ML17256A861

Forwards Results of Steam Generator Tube Metallurgical Exam

ML17256A861
Person / Time
Site:	Ginna
Issue date:	04/23/1982
From:	Maier J ROCHESTER GAS & ELECTRIC CORP.
To:	Crutchfield D Office of Nuclear Reactor Regulation
References
NUDOCS 8204290285
Download: ML17256A861 (60)

Text

F REGULATORY ~FORMATION DISTRIBUTION SVM (RIDE)

ACCESSION NBR:8204290285 DOC SEDATE: 82/04/23 NOTARIZED! NO, DOCKET FACIL:50"240 Robert Emmet Ginna Nuclear Planti Uni't 1i Rochester G

05000240 AUTH BYNAME AUTHOR AFFILIATION MAIERFJ ~ E ~

Rochester Gas L Electric Corp'EC IP ~ NAME RECIPIENT AFFILIATION CRUTCHFIELDF 0 ~

Operating Reactors Branch 5

SUBJECT:

Forwards results of steam generator tube metallurgical rept'ISTRIBUTION CODE:

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ROCHESTER GAS AND ELECTRIC CORPO JOHN E. MAIER Vice PreeiOent

~ 89

~

VENUE, ROCHESTER, N.Y. 14649 Qi 9

TELEPHONE AREA coDE Tie.546-2700 V'y April 23, l982 Director of Nuclear Reactor Regulation Attention:

Mr. Dennis M. Crutchfield, Chi'ef Operating Reactors Branch No.

5 U.S. Nuclear Regulatory, Commission Washington, D.C.

20555

Subject:

Steam Generator Tube Metallurgical Examination R.

E. Ginna Nuclear Power Plant Docket No. 50-244

Dear Mr.'rutchfield:

,By letter'ated March l, l982, you authorized the xemoval of a limited number of tube,'samples from the Ginna'-Steam Generator.

These tubes were subsequ'ently removed and sent,'to our contractor, Westinghouse Electric Corporation for examination.

The enclosed report provides the -results of that examination.

Ten copies of this letter an'd the eneclosed report are provided.

Additional copies of the report will be provided in conjuction with submittal of our complete Steam Generator Evaluation report next week.

Very truly yours, John E. Maier Enclosures

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Metallur ical Examination of Ginna Steam Generator Tubes 0165s:10

Abstract 0 tai led microscopic examinations were performed on a section of Row 42

- Column 55 (R42-C55) tubing taken from the hot leg side of the R.

E.

Ginna "B" steam generator in the region where the tube burst.

Five neighboring previously plugged tubes were also examined.

All of these Inconel 600 tubes displayed on their 0.0.

surfaces one or more axially oriented flat zones which contained circumferential striations.

Thir ty-eight of the forty flat zones'that were examined exhibited cold work (0.0.) surface layers, a feature which is consistent with a wear pro-cess.

The burst in R42-C55 occurred at one of these flats where the wall thickness had been reduced from the nominal 0.050 in. to 0.008 in.

Cold work was not identified on the flat that burst.

Fractography revealed a normal ductile tensile overload failure at the burst.

Fatigue cracking was identified as one mode of breakage of previously plugged tubes.

Normal metallurgical properties were identified for the burst tube and for one plugged tube.

0165s:10

1.0 Introduction 0

On January 25,

1982, a tube ruptured in the "8" nuclear steam generator of the Rochester Gas and Electric Corporation (RGE)

R.

E. Ginna Power Plant.

The burst tube was determined to be three tube-rows in from the periphery on the hot leg side at Row 42 - Column 55 (R42-C55).

The leak was due to an axially oriented "fish-mouth" opening just above the top of the tubesheet.

In addition, some of the previously plugged neighboring peripheral tubes exhibited collapse, deformation, or frac-ture conditions which were not present at the time these tubes were plugged.

A hole was cut in the shell at Column 55 and nine-inch lengths of the leaking and neighboring tubes were removed.

Sections of six tubes were sent to the Westinghouse R&0 Center, Pittsburgh, Pennsylvania for metal-lurgical characterization.

These consisted of the leaking tube (R42-C55) and five neighboring and previously plugged tubes (R44-C54, R43-C54, R44-C55, R43-C55 and R43-C56).

2.0 Nondestructive Examinations Prior to removal of each section from the steam generator, a yellow dot was placed on each section to define the tube surface closest to the perimeter of the generator.

In the current examination this dot was taken as the Oo position.

Each tube length was received in one or two sections, originally extending from near the top of the tubesheet to ten in. above the top of the tubesheet.

Photographs of the leaking tube from Row 42 - Column 55 (R42-C55) show "fish-mouth" opening at Oo and axially oriented flats at 0, 60 and 315o.

These flats had circumferential striations, Figures 2-1 and 2-2.

Photographs in Figures 2-3 to 2-8 are of the neighboring pre-viously plugged tubes:

R43-C55, R44-C55, R43-C54, R44-C54 and R43-C56.

imilar flats were observed on all tubes at various angular positions.

There is extensive metal loss and apparent deformation on all tube sections.

Tubes from R44-C55 and R44-C54 arrived in two sections.

Wall thickness measurements were consistent with a nominal 50 mil wall away from the flats and a wall thickness r eduction at the flats, Figure 2-9, Table 2-1.

Oouble wall x-ray radiographs were made of all tube sections at 0, 45, 90 and 315o.

A Seifert Industrial X-ray unit was used with the fol-lowing settings:

5 min. exposure

time, 110 to 70 kV, 10 milliamperes, 60 in. source-to-film distance, large focal spot, and Kodak N-8 lead pack film.

Wall thickness reductions were easily seen; however, there was no evidence of intergranular attack or stress corrosion cracking.

0165s:10

Prints of typical radiographs on the C55 tubes are shown in Figures 2-10 to 2-12, together with diagrams which depict the locations and orien-tations of the laboratory cuts that were made for microscopic examina-tions.

The other three tubes were examined metallographically on transverse cross sections at elevations of 2-1/2 and 4 in. from the tops of the sections; cutting diagrams are not indicated for these three tubes.

After cutting in the laboratory, all sections were notched at Oo on the tubesheet end to maintain orientation.

The metallographic mounts are positioned on tubesheet maps in Figures 3-1 and 3-2 in an attempt to aid others in constructing the sequence of events leading to tube leakage.

Microstructures through the leaking tube R42-C55 are shown in Figures 3-3 and 3-4.

These microstructures were etched with two percent bromine-methanol solution (only etchant used in this study).

Cold work was not evident on the flat that burst, but was apparent

'on the 60o flat.

The fracture face was not intergranular and was of the tensile, overload type.

The microstructure appeared 'normal and had carbide banding occurring to a greater degree near the I.D.

At O.D. surfaces away from the flats, shallow amounts of cold work were observed and probably resulted from belt polishing in the manufacture of the tubing, e.g.,

0.2 mils depth of cold work at 270 in Figure 3-4.

Metallography on the other tubes is presented in Figures 3-5 to 3-17 and the depth of cold work on the flats is summarized in Table 3-1.

Thirty eight of forty examinations of the flats showed evidence of cold work up to a depth of 1.1 mils.

One of the two flats not showing evidence of cold work. was at 0o on tube R42-C55 and was the flat that ruptured.

The heaviest degrees of cold work were observed on the bottom of the concave surface of R44-C55, Figures 3-9 to 3-11.

Some transgranular cracks were present and may have resulted from fatigue.

Microhardness traverses, Figure 3-18 and Table 3-2, confirmed that the.Oo flat on tube R42-C55 had no detectable cold work and that O.D. surfaces away from flats and other flats had cold work (increase in hardness at the surface).

4.0 Scannin Electron Microsco Examinations were made of surfaces with the scanning electron microscope (SEM - also used to designate scanning electron micrograph) and with the Energy Dispusive X-ray Spectrometer (EDS).

For tube R42-C55, the flat that ruptured had circumferential striations, and the fracture surface had some dimples that are characteristic of tensile overload, Figures 4-1 and 4-2.-

Fractography on a horizontal fracture near the center of R43-C55 sug-gested that fatigue contributed to cracking, Figures 4-3 and 4-4.

0165s:10

'0 On tube R44-C55, an EDS analysis on a flat was rich in Al, Si, Cr, Fe, Cu and Zn as compared to Inconel 600, Figure 4-5.

The fracture surfaces near the bottom of the tube were not well defined and contained

deposits, Figures 4-6 to 4-9.

Other fractographs on R44-C54 indicated that fatigue contributed to the fracture; Figures 4-10 and 4-11.

5.0 Com osition and Mechanical Pro erties of Tubes An EDS analysis of Section lA of tube R44-C55 indicated that the prin-cipal elements were within specification.

The mechanical properties of the Inconel 600 tubing were estimated and tabulated in Table 5-1.

Knoop (500 g) hardness readings were made mid-wall on the metallographic mounts 4 inches down on Tubes R42-C55 and R44-C55.

These were converted to Rockwell "8", RB, readings which were then used to estimate yield strength by two methods.

One was a correlation established previously on Inconel 600 tubing, Figure 5-2, and the other was an International Nickel Company correlation on Inconel 600 sheet and strip.

Reasonable agreement existed between the two conversions:

all estimates of yield strength were between 45,000 and 62,000 psi.

An estimate of ductility of the Inconel tubing was obtained with bends.

Rings 7A, 78 and 7C from Tube R44-C55 and 7A and 78 from tube R42-C55 were used.

Each ring was positioned such that a location free of flats between 145o and 225o would be at the apex of a U-bend.

The bend was made by placing the ring over a 3/32 in. diameter mandrel with a line of contact at the desig-nated position and deforming the ring at this location around the bar.

This strained the O.D. circumference in tension.

No fissures were observed on the O.D. surface at the apex and the calculated outer fiber strain was twenty-eight percent.

6. 0 Conc lus ions 1.

The microstructure and mechanical properties of the burst tube and a

neighboring plugged tube were determined and were normal for the mill annealed Inconel 600 tubing material.

2.

There was no evidence of stress-corrosion cracking or intergranular attack on I.D. or O.D. surfaces of any tube.

3.

All tubes displayed flat zones of O.D. wall reduction with circum-ferential striations within the flats.

4.

Thirty-eight of the forty flats that were studied showed cold work on the O.D. surface, indicating that a wear process produced the flats.

5.

The "fish-mouth" burst occurred at a flat where the wall thickness had been worn to 0.008 in. from the nominal 0.050 in. original wall; cold work was not identified on this flat.

0165s:10 6.

The fracture of the "fish-mouth" was consistent with a tensile overload failure.

7.

The most severe cold work was observed on a concave indented surface at the bottom of a peripheral tube R44-C55.

8.

Fatigue striations were identified on fractures associated with breakage of two of the previous ly plugged tubes.

0165s:10

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Fish mouth crack at near 0'n Tube R42-C55 from RGE (GXNNA), SGB, hot leg RM-94656

5'70'80 90'0 Fig. 2-2.

Tube R42-C55 from RGE (GINNA)> SGB> hot leg RM-94657

(

I, 270'25'f 180 90'f II5 45 00 Fig. 2-3.

Tube R43-C55 Erom RGE (GINNA), SGB, hot leg RM-94658

1 270'25" 180'35 90 00 Pig

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Tube R44-C55 from RGE (GINNA), SGB, hot leg RM-94659

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Tube R44-C55 from RGF.

(GINNA)> SGB, hot leg RM-94660

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Tube R43-C54 from RGE (GONNA)> SGB, hot leg RM-94661

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Tube R44-C54 from RGE (GINNA), SGB, hot 1eg RM-94662

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Tube R43-C56 from RGE (GINNA)> SGB, hot leg RM-94663

, 53.45,32,23,37,55,55 FJ 56>44>26>17 23,44,55 56

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Wall thickness measurements (mals) superimposed on 0'hotograph of R42-C55 RM-94664

Table 2-1 Wall thickness measurements (mils) at various positions on Column 55 tubes Tube No.

(Axial position)

Angular Position 0'5 90 135 180 225

= 270 315 R42 (1/2" below top) 50 54 53 54, 56 57 51 57 (1/2" above bottom)

(1/4"'-above bottom)

R43 (1/2" below top)

(1/2" above bot tom) 56 53 53 53 53 57 53 53 53 52 47 46 51 52 53 46 53 47 49 54 56 56 51 48 10 56 R44 (1/ 2ll (3/4 ll (1/ 2ll (1/4" below top) above bottom) above bottom) above bottom) 53 53 51 50 48 46 36 50 45 30 53

7C eJ cv 7B-Mech.

7A-Mech.

SEM - Fracture face L - Surface studied in metallography SEM - Fracture face Print of double wall X-ray radiograph at 0

for Fig. 2-10.

Tube R42-C55 and diagram showing cuts, section ident'ification, and sample use.

EM-94665

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2A Fracture surface shown in 270'hotograph - SKH 2B CP CI lO

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7C mech.'goo 7A. mech.

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II Chemical Analyses pO Fractography Print of double wall X-ray radiograph at 0'or top portion of Tube R44-C55 and cutting diagram RH-94667

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C54 C55 C56 Fig. 3-1.

Transverse cross-sections at ~

2 from tops ill 2

of the sections (Small circle designates 0')

RM-94668

R42 ac i'I R43

~secs iiiit R44 C54 C55 C56 Fig. 3-2.

Transverse cross-sections at ~ 4" from the tops of the sections RM-94669

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Two and one half inches towards tubesheet on section from Tube R42-C55 RM-94670

OD Fig. 3-4.

Metallography on transverse cross-section M" towards tubesheet on section from Tube R42-C55

Fig. 3-5.

OD surfaces 2" down from the top of the section from Tube R43-C55 RM<<94672

Fig. 3-6.

OD surfaces 4" down from the top of the section from Tube R43-C55 RM-94673

First polish and etch After removal of and additional 0.025" Fig. 3-7.

Four inches down from top portion of Tube R44-C55 m-94674

Fig. 3-8.

Metallography on transverse cross-section down 6" from top of top portion of Tube R44-C55.

Similar results were observed after polishing an additional 24 mils.

RM-94675

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Metallography 7" from top of top portion of Tube R44-C55 RM-94676

Fig. 3-lO.

Continuation of metallography 7" from top of top portion of Tube 444-C55 RM-94677

4 OD t+

pig.

3 ll.

Metallography at the OD (0')

8" down from the top of the top portion of 844-C55 RM-94678

n'i' Fig. 3-12.

Metallography 2-" down from the top of section from Tube R43-C54 RH-94679

Fig. 3-13.

OD surfaces 3" down from top of section from 4

Tube R43-C54 RM-94680

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Fig. 3-14.

Transverse cross-section 2-" down from the top of the 2

top portion og Tube R44-C54 RM-94681

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Metallography 3-" down from top end of top portion of R44-C54 RM-94682

Fig. 3-16.

OD surfaces 2" down from the top of the section from 2

Tube R43-C56 RM-94683

Fig. 3-17.

OD surfaces 3<" down from the top of the section from Tube R43-C56 RM-94684

Table 3-1 Depth of cold work t;o the nearest 0.1 mil on wall reduced areas (Tabulated values are angular position-max.

depth in mils)

Tube No.

(Approximate Axial Position From Top of Tube Section)

R42-C55 2-1/2" 4 II R43-C55 2-1/2" 4 II R44-C55 2-1/2" 4 II 6"

7 II R43-C54 2-1/2" 4ll (0'

0.0)* (60' 0.4)*

(0' 0.0)* (60' 0.4)

(30'-1.3

) (225'-0.5) ('270'-0.4) (330'-0.2)

(30'-0.3) (45'-0.5) (225'-0.5) (300'-0.4)

(60'-P. 5) (225'-0. 6) (270'-0.3)

P 2)* (1P5o P 2) *(15Po 1 P)(2PPO P 6)(27PO,P (105'-0. 5) (150'-0. 8) *(270'-0. 6) *

(90'-:Q. 0) A(180'-0. 5) (240'-0. 6) *

(30-0.9)*

(30'0. 9) *(195'-0. 5) (31 5'-0. 5)

R44-C54 2-1/2" (6Q'-Q.9)*(9Q-1.Q)*(270 -0.6 ) (3QQ'-Q.9) 41I

• (1P5o 1 P)*(18Po P 6) (27Po P 7)

R43-C56 2-1/2" 4ll (0'-0.3)*

(0'-0.5)*

• Shown in photomicrographs on transverse cross-sections

Four inches from top of R42-C55

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I'our inches from top of R44-C55 FiR. 3-18 Locations of Knoop microhardness traverses RM-94685

Table 3-2 Knoop (100g) microhardness traverses at various locations on Tubes R42-C55 and R44-C55 Tube Position No. Remarks

~ Depth from OD surface in mils 1

2 4

9 14 19 R42-C55 1

-2 3

Flat Flat No Flat 224 228 231 237 180 194 195 192 258 224 229 2

9 R44-C55 4

5 6

Flat No Flat Flat 321 300 223 224 254 364 261 312 289 261 209 321 312 248 214 226 194

Plat Fracture face iS 4 l SEH's of flat and fracture face above center of fish mouth crack on Tube R42-C55 RM-94686

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plat on OD practure surface

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SEN's on horizontal fracture surface of specimen from Tube R43-C55 RM-94688

OD surface near peak in prior figure SEH's near peak in prior figure and on fracture face.

RM-94689

Elanent

& Line Weight Petcent CU 2H Al Ka Si Ka Ti Ka Ct Ka Fe Ka Ni Ka Cu Ka Zn Ka TOTAL 0.93 1.69 0.39 23.59 13.20 49.25 5.23 5.63 100.00 Fig.

4 5.

EDS analysis on lower left area of 270'lat that was 1" down from the top of top portion of Tube R44-C55 (Section 7A).

RM-94690

Cut surface

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>135 Axial Fracture 135'135 Axial Fracture Fig. 4-6, Fractography was performed on two axial fracture surfaces l-l/2" from the bottom of the top portion of Tube R44-C55 RM-94691

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Fractography on >135'xial fracture RM-94692

Flat Axial Fracture at <135 Fracture'urface j/EA!/$p jig/

I 4-8 Fractography on <135'xial fracture RM-'94693

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SEH's of the fracture face at the bottom of the top portion of Tube R44-C55 RH-94694

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"i ~ Latching surfaces Fig. 4-10.

180'iew of ring at bottom of Tube R44-C54 (Top) and fractography on bottom fracture surface showing areas studied in more detail RM-94695

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Fractography on bottom fracture surface of Tube R44-C54; Area 1 (left) and Area 2(right)

RM-94696

Table 5-1 Mechanical Properties Tube No.

Knoop Hardness (500 g)

R Hardness (1)

Yield Strength (0.2% offset)

Ref.

(2)

Ref (3)

Percent (4)

Elongation R44-C55 R42-C55 206.6 171 '

88 80 56,000 45,000 62,000

> 28 45,000

>28 1)

Converted by ASTM E140-79 2)

Correlation establish on 24 tubes of Inconel 600 by R. G. Aspden 3)

Estimated by correlations established in Inconel alloy 600, Hunting Alloy Products Division, the International Nickel Company, Inc.

4)

No fissures developed when bent around a 3/32" dia. mandrel-calculated values.

70 65 X

~ 60 55 50 45 o

40

~O CV D

35 0

0 0

0 I

0 00 0

Slope:

1,423 psi/RB 72 74 76 78 80 82 84 86 88 90 92 Rockwell "B"Hardness Fig. 5-2.

Correlation of Rockwell "B" hardness and yield strength on 24 heats of Inconel 600 tubing and estimated strengths of two Ginna tubes (dashed lines).