36.3 0.271 2.44E-11 CL + PU 

23 38.2 0.547 1.83E-11 CL + PU 

97 40.3 2.457 4.04E-12 CL + PU 

98 40.2 2.465 5.37E-12 CL 

 

13 32.8 -0.319 4.11E-11 est cycle+hold 

16 34.4 -0.037 2.84E-11 est cycle+hold 

19 36.1 0.233 2.20E-11 est cycle+hold 

22 38.0 0.508 1.31E-11 est cycle+hold 

88 35.5 2.226 5.32E-12 est cycle+hold 

95 40.2 2.453 5.93E-12 est cycle+hold 

 

4 26.2 -1.214 4.47E-10 

8 27.8 -0.813 3.49E-10 

12 32.4 -0.384 1.98E-10 

15 34.1 -0.077 1.80E-10 

18 35.9 0.210 1.79E-10 

21 37.8 0.476 1.67E-10 

83 34.9 2.142 3.31E-11 

87 35.4 2.216 2.68E-11 

91 36.3 2.323 2.10E-11 

To summarize this test, the CGRs shown in Table 3-2 are plotted as a function of the distance 

to the 52M WOL interface in Fig. 3-16. As described previously, the crack was transitioned to 

IG SCC in Alloy 182, and the average SCC CGR at 1.2 mm from the interface was 1.3x10-10

m/s. This CGR is consistent with the CGR measured for the same alloy without the WOL. As 

the crack approached the interface, the measured CGRs decreased to approximately 2x10-11

m/s. At the interface, the crack branched. The crack continuing in Alloy 52M along the initial 

propagation plane grew at a rate of approximately 2x10-11 m/s. The resulting fracture surface 

corresponds to regions A+B in Fig. 3-12b, and the average crack advance and CGR estimates 

based on the fracture surface are consistent with the average growth and rates measured by 

DC potential. Crack advance resumes in a TG mode after fast cycling is introduced, however, 

both cyclic and SCC CGRs are retarded beyond this point because of the presumably reduced 

stress intensity factor. The overall behavior of the SCC CGRs vs. distance is mirrored by the 

behavior of the control cycle. It should be noted that the rates shown in Fig. 3-16 are not 

normalized by the stress intensity factor. If that were accomplished, the effect of the interface 

on the SCC CGRs would perhaps be even more dramatic. 
36 

Figure 3-16 SCC CGR in Specimen A52M-182-TS-3 as a function of distance to the 

182/52M interface. 

3.1.2 Specimen A52M-182-TS-1 

The test on specimen A52M-182-TS-1 (Fig. 2-3) was essentially a repeat of the test described 

in the previous section, except this specimen was a 1T-CT as a test system that could 

accommodate the larger specimen size became available. The objective of this test was similar 

to the first one, i.e. to observe the behavior of a SCC crack propagating from Alloy 182 towards 

the Alloy 52M WOL. The distance from the notch to the interface was approximately 8 mm. 

(a) (b) 

Figure 3-17 Photographs of the two sides of the 52M/182 weld overlay specimen 

A52M-182-TS-1. 

The testing conditions for specimen A52M-182-TS-1 are given in Table 3-3; as with the prior 

test, the part that took place in Alloy 182 is shaded with gray. The changes in crack length and 

Kmax with time are shown in Fig. 3-18. The crack was transitioned in Alloy 182, and a first SCC 

10-12

10-11

10-10

10-9

-2.0 -1.0 0.0 1.0 2.0 3.0

Data 18

SCC CGR (CL, CL + pu)

est SCC CGR (cycle + hold)

Control cycle

CGR (m/s)

Distance from the 52M WOL interface (mm)

Alloy 182 Alloy 52M
37 

CGR was determined in period 7, approximately 4.1 mm from the interface. Next, in order to 

simulate the conditions from the previous test (IG SCC in Alloy 182 approximately 1 mm from 

the interface with the WOL), the crack was advanced in fatigue and was transitioned again at a 

higher stress intensity factor at approximately 1.9 mm from the interface. Both SCC CGRs 

(periods 7 and 20) are consistent with rates measured previously for this Alloy 182 weld. Next, 

the crack was advanced towards the interface by a succession of gentle cycling and constant 

load with periodic unloading. The resulting rate at 1.3 mm from the interface (period 22) was 

slower than that observed previously, but the trend was expected based on the prior test. The 

routine was repeated in periods 23-26, 1.2 mm from the interface. Next, the crack was 

advanced under cyclic loading in period 27; as the rate appeared similar to that measured just 

prior to the interface in the previous test, the specimen was set at constant load with periodic 

unloading in period 28, 0.5 mm from the interface. The crack was further advanced until the 

interface by gentle cycling in period 29, and set at constant load with periodic unloading in test 

period 30. The CGR was initially slow (1.5x10-11 m/s), subsequently appeared to go through 

slow (1.5x10-11 m/–) - fast (8.0x10-11 m/s) periods of growth, on average 4.7x10-11 m/s, Fig. 

3-18i. The reason for this behavior is unknown, nevertheless, growth is very different from the 

“well-behaved” appearance of the previous test periods. As the rate apparently stabilized at 

5.3x10-11 m/s, the specimen was set at constant load. The behavior observed in period 31 

suggests that as with the previous specimen, the fracture is complex with perhaps one or 

several cracks having developed at the interface, and a possible flake shorts the DC potential 

measurements in the absence of periodic unloading. Periodic unloading was reintroduced in 

period 32. Growth resumed at the previous (test period 30) rate, then fell into the 10-12 m/s 

range, suggesting that the SCC growth has stopped. It was decided to finish the test to assess 

the fracture surface. Overall, the resulting SCC CGRs vs. distance behavior appears similar to 

that observed on the previous WOL specimen. 

A final set of fatigue measurements were undertaken in periods 33-42. The crack was 

advanced by a substantial amount (6.5 mm) in order to preserve as much as possible of the the 

fracture surface at the interface. It is worth noting the jump at the beginning of period 33, Fig. 

3-18j, suggesting that some ligaments were broken. Also, it is interesting that overall the fatigue 

response is approximately an order of magnitude lower than expected for a Ni-base weld (Eqs. 

2 and 5). This response is similar to that observed in the prior test (Fig. 3-15d) and suggests 

that cracking occurred along the interface between the two welds resulting is a reduced stress 

intensity factor at the crack tip. 
38 

Table 3-3 Crack growth data for WOL specimen A52M-182-TS-1 in PWR watera,b

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time, 

Down 

Time, 

Hold 

Time, Kmax, ∆K, CGRenv, 

Estimated 

CGRair, Crack 

Length, 

Period h C R s s s MPa·m1/2 MPa·m1/2 m/s m/s mm

Pre a 316 320.2 0.32 0.5 0.5 19.5 13.3 3.07E-08 4.35E-08 12.665 

Pre b 333 320.1 0.32 50 50 19.6 13.3 1.44E-09 4.41E-10 12.734 

Pre c 339 320.1 0.32 0.5 0.5 20.1 13.7 4.88E-08 4.93E-08 13.253 

Pre d 404 320.2 0.32 100 100 20.3 13.8 1.20E-09 2.54E-10 13.391 

Pre e 410 319.8 0.32 0.5 0.5 21.3 14.5 1.15E-07 6.17E-08 14.309 

Pre f 428 319.8 0.32 50 50 21.4 14.5 3.88E-09 6.31E-10 14.426 

Pre g 432 319.8 0.32 2 2 21.7 14.8 4.94E-08 1.68E-08 14.724 

Pre h 452 319.5 0.32 50 50 21.9 14.9 4.39E-09 6.90E-10 14.865 

Pre i 457 319.9 0.32 2 2 22.7 15.4 6.21E-08 2.00E-08 15.561 

1 477 319.9 0.32 108 12 22.3 15.2 2.79E-09 3.47E-10 15.670 

2 575 319.8 0.32 650 12 22.4 15.2 5.64E-10 5.84E-11 15.728 

3 597 319.8 0.49 600 12 22.6 11.5 2.90E-10 3.19E-11 15.880 

4 741 319.9 0.49 1000 12 22.6 11.5 1.62E-10 1.93E-11 15.935 

5 791 320.0 0.49 1000 12 22.7 11.6 2.02E-10 1.96E-11 15.985 

6 859 319.9 0.49 1000 12 22.7 11.6 2.30E-10 1.96E-11 16.003 

7 1,220 320.3 0.49 12 12 7,200 22.8 11.7 5.85E-11 - 16.003

8 1,229 319.7 0.49 12 12 22.9 11.7 3.91E-09 1.71E-09 16.171 

9 1,244 319.8 0.49 300 12 23.0 11.7 8.62E-10 6.86E-11 16.198 

10 1,252 320.0 0.49 12 12 23.0 11.7 2.40E-09 1.73E-09 16.266 

11 1,268 319.9 0.49 300 12 23.0 11.7 6.48E-10 6.96E-11 16.308 

12 1,277 319.9 0.32 2 2 23.8 16.2 2.17E-08 2.46E-08 16.983 

13 1,292 319.9 0.32 100 100 24.4 16.6 1.92E-09 5.45E-10 17.058 

14 1,300 319.9 0.32 2 2 25.5 17.3 3.22E-08 3.25E-08 17.911 

15 1,318 319.8 0.32 100 100 25.7 17.5 3.09E-09 6.73E-10 18.082 

16 1,324 319.8 0.49 300 12 25.7 13.1 8.41E-10 1.09E-10 18.099 

17 1,364 319.8 0.49 600 12 25.9 13.2 7.00E-10 5.58E-11 18.216 

18 1,413 319.6 0.49 1000 12 26.0 13.3 1.91E-10 3.44E-11 18.325 

19 1,485 319.5 0.49 1000 12 7,200 26.0 13.2 1.32E-10 4.14E-12 18.254 

20 2,564 320.0 0.49 12 12 7,200 26.7 13.6 1.23E-10 - 18.743

21 2,950 319.6 0.49 1000 12 27.5 14.0 2.54E-10 4.33E-11 19.210 

22 3,406 319.9 1.00 12 12 7,200 27.9 14.2 6.80E-11 - 19.324

23 3,411 319.6 0.49 50 12 27.9 14.2 3.24E-09 9.14E-10 19.387 

24 3,432 319.5 0.49 300 12 28.0 14.3 7.16E-10 1.54E-10 19.497 

25 3,476 319.0 0.49 1000 12 27.9 14.2 2.57E-10 4.55E-11 19.409 

26 4,725 319.6 0.49 12 12 7,200 28.1 14.0 3.51E-11 - 19.460

27 5,060 319.8 0.50 1000 12 28.4 14.2 1.66E-10 4.71E-11 19.923 

28 6,603 319.9 0.50 12 12 7,200 28.8 14.4 2.58E-11 - 20.088

29 6,905 321.1 0.50 1000 12 29.7 14.9 1.43E-10 5.73E-11 20.680 

30 8,213 321.7 0.50 12 12 7200 30.0 15.3 5.27E-11 - 20.846

31 8,457 321.4 0.50 0 0 30.0 0.0 negligible - 20.846

32 9,516 320.0 0.50 12 12 7200 30.4 15.2 1.74E-11 - 20.904

33 9,522 319.5 0.3 1 1 32.0 22.4 1.35E-08 1.75E-07 21.597 

34 9,539 319.5 0.32 50 50 32.0 21.8 1.65E-09 3.28E-09 21.629 

35 9,546 319.5 0.32 0.5 0.5 33.2 22.6 2.51E-08 3.81E-07 22.302 

36 9,561 319.5 0.32 50 50 33.3 22.6 2.58E-09 3.84E-09 22.338 

37 9,571 319.5 0.32 0.5 0.5 35.3 24.0 3.36E-08 4.88E-07 23.379 

38 9,585 319.5 0.32 50 50 35.4 24.1 3.55E-09 4.98E-09 23.471 

39 9,594 319.5 0.32 0.5 0.5 38.6 26.3 5.63E-08 7.10E-07 24.958 

40 9,626 319.5 0.32 50 50 39.2 26.7 2.72E-09 7.56E-09 25.214 

41 9,632 319.5 0.32 0.5 0.5 45.1 30.7 1.12E-07 1.34E-06 27.414 

42 9,648 319.5 0.32 50 50 45.7 31.0 3.52E-09 1.41E-08 27.604 

a

 Simulated PWR water with 2 ppm Li, 1000 ppm B, and 2 ppm. DO<10 ppb. Conductivity was 213 μS/cm, and pH 6.4. b

 Data was checked against fractography. 
39 

(a) 

(b) 

(c) 

Figure 3-18 Crack–length–vs.–time for WOL specimen A52M-182-TS-1 in simulated PWR 

environment during test periods (a) precracking-2, (b) 3-5, (c) 6-11, (d) 12-19, 

(e) 20-21, (f) 22-25, (g) 26-27, (h) 28, (i) 30, (j) 31-32, (k) 33, and (l) 33-42. 

 

12.50

13.00

13.50

14.00

14.50

15.00

15.50

16.00

0

20

40

60

80

300 350 400 450 500 550 600

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

Kmax

Crack Length

Period 2 1

Pre

 a

Pre

b

Pre

d

Pre

f

Pre

h

Crack Length (mm)

Kmax (MPa m0.5)

15.50

15.60

15.70

15.80

15.90

16.00

16.10

16.20

16.30

0

20

40

60

80

550 600 650 700 750 800

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

Kmax

Crack Length

Period 3

Period 4

Period 5

Crack Length (mm)

Kmax (MPa m0.5)

15.70

15.80

15.90

16.00

16.10

16.20

16.30

0

20

40

60

80

800 900 1000 1100 1200 1300

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

Kmax

Crack Length

Period 6

8

Period 7

5.9 x 10–11 m/s

22.8 MPa m0.5

Constant load with 

periodic unloading

Crack Length (mm)

Kmax (MPa m0.5)
40 

Figure 3-18 (Cont.)

(d) 

(e) 

(f) 

16.00

16.50

17.00

17.50

18.00

18.50

19.00

0

20

40

60

80

1200 1250 1300 1350 1400 1450 1500

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

Kmax

Crack Length

15 16 17 18

Time (h)

Crack Length (mm)

Kmax (MPa m0.5)

17.50

18.00

18.50

19.00

19.50

0

20

40

60

80

1500 2000 2500 3000

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

Kmax

Crack Length

Period 21

Period 20

1.3 x 10–10 m/s

25.6 MPa m0.5

Constant load with 

periodic unloading

Time (h)

Crack Length (mm)

Kmax (MPa m0.5)

18.40

18.60

18.80

19.00

19.20

19.40

19.60

19.80

0

20

40

60

80

2700 2800 2900 3000 3100 3200 3300 3400 3500

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

Kmax

Crack Length

Period 22

6.8 x 10–11 m/s

25.6 MPa m0.5

Constant load with 

periodic unloading

23 25

Time (h)

Crack Length (mm)

Kmax (MPa m0.5)
41 

Figure 3-18 (Cont.) 

(j) 

(k) 

(l) 

20.60

20.80

21.00

21.20

21.40

21.60

21.80

0

50

100

150

8000 8500 9000 9500

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

calculated 52M/182 interface

5.0 x 10–11 m/s

Period 32

1.7 x 10–11 m/s

30.1 MPa m0.5

Constant load with 

periodic unloading

5.3 x 10–11 m/s

Time (h)

Crack Length (mm)

Kmax (MPa m0.5)

20.60

20.80

21.00

21.20

21.40

21.60

21.80

20

25

30

35

40

45

50

55

60

9510 9515 9520 9525

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

calculated 52M/182 interface

Period 33

1.7 x 10–11 m/s

30.1 MPa m0.5

R=0.3, 0.5 Hz

Time (h)

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

21.00

22.00

23.00

24.00

25.00

26.00

27.00

28.00

20

25

30

35

40

45

50

55

60

9520 9560 9600 9640 9680

Time (h)

Alloy 52M/182 WOL

Specimen # A52M-182-TS-1

PWR environment

calculated 52M/182 interface

33

Time (h)

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

34 35 36

37 38

39

40

41

42
42 

Following approximately 6.5 mm of crack advance past the interface in fatigue, the test was 

stopped and the specimen was fractured open, as shown in Fig. 3-19. As was seen in the 

previous experiment, the fracture surface at the interface was complex, with substantial cracking 

along the interface along with crack propagation in Alloy 52M along a different plane than the 

original. Hence, the resulting large ligament observed in the pictures. 

(a) (b)

(c) (d)

Figure 3-19 (a, b) The two halves of fractured specimen A52M-182-TS-1. Crack advance is 

from bottom to top. (c, d) Same fracture surfaces photographed at an angle to 

show the cracking pattern at the interface. 

The fracture surface of specimen A52M-182-TS-1 was examined by both optical microscopy 

and SEM. The optical image is shown in Fig. 3-20, and the WOL interface is indicated by black 

arrows. The various features are in very good agreement with the DC potential measurements: 

the first IG band (IG-1) starts approximately 4 mm from the interface, the second IG band (IG-2) 

starts approximately 1.5 mm from the interface, and most importantly, the interaction with the 

interface occurs after approximately 8 mm of growth as was measured by the DC potential. As 

such, no correction of the DC potential measurements was needed for this specimen. 
43 

Figure 3-20 Fracture surface of specimen A52M-182-TS-1. The interface is indicated by 

black arrows. Crack advance is from bottom to top. The units of the bottom 

and side rulers are mm. 

The fracture surface of specimen A52M-182-TS-1 was also examined by SEM with the focus on 

the interaction of the crack with the WOL interface. Figures 3-21 and 3-22 show detail at select 

locations on the first half of the fracture surface, and Fig. 3-23 shows additional detail at two 

locations on the second half. Both Figs. 3-21a and 3-23a shows a straight, fully IG-engaged, 

SCC front ahead of the interface, just as in the prior specimen. Additional micrographs of 

features of interest were taken at higher magnifications. As such, Figs. 3-21b, c were taken at 

locations 1 and 2 in Fig. 3-21a and show cases where the IG crack propagated from Alloy 182 

into Alloy 52M along the original direction. Such direct crack propagation through the interface 

was also observed on the previous specimen. Figures 3-22b, c (locations 3, 4 in Fig. 3-21a) 

show cases where the crack first propagated along the interface, then into Alloy 52M. Again, 

propagation along interface and branching into Alloy 52M was also observed in the previous 

specimen. Figures 3-22b, c (locations 1, 2 in Fig. 3-21a) focus on the region along the large 

ligament formed past the interface. Figure 3-23b shows IG fracture mode on the side of this 

ligament. It is likely that such preferential propagation lead to the formation of this ligament in 

the first place. Fig. 3-23c focuses on the fracture mode at the interface. Interdendritic features 

are visible suggesting that this was a favorable direction despite being normal to the direction of 

the dendrites. 

 
44 

(a) 

(c) (b) 

Figure 3-21 Specimen A52M-182-TS-1: (a) first half of fracture surface, (b) detail at location 

1, and (c) detail at location 2. Crack advance is from bottom to top. 
45 

(a) 

(b) 

Figure 3-22 Specimen A52M-182-TS-1: (a) detail at location 3, and (b) detail at location 4 in 

Fig. 3-21a. Crack advance is from bottom to top. 

 
46 (a) 

(c) (b) 

Figure 3-23 Specimen A52M-182-TS-1: (a) second half of fracture surface, (b) detail at 

location 1, and (c) detail at location 2. Crack advance is from bottom to top. 
47 

Figure 3-24 summarizes the cyclic CGR data obtained on the WOL specimen A52M-182-TS-1. 

The corrosion fatigue curve for Alloy 182 is included for comparison. Also included in Fig. 3-24a 

are data obtained on the 1/2T CT specimen A52M-182-TS-3, and data obtained previously on 

the same Alloy 182 weld without the WOL. Initially, the cyclic rates from the current specimen 

appeared to be smaller (Fig. 3-24a) – perhaps due to the fact that the crack is deeper in the 

weld than it was in the previous tests. However, after approximately 1 mm of advance, the data 

begins to match the behavior observed previously for this alloy. Figure 3-24b shows the data 

obtained at the end of the test in Alloy 52M. The fatigue response appears to be approximately 

one order of magnitude lower than expected. This effect was observed previously in specimen 

A52M-182-TS-3 (Fig. 3-15d), and was interpreted to have been caused by a decreased stress 

intensity factor at the crack tip due to the extensive cracking along the interface between the two 

welds. The fracture shown in Fig. 3-19 exhibits a similar cracking pattern at the interface to that 

of specimen A52M-182-TS-3 (Fig. 3-18), thus, this similarity supports the 

previous interpretation. 

(a) (b) 

Figure 3-24 Cyclic CGR data for Alloy 52M WOL specimen A52M-182-TS-1 in simulated 

PWR environment during (a) precracking and transitioning in Alloy 182, and 

(b) at the end of the test in Alloy 52M. The dotted blue line shows the “air line” 

for Alloy 52M obtained in the prior test. 

Figure 3-25 compares the SCC CGR vs. distance data obtained on the two Alloy 52M-182 WOL 

specimens tested in the TS orientation. The SCC CGR behavior observed in those two 

specimens seems very similar. In both tests, the SCC CGR data obtained in Alloy 182 with the 

Alloy 52 WOL at distances larger than 1 mm from the WOL, are similar to the rate obtained in 

the same weld without the WOL. However, the SCC CGRs decreased by approximately one 

order of magnitude ahead of the interface. The two higher data points obtained on specimen 

A52M-182-TS-1 most likely reflect propagation along the interface and/or cracking in Alloy 52M 

on planes other than the original. 

 

10-12

10-11

10-10

10-9

10-8

10-7

10-12 10-11 10-10 10-9 10-8 10-7

A52M-182-TS-1

A52M-182-TS-3

A182-TS-1

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloy 182 Weld

Simulated PWR Water at 320°C 

Best Fit Curve for Alloy 182

CGRair + 0.018 (CGRair)

0.78

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-12 10-11 10-10 10-9 10-8 10-7 10-6

A52M-182-TS-1

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloy 52M Weld

Simulated PWR Water at 320°C 

Best Fit Curve for Alloy 182

CGRair + 0.018 (CGRair)

0.78

Alloy 52M WOL

air line, A52M-182-TS-3
48 

Figure 3-25 SCC CGR vs. distance for the two Alloy 52M-182 WOL specimens tested in the 

TS orientation. 

In both TS-oriented specimens, severe cracking was observed along the interface between the 

two welds as well as in Alloy 52M near the interface. As described previously, estimates based 

on the fracture surface indicated that the SCC CGRs in the 1st layer of Alloy 52M WOL could be 

in the 10-10 m/s range. As such, SCC CGR testing was next undertaken along those planes 

with the objective of measuring those SCC CGRs directly. In order to accomplish this, the next 

two tests were conducted on specimens in the ST orientation (Fig. 3-26). In both ST 

specimens, the test plane was tilted approximately 15o with respect to the Alloy 52M-182 

interface. In one case (specimen WOL-ST-1), the crack is growing from Alloy 182 towards the 

interface with Alloy 52M. In the second case (specimen WOL-ST-2), the crack is initiated in 

Alloy 52M and grows towards the interface with Alloy 182. 

10-12

10-11

10-10

10-9

-2.0 -1.0 0.0 1.0 2.0 3.0

Data 18

A52M-182-TS-3 (CL, CL + pu)

A52M-182-TS-3 (cycle + hold)

A52M-182-TS-1 (CL + pu)

CGR (m/s)

Distance from the 52M WOL interface (mm)

Alloy 182 Alloy 52M
49 

Figure 3-26 Specimens for SCC CGR testing of Alloy 52M-182 WOL in the ST orientation. 

3.1.3 SCC Along the Alloy 52M-182 Interface, Specimen WOL-ST-1 

The objective of this test was to measure the SCC CGR along the interface between the Alloy 

52M WOL and Alloy 182. In this specimen (Fig. 3-27), the crack was initiated in Alloy 600, was 

expected to reach the Alloy 182 weld after approximately 1 mm, and then was advanced in Alloy 

182 until it reached the Alloy 52M/182 interface. At that point, the specimen was set at constant 

load to measure the SCC CGR along the interface. The fatigue behaviors of Alloys 600 and 

182 are well-known, and were used to manage the test. The testing conditions and CGR 

responses are given in Table 3-4. These data have been corrected based on fractography. 

The specific configuration of specimen WOL-ST-1 (Fig. 3-27) also offered an opportunity to 

assess the cyclic and SCC behavior in Alloy 600 HAZ. As such, two sets of cyclic and SCC 

measurements were conducted in the Alloy 600 HAZ. The SCC CGR was first evaluated in test 

period 3 at approximately 0.7-0.65 mm from the Alloy 182 weld interface. Next, the crack was 

advanced for approximately 0.45 mm, and the SCC CGR was evaluated again in a region 

0.2-0.1 mm from the interface in test period 8. 

 
50 

Figure 3-27 Notch area in specimen WOL-ST-1. P3 and P8 represent the approximate 

locations where SCC CGR measurements were made in Alloy 600 HAZ, and 

P19 represents the approximate location where the crack was to intersect the 

interface with the Alloy 52M. 

Figure 3-28 summarizes the cyclic and SCC CGRs measured in the Alloy 600 HAZ region of 

specimen WOL-ST-1. Figure 3-28a shows the measured cyclic CGR data vs. the expected 

CGRs in air under the same loading conditions, and for comparison, the expected curves in air 

and environment for Alloy 600 (blue) and Ni-base weld (green) are included in the figure. As 

expected, the cyclic CGRs measured in this stage of the test are consistent with the known 

response of Alloy 600. The data obtained prior to the first test period at constant load (3, dark 

blue symbols) seem lower than the data obtained prior to the second test period at constant 

load (8, light blue symbols). The comparison shown in Fig. 3-28a seems to suggest that the 

cyclic CGRs of the HAZ increase as the crack approaches the Alloy 182 weld interface. Figure 

3-28b shows the SCC CGRs measured for Alloy 600 HAZ in test periods 3 (dark blue symbol)

and 8 (light blue symbol), and these also increase as the crack approaches the fusion line. As

such, Fig. 3-28 suggests that both cyclic and SCC CGRs appear to increase as the crack

advances towards the interface. However, Fig. 3-28b also includes a “reference” SCC CGR

obtained from the same heat of Alloy 600 (NX 131031), tested in the same ST orientation

separately. The similarity in responses between the “reference” and test period 3

(approximately 0.6 mm from the fusion line) suggests that in this case, the HAZ does not extend

more than approximately 0.6 mm from the fusion line. In this test, the effect of the HAZ on the

SCC CGR response was approximately a factor of two and was measured approximately 0.1

mm from the weld interface.
51 

Table 3-4 Crack growth data for specimen WOL-ST-1 in PWR watera,b

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time

, 

Down 

Time, 

Hold 

Time, Kmax, ∆K, CGRenv, 

Estimated 

CGRair, 

Crack 

Length, 

Period h C R s s s MPa·m1/2 MPa·m1/2 m/s m/s mm 

Pre a 173 321.6 0.30 1 1 24.8 17.4 7.15E-09 2.05E-08 12.015 

Pre b 189 321.6 0.30 50 50 24.9 17.4 4.98E-10 4.15E-10 12.028 

Pre c 193 321.6 0.30 0.5 0.5 25.3 17.7 1.77E-08 4.47E-08 12.163 

Pre d 196 321.6 0.30 1 1 25.5 17.8 1.28E-08 2.30E-08 12.218 

Pre e 213 321.6 0.30 50 50 25.6 17.9 7.77E-10 4.66E-10 12.242 

1 237 321.7 0.50 50 12 25.7 12.8 2.56E-10 2.04E-10 12.271 

2 263 321.7 0.50 300 12 25.6 12.8 9.24E-11 3.37E-11 12.275 

3 406 321.7 1.00 0 0 25.7 0.0 7.93E-11 - 12.312 

4 408 321.9 0.20 0.5 0.5 26.5 21.2 5.31E-08 7.45E-08 12.495 

5 411 321.7 0.20 0.5 0.5 24.6 19.7 5.72E-08 5.47E-08 12.704 

6 429 321.7 0.50 50 12 24.8 12.4 3.89E-10 1.78E-10 12.771 

7 433 321.8 0.50 300 12 24.8 12.4 2.04E-10 2.98E-11 12.779 

8 668 321.6 1.00 0 0 25.2 0.0 1.63E-10 - 12.885 

9 671 321.6 0.20 0.5 0.5 26.8 21.4 5.29E-08 7.76E-08 13.345 

10 676 321.6 0.20 0.5 0.5 23.0 18.4 2.01E-08 1.27E-07 13.451 

11 692 321.6 0.20 50 50 23.0 18.4 1.41E-09 1.28E-09 13.464 

12 701 321.8 0.20 1 1 23.2 18.6 3.40E-10 6.69E-08 13.528 

13 717 321.6 0.20 50 50 23.3 18.6 1.00E-09 1.34E-09 13.528 

14 724 321.7 0.20 0.5 0.5 23.8 19.1 1.64E-08 1.49E-07 13.719 

15 741 321.6 0.20 50 50 24.0 19.2 2.38E-09 1.53E-09 13.770 

16 748 321.7 0.20 0.5 0.5 25.0 20.0 7.73E-08 1.79E-07 14.013 

17 764 321.7 0.50 50 12 26.3 13.2 9.22E-10 6.98E-10 14.379 

18 837 321.7 0.50 300 12 26.7 13.4 2.68E-10 1.24E-10 14.446 

19 6,472 321.3 1.00 0 0 46.6 0.0 1.30E-10 - 17.265 

a

 Simulated PWR water with 2 ppm Li, 1000 ppm B, and 2 ppm. DO<10 ppb. Conductivity was 213 S/cm, and pH 6.4. b

 Data was corrected using fractography. 

(a) (b) 

Figure 3-28 (a) Cyclic CGR data for the Alloy 600 (HAZ) region of specimen WOL-ST-1 in 

simulated PWR environment; (b) SCC CGR data for the Alloy 600 (HAZ) region 

of specimen WOL-ST-1 and MRP-55 disposition curve for Alloy 600 [11]. The 

data obtained prior to the first test period at constant load (3) is shown with 

dark blue symbols, and the data obtained prior to the second test period at 

constant load (8) is shown with light blue symbols). 

10-12

10-11

10-10

10-9

10-8

10-7

10-12 10-11 10-10 10-9 10-8 10-7

WOL-ST-1

CGR air 600 (NUREG-6721)

CGR env 600 (NUREG-4667)

CGR env weld (NUREG-6921)

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloy 600 HAZ

Simulated PWR Water at 320°C 

Best Fit Curve for 

Alloy 182 in PWR env

CGRair + 0.018 (CGRair)

0.78

CGR air 

A600

CGR env

A600

CGR air

Ni-weld

10-11

10-10

10-9

10 15 20 25 30 35 40 45

WOL-ST-1

A690-ST-1

Experimental CGR (m/s)

Stress Intensity K (MPa·m1/2)

95th

Alloy 600 HAZ Specimen WOL-ST-1

Simulated PWR Water at 325°C 

90th

75th Percentile 

(MRP-55)

reference 25th

0.1 mm from interface

0.6 mm from interface
52 

Next, the crack was advanced in fatigue across the Alloy 600-182 interface into Alloy 182, and 

Fig. 3-29 shows the cyclic response in Alloy 182. For comparison, the expected curves in air 

and environment and for Alloy 600 (blue) and Ni-base weld (green) are included in the figure. 

The response seems lower than expected, and this was interpreted as an off-plane advance. 

As such, it was estimated that the crack turned towards the interface with Alloy 52M, hence, the 

specimen was set at constant load in what was estimated to be the vicinity of the Alloy 52M-182 

interface in test period 19. 

Figure 3-29 Cyclic CGR data for the Alloy 182 region of specimen WOL-ST-1 in simulated 

PWR environment. 

Figure 3-30 shows the changes in crack length and Kmax with time for the entire test, and Fig. 

3-30g shows the constant load SCC response of the Alloy 182-Alloy 52M interface. The initial

SCC CGR of 2.8x10-10 m/s (up to approximately 1240h) was unexpectedly high given the

orientation of the crack front with respect to the dendrites, then began to diminish and continued

at the diminished rate of approximately 1.3x0-10 m/s for the remainder of the test. The

calculated Kmax appears to increase from approximately 27 MPa m1/2 to approximately 47 MPa 

m1/2, primarily as a result of the factor 8.2 correction (Fig. 3-30g). However, the SCC CGR 

does not increase accordingly. As such, it appears that the unbroken ligaments responsible for 

the correction prevented the actual Kmax from reaching the calculated values. Also, small 

“jumps” have been observed and these are indicated by arrows in the figure. It was verified that 

these jumps are neither the result of some errant loading nor an electrical artifact. In fact, they 

are regions of fast growth (10-8 m/s) that occur over short periods of time (15-20 min). The 

cause of the “jumps” is unknown, however, as it will be shown during the next test, they are a 

signature of SCC propagation along an interface between the two welds. 

10-12

10-11

10-10

10-9

10-8

10-7

10-12 10-11 10-10 10-9 10-8 10-7

WOL-ST-1

CGR env weld (NUREG-6921)

CGR air 600 (NUREG-6721)

CGR env 600 (NUREG-4667)

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloys 600 and 52M Weld

Simulated PWR Water at 320°C 

Best Fit Curve for 

Alloy 182 in PWR env

CGRair + 0.018 (CGRair)

0.78

CGR air 

A600

CGR env

A600
53 

(a) 

(b) 

(c) 

Figure 3-30 Crack–length–vs.–time for specimen WOL-ST-1 in simulated PWR 

environment during (a) precracking-2, (b) 3, (c) 4-7, (d) 8, (e) 9, (f) 10-18, and 

(g) 19. 

 

11.90

11.95

12.00

12.05

12.10

12.15

12.20

12.25

12.30

10

20

30

40

50

60

70

80

100 120 140 160 180 200 220 240 260

Time (h)

Alloy 600 Specimen WOL-ST-1

PWR env ironment

Kmax

Crack Length (mm)

Crack Length Kmax (MPa m0.5)

Period 1

R=0.5

50/12 

Pre a

Period 2

R=0.5

300/12 Pre b

Pre e c d

12.260

12.270

12.280

12.290

12.300

12.310

12.320

20

22

24

26

28

30

260 280 300 320 340 360 380 400

Time (h)

Alloy 600 Specimen WOL-ST-1

PWR env ironment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 3

7.9 x 10 –11 m/s

25.7 MPa m 0.5

CL

12.300

12.400

12.500

12.600

12.700

12.800

20

22

24

26

28

30

400 405 410 415 420 425 430 435

Time (h)

Alloy 600 Specimen WOL-ST-1

PWR env ironment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 6

R=0.5, 50/12

4

5

Period 7

R=0.5, 300/12
54 

Figure 3-30 (Cont.) 

(d) 

(e) 

(f) 

12.740

12.760

12.780

12.800

12.820

12.840

12.860

12.880

12.900

20

22

24

26

28

30

450 500 550 600 650

Time (h)

Alloy 600 Specimen WOL-ST-1

PWR env ironment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 8

1.63 x 10 –10 m/s

25.2 MPa m 0.5

CL

12.880

12.960

13.040

13.120

13.200

13.280

13.360

13.440

20

22

24

26

28

30

668 668 669 670 670 670 671 672 672

Time (h)

Alloy 600 Specimen WOL-ST-1

PWR env ironment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 9

5.3 x 10 –8 m/s

0.2, 1 Hz

13.200

13.400

13.600

13.800

14.000

14.200

14.400

20

22

24

26

28

30

680 720 760 800 840

Time (h)

Alloy 600 Specimen WOL-ST-1

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 17

0.5. 50/12

16 Period 18

0.5. 300/12 10 14131211 15
55 

Figure 3-30 (Cont.) 

(g) 

The post test-examination of this specimen involved both the side surfaces and that of the 

fracture surface. 

In order to show the side cross sections, the side surfaces were ground to eliminate the side 

grooves, polished and electrochemically etched in a nital solution. The two side surfaces 

(Fig. 3-31) show that the test progressed largely as anticipated (Fig. 3-27), and confirm that 

cracking initiated in Alloy 600, transitioned into Alloy 182 weld, and then along the Alloy 

182/52M interface. 

(a) (b) 

Figure 3-31 Post-test specimen WOL-ST-1 seen from both sides: (a) side 1, and (b) side 2. 

The red arrows indicate the Alloy 52M WOL interface. Crack advance is from 

left to right. 

 

14.500

15.000

15.500

16.000

16.500

17.000

17.500

20

30

40

50

60

70

800 1600 2400 3200 4000 4800 5600 6400

Time (h)

Alloy 600 Specimen WOL-ST-1

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 19

1.3 x 10–10 m/s

46..6 MPa m0.5

CL

2.8 x 10–10 m/s

1.6 x 10–10 m/s
56 

The two side surfaces were further examined by optical microscopy, as shown in Fig. 3-32. The 

blue arrows indicate the Alloy 600/182 interface, and the red arrows indicate the Alloy 182-52M 

interface. Both cross sections show that after passing through the Alloy 600-182 interface, the 

crack turns towards the Alloy 52M WOL interface. This off-plane cracking caused the Alloy 182 

cyclic data to appear less than expected, Fig. 3-29. The two cross sections show that the crack 

was driven in the vicinity of the Alloy 182-52M WOL as anticipated: on one surface (side 1), the 

crack under cyclic loading overshoots slightly the WOL interface, while on the second surface 

(side 2), the crack ends up slightly below the interface. Overall, the two images shown in Fig. 

3-32 demonstrate that the specimen was set at constant load in the vicinity of the Alloy 182-52M

WOL interface, and, hence, test period 19 represents cracking along the interface.

Figure 3-33 provides additional detail on the crack path. Figure 3-33a was taken at location 1A 

in Fig. 3-32a, the area where the crack overshot the WOL interface. The fracture appears TG, 

consistent with the fatigue loading. Figure 3-33b was taken at location 1B in Fig. 3-32a, at the 

end of the test. EDX analysis show that the preferred crack path was through a region with an 

average Cr concentration of 18%. Figures 3-33c and 3-33d were taken at locations 2A and 2B 

in Fig. 3-32b, and the EDX analysis shows that the preferred crack path was through a region 

with an average Cr concentration of 18-20%. In addition, Figs. 3-33b and 3-33c show that the 

dilution of Cr on the Alloy 52M WOL side within 20-30 μm from the interface is significant. 

Nevertheless, the EDX analysis shows that in this test, cracking occurred preferentially along 

the Alloy 182-52M WOL interface with Cr concentrations of 18-20%. 

Following the examination of the side surfaces, the specimen was fatigued in air at room 

temperature to break some of the remaining ligaments, and was fractured after cooling in 

liquid nitrogen. The fracture surface was photographed (Fig. 3-34) and was examined in the 

SEM (Fig. 3-35). 
57 

(a) (b) 

Figure 3-32 Cross sections of specimen WOL-ST-1: (a) side 1, and (b) side 2. Blue arrows 

indicate the Alloy 600/182 interface and the red arrows indicate the Alloy 

182-52M interface. Crack advance is from left. 
58 

(a) (b) 

(c) (d) 

Figure 3-33 Micrographs on the cross section of specimen WOL-ST-1 on: side 1 taken 

at location (a) 1A, and (b) 1B in Fig. 3-32a, and side 2 taken at location (c) 

2A and (d) 2B in Fig. 3-32b. Inserts show the local Cr concentrations 

(wt. %). Crack advance is from left to right. 

The photograph, Fig. 3-34, provides a good visual contrast between the various alloys that were 

tested. Blue arrows indicate the Alloy 600-Alloy 182 interface, green arrows indicate the Alloy 

182-Alloy 52M interface, and the red arrows and line mark the end of the test. The locations of

the two test periods in Alloy 600 (P3 and P8) and along the Alloy 52M-182 interface (P19) are

indicated in the figure. Measurements show that the Alloy 600-182 interface is 1.06 mm from

the notch, in good agreement (5%) with expectations. The crack reached the Alloy 52M-Alloy

182 interface after 2.61 mm, again in good agreement (2%) with the distance measured by DC

potential through test period 18, Table 3-4, which was 2.54 mm. The end of the test is 5.50 mm

from the specimen notch, hence, the crack extension under constant load in test period 19 is

2.89 mm, a factor of 8.2 higher than the 0.339 mm extension measured by DC potential. The

final crack extension was re-measured on the SEM image (Fig. 3-35) and was found to be in

very good agreement (7%) with the determination based on Fig. 3-34. As such, test period 19

was corrected by a factor 8.2, and the corrected outcome was already shown in Fig. 3-30g.

Table 3-4 also already reflects the corrected rate.
59 

Figure 3-34 Fracture surface of specimen WOL-ST-1. Blue arrows indicate the Alloy 600-

Alloy 182 interface, green arrows indicate the Alloy 182-Alloy 52M interface, 

and the red arrows and line mark the end of the test. The locations of the two 

test periods in Alloy 600 (P3 and P8) and along the Alloy 52M-182 interface 

(P19) are indicated in the figure. Crack advance is from bottom to top. 

The SEM examination allowed for a closer inspection of the fracture features. Several areas of 

interest are marked in Fig. 3-35, and will be presented next. 

 
60 

Figure 3-35 Fracture surface of specimen WOL-ST-1. Blue arrows indicate the Alloy 600-Alloy 

182 interface, green arrows indicate the Alloy 182-Alloy 52M interface, and the red 

arrows and line mark the end of the test. Crack advance is from bottom to top. 
61 

Figure 3-36 is an image taken at location 1 in Fig. 3-35 and focuses on the Alloy 600 region. 

Given the short distance to the interface, the specimen was transitioned to IG and set at 

constant load relatively quickly. The blue arrows designate the intersection with the Alloy 182 

weld, and the white arrows show areas of TG obtained most likely during fast cycling in at the 

beginning of test period 9, Table 3-4. Overall, the fracture surface is predominantly IG despite 

the fact that fast cycling was also used in test periods 4-5 to separate the two constant load test 

periods conducted in Alloy 690. This behavior suggests that this Alloy 600 HAZ is rather 

susceptible to SCC, and the rather high SCC rates that were measured (Fig. 3-28b) reflect that. 

Figure 3-36 Fracture surface of specimen WOL-ST-1 at location 1 in Fig. 3-35. The 

blue arrows designate the intersection with the Alloy 182 weld, and the 

white arrows show areas of TG obtained most likely during fast cycling in 

at the beginning of test period 9, Table 3-4. Crack advance is from bottom 

to top. 

Figures 3-37 and 3-38 are images taken at locations 2 and 3 in Fig. 3-35, and focus on the Alloy 

182-Alloy 52M transition. The blue arrows in Fig. 3-37 indicate the onset of cracking in Alloy 

182, and the image seems to show that occasional TG features (white arrows) occurred prior to 

transitioning into Alloy 52M. These correspond to location 1A in Fig. 3-32a where the crack, 
62 

under fatigue loading, overshot the WOL interface. Nevertheless, the crack seems to have 

eventually transitioned to IG, and one of the early occurrences is indicated with a green arrow. 

At the opposite end of the fracture surface, Fig. 3-38 shows that in that area the transition 

occurred more readily. The green arrows indicate the region where the fracture mode changes 

its appearance from TS to ST, i.e., from parallel to normal to the direction of dendrites. 

Figure 3-37 Fracture surface of specimen WOL-ST-1 at location 2 in Fig. 3-35. The blue 

arrows indicate the onset of cracking in Alloy 182, and white arrows 

indicate the occasional TG fracture that occurred prior to transitioning into 

Alloy 52M. An early occurrence of IG is indicated with a green arrow. 

Crack advance is from bottom to top. 

 
63 

Figure 3-38 Fracture surface of specimen WOL-ST-1 at location 3 in Fig. 3-35. The green 

arrows indicate the onset of IG along the interface. Crack advance is from 

bottom to top. 

Figures 3-39 and 3-40 shows images taken at locations 4, 5 and 6 in Fig. 3-35, and illustrate the 

fracture mode obtained under constant load in this specimen. Out-of-plane cracking was 

observed at several locations but this did not appear to be a predominant feature. The lack of 

out-of-plane cracking suggests that the interface was indeed the most susceptible 

microstructure for crack propagation. Figure 3-40a shows an area with less out of plane 

cracking, and Fig. 3-40b provides a higher magnification image of the fracture mode at the 

location indicated by the arrow in Fig. 3-40a. Overall, the general aspect of the fracture mode 

was as expected from the geometry of this specimen, i.e., with the dendrites normal to the plane 

of the figure. Figure 3-41 shows images from locations 7 and 8 in Fig. 3-35, and focus on areas 

at the end of the test. In both images the IG fracture mode at the end of the test is indicated by 

red arrows. 

In summary, this section has documented the crack path from Alloy 600 to Alloy 182 and onto 

the Alloy 52M-Alloy 182 interface. SCC under constant load occurred along the interface in an 

IG/interdendritic fracture mode. The overall appearance – with minimal crack branching and offplane cracking – suggests that the interface was the preferred crack path. 

 
64 

(a) (b)

Figure 3-39 Fracture surface of specimen WOL-ST-1 at (a) location 4, and (b) location 5 in 

Fig. 3-35. Crack advance is from bottom to top. 

(a) (b)

Figure 3-40 Fracture surface of specimen WOL-ST-1 at (a) locations 6 in Fig. 3-35, and (b) 

detail at the white arrow in (a). Crack advance is from bottom to top. 
65 

(a) (b) 

Figure 3-41 Fracture surface of specimen WOL-ST-1 at (a) location 7, and (b) location 8 in 

Fig. 3-35. The red arrows indicate IG fracture mode at the end of the test. 

Crack advance is from bottom to top. 

3.1.4 SCC in Alloy 52M Near the Interface with Alloy 182, Specimen WOL-ST-2 

The objective of the test on Specimen WOL-ST-2 was to measure the SCC CGR in Alloy 52M 

near the interface with Alloy 182. In this specimen the crack was initiated in Alloy 52M and was 

expected to reach the Alloy 182 weld after approximately 6 mm of growth, Fig. 3-42. Based on 

prior observations and SCC CGR estimates (Fig. 3-12), the expectation for this test was for the 

crack to find a highly SCC-susceptible region in Alloy 52M near the interface, then continue on 

the interface between the two welds as the prior WOL-ST-1 test showed that that is the most 

susceptible path; moreover, prior testing (Fig. 3-25) showed that Alloy 182 near the WOL was 

relatively resistant. 

Figure 3-42 Notch area in specimen WOL-ST-2. P16 and P33 represent the approximate 

locations where SCC CGR measurements were made in this specimen. 

The testing conditions and CGR responses are given in Table 3-5, and these data have been 

corrected based on fractography. The test was initiated with precracking in the PWR 
66 

environment (as usual), and this was followed by transitioning steps, and the known [24, 25] 

fatigue and corrosion fatigue behavior for the Ni-base weld were reproduced (Fig. 3-43). Early 

attempts at measuring an SCC CGR yielded very low SCC rates (10-12 m/s), and it is not clear 

whether the unfavorable orientation with respect to the dendritic grains played a role or not. 

Nevertheless, regions of high SCC susceptibility were known to exist from the earlier TS tests 

(Fig. 3-12), hence it was decided to advance the crack while closely monitoring the 

environmental enhancement of the cyclic rates. This was accomplished in test periods 20-31. 

When the cyclic response in test period 31 was believed to be indicative of a microstructure 

susceptible to SCC based on Alloy 152 experience (see Figs. 3-44 and 2-10), the SCC CGR 

component was verified briefly by superposition in test period 32, and the specimen was set at 

constant load in test period 33. 
67 

Table 3-5 Crack growth data for 52M specimen WOL-ST-2 in PWR watera,b

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time, 

Down 

Time, 

Hold 

Time, Kmax, K, CGRenv, 

Estimated 

CGRair, 

Crack 

Length, 

Period h C R s s s MPa·m1/2 MPa·m1/2 m/s m/s mm 

Pre a 196 319.5 0.31 0.5 0.5 20.0 13.8 1.20E-08 4.94E-08 11.229 

Pre b 214 319.4 0.31 50 50 20.2 13.9 4.63E-10 5.12E-10 11.241 

Pre c 216 319.5 0.31 0.5 0.5 20.2 14.0 1.07E-08 5.20E-08 11.260 

Pre d 221 319.5 0.31 1 1 20.4 14.1 6.12E-09 2.67E-08 11.314 

Pre e 237 319.5 0.31 50 50 20.4 14.1 4.52E-10 5.35E-10 11.324 

Pre f 241 319.5 0.31 1 1 20.5 14.2 9.34E-09 2.76E-08 11.395 

Pre g 298 319.5 0.31 100 100 20.7 14.2 3.79E-10 2.82E-10 11.432 

Pre h 302 319.4 0.31 1 1 20.9 14.4 1.12E-08 2.95E-08 11.523 

Pre i 416 319.1 0.31 50 50 21.1 14.6 5.67E-10 6.19E-10 11.611 

Pre j 420 318.7 0.31 1 1 21.6 14.9 2.45E-08 3.36E-08 11.764 

Pre k 423 318.7 0.31 2 2 21.8 15.0 1.41E-08 1.74E-08 11.828 

Pre l 462 318.9 0.31 50 50 22.0 15.2 1.30E-09 7.29E-10 11.921 

Pre m 467 319.3 0.31 1 1 23.2 16.0 4.07E-08 4.50E-08 12.307 

Pre n 469 319.5 0.31 2 2 23.3 16.1 2.65E-08 2.33E-08 12.365 

1 533 319.1 0.49 300 12 27.1 13.8 3.76E-10 1.33E-10 12.465 

2 804 319.9 0.49 600 12 27.6 14.1 1.58E-10 7.28E-11 12.618 

3 870 319.9 0.49 600 12 7200 27.7 14.1 2.86E-11 5.72E-12 12.621 

4 999 319.1 1.00 0 0 27.7 0.0 3.69E-12 12.621 

5 1,060 319.4 0.49 600 12 7200 27.6 14.1 1.95E-11 5.59E-12 12.627 

6 1,099 320.2 0.49 600 12 27.1 13.8 1.05E-10 6.77E-11 12.645 

7 1,516 320.2 0.49 600 12 7200 27.7 14.1 1.76E-11 5.68E-12 12.673 

8 1,607 320.4 0.49 600 12 28.4 14.5 1.28E-10 8.24E-11 12.711 

9 2,191 320.4 0.49 600 12 7,200 28.6 14.6 1.47E-11 6.55E-12 12.743 

10 2,383 320.6 0.49 600 12 29.1 14.8 1.10E-10 9.15E-11 12.817 

11 2,815 320.7 0.49 600 12 7,200 29.0 14.8 1.29E-11 6.97E-12 12.838 

12 3,157 320.2 0.49 600 12 29.4 15.0 1.25E-10 9.37E-11 12.970 

13 3,415 320.2 0.49 120 12 29.8 15.2 6.61E-10 5.03E-10 13.380 

14 3,487 320.8 0.49 600 12 29.6 15.1 2.05E-10 9.85E-11 13.432 

15 3,487 320.8 0.49 600 12 7,200 29.7 15.1 2.63E-11 7.58E-12 13.442 

16 4,308 320.6 1.00 0 0 29.9 0.0 2.75E-12 13.450 

17 4,408 319.9 0.49 120 12 28.8 14.7 8.14E-10 4.32E-10 13.629 

18 4,477 320.0 0.49 600 12 29.3 14.9 2.18E-10 9.33E-11 13.679 

19 4,992 320.6 0.49 600 12 7,200 29.5 15.0 2.33E-11 7.40E-12 13.718 

20 5,051 320.1 0.49 120 12 29.3 14.9 7.31E-10 4.65E-10 13.866 

21 5,214 320.3 0.44 120 12 26.4 14.8 6.39E-10 3.86E-10 14.101 

22 5,285 320.4 0.42 600 12 26.2 15.2 1.87E-10 8.18E-11 14.149 

23 5,454 320.4 0.43 120 12 28.4 16.2 8.39E-10 5.51E-10 14.563 

24 5,549 320.1 0.49 120 12 29.2 14.9 7.70E-10 4.61E-10 14.788 

25 5,617 319.9 0.49 600 12 29.4 15.0 2.28E-10 9.46E-11 14.836 

26 5,687 319.7 0.49 120 12 30.7 15.7 9.11E-10 5.65E-10 15.035 

27 5,806 319.6 0.47 120 12 30.5 16.1 1.10E-09 6.02E-10 15.372 

28 5,977 319.9 0.48 120 12 30.8 16.0 9.49E-10 6.06E-10 15.815 

29 5,996 319.9 0.48 600 12 30.8 16.0 2.68E-10 1.20E-10 15.830 

30 6,144 318.9 0.50 120 12 31.3 15.7 8.81E-10 5.78E-10 16.172 

31 6,210 319.6 0.50 600 12 31.4 15.7 4.38E-10 1.18E-10 16.244 

32 6,282 320.4 0.50 600 12 7,200 32.8 16.4 5.32E-10 1.09E-11 16.371 

33 7,867 319.2 1.00 0 0 44.2 0.0 2.97E-10 - 17.815 

34 7,986 319.4 1.00 0 0 31.1 0.0 5.88E-11 - 17.818 

a

 Simulated PWR water with 2 ppm Li, 1000 ppm B, and 2 ppm. DO<10 ppb. Conductivity was 213 S/cm, and pH 6.4. b

 Data was corrected using fractography. 

 
68 

Figure 3-43 Cyclic CGRs for Alloy 52M specimen WOL-ST-2 in simulated PWR 

environment. Also included are Alloy 52 data from the literature [24, 25] 

obtained in air at room temperature and in PWR environment.

Figure 3-44 Environmental enhancement of two control test conditions vs. calculated 

distance to the interface. Crack propagation is from right to left (see also Fig. 

3-25 for guidance). 

Figure 3-45 shows the changes in crack length and Kmax with time for the entire test, and 

Fig. 3-45l shows the response under constant load conditions in test period 33. The initial SCC 

CGR of 1.6x10-10 m/s (Kmax = 32.3 MPa m1/2) was maintained until approximately 7,100h for 

the first 0.46 mm of growth, and this rate will be reported for the first layer of Alloy 52M as the 

post-test examination will establish unequivocally that the growth occurred in the Alloy 52M 

WOL. Next, the rate appeared to increase, and the SCC CCR was on average approximately 

double, 3.8x0-10 m/s. It is interesting to note that in the latter part of this test period (7,700 h, 

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-12 10-11 10-10 10-9 10-8 10-7 10-6

A52, 25C air (van Der Sluys)

A52, PWR water (Dombrowski)

WOL-ST-2

CGRenv (m/s)

CGRair Ni-weld alloys (m/s)

Alloys 52 and 52M Welds

Simulated PWR Water at 320°C 

Best Fit Curve for 

Alloy 182 in PWR env

CGRair + 0.018 (CGRair)

0.78

Alloy 52 air line

13

14

31

0.00

1.00

2.00

3.00

4.00

5.00

10-12

10-11

10-10

-0.2 0 0.2 0.4 0.6 0.8

R=0.5, 120/12

R=0.5, 600/12

SCC

SCC CGR (m/s)

CGRenv/CGRair

Distance from the 52M WOL interface (mm)

Alloy 182 Alloy 52M

Alloy 52M WOL

Specimen WOL-ST-2
69 

Fig. 3-45n), 5-10 μm “jumps” similar to those seen in specimen WOL-ST-1 (Fig. 3-30g) were 

observed; given that in the WOL-ST-1 specimen the SCC growth was along the Alloy 52M-182 

interface, the “jumps” in the current test likely suggest that the crack reached the interface with 

Alloy 182. Towards the end of the test period, the SCC CGR reached 1.4x10-9 m/s (after 

7,855h). The calculated Kmax also appears to increase from 32.3 MPa m1/2 to approximately 

44.2 MPa m1/2, primarily as a result of the factor 4.2 correction (Fig. 3-30g). Nevertheless, in 

the latter part of the test it is uncertain whether the SCC CGR increases because of the larger 

stress intensity factor or because of the faster SCC path along the interface between the two 

welds. Finally, the specimen was unloaded and it is interesting to note that although the unload 

at the end of test period 33 was intended to stop the growth (and effectively end the test), the 

crack continued to grow at a substantial rate even after the stress intensity factor was drastically 

decreased. Hence, this last period received its own designation, test period 34 in Table 3-5. 

Post-test measurements on three cross sections (the two sides of the specimen and one 

additional cross section in the middle of the specimen, as presented later in this section, 

confirmed that the SCC crack initiated in Alloy 52M, at least 0.8 mm from the interface with Alloy 

182. The early response shown in Fig. 3-45l confirms the previous SCC CGR estimate based 

on fractgraphy of specimen A52M-182-TS-3 (Fig. 3-12). 

(a) 

Figure 3-45 Crack–length–vs.–time for Alloy 52M specimen WOL-ST-2 in simulated PWR 

environment during test periods (a) precracking, (b) 1-3, (c) 4-7, (d) 8-9, (e) 

10-12, (f) 13-15, (g) 16, (h) 17-19, (i) 20-27, (j) 28-32, (k) 31, (l) 33, (m) detail in the 

first part of test period 33, (n) detail in the second part of test period 33, and 

(o) 34. 

 

11.20

11.40

11.60

11.80

12.00

12.20

12.40

10

20

30

40

50

60

70

80

160 200 240 280 320 360 400 440 480

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Pre a c

b

Pre l

Pre i

de f Pre g

h

j k m n
70 

Figure 3-45 (Cont.)

(b) 

(c) 

(d) 

12.20

12.30

12.40

12.50

12.60

12.70

10

20

30

40

50

60

70

80

500 550 600 650 700 750 800 850 900

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 1

R=0.5

300/12

Period 2

R=0.5

600/12

Period 3

R=0.5

600/12 + 2h

12.58

12.60

12.62

12.64

12.66

12.68

10

20

30

40

50

60

70

80

900 1000 1100 1200 1300 1400 1500

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 4

5.0 x 10–12 m/s

27.7 MPa m0.5

CL

Period 5

R=0.5

600/12 + 2h

Period 7

1.8 x 10–11 m/s

27.7 MPa m0.5

R=0.5, 600/12 + 2h

12.65

12.70

12.75

12.80

10

20

30

40

50

60

70

80

1500 1600 1700 1800 1900 2000 2100 2200

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR env ironment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5

Period 8 )

R=0.5

600/12 

Period 9

1.5 x 10 –11 m/s

28.6 MPa m 0.5

R=0.5, 600/12 + 2h
71 

Figure 3-45 (Cont.)

(e) 

(f) 

(g) 

 

12.70

12.75

12.80

12.85

12.90

12.95

13.00

10

20

30

40

50

60

70

80

2200 2400 2600 2800 3000 3200

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR env ironment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 10

R=0.5

600/12 

Period 11

1.3 x 10 –11 m/s

29.0 MPa m 0.5

R=0.5, 600/12 + 2h

Period 12

R=0.5

600/12 

12.90

13.00

13.10

13.20

13.30

13.40

13.50

10

20

30

40

50

60

70

80

3100 3200 3300 3400 3500 3600 3700

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 13

6.6 x 10–10 m/s

29.0 MPa m0.5

R=0.5, 120/12 

Period 14

2.0 x 10–10 m/s

29.0 MPa m0.5

R=0.5, 600/12 

Period 15

2.6 x 10–11 m/s

30.0 MPa m0.5

R=0.5, 600/12 +2 h

13.430

13.435

13.440

13.445

13.450

13.455

10

20

30

40

50

60

70

80

3600 3700 3800 3900 4000 4100 4200 4300

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Period 16

2.8 x 10–12 m/s

30.0 MPa m0.5

CL

Kmax

Crack Length
72 

Figure 3-45 (Cont.) 

(h) 

(i) 

(j) 

13.450

13.500

13.550

13.600

13.650

13.700

13.750

13.800

10

20

30

40

50

60

70

80

4300 4400 4500 4600 4700 4800 4900 5000

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Period 17

8.1 x 10–10 m/s

30.0 MPa m0.5

R=0.5, 120/12

Kmax

Crack Length

Period 18

2.2 x 10–10 m/s

30.0 MPa m0.5

R=0.5, 600/12

Period 19

2.3 x 10–11 m/s

30.0 MPa m0.5

R=0.5, 600/12 +2 h

14.000

14.400

14.800

15.200

15.600

10

20

30

40

50

60

70

80

5000 5200 5400 5600 5800

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Period 20

7.3 x 10–10 m/s

29.3 MPa m0.5

R=0.5, 120/12

Kmax

Crack Length

Period 23

8.4 x 10–10 m/s

28.4 MPa m0.5

R=0.5, 120/12

Period 24

7.7 x 10–10 m/s

29.2 MPa m0.5

R=0.5, 120/12

Period 21

6.4 x 10–10 m/s

26.4 MPa m0.5

R=0.5, 120/12

Period 26

9.1 x 10–10 m/s

30.7 MPa m0.5

R=0.5, 120/12

Period 27

1.1 x 10–9 m/s

30.5 MPa m0.5

R=0.5, 120/12

14.800

15.200

15.600

16.000

16.400

10

20

30

40

50

60

70

80

5700 5800 5900 6000 6100 6200 6300

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 28

9.4 x 10–10 m/s

30.8 MPa m0.5

R=0.5, 120/12

Period 31

4.4 x 10–10 m/s

31.4 MPa m0.5

R=0.5, 600/12

Period 32

5.3 x 10–10 m/s

32.8 MPa m0.5

R=0.5, 600/12 + 2h

Period 30

8.8 x 10–10 m/s

31.3 MPa m0.5

R=0.5, 120/12
73 

Figure 3-45 (Cont.) 

(k) 

(l) 

(m) 

16.16

16.18

16.20

16.22

16.24

10

20

30

40

50

60

70

80

6140 6150 6160 6170 6180 6190 6200 6210

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 31

5.3 x 10–10 m/s

32.8 MPa m0.5

R=0.5, 600/12

16.40

16.80

17.20

17.60

18.00

20

40

60

80

100

6400 6600 6800 7000 7200 7400 7600 7800

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 33

3.0 x 10–10 m/s

Constant load

33f

5.1 x 10–10 m/s

44.2 MPa m0.5

specimen unloaded

3.8 x 10–10 m/s

43.1 MPa m0.5

33i

1.6 x 10–10 m/s

32.3 MPa m0.5

Alloy 52M/182 interface

16.40

16.60

16.80

17.00

17.20

17.40

20

40

60

80

100

6500 7000 7500

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 33i

1.6x 10–10 m/s

32.3 MPa m0.5

Constant load

Alloy 52M/182 interface

3.8 x 10–10 m/s

43.1 MPa m0.5
74 

Figure 3-45 (Cont.) 

(n) 

(o) 

The post test-examination of this specimen involved the examination of the side surfaces (cross 

sections) as well as that of the fracture surface. 

For this test, the examination of the side surfaces was essential for determining the crack path. 

For this purpose, the side surfaces of the specimen were ground to eliminate the side grooves, 

polished and electrochemically etched in a nital solution. The two side surfaces (Fig. 3-46) 

show that the test progressed as anticipated, and confirm that the test took place in the Alloy 

52M dilution – interface area, as was intended. 

The two side surfaces were further examined by optical microscopy, Fig. 3-47. The crack 

advance was straight, and the large opening suggests a TG fracture mode for the most part of 

the test. The average TG advance measured on the two side surfaces is 5.01 mm, a value 

which corresponds to test period 31 (Table 3-5). This finding suggests that the onset of high 

environmental enhancement in test period 31 corresponds to a change in fracture mode from 

TG to IG. 

17.20

17.28

17.36

17.44

17.52

17.60

17.68

17.76

17.84

30

35

40

45

50

55

60

65

7560 7600 7640 7680 7720 7760 7800 7840 7880

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 33f

5.1 x 10–10 m/s

44.2 MPa m0.5

Constant load

specimen unloaded

1.4 x 10–9 m/s

Alloy 52M/182 interface

17.76

17.78

17.80

17.82

17.84

20

25

30

35

40

45

50

7860 7880 7900 7920 7940 7960 7980 8000

Time (h)

Alloy 52M Specimen WOL-ST-2

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 34

5.9 x 10–11 m/s

31.1 MPa m0.5

Constant load

specimen unloaded
75 

(a) (b) 

Figure 3-46 Notch area post-test in specimen WOL-ST-2 seen from both sides: 

(a) side 1, and (b) side 2. The red arrows indicate the WOL interface. 

Crack advance is from right to left. 

The IG regions initiating in the areas marked 1A and 2A in Figs. 3-47a and 3-47b, respectively, 

were further examined in the SEM. Figure 3-48 shows the IG region on side 1 of the specimen. 

Chemical composition measurements show that Cr levels were on average 25.5 wt. % along the 

IG crack path, and no Cr gradient seems present. By contrast, Cr levels at location 1B –

corresponding to test period 16 with no SCC growth – were 27.1 wt. %. The figure also reveals 

that the IG crack appears to have taken a more favorable orientation towards the interface, but 

the clear path seems to be obstructed by a ligament. Nevertheless, cracking along the interface 

seems extensive, 1.6 mm from the end of the TG region. Secondary cracking in Alloy 182 is 

also visible. Figure 3-49 shows the IG region on side 2 of the specimen (beginning at location 

marked 2A in Fig. 3-47b). Chemical composition measurements at the TG-IG transition area 

show that Cr levels were on average 26.6 wt. %, however, the crack did not seem to propagate 

much. For comparison, Cr levels at location 2B in Fig. 3-47b –corresponding to test period 16 

with no SCC growth – were 28.1 wt. %. Nevertheless, the crack appears to have taken a more 

favorable orientation towards the interface, and it resurfaces at the interface with Alloy 182, 

0.9 mm away. As with the previous cross section, cracking along the interface seems 

extensive, and ends 1.2 mm from the TG region. Extensive secondary cracking in Alloy 182 is 

also visible. 

In order to gain additional information regarding the crack propagation in the Cr dilution zone of 

Alloy 52M, an additional cross section was created by sectioning the specimen in the middle. 

This middle cross section (side M) is shown in Fig. 3-50. As with the two side surfaces, the 

crack advance was straight with a large opening suggesting a largely TG fracture mode. 

Nevertheless, Fig. 3-50 shows that following the TG growth, the crack propagated in an IG 

fashion towards the interface, perhaps along a more favorable weld orientation. Figure 3-51 

(taken at location A in Fig. 3-50) shows that the average Cr content along the crack path was 

24.2 wt. %. By contrast, Cr levels at location B in Fig. 3-50 – corresponding to test period 16 

with no SCC growth – were on average 27.1 wt. %. As with the previous two examples, 

cracking along the interface seems extensive, 2.2 mm from the end of the TG region. Extensive 

secondary cracking in Alloy 182 is also visible. 

 
76 

a) 

(b)

Figure 3-47 Cross section of specimen WOL-ST-2: (a) side 1, and (b) side 2. Crack 

advance is from right to left. The red arrows indicate the WOL interface.
77 

Figure 3-48 Crack tip region on the first side surface of specimen WOL-ST-2 (side 1, 

location 1A in Fig. 3-47a). Crack advance is from right to left. Cr 

concentration at select locations is indicated in the figure. The red arrows 

indicate the WOL interface.
78 

Figure 3-49 Crack tip regions on the second side surface of specimen 

WOL-ST-2 (side 2, location 2A in Fig. 3-47b). Crack advance is from 

right to left. Cr concentration at select locations is indicated in 

the figure. The red arrow indicates the WOL interface. 
79 

Figure 3-50 Cross section of specimen WOL-ST-2: taken in the middle of the specimen 

(side M). Crack advance is from right to left. The red arrows indicate the 

WOL interface. 
80 

Figure 3-51 Crack tip regions on the second side surface of specimen 

WOL-ST-2 (side M, location A in Fig. 3-50). Crack advance is 

from right to left. Cr concentration at select locations is 

indicated in the figure. The red arrow indicates the WOL 

interface. 
81 

In summary, the examination of three cross sections revealed that the test evolved as planned: 

the crack was transitioned to IG in the diluted area of Alloy 52M WOL, was allowed to propagate 

towards the interface, and towards the end of the test it reached and propagated along the 

interface. SCC cracking at constant load seemed to span three regions: Cr diluted Alloy 52M 

WOL in the beginning, Alloy 52M-182 interface at the end, and most likely a combination of the 

two in the middle. This sequence seems to describe the evolution observed during test period 

33 in Fig. 3-45l. 

The Cr content of the diluted Alloy 52M WOL seems to play a role: SCC occurred in regions 

with a Cr content which was on average 25.4 wt. %, and did not occur in regions with Cr content 

of 27.1 wt. %. Also, qualitatively, cracking appeared to be the most extensive in the middle 

cross section (24.2 wt. %), followed by side 1 (25.5 wt. %); side 2 (26.6 wt. %) showed the least 

amount of propagation. 

After the cross sections were examined, the two halves of the specimen were fractured apart 

after cooling in liquid nitrogen. Both appeared to have fractured along the initial direction of the 

crack front, i.e., along the direction labeled “1” in Fig. 3-50. This outcome was somewhat 

unexpected, as cracking along direction “2” (along the dendrites) seemed to feature prominently 

in at least two of the three cross sections examined. 

The fracture surface of specimen WOL-ST-2 is shown in Fig. 3-52. With respect to the CT 

specimen geometry, the fracture surface shown corresponds to the bottom part of the specimen 

as shown in Fig. 3-42, i.e., the Alloy 182 weld is below the plane of the crack. The yellow 

arrows indicate the beginning of SCC growth, the red arrows show the end of the test, and the 

green arrows indicate the region where the crack would have intersected the interface. The 

relative location of each cross section, side 1 (CS 1), side 2 (CS 2), and the middle cross 

section (CS M) described previously is indicated in the figure. Crack advance measurements 

on the fracture surface and the DC potential measurements are in excellent agreement (4%) for 

the precracking and transitioning stage. However, the crack advance under constant load was 

approximately 4.2 times higher than the determination by DC potential. The disparity between 

the DC potential and the actual measurements is not surprising given the complicated crack 

pattern and the large unbroken ligaments that have been observed on the cross sections. As 

such, a correction factor of 4.2 was applied uniformly to test periods 32-34. Table 3-5 and Fig. 

3-45l-o already reflect that correction. 

 
82 

Figure 3-52 Fracture surface of specimen WOL-ST-2. The yellow arrows indicate the 

beginning of SCC growth, the red arrows show the end of the test, and the 

green arrows indicate the region where the crack would have intersected 

the interface. Crack advance is from bottom to top. 

Figure 3-53 shows the first half of the fracture surface, and focuses on the region at constant 

load. As before, the yellow arrows indicate the beginning of SCC growth, the red arrows show 

the end of the test, and the green arrows indicate the region where the crack would have 

intersected the interface. Several locations of interest are identified in the figure. For the most 

part, the crack transitioned readily to an IG/interdendritic fracture mode, as observed at 

locations 1 and 2 (Figs. 3-53b, c). The morphology is consistent with an ST orientation 

(perpendicular to the direction of dendrites, i.e., along direction 1 in Fig. 3-50), and several 

secondary cracks can be observed. Further along, more prominent secondary cracks seem to 

develop, most likely along direction 2 in Fig. 3-50, Figs. 3-53d. 
83 

(a) 

 (b) (c) 

(d) 

Figure 3-53 (a) First half (right hand side of Fig. 3-52a) of the fracture surface of specimen 

WOL-ST-2 obtained under constant load in simulated primary water. (b) 

location 1, (c) location 2, and (d) location 3. Crack advance is from bottom 

to top. 

 
84 

Figure 3-54 focuses on the later part of the test. Figure 3-54a (location 4 in Fig. 3-53a) shows a 

combination of fracture modes: IG/interdendritic with secondary cracks, ductile rupture (white 

arrow) – most likely a ligament, and in the upper left hand corner, a fracture mode that seems 

consistent with that of the interface. Figure 3-54b (location 5 in Figs. 3-53a) shows the fracture 

surface at the end of the test. This exhibits an IG/interdendritic fracture mode as well as 

secondary IG cracks. 

(a) (b) 

Figure 3-54 Fracture surface of specimen WOL-ST-2 at (a) location 4, and (b) location 5 in 

Fig. 3-53a. The white arrow indicates an unbroken ligament. Crack advance is 

from bottom to top. 

Figure 3-55 shows the second half of the fracture surface in the constant load region. The 

yellow arrows indicate the beginning of SCC growth, the red arrows show the end of the test, 

and the green arrows indicate the region where the crack would have intersected the interface. 

Several locations of interest are identified in the figure. For approximately 1/3 of the fracture 

surface, the appearance is similar to that shown in Fig. 3-53a. However, out of plane cracking – 

most likely along direction 2 (along the dendritic grains) in Fig. 3-50 – seems dominant. On this 

half of the specimen, cracking along the dendrites occurred early, Fig. 3-55b, and seems to 

have also been extensive. Figure 3-55c shows a region displaying what appears to be deep 

secondary cracking. Fracture morphology consistent with the weld interface (white arrow) also 

seems to be present. 

The right hand side of Fig. 3-55a corresponds to the cross section shown in Fig. 3-49. In this 

particular case, the crack path was obstructed by a large ligament (Figure 3-49 suggested it was 

also off plane), but resurfaced along the weld interface. Fig. 3-55a provides confirmation for 

that initial inference, and pictures taken at location 3 provide the fracture morphology of the 

cracked weld interface. These images are shown in Fig. 3-56. 

In summary the examination of the fracture surface confirmed the earlier observations on the 

cross sections. The crack transitioned readily to an IG/interdendritic fracture mode, and 

propagated in the Cr diluted area of Alloy 52M along two main directions, labeled 1 and 2 in 

Fig. 3-50. Direction 1 (normal to the dendrites) appeared to be the dominant direction, and the 

secondary cracking observed on the fracture surface was mostly due to of propagation along 

direction 2. Upon reaching the interface, IG/interdendritic fracture mode continued. 
85 

(a) 

(b) (c) 

Figure 3-55 Second half (left hand side of Fig. 3-52a) of the fracture surface of specimen 

WOL-ST-2 obtained under constant load in simulated primary water. (b) 

location 1, and (c) location 2. Crack advance is from bottom to top. 

 (a) (b) 

Figure 3-56 Fracture surface of specimen WOL-ST-2 at location 3 in Fig. 3-55a. Crack 

advance is from bottom to top. 
86 

3.2 SCC CGR Testing of Alloy 152-LAS 1st Dilution Layer 

Two tests were completed on Alloy 152 in a first layer configuration (Fig. 3-57), and the results 

will be presented in this section. There was no microstructural characterization conducted prior 

to machining the specimens. The only requirement for the specimens – produced at ANL 

Central Shops - was that they be aligned in the first weld layer, hence, the specimens sampled 

random locations in that first layer. The microstructural characterization (with a special attention 

to Cr concentration) was conducted post-test, along the actual crack path. 

Figure 3-57 Photograph of the Alloy 152 weld joining Alloy 690 and Alloy 533 LAS. SCC 

CGR test specimens were aligned in the 1st layer of Alloy 152 butter. 

3.2.1 SCC CGR Test on 1st layer Alloy 152 Weld Butter Specimen N152-LAS-1 

Specimen N152-LAS-1 was a 1T CT specimen aligned along the first layer of the Alloy 152 

butter, with the notch located approximately at the end of the blue arrow shown in Fig. 3-57. 

Figure 3-58 shows both sides of that specimen prior to the SCC CGR test. Pictures taken 

before and after machining the notch have been overlapped to show alignment. The alignment 

was aimed at the outer region of the Alloy 152, as close to the LAS as was possibly achievable. 

Both sides of this specimen seem to indicate that one lobe of the butter weld is ahead of the 

crack tip. 
87 

(a) (b) 

Figure 3-58 Specimen N152-LAS-1, overlapped images before and after the specimen 

notch was machined: (a) side 1, and (b) side 2. Units of the rulers are mm. 

The testing conditions for specimen N152-LAS-1 are given in Table 3-6 (data has been 

corrected based of fractography). The crack was advanced approximately 1.65 mm in fatigue, 

slightly into the first weld lobe, and transitioning steps were undertaken. The SCC CGR 

component was first calculated by superposition in test period 4 to be approximately 1.9x10-11

m/s, and this rate suggested that the fracture mode was IG. However, it became clear rather 

quickly that the preferred crack path is off-plane, hence a correct SCC CGR will be difficult to 

measure by DC potential. To illustrate this point, a visual representation of the test in the 

approach described previously in Section 2.5. and applied successfully in a previous test (Fig. 

3-44) is shown in Fig. 3-59. The plots tracks the environmental enhancement of two loading 

conditions – rise 50s and rise 600s, R = 0.5 – vs. crack advance from the notch. The purpose 

of the fast cycle is to advance the crack, and the purpose of the slow cycle is to probe for 

environmental enhancement. The dotted red and blue horizontal lines represent the 

enhancement levels of a forward advancing IG crack based on the Alloy 152 experience (Fig. 

2-10). The large scatter observed in the cyclic response was judged to be indicative of primarily 

off-plane crack propagation. Overall, Fig. 3-59 also provides the SCC CGRs and shows that 

such measurements were attempted mainly at two locations in the specimen where the 

“conditions” were judged to be optimal from an experimental standpoint. 

 

152 LAS LAS 152 
88 

Table 3-6 Crack growth data for dilution specimen N152-LAS-1 in PWR watera,b,c

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time, 

Down 

Time, 

Hold 

Time, Kmax, ∆K, CGRenv, 

Estimated 

CGRair, 

Crack 

Length, 

Period h C R s s s MPa·m1/2 MPa·m1/2 m/s m/s mm 

Pre a 145 321.3 0.2 0.5 0.5 21.7 17.4 4.48E-08 1.02E-07 10.480 

Pre b 160 321.2 0.2 50 50 21.8 17.4 1.06E-09 1.02E-09 10.515 

Pre c 169 321.1 0.2 0.5 0.5 23.1 18.5 9.06E-08 1.30E-07 11.430 

Pre d 184 321.2 0.2 50 50 23.3 18.6 1.15E-09 1.34E-09 11.534 

Pre e 189 321.1 0.2 0.5 0.5 24.3 19.4 9.01E-08 1.59E-07 12.196 

Pre f 193 321.1 0.2 1 1 24.7 19.7 3.60E-08 8.48E-08 12.466 

Pre g 208 321.2 0.2 50 50 24.7 19.8 2.26E-09 1.72E-09 12.506 

Pre h 214 321.3 0.2 1 1 25.3 20.3 3.56E-08 9.50E-08 12.885 

1 234 321.2 0.5 50 12 25.4 12.7 1.12E-09 6.04E-10 12.966 

2 305 321.7 0.5 300 12 25.5 12.8 2.66E-10 1.03E-10 13.039

3 575 320.0 0.5 600 12 25.8 12.9 1.32E-10 5.25E-11 13.133

4 976 320.4 0.5 600 12 7,200 25.8 12.9 4.16E-11 4.09E-12 13.171

5 1,742 320.3 1.0 0 0 25.8 0.0 1.99E-11 - 13.201

6 2,421 319.4 0.5 12 12 7,200 26.0 13.0 1.98E-11 4.47E-12 13.262 

7 2,680 320.5 1.0 0 0 26.0 0.0 1.47E-11 - 13.279

8 2,917 320.9 0.49 600 12 25.9 13.2 7.49E-11 5.72E-11 13.358 

9 3,024 321.1 0.49 50 12 26.1 13.3 6.36E-10 7.07E-10 13.541 

10 3,454 320.9 0.49 600 12 26.2 13.4 4.57E-11 6.01E-11 13.628 

11 3,862 320.5 0.49 50 12 27.8 14.2 8.37E-10 9.04E-10 14.530 

12 3,934 320.1 0.49 600 12 27.8 14.2 1.17E-10 7.54E-11 14.545 

13 4,151 320.0 0.49 50 12 29.3 14.9 1.49E-09 1.12E-09 15.366 

14 4,294 320.1 0.49 600 12 29.5 15.0 2.13E-10 9.55E-11 15.474 

15 4,318 320.0 0.49 50 12 29.6 15.1 1.53E-09 1.18E-09 15.565 

16 4,367 320.0 0.49 600 12 29.8 15.2 2.48E-10 9.95E-11 15.605 

17 4,534 320.0 0.49 600 12 7,200 29.9 15.3 1.12E-10 7.82E-12 15.693 

18 6,879 319.6 1.0 0 0 30.1 0.0 1.82E-11 - 15.839

19 7,026 319.1 0.49 600 12 30.3 15.5 2.48E-10 1.06E-10 16.034 

20 7,237 319.5 0.49 600 12 7,200 30.2 15.4 5.46E-11 8.12E-12 16.073 

21 7,977 318.7 1.00 0 30.2 0.0 no growth - 16.073

22 9,701 318.8 0.49 12 12 28,800 30.6 15.6 9.90E-12 2.29E-12 16.115 

23 11,411 318.7 0.49 12 12 7,200 30.7 15.6 1.44E-11 9.25E-12 16.211 

24 13,060 318.3 1.0 0 0 30.7 0.0 no growth - 16.211

25 13,068 27.3 0.2 1 1 32.3 25.8 2.80E-08 7.88E-08 16.961 

a

 Simulated PWR water with 2 ppm Li, 1000 ppm B, and 2 ppm. DO<10 ppb. Conductivity was 213 S/cm, and pH 6.4. b

 CGR rates in air are calculated assuming typical behavior for a Ni-base weld. The 152-LAS rates are approximately a factor of two lower. c

 Data was corrected using fractography. 
89 

Figure 3-59 Environmental enhancement of two control test conditions and SCC CGRs vs. 

distance from the specimen notch for Specimen N152-LAS-1. Test periods are 

indicated in the figure. 

The changes in crack length and Kmax vs. time are shown in Fig. 3-60. As described previously, 

the SCC CGR component was first calculated by superposition in test period 4 to be 

approximately 1.9x10-11 m/s, and this rate is substantiated by the rate measured in the 

subsequent test period at constant load only if the jump observed when cyclic is re-introduced is 

considered an unbroken ligament and in taken into account in the rate calculation, as shown in 

Fig. 3-60c. Nevertheless, the rates measured during the following test periods 6 and 7 seem to 

substantiate these early SCC CGR determinations. However, the rates measured in test period 

8 under cyclic loading is approximately half of that measured under similar conditions in test 

period 3, suggesting that the preferred crack path is off-plane. Some of the challenges posed 

by off-plane cracking will be highlighted next. After a favorable location was identified in test 

periods 14 and 16, and an approximately 2x10-10 m/s SCC CGR component was estimated by 

superposition in test period 17 (Fig. 3-59), the specimen was set at constant load in period 18 

(Fig. 3-60g). The resulting SCC CGR was approximately 1.8x10-11 m/s for the first 1000h of 

this test period, then diminished to approximately 7x10-13 m/s. At that stage, cycling was 

reintroduced in test period 19, and it is interesting to note that under cyclic loading the initial 

measured CGR of 1.2x10-9 m/s decreases by a factor 5 by the end of the test period (Fig. 

3-60h), suggesting that the ligaments that that had formed during the constant load test period 

were being broken. If the rate of growth in test period 18 is assumed to have been 1.8x10-11

m/s for the entire test period, the subsequent (remaining) growth in test period 19 still displays a 

pronounced curvature (Fig. 3-60h), and this shape is atypical of corrosion fatigue growth. 

Hence, a more conservative approach would have been to assume that growth in test period 18 

ended where the CGR in test period 19 stabilizes and reaches the expected value of 2.4x10-10

m/s, making it consistent with test period 16. In this latter case, the conservative SCC CGR for 

test period 18 is estimated to be 3.7x10-11 m/s. 

An additional example of SCC growth determination is shown in Fig. 3-60j. As the measured 

SCC CGR under constant load conditions in the preceding test period 21 was very small, 

0.00

1.00

2.00

3.00

4.00

5.00

10-12

10-11

10-10

2.5 3 3.5 4 4.5 5 5.5 6 6.5

R=0.5, 600/12

R=0.5, 50/12

SCC CGR

CGRenv/CGRair

Crack advance from specimen notch (mm)

1

9

11

3

8

10

12

13

14

16

15

5

7 18

Alloy 152 dilution

Specimen # N152-LAS-1

PWR environment

19

22

23

Solid symbols: CL

SCC CGR (m/s)

no growth

2124

20

4 6

17
90 

periodic unloading (8h hold, CGRair ≈ 1x10-12 m/s) was introduced in test period 22 to 

investigate whether unbroken ligaments are present or not. The SCC CGR measured initially 

(first 1,000h) in test period 22 was approximately 9.9x10-12 m/s, then the growth appeared to 

stop. In order to re-activate the growth, a somewhat more aggressive loading (2h hold, CGRair

≈ 5x10-12 m/s) was introduced in test period 23 and the response was similar to that observed at 

the beginning of test period 22. The fact that a similar rate was measured under two different 

hold times (8h in period 22, and 2h in period 23) confirms that fatigue is not the dominating 

driving force for crack growth in this specimen. After another “no growth” measurement under 

constant load conditions in test period (24), the test in water ended, and that was followed by a 

final fatigue test period in room temperature air. 

It is important to note that while the above seemingly “benign” SCC CGR determinations were 

made by DC potential, massive SCC was taking place off-plane, in a direction almost normal to 

the test plane. 

(a) 

(b) 

Figure 3-60 Crack–length–vs.–time for dilution specimen N152-LAS-1 in simulated PWR 

environment during test periods (a) precracking-2, (b) 3-4, (c) 5, (d)6, (e) 7-10, 

(f) 11-17, (g) 18, (h) 19-20, (i) 21, (j) 22-23, and (k) 24.

10.400

10.800

11.200

11.600

12.000

12.400

12.800

13.200

20

22

24

26

28

30

150 200 250 300

Time (h)

Specimen N152-LAS-1

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Pre a Pre b Pre c Pre d

e f

Pre g

h Period 1 Period 2

12.900

12.950

13.000

13.050

13.100

13.150

13.200

13.250

13.300

20

22

24

26

28

30

300 400 500 600 700 800 900 1000

Time (h)

Specimen N152-LAS-1

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 3

1.32 x 10–10n m/s

25.8 MPa m0.5

R=0.5, 600/12

Period 4

4.2 x 10–11 m/s

25.8 MPa m0.5

R=0.5, 600/12 +2 h
91 

Figure 3-60 (Cont.)

(c) 

(d) 

(e) 

13.100

13.150

13.200

13.250

13.300

10

20

30

40

50

60

1000 1200 1400 1600 1800

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Period 5

7.1 x 10–12 m/s

25.8 MPa m0.5

CL

Kmax

Crack Length

2.0 x 10–11 m/s

13.100

13.150

13.200

13.250

13.300

13.350

13.400

10

20

30

40

50

60

1700 1800 1900 2000 2100 2200 2300 2400 2500

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Period 6

2.0 x 10–11 m/s

26.0.0 MPa m0.5

CL + PU(2h)

Kmax

Crack Length

13.200

13.300

13.400

13.500

13.600

13.700

10

20

30

40

50

60

2400 2600 2800 3000 3200 3400

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Period 7

1.5 x 10-11 m/s

26.0 MPa m0.5

CL

Kmax

Crack Length

Period 8

7.5 x 10–11 m/s

26.0 MPa m0.5

R=0.5, 600/12

Period 9

6.4 x 10–10 m/s

26.1 MPa m0.5

R=0.5, 50/12

Period 10

4.6 x 10–11 m/s

26.2 MPa m0.5

R=0.5, 600/12
92 

Figure 3-60 (Cont.)

(f) 

(g) 

(h) 

14.000

14.500

15.000

15.500

16.000

10

20

30

40

50

60

3400 3600 3800 4000 4200 4400 4600

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 11

8.4 x 10–10 m/s

27.8 MPa m0.5

R=0.5, 50/12

Period 13

1.5x 10–9 m/s

29.3 MPa m0.5

R=0.5, 50/12

Period 17

1.1 x 10–10 m/s

29.9 MPa m0.5

R=0.5, 600/12 + 2h

15.600

15.700

15.800

15.900

16.000

16.100

10

20

30

40

50

60

70

80

4500 5000 5500 6000 6500 7000

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax Crack Length

Period 18

1.8 1x 10–12 m/s

30.1 MPa m0.5

CL

1.8 x 10–11 m/s

7.5 x 10–13 m/s

3.7 x 10–11 m/s

1.8 x 10–11 m/s

15.700

15.750

15.800

15.850

15.900

15.950

16.000

16.050

16.100

10

20

30

40

50

60

6800 6900 7000 7100 7200

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

1.2 x 10–9 m/s

Period 19

2.5 x 10–10 m/s

30.3 MPa m0.5

R=0.5, 600/12

Period 20

3.3 x 10–11 m/s

26.0 MPa m0.5

R=0.5, 600/12 + 2h

1.8 x 10–11 m/s

3.7 x 10–11 m/s

2.5 x 10–10 m/s
93 

Figure 3-60 (Cont.) 

(i) 

(j) 

(k) 

 

15.900

15.950

16.000

16.050

16.100

16.150

16.200

10

20

30

40

50

60

7200 7300 7400 7500 7600 7700 7800 7900 8000

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 21

no growth

30.2 MPa m0.5

CL

16.000

16.050

16.100

16.150

16.200

16.250

10

20

30

40

50

60

8000 8500 9000 9500 10000 10500 11000 11500

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Period 22

9.9 x 10–12 m/s

30.6 MPa m0.5

CL + PU (8h)

9.9 x 10–12 m/s

4.5 x 10–12 m/s

Period 23

1.4 x 10–11 m/s

30.7 MPa m0.5

CL + PU (2h)

1.0 x 10–11 m/s

Crack Length

1.4 x 10–11 m/s

16.100

16.150

16.200

16.250

16.300

16.350

16.400

10

20

30

40

50

60

70

80

11500 12000 12500 13000

Time (h)

Specimen N152-LAS-1

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 24

no growth

30.7 MPa m0.5

CL 
94 

Figure 3-60 (Cont.) 

(l) 

The post-test examination of specimen N152-LAS-1 involved the examination of both the side 

surfaces and that of the fracture surface. For the examination of the side surfaces, the sidegrooved sections of the specimens were removed by wire cutting, and the resulting flat surfaces 

were polished and etched electrochemically in a 10% nital solution. Following this exposure, 

the resulting weld surface was still shiny while the LAS surface became dull. Nevertheless, the 

outcome (Fig. 3-61) shows that the test went largely as planned (see for comparison Fig. 3-58). 

Figures 3-62 and 3-63 are SEM images of the side surfaces. Areas of interest are shown at 

higher magnification in each figure. As described previously, the crack started from the notch in 

the LAS, then, upon reaching the Alloy 152 interface, it continued along the interface. 

Eventually, in both cases, the crack made its way into the weld. The crack hit the LAS interface 

once more towards the end of the test. This location is marked LAS-i in Fig. 3-62. 

(a) (b) 

Figure 3-61 The two sides of the dilution specimen N152-LAS-1 after testing in primary 

water: (a) side 1, and (b) side 2. The red arrows indicate the approximate 

location of the end of the test as determined on the fracture surface. Units of 

the side rulers are mm. 

As the fracture surface will show later, Figure 3-62 is the best illustration of the evolution of this 

test. After advancing in the LAS and along the LAS-Alloy 152 interface in fatigue, the crack 

16.200

16.300

16.400

16.500

16.600

16.700

30

35

40

45

13060 13062 13064 13066 13068 13070

Time (h)

Specimen N152-LAS-1

RT air

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length Period 25

2.8 x 10–8 m/s

32.6 MPa m0.5

R=0.2, 0.5 Hz

6.8 x 0–8 m/s

1

2

1.2 x10–7 m/s
95 

turned into the weld, and the first attempts at an SCC CGR measurement were made at location 

1 in Fig. 3-62a. The crack appears to follow the direction of the interdendritic grains rather than 

that of the test plane. The first set of chemical composition measurements were conducted at 

this location by SEM EDX and yielded an average 27 Cr - 21.4 Fe – 51.5 Ni (Fig. 3-62b). Next, 

the crack advanced into the weld, intersected the LAS interface one more time (location marked 

LAS-i), then turned decisively into the weld, and propagated along the direction of the dendritic 

grains, normal to the original crack direction, shown in Fig. 3-62c. Chemical composition 

measurements were conducted in this region and yielded an average 24.1 Cr - 31.4 Fe – 

43.5 Ni (Fig. 3-62c). The latter measurements confirm that Cr dilution in the first weld layer at 

least 0.1 mm from the interface with the LAS. 

Figure 3-63 shows that on second side, after the initial advance in the LAS and the subsequent 

propagation in fatigue along the interface, the crack appears to stay mostly on the interface, and 

enters the LAS at the end of the test during fatigue in room temperature air. The micrograph 

shown in Fig. 3-63b illustrates crack propagation along the interface under cyclic loading. 

However, as with the first side surface, the first attempts at an SCC CGR measurement resulted 

in IG growth into the weld, in a direction normal to the test plane (Fig. 3-63c). 

In summary, the two cross sections show that while the LAS-Alloy 152 interface is a preferred 

path for fatigue crack propagation, it appears to be highly resistant to IG SCC. In fact, in this 

test, the crack had ample opportunity to propagate along the interface, but turned towards the 

weld each time transitioning to IG SCC was attempted. These observations are consistent with 

those generated within a co-operative research program between the Fracture & Reliability 

Research Institute (FRI) at Tohoku University and Paul Scherrer Institute (PSI) [26, 27]. In that 

program, the objective was to determine whether a fast growing IG SCC crack in the highly 

susceptible Alloy 182 weld metal can easily cross the fusion line and significantly propagate into 

the adjacent low-alloy RPV steel. The outcome of that research was that in high-purity or 

sulphate-containing oxygenated water under constant or periodic partial unloading conditions, 

IG SCC growth was arrested whenever it reached the LAS fusion line. The authors further 

speculated that a similar outcome was to be expected in PWR water because of the very low 

SCC and moderate corrosion fatigue susceptibilities of LAS at low ECP. While the results from 

the current test already seem to confirm that expectation, they will be substantiated further 

during the examination of the fracture surface. 

 
96 

(a) 

(c) (b) 

Figure 3-62 (a) Cross section 1 of Specimen N152-LAS-1, (b) detail at location 1 in (a), and 

(c) detail at location 2 in (a). The local Cr concentration is shown in red. Crack

advance is from left to right.
97 

(a) 

(c) (b) 

Figure 3-63 (a) Cross section 2 of Specimen N152-LAS-1, (b) detail at location 1 in (a), and 

(c) detail at location 2 in (a). Crack advance is from left to right. 

 
98 

Next, the specimen was broken open to allow for the examination of the fracture surface. This 

is shown in Fig. 3-64, and the major landmarks of the test are indicated in the figure. As 

described previously (Fig. 3-62), the crack started in the LAS, propagated along the interface 

and into the weld (note that there is no difference in appearance between the interface and the 

weld), and the first set of SCC CGR determination were made at location IG-1. Then, the crack 

was advanced through the weld, transitioned to IG SCC, hit the LAS interface again at location 

marked LAS-i, then continued its advance in an IG/interdendritic mode in the weld, IG-2. Rather 

large ligaments were observed on the left hand side of the fracture surface that developed 

during fatigue and corrosion fatigue propagation through the weld. It should be noted that in 

Fig. 3-64, the fracture surface was photographed slightly tilted to show the full extent of IG-2 

and ligaments (marked with red arrows) that developed in that region. 

Measurements performed on the un-tilted the fracture surface yielded an overall crack advance 

measurement error of 39%, and because ligaments have been observed in all stages of the 

test, this correction was applied uniformly along the DC potential data set. However, it is 

important to observe that especially in the tilted photograph (Fig. 3-64), the extent of IG-2 

appears to be approximately 5 times higher than the crack advance of 0.3 mm measured by DC 

potential for this region where the crack propagated off-plane. Hence, one conservative way to 

evaluate the SCC CGR for this entire region would be to simply divide the full extent of the crack 

by the time, and obtain approximately 5x10-11 m/s. 

Figure 3-64 Fracture surface (A, Fig. 3-63) of specimen N152-LAS-1 tilted to show the final 

IG region. Two regions of interest, R1 and R2 are marked in the figure. Crack 

advance is from bottom to top. 
99 

Figure 3-64 identifies two areas of interest, R1 and R2, and these will be discussed next. 

Figure 3-65 shows the image obtained in region R1 of Fig. 3-64. This image shows the 

ligaments that developed in the weld, in the close proximity to the LAS interface during the 

fatigue and corrosion fatigue stages of the test. Two additional locations of interest are further 

identified: IG-1 (location 1) and the second intersection of the crack with the LAS interface 

(location 2), labeled LAS-i. These are shown at higher magnification in Fig. 3-66. In region 

IG-1, the crack propagated mostly off-plane – and it appears mostly like a line in Fig. 3-64. At 

location 1 in Fig. 3-65, the geometry is further complicated by the presence of the weld 

ligaments. Nevertheless, Fig. 3-66a shows a mixed IG and TG fracture mode with quite 

prevalent secondary IG cracking. It is important to note that wherever the IG cracking is in the 

plane of the test, the dendritic features are normal to it. Figure 3-66b focuses on the crack 

intersection with the LAS at location 2 in Fig. 3-65. One observes that what appears to be a 

fully engaged IG crack in the weld does not propagate into the LAS, and somehow manages to 

continue as an IG crack in the weld only after it reaches the weld material again at the top of 

the picture. 

Figure 3-65 Region R1 on the fracture surface A of specimen N152-LAS-1 (Fig. 3-64). 

Blue arrows indicate the transition from LAS to Alloy 152, and two 

additional locations of interest: IG-1 (location 1) and the second 

intersection of the crack with the LAS interface (location 2), labelled LAS-i. 

Crack advance is from bottom to top. 

 
100 

(a) 

(b) 

Figure 3-66 Fracture surface of specimen N152-LAS-1, locations: (a) 1, and (b) 2 in region 

R1, Fig. 3-65. Crack advance is from bottom to top. 

Figure 3-67 shows an image obtained in region R2 of Fig. 3-64. Unlike region R1 (Fig. 3-65), 

the weld ligaments formed during the fatigue and corrosion fatigue stages of the test are less 

prominent. Two additional locations of interest, IG-1 (location 1) and the second intersection of 

the crack with the LAS interface (location 2), labeled LAS-i, are indicated in the picture. These 

locations are shown at higher magnification in Fig. 3-68. In region IG-1, while the crack 

propagated mostly off-plane, secondary cracks as well as a somewhat uniform IG/interdentritic 

mode can be observed, Fig. 3-68a. Again, it is important to note that the dendritic features are 

normal to the test plane. Figure 3-68b focuses on the intersection with the LAS at location 2 in 

Fig. 3-67. Again, one observes that what appears to be a fully engaged IG crack in the weld is 

essentially arrested at the LAS, and continues as an IG crack in the weld after it reaches the 

weld again at the top of the picture. Such areas would have likely remained as un-broken 

ligaments if the crack was not advanced under gentle cyclic loading. 
101 

Figure 3-67 Region R2 on the fracture surface A of specimen N152-LAS-1 (Fig. 3-64). Blue 

arrows indicate the transition from LAS to Alloy 152, and two additional 

locations of interest: IG-1 (location 1) and the second intersection of the crack 

with the LAS interface (location 2), labelled LAS-i. Crack advance is from 

bottom to top. 

Figures 3-69 and 3-70 focus on region IG-2 (Fig. 3-64), and in order to show some detail, the 

fracture surface was broken down into two halves. Areas of interest are identified in both 

pictures. As such, Fig. 3-69b shows the IG interdendritic cracking observed at location 1 in Fig. 

3-69a, and Fig. 3-69c focuses on a large ligament observed at location 2, also in Fig. 3-69a. 

Figure 3-69a also indicates the interaction between the crack and the LAS interface, e.g., L1 

and L2. As noted previously, one observes that what appears to be a fully engaged IG crack in 

the weld does not propagate into the LAS, but manages to continue as an IG crack in the weld 

after it reaches the 
102 

(a) 

(b) 

Figure 3-68 Fracture surface of specimen N152-LAS-1, locations: (a) 1, and (b) 2 in region 

R2, Fig. 3-67. Crack advance is from bottom to top. 

weld again at the top of the picture. As described previously, it is likely that this area would 

have remained as an un-broken ligament if not for the cyclic loading. Likewise, Fig. 3-70 shows 

the second half of region IG-2 (Fig. 3-64). Figure 3-70b shows the IG interdendritic cracking 

observed at location 3 in Fig. 3-70a, and Fig. 3-70c focuses on a large ligament and 

surrounding IG cracking observed at location 4 in Fig. 3-70a. Overall, the fracture mode in the 

IG-2 region was almost completely IG. However, as noted previously, the direction of 

propagation was off-plane, and, hence, there should be no surprise that the DC potential 

recorded very low or “no growth” SCC CGRs. 

In summary, the conclusions and, more importantly, the “lessons learned” from the first test are 

as follows: the Cr-diluted Alloy 152 butter is susceptible to SCC, the IG fracture mode was found 

to occur readily, and the measured SCC rates are high enough to warrant further investigation. 

However, cracking tends to occur off-plane, hence, constant load should follow quickly once a 

“susceptible” region is identified. This could be accomplished by eliminating the test periods 

with a hold. Also, consistent with similar observations from the literature [26, 27], the LAS and 

LAS-weld interface appears to be resistant to IG SCC as no evidence of IG cracking was found 

at the LAS interface or in the LAS despite ample opportunity. As such, in order to avoid crack 

arrest at the LAS-152 interface, future specimens should be aligned further away from the Alloy 

152-LAS interface.
103 

(a) 

(c) (b) 

Figure 3-69 Fracture surface of N152-LAS-1, region IG-2 (Fig. 3-64): (a) first half of the 

fracture surface, (b) detail at location 1, and (c) detail at location 2. Crack 

advance is from bottom to top. 
104 

(a) 

(c) (b) 

Figure 3-70 Fracture surface of N152-LAS-1, region IG-2 (Fig. 3-64): (a) second half of the 

fracture surface, (b) detail at location 3, and (c) detail at location 4. Crack 

advance is from bottom to top. 
105 

3.2.2 SCC CGR Test on 1st Layer Alloy 152 Weld Butter Specimen N152-LAS-11 

Specimen N152-LAS-11 was cut from the same general area as the prior specimen, and the 

notch location was perhaps two weld beads removed from that of specimen N152-LAS-1, Fig. 

3-71. The specimen arrangement shown in Fig. 3-71 was chosen because it allowed for two 

test specimens to be machined from the same piece of material. However, the positioning of 

the N152-LAS-11 specimen with respect to the weld-LAS interface benefitted from the “lessons 

learned” in the first test. As such, in order to avoid crack interaction and arrest at the Alloy 

152-LAS interface, the notch of Specimen N152-LAS-11 was still machined in the 1st layer of 

Alloy 152 weld, but further away from the interface with the LAS, Fig. 3-72. 

Figure 3-71 Approximate locations of the CT specimen blanks for first layer and second 

layer weld butter SCC CGR testing. The specimen blank that will later become 

CT test specimen N152-LAS-11 is indicated in the figure. 

 

N152-LAS-11 
106 

(a) (b) 

Figure 3-72 The two sides of specimen N152-LAS-11 prior to the SSC test: (a) side 1, and 

(b) side 2. Alloy 152 is in the top half, and the LAS is in the bottom half of both

pictures.

The test on specimen N152-LAS-11 was initiated with precracking in the PWR environment, 

followed by transitioning. The testing conditions are given in Table 3-7, and a visual 

representation of the test in the framework described previously is shown in Fig. 3-73. As 

before, the plots tracks the environmental enhancement of two loading conditions – rise 50s and 

rise 600s, R = 0.5 – vs. crack advance from the notch. The purpose of the fast cycle is to 

advance the crack, and the purpose of the slow cycle is to probe for environmental 

enhancement. The dotted red and blue horizontal lines represent the enhancement levels of a 

forward advancing crack based on the prior Alloy 152 experience (Fig. 2-10). The changes in 

crack length and Kmax vs. time are shown in Fig. 3-74. 

Early data (Fig. 3-73) seem to show an environmental enhancement exceeding the highest that 

was observed in the N152-LAS-1 specimen (and in the Alloy 152 tested previously, Fig. 2-10), 

hence, the current specimen was set at constant load fairly early in test period 4. Upon 

measuring a small SCC CGR, the cyclic routine was repeated, allowing more time in test period 

6 to assess the SCC CGR component. Based on superposition in test periods 5 and 6, this was 

calculated to be 1.7x10-12 m/s. The rate was next measured at constant load in test period 7 

and was found to be indeed very small, 1.4x10-12 m/s. Subsequent cycling in test period 8 

found significantly less environmental enhancement (Fig. 3-73). The dramatic drop in cyclic 

response suggests that SCC occurred off-plane, and the SCC CGR measurements conducted 

in the interim are perhaps of little significance. 

Next, the crack was advanced incrementally using the fast/slow loading conditions described 

previously, monitoring the environmental enhancement in an attempt to identify another “SCCsusceptible” microstructure. A condition yielding comparable enhancement to that resulting in a 

1.81x10-11 m/s SCC CGR in the prior test was identified in test period 27. Next, the test was 

converted directly to constant load in test period 28, assuming that the more susceptible 

material was at that point still ahead of the crack. The test ended after approximately 2,700h in 

this condition resulting in approximately 1.4 mm of growth (after a factor 10 correction based on 
107 

the fracture surface was applied to the DC potential data). One notes that following this large 

correction factor applied uniformly, the Kmax for test period 18 became almost 38 MPa m0.5. 

This is likely highly overestimated because - as the fractography will later show – large 

unbroken ligaments “shielded” the crack tip. While the average SCC CGR was approximately 

1.4x10-10 m/s, the rate was observed to accelerate locally to rates as high as 3.1x10-10 m/s, 

and slow down to rates as low as 4.0x10-11 m/s, Fig. 3-74i. In summary, there are two regions 

in this specimen (test periods 7-14 and 28) with SCC CGRs differing by a factor 100, and the 

subsequent post-test examination will have to elucidate the reason for the difference. 

Table 3-7 Crack growth data for Alloy 152 dilution specimen N152-LAS-11 in PWR 

watera,b,c

Test 

Test 

Time, Temp. 

Load 

Ratio 

Rise 

Time, 

Down 

Time, 

Hold 

Time, Kmax, ∆K, CGRenv, 

Estimated 

CGRair,

b

Crack 

Length, 

Period h C R s s s MPa·m1/2 MPa·m1/2 m/s m/s mm 

Pre a 55 320.0 0.30 1 0.5 22.8 15.9 2.26E-08 8.75E-08 11.784 

Pre b 71 320.0 0.30 50 50 22.9 16.0 1.24E-09 8.98E-10 11.819 

Pre c 74 319.8 0.30 1 0.5 23.5 16.5 5.17E-08 1.00E-07 12.029 

1 78 320.5 0.50 50 12 23.5 11.7 8.74E-10 4.33E-10 12.043 

2 143 319.9 0.50 600 12 23.6 11.8 1.41E-10 3.66E-11 12.076 

3 176 319.9 0.50 600 12 7,200 23.6 11.8 2.43E-11 2.83E-12 12.084 

4 493 320.0 1.00 0 0 23.7 0.0 5.34E-12 - 12.095 

5 504 320.1 0.50 600 12 23.8 11.9 1.60E-10 3.76E-11 12.104 

6 912 320.1 0.50 600 12 7,200 23.8 11.9 1.89E-11 2.92E-12 12.131 

7 1,442 320.1 1.00 0 0 23.7 0.0 1.47E-12 - 12.131 

8 1,488 320.1 0.50 600 12 23.6 11.8 9.78E-11 3.65E-11 12.145 

9 2,067 320.1 0.50 600 12 7,200 23.5 11.8 1.42E-11 2.78E-12 12.181 

10 3,026 320.1 1.00 0 0 23.8 0.0 1.25E-12 - 12.189 

11 3,864 320.0 0.50 12 12 14,400 24.0 12.0 3.67E-12 1.64E-12 12.204 

12 3,888 320.1 0.50 600 12 26.9 13.4 1.68E-10 6.26E-11 12.216 

13 4,009 320.2 0.50 600 12 7,200 27.0 13.5 2.81E-11 4.90E-12 12.233 

14 5,713 320.1 0.50 12 12 28,800 27.3 13.6 4.87E-12 1.38E-12 12.265 

15 6,025 320.2 0.50 600 12 - 27.6 13.8 1.20E-10 6.98E-11 12.374 

16 6,049 320.1 0.50 50 12 27.8 13.9 1.23E-09 8.63E-10 12.458 

17 6,239 320.2 0.50 600 12 28.3 14.2 1.50E-10 7.76E-11 12.560 

18 6,287 320.2 0.50 50 12 27.9 14.0 1.13E-09 8.77E-10 12.700 

19 6,365 320.3 0.50 600 12 28.2 14.1 1.53E-10 7.61E-11 12.742 

20 6,408 320.1 0.50 50 12 28.2 14.1 1.54E-09 9.08E-10 12.901 

21 6,528 320.2 0.50 600 12 28.7 14.3 1.84E-10 8.13E-11 12.982 

22 6,550 320.3 0.50 50 12 29.0 14.5 1.41E-09 1.03E-09 13.073 

23 6,597 320.2 0.50 600 12 29.3 14.6 1.90E-10 8.84E-11 13.106 

24 6,621 320.3 0.50 50 12 29.8 14.9 1.48E-09 1.15E-09 13.208 

25 6,699 320.1 0.50 600 12 30.1 15.1 2.35E-10 9.97E-11 13.273 

26 6,718 320.1 0.50 50 12 30.4 15.2 1.76E-09 1.23E-09 13.362 

27 6,743 320.0 0.50 600 12 30.7 15.3 2.79E-10 1.07E-10 13.374 

28 9,417 320.2 1.00 0 0 37.9 0.0 1.42E-10 - 14.728 

a

 Simulated PWR water with 2 ppm Li, 1000 ppm B, and 2 ppm. DO<10 ppb. Conductivity was 213 S/cm, and pH 6.4. b

 CGR rates in air are calculated assuming typical behavior for a Ni-base weld. The 152-LAS rates are approximately a factor of two lower. c

 Data was corrected using fractography. 

 
108 

Figure 3-73 Environmental enhancement of two control test conditions and SCC CGRs vs. 

distance from the specimen notch for Specimen N152-LAS-11. Test periods 

are indicated in the figure. 

(a) 

Figure 3-74 Crack–length–vs.–time for dilution specimen N152-LAS-11 in simulated PWR 

environment during test periods (a) precracking-2, (b) 3-5, (c) 6, (d) 7 9, (e) 10, 

(f) 11-13, (g) 14-15, (h) 16-27, and (i) 28.

0.00

1.00

2.00

3.00

4.00

5.00

10-12

10-11

10-10

0 0.5 1 1.5 2 2.5 3 3.5

R=0.5, 600/12

R=0.5, 50/12

SCC CGR

SCC CGR (m/s)

CGRenv/CGRair

Crack advance from specimen notch (mm)

1

2

Alloy 152 dilution

Specimen # N152-LAS-11

PWR environment

5

4

8

7

12

10

11

14 15

16

17

18

19

20

21

22

23

24

25

26

27

28

Solid symbols: CL

11.700

11.800

11.900

12.000

12.100

20

22

24

26

28

30

60 80 100 120 140

Time (h)

Specimen N152-LAS-11

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Pre a

Pre b

Pre c

Period 1

Period 2

1,4 x 10–10 m/s

23.6 MPa m0.5

R=0.5, 600/12
109 

Figure 3-74 (Cont.) 

(b) 

(c) 

(d) 

12.040

12.050

12.060

12.070

12.080

12.090

12.100

12.110

12.120

20

22

24

26

28

30

150 200 250 300 350 400 450 500

Time (h)

Specimen N152-LAS-1

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5

Period 3 )

Period 5

Period 4

5.37 x 10–12 m/s

23.7 MPa m0.5

CL

12.060

12.080

12.100

12.120

12.140

12.160

20

25

30

35

40

500 600 700 800 900 1000

Time (h)

Specimen N152-LAS-1

PWR environment

Kmax

Crack Length

Crack Length (mm)

Kmax (MPa m0.5)

Period 6

1.9 x 10–11 m/s

23.8 MPa m0.5

R=0.5, 600/12 + 2h

12.120

12.130

12.140

12.150

12.160

12.170

12.180

12.190

12.200

10

15

20

25

30

35

40

1000 1200 1400 1600 1800 2000

Time (h)

Specimen N152-LAS-11

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 7

1.4 x 10–12 m/s

23.7 MPa m0.5

CL

Period 8

9.8 x 10–11 m/s

23.6 MPa m0.5

R=0.5, 600/12

Period 9

1.4 x 10–11 m/s

23.5 MPa m0.5

R=0.5, 600/12 + 2h
110 

Figure 3-74 (Cont.) 

(e) 

(f) 

(g) 

12.160

12.170

12.180

12.190

12.200

12.210

10

15

20

25

30

35

40

2000 2200 2400 2600 2800 3000 3200

Time (h)

Specimen N152-LAS-11

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 10

1.2 x 10–12 m/s

23.8 MPa m0.5

CL

12.160

12.180

12.200

12.220

12.240

10

15

20

25

30

35

40

3000 3200 3400 3600 3800 4000 4200

Time (h)

Specimen N152-LAS-11

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 11

3.7 x 10–12 m/s

24.0 MPa m0.5

CL + PU (4h)

Period 13

12.200

12.240

12.280

12.320

12.360

0

10

20

30

40

50

4000 4500 5000 5500 6000

Time (h)

Specimen N152-LAS-11

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

4.3 x 10–12 m/s

Period 14

4.8 x 10–12 m/s

27.3 MPa m0.5

CL + PU (8h)

4.8 x 10–12 m/s

Period 15

1.2 x 10–10n m/s

27.6 MPa m0.5

R=0.5, 600/12
111 

Figure 3-74 (Cont.) 

(h) 

(i) 

After the test was completed, the sample was removed from the autoclave and the side 

surfaces were ground to remove the side grooves. No fatigue in air was done immediately 

following the completion of the test in water in order to be able to establish precisely on the side 

surfaces where the test ended. The images shown in Fig. 3-75 seem to indicate that the test 

started and ended in the 1st layer of Alloy 152. 

 

12.400

12.600

12.800

13.000

13.200

13.400

10

15

20

25

30

35

40

45

50

6000 6100 6200 6300 6400 6500 6600 6700

Time (h)

Specimen N152-LAS-11

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

24

Period 17

1.5 x 10–10 m/s

28.3 MPa m0.5

R=0.5, 600/12

Period 21

1.8 x 10–10 m/s

27.7 MPa m0.5

R=0.5, 600/12

25

22 23

20

19 18

16

25

27

13.200

13.600

14.000

14.400

14.800

10

20

30

40

50

60

7000 7500 8000 8500 9000 9500

Time (h)

Specimen N152-LAS-11

PWR environment

Crack Length (mm)

Kmax (MPa m0.5)

Kmax

Crack Length

Period 28

1.4 x 10–10 m/s

37.9 MPa m0.5

CL

2.0 x 10–10 m/s

1.5 x 10–110n m/s

6.0 x 10–11 m/s 4.0 x 10–11 m/s

3.1 x 10–10 m/s

1.8 x 10–10n m/s

1.1 x 10–10 m/s

2.2 x 10–10 m/s

2.2 x 10–10 m/s
112 

(a) (b) 

Figure 3-75 SEM images of the two sides of the dilution specimen N152-LAS-11 after the 

test: (a) side 1, and (b) side 2. Alloy 152 and the LAS are as marked in each 

picture. The red arrows mark the end of the test. 

The side surfaces were examined in the SEM to investigate the difference in cracking between 

the regions in this specimen with SCC CGR differing by a factor 100, namely between test 

periods 7-14 and 28. Side surface 1, Fig. 3-75a, does not seem to provide much revealing 

information. By contrast, side surface 2, Fig. 3-75b, appears to shows some detail at the 

locations of interest. As such, Fig. 3-76 identifies the regions of low SCC CGR (location 1) and 

high SCC CGR (location 3). The average composition (wt. %) at location 1 (Fig. 3-76b) is 26.1 

Cr-24.4 Fe-49.5 Ni, and the average composition (wt. %) at location 3 (Fig. 3-76c) is nearly 

identical, 25.4 Cr–26.6 Fe–48.0 Ni. Hence, the chemical composition does not seem to account 

for the apparent factor 100 difference in SCC CGRs measured at the two locations. However, 

SCC at location 1 (Fig. 3-76b) is clearly off-plane; hence, the low SCC CGRs measured by DC 

potential at this location could be due to off-plane cracking. 

Of high interest was also the interaction of the crack front with the two “swirls” shown at 

locations 2 and 3 in Fig.3-76 a. The “swirls” appear in the form of equiaxed dendrites composed 

of partly melted base metal that is diluted with Ni-base filler metal, and at closer inspection, 

Fig. 3-77, they seem to either slow (location 2) or arrest (location 3) the crack advance. The 

average composition (wt. %) for the “swirls” was 19 Cr–44 Fe–36 Ni, hence, a low Cr 

concentration does not seem to necessarily translate into an increased SCC-susceptibility. 
113 

(a) 

(b) 

 (c) 

Figure 3-76 (a) Side surface 2 of Specimen N152-LAS-11; Regions with low (b) and high (c) 

SCC CGRs as observed on the side surface “2” at locations 1 and 3. Local Cr 

concentration (wt. %) measurements are indicated with red in each figure. 

Crack propagation is from left to right. 

 
114 

Figure 3-77 “Swirls” appearing to slow down/arrest crack propagation observed on the 

side surface 2 in specimen N152-LAS-11 (locations 2 and 3 in Fig. 2-9b). 

Measured Cr concentration (wt. %) for each “swirl” is indicated with red in the 

figure. Crack propagation is from left to right. 

After the examination of the side surfaces, the specimen was fatigued in air for an additional 

2 mm, and then broken open to examine the fracture surface, Fig. 3-78. The milestones of the 

test are indicated in the figure: the specimen was set at constant load fairly early in the test 

(IG-1), then the crack was advanced by cyclic loading (test periods 15-27, Table 3-7), and finally 

the specimen was set at constant load in test period 28. Advance under cyclic loading produces 

a relatively straight fracture surface with no ligaments, and this is especially true for test period 

27 which reproduced the expected CGR for Alloy 152 (Fig. 2-10). Hence, the red lateral arrows 

in Fig. 3-78 indicate the end of cyclic loading (including test period 27). Finally, the last test 

period 28 produced the region labeled IG-2. This region was measured to be on average 10 

times higher than the DC potential measurement of 0.140 mm, and hence, the correction for the 

DC potential data in test period 28 was a factor 10. The general appearance in the later part of 

the test – with several unbroken ligaments – was unexpected, and these areas were 

investigated further as it will be documented later in this section. 
115 

Figure 3-78 Fracture surface of specimen N152-LAS-11. The red lateral arrows indicate 

the end of cyclic loading and the beginning of the final constant load test 

period. Measured Fe concentration (wt. %) for at several locations is indicated 

on a blue background in the figure. Crack advance is from bottom to top. 

Figure 3-78 also shows the local Fe concentrations of several of the unbroken ligament regions, 

confirming that these regions are the result of crack interaction with the SCC-resistant Alloy 

152-LAS interface. These resistant regions were not suspected initially to be LAS because the 

post-test examination of the side surfaces (Fig. 3-75) suggested that the crack was contained in 

the Alloy 152 weld. Nevertheless, it appears that, unlike the previous specimen (N152-LAS-1) 

where the crack was advanced with gentle cycle + hold and constant load with periodic 

unloading and overcame the LAS regions, in the current specimen under constant load the 

areas where the crack interacted with the LAS remained as unbroken ligaments. However, it 

seems that the crack found a path around those regions, and appeared to propagate as long as 

there was weld metal available. Overall, the fracture surface suggests that the crack was 

eventually arrested at the intersection with the LAS on the left side, but propagated quite 

extensively in the weld on the right side. Given the extent of the unbroken ligaments, the large 

correction factor was not surprising. 

Figure 3-79 shows the entire fracture surface of specimen examined in the SEM. Additional 

images at areas of interest were acquired and will be discussed next. 

 
116 

Figure 3-79 Fracture surface of specimen N152-LAS-11. Crack advance is from bottom 

to top. 
117 

Figure 3-80 focuses on what was believed to be (based on the DC potential measurement) the 

SCC-resistant region IG-1, locations 1 and 2 in Fig. 3-79. The presence of IG fracture very 

early in the test explains the high environmental enhancement observed in test periods 2 and 5 

(Fig. 3-73). Eventually, the environmental enhancement is lost as the preferred crack direction 

is off-plane. The fracture mode for this region appears on the fracture surface as mixed IG-TG 

mode, with extensive secondary (off-plane) cracking. 

(a) 

(b) 

Figure 3-80 Fracture surface of specimen N152-LAS-11 at locations (a) 1, and (b) 2 in 

Fig. 3-79. Crack advance is from bottom to top. 
118 

Figure 3-81 illustrates the interaction of the crack front with the LAS, locations 3 and 4b in Fig. 

3-79. As described previously in the context of discussing Fig. 3-78, these regions are resistant

to SCC, and remained as un-broken ligaments on the fracture surface under constant load

conditions. The crack eventually found a path around them and propagated as long as there

was weld metal available. Figure 3-82 obtained at location 4a in Fig. 3-79 presents a similar

situation.

(a) 

(b) 

Figure 3-81 Fracture surface of specimen N152-LAS-11 at location: (a) 3, and (b) 4b in 

Fig. 3-79. Crack advance is from bottom to top. 
119 

Figure 3-82 Fracture surface of specimen N152-LAS-11 at location 4a in Fig. 3-79. Crack 

advance is from bottom to top. 

 
120 

Figure 3-83 provides additional detail at locations 5 and 6 in Fig. 3-79. At location 5 (Fig. 

3-83a), several IG SCC directions appear visible – both along and normal to the dendritic

grains. Past the LAS (unbroken ligament), the crack seems to settle along a direction normal to

the dendritic grains, and the crack plane appears to be flat. This type of fracture appears almost

exclusively by the time the crack reaches location 6, Fig. 3-83b.

(a) 

(b) 

Figure 3-83 Fracture surface of specimen N152-LAS-11 at location: (a) 5, and (b) 6 in 

Fig. 3-79. Crack advance is from bottom to top. 
121 

Figure 3-84 shows two locations from final part of the test (7 and 8 in Fig. 3-79). Propagation is 

flat, in an IG mode, in a direction perpendicular to the direction of the dendrites, and in a fingerlike manner that leaves unbroken ligaments behind. Overall, a similar fracture mode was 

observed in the first layer of Alloy 52M deposited on an Alloy 182 interface. 

(a) 

(b) 

Figure 3-84 Fracture surface of specimen N152-LAS-11 at location: (a) 7, and (b) 8 in 

Fig. 3-79. Arrows indicate unbroken ligaments. Crack advance is from bottom 

to top. 
122 

Finally, in order to obtain additional confirmation on the crack path, the test specimen was 

further sectioned along directions “11” and “22”, as shown schematically in Fig. 3-85. Cross 

section “11” was chosen in an area where the crack was arrested at the LAS, and cross section 

“22” was chosen in an area where the crack propagated over several millimeters. Figure 3-85b 

indicates that the crack observed on cross section “11” was indeed arrested at the interaction 

with the LAS and, along with Fig. 3-81a, demonstrates that the crack continued to propagate as 

long as there was some weld metal available. Figure 3-85c demonstrates that the crack 

observed on cross section “22” propagated freely into the Alloy 152 weld with no interference 

from the LAS interface. This behavior is similar to that observed for specimen N152-LAS-1 

where the SCC crack front was also found to propagate away from the interface (Fig. 3-62c). 

The type of SCC fracture (flat, and in a direction normal to the dendritic grains) that was 

occasionally observed in these first layer Alloy 152 weld specimens, as well as the resulting fast 

propagation rates have generated interest in the SCC community. As such, the current 

specimen was made available to other laboratories for additional investigations. Figure 3-86 

shows SEM and Electron Backscatter Diffraction (EBSD) maps obtained at Pacific Northwest 

National Laboratory (PNNL) on cross section “22” (Fig. 3-85c). The EBSD inverse pole figure 

(IPF) map set to only display FCC structure shows a grain boundary ~125 μm from the fusion 

boundary as indicated by the yellow arrow [28]. This boundary is aligned to the target cracking 

direction, and the PNNL investigators have proposed that such a boundary could explain the flat 

appearance and overall the crack path in this test. An additional, similar EBSD investigation 

was conducted at Tohoku University [29] on side surface 2 (Figs. 3-75b and 3-76), and the 

resulting SEM and EBSD images are shown in Fig. 3-87. On that side surface, the SCC 

propagation was more “traditional”, i.e. along the dendritic grains, and similar to that observed in 

the first N152-LAS-1 specimen. However, as indicated by the blue arrows in Fig. 3-87, two sets 

of flat boundaries would have been readily available in the next weld bead should those 

boundaries prove themselves to be particularly prone to SCC propagation. 

Other researchers [30] have suggested that the feature identified by the yellow arrow in Fig. 

3-86 could be a Type II boundary. Type II boundaries require a ferrite/austenite phase

boundary at elevated temperatures to form, i.e., the weld metal solidifies in the austenite mode

despite the dilution from the base metal, while the LAS solidifies as delta ferrite which then

undergoes a transformation first to austenite and then to ferrite/bainite/martensite [31]. Type II

boundaries exist parallel to the fusion boundary and are located in the chromium dilution zone,

as illustrated in Fig. 3-87b. They have been identified in the literature as prone to SCC [26],

owing to the large stress concentrations in their vicinity. However, as indicated by the large

variation in crystal orientations above and below the boundary shown in Fig. 3-86, this appears

to be simply a collection of high angle boundaries. Figure 3-87 shows that, in fact, both type II

and flat high angle boundaries were present in this butter weldment. Moreover, a similar

fracture mode – flat and normal to the dendritic grains – was observed for Alloy 52M WOL

deposited on Alloy 182 (Figs. 3-52 - 3-56) – which is not a ferrite/austenite phase boundary,

hence Type II boundaries do not occur in that material. Thus, it appears that Type II boundaries

cannot explain the observed cracking in first layer Alloy 52M and 152 weldments. Additional

analysis may be needed to better understand how the weld microstructure affects the crack

growth behavior.

In summary, the test on specimen N152-LAS-11 confirmed the prior observations on specimen 

N152-LAS-1. The first layer of the Alloy 152-LAS weld is susceptible, extensive IG SCC was 

observed in both specimens, and in this test, in a favorable orientation, a SCC CGR in the 

10-10 m/s range was measured.
123 

(a) 

(b) 

(c) 

Figure 3-85 (a) Fracture surface of specimen N152-LAS-11. Additional cross sections 

were obtained along directions “11” (a), and “22” (b). Red arrows are placed 

at the specimen notch and indicate the direction of propagation. Green 

arrows indicate the end of the test. 

 
124 

(a) (b) 

Figure 3-86 SEM (a) and EBSD (b) map obtained on cross section “22” (Fig. 3-85) of 

Specimen N152-LAS-11. The yellow arrow points to a set of aligned 

boundaries that could plausibly explain the crack path in this test [28]. Crack 

propagation is from right to left. 
125 

(a) 

(b) 

Figure 3-87 SEM (a) and EBSD (b) map obtained on side surface 2 (Figs. 3-75b and 

3-76) of specimen N152-LAS-11. The blue arrows point to sets of aligned 

boundaries in the next weld bead [29]. Red arrows are placed at the 

specimen notch and indicate the direction of propagation. Green arrows 

indicate the end of the test. Crack propagation is from left to right.

127 

4 DISCUSSION 

The section summarizes the cyclic and SCC CGR results obtained on the Alloy 52M-182 WOL 

and Alloy 152–LAS butter specimens. A comparison of outcomes is made, and the role of the 

microchemistry and that of the substrate are discussed. 

4.1 SCC CGR Response of Alloy 52M WOL 

SCC CGR testing on the Alloy 52M-182 WOL was conducted in two orientations: TS and ST. 

Figure 4-1 illustrates these orientations and the SCC CGRs that were measured in each 

orientation. As described previously, the SCC CGRs in Alloy 182 are unaffected by the Alloy 

52M WOL at distances larger than 1-1.5 mm from the WOL interface. However, as those 

cracks approached the interface in the TS orientation, the SCC CGRs in Alloy 182 were found 

to decrease by approximately one order of magnitude in the 1 mm leading up to the interface. 

The reason for the decrease is unknown, however, it may be due to the compressive stress 

exerted by the WOL. In both TS-oriented tests, significant cracking was found to develop at the 

interface between the two welds, and this prevented an unambiguous measurement of the SCC 

CGRs in Alloy 52M past the interface. Nevertheless, estimates based on fractography (Fig. 

2-12) suggested that the maximum SCC CGR in the first layer of Alloy 52M can be relatively

high. As such, additional testing was undertaken in the ST orientation to measure the SCC

CGRs at the interface between the two welds and the first layer of Alloy 52M directly. Both the

Alloy 52M-182 interface and the first layer of Alloy 52M were found to be highly susceptible.

Given the long crack extensions for these measurements, and the fact that the SCC region was

readily identifiable on the fracture surface, these SCC CGRs are thought to be highly reliable.

(a) (b)

Figure 4-1 SCC CGRs in an Alloy 52M-182 overlay: (a) Schematic showing the test 

specimen orientations with respect to the Alloy 52M-182 WOL, and (b) SCC 

CGRs vs. distance to the Alloy 52M-182 interface. 

10-12

10-11

10-10

10-9

-2.0 -1.0 0.0 1.0 2.0 3.0

Data 18

A52M-182-TS-3 

A52M-182-TS-1 

WOL-ST-1

WOL-ST-2

CGR (m/s)

Distance from the 52M WOL interface (mm)

Alloy 182 Alloy 52M

Solid symbols: CL

TS

ST
128 

In order to put the Alloy 52M WOL data into perspective, Figure 4-2 summarizes the SCC CGR 

data obtained from the two ST-oriented specimens presented in this report, along with data for 

Alloy 152 heat WC04F6 (28.7 wt. %) tested previously at ANL [22, 23]. Also included for 

comparison is the MRP-115 75th percentile curve [1]. The local Cr concentration that was 

measured in close proximity of each crack is also included. 

Figure 4-2 suggests that the SCC CGRs along the interface between the two welds can be as 

high as the MRP-115 75th percentile curve [1]. The Cr concentration for the Alloy 52M-182 

interface was measured to be approximately 20 wt. %. For Alloy 52M (Fig. 4-2b), the Cr 

concentration seems to be playing a role. The SCC CGR in a region with 27.4 wt. % Cr was 

low, however, the unfavorable orientation of the crack with respect to the dendritic grains could 

have also played a role. Additionally, in the first layer of Alloy 52M weld, in a region with an 

average Cr concentration of 25.4 wt. %, the SCC CGR was relatively high (factor of two lower 

than the MRP-115 75th percentile curve [1]) despite the unfavorable orientation with the dendritic 

grains. Nevertheless, it is important to note that the SCC CGR measured in the latter case in 

the unfavorable orientation matches almost exactly the maximum SCC CGR estimated on the 

fracture surface in a case where propagation was along the “traditional” direction, i.e., along the 

dendritic grains (see Fig. 2-12). Hence, it is not clear at this stage whether crack orientation 

with respect to the dendrites plays a major role in the case at hand. 

(a) (b)

Figure 4-2 SCC CGRs in the Alloy 52M-182 overlay: (a) along the Alloy 52-182 interface 

in specimen WOL-ST-1, and (b) as a function of average Cr content in 

specimen WOL-ST-2. Also included are Alloy 152 data generated at ANL 

[22, 23] and the MRP-115 disposition curve for Alloys 82/182 [1]. 

10-13

10-12

10-11

10-10

10-9

10 20 30 40 50

A152-TS-2

A152-TS-4

A152-TS-5

N152-TS-1

WOL-ST-1

Experimental CGR (m/s)

Stress Intensity K (MPa·m1/2)

Alloy 152 Weld and 52M WOL

320°C

Solid symbols: CL

18.6% Cr

MRP-115 

75th Percentile

10-13

10-12

10-11

10-10

10-9

10 20 30 40 50

A152-TS-2

A152-TS-4

A152-TS-5

N152-TS-1

WOL-ST-2

Experimental CGR (m/s)

Stress Intensity K (MPa·m1/2)

Alloy 152 Weld and 52M WOL

320°C

Solid symbols: CL

25.4% Cr

20.1% Cr

27.4% Cr

MRP-115 

75th Percentile
129 

4.2 1st Layer Alloy 152-LAS Cyclic and SCC CGR Response 

The cyclic and SCC CGRs generated in the two first layer Alloy 152-LAS specimens are shown 

as a function of crack advance in Fig. 4-3. Overall, the cyclic data for the two specimens is in 

excellent agreement, and the approach based on measuring the local environmental 

enhancement was instrumental for identifying the locations where an SCC CGR could be 

measured by DC potential. 

(a) (b) 

Figure 4-3 Environmental enhancement of two control test conditions and SCC CGRs vs. 

distance from the specimen notch for (a) N152-LAS-1, and (b) N152-LAS-11. 

Crack propagation is from left to right. 

Figure 4-4 shows the SCC CGR data measured for the two first layer Alloy 152-LAS specimens 

along with the Alloy 152 data obtained previously on a double-J symmetrical Alloy 152 weld [22, 

23]. Despite the un-favorable orientation with respect the weld dendrites, some locations of 

these first layer Alloy 152-LAS dilution welds yielded SCC CGRs higher than those measured 

for bulk Alloy 152. These SCC CGRs show a factor 100 variation depending on the location in 

the specimen where they were measured, as was already illustrated in Fig. 4-3. Nevertheless, 

the crack direction versus test plane and the ability of the DC potential to measure correctly the 

SCC CGRs in those directions emerge as major contributors to the scatter. While the Alloy 52M 

results discussed in the previous section suggest that the test plane versus grain orientation can 

yield similar SCC CGRs, the situation for the Alloy 152-LAS specimens is less clear. As 

described in this report, extensive SCC was observed in directions both parallel (specimen 

N152-LAS-1) and normal (specimen N152-LAS-11) to the dendritic grains, yet only the normal 

direction coincided with the test plane where the CGRs were readily measurable by DC 

potential. As such, the SCC propagation normal to the dendrites in specimen N152-LAS-11 

may appear at first sight to be faster than that along the dendrites in specimen N152-LAS-1, yet 

a lone data point in the latter specimen (as seen in test period 17, Figs. 4-3a and 4-4) seems to 

suggest that the SCC CGRs in the two orientations may in fact be similar, just as was the case 

with Alloy 52M WOL. Nevertheless, given the severe off-plane crack direction in specimen 

N152-LAS-1, the lone observation in test period 17 could not be later substantiated by 

subsequent determinations in the same test. By contrast, with an SCC crack propagating 

favorably in the test plane, specimen N152-LAS-11 yielded one SCC CGR that was within a 

factor of two of the 75th percentile MRP-115 disposition curve for Alloys 82/182 [1], and was 

0.00

1.00

2.00

3.00

4.00

5.00

10-12

10-11

10-10

2.5 3 3.5 4 4.5 5 5.5 6 6.5

R=0.5, 600/12

R=0.5, 50/12

SCC CGR

CGRenv/CGRair

Crack advance from specimen notch (mm)

1

9

11

3

8

10

12 13

14

16

15

5

7 18

Alloy 152 dilution

Specimen # N152-LAS-1

PWR environment

19

22

23

Solid symbols: CL

SCC CGR (m/s)

no growth

2124

20

4 6

17

0.00

1.00

2.00

3.00

4.00

5.00

10-12

10-11

10-10

0 0.5 1 1.5 2 2.5 3 3.5

R=0.5, 600/12

R=0.5, 50/12

SCC CGR

SCC CGR (m/s)

CGRenv/CGRair

Crack advance from specimen notch (mm)

1

2

Alloy 152 dilution

Specimen # N152-LAS-11

PWR environment

5

4

8

7

12

10

11

14 15

16

17

18

19

20

21

22

23

24

25

26

27

28

Solid symbols: CL
130 

based on a crack advance larger than 1 mm. Because of the size of this crack, and the fact that 

it was readily identifiable on the fracture surface, this SCC CGR is deemed by the authors of 

this report to be highly reliable. However, as discussed previously, it is not clear at this stage 

whether or how the crystallographic orientation affects the magnitude of the measured SCC 

CGRs in those first layer weldments. 

Figure 4-4 SCC CGRs in and 1st layer Alloy 152-LAS specimens. Also included are Alloy 

152 data generated at ANL [22, 23] and the 75th percentile MRP-115 

disposition curve for Alloys 82/182 [1]. 

4.3 Comparison of Cyclic and SCC CGR Responses in 1st Layer Alloy 152-LAS 

and 1st Layer Alloy 52M-182 WOL 

In order to put the first layer Alloy 52M-182 and Alloy 152-LAS data into perspective, Fig. 4-5 

provides a side-by-side comparison of the cyclic and SCC CGR data obtained on the two welds. 

The two sets of cyclic and SCC responses are in excellent agreement with each other, with no 

apparent effect from the nature of the substrate or the interface. In both cases, the 

environmental enhancement was a good predictor for the SCC response. Also, in both cases, 

as discussed previously (Figs. 4-2 and 4-4), in the most favorable orientations, the SCC CGRs 

were within a factor of two of the MRP-115 75th percentile curve [1]. It is also interesting to note 

that in both first layer welds, the fastest measured SCC propagation occurred in a direction 

normal to the dendrites, as shown in Fig. 4-6. While it is not clear whether this propagation 

mode even exists in Alloy 182 or it is specific to those high-Cr weld layers near an interface, 

favorable crystallographic planes allowing such propagation were identified for the Alloy 

152-LAS weldment, shown in Figs. 3-86 and 3-87. However, as discussed in the prior section, it

is not clear at this stage whether SCC growth along such planes is faster or not than that

occurring along more “traditional” directions, i.e., along the dendritic grains.

10-13

10-12

10-11

10-10

10-9

10 20 30 40 50

A152-TS-2

A152-TS-4

A152-TS-5

N152-TS-1

N152-LAS-1

N152-LAS-11

Experimental CGR (m/s)

Stress Intensity K (MPa·m1/2)

Alloy 152 Weld and 152-LAS

320°C

Solid symbols: CL

25.4% Cr

26.1% Cr

24.1% Cr

27.0% Cr

MRP-115 

75th Percentile

24.1% Cr
131 

(a) (b) 

Figure 4-5 Environmental enhancement of two control test conditions and SCC CGRs vs. 

distance from the specimen notch for 1st layer (a) Alloy 52-182 specimen 

WOL-ST-2, and (b) Alloy 152-LAS specimen N152-LAS-11. 

(a) (b) 

Figure 4-6 SCC fracture modes the regions near the interface in (a) Alloy 152 – LAS, 

and (b) Alloy 52M WOL specimens tested in simulated primary water 

environment. SCC propagation is from bottom to top. 

4.4 The Effect of Local Cr Concentration and that of the Substrate on the 

Cyclic and SCC CGR Response of a Cr-Depleted 1st Layer High Cr 

Ni-Base Weldment 

The effect of the local elemental concentration of Cr is unclear. While the Alloy 52M WOL SCC 

CGR data (Fig. 4-2) appears to show a trend, the Alloy 152-LAS SCC CGR data (Fig. 4-4) 

shows a large scatter, and no clear Cr effect. The plausible reasons for the scatter are off-plane 

cracking as well as possible differences in the local microstructure and Cr concentration. Offplane cracking was well-documented in these tests, hence the inability of the DC potential 

method to measure the SCC CGRs correctly in such cases may be partly responsible for the 

data scatter. However, it is important to note that relatively fast SCC in the first layer of Alloy 

152-LAS (approximately 25 wt. % Cr) was observed in both weld directions, along and normal to 

0.00

1.00

2.00

3.00

4.00

5.00

10-12

10-11

10-10

-0.2 0 0.2 0.4 0.6 0.8

R=0.5, 120/12

R=0.5, 600/12

SCC

SCC CGR (m/s)

CGRenv/CGRair

Distance from the 52M WOL interface (mm)

Alloy 182 Alloy 52M

Alloy 52M WOL

Specimen WOL-ST-2

0.00

1.00

2.00

3.00

4.00

5.00

10-12

10-11

10-10

0 0.5 1 1.5 2 2.5 3 3.5

R=0.5, 600/12

R=0.5, 50/12

SCC CGR

SCC CGR (m/s)

CGRenv/CGRair

Crack advance from specimen notch (mm)

1

2

Alloy 152 dilution

Specimen # N152-LAS-11

PWR environment

5

4

8

7

12

10

11

14 15

16

17

18

19

20

21

22

23

24

25

26

27

28

Solid symbols: CL
132 

the dendritic grains (Fig. 3-64, IG-2 and Fig. 3-78, IG-2). The mechanism that triggers one 

fracture mode over the other is not at all understood. Further complicating the analysis is the 

fact that microstructures having even less Cr (approximately 20 wt. % Cr, see for example the 

“swirls” in Fig. 3-77) appeared to slow down/arrest crack propagation. Moreover, the cross 

sections shown in Figs. 3-62 and 3-85c does not suggest that SCC tends to propagate towards 

the interface with the LAS, or along an expected Cr gradient as one would expect if Cr content 

were to play a dominant role in the SCC at hand. In fact, for both Alloy 152-LAS specimens that 

were tested, the SCC propagation was away from the interface with the LAS. In summary, it 

appears that the elemental concentration of Cr, in itself, does not fully predict the (local) 

SCC susceptibility. 

Despite the lack of clear trends in the SCC CGR data or an understanding of the mechanism(s) 

at work, the SCC in the first layer of Alloy 52M-182 WOL and Alloy 152-LAS (approximately 

25 wt. % Cr) was found to occur in similar fracture modes (Fig. 4-6) and have equivalent SCC 

CGRs (Figs. 4-2 and 4-4). Moreover, the cyclic responses were found to be similar (Figs. 4-3 

and 4-5), and overall consistent with those expected for a Ni-base weld. As such it appears that 

the type of material on which the weld is deposited, either Alloy 182 or Alloy 533 LAS, does not 

affect the cyclic and SCC CGR response in those first layer welds. The only difference was 

found to occur in cases where the cracks intersected the interface with the substrate: at the 

Alloy 52M-182 interface, the SCC CGR is even faster than in the first layer of Alloy 52M, while 

SCC is arrested at the intersection with the Alloy 152-LAS interface. The latter observation is 

consistent with those from the literature [26, 27]. As such, attempts to transition SCC cracks in 

high-purity or sulphate-containing oxygenated water under constant or periodic partial unloading 

conditions from Alloy 182 into LAS were unsuccessful, and were found to slow down and arrest 

[27] or blunt at the LAS interface [26].
133 

5 CONCLUSIONS 

This report summarizes testing performed at ANL to investigate the SCC susceptibility at or 

near the interface between the high Cr weld metals, Alloys 52 and 152, and low Cr weld metals 

or steel, where localized Cr dilution could affect the cracking behavior. The tests were 

performed using two mockups. The first was a WOL mockup of Alloy 52M to Alloy 182, and the 

second was a butt weld mockup of Alloy 152 to LAS. 

SCC testing on the Alloy 52M-182 WOL was conducted in two orientations, TS (weld interface is 

perpendicular to the crack growth direction) and ST (crack growth direction is parallel to the 

weld interface). SCC CGRs were measured as a function of orientation and distance from the 

interface between the two materials. It was found that in the TS orientation, as SCC cracks in 

Alloy 182 approached within 1 mm of the interface with Alloy 52M, the CGRs decreased by 

approximately one order of magnitude. When the crack intersected the interface, branches 

extended along the boundary between Alloy 52M and 182, even as the leading crack front 

advanced into the Alloy 52M. Testing was undertaken in the ST orientation to measure the 

SCC CGRs at the interface between the two welds and in first layer of Alloy 52M weld beads 

within the WOL. The SCC CGRs along the interface between the two welds was measured to 

be as high as the MRP-115 75th percentile curve for Alloys 82/182 [1]. The SCC CGR in the 

first layer of Alloy 52M weld beads was a factor of two lower than the MRP-115 75th percentile 

curve [1], though the dendritic grains were not favorably oriented for cracking. 

SCC CGR testing on the butt weld mockup was conducted on two specimens aligned in the first 

layer of Alloy 152 weld beads adjacent to LAS. The environmental enhancement of the fatigue 

CGR was found to be a good predictor for the SCC response. Both fatigue and SCC CGR 

responses were similar to those observed in the first layer of Alloy 52M weld beads within the 

WOL. In both cases, in the most favorable orientations, the SCC CGRs were within a factor of 

two of the MRP-115 75th percentile curve [1]. Material compositional analyses taken along the 

crack path indicated that locations with the highest measured crack growth did not necessarily 

correlate with the lowest chromium content. This suggests that microstructural factors, in 

addition to the chromium content, could affect the SCC susceptibility near the interface. EBSD 

analyses identified apparent grain or dendrite packet boundaries in the Alloy 152 weld metal 

that are oriented parallel to the Alloy 152-LAS interface and in the direction of the crack growth. 

These may be preferential crack paths that contribute to the relatively fast growth, but it will 

require analysis of additional welds to confirm this hypothesis. 

The fatigue and SCC growth rates near the interfaces were similar in the Alloy 52M-182 WOL 

and the Alloy 152-LAS butt weld mockups, respectively, as were the fracture modes. As such, it 

appears that the type of material on which the weld is deposited, whether Alloy 182 or Alloy 533 

LAS, does not uniquely affect the SCC susceptibility in the adjacent high-Cr weld metal. The 

only difference was found to occur when the crack actually intersected the interface. At the 

Alloy 52M-182 interface, the SCC CGR is even faster than in the first layer of Alloy 52M weld 

beads, while SCC is arrested when in intersects the Alloy 152-LAS interface. 

These data suggest that safety evaluations to determine the appropriate in-service inspection 

requirements for components that could be affected by SCC, should consider the potential for 

preferential cracking along weld interfaces. However, additional testing is needed to further 

assess the mechanistic cause of this behavior and to understand whether this would manifest in 

welds in actual plant service, where the geometries, fabrication methods, and other properties 

may differ from those of the welds described in this report. 

135 

6 REFERENCES 

1. Materials Reliability Program: Crack Growth Rates for Evaluating Primary Water Stress 

Corrosion Cracking (PWSCC) of Alloy 82, 182, and 132 Welds (MRP-115), EPRI, Palo 

Alto, CA: 2004. 1006696. 

2. Materials Reliability Program: Resistance of Alloys 690, 52 and 152 to Primary Water 

Stress Corrosion Cracking (MRP-237, Rev. 1): Summary of Findings From Completed and 

Ongoing Test Programs Since 2004. EPRI, Palo Alto, CA: 2008. 1018130. 

3. Materials Reliability Program: Resistance of Alloys 690, 152, and 52 to Primary Water 

Stress Corrosion Cracking (MRP-237, Rev.2): Summary of Findings Between 2008 and 

2012 from Completed and Ongoing Test Programs. EPRI, Palo Alto, CA: 2013. 

3002000190 

4. Materials Reliability Program: Resistance to Primary Water Stress Corrosion Cracking of 

Alloy 690 in Pressurized Water Reactors (MRP-258). EPRI, Palo Alto, CA: 2009. 1019086. 

5. Dunn, D., Alexandreanu, B., Toter, W., “Shielded Metal Arc Welding Parameters for 

Primary Water Stress Corrosion Cracking Test Materials,” Technical Letter Report 

ML13171A113, June 2013. 

6. Alexandreanu, B., O. K. Chopra, and W. J. Shack, “Crack Growth Rates and 

Metallographic Examinations of Alloy 600 and Alloy 82/182 from Field Components and 

Laboratory Materials Tested in PWR Environments,” NUREG/CR–6964, ANL–07/12, May 

2008. 

7. Material Documentation Report for Consumers Power Midland (620-0012-51) and TMI-2 

(620-0006-51) Reactor Vessel Lower Head Material, The Babcock & Wilcox Company, 

BAW-2071, January 1989. 

8. American Society for Testing and Materials, “Standard Test Method for Measurement of 

Fatigue Crack Growth Rates,” ASTM E647-08, DOI 10.1520/E0647-08, West 

Conshohocken, PA, 2008. 

9. American Society for Testing and Materials, “Standard Test Method for Determining a 

Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic 

Materials,” ASTM E1681-03, DOI 10.1520/E1681-03R08, West Conshohocken, PA, 2008. 

10. Electric Power Research Institute, “PWR Primary Water Chemistry Guidelines,” Volume 1, 

Revision 4, EPRI, Palo Alto, CA, 1999. 

11. Electric Power Research Institute, “Materials Reliability Program (MRP) Crack Growth 

Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall 

Alloy 600 Materials (MRP-55),” Revision 1, 1006695, Palo Alto, CA, 2002. 

12. Ruther, W. E., W. K. Soppet, and T. F. Kassner, “Corrosion Fatigue of Alloys 600 and 690 

in Simulated LWR Environments,” NUREG/CR-6383, ANL-95/37, April 1996. 
136 

13. Ruther, W. E., W. K. Soppet, T. F. Kassner, and W. J. Shack, “Environmentally Assisted

Cracking of Alloys 600 and 690 in Simulated LWR Water,” in Environmentally Assisted

Cracking in Light Water Reactors, Semiannual Report, January 1998-July 1998,

NUREG/CR-4667, Vol. 26, ANL-98/30, pp. 25-32, March 1999.

14. Chopra, O. K., W. K. Soppet, and W. J. Shack, “Effects of Alloy Chemistry, Cold Work, and

Water Chemistry on Corrosion Fatigue and Stress Corrosion Cracking of Nickel Alloys and

Welds,” NUREG/CR-6721, ANL-01/07, April 2001.

15. Cassagne, T. B., and A. Gelpi, “Crack Growth Rate Measurements on Alloy 600 Steam

Generator Tubes in Steam and Primary Water,” Proc. of the Fifth Intl. Symp. on

Environmental Degradation of Materials in Nuclear Power Systems--Water Reactors,

American Nuclear Society, La Grange Park, IL, pp. 518-524, 1991.

16. Foster, J. P., W. H. Bamford, and R. S. Pathania, “Initial Results of Alloy 600 Crack

Growth Rate Testing in a PWR Environment,” Proc. of the Seventh Intl. Symp. on

Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors,

NACE International, Houston, TX, pp. 25-39, 1995.

17. Magdowski, R., F. Vaillant, C. Amzallag, and M. O. Speidel, “Stress Corrosion Crack

Growth Rates of Alloy 600 in Simulated PWR Coolant,” Proc. of the 8th Intl. Symp. on

Environmental Degradation of Materials in Nuclear Power Systems--Water Reactors,

S. M. Bruemmer, ed., American Nuclear Society, La Grange Park, IL, pp. 333-338, 1997.

18. Le Hong, S., C. Amzallag, and A. Gelpi, “Modeling of Stress Corrosion Crack Initiation on

Alloy 600 in Primary Water of PWRs,” Proc. of the Ninth Intl. Symp. on Environmental

Degradation of Materials in Nuclear Power Systems--Water Reactors, F. P. Ford,

S. M. Bruemmer, and G. S. Was, eds., Minerals, Metals, and Materials Society,

Warrendale, PA, pp. 115-122, 1999.

19. Raquet, O., and G. Santarini, “Stress Corrosion Crack Propagation Rate of Alloy 600 in

the Primary Water of PWR Influence of a Cold Worked Layer,” Proc. of the Ninth Intl.

Symp. on Environmental Degradation of Materials in Nuclear Power Systems--Water

Reactors, F. P. Ford, S. M. Bruemmer, and G. S. Was, eds., Minerals, Metals, and

Materials Society, Warrendale, PA, pp. 207-213, 1999.

20. Alexandreanu, B., O. K. Chopra, and W. J. Shack, “Crack Growth Rates of Nickel Alloys

from the Davis-Besse and V. C. Summer Power Plants in a PWR Environment,”

NUREG/CR–6921, ANL–05/55, November 2006.

21. Alexandreanu, B., O. K. Chopra, and W. J. Shack, “Crack Growth Rates of Nickel Alloy

Welds in a PWR Environment,” NUREG/CR–6907, ANL–04/3, May 2006.

22. Alexandreanu, B., Chen, Y., Natesan, K., and Shack, W. J., SCC Behavior of Alloy 152

Weld in a PWR Environment, 15th International Conference on Environmental Degradation

of Materials in Nuclear Power Systems – Water Reactors, Cheyenne Mountain Resort,

Colorado Springs, Colorado, August 7-11, 2011.

23. Alexandreanu, B., Y. Yang, Y. Chen, and W. J. Shack, “Stress Corrosion Cracking in

Nickel-Base Alloys 690 and 152 Weld in Simulated PWR Environment - 2009,”

NUREG/CR–7137, ANL–10/36, June 2012.
137 

24. Van Der Sluys, W. A., B. A. Young, and D. Doyle, “Corrosion Fatigue Properties on Alloy 

690 and some Nickel–Based Weld Metals,” Assessment Methodologies for Preventing 

Failure: Service Experience and Environmental Considerations, PVP Vol. 410-2, ed., 

R. Mohan, American Society of Mechanical Engineers, New York, pp. 85–91, 2000. 

25. Psaila–Dombrowski, M. J., C. S. Wade, J. M. Sarver, W. A. Van Der Sluys, and 

P. E. Doherty, “Evaluation of Weld Metals 82, 152, 52, and Alloy 690 Stress Corrosion 

Cracking and Corrosion Fatigue Susceptibility,” Proc. of the 8th Intl. Symp. on 

Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors, 

S. M. Bruemmer, ed., American Nuclear Society, La Grange Park, IL, pp. 412–421, 1997. 

26. Hou, J., Peng, Q., Takeda Y., Jiro, K., Shoji, T., Microstructure and stress corrosion 

cracking of the fusion boundary region, in an alloy 182-A533B low alloy steel dissimilar 

weld joint, Corrosion Science 52 (2010) 3949–3954. 

27. Seifert, H.P., Ritter, S., Shoji, T., Peng, Q.J., Takeda, Y., Lu, Z.P., Environmentallyassisted cracking behaviour in the transition region of an Alloy182/SA 508 Cl.2 dissimilar 

metal weld joint in simulated boiling water reactor normal water chemistry environment, 

Journal of Nuclear Materials 378 (2008) 197–210. 

28. Toloczko, M., Olszta, M., Overman, N., and Bruemmer, S., Alloy 152-LAS Dilution Zone 

PWSCC Testing, Alloy 690/52/125 Research Collaboration Meeting, Tampa, Florida, 

December 2-5, 2014. 

29. Yonezawa, T., personal communication, December 2015. 

30. Hanninen, H., personal communication, September 2015. 

31. Nelson, T.W., Lippold, J.C., and Mills, M.J., Nature and Evolution of the Fusion Boundary 

in Ferritic-Austenitic Dissimilar Metal Welds — Part 2: On-Cooling Transformations, 

Supplement to the Welding Journal, October 2000, 267. 

 



NUREG/CR-7226 

B. Alexandreanu, Y. Chen, K. Natesan, and W. J. Shack 

Argonne National Laboratory 

Argonne, IL 60439 

M. Audrain

Division of Engineering 

Office of Nuclear Regulatory Research 

U.S. Nuclear Regulatory Commission 

Washington, D.C. 20555-0001 

The report summarizes the SCC susceptibility at or near interfaces between Alloy 52 and 152 weld metals 

and other weld or base metals. Alloy 52/152 are high-chromium weld metals used in RPV penetration 

nozzles and as overlays, inlays, or onlays for DM welds. Alloys 52 and 152 typically show very low SCC 

growth rates in testing and are not known to have cracked in service. Questions remain if localized 

dilution of chromium content or microstructural features near the interface with the low-chromium weld 

metals Alloy 82/182 could affect the SCC response. For this study, SCC growth rates were measured on 

a WOL mockup with Alloy 52M, Alloy 182 and on a butt weld mockup with Alloy 152 joined to LAS. Both 

mockups resulted in CGRs that are higher than previously reported for weld metals, even though the 

dendrites were not favorably oriented for cracking. In the WOL mockup, crack branching along the 

interface was observed when the cracking direction was perpendicular to the interface. In the butt weld 

mockup, material compositional analyses indicated that locations with the highest measured CGRs did not 

necessarily correlate with the lowest chromium content. This suggests microstructural factors could affect 

SCC susceptibility near the interface. 

Alloy 690 

Nickel alloys 

Cold work 

Stress corrosion cracking 

January 2018 

Technical 

Primary Water Stress Corrosion Cracking of High-Chromium, NickelBase Welds Near Dissimilar Metal Weld Interfaces 



NUREG/CR-7226 Primary Water Stress Corrosion Cracking of High-Chromium, Nickel-Base 

Welds Near Dissimilar Metal Weld Interfaces 

January 2018