Text

Exam of Crystal River-3 Pulled SG Tubes
	ML20080B555
Person / Time
Site:	Crystal River
Issue date:	11/30/1994
From:	; FLORIDA POWER CORP.
To:	;
Shared Package
ML20080B554	List: 3F1194-10, Submits Preliminary Results of Refuel 9 OTSGs Tube Pull,Per Commitment in Response to 940426 Cal,Item 8.Preliminary Rept, Exam of Crystal River-3 Pulled SG Tubes Encl.Final Rept Will Be Provided by 950531; ML20080B555;
References
	NUDOCS 9412050323
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i EXAMINATION OF CRYSTAL RIVER-3 PULLED STEAM GENERATOR TUBES i

Submitted by:

Florida Power Corporation Written by:

B&W Nuclear Environmental Services B&W Nuclear Technologies Electric Power Research Institute Florida Power Corporation Packer Engineering November 30,1994 9412050323 941130 PDR ADOCK 05000302 P

PDR 4

it 1.

i NOMENCLATURE I

j AVB-Anti-Vibration Bar AVT-All Volatile Treatment i

BWNT-B&W Nuclear Technologies BWOG-B&W Owners Group i

EC-Eddy Current EDS-Energy Dispersive Spectroscopy l

EPRI-Electric Power Research Institute i

FPC-Florida Power Corporation IGA-Intergranular Attack j

NDE-Non-Destructive Examinations OD-Outside Diameter OTSG-Once-Through Steam Generator 4

j POD-Probability of Detection i

RFEC-Rotating Field Eddy Current i

RPC-Rotating Pancake Coil j

RSG-Recirculating Steam Generator SAM-Scanning Auger Microscopy SEM-Scanning Electron Microscopy j

SG-Steam Generator TSP-Tube Support Plate i

TW-Through-Wall l

UT-Ultrasonic Testing WDS-Wave Dispersive Spectroscopy j

XPS-X-ray Photoelectron Spectroscopy t

I I

i i

4 b

i.

l 2

i

6 TABLE OF CONTENTS Section Pace 1

1 Backgro un d......................................

1-1 1.1 Steam Generator Condition.......................

1-1 1.2 Purpose of 1994 Tube Pulls 1-3 1.3 Rationale for Selection of Tubes Pulled.............

1-3 l

l 2

Examination of 1992 Archived Tube and 1994 Pulled Tubes...

2-l' 2.1 Field Nondestructive Examinations.................

2-1 2.2 Laboratory Nondestructive Examinations.

2-1 2.3 N D E Test Resul ts... -..........................

2-2 j

2.4 Destructive Examinations........................

2-3 3

Discussion of Results.................................

3-1 L

3.1 Observed Tubewall Degradation...................

3-1 3.2 Structural Integrity Implications '...................

3-3 3.3 Leakage Integrity Implications....................

3-5 3.4 NDE Field Detection Capabili as..................

3-6 l

4 Conclusions................

4-1 i

r 5

Refe ren ces.........................................

5-1 Appendix A Estimate of Burst Pressures for Crystal River 3 Steam Generator Tubine Burst Tested in 1992...........................

A-1 Appendix B Industry Experience with Tube Wear....................

B-1 1

j

c.

4 Section 1 BACKGROUND l

1.1 Steam Generator Condition Florida Power Corporation's (FPC) Crystal River-3 once-through steam generators (OTSGs) consistently exhibit minimal tube degradation due to_either corrosion or mechanical damage. Six (6) tubes were plugged pre-service. Twenty-seven (27) tubes were plugged from 1978 - 1981 due to tube end/ tube-to-tubesheetjoint damage caused by a burnable poison rod assembly that broke loose and was transported to the upper bowl of the "B" SG by the primary coolant flow. The first time tubes were plugged due to in-service degradation was in 1987 when three (3) tubes were plugged in the "A" SG because of wear..By the end of 1989, a total of only 36 tubes had been plugged in the Crystal River-3 SGs. Currently, 182 (0.59%) of the total of 31,062 SG tubes at Crystal River-3 are plugged.

)

In 1989, FPC began to pro-actively inspect more SG tubes than the minimum number required by plant technical specifications. This increase in inspection scope was based both on industry guidelines, (i.e., EPRI Report NP-6201, PWR Steam Generator Examination Guidelines: Revision 2 which was issued December 1988 and recommended an inspection sample of 20% of the active tubes), and on the implementation of a more pro-active SG management philosophy. From 1989 - 1992, the population of tubes inspected was increased significantly to include more of the tubes that had not previously been inspected in-service. As a result of the 1989,1990, i

1992, and 1994 SG eddy current (EC) inspections, all active tubes in both SGs have -

been inspected at least once since 1987, i.e.,100%_ of the tubes have been inspected l

in seven (7) years (three fuel cycles).

Most of the tubes, however, had not been inspected in-service by EC since the pre-startup full-bundle inspection of the SGs. As the inspection scope increased, the number of EC indications increased, as well as the number of tubes plugged. The majority of these bobbin coil indications were below a 5:1 signal-to-noise ratio (S/N),

j and were in tubes that had no prior in-service EC inspection. Most of these EC indications were in the "B" SG. All of the tubes with EC indications (including low S/N indications) were re-inspected in subsequent outages to determine if they were j

growing. With the 1990 inspection results, concentrations of S/Ns in certain regions of the "B"' SG became obvious. The regions with the highest number of S/N indications were the first span, 6" - 18" above the lower tubesheet secondary face (LTSF); the 7th tube support plate (TSP); and the 9th TSP (see Figures 1-1,1-2, and 1-3). More than 90% of these indications have bobbin coil signals ofless than 1 volt (see Figure 1-4).

Consistent with industry practice prior to 1992, FPC did not attempt to size any of the S/N indications. All S/Ns were however tracked and re-inspected each outage to 1-1 i

i o

4

~

monitor for change in single amplitude. During this time it was not known whether 1

S/Ns represented real degradation in the tube, or if they were caused by tube deposits. Further, because of the low signal-to-noise ratio, any real tube degradation could not be sized accurately by bobbin phase angle. Due to their small volume, the indications were not considered to be structurally significant even if they did have appreciable wall penetration. Therefore, leaving these indications in service was not considered a safety concern.

In 1992, however, industry practice began to change, and more focus was placed on trying to size S/Ns and disposition them according to the depth plugging criterion specified in plant technical specifications. FPC decided to pull tubes from the "B" SG during the Refuel 8 outage (in 1992) to determine if degradation was actually present where low S/N indications were being observed, to determine the probability of detection and accuracy in sizing of S/Ns by the available non-destructive examination (NDE) techniques, and to determine the structural significance of any degradation that might be present in the tubes.

The first span of the "B" SG had the most S/Ns, and afforded the highest potential for a successful tube pull due to the short length of tube that would require removal.

Therefore, six (6) tubes with first span S/Ns were removed in June 1992. These tubes were cut just below the 2nd TSP and pulled from the bottom of the SG. A seventh tube with an EC indication at the 7th TSP was cut below the 8th TSP and its removal was attempted. However, it became stuck in the LTS before the area of interest could be removed. This tube was stabilized in place, and the tubesheet holes plugged.

These tubes were destructively examined in the laboratory by B&W Nuclear Technologies (BWNT) in collaboration with the Electric Power Research Institute (EPRI). The results of these examinations have been reported previously to the staff in Reference 1.

A detailed description of the examinations and the results are documented in EPRI Report TR-103756, dated April 1994. These examinations revealed that real degradation was present in the tubes. The S/Ns were not caused by tube deposits. Small patches of pit-like intergranular attack (IGA) were present on the tubes. Burst testing showed that the pit-like IGA did not significantly lower the burst pressure of the tubes that were pulled.

Analysis of EC data showed that bobbin coil and rotating pancake coil (RPC) l inspection techniques could not reliably detect this degradation type when the depth was less than 20% through-wall. The bobbin coil was found to have a probability of detection (POD) of 80% for a 45% or deeper through-wall IGA patch. The POD for RPC was somewhat less. It was further found that the pit-like IGA could not be accurately sized by bobbin coil phase angle.

1 i

1-2 l

l l

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~

4 Evaluation of the available historical EC data for the 1992 pulled tubes indicated that the pit-like IGA was present as early as 1980. No change in EC voltage has been observed since that time. The pit-like IGA inferred to be in other tubes, was

(

determined by reviewing the historical EC data to have been dormant since at least l

1989.

1.2 Purpose of 1994 Tube Pulls Having determined the cause of the EC indications in the first span of the "B" SG, attention was turned to determining the cause of the EC indications at the 7th and 9th TSPs, the other large concentration of S/Ns in the "B" SG. FPC therefore decided to pull tubes with S/Ns at these locations in the 1994 Refuel 9 outage.

Other OTSGs also have varying numbers oflow S/N indications. In 1993, the Steam Generator Committee of the B&W Owners Group (BWOG), began development of a pro-active tube pull program. The purpose of the program was to pull tubes with similar EC indications at similar elevations within the SGs from different plants in order to determine the cause of the indications, to determine their effect on tube structural integrity, and to determine the detection and sizing capabilities of a range of NDE techniques. This program would also aid in both the early identification of any degradation that might be active in OTSGs in general, and the development of preventative measures.

Based on a comparison of the quantity and location (elevation) of EC indications within each OTSG, the BWOG SG Committee recommended pulling at least four (4) tubes with EC indications in the 7th - 10th TSP region from the Crystal River-3B and Oconee-1B OTSGs in 1994, and Oconee-3 in 1995. The Crystal River-3 tube pull was thus incorporated into the BWOG program. Based on the results of this first phase of tube pulls, a determination would be made by the SG Committee whether additional tubes needed to be pulled. EPRI technical involvement was solicited by the i

SG Committee, and the tube pull program became ajoint BWOG/EPRI collaborative program. The combined technical expertise of all five BWOG member utilities (i. e.,

l Duke Power Company, Entergy Operations, GPU Nuclear, Toledo Edison, and Florida Power Corp.), B&W Nuclear Technologies, and EPRI was thus obtained for the tube pull program.

1.3 Rationale for Selection of Tubes Pulled In May 1994, four (4) tubes were pulled from the Crystal River-3 "B" SG: 68-46,72-49, 109-71, and 136-26 (see Figure 1-5). The criteria used to select the tubes to be pulled are listed below in order of priority:

1-3

l 4

(1)

Adeouate dome heicht to null the tube.

(2)

Multiple eddy current indications on the same tube. Within acceptable i

dome height, a maximum of two EC indications per tube was found in the 7th through 9th TSP region.

i (3)

Tubes with sienificant eddy current history. Over 2/3 of the tubes had l

been previously inspected only once (1992).

(4)

Tubes with only one eddy current indication.

(5)

Tubes which contained distorted tubesheet eddy current indications in l

the lower tubesheet.

l l

Using the above criteria and the 1992 EC findings, eight (8) tubes were selected as l

candidates for pulling. From these eight candidates, four tubes were pulled based on their 1994 EC inspection results as described below.

l Tube 68-46 had a distorted tubesheet signal at the LTSF; a low S/N indication at the 7th TSP; and a low S/N indication at the 9th TSP. This tube was inspected l

previously in 1992.

Tube 72-49 had a distorted tubesheet signal at the LTSF; a low S/N indication at the 7th TSP; and a low S/N indication at the 9th TSP. This tube was inspected previously in 1992.

Tube 109-71 had a low S/N indication at the 3rd TSP; and a 35% through-wall indication at the 7th TSP. This tube was inspected previously in 1992.

Tube 136-26 had a distorted tubesheet signal at the LTSF, and a 36% through wall EC indication at the 7th TSP. This tube was inspected previously in 1985,1989,1990, and 1992.

The four tubes were sent to BWNT for examination. This report summarizes the examinations performed and their results to date. Additionally, an archived tube,41-44, from the 1992 tube pull was examined by BWNT. This tube contained low S/N indications in the first span,6"- 18" above the LTSF, that were inferred to be pit-like IGA as observed in the other tubes pulled in 1992. The results from this tube are also l

meluded in this report.

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EXAMINATION OF 1992 ARCHIVED TUBE AND 1994 PULLED TUBES l

2.1 Field Nondestructive Examinations A non-destructive examination (NDE) matrix was developed by the BWOG SG Committee for the field and laborntory inspections of the pulled tubes. This matrix was developed to compliment the BWOG SG Committee Tube Integrity Project by investigating the probability of detection and accuracy in sizing of all NDE techniques and probes that can be used in OTSG size tubes. The Tube Integrity Project is a comprehensive program to determine at what size flaws possible in OTSGs become l

structurally significant, i.e. have unacceptably low burst pressures. The project will utilize machined and laboratory grown defects. The flaws that the BWOG Tube Integrity Project will investigate are wear, OD stress corrosion cracks, OD IGA, pitting, and dings. These tube specimens will also be subjected to the same battery of NDE prior to burst testing as were the pulled tubes. Thus a comparison will be able l

to be made between the burst testing and NDE behavior of the machined and lab grown flaws to those in the field from the pulled tubes.

2.1.1 Field NDE Test Matrix l

l The pre-pull NDE matrix included extensive bobbin coil, rotating pancake coil (RPC),

rotating field eddy current (RFEC), and UT probe examinations.. The bobbin coil examinations utilized a 0.510" magnetic-bias universal long-cone, high-frequency l

(M/ULC/HF) and mid-frequency (M/UL/MF) probes; and a 0.540" high frequency l

(M/ULC/HF) and mid-frequency (M/UL/MF) probes. The sample frequencies were 600, 400, 200, and 35 kHz in the differential and absolute modes.

The RPC examinations utilized a 0.520" 3-coil, 0.080" diameter coil probe, and also a 0.115" diameter coil probe at frequencies of 300,200,100, and 10 kHz in the absolute mode.

1 The RFEC examinations utilized a 0.510" probe at frequencies of 350,200,150 and 35 kHz in the absolute mode. All data was acquired and analyzed using Zetec's Eddynet system. The RFEC analysis used BWNT's EDDY-360 software. The examination of tubes by ultrasonic testing (UT) used a system called UT-360. The inspection involved j

l sending the ultrasonic wave radially (zero degrees) in the tube wall. All RPC, RFEC, and UT was performed at 6" below to 6" above the LTSF, and at 2" above to 2" below the center of each TSP. Each bobbin coil probe was run three (3) times full-length through each tube to study signal repeatability. Due to outage time restraints, UT was not performed in the field on tube 109-71.

I l

2.2 Laboratory Nondestructive Examinations l

The purpose of the nondestructive evaluations was twofold: (1) to confirm the field NDE indications and (2) to identify any additional defect indications that were 2-1

i defect indications that were present. This was accomplished with extensive visual examination and photography, eddy current and ultrasonic inspections, radiography, and leak testing.

Results of the nondestructive evaluation were also used in l

formulating the test plan for destructive evaluation of the tube segments. Results of the nondestructive evaluations are summarized in the following discussion.

I 2.2.1 Laboratory NDE Test Matrix The post-pull NDE repeated a portion of the field ECT, but included more extensive UT than was performed in the field. The bobbin coil examinations utilized a 0.510" magnetic-bias universal long-cone, high-frequency (M/ULC/HF) probe on the four 1994 pulled tubes. The archived tube 41-44 was inspected with both the 0.510" M/ULC/HF and 0.540" M/ULC/HF probes. The test frequencies were 600,400,200, and 35 kHz in the differential and absolute modes. The RPC examinations utilized I

a 0.520" 3-coil,0.80" diameter coil probe at frequencies of 300,200,100, and 10 kHz j

in the absolute mode. The RFEC examinations utilized a 0.510" probe at frequencies of 350,200,150 and 35 kHz in the absolute mode.

i l

The examination of tubes by UT used the UT-360 system and included both zero degree and 45 degree shear wave examinations. The beam directions used in the examinations involved sending the ultrasonic waves radially (zero degrees) and l

circumferentially (45 degree circumferentially clockwise and counter-clockwise) in the tube wall.

1 Double wall radiography was also performed in the laboratory on those tube sections that had EC indications in the field.

The laboratory NDE test matrix is shown in Table 2-1.

l 2.3 NDE Test Results The pre and post-pull NDE of both the Crystal River-3 and Oconee-1 pulled tubes was l

performed as a BWOG SG Committee project. A comparison of the NDE results to the tube metallography results from both plants will be performed later as a BWOG project. A detailed comparison will be performed to determine the probability of l

detection and accuracy in sizing of each probe / technique. This project will start l

during the first quarter of 1995. Preliminary evaluations of the Crystal River-3 l

nondestructive examination data have provided the following summary results:

1.

No visual evidence of corrosion was found during the nondestructive evaluation.

l 2.

Laboratory and field EC techniques agreed in most cases, with the l

following exceptions:

2-2 1

t Eddy current distorted tubesheet signals at the lower tubesheet secondary face were not seen by EC in the laboratory, thus these signals do not appear to be connected with any tube degradation.

Several volumetric indications were found in the lower tubesheet crevice region of tubes number 68-46 and 72-49 which were not detected in the field eddy current examinations.

3.

Most defect indications that were found by EC appear to correlate both visually and radiographically with " wear" marks at the broached tube support plate " lands".

At the 7th TSP, circular or "D"-shaped wear marks were observed at the bottom edge of the lands on all four pulled tubes. Figure 2-1 is an example of this type of defect.

l At the 9th TSP, " tapered" wear marks (see Figure 2-2) were observed at the top edge of one TSP land and the bottom edge of a second, adjacent TSP land.

These marks were axial in orientation and deepest at the edge of the support plates.

l 4.

Spots of yellow deposit " nodules", as shown in Figure 2-3, were observed, most predominantly within the lower tubesheet crevice regions and first (lowermost) tube span of tubes 68-46 and 72-49. Streaks of white deposit were also observed in the upper elevations (Figure 2-4) on all four 1994 pulled tubes.

5.

No through-wall penetrations were found to be associated with any of the defect indications, as confirmed by helium leak test.

In general, for all laboratory eddy current examination techniques, the majority of the l

indications reported in the field were confirmed in the laboratory. Discrepancies in voltage and additional calls in the laboratory were the result of the effect of TSPs or tubesheet on the signals analyzed in the field.

No new or different modes of degradation were detected. Preliminary comparisons of the eddy current results and I

the findings from metallographic examination of the pulled tubes, indicate that the j

detection and sizing capabilities of the eddy current for the LTS-to-first span indications are consistent with that reported previously in Reference 1 for the pit-like IGA.

2.4 Destructive Examinations Based on the nondestructive examination results, a detailed test plan was formulated 2-3 i

for the destructive examination, as shown in the Task 2 matrix of Table 2-1. The objectives of the destructive examinations carried out were to (1) verify base tubing material properties, (2) establish the damage mechanism for any degradation identifled, (3) establish correlations between tube condition and EC signals, especially low S/N indications, (4) determine the effect of degradation on the burst strength of the tubing, and (5) determine the thickness, morphology, and chemical composition of any deposits present on the tube OD surfaces. Although not all of the analyses have been completed at the time of this report, those results that are available and that are pertinent to this submittal are summarized in the following discussion. All of the results will be presented in the final report to EPIU, scheduled for completion in 1995.

2.4.1 Defect Evaluation Destructive examinations were carried out on tube sections with defect indications and included deposit collection and chemical analysis, tube swelling to facilitate deposit collection and/or to open up small defects for sectioning, burst testing to characterize the effect of tubewall degradation on burst pressures, defect metallography and fractography, and base metal characterization.

2.4.1.1 Burst testing Burst testing was conducted to determine the effect of the observed degradation on the pressure-holding capacity of the tubes and to open up any intergranular degradation that might be present. Burst testing was performed in strict accordance with industry guidelines established by EPRI (see Reference 2) for steam generator tubes. For baseline comparisons, one defect-free section from each of the pulled tubes, including archived tube numbers 41-44, 97-91, and 106-32, was also tested.

Results are shown in Table 2-2.

During expansion of a section of tube number 68-46 from the lower tubesheet region for collecting deposits, a leak developed at ~ 6914 psi at an elevation ~ 0.6 inch below the secondary face of the tubesheet. The tube was then shimmed and the actual burst pressure per EPRI guidelines was obtained, as shown in Table 2-2. The IGA patch at which rupture occurred (see Figure 2-5) was about 0.23"in length (axial) and ~70%

i throughwall. Its location corresponded to large amplitude volumetric indications found during laboratory eddy current inspection by both bobbin and RPC. This large amplitude signal condition was not observed during field exmainations where instead a small amplitude low singal-to-noise ratio was observed. The increase in voltage observed in the laboratory exam is due, presumably, to trauma experienced by the tube during removal operations (cutting, pulling, shipping, etc.). Metallography determined the degradation to be similar to the pit-like IGA that was present in the first span and lower tubesheet region of tubes pulled in 1992, although the axial length is greater.

2-4 i

Defect-free sections of archived tubes 97-91 and 106-32 were also tested for comparison with burst pressures obtained during the previous tube pull (see Referenco 3). In both cases, the defect-free burst pressurc was less than the burst 1

pressures obtained in 1992 for sections having pit-like IGA. The reason for the discrepancy has been determined to be a result of error introduced by the higher rate of pressurization used in the 1992 tests (prior to the issuance of standardized test procedures by EPRI). The discrepancy is explained in detail in Appendix A, along with corrections applied to the previous data.

As can be seen in Table 2-2, the effect of the observed tubewall degradation on burst pressure is minimal with the exception of the IGA patch on tube number 68-46.

However, as discussed in Section 3.2, no structural margins were exceeded in any of the tubes because of the degradation present.

2.4.1.2 Defect Metallography Extensive metallography was carried out on selected tube sections to obtain dimensional information (extent and depth) and to confirm the presence or absence of degradation. Results are summarized in Table 2-3 (detailed results will be presented in the fm' al EPRI report).

For archived tube number 41-44, a total of 33 patches of pit-like IGA were found in the first span section, in a band from 5 to 19 inches above the secondary face of the lower tubesheet (Figure 2-6). Typically, these patches were ~30% throughwall and similar in size to those seen in the other tube sections removed in 1992. Burst i

occurred at a defect ~50% throughwall. The location and morphology of these defects are identical to those found in other tubes removed from Crystal River-3 in 1992.

For the pit-like IGA defects found in the lower tubesheet crevice regions on tube numbers 68-46 and 72-49, strong sulfur peaks were noted on all grain faces and on adjacent deposits by energy dispersive spectrometer / wave dispersive spectrometer (EDS/WDS) analysis. This would suggest that the corrosion mechanism is similar both to that reported previously in Reference 3, and, to that found also on tube l

number 41-44 as noted above; i.e., reduced-sulfur IGA.

l The wear marh observed at the tube support plate edges appear to be simple i

mechanical wear. No conclusive evidence of corrosion was found associated with these defects.

l 2.4.2 Deposit Analysis In general, the tube OD surfaces were covered with a thin, tenacious layer of black deposit. First span regions exhibited a " mottled" appearance, similar to the tubes pulled during in 1992. Tube support plate land contact areas were easily seen due to 2-5 i

i

the general absence of deposit at the contact area. In some cases, the flow patterns through the support plate broaches were clearly visible as the result of differences in deposit buildup and color. Deposit loading increased with elevation, reaching a maximmn of ~0.34 grams / inch (2.25 mils thick) at approximately the 6th TSP elevation and decreasing rapidly above this elevation (Figure 2-7). This pattern of deposit loading is typical for once through steam generators which reach dryout at about mid-length in the bimdle.

In the lower tubesheet crevice regions, which are relatively free of deposit, yellow deposit nodules (Figure 2-3) were observed. EDS/WDS analysis confirmed that this deposit is elemental sulfur.

In the upper elevations, white streaks of deposit were observed. Scanning electron microscope (SEM)/EDS/WDS analysis suggests that this deposit is thin, relatively fine-grained and rich in manganese and other hardness contacinants. The thin streaks are deposited on top of the magnetite deposits on the tube.

Samples of OD deposits were removed from regions of degradation and from the free span areas at several elevations for chemical analysis, for deposit loading, and for density and porosity determination. Chemical analysis of the deposits has only recently been completed and both results and evaluation discussion will be included in the final EPRI report. Preliminary resulte suggest that the deposit is primarily magnetite, which typically forms on boiling sun' aces in steam generators using all volatile treatment (AVT) water diomistiy control.

l 2.4.3 Material Properties Material properties were determined for each of the four pulled tubes and for the archived tube number 41-44. Results are tabulated in Table 2-4.

All material properties are typical of sensitized OTSG tubing; nothing unusual was noted.

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8

- $Q en

/

n g

/

a

=g

W m

}

h J

o W

a g

8 i

.t::

i

~

4 n

U>

O qe

.M Q

1 I

I l

i i

i o

f4 N

in to o

a N

O S 11RI 'SSBN>iOlH13 lVOS 1

j Figure 2-7 a

j 2-13 W

l,

.._----_.._.._.s_m.

- -__.~_ -_

--..-m.._.

..m m_~

m.__

.m.-_-.m--

~~m.

~

u

- e TABLE 2-1 CR-3 Ofte TUBE EXAAENATION TEST IIATRIK (Rottend Anguet E 1994) 1 Test Desertueen i

Taeo Sectane to to Tested i

TASM 1: NONDESTRUCTWE SCOPE.

?-_^^'

AN Wieuel ^ _

fPhell AN: _

_ _ _ _ ene taste (138 28b in one estentueen AsN Gensth.

^

Bethin ces ECT AN i

F2 45 5 45 1:845 155 F1 41 44 2

5 7

13 17 1&2 3

14 15 2

9 15 7

14 I

LTSP 2nd TSP 3rd TSP FueTSP 90sTSP LTSP LTSP FWaTOP SunTOP LTap 3rd TOP FW TOP ase TOP FWaTOP LTSP C3 SAG IIPOC SAG IWEC emm__mVI 850 tAOwl C4 89811JEEWI SSllEFtd Cd GSE EESW TWE ISf tel Georgevleust _

Y Y

T T

^^

IftPC BCT Y

Y Y

Y l= nan== Ploed ECT Y

Y Y

Y

.T_ _ _

_ Teodum Y

Y Y

lJtes ? -

Y Y

Y Idegene Laeli Tegena Y

Y Y

+

TASM 2: DESTRUCTWE SCOPE.

t.O H

^

Y W

2 1 S

T 13 17 182 3

14 18 2

9 15 7

14 2

N LTSP 2nd TSP 3rd 79P FunTSP 9etTSP LTap ist Spa FeiTSP

$8eTSP LTSP 3rd TSP FunTSP 3rd TOP FWeTSP Lisp O

Defect E*==orwi-DenmeeA am etrec SAf ftPEC aAEA2WI

'UWEAR WEAR VIEAR

' ECI ~

8881108C WWEAR

-_^r DUEAft faneel

. c~ DepoeIIe YDes.

YDES-

. Descale Y

C*

Y Y

Y" Y

C' Y

Y Y***

.Visueyssarnevenues enes, Deum.

Y S&A Dra

^ ^ ^

Y Y

Y e&A Ofs eta cfs Is&A Ofs IsosAIC

. Dernenesens et Defects Day Otv DSW D&V

. Tube Supemne C*

Y C*

. Surat Temena Y_

P Y

Y Y

. ;- ^ _ _ _ _

" Ines.

Y P

Y Y

DesesR Ceencuen Y

. Tube- -

Y Y

Y Y.Dem, Y

R&A Oft Y.Dem.

Y Y

M S&A Of5 BSA Of3 BSA OfS Y

.i esset - _

.' degNPs Y

VIIB Y

Y Y

Yt3 Y

Y Y

RDiThin Phuel Y

Y Y

"a0 "eD

'sD BD Y* = BURST TEST 724SS & 138 250 00pmNGENT ON NO CORROSION nonsstVED ON 72-40 7

'BD

'3D

'3D C* = IMfELL & DESCALE T2-4SS & 138-264 CONTINGENT ON CORROOION 081MytVED ON T2-40 7 pnesqr p moly V Inns W IIIIe DeAnd Em tourehundi' 00mslalet 80mdese2 Steek1 Stree82 Y"

SCOPE FOR 8841k14 CONT 960ENT ON NO CORROSION 085ERVED ON 72-40-13

.CeasetDessens OTHEftWISE HOLD AND RECONSIDER

. Desesse Y*** = SCOPE FOR 10H1 14 CONTW6 GENT ON IGA namERVED ON 131k28-15; OTHERWISE. HOLD & RE!CONBl

' hum

.T et geposs

- = EM BOTH ON VWHOLE 8AnsPLE APO ON GETALLOORAPHICCROG8 NECTION

-Tube Desens

.Surat Teagam Y. Dest

= SCRAPE APO ANN.YZE YELLOW DEPO 8tTS

.veaunggesreseemuel snen.

DRV

= OSTAM DEPTH AND VOLundE OF VWEAR DEFECTS

.Dessen em BRA Of5 = BEFORE APD AFTER DESCAUNG

. Tune Seceentum Y

Y Y

Y n40SAIC = FULL LENGTK SIX ANGLE PHOTO 4AOSAICS TO FULLY DOCUMENT TUBE

. SONEDSANDs

' Y(2)

= TWO META 1100RAPHIC S400PLES ASSubsED

=

. Detect ^ _ __

Y Y

Y(conto) = SEM ANALYSIS CONTINGENT ON OBSERVING CORROGION AT DEFEK:T 8-a"en Pternt

. NRD (Th i

.._.______._._..____..._.~______.____.___.____.__.______m___.__.m.,

~

1 e

i TABLE 2-1 CM4 01 SG TUBE EXAIAINATION TEST MATRIX continued 7249 6644 5646 5844 6844 8848 6848 136-26 13s-26 134-26 136-26 136 2 1&2 3

8 to 13 17 4

8 11 14 18 Deposu Anahele Y.Dep.

LTS ist Seen 3rd See 8th Soon 7m Span 9th See 1st Spen 3rd Seen 5th Seen 7m Seen 9th soon

- Swe4 & CA; Depooft h..

h v.

L1, Y

Y Y

-Elemental Anet,iKF FAAl V

Y Y

Y

- Total Carbon.^N ^.^.. Elmert Y

Y Y

Y

-Total sulhsrisCP or Turt.)

Y Y

- XRD l8ulk)

Y.Dec.

YDec.

Y Y

i. ^^_ _ _.. (Plekeel Y

Y Y

Y

- arwve(Plakeel Y

V Y

Y Y

Y a L;_ ^^ __ IMet. & F _ __ _.._,

"_.; 5 eleyspons on one setected tube 1136-261 to pronle depooft W tthicknese end weenht onewt

-Donelty & N.a.

Sample 3 _,._._ on estatted tube (136 20110 determine donelty and porcelty

- Gemme Scen

".-.. J. 2.;...;^...; thleh and lowl on metecied tute (138-281 to ^.... lootopic loading.

^

724 s esas 13s-2s too-71 41-44 w

Base Idetet Cheruriertzetion:

fit)

(TBD)

(T90)

(TBD)

C7t

- TensHe Testine Y

Y Y

- Burst Teattne Y

Y Y

2.MeteMooraphy (Duel Etch)

Y Y

Y

- M6croheroness Testing Y

Y Y

- Bulk Chemistry Y

Y Y

- Sennettretton Testina (Huey)

Y Y

Y G

. m..

-m

Table 2-2: Burst Pressure Test Results TUBE DEFECT BURST NUMBER LOCATION PRESSURE COMMENTS (psi) 68-46 LTS/1st Span 7000' Burst at IGA defect that leaked i

during swelling 7th TSP 10850 Burst initiated at wear mark 9th TSP 10700 Burst initiated at wear mark defect-free 10850 Burst in freespan 72-49 LTS/1st Span 10650 Burst initiated at small IGA patch l

2nd TSP 10650 Burst in freespan just above T!,P region 3rd TSP 10650 Burst outside 'ISP region l

l 7th TSP 10550 Rupture passes through wear mark, but did not initiate at it 10th TSP 10550 Burst outside TSP region (defect-free) l 109-71 defect-free 11100 Burst in freespan 136-26 defect-free 10750 Burst in freespan 41-44 LTS/1st Span 9800 Burst initiated at small IGA patch defect-free 10100 Burst in freespan 2

97-91 defect-free 10450 Berst in freespan 2

106-32 defect-free 11250 Burst in freespan NOTES:

l 1.

The burst pressure reported in the table for tube number 68-46-3A has been adjusted for the presence of the brass shim.

2.

Tube pulled in 1992.

2-16 l

Table 2-3: Field NDE Results vs Destructive Examination Results Tube Number location Defect Field Bobbin Defect Dimensions,10 inches (Row / Column) inches Identification Call Volts Depth (%TW)

Axial length Width Volume (in')

(%TW) l 138(10)*

68-46 LTSF - 0.60 pit.like IGA NDD (70%)

l l

228 89 7th TSP - 0.56 "D"-shaped 1.36(27 %)

12 (30 %)

90 119 68(10)*

wear 9th TSP + 0.81 Tapered wear 0.65(S/N) 7.0 (22%)

425 141 157(10)*

9th TSP - 0.58 Tapered wear 0.38(S/N) 4.9 (15.2%)

515 148 135(10)*

l l

l 72-49 Beh>w LTSF pit.like IGA NDD 10 (29.4 % )

41 29 3(10)*

7th TSP - 0.69 Oval wear 0.50(39 % )

6 (17.6%)

94 134 35(10)*

9th TSP + 0.82 Tapered wear 0.49(S/N) 3.8 (11.3%)

640 134 62(10)*

9th TSP -

Tapered wear NDD 812 145 s

109-71 3rd TSP - 0.67 "D"-shaped 0.17 (S/N) 5 (14.7%)

86 97 17.l(10)*

wear 7th 'ISP - 0.68 Circular wear 0.17(40 %)

12 (35.9 % )

112 101 66(10)*

136-26 LTSF None LC1 @ LTS j

3rd TSP None NDD 7th TSP - 0.70 "D*-shaped 1.29(31 % )

3 (8.9%)

112 170 68(10)*

wear 2-17

~

Table 2-4: Materials Properties Summary PROPERTY TUBE IDENTIFICATION 68-46 72-49 109-71 136-26 41-44 Yield Strength, ksi 49.5 46.4 49.5 45.9 42.3 Ultimate Tensile Strength, ksi 102.6 100.2 102.5 102.9 96.5 Reduction in Area, %

24.9 24.1 24.9 26.8 22.4 Burst Strength, psi 10,850 10,550 11,100 10,750 10,100 Microhardness ID 186.7 189.2 194.2 188.2 176.9 HV Midwall 175.8 170.2 181.6 188.5 168.1 OD 184.3 187.8 198.3 182.3 177.8 Grain Size 7.8 7.6 8.0 6.7 6.4 Carbide Distribution Sensitization Test (Modified 3289 6012 992 1199 2028 Huey), rng/dm / day 2

a Composition, %

C 0.047 0.034 0.041 0.033 0.035 S

< 0.001 0.003

< 0.001 0.003 0.002 P

0.014 0.012 0.008 0.008 0.013 Fe 7.11 7.37 6.94 7.26 6.90 Cr 14.09 15.29 15.15 15.06 14.66 Mn 0.29 0.31 0.32 0.30 0.31 Co

< 0.05 0.052 0.050

<0.05

<0.05 l

Cu

<0.05

<0.05 0.054

<0.05

(

l Si 0.37 0.28 0.33 0.28 0.34 Al 0.067 0.11 0.21 0.11 0.12 Ti 0.13 0.18 0.21 0.16 0.21

- Carbides are predominately intergranular, with apparent decoration on the grain l

boundanes.

- - Huey test samples disintegrated prior to completion of the full 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of testing l

2-18 r

o Section 3 DISCUSSION OF RESULTS 3.1 Observed Tubewall Degradation Tube degradation that occurred in the Crystal IUver-3 "B" steam generator, as evidenced by the sections of removed tubing, can be placed into two categories:

1.

Intergranular degradation that occurred in the lower tubesheet crevice and first tube span, and l

2.

Mechanical wear at the contact points between the tube and tube support plate lands.

No other forms of degradation were found in either this examination or in the examination of archived tube sections removed in 1992. No degradation was found at locations where distorted tubesheet signals were observed in the field by EC testing. Preliminary conclusions regarding these two types of defects are discussed below.

3.1.1 Inter 3mnule.r * +

udation The intergranular degradation found within the lower tubesheet crevice region of i

l tubes 68-46 and 72-49 was located within the first 2 inches below the LTSF for tube l

68-46; and within the first 5 inches below the LTSF for tube 72-49. Four (4) spots of IGA were found in the free span of tube number 72-49. Metallography confirmed the degradation on 68-46 at which burst occurred to be intergranular in nature and EDS/WDS detected a sulfur-rich corrosion film on the grain facets. Preliminary l

results from the Scanning Auger Microscopy /X-Ray Photoelection Spectroscopy (SAM /XFS) analysis of the corrosion film indicate that the IGA fracture surface is covered with a duplex film (Reference 6). The outer layer is nickel oxide. After one micron of sputtering, sulfur is found, probably as nickel sulfide.

l In the previous examination of tubes removed from Crystal River-3, similar spots of IGA were seen to occur in a region extending from ~6 inches below to 18 inches above the secondary face of the lower tubesheet. It was concluded in Reference 3 that the observed corrosion was likely caused by reduced sulfur species while at low temperatures (<170aF) sometime during the period from startup in 1977 to early 1980. The source of sulfur was postulated to be either chronic leakage of cation resin from the condensate polishers or a significant intrusion of sulfur contaminant. It was further postulated that propagation (of the IGA) ceased when conditions were no longer favorable to corrosion. A review of prior eddy current data for the 1992 pulled tubes was consistent with this hypothesis, suggesting that the IGA initiated as early 3-1

)

as 1980 and is currently dormant or at least growing very slowly.

j For the present case, it is postulated that the corrosion mechanism is the same as postulated in Reference 3; i.e., reduced sulfur IGA. This conclusion is based on the l

following observations:

j 1.

The defects are intergranular in nature and conf ~med to the same regions of the tube as reported in Reference 3; i.e.,6 inches below to 18 inches above the lower tubesheet secondary face. Inasmuch as the tubes are not expanded into the tubesheet, a path for contaminant ingress into the crevice exists.

J 2.

Sulfur is present within the corrosion film present on the grain facets, probably as nickel sulfide. It has been well established that OTSG tubing is susceptible to intergranular attack in acidic solutions containing reduced sulfur oxyanions (Reference 4). Further, sensitized Alloy 600 tubing is far less susceptible to intergranular stress corrosion cracking in caustic environments than is mill annealed Alloy 600 (Reference 5).

Additional evidence that caustic-forming species are not involved in the tubesheet crevice region corrosion is the limited depth within the tubesheet crevice that IGA was found. Experience with unexpanded tubesheet crevices in recirculating steam generators (RSGs) has shown that a concentrated caustic solution can exist throughout the whole crevice region and lead to intergranular corrosion deep within the crevice. Further, the OTSG lower tubesheet is subjected to primary system cold leg temperatures, whereas, most caustic-induced IGA has occurred in RSG hot legs.

3.

Preliminary corrosion film data from the analysis being performed at Rockwell International (Reference 6) indicates the presence of a duplex corrosion film on IGA grain facets, with sulfur incorporated in the inner film. This suggests that the environment responsible for the initial wttack may no longer be present; i.e., the reduced sulfur species have

' 2en depleted and the corrosion process has stopped.

The elemental sulfur deposits observed in the first tube span and within the lower tubesheet crevices may or may not be associated with the intergranular defects.

Elemental sulfur is not in the right oxidation state to initiate IGA; although changing environmental conditions during startup, shutdown, and layup could create conditions which could make the sulfur aggressive. Since there is not a direct correlation of the IGA patches with the spots of yellow deposit, it is concluded that the yellow sulfur deposits do not pose a significant corrosion risk.

3-2

3.1.2 7'ube-to-TSP Wear Defects There were two types of defects observed at the tube-to-TSP land contacts: at the 7th TSP and 3rd TSP, oval or "D" shaped wear marks were found at the lower edge of a tube support land; at the 9th TSP, tapered wear marks were found at both the upper and lower edges of the support plates. Tapered wear has been observed in i

tubes pulled previously from other OTSGs (Reference 7). The oval or "D" shaped wear was not observed in previously pulled OTSG tubes, but has been observed in recirculating steam generators as described in Appendix B.

No conclusive evidence of corrosion was found in the wear marks. Therefore, it is concluded that the degradation was the result of mechanical wear from the tube 4

rubbing against the tube support plate land, or against oxides or other debris wedged between the tube and TSP land (abrasive wear). Appendix B includes a description j

of wear observed in nuclear steam generators and a discussion ofindustry experience with the detection of wear.

Based on the observation that these defects were present as early as 1985 at the 7th TSP for tube 136-26, it is concluded that their rate of growth is minimal, and that this j

mode of degradation is both easily monitored and managed. Previous review of 607 wear indications (Reference 8) also concluded that wear growth is slow in OTSGs. As a

demonstrated, the effect of the wear defects on burst pressure is minimal.

The previously performed growth rate study for all indications in both OTSGs at Crystal River-3 will be updated. This study will be performed in 1995 and will i

determine growth rate for indications present at the freespan and each tubesheet or TSP for each steam generator in order to determine if growth rates differ by elevation, and/or by steam generator.

i 3.2 Structural Integrity Implications 3.2.1 Pit-like IGA In a previous submittal to the NRC (see Reference 1), the structural margins specified i

in Regulatory Guide 1.121 were shown to be met for 100% through wall axial cracks equal to or less than 0.25 inch in length; 100% through wall circumferential cracks equal to or less than 122 in total circumferential extent were also shown to meet the required structural margins. A total of nine burst tests (see Tables 3-1 and 3-2) are now available on pulled tubes from Crystal River-3. These burst tests indicate that expected structural margins are conservative as discussed below.

Table 3-1 lists burst tests results on undegraded sections of five pulled tubes from Crystal River-3. This burst test data establishes baseline, undegraded burst pressures.

Calculated undegraded burst pressures from yield and ultimate strength values agree 3-3

i well with actual measurements.

i Burst pressures of 1992 and 1994 pulled tube sections with pit-like IGA are listed in Table 3-2. The burst modes of these tube sections were axial. Hence these burst test results reflect the ability of tubes with IGA degradation to meet the required burst strength margin of 3 times the normal operation pressure differential, i.e. 4050 psi.

The lowest measured burst pressure is 7000 psi for tube section 68-4G 3 with a IGA patch 0.6 inch below the LTSF. By comparison, for a tube with lower bound tensile properties (95% probability,95% confidence), the corresponding burst pressure would be 5848 psi. This conservative value is also well above the required value of 4050 psi.

As illustrated in Table 3-2, there are a number of approaches which may be followed in calculating the burst pressure of tubes with local regions of IGA. One extreme bounding model rocld be to assume uniform thinning around the circumference of the tube and apply the burst equation of NUREG/CR-0718 (Reference 9). The axial burst mode suggests the use of partial through wall axial crack models. Several have been applied. These include the Framatome equation (Reference 10) and two similar models (References 11,12) where the burst pressure is a linear function of depth of l

degradation between the undegraded burst pressure and that of a through wall crack.

These are designated the PNL Slot equation and the Begley-Houtman-Keating, BHK, equation.

Figure 3-1 illustrates a comparison of burst pressure predictions from these equations for a degradation length of 0.25 inches. The degradation depth is expressed as a fraction of the tube wall thickness. For conservatism, lower 95/95 tensile properties are assumed. At shallow degradation depths, burst pressure predictions are very similar. At large depths of degradation, the uniform thinning model must extrapolate to zero burst pressure at through wall penetration. The partial through wall axial crack models extrapolate to the through wall crack burst pressure limit.

The best experimental burst pressure determination for through wall axial cracks in steam generator tubes has been performed by Hernalsteen (Reference 13). Very high flow capacity tests eliminated the need for sealing bladders of any description and settled the question of the effect of sealing systems on burst pressure measurements.

l The BHK model extrapolates to a through wall limit below the Hernalsteen value as does the PNL Slot equation and hence are conservative in the limit of a through wall crack. Figure 3-1 demonstrates that there is margin beyond the 3AP requirement for a 0.25 inch long,100% through wall crack.

The burst pressure for tube section 68-46-3 with a 0.25 inch long region of degradation (the actual degradation length is 0.228 inch, but was rounded up to 0.25 inch for this discussion) is also plotted on Figure 3-1.

For conservatism, the measured burst pressure was reduced to match the assumption of lower limit tensile properties.

j When burst strength is computed on the basis of the maximum depth of degradation l

3-4 i

I i.

J (70%), the measured burst pressure lies above predictions from all models, but is closest to the BHK model. The same statement is true for all of the test results in Table 3-2. Pulled tube burst test results are consistent with expectations of structural evaluations and behave in a consistent, predictable fashion.

The degradation present in tube 68-46 is consistent with the range of morphologies observed to date at Crystal River-3 which have been dispositioned with a combination bobbin voltage and RPC sizing criteria. The mode of degradation is considered to be static as supported by evaluation of past NDE records. The degradation evident in i

tube 68-46 just below the top of the LTS was not detected during field inspection.

This is consistent with other industry experience with this damage mechanism.

l There is a small chance that degradation on the order of that experienced by tube 68-l 46 may not be detected by NDE in other tubes. The demonstrated margin of tube 68-46 with respect to structural requirements and the static nature of the degradation show that this possible circumstance does not pose a threat to structural margins.

l 3.2.2 Wear Table 3-3 shows the burst testing results from four tube sections containing wear i

degradation. The burst pressures of the degraded tube sections are compared to the l

burst pressures for undegraded sections of the same tubes using data from Table 3-1.

As can be seen from Table 3-3, the wear scars had practically no detrimental effect on the tube burst pressure. The wear observed on the pulled tubes is therefore concluded to also pose no threat to the structural margins.

3.3 Leakage Integrity Implications Helium leak testing was performed on eight (8) sections of the 1994 pulled tubes and the 1992 archived tube that contained eddy current indications as shown in Table 2-1.

No leaks were found in the 8 sections that were tested. In a previous submittal (Reference 1), it was shown that the minimum tube wall thickness required to avoid developing a leak during a main steam line break (MSLB) accident was 8% of the tube wall. A defect with a depth of 92% through wall would thus not leak at a tube differential pressure of 2250 psi imposed during a MSLB.

The minimum wall i

thickness for a higher tube loading of 2600 psi was also calculated in Reference 1.

The maximum defect depth that would not leak at 2600 psi was calculated to be 87%

through wall. The deepest defect in the 1994 pulled tubes was ~70% through wall.

Therefore, previous laakage considerations concerning the pit-like IGA are presently still valid, and the 1994 S/N plugging criteria has been effective in not leaving

)

potential leaking tubes in service.

1 l

3-5 l

1 i

3.4 NDE Field Detection Capabilities In comparing the 1992 and 1994 EC field data for the four 1994 pulled tubes, it was found that the probability of detection (POD) for the intergranular degradation was i

consistent with that reported in Reference 1 for the 1992 pulled tubes. The small differences between the data is accounted for by the fact that the 1994 data was taken with new probes which resulted in ' cleaner' signals.

NDE detection and sizirc performance on the Crystal River-3 pulled tubes is a BWOG SG Committee project. cobbin 0.510" MF and HF, and 0.540" MF and HF probes; 0.080" and 0.115" RPC probes; RFEC; and UT were all utilized in the field inspection of the pulled tubes. This data will be integrated into the BWOG Tube Integrity Project to provide POD and sizing accuracy of the various NDE techniques for different defects: field, laboratory grown, and machined.

The next phase of this BWOG task will compare all of the field NDE for pulled tubes to the metallurgical results to determine the POD and sizing accuracy (% through wall, length, width) for each probe type / technique utilized in the field inspections.

Scatter plots for IGA and wear will be utilized to show length and width as called in the field vs. laboratory metallurgical results, and % through wall where appropriate, for each inspection technique used. The Oconee Unit 1 pulled tubes will be included in this task at a later date. This BWOG task will be performed in 1995.

)

Table 3-L Undegraded Burst Pressure J

TUBE YIELD ULTIMATE MEASURED CALCULATED STRENGTH STRENGTH BURST BURST (psi)

(psi)

PRESSURE PRESSURE (psi)

(psi)

~

68-46 49500 102600 10,850 10500 72-49 46400 100200 10,550 10120 109-71 49500 102500 11,100 10493 i

136-26 45900 102900 10,750 10272 41-44*

42300 101000 10,100 9582 97-91*

TBD TBD 10,450 TBD 106-32*

TBD TBD 11,250 TBD

Tube pulled in 1992.

TBD = To Be Determined 1

l 3-6

Table 3-2.

Burst Pressure of Tubes with IGA Degradation TUBE DEGRADATION MAXIMUM MEASURED CALCULATED CALCULATED CALCULATED CALCULATED SECTION LENGTH DEGRADATION BURST BURST BURST PRESSURE BURST PRESSURE BURST (inches)

DEPTH PRESSURE PRESSURE (psi) -

(psi)

PRESSURE

( % TW)

(psi)

(BHK EQUATION)

(UNIFORM (psi)

(FRAMATOME THINNESS (PNL SLOT g

EQUATION)

EQUATION) t 41-44-2 0.030 50 9300 8593 9570 9532 9370 68-46-3 0.250' 70 7000 4853 6714 6132 6(M9 2

97-91-2' O.075 54 10300 7540 9301 9245 8907 2

106-32-2' O.060 40 10900 8546 9696 9767 9435 p

NOTES:

1. Tube pulled in 1992.

2.1992 burst pressure adjusted per discussion in Appendix A.

3. Actual length is 0.228 inch. Rounded up to 0.250 inch for these calculations.

3-7

Table 3-3. Burst Pressure Of Tubes with Wear Degradation TUBE SECTION MAXIMUM MEASURED

% OF DEGRADATION-BURST UNDEGRADED DEPTH (%TW)

PRESSURE (PSI)

BURST PRESSURE 68-46-(7th TSP) 30 %

10,850 100 %

68-46-(9th TSP) 22 %

10,700 99 %

72-49-(3rd TSP)

No Wall Loss 10,650 101%

Obsented 72-49-(7th TSP) 18 %

10,550 100 %

NOTE:

Maximum degradation depth reported is as determined by destructive.

examination. Undegraded burst pressure for tubes are shown in Table 3-1.

f i

3-8 i

l

i.

I CALCULATED BURST PRESSURE VERSUS RELATIVE f

DEGRADATION DEPfH FOR A CRACK LENGTH OF 0.25 INCH 9000 8000 UNIFORM THINNING Degradatwn on Tube 68-46-3 modelled as a crack assundng l

lower 95/95 tensileproperties 7000 --

1 l

BHK PARTIAL WALL I

AXtAL CRACK Y

E

~~

O HERNALSTEEN 3

THROUGH WALL

=

Y g

PNL SLOT l

A 5000 --

g i

ocmao

4000 --

(4050 PSI)

REQUIRED STRUCTURAL MARGIN i

a 3 sigmoe ft S

l l

}De-l o

5 l

jOd-t 2

b 02-l l

l 00

(

0 20 40 60 80 00 Metallographic depth, %

(a) Detection scatter plot for wear showing reliable detection at 20% through-wall.

co N l' m--

Y = 0 04 ' X + 31 R = 0 97 S0

3 96 N s $1 data poorts

.. f 9

'A e

ge gb v'

E 1

1 po 1-b

=

l20

.pE

+

x E

.=-: s l

\\

w

., a 0

0 E

N m

m 2

Wtallographic depth, % through-wall (b) Depth sizing accuracy for regular-shaped wear scars.

Figure 4. Eddy current bobbin coil detection and sizing performance for wear.

B9

l~

,e O

l lb C anntit

.trT retcytwC T e 6 M*. s ! 3DC l

Cu ? IOC CDL: lie PLR7C: TSP !!

l er 3 @ re t t.31 l

vtF73CRL INDirT @ r 25 L115 rLLL LCRLE 728.D v 1

'I gM oc

Cf LCC L2t$ P*Et its KG

., oc p....., u,

r vse-i.s i=Cw 3.c3cRT20 o tenca L!su

.A

, i.

l is.e votts a

s

] Qy'

,<t h>g g; '$%., g..., g

-y t-]

l

~

ses ii l

. e.

re t

ise at3% LEET *-3tC4E ga M C-KGREE5 t

,o. o re a

I l

l (a) Rotating probe data showing wear scar at one of the broached i

support plate land contact areas.

l l

m Y = 0 97 'X 014

...,..m

.,e "8

8. is e.t. pooe.

, c..

f

., o.

c a

1 5m

/ :r l

g l

g A

o o

a e

e I

True degh, % tryough-wd (b) Depth sizing accuracy.

l Scatter plot with least-squares fit to data.

Figure 5.~ OTSG broached wear scar sizing accuracy using pancake coil signal amplitude.

l B-10 I

i

ML20080B555

Text

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