ML20069H219

Investigation of Flaws on Inside Surface of Type 304 Stainless Steel Schedule 80 Pipe

ML20069H219
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Site:	FitzPatrick
Issue date:	07/30/1982
From:	Battelle Memorial Institute, COLUMBUS LABORATORIES
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ML20069H163	List: ML20069H162 ML20069H198 ML20069H219 ML20069H239
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NUDOCS 8210190428
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I i

I FINAL REPORT

)

I on I

I AN INVESTIGATION OF FLAWS ON THE I

INSIDE SURFACE OF A TYPE 304 STAINLESS STEEL SCHEDULE 80 PIPE to POWER AUTHORITY OF THE STATE OF NEW YORK JAMES A. FITZPATRICK NUCLEAR POWER PLANT July 30, 1982 I

by R. D. Buchheit I

BATTELLE I

Columbus Laboratories f

505 King Avenue Columbus, Ohio 43201 Battelle is not engaged in research for advertising,

~I sales promotion, or publicity purposes, and this report may not be reproduced in full or in part for such purposes.

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I OBattelle Columbus 1.aboratories 501 bog Awnue I

Columbus, Ohio 43201

'Ielephone < 614a 424-6424 Tc!cs 24-5454 July 30, 1982 I

Mr. A. V. Sorentino Power Authority of the State of New York I

10 Columbus Circle New York, New York 10019

Dear Mr. Sorentino:

Enclosed are 10 copies of our final report entitled "An Investigation I

of Flaws on the Inside Surface of a Type 304 Stainless Steel Schedule 80 Pipe". This report describes the details of our investigation, con-ducted as was proposed in our letter of March 26, 1982, and the results I

we obtained. The report is a sequel to our report entitled "A Metal-lographic Investigation af a Type 304 Stainless Steel Schedule 80 Pipe",

dated March 25, 1982.

Briefly, the results of the investigation led to the basic conclusions that (1) the flaws on the inside surface of the subject pipe were in-duced during pipe-fabrication processing and (2) that surface flaws located within the region of the sensitized heat-affected zone of the circumferential weld probably served as the initiation sites of inter-I granular stress-corrosion cracking IGSCC). Surface flaws that were located away from the weld beyond the heat-affected zone apparently did not induce IGSCC or any other mode of failure.

The interest in this investigation was very high among all of our per-sonnel involved in the work, and we enjoyed performing the various I

tasks described in the report.

If you have any questions concerning our work or the results obtained, please feel free to contact me.

Very truly yours, g

.ALL6 R. D. Buchheit Physical Metallurgy Section RDB:rw Enc. (10)

J

TABLE OF CONTENTS l

Page INTRODUCTION.......................

1

SUMMARY

2 EXPERIMENTAL PROCEDURE.......................

3 EXAMINATIONS AND RESULTS......................

6

'I Chemical Analyses.......................

6

'l Crack-Profile Determinations..................

6 Fl aw No. 1 i n Fi gu re 1..................

6 I

Fl aw No. 4 in Fi gure 1..................

14 ll Examinations of Other Surface Flaws..............

19 l

Energy-Dispersive X-ray Analyses................

24 Corrosion Products in Flaw No. 1.............

24 Corrosion Products in Flaw No. 2.............

33 Corrosion Products in Flaw No. 5.............

35 I

I Electrochemical-Polarization-Reactivation (EPR) Tests.....

41 DISCUSSION.............................

45 CONCLUSIONS.............................

46 LIST OF TABLES TABLE 1.

Results of Emission-Spectrographic Analyses of the Type 304 Stainless Steel Pipe and the Stainless j

l Steel Weld Metal of the Circumferential Weld.......

7

I TABLE 2.

Crack-Depth and Crack-Length Data for the IGSCC Associated with Flaw No.1................

10 I

TABLE 3.

Crack-Depth and Crack-Length Data for the IGSCC Associated with Flaw No. 4................

16 ll

.I 1

I I

LIST OF TABLES (Continued)

Page l

TABLE 4.

Results of Semiquantitative (a) Electron-Microprobe Analyses of Corrosion Products by Energy-Dispersive-X-ray Analytical Techniques in Specimen 1-S-S I

of Flaw No. 1 25 TABLE 5.

Results of Semiquantitative (a) Electron-Microprobe I

Analyses of Corrosion Products by Energy-Dispersive-X-ray Analytical Techniques in Specimens 2-N-N and 2-R-R of Flaw No. 2 34 TABLE 6.

Results of Semiquantitative (a) Electron-Microprobe Analyses of Corrosion Products by Energy-Dispersive X-ray Analytical Techniques in Specimen 5-U-U-of Flaw No. 5 41 l

1 LIST OF FIGURES l

1 FIGURE 1.

Inside Surface of the Schedule 80 Stainless Steel Pipe

{

Showing Surface Flaws, the Locations of Metallographic l

and EPR Test Specimens, and the Circumferential Weld..

4

{

FIGURE 2.

Profile of Intergranular Stress-Corrosion Crack i

at Flaw No. 1 9

l I

FIGURE 3.

The IGSCC Associated With Flaw No.1 at Several Locations Along the Length of the Crack.........

11 FIGURE 4.

Flaw No. 1 Near the End of the IGSCC Farthest From the Weld......................

12

.I FIGURE 5.

The Flow Pattern of Metal Around Flaw No.1 at the 0.72-Inch Location in Figure 2.............

13 FIGURE 6.

Profile of Intergranular Stress-Corrosion Crack at Flaw No. 4 15 FIGURE 7.

The IGSCC Associated With Flaw No. 4 at Several Locations Along the Length of the Crack.........

17 l

FIGURE 8.

The Flow Pattern of Metal Around Surface Flaw No. 2 Observed in Specimen 2-P-P...............

20 FIGURE 9.

The Flow Pattern of Metal Around Surface Flaw No. 2 in Specimen 2-N-N 21 I

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LIST OF FIGURES (Continued)

Page I

FIGURE 10. The Flow Pattern of Metal Around Surface Flaw No. 2 in Specimen 2-R-R 22 FIGURE 11. The Flow Pattern of Metal Around Surface Flaw No. 5 in Specimen 5-U-U 23 FIGURE 12. Energy-Dispersive X-ray Spectrum Obtained From an Analysis of the Type 304 Stainless Steel Matrix in I

Specimen 1-S-S of Flaw No. 1 (Area 1 in Table 4)....

27 FIGURE 13. Cross Section of Flaw No.1 in Section 1-S-S......

28 FIGURE 14. Energy-Dispersive X-ray Spectrum Obtained From an Analysis of Corrosion Products in Flaw No.1 Observed I

in Specimen 1-S-S (Area 3 in Table 4)..........

29 FIGURE 15. Corrosion Products in the IGSCC Near the Inside Surface of the Pipe...................

30 FIGURE 16. Energy-Dispersive X-ray Spectrum Obtained From an l

Analysis of Corrosion Products in the Crack (Area 4 in Table 4)...................

31 FIGURE 17. Energy-Dispersive X-ray Spectrum Obtained From an Analy.c4 of Corrosion Products in a Branch Crack (Area' in Table 4)...................

32 FIGURE 18. Energy-Dispersive X-ray Spectrum Obtained from an Area Scan of Corrosion Products in Flaw No. 2 l

Specimen 2-N-N (Area 1 in Table 5)...........

36 FIGURE 19. Corrosion Products in Flaw No. 2 That Were Subjected l

to Electron-Microprobe Analyses.............

37 FIGURE 20.

EPR Curves for Sample EPR-2 From the Weld Heat-Affected Zone...................

43 FIGURE 21. EPR Curves for Samples EPR-1 ID and EPR-1 OD, AISI I

Stainless Steel Pipe Remote From the Region of the Weld.................

44 I

I I

I

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I AN INVESTIGATION OF FLAWS ON THE INSIDE SURFACE OF A TYPE 304 STAINLESS I

STEEL SCHEDULE 80 PIPE by R. D. Buchheit I

INTRODUCTION I

The subject investigation is a sequel to a previous investigation I

conducted by Battelle's Columbus Laboratories (BCL) of a linear defect that was detected on the inside surface of a pipe section using nondestructive ultrasonic-inspection techniques. The pipe section was a section of a 12-inch-diameter Type 304 stainless steel Schedule 80 seamless pipe that was a part of the core-spray system for a boiling-water reactor at the James A. Fitzpatrick Nuclear Power Plant of the Power Authority of the State of New York (PASNY). Descriptions of the details and the results of the previous investigation are contained in the BCL report entitled " A Metal-lographic Investigation of a Type 304 Stainess Steel Schedule 80 Pipe", dated March 25, 1982. The summary of that report is repeated below.

" Macroscopic examination of the inside surface of a 12-inch-diameter Type 304 stainess steel seamless pipe revealed the presence of numerous linear defects in addition to one that was detected by PASNY using nondestructive ultrasonic-inspection techniques. A cross section through one of the linear defects that was located close to a weld was ex-amined metallographically. The results of the examination indicated that the linear defect was most likely a fabrication-induced surface flaw that resembled a lap or seam. The surface flaw apparently acted as a stress raiser and, in the presence of a corrosive environment (the water contained in the pipe) and under the influence of hoop stresses induced by the internal pressure and possibly residual stresses in the hoop direction, it led to the I

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initiation and propagation of an intergranular stress-l corrosion crack through a sensitized region in the weld heat-affected zone."

The objectives of the subject investigation of the same section of pipe that was examined previously were (1) to examine and characterize other selected surface flaws and determine the p.esence or absence of cracks associated with those flaws, (2) to detarmine the profile of the cracks found to be present, (3) to obtain qualitative chemical analyses of corro-sion products found in surface flaws and in cracks, (4) to evaluate the susceptibility of the subject pipe material to intergranular stress-corrosion cracking (IGSCC), and (5) to determine the chemical compositions of the sub-ject pipe material and the circumferential weld metal contained in the pipe The procedures used to meet the objectives of the investigation conducted by BCL and the results obtair.ed are described in this report.

SUMMARY

I Cross sections of several surface flaws were examined metallo-l graphically with the light microscope, and the susceptibility of the Type

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304 stainless steel pipe to intergranular stress-corrosion cracking (IGSCC) was evaluated by electrochemical-polarization-reactivation (EPR) tests.

The cross sections through surface flaws located in the weld heat-affected zone exhibited IGSCC that had initiated and propagated from the base of those flaws. Profiles of two IGSCC's were determined from l

measurements of the crack depth versus crack length obtained on metallo-graphic serial sections prepared at various intervals along the lengths of the cracks.

The cross sections through surface flaws located in regions remote l

from the weld heat-affected zone did not reveal the presence of IGSCC or other modes of failure associated with the surface flaws. All surface flaws l

exhibited characteristics of laps or seams. The appearance of the flaws and the flow patterns of metal around them indicated that the flaws were fabrication-induced during the process of forming the seamless pipe.

I I

.I 3

I EPR tests indicated that the weld heat-affected zone that was sensitized was susceptible to IGSCC, whereas parent metal remote from the weld heat-affected zone was not. However, there appeared to be no IGSCC in the weld heat-affected zone in the absence of a surface flaw in that region. Hence, the surface flaws, probably acting as stress raisers, were apparently a major factor that contributed to the initiation and propaga-tion of the IGSCC's.

Electron-microprobe analyses of corrosion products in the surface flaws and in the IGSCC's using energy-dispersive X-ray analytical techniques did not identify the corrodent(s). The corrodent was most likely the water I

in the core-spray system that may have contained low concentrations of oxygen and chloride that were not detected by the electron-microprobe analyses.

The chemical compositons of both the weld metal and the pipe I

material were found to conform to the AISI specificiations for Type 304 stainless steel.

EXPERIMENTAL PROCEDURE The photograph in Figure 1 shows the portion of the inside surface I

of the Schedule 80 pipe and the surface flaws that were observed during the previous investigation.

(This photograph appeared as Figure 3 in the BCL I

report of the previous investigation and, also, as Figure 1 in BCL's pro-posal for this present investigation.)

The surface flaws that were selected i

I for further studies are identified in Figure 1 by the arrows numbered 1, 2, 4 and 5.

Those flaws, as numbered, conform to the manner in which those I

flaws were identified in BCL'r proposal for this investigation. The feature identified by the arrow that was numbered 3 in that pro,.osal is actually a I

part of Flaw No. 2 and is now identified as Section R-R of Flaw No. 2 in Figure 1.

I Metallographic cross sections through each of the four selected flaws and perpendicular to them, as shown in Figure 1, were prepared for I

microscopic examinations. The resulting metallographic specimens were identi-fied as Specimen 1-S-S for Section S-S of Flaw No.1, Specimen 1-T-T for I

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FIGURE 1.

INSIDE SURFACE OF THE SCHEDULE 80 STAINLESS STEEL PIPE SHOWING SURFACE FLAWS, THE E

LOCATIONS OF METALL0 GRAPHIC AND EPR TEST SPECIMENS, AND THE CIRCUMFERENTIAL WELD

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I Section T-T of Flaw No.1, Specimen 2-P-P for Section P-P of Flaw No. 2, I

et cetera, for the remainder of the cross sections indicated in Figure 1.

The cross sections that revealed cracks, namely, Specimens 1-5-S, I

1-T-T, 4-K-K, and 4-L-L, were successively ground, polished, and examined at measured incremental depths below each successive polished surface to I

establish the profiles of the cracks along the lengths of the flaws. The incremental depth measurements served as intervals of distance along the I

length of the crack. At each successive plane of polish, the depth of the crack below the inside surface of the pipe and the maximum width of the I

crack were measured using a digital measuring microscope. Maximum crack widths always were found at or near the surface unless the crack did not I

penetrate the surface. The crack-depth and crack-length measurements were plotted to reveal the profile of the crack in two dimensions.

Chemical analyses of corrosion products observed in surface flaws and in cracks were obtained using energy-dispersive-X-ray (EDAX) analytical techniques in conjunction with a scanning electron microscope. Both area-scan and spot analyses were performed. The EDAX results were reported as semiquantitative analyses. The semiquantitative analysis is a standardless quantitative analysis of the X-ray-energy-spectrum data that includes a full ZAF (atomic number, absorption, and fluorescence factors) matrix-correction calculation. The relative concentrations of the elements detected are normalized to obtain a sum of 100 percent. The energy-dispersive system 7

does not detect the lighter elements, i.e., elements of atomic nurber lower than 11 (sodium). Thus, for example, the concentration of oxygen that is frequently a major element in corrosion products is not included in the results of EDAX analyses.

i The locations of samples used to evaluate the susceptibility of the pipe material to IGSCC are identified in Figure 1 by EPR-1 ID, EPR-1 OD, l

and EPR-2. The evaluation was accomplished by performing electrochemical-i polarization-reactivation (EPR) tests of the inside and outside pipe surfaces I

some distance from the weld and of a region of the weld heat-affected zone.

A through-wall piece of the pipe approximately 1/2 inch square was sectioned in half at the midwall to provide Sample EPR-1 ID for the inside pipe sur-face and Sample EPR-1 OD for the outside pipe surface.

Those surfaces were I

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ground slightly and polished to provide suitable flat surfaces for the EPR tests. A polished cross section of the weld heat-affected zone was obtained to provide Sample EPR-2. Since experience has shown that the presence of weld metal in the test sample interferes with the results of the EPR test, all of the weld metal in Sample EPR-2 was ground away.

Quantitative chemical analyses of the pipe material and the weld metal were obtained using emission-spectographic analytical techniques.

The analysis of the pipe material was determined on the surface of a through-wall section of the pipe that was obtained from a location adjacent to the location of the EPR-1 ID and E0R-1 OD samples. The analysis of the weld metal was determined on the surface of a through-wall section of the pipe along the center line of the weld; that section of the weld was obtained from a location that was adjacent to the location of the EPR-2 sample.

I EXAMINATIONS AND RESULTS Chemical Analyses I

The chemical compositions of the Type 304 stainless steel Schedule 80 pipe and the circumferential weld metal that joined the straight-pipe section to an elbow section are presented in Table 1.

The specified composition of AISI Type 304 stainless steel is included in Table 1 for comparison. The chemical compositions of both the pipe and the weld metal were found to conform to the AISI specifications for Type 304 stainless steel.

Crack-Profile Determinations Flaw No.1 in Figure 1 I

The metallographic examination of Specimen 1-S-S (see Figure 1) during the previous investigation of the Schedule 80 pipe revealed the I

presence of IGSCC extending from the bottom of Flaw No. 1 at the inside pipe surface toward the outside surface through about 77 percent of the wall thickness.

In the present investigation, the profile of that crack along I

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TABLE 1.

RESULTS OF EMISSION-SPECTR0 GRAPHIC ANALYSES OF THE TYPE 304 I

STAINLESS STEEL PIPE AND THE STAINLESS STEEL WELD METAL OF THE CIRCUMFERENTIAL WELD I

Content, weight percent AISI Type 304 Element Pipe Specifications Weld Metal I

Carbon 0.045 0.08 max 0.032 Manganese 1.73 2.0 max 1.42 Phosphorus 0.021 0.045 max 0.014 I

Sulfur 0.016 0.030 max 0.007 Silicon 0.65 1.0 max 0.63 Nickel 10.3 8-10.5 9.6 I

Chromium 18.3 18-20 19.1 Polybdenum 0.18 0.10 Vanadium 0.05 0.05 I

Aluminum 0.007 0.042 Copper 0.10 0.065 Tin 0.008 0.006 I

Columbium 0.008 0.011 Zirconium 0.005 0.006 Ti tanium 0.004 0.006 I

Boron 0.0005 0.0007 Cobalt 0.11 0.10 Tungsten 0.00 0.00 l

Iron 68.73 68.78 I

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its length was obtained from serial sections of Specimen 1-S-S and Specimen I

1-T-T; the profile is revealed in Figure 2 by a plot of the depths of the crack below the inside pipe surface at various intervals of distance along I

the length of the crack.

Zero distance in Figure 2 corresponds to the loca-tion (termed a reference plane) where no crack was observed beyond the end I

of the flaw next to the weld metal; in this case, the reference plane was entirely within the weld metal The ab cissa in Figure 2 extends away from the weld through its heat-affected zone and in a direction along the length of the flaw. The crack-depth and crack-length data that are plotted in Figure 2 are given in Table 2.

The cross-hatched region in Figure 2 represents the extent of the IGSCC surface.

Included in Figure 2 are the approximate locations of the inside and outside pipe surfaces and portions of the weld line with respect to the crack. Note that IGSCC penetrated weld metal where crack propagation eventually arrested. However, crack propagation extended a short distance beyond the final pass of weld metal on the outside pipe surface and, in fact, reached the outside surface in one small region.

It is interesting to note here that no leakage of the core-spray pipe system was reported.

Figure 3 shows the appearance of the IGSCC at a few locations along its length.

Figure 3a exhibits the crack at the 0.060-inch position.

At that location the crack was subsurface and entirely within weld metal.

At the 0.290-inch position, Figure 3b, the crack extended through approxi-mately 77 percent of the pipe wall.

Figure 3c exhibits the portion of the crack near the outside surface of the pipe at the 0.702-inch position (at much higher magnification); essentially the entire crack in the through-wall direction is shown.

The appearance of the surface flaw at the 0.70-inch position is revealed in Figure 4.

The flaw exhibited two surface imperfections that were approximately 0.1 inch apart; those two inperfections are shown in Figures 4a and 4b respectively. A little IGSCC was still evident at the flaw shown in Figure 4b.

The flow pattern of the metal that developed around the flaw during the fabrication of the pipe was revealed by etching metallographically polished specimens, as is shown in Figure 5 at a magnification of 50X. At I

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Distance From Reference Plane, inches FIGURE 2.

0FI F INTERGRANULAR STRESS-CORROSION CRACK I

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10 TABLE 2.

CRACK-DEPTH AND CRACK-LENGTH DATA FOR THE IGSCC ASSOCIATED WITH FLAW NO. 1 l

Distance from Depth of Crack Maximum Width Specimen of Reference Plane,(a)

Below Inside Pipe of Crack, Flaw No.1 inches Surface, inches mils 1-5-S 0

No crack 0.030 0.092 to 0.255 0.4 0.060 0.059 to 0.328 0.7 0.100 0.008 to 0.373 1.0 (Surface Flaw

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No. 1 begins) 0.130 0.357 1.0 0.170 0.364 1.4 0.210 0.366 1.4 0.250 0.366 1.7 0.290 0.410 2.0 1-T-T 0.322 0.429 2.0 0.362 0.443 3.0 0.412 0.448 1.0 4

0.462 0.443 2.0

0. 51 2 0.447

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l ODends) 0.61 2 0.108 and 0.305 to 0.482 0.8 and 0.6 0.622 0.087 and 0.326 to 0.487 0.5 and 0.4 l

0.637 0.083 and 0.337 to 0.492 0.8 and 0.4 0.652 0.069 and 0.349 to 0.497 0.9 and 0.3 0.677 0.043 and 0.391 to 0.496 0.7 and 0.3 0.702 0.019 and 0.452 to 0.470 0.4 and 0.1 (Flaw No. 1 ends)

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0.717 No crack (a) The distance from a reference plane of polish just beyond the end of the crack that was in the weld.

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IGSCC Near the Outside Surface Inch Position Inch Position of the Pipe at the 0.70-Inch Position FIGURE 3.

THE IGSCC ASSOCIATED WITH FLAW NO.1 AT SEVERAL LOCATIONS ALONG THE LENGTH OF THE CRACK

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FLAW NO.1 NEAR THE END OF THE IGSCC FARTHEST FROM THE WELD I I

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THE FLOW PATTERN OF METAL AROUND FLAW NO.1 AT THE 0.72-INCH LOCATION IN FIGURE 2 The photomicrograph was taken using Nomarski interference-contrast microscopy to enhance the metal-flow pattern.

14 that magnification, the two surface imperfections shown in Figure 4a and 4b are evident. The cross section of the flaw in Figure 5 is located at approxi-mately the 0.72-inch position in Figure 2; that cross section is about 0.02 inch beyond the cross section shown in Figure 4.

In Figure 5, the surface l

imperfection shown in Figure 4a is observed to be sl',ghtly larger, and the surface imperfection shown in Figure 4b is observed to be slightly smaller with little or no evidence of IGSCC, 1

Flaw No. 4 in Figure 1 Flaw No. 4, like Flaw No.1, was located in close proximity to the weld in the region of the weld heat-affected zone. At that location, the propagatiort of IGSCC from the flaw was suspected and was observed in metal-lographic cross sections of the flaw. The profile of the crack was obtained from serial sections of Specimen 4-K-K and Specimen 4-L-L.

When Specimen 4-K-K was prepared metallographically, it was anticipated that no crack would be present in the initial section, because the section was obtained I

beyond the end of the flaw that was visible on the surface of the pipe.

I However, a crack was present; therefore Specimen 4-L-L was prepared in order to determine the extent of the crack in a direction away from the weld. The I

profile of the IGSCC crack at Flaw No. 4 is revealed in Figure 6 in the same manner as was the crack-profile presented in Figure 2.

The data for crack depth and crack length that are plotted in Figure 6 are given in Table 3.

The cross-hatched region in Figure 6 represents the extent of the IGSCC surface.

Included in Figure 6 are the approximate locations of the inside and outside pipe surfaces and a portion of the weld line, with respect to the crack. Although the crack-surface area was smaller, the general outline of that area was similar to that of the IGSCC at Flaw No.1 (compare Figures 2 and 6). Also, arrest of the crack propagation in the 1

through-wall direction again apparently occurred in we;d metal.

g Figure 7 shows the appearance of the IGSCC at a few locations along e

its length.

Figure 7a exhibits the crack at the 0.10-inch position. At that I

location, the crack was subsurface and was entirely within weld metal except for a very small portion near middepth. At the 0.125-inch position (Figure 7b),

the crack was slightly beneath the inside surface of the pipe and had begun to I

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Distance From Reference Plane, inches FIGURE 6.

PROFILE OF INTERGRANULAR STRESS-CORROSION CRACK AT FLAW NO. 4 l

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TABLE 3.

CRACK-DEPTH AND CRACK-LENGTH DATA FOR THE IGSCC ASSOCIATED WITH FLAW NO. 4 I

Distance from Depth of Crack Maximum Width Specimer. of Reference Plane,(a)

Below Inside Pipe Surface, of Crack, W

Flaw No. 4 inches inches mils l

4-K-K 0

No crack 0.010 0.133 to 0.213 0.2 0.022 0.081 to 0.256 0.5 I

0.047 0.069 to 0.296 1.0 0.097 0.023 to 0.315 1.0 0.112 0.014 to 0.315 1.0 I

0.127 0.004 to 0.341 1.0 0.142 0.345 1.2

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0.187 0.338 1.8 0.212 0.346 1.3 0.262 0.367 1.6 I

0.312 0.41 5 1.0 0.372 0.415 1.5 0.431 0.437 1.0 I

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0.511 0.008 to 0.441 0.5 0.517 0.012 to 0.444 0.5 4-L-L 0.554 0.295 to 0.438 0.3 0.559 0.299 to 0.437 0.2 I

0.565 0.305 to 0.431 0.15 0.575 0.313 to 0.425 0.15 0.585 0.373 to 0.415 0.1 I

0.597 0.376 to 0.385 0.05 0.607 No crack I

(a) The distance from a reference plane of polish just beyond the end of the crack that was in the weld.

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IGSCC at the 0.161 Inch Position Inch Position Inch Position FIGURE 7.

THE IGSCC ASSOCIATED WITH : LAW NO. 4 AT SEVERAL i.0 CATIONS ALONG THE LENGTH OF THE CRACK

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Figure 7c shows the crack at the 0.161-inch position.

The first plane of polish in Specimen 4-K-K revealed the IGSCC as shown in Figure 7d. As was mentioned earlier, the presence of a crack in this plane of polish was not anticipated, because Specimen 4-K-K was

. beyond the visible end of Flaw No. 4.

Not only was the crack present, but the depth of the crack was nearly a maximum and a second, adjacent crack

'was observed. The second crack is evident in Figure 7d to the left of the primary crack.

In this section, both the primary crack and the secondary crack began below the inside surface of the pipe. Neglecting the distance between the pipe surface and the beginning of the crack below the pipe surface, the primary crack extended in depth about 89 percent of the pipe-wall thickness. The secondary crack was not plotted in Figure 6, because its presence was observed only between the 0.49-and 0.52-inch locations and it did not extend beyond a depth below the pipe surface of about 0.12 inch. The secondary crack may have been a branch of the primary crack.

Figure 7e exhibits the IGSCC crack near the outside suface of the pipe at about the 0.60-inch position at high magnification; the entire crack in the through-wall direction is shown. No crack was observed in the next serial section beyond 0.60 inch.

Examinations of Other Surface Flaws The examinations of cross sections of other surface flaws, namely Specimens 2-P-P, 2-N-N, 2-R-R, and 5-U-U (see Figure 1), did not reveal the presence of IGSCC nor any other mode of failure induced by the surface flaws.-

All of the surface flaws examined exhibited characteristics similar to those generally observed for seams or laps in billet surfaces.. Examples of those

,i characteristics are shown in Figures 8 through 11. The three cross sections of Flaw No. 2 are presented in Figures 8 through 10.

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. Figure 8, the depth of Flaw No. 2 was observed to be relatively shallow.

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THE FLOW PATTERN OF METAL AROUND SURFACE FLAW NO. 2 IN SPECIMEN 2-R-R The photomicrograph was taken using Nomarksi interference-contrast microscopy to enhance the metal-flow pattern.

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THE FLOW PATTERN OF METAL AROUND SURFACE FLAW NO. 5 IN SPECIMEN 5-U-U The photomicrograph was taken using Nomarski interference-contrast microscopy to enhance the metal-flow pattern.

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In that section, shown in Figure 9, the flaw appears very much like a surface fold, or lap. The depth of the flaw was about g

E 0.035 inch. Specimen 2-R-R was taken across a thin sliver of surface metal E

that had been lifted, but not removed, from the surface; the appearance of the sliver can be seen in Figure 10. Part of the sliver was detached from the surface of the pipe at the location of Specimen 2-R-R.

Specimen 5-U-U across Flaw No. 5 is shown in Figure 11. The characteristics of Flaw No. 5 were similar to those of Flaw No. 2 (and Flaw No.1 that was presented earlier in this report and in the report of the E-previous investigation). The depth of Flaw No. 5 was about 0.030 inch.

7 The flow patterns of metal that were revealed around the flaws

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seamless pipe; hence, the flaws were present in the pipe when the pipe was

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E Energy-Dispersive X-ray Analyses E

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Chemical analyses of the corrosion products observed in Flaw No. 1 b

and the IGSCC associated with that flaw were made in Specimen 1-S-S before m

the serial sections were prepared. Analyses of the corrosion products in other surface flaws were made in Specimens 2-N-N and 2-R-R of Flaw No. 2 and in Specimen 5-U-U of Flaw No. 5.

P Corrosion Products in Flaw No. 1 9

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The results of the semiquantitative energy-dispersive X-ray (EDAX)

E electr n-micr pr be analyses f c rr si n pr ducts bserved within Flaw E

53 No.1 in the IGSCC associated with the flaw are presented in Table 4.

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results of EDAX analyses of the AISI 304 stainless steel pipe and the weld 5

metal in Specimen l'-S-S are included in Table 4 as base data for comparison E

with the results obtained from the analyses of the corrosion products.

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I 25 TABLE 4.

RESULTS OF SEMIQUANTITATIVE (a) ELECTRON-MICR0 PROBE I

ANALYSES OF CORR 0SION PRODUCTS BY ENERGY-DISPERSIVE-X-RAY ANALYTICAL TECHNIQUES IN SPECIMEN 1-S-S OF FLAW N0. 1 Relative Concentr9tjon of the I

Area Elements Detected (b), percent Analyzed Fe Cr Ni Si I

1 304 SS matrix 69.6 18.9 10.4 1.0 2

304 SS weld metal 69.4 19.7 9.8 1.1 l

3 Corrosion products in Flaw No. 1 56.4 36.1 6.3 1.2 (see Figure 13) 4 Corrosion products in the main 93.9 0.9 5.3 ND(c) crack near the inside pipe surface (see Figure 15) 5 Corrosion products in a branch 69.0 24.2 5.9 0.9 I

crack 6

Corrosion products in a branch 47.9 44.0 6.5 1.5 crack near Area 5 7

Corrosion products in the main 93.3 1.3 5.3 ND crack at about middepth 8

Corrosion products in the main 92.1 2.9 5.0 ND I

crack near the crack tip in the weld metal I

I (a) The semiquantitative analysis is a standardless quantitative analysis of the X-ray-energy-spectra data that includes a full ZAF (atomic number, absorption, and fluorescence factors) matrix-correction calculation. The relative concen-I trations of the elements detected are normalized to obtain a sum of 1.0 (100 percent).

I (b) Elements lighter than Atomic Number 11 (sodium) are not detected, so oxygen could not be determined.

(c) ND = not detected.

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26 The relative concentrations of chromium and nickel in the pipe (Area 1 in Table 4) and in the weld metal (Area 2 in Table 4) agree quite I

well with the contents of those two elements that were obtained by emission-spectrographic analytical techniques.

(Refer to Table 1 for the compari-I son.) The X-ray-energy spectrum for the pipe, which was nearly the same as the spectrum for the weld metal, is shown in Figure 12.

I The corrosion products that were analyzed in Flaw No.1 (Area 3 in Table 4) are identified by the arrow in Figure 13, a cross section of I

Flaw No.1 observed in Specimen 1-S-S. The X-ray-energy spectrum for Area 3 is presented in Figure 14. The analysis of the chromium present in the I

corrosion products indicated that the chromium content was nearly twice the chromium content of the pipe. The increase in the chromium content was I

accompanied by decreases in the iron and nickel contents.

The region represented by Area 4 in Table 4, a region of corrosion I

products in the IGSCC below Flaw No.1 near the inside surface of the pipe, is shown in Figure 15a. Those corrosion products contained a relatively low concentration of chromium, as was indicated also by the X-ray-energy spectrum of Areit 4 presented in Figure 16. The X-ray distribution map of chromium presented in Figure 15b indicates the low concentration of chromium in the major portion of the corrosion products in the grain boundaries.

(A region that exhibits a relatively sparse population of white dots in an X-ray-distribution map of an element indicates that the regior[contains a lower concentration of the element than do the regions that exhibit more dense populations of white dots.) The major decrease in the chromium content was balanced by a major increase in the iron content.

Areas 5 and 6 in Table 4 were the regions of corrosion products observed in two different, but nearby, intergranular cracks that branched out from the main intergranular crack. The chromium and iron contents appeared to differ significantly between those two areas, and the chromium content in both areas was well above that in the pipe. The X-ray-energy spectrum of Area 6 is shown in Figure 17.

The analyses of corrosion products in the main crack at about middepth below the inside pipe surface and of corrosion products near the crack tip in the weld metal both exhibited relatively low concentrations of I

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ENERGY-DISPERSIVE X-RAY SPECTRUM OBTAINED FROM AN ANALYSIS OF THE TYPE 304 i

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8.208 1.BBB 2.BBB 3.908 4.158 5.85!

S.BER 7.8EE 8.829 9.EEB 18.BBB ENERGY (kev)

FIGURE 14.

ENERGY-DISPERSIVE X-RAY SPECTRUM OBTAINED FROM AN ANALYSIS OF CORROSION PRODUCTS IN FLAW N0. 1 OBSERVED IN SPECIMEN 1-S-S (AREA 3 in TABLE 4)

I I

I I

I I

I p

I

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l 1000X 34692 a.

Region of the IGSCC Identified As I

Area 4 in Table 4 (SEM Micrograph)

..m ;, <:. L ny a : ;. -:. ].,w'-

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1000X 34693 m

b.

X-ray-Distribution Map of Cr in the l

Region Shown in (a) Above FIGURE 15. CORROSION PRODUCTS IN THE IGSCC NEAR THE I

INSIDE SURFACE OF THE PIPE I

I

aus em sum aus em e n aus aus num amo mas aus aus amo sus amm ama aus aus uma sus mas LT=

200 SECS 1-S-S CORR IN CRACK F

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s.ae 1.we 2.m 3.m 4.s 5.m s.m 7.res

8. Pie 9.m 18.m l

ENERGY (kev) l FIGURE 16.

ENERGY-DISPERSIVE X-RAY SPECTRUM OBTAINED FROM AN ANALYSIS OF CORR 0SION PRODUCTS IN THE CRACK (AREA 4 IN TABLE 4) 1 l

u_.___._._____.________

LT" 200 SECS 1-S-S CORR IN CRACK R

sees -

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8.M 1.9EE 2.EfB 3.82E 4.EEE 5.59 6.20B 7.EN B.PNI 9.M llL!!EU ENERGY (kev)

FIGURE 17.

ENERGY-DISPERSIVE X-RAY SPECTRUM OBTAINED FROM AN ANALYSIS OF CORROSION PRODUCTS t

IN A BRANCH CRACK (AREA 6 IN TABLE 4) i I

L l

i

i----.==--

m I

I 33 I

chromium; the low chromium concentrations were similar to that found in the corrosion products in the main crack near the inside surface (Area 4 in I

Table 4).

A summary of the results presented in Table 4 indicates the I

following:

e The relative concentrations of nickel among the various I

corrosion products that were analyzed were on the order of 50 to 60 percent of the relative concentrations of I

nickel in the pipe or in the weld metal.

e The relative concentration of chromium in the corrosion I

products found along the principal IGSCC was significantly lower and the relative concentration of iron was signi-I ficantly higher than those respective relative concentra-tions found in the pipe and in the weld metal.

I e The relative concentrations of chromium and iron varied among the corrosion products in different branch cracks.

I e The relative concentrations of iron, chromium, and nickel in the corrosion products in the surface flaw appeared to I

be similar to the concentrations of those elements in the corrosion products in branch cracks.

I e The analyses of the pipe and the weld metal were similar, and they were nominally the same as the emission-spectrographic analyses obtained for those materials.

Corrosion Products in Flaw No. 2 I

The results of the EDAX electron-microprobe analyses of corrosion products observed within Flaw No. 2 are presented in Table 5.

Those results were obtained from Specimen 2-N-N and Specimen 2-R-R of Flaw No. 2 (Specimen 2-N-N and Specimen 2-R-R of Flaw No. 2 are shown in Figures 9 and 10, I

respectively.)

Area 1 in Table 5 was located in the vicinity of the midlength of Flaw No. 2 with reference to Figure 9.

The EDAX analysis of Area 1 was I

I

I l

34 I

TABLE 5.

RESULTS OF SEMIQUANTITATIVE (a) ELECTRON-MICR0 PROBE ANALYSES OF CORROSION PRODUCTS BY ENERGY-DISPERSIVE-4 X-RAY ANALYTICAL TECHNIQUES IN SPECIMENS 2-N-N AND

{

2-R-R OF FLAW NO. 2 I

1 Relative Concentr on of the Area Elements Detected

, percent Analyzed Fe Cr Ni Si Al Ti S

Specimen 2-N-N (Figure 9) 1 Midlength of the flaw 67.1 19.6 8.5 0.8 2.5 0.7 0.8 (see Figure 19a) 2 Large particle in the 23.0 56.1 ND(c)

ND 15.8 5.2 ND center of Figure 19a 3

Another area near Area 1 68.4 5.8 18.8 0.6 0.6 ND 5.8 i

4 Tip of the flaw 72.1 14.7 10.5 1.8 0.6 ND 0.2 l

Specimen 2-R-R (Figure 10) 5 Midlength of the flaw 66.4 21.6 9.2 1.0 1.8 ND ND 6

Tip of the flaw 44.1 48.3 6.0 1.1 ND ND 0.5 I

(a) The semiquantitative analysis is a standardless quantitative analysis of the I

X-ray-energy-spectra data that includes a full ZAF (atomic number, absorption, and fluorescence factors) matrix-correction calculation. The reictive concen-trations of the elements detected are normalized to obtain a sum of i.0 l

(100 percent).

(b) Elements lighter than Atomic Number 11 (sodium) are not detected, so oxygen could not be determined.

(c) ND = not detected.

I

.I

I 35 I

obtained by an area scan at a magnification of 2000X. The X-ray-energy spectrum for Area 1 is presented in Figure 18; Area 1 is revealed in Figure I

19a. Area 2 in Table 5 was a spot analysis of the large particle within Area 1 that is. visible in the center of Figure 19a.

Nickel, silicon, and I

sulfur were not detected in the large particle, whereas those elements, in addition to iron, chronium, aluminum, and titanium, were detected within Area 1 (Figure 19a) that included the particle.

X-ray-distribution maps of the elements detec.ted in Area 1, except silicon, are presented in I

Figures 19b through 19.

Figures 19f and 19g show, respectively, that the 3

nickel and sulfur were concentrated in a small particle, apparently nickel I

l sulfide, adjacent to the large particle.

The results presented in Table 5 seem to indicate that the compo-sition of the corrosion products in Flaw No. 2 varies extensively from one t

area to another. The elements usually detected in the different areas were I

iron, chromium, nickel, aluminum, and silicon. Less frequently detected elements were titanium and sulfur.

r I

Corrosion Products in Flaw No. 5 I

The results of the EDAX electron-microprobe analyses of corrosion I

i products observed within Flaw No. 5 are presented in Table 6.

Those results were obtained from Specimen 5-U-U (Figure 11) of Flaw No. 5.

'I The principal elements detected in the corrosion products in Flaw No. 5 were the same as those elements detected in the corrosion pro-ducts in Flaw No.1 and Flaw No. 2.

As with those other flaws, variations in the compositions of the corrosion products were evident among different areas that were analyzed.

I I

3 I

LT=

200 SECS 2-N-N CORR IN FLAW F

asBB <-

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4. 91 9 5.BBB 6.BIE 7.Pl!O 8.N!B 9.M 18.PBB ENERGY (kev)

FIGURE 18.

ENERGY-DISPERSIVE X-RAY SPECTRUM OBTAINED FROM AN AREA SCAN OF CORROSION j

PRODUCTS IN FLAW N0. 2, SPECIMEN 2-N-N ( AREA 1 IN TABLE 5) 4

}

i

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Area 1 Reported in Table 5 (SEM Micrograph)

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,I 2000X 34699 b.

X-ray-Distribution Map for Chromium in (a) Above FIGURE 19. CORROSION PRODUCTS IN FLAW NO. 2 THAT WERE SUBJECTED TO ELECTRON-MICR0 PROBE ANALYSES f

I

l 38 I

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X-ray-Distribution Map for Aluminum in (a) Above I

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X-ray-Distribution Map for Titanium in (a) Above

{

FIGURE 19.

(Continued)

[

39

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anw

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2000X 34702 X-ray-Distribution Map for Iron in (a) Above e.

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X-ray-Distribution Map for Nickel in (a) Above FIGURE 19.

(Continued) 4 e

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X-ray-Distribution Map for Sulfur in (a) Above FIGURE 19.

(Continued) l 1

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I 41 I

TABLE 6.

RESULTS OF SEMIQUANTITATIVE (a) ELECTRON-MICR0 PROBE ANALYSES OF CORROSION PRODUCTS BY ENERGY-DISPERSIVE X-RAY ANALYTICAL TECHNIQUES IN SPECIMEN 5-U-U OF FLAW NO. 5 I

on of the RelativeConcentrgi, percent I

Elements Detected Area Analyzed Fe Cr N1 Si Al S

I Midlength of the flaw 86.9 2.3 9.1 1.5 ND(c) 0.3 (seeFigure11) 2 Tip of the flaw 92.1 2.7 3.6 1.1 0.3 0.2 I

(a) The seniquantitative analysis is a standardless quantitative analysis of the X-ray-energy-spectra data that includes a full I

ZAF (atomic number, absorption, and fluorescence factors) matrix-correction calculation.

The relative concentrations of the ele-ments detected are nonnalized to obtain a sum of 1.0 (100 percent).

i I

(b) Elements lighter than Atomic Number 11 (sodium) are not detected, so oxygen could not be determined.

I (c) ND = not detected.

I Electrochemical-Polarization-Reactivation (EPR) Tests The EPR test

• was developed by General Electric Company as a.neans to reveal the susceptibility of austenitic stainless stoel piping to inter-l granular stress-corrosion cracking (IGSCC) in nuclear applications. The need I

for such a test arose from major problems in the past in the nuclear power industry with IGSCC in the weld-heat-affected zones of Type 304 stainless steel primary-coolant piping. The corrodent has been high-purity water that contained less than 9 ppm oxygen and less than 0.3 ppm chloride.

I Clarke, W.

L.,

et al, " Detection of Sensitization in Stainless Steel I

Using Electrochemical Techniques", Paper 180, in Corrosion '77, National Association of Corrosion Engineers, Houston, Texas (1977).

Cihal, V., "A Potentiokinetic Reactivation Method for Predicting the I

I.G.C. and I.G.S.C.C. Sensitivity of Stainless Steels and Alloys".

2_0, 737 (1980).

Corrosion Science, 0

I I

I 42 In the EPR test, a stainless steel specimen, in a strong acid I

electrolyte, is cathodically cleaned and then held at an anodic potential to passivate the surface. The potential is then shifted in the cathodic I-direction through the corrosive range to test the passivating film produced previously. The resulting corrosion current during this shift (electro-I chemical reverse scan) is indicative of the degree of protection provided by the prior passivation treatment. A protective film will yield only a 1

very small corrosion current, whereas a poorly protective film, such as I

the film over the chromium-depleted region adjacent to grain-boundary chromium carbides in a sensitized stainless steel, will yield a large cor-I rosion current in the reverse scan. The ratio of the maximum corrosion h

current during the cathodic scan to the maximum corrosion current during the original anodic scan (EPR ratio) is used as a measure of the degree of sensitization. Limited experience has indicated that austenitic stainless I

steels having corrosion-current ratios of less than 0.04 in the EPR test

' I are not sensitized and are not susceptible to intergranular cracking. More-over, past experience with cast AISI 316 stainless steel indicated that material with an EPR ratio of approximately 0.01 was not susceptible to I

IGSCC, whereas material with EPR ratios that exceeded about 0.08 were sus-ceptible. At the present time, a definite threshold value of the EPR ratio for the occurrence of IGSCC cannot be defined and probably varies with material.

I The EPR test' v a conducted during this investigation as a means of evaluating the e-,, m

' sensitization in the weld heat-affected zone and I

at the inside ant.:.M, afaces of the subject pipe away from weld-heat effects. The initial EPR tests were made using an electrolyte that consisted I

of 2M H SO4 and 0.lM KCL. Those tests showed no evidence of sensitization 2

in either the weld-heat-affected-zone sample, EPR-2 in Figure 1, or the I

pipe samples, EPR-1 10 and EPR-1 OD, remo@ from the welded region. A I

review of the literature indicated that the eiectrolyte was probably too weak. The EPR tests were repeated, therefore, in an electrolyte that con-sisted of 2M H 504 and 0.5M kcl.

I 2

The results of the tests performed in the stronger solution are revealed in Figures 20 and 21 by a plot of current, mA, versus saturated I

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3o 40 20 30 40 50 so 70 80 90 10 0 110 120 130 14 0 15 0 Current, mA FIGURE 21.

EPR CURVES FOR SAMPLES EPR-1 ID AND EPR-10D, AISI 304 STAINLESS STEEL PIPE REMOTE FROM THE REGION OF THE WELD The same curve was obtained for both samples.

l

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45 I

calomel electrode potential, VSCE.

For the weld heat-affected zone, the l

ratio of the maximum corrosion current during the cathodic scan to the maximum corrosion current during the original anodic scan was calculated to be 0.048 (Figure 20); the EPR ratio for the pipe samples remote from the welded region was calculated to be 0.009 (Figure 21). Thus, the weld heat-affected zone adjacent to the weld was more susceptible to IGSCC than was the stainless steel pioe. The higher susceptibility to IGSCC of the heat-affected zone appare. :y was a result of the sensitized condition of that zone.

I DISCUSSION The investigation of surface flaws revealed evidence similar to I

that reported in the earlier metallographic examinations, namely, evidence that the surface flaws were introduced during the production of the seam-I less pipe. The evidence indicated further that the fabrication-induced flaws were similar to laps or seams. Such flaws probably originated during I

the piercing operation.

IGSCC's were found to be associated with flaws that were located I

in the region of the girth-weld heat-affected zone; IGSCC's were not observed at flaws located outside the heat-affected zone. Meta 11ographic I

examination revealed that the weld heat-affected zone had been sensitized.

Based on the results of the EPR tests, the presence of IGSCC's in the weld I

heat-affected zone is not unexpected. The sensitized condition of the weld heat-affected zone apparently caused the zone to possess a degree of I

susceptibility to IGSCC, as was indicated by the EPR-test results; in the parent metal outside the heat-affected zone, no degree of susceptibility I

of the pipe to IGSCC was indicated. However, evidence of IGSCC was not observed in regions of the heat-affected zone where surface flaws were I

absent. Thus the presence of a surface flaw in the region of the heat-affected zone was apparently a major factor that contributed to the initiation of U

IGSCC. The contribution of the surface flaw to the onset of IGSCC Nas most likely in the manner of a stress raiser.

I

I 46 The profiles of the IGSCC's indicated that the major portions of the IGSCC surfaces were within the sensitized region underneath the surface flaws. The extremities of the cracks extended short distances beyond the ends of the flaws that were observed on the inside surface of the pipe.

The depth of one crack below the inside pipe surface extended nearly through the thickness of the pipe wall and the other crack apparently penetrated the wall. For the most part, the propagation of the cracks appeared to be arrested in the through-wall direction by the broad, final passes of weld

~

metal on the outside pipe surface and, in the pipe-axis direction, by the welded zone through the pipe wall at one end of the crack, and by tiia non-sensitized parent metal at the other end of the crack.

The electron-microprobe analyses of corrcsion products in the surface flaws and in the IGSCC's did not identify the presence of a specific I

Most likely the corrodent was the water in the core-spray system corrodent.

that contained low concentrations of oxygen and perhaps chloride that could not be detected by energy-dispersive X-ray analysis.

CONCLUSIONS The results of the investigation led to the following cor-lusions:

Linear indications on the inside pipe surface were e

fabrication-induced surface flaws.

IGSCC was associated only with surface flaws that were e

located in the region of a sensitized weld heat-affected zone.

Surface flaws acting as stress raisers were a major e

factor that led to the initiation of IGSCC.

In the weld heat-affected zone, the IGSCC's extended e

through most of the pipe wall.

Propagation of IGSCC was apparently arrested by weld e

metal and nonsensitized parent metal that surrounded the weld heat-affected zone.

In the absence of the fabrication-induced surface flaws, e

'GSCC may not have occurred in the weld heat-affected zone.

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k ATTACHMENT e

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