ML20206B204

Metallurgical Evaluation of an 18-INCH Feedwater Line Failure at the Surry Unit 2 Power Station

ML20206B204
Person / Time
Site:	Surry
Issue date:	03/31/1987
From:	Czajkowski C BROOKHAVEN NATIONAL LABORATORY
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II), Office of Nuclear Reactor Regulation
References
CON-FIN-A-3851 BNL-NUREG-52057, NUREG-CR-4868, NUDOCS 8704090019
Download: ML20206B204 (43)

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NUREG/CR-4868 BNL-NUREG-52057 i

l l Metallurgical Evaluation of an l18-Inch Feedwater Line Failure l

'at the Surry Unit 2 Power Station I Prepared by C. J. Czajkowski I Brookhaven Nat' anal Labort tory l

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Prcpered for U.S. Nuclear Regulatory Commission l

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NOTICE This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability of re-sponsibility for any third party's use, or the results of such use, of any information, apparatus, i product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights.

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NUREG/CR-4868 BNL-NUREG-52057 Metallurgical Evaluation of an i 18-Inch Feedwater Line Failure at the Surry Unit 2 Power Station Manuscript Completed: February 1987 D:ta Published: March 1987 Prgpired by C. J. Czajkowski Brookhaven National Laboratory Upton, NY 11973 i Pr:p: red for 4

R:ginn il l

U.S. Nuclear Regulatory Commission 101 Marietta Street

Atl:nta, GA 30303 cnd 1

Division of PWR Licensing A Offico of Nuclear Reactor Regulation

( U.S. Nuclear Regulatory Commission W:shington, DC 20666

' NRC FIN A3861 I

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ABSTRACT A metallurgical failure analysis was performed on pieces from a i catastrophically f ailed 18-inch diameter feedwater line from the Surry Unit 2 Muclear Power Station. The analysis consisted of optical microscopy, chemical j analysis, mechanical and Charpy impact testing and evaluation of the material by scanning electron nicroscopy. The mechanical tests indicate that the materials of construction met the appropriate specified requirements. The failed elbow had been globally thinned on the inside surface and had a scalloped appearance. The elbow material had been reduced in some areas to below .040 inch (1.02 mm) from an installed thickness of 0.500 inch (12.7 mm). Fraccography disclosed a dimpled ruptured (ductile) appearance on all fracture faces and no evidence of cold work on the pipe's inside surface. The j conclusion of the investigation is that the Sorry failure occurred due to the 4

overall thinning of the pipe (below the design requirements) by a erosion-corrosion mechanism.

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' TABLE OF CONTENTS E*K*.

Abstract.......................................................... iii List of Figures................................................... Vi I List of Tah1es.................................................... ix j 1.0 Introduction................................................. 1 i

2.0 Visual / Photography........................................... 2 l

} 3.0 optical Microscopy / Meta 11ography............................. 2 i 4.0 Chemical Analysis / Impact Testing / Bend Testing j

! Hardness Testing / Tensile Testing............................. 3  :

l 4.1 Chemical Analysis....................................... 3 4.2 Impact Testing.......................................... 3 4

i 4.3 Be n d Te s t i n g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1 1 l 4.4 liardness Testing........................................ 4 4.5 Tensile Testing......................................... 4

5.0 Scanning Electron Microscopy /Engergy Dispernive Spectroscopy. 5 i

j 5.1 Scanning Ecletron Hieroscopy............................ 5 i

! 5.2 Energy Dispersive Sepctroscopy.......................... 6 1

4 6.0 Dincunnion/ Conclusions....................................... 7 l

7.0 Acknowledgements............................................. 8 8.0 Referencen................................................... 9 L

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l LIST OF FIGURES Page Figure 1 Photograph of inside surface of IA-3...................... 10 Figure la Photograph of outside surface of IA-3..................... 10 Figure 2 Photograph of inside surface of 1A-4...................... 11 l

Figure 2a Photograph of outside surface of 1A-4..................... 11 Figure 3 Photograph of specimens 4A-1 and 4A-2..................... 12 Figure 4 Wear pattern on 4A-1 and 4A-2............................. 13 Figure 5 Metallurgical cross section of 1A......................... 14 Figure 6 Pipe microstructure....................................... 15 Figure 6a Elbow microstructure...................................... 15 Figure 6b HAZ microstructure........................................ 15 Figure 6e Weld microstructure....................................... 15 Figure 7 Photomicrograph of worn area of IA-4...................... 16 l Figure 8 Macrophotograph of inside surface of e1how................ 17 Figure 9 SEM photograph of elbow impact specimen................... 18 Figure 10 Fractograph of pipe impact specimen....................... 18 Figure !! phot oin t e rog ra ph o f inclus ion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 12 SEM nhoto of specimen IA-3................................ 19 Figure 11 Dimpled rupture surface of IA-4........................... 19 Figure 14 liighe r magni ficat ion SEH photo of duct ile area. . . . . . . . . . . . 19 Figure 15 FaAA layout of Surry p1pc................................. 20 Figure 15a FaAA photograph of failuru................................ to Figurn 16 Fracture surfaen of 2A-20................................. 20 Figuro 164 liigher magniftration SEH photo of 2A-20................... 20 l

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LIST OF FIGURES (CONT'D)

Page Figure 17 SEM photo of area 2A-2A-C................................. 21 Figure 17a Higher magnification SEM, photo of 2A-2A-C................. 21 Figure 18 Low magnification fractograph of 2A-2A-A.................. 21 Figure 18a Higher magnification photo of 2A-2A-A..................... 21 Figure 19 Duc t ile t ea ring in a rea I A-9A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 19a Higher magnification photo of 1A-9A....................... 22 Figure 20 Fractograph of 2A-2A-C.................................... 22 Figure 20a Possibic area of initiation in 2A-2A-C.................... 22 Figure 20b Higher magnification photo of 2A-2A-C..................... 23 Figure 20c Possible linear tearing in 2A-2A-C........................ 23 Figure 21 Inside surface of e1 bow................................... 24 Figure 22 Inside surface of pipe.................................... 25 Figure 23 Elbow material after deoxidation.......................... 26 Figure 24 Pipe material after deoxidation........................... 26 Figure 25 1A-4 " worn" area insido surface........................... 26 i Figure 26 SEM photo of polished surface............................. 27

Figure 27 Co r r od e d a re a a n c 1 bow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 27a EDS nean of aren.......................................... 28 Figure 28 SEM photo of inclusion.................................... 28 Figuro 28a EDS nean (FaAA) of inclusion.............................. 28 vit

LIST OF TABLES l

' fagg Table 1 Chemical Analysis of Surry Materials......................... 29 j Table 2 Results of Surry Impact Testing.............................. 30

! Tcble 3 Knoop Hardness Values for Surry Materials.................... 31 i

Tcble 4 Tensile Test Results......................................... 32 i

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1.0 INTRODUCTION

In December 1986, an 18-inch suction line to the main feedwater pump A for the Surry Unit 2 power plant f ailed in a catastrophic manner. Four of the cight men working nearby on another pipe were killed during the event.

The condensate feedwater system flows from a 24-inch header to two 18-inch suction lines each of which supplies one of two feedwater pumps. The line temperature at this location is approximately 370'F (188'C), with a pressure of approximately 370 psig and a maximum flow rate of 5 million Ih./hr. The fluid in the pipe at this point is considered to be liquid phase j with no vapor present.

I A preliminary description of the incident was documented by the U.S.

Nuclear Regulatory Commission (USNRC) in SSINS No. 6835, Information Notice 86-106, dated December 16, 1986, entitled "Feedwater Line Break."

j Additional information about the incident derived either from the Information Notice or in discussion with utility personnel follows:

1. The pipe material is ASTM A-106 Grade B carbon steel. The pipe is 1 18-inch (46cm) diameter with a nominal wall thickness of 0.500 inches (1.27cm).

l 2. The elbow material is ASTM A-234 Grade WPB carbon steel, also with a nominal wall thickness of 0.500 inches (1.27cm).

] 3. Localized areas measured on the elbow were thinned to as low as .046 inch (1.17mm).

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4. The flow velocity of the header was 12 fps (3.05 m/s) while the pipe wan 17 fps (4.32 m/s).

Both ruptures in the elbow were

) 5. The elbow developed two ruptures.

j separated by four inches and approximately two inches from the weld.

l As a result of this incident, the USNRC, Office of Nuclear Reactor

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gulation (ONRR) PWR-A and USNRC, Region II office (Atlanta, CA) initiated an independent failure analysis of some nections of the failed elbow adjacentpipe 4 ct Brookhaven National Laboratory (BNL). The analysis was to encompass an l

evaluation of the failure mechantam and a confirmation of the pipe-c1how-weld mechanical, chemical and impact properties. The test methods utilized in this enslysis were I a. Visual / Photography

b. Optical Microscopy /Mota11ography

c. Chemical Analysin/ Impact Testing / Bend Testing / Hardness Testing /Tonsile Testing

d. Scanning Electron Microscopy (SEM)/ Energy Dispersive Spectroscopy (EDS)

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2.0 VISUAL / PHOTOGRAPHY A total of five specimens from the failure were evaluated at BNL.

Additionally, one replica of the inside surface of the elbow (casting made by Failure Analysis Associates [FaAA}) was visually examined. Note: FaAA was employed by Virginia Electric Power Co. to evaluate the failure for the utility.

The first specimen evaluated was identified as piece 1A (no photograph),

and was picked up at FaAA by BNL personnel on December 30, 1986. This specimen had material from the pipe, elbow and weld. From this specimen, the chemical analysis samples and an optical mount were cut, with the balance of the material being used for mechanical testing.

On January 5, 1987, two additional samples were received at BNL. They were identified as samples IA-3 and 1A-4 (Figures 1, la, 2 and 2a). Both sections had a mottled and granular appearance on the inside surface. The inside surfaces also had two distinct types of oxide present, a blackish, tight adherent film (magnetite) and a rust colored, powdery oxide (similar to hematite in appearance). A deep gouge (or " worn" area) was noted on IA-4 and subsequently sectioned for optical and SEM evaluations. These specimens were both sectioned for mechanical testing and SEM evaluation. l

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On January 9,1987, pieces of the joint between the header and the f abricated " tee" joint were received at BNL. These had been mechanically ground and then macroetched (10% Nital) by FaAA prior to shipping to BNL. The i

specimens were identified as pieces 4A-1 and 4A-2 (Figure 3). These samples l are the two sections which were taken from one large section. When the two l pieces were put in close juxtaposition to one another, a definite wear pattern was seen on the inside surfaces (Figure 4). The inside surfaces of these specimens were similar in appearance to those of the previously discussed specimens. These two specimens were photographed and then lef t intact for shipment back to FaAA.

Visual examination of the fracture surfaces on the specimens disclosed no gross indications of fatigue (beach marks, ratchetting, etc.).

3.0 OPTICAL MICROSCOPY /METALLOCRAPHY A section of specimen I A was removed for metallurgical mounting, grinding The specimen was etched in a 10% Nital solution and then 1

and polishing.

examined. Figure 'i is a macrophotograph of the mounted cross section of theweldment. The weld appeared to be multipans, shielded metal are weld (not verified by utility), welded from one side only. We outline of the weld bent affected zone (HAZ) is clearly defined, as well as the rough, scalloped inside Hurface of both the pipe and the elbow. The elbow side appears to have been thinned to o greater extent than the pipe side of the weldment.

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Higher magnification photomicrographs (Figures 6-6d) of both base metals, the weld HAZ and the weld metal snow that the microstructures were all consistent with that of a welded low carbon steel.

A metallurgical cross section was also made of the worn area of specimen IA-4. This cross section (Figure 7) depicts the extent of thinning seen by the elbow. The thinnest section of the mount measured approximately .015 inch (0.38mm).

The inside surface of the elbow was examined at higher magnification.

Figure 8 is a close-up macrophotograph of the inside surface of the elbow.

The black, glossy impressions appear to be a tight, adherent magnetite film, while the greyish oxide (visually seen as a rust color) appears to be areas of cctive oxidation on the elbow. The scalloped shape of the inside surf ace is typical of an erosion type mechanism.

4.0 CHEMICAL ANALYSIS / IMPACT TESTING / BEND TESTING / HARDNESS TESTING / TENSILE TESTING 4.1 Chemical Analysis A chemical analysis was performed on the piping material (A106 Grade B), the elbow material (A234 Grade WPB) and the weld metal deposit (assumed to ba E7018). Table I is a comparison of the chemical analysis results versus that required by their specifications. In each inatance, the obtained result fell within the requirements of the quoted specification. Note:

v nadium was not analyzed in the weld metal sample, but the chenical requirement for E7018 is established only to verify that the metal electrode is composed of a carbon steel.

4.2 Impact Testing A total of eighteen subsized impact specimens were machined. Six cach were machined from the piping material, the cibow material, and the specimens with the notch in the center of the weld. All of the subsized specimens were machined in accordance with the dimensions of ASTM E23

" Standard Methods for Notched Bar Impact Testing of Metallic Materials."

Three of each group of six specimens vere tested at room temperature (70*F/21'C) and three at 375'F (190.6*C), the estimated temperature at which the failure occurred. After impact testing the fracture faces were examined under the SEM to verify the morphology of the failure.

Table 2 is a tabulation of the results from the eighteen specimens tested. The piping material had average values of absorbed energy of 26 ft.-lb. at(70'F/21'C) and 34 ft.-lb. at 375'F/190*C. The weld metal averaged 19 ft.-lbs at 70'F/21'c and 21.5 ft.-lbs. at 375'F/190'C. The elbow material averaged 13.3 ft.-lbs. at 70*F/21'c and 13.25 ft.-Ibs. at 375*F/190'C. No cttempt was made to determine the nil ductility transition temperature (NDTT) for the various materials. It appears, however, that the cibow material was in the " upper shelf" range for all six specimens. (The upper shelf is a region of relatively constant toughness which occurs after the NDTT has been curpassed).

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Figures 9-10 are low magnification fractographs of the number 5 specimens (elbow, pipe) at 375"F/190*C (see Table 2). It was observed that each of the specimens exhibited a dimpled ruptured appearance, which indicates a ductile failure mode. The two photographs are typical.

4.3 Bend Testing Two face bend specimens were machined from specimen I A and subjected to a bending moment similar to that depicted in Part OW-466.1 of Section IX of the ASME Boiler and Pressure Vessel Code. With the exception of one small tear

(<.030 inch /.76 mm), all of the weld /HAZ/ base metal welds showed no cracks or defects after bending. Figure 11 is a photomicrograph of the small tear that appeared to have occurred at an inclusion in the weld.

4.4 Hardness Testing Knoop (microhardness) hardness measurements were performed on the cross section removed fron specimen IA. They are recorded in Table 3. All of the values recorded are consistent with those expected of the materials.

Converting the average values obtained to tensile values, produced the following results:

Tensile strength (approx. Ksi)

Pipe 68.5 IIAZ (pipe side) 75.0 Weld 85.0 HAZ (elbow side) 77.0 l Elbow 73.5 All of which would be normal for these materials.

4.5 Tensile Testing A total of six subsized tensile specimens were machined in accordance with ASTM A-370, " Standard Methods and Definitions for Mechanical Testing of Steel Products." Two specimens each were machined from the elbow, piping, and weld material (with veld in center of specimen). No t e : due to a machining error, only one tensile specimen was cut from the pipe section.

The results of the five tensile tests are listed in Table 4. It is evident f rom the Table that both the tensile and yield strengths for the elbow j and pipe material exceed the minimum, requirements of the referenced i standards. The values of total elongation in two instances (1 pipe, 1 elbow) fall slightly below the required minimum but this difference is considered negligible due to the use of the subsized specimens for the testing. The %

reduction in area values and the results of the tensile tests with the welds in the center of the gage length are reported for information.

The overall results show that the materials had good tensile and ductile properties and are considered to have net the specification requirements.

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4 5.0 SCANNING ELECTRON MICROSCOPY / ENERGY DISPERSIVE SPECTROSCOPY 5.1 Scanning Electron Microscopy Various areas around the fast fracture edges of the specimens were examined by the SEM (Figures 12-14). All of the f ractures examined exhibited a dimpled ruptured (ductile) appearance with characteristics typical of a fast ductile fracture. In no instances was there any evidence of any mechanism other than ductile overload apparent in the examination. None of the specimens examined at BNL had the probable initiation area of the failure on them.

In order to minimize undue handling of the specimens and also to keep intact certain large fracture surfaces in and about the area of probable initiation, a mutual agreement was reached by Virginia Electric Power Co.

(VEPCO), the USNRC, BNL and FaAA that various fracture surfaces would be examined at the FaAA facility (Alexandria, VA) by BNL personnel on equipment supplied by FaAA. To facilitate the SEM work at FaAA, a BNL investigator would direct an FaAA microscopist as to which sections to examine and which

. photographs / magnifications would be taken. Independence of the examination was maintained, since the areas were chosen by BNL, and all photographs shot were taken back to BNL by the investigator. Negatives were lef t on file at FaAA.

Figures 15 and 15a are a layout sketch and a photograph (both supplied by FaAA) showing the relationship of various specimens and fracture faces to each other.

Various sections from the pipe were examined at the FaAA facility.

Figures16-19a are SEM photographs of the type of fractures observed (specimens are identified using FaAA numbering system). In all cases, the fractures displayed a dimpled ruptured appearance indicative of a ductile failure. There was no evidence of fatigue interaction nor of any other failure mechanism other than ductile overload and fast fracture. Ductile tearing was observed on the edges of small tears on the fracture surfaces as well as any tears which may have been associated with possible inclusions.

The possible failure initiation site was located on fracture face 2A-2A-C (Figure 20). Progressively higher magnification SEM photographs indicate a high probability that this area is a good candidate for the f ailure initiation site (Figures 20a -20c). These fractographs show a possibly diametrically opposite tearing in the area shown.

The inside surfaces of both the elbow and the piping material were examined by SEM at BNL. Low magnification f ractographs (Figures 21 and 22) showed a scallop-like, almost peened appearance, with areas of dense oxide film. The elbow material (visually) appeared to be in general more highly oxidized than the piping material.

i These two surfaces, as well as a significantly thinned area from the elbow (IA-4), were deoxidized by the following treatment:

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i A working solution of Endox-214 was prepared by adding 8 ounces of Endox-214 powder to 1000 ml of cold water and stirring until it was completely dissolved. A small amount of Photoflow was added to the solution to aid the wetting of the specimen and eliminate some of the featuring which may result during the process. A glass beaker with 500 ml of the Endox_214 solution was placed in an ultrasonic cleaner. The specimen was made the cathode, and a platinum wire loop was used as an anode. A current density of 250 mA/cm 2 y,,

applied for one minute. The specimen was removed from the electrolyte and ultrasonically washed in a detergent solution consisting of Alconox and Photoflow for another minute, then rinsed in clean water, dipped in methanol and dried in hot air. The above procedure comprises one cycle. It was occasionally necessary to repeat the above cycle several times before removing all the corrosion products. It was not possible to pre-determine the exact number of cleaning cycles for any given specimen, since it depended upon the severity of the oxidation, roughness of surface, and the physical size of the sample. The specimen was observed optically after each cycle to determine if the oxide or the corrosion product was removed and the specimen surface looks

clean. After the specimen was thoroughly dried, it was examined immediately, since it may be prone to reoxidization at ambient atmosphere, and it was stored in a good desiccator.

Figures 23-25 show the surfaces of these specimens after deoxidation treatment. It was observed that many areas beneath the oxide film were heavily corroded and pitted, giving the indication that an active corrosion process was in progress during the operational life of the materials.

In order to verify that the scalloped ef fect seen on the inside surfaces was not due to any mechanical erosion mechanism, the polished cross section from section IA was examined under the SEM to ascertain if any cold work existed on the inside surface of the material. Figure 26 is a low magnification SEM photograph of the polished surface after etching. The etched grain boundaries are clearly visible with no evidence of distortions that would indicate cold work had occurred.

5.2 Energy Dispersive Spectroscopy Various EDS scans were performed on the inside surface of the pipe and elbow in search of any potential contaminants which may have been present.

This investigation was prompted by comments made during a USNRC generic meeting [1] that the extent of an erosion-corrosion process could be enhanced through demineralizer leakage. Figures 27 and 27a show a typical area of corrosion with the oxide films intact and the corresponding.EDS scan. None of the scans showed any contaminants.

Since various photographs taken at the FaAA facility showed the probahility of nonmetallic inclusions present in the material, one such inclusion was analyzed at the FaAA facility. The scan (Figures 28 and 28a) identified the inclusion as manganese sulfide, which is normally present in the steels investigated.

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6.0 DISCUSSION / CONCLUSIONS The accelerated or increased rate of attack on a metal due to the relative movement of a corrosive liquid and the surface of the metal is generally termed " erosion-corrosion."

This type of attack is recognizable through the appearance of waves, gullies, rounded holes, valleys and grooves [2].

Additional characteristics which may occur [3] are the forming of overlapping " horse shoe" shaped pits which causes the material to take on a scalloped appearance. Additionally, the selectively increased attack on pearlite (carbon steel systems) can also result in micropitting of the steel.

This type of corrosive attack generally occurs in areas of significant fluid turbulence near a metal surface and is associated with restrictions in a system (e.g. bends, orifices, elbows, tees [1,2,3]).

Since this type of failure mechanism can occur on systems similar to the

. Surry failure, it is worthwhile to disuss the possible variables which can j affect the rate of erosion-corrosion of a carbon steel e.g. fluid velocity, temperature, design, pH, dissolved oxygen and finally materials of construc-tion.

It is generally agreed that an increase in velocity will most probably result in an increased erosion corrosion attack [1-5]. This increased attack may proceed continuously with increased velocity [5] or may be negligent until a critical velocity [2] is reached and then proceed at a greatly accelerated rate. There is no doubt, however, that velocity has a significant effect on the rate of erosion-corrosion in these types of systems.

Temperature can also play a significant role in contributing to the erosion corrosion phenomenon. The majority of incidents involving single-phase flow conditions have occurred in the 50-230*C (122-446*F)temperture range [3] with 140-260*C (284-500*F) being the normal range for two phase flow conditions. It appears that the critical temperature for carbon steels occurs in the 130*-150*C range (266-302*F). Again, it is a general concensus [1-5] that a decrease in temperature below the critical range can significantly decrease the erosion-corrosion propensity of a material. This peak rate occurs at approximately the same temperature as the maximum solubility of iron ions in pure to slightly acid water, suggesting that dissolution of protective oxides in high velocity water is the rate controlling mechanism.

Design considerations for reducing this kind of attack would include such methods as: increasing the pipe diameter of a given system (to effectivelydecrease velocity), increasing in thickness of certain sections, and streamlining or eliminating sharp bends or transitions in a given system

[2,4].

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c-One paper [3] has cited a reference which showed that an increase of pH in water up to 9.2 (at room temperature) can cause a decrease in erosion-corrosion of greater than one order of magnitude. This paper also referenced articles that presented data to the effect that the erosion-corrosion rate in carbon steel was decreased up to two orders.of magnitude (over the temperature range of 38-204*C) if the oxygen concentration was increased from 1 to 200 ppb. This paper also states that this addition of oxygen has not been extensively examined and that some conflicting (e.g. an increase in erosion-corrosion rates) data exists in the literature.

By far, the most common method of reducing the possibility for erosion-corrosion f ailures is by using materials that are more resistant to the phenomenon. The addition of even small amounts (approximately 2%) of chromium to a steel has shown significant decreases in the rate of erosion-corrosion [1-4] with stainless steels being almost immune [2,3]'to the phenomenon.

The previous discussion and metallurgical evaluation has led to the following conclusions regarding the Surry Unit 2 pipe failure:

1. The chemical and mechanical properties of the pipe, elbow and weld materials involved in the Surry failure were consistent with the expected properties of the specified materials.

2. The impact tests performed on the' elbow, piping and weld material indicate that these materials had adequate toughness properties at temperature of operation.

3. The overall thinning of the elbow and pipe material coupled with the ductile tearing of the examined fractures by SEM provide adequate indication that the Surry Unit 2 feedwater pipe failed as a result of an erosion corrosion mechanism which thinned the wall sufficiently to cause a rapid, ductile tearing of the material after its design stress had been exceeded.

7.0 ACKNOWLEDGEMENTS The author wishes to thank both VEPCO and FaAA for their efforts ini providing both samples and information for the analysis. The author also wishes to thank M.H. Schuster for his helpful disucssions; J. Svandrlik, D.

Horne and A. Cendrowski for metallurgical services; A. Donegain for typing this report and Dr. J.R. Weeks for his constant support.

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4 8.0- REFERENCES

l. " Technical Meeting to Discuss the Generic Implications of the Surry Feedwater Line Failure," USNRC, January 15, 1987, Washington, DC.

2. CORROSION ENGINEERING, Fontana, M.G. , Greene, N.D. , Second Edition, McGraw-Hill.

3. Cragnolino, G., Paper Number 86, NACE-Corrosion 87, San Francisco, CA, March 9-13, 1987.

4. CORROSION IN POWER GENERATING EQUIPMENT, chapter entitled

" Erosion-Corrosion of Steam Turbine Components," Svoboda, R., Faber, G., 1985, Plenum Press.

5. Berge , Ph. , Ducreaux,~ J. , Saint-Paul,~ P. , "Ef fects of Chemistry on Erosion-Corrosion of Steels in Water and Wet Steam," pg. 19., Water

Chemistry of Nuclear Reactor Systems 2, British Nucler Energy Society, London, 1981.

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i. .w .w .'((A s Figure la. Photograph of the outside surface of specimen lA- 3.The numbers are thicknesses of the material as measured by the utility ( VEPCO ).

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Figure 2. Photograph of the inside surface of " as received " specimen lA- 4. Note the worn area near the center of the weld ( arrows ) .

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i Figure 3. Photograph of " as re e pred " pieces 4A- 1 ( top ) and 4A- 2( bottom ). Note the worn area of 4A- 2 in the region of the weld ( arrows ).

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ke IN k 46$$y' 8 Figure 6. A ferrite + pearlite micro- Figure 6a. A similar microstructure was

structure was observed on the pipe mater- also observed on the elbow material.

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Figure 16. Fract.ure surface 2A-2C displayed Figure 16a. A higher magnification SDI photo a dimpled ruptured appearance. of the tip of the void left by an inclusion i

i showing ductile tearing.

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i Figure 20b. Higher magnification fractograph i

i of 2A-2A-C. tearing characteristics of fracture in 2A-2A-C.

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Figure 21. Low magnification fractograph of the inside surface of the elbow material exhibiting scallop-like features and a highly oxidized surface.

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observation ) with a more defined scallop-like surface.

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i Figure 23. SEM photo showing pitting on the Figure 24. The piping material also showed Pitting after treatment.

elbow inside surface after deoxidation I

treatment.

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lar< 17159 . Preset. 800 secs ,

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that the inclusion is manga.:ese sulfide.

h 4

i TABLE 1 Typical Chemical Compositions of A106 Crade B,

A234 Grade WPB and E7018 Weld Metal i

3 A106 Grade B 4

I Chemical Requirement  % Actual Sepcimen Material i

i Carbon, max. 0.30 0.20 1

Magnanese 0.29-1.06 0.83

! Phosphorous, max. 0.048 < .005 Sulfur, max. 0.058 .023

, Silicon, min. 0.10 0.~ 10 [

! Chromium N.R. 0.07 N.R. 0.02 j Nickel j Molybdenum N.R. 0.01 l I

N.R. = No requirement < = Less than  !

}

1 A234 Crade WPB 1 ..

j Chemical Requirement  % Actual Sepcimen Material i i

( Carbon, max. .030 0.23 Magnanese 0.29-1.06 0.69 f Phosphorous, max. 0.050 <0.005

Sulfur, max. 0.058 0.013 i Silicon, min. 0.10 0.22 l Chromium N.R. 0.07 1 Nickel N.R. 0.01 1 Molybdenum N.R. 0.01 4

f N.R = No requirement < = Less than i

E7018*

Chemical Requirement  % Actual Sepcimen Material l

i Carbon N.R. 0.11 l Magnanose, max. 1.06 0.77 .

i Silicon, max 0.75 0.56  !

Nickel, max. 0.30 0.02 Chromium, max. 0.20 0.04 .l

. Molybdenum, max. 0.03 (0.01 l

[ Vanadtun, max. 0.03 Not analyzed for I Phosphorous N.R. <0.005 l

Sulfur N.R. 0.016 N.R = No requirement < = Less than i

• Requireannts for E70!d electrode were found in the ASME Boiler and Pressure Vessel Code,Section II, Part C, Section SFA 5.1, 1983 Edition.

29

_ ~ . . . . _ _ . -

TABLE 2-Results of Surry Impact Testing 4

Pipe (A106 GrB) i Specimen Temperature Absorbed Energy

• F/*C -(Ft.-Lb.)

i'

~

1 70/21 25.5 2 70/21 26.0

, 3 70/21 26.25 j 4 375/190.6 '33.75 5 375/190.6 34.25 6 375/190.6 34.25 Wald

, 1 70/21 19.0 J 2 70/21 19.0 3 70/21 18.75

! 4 375/190.6 21.5 I 5 375/190.6 '22.0 j 6 375/190.6 21.0 1

1 Elbow (A234 Gr WPB) i 1 70/21 14.0 j 2 70/21 13.0-3 70/21 13.0 i 4 375/190.6 13.25 '!

5 375/190.6 13.0 '

6 375/190.6 13.5 t

l

)

i

) I l 30 h

TABLE 3 KNOOP HARDNESSS VALUES FOR SURRY SPECIMEN (KN/500gms)

Pipe 160 160 158 158 158 158 158 156 170 162 Average 159 KN/500gms HAZ (Pipe Side) 174 179 179 174 172 177 181 181 176 172 Average 176 KN/500gms Wald 199 195 193 197 195 199 203 193 203 199 Average 197 KN/500gms HAZ (Elbow Size) 179 177 183 179 181 176 170 181 181 181 Average 179 KN/500gms

Elbow 163 169 170 169 170 163 167 176 179 179 Average 170 KN/500 gms

! i l i i

l l 31 .

1 l

1

._. ~ _.

TABLE 4:

Tensile Test Results - Surry Pipe Elbow Matrial 'A106 GrB Tensile strength 1 72,265 psi 2 72,289' psi 60,000' psi-(min.)

Yield Strength (.2% offset) 1 51,939 psi 2 50,354 psi' 35,000 psi (min.)

Total elongation

(.450" gage length) 1 29,113% 2 33.305% 30% min.

% Reduction in area 1 64.42% 2 66.67%

i Pipe Material A234 Gr WPB-Tensile strength 75,299 psi 60,000 psi (min.')

Yield strength (.2% ofsett) 66,707 psi 35,000 psi (min.)

Total elongation

(.450" gage length) 29.866% 30% min.

% Reduction in area 65.69%

Wald Material Tensile strength 1 73,768 psi 2 74,148 psi Yield strength (.2% offset) 1 57,579 psi 2 58,906 psi Total elongation

(.450" gage length) 1 38.082% 2 33.026%

% Reduction in area 1 77.35% 2 79.25%

i j

4 i

! 32 i

1

l l

NRC U S. NUCLE AR REGULATOR v CoaseseSSION I REPORY NUMSER # Ass faed e, Troc. een vet No , ,e e yJ l'Rc,s NUREG/CR-4868 m.m BIBLIOGRAPHIC DATA SHEET BNL-NUREG-52057 SEE r457RU ON THE REVER$E 2 TefLE AND SU E 3 LE AVE SLANE Metallurgi Evaluation of an 18-Inch Feedwater Line Failure at ' Surry Unit 2 Power Station 5

4 DATE REFT COMPLETED won T .,

gl

• EAR

. .U T ,,oR .. February 1987 r_ [ ATE REPORT ISSUED vt.R C. J. Czajkowski s Mar / ..

A5st, WORK UNeY NUMSER 1987 7 o EnFORufNG ORGANr2AleON Naut ANSbAILING ADDRESS reacNeele Coat 8 PROJE

.h Brookhaven National Laboratory Department of Nuclear E%rgy .,"F"'"'"*""

Upton, NY 11973 4

,eR , N eRe.N,, A T,eN N A.E g  ;

j A3851

.. .P A,. . A. L ,N. .gR E ,, ,,_.e ,. ,

. .. . .PE .. R EPeR T Division of PWR Licensing-A '. Region II, U.S. N ea r Off. of Nuclear Reactor Regul . ion Regulatory Co ' sior Technical-U.S. Nuclear Regulatory Conmis' son 101 Marietta St - = "a'a cou ano =~~ ~~

Washington, DC 20555 3. Atlanta, GA 36303

/

12 SUPPLEMENT ARY NOTES

,3 ...T R .c T , ., _

s h

A metallurgical failure analysis was pe& rmed on pieces from a catastrophically failed 18-inch diameter feedwater line from th hrry Unit 2 Nuclear Power Station. The failed pipe had been globally thinned d 4d a scalloped appearance on the inside surface. All fracture surfaces exam' ed shbised a ductile failure mode. The materials of construction met the appropriate pecificit, ion requirements (both mechanical and chemical). The report has as its excessive thinning by an erosion- rrosionmech(inism.nal concitT ion that the pipe failed due to k4, t.

b.

n 14 DOCUMtNT Analyses . ut vwoRD E SC RiPT OR S Q 55 AW AsLASILtiv r

erosion-corrosion 'y ^""'

feedwater pipe ductile failure

• Unlimited A106 Gr.B \ 'e sicuairT ctAss'" car'ON A234 Gr. WPB '"***t

. .oENrinERs onN ENoto iRos Unclassified iTne reportl Unclassified

• F NuuaER Os PAGES op.5.CovtR4slEnf pm!4T!h0 OrrICCs1987-191-697:63M s

I - -

[. , .

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J '

- UNITED STATES . - w,,

r NUCLEAR REGULATORY COMMISSION -

roswages caso

WASHINGTON, D.C. 20066 we.

l 1'

renwr o.c. om I OFFICIAL BUSINESS . '

l PENALTY FOM PRlVATE USE,0300 '

4i L

v  !

l 1 LAN1R5 '

120555078877 US NRC N, A04-3IV OF pud SVCS 00LICY t PU1 MGT BR-POP NUREr, W-501 DC 205GS WASHINGTON 4

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