Text

Point 1 Isolation Condenser & Shutdown Cooling Sys Piping Cracks
	ML20052E231
Person / Time
Site:	Millstone
Issue date:	01/28/1982
From:	Carnahan R, Cutt J; NORTHEAST NUCLEAR ENERGY CO.
To:	;
Shared Package
ML20052E224	List: A02113, Forwards Isolation Condenser Sys Water Hammer Events, in Response to NRC Questions Re 810810 Transient & Millstone Point 1 Isolation Condenser & Shutdown Cooling Sys Piping Cracks; ML20052E226; ML20052E231;
References
	81NED330, NEDE-25400, NUDOCS 8205100215
	Download: ML20052E231 (70)
	v • d • e

{{#Wiki_filter:f a NYo N CLASS ll May 1981 k V MILLSTONE POINT I ISOLATION CONDENSER AND SHUTDOWN COOLING SYSTEM PIPING CRACKS R. A. Carnahan J. C. Cutt p. l5 GEN ER AL h ELECTRIC e20310021e e20427 DR ADOCK 05000

l NEDE-25400 81NED330 Class 11 May 1981 MILLSTONE POINT I ISOLATION CONDENSER AND SilUTDOWN COOLING SYSTEM PIPING CRACKS i R. A. Carnahan J. C. Cutt Approved: Approved: J. C. Lemaire, Manager G. M. Gordon, Manager Plant Component Plant Materials Engineering Behavior Analysis and Technology Approved: M E. Kiss, Mantger 7 Plant !!aterials and Mechanics Techno'1, gy

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NUCLE AR ENGINEERING DIVISION e GENERAL ELECTRIC COMPANY SAN JOSE, CALIFORNI A 95125 GENER AL $ ELECTRIC 3

h' DISCLAIMER OF RESPONSIBILITY This document was prepared by or for the General Electric Company. Neither the General Electric Company nor any of the contributors to this documerrt: I A. Makes any warranty or representation, express or implied, with respect to the i accuracy, Completeness, or usefulness of the information contained in this docu-ment, or that De use of any information disclosed in this document may not j infringe privately owned rights; or B. Assumes any responsibikty for liability or damage of any kind which may result from the use of anyinformation disclosed in this document. i .I 1 l L2 j ')

CONTENTS L Page ACKNOWLEDGMENTS xi 1. INTRODUCTION 1-1 -2. OBSERVATIONS AND CONCLUSIONS 2-1 2.1 Pipe to Isolation Condenser Safe-End Weld ICAC-F-19 2-1 2.2 Isolation Condenser Supply Line Welds ICAJ-3,11 2-1 2.3 Shutdown Cooling "A" Line Weld SCAJ-2 2-1 l 3. BACKGROUND 3 4. TERMINOLOGY 4-1 i 5. VISUAL AND DYE PENETRANT EXAMINATIONS, AND SECTIONING PLANS 5-1 [ 5.1 Weld ICAC-F-19, Pipe to Isolation Condenser Safe-End 5-1 5.2 Isolation Condenser Pipe.to Elbow Weld ICAJ-3 5-6 5.3 Shutdown Cooling System Pipe _to Elbow Weld SCAJ-2 5-7 5.4 Isolation Condenser Pipe to Elbow Weld ICAJ-11 5-13 i { 6. EI. ECTR 0 CHEMICAL POTENTI0 KINETIC REACTIVATION (EPR) 6-1 l 7. METALLOGRAPHY 7-1 7.1 Section ICAC-F-19 7-1 ) 7.2 Section-ICAJ-3 7-23 l 7.3 Section ICAJ-11 7-23 7.4 Section SCAJ-2 7-33 8. HARDNESS MEASUREMENTS 8-1 9. MATERIAL TEST CERTIFICATES AND CHEMICAL ANALYSIS 9-1 DISTRIBUTION 1 s;- Y.' .u jAN 2 O ISS En w* 4 8 lii/iv A --

NEDE-25400 ILLUSTRATIONS Figure Title Page / 1 Millstone Isolation Condenser Supply Piping Class 2 5-2 2 Pipe to Safe End Weld ICAL-Fr 19 5-3 3 Circumferential Dye Penetrant Indication (0-180*) 5-3 4 180* - 330* Segment After Dye Penetract Examination 5-4 5 250* - 360* Segment After Dye Penetrant Examination 5-4 6 Short Dye Penetrant Indications on Machined Area of Safe End 5-5 7 Pipe to Elbow Weld ICAJ-3 5-7 8 Millstone Isolation Condenser Supply Line - Class 1 5-8 9 Dye Penetrant Indication on Elbow Side of ICAJ-3 at 7:30 5-9 { 10 Dye Penetrant Indication on Elbow Side of ICAJ-3 at 12:00 5-9 11 Forked Dye Penetrant Indication on Pipe Side of Weld at 1:00 ICAJ-3 5-10 12 Dye Penetrant Indication on Pipe Side of Weld at 11:00 ICAS-3 3-10 13 Location of Metallographic Samples from Section ICAJ-3 5-11 14 Millstone Shutdown Piping "A" 5-12 4 15 As Received Condition of Section SCAJ-2 5-12 16 Longitudinal Indication on Pipe Side of SCAJ-2 at 33" 5-13 17 Faint Circumferential Indication 3" from Weld on Pipe Side 5-14 18 12-3-6 Segment of Section ICAJ-ll After Dye Penetrant Testing 5-15 19 Short Dye Penetrant Indication on Elbow Side of ICAJ-ll 7 at 4:00 5-15 20 Faint Dye Panetrant Indication on Pipe Side of ICAJ-ll between 1:00 and 2:00 5-16 v/vi i ~

NEDE-25400 L ILLUSTRATIONS (Continued) Figure Title Pjyg; 21 Safe End Side of ICAC-F-19 at 0*, 8X 7-2 22 Intergranular and Transgranular Cracks on Safe End Side of 0*, 128X 7-3 23 Cracking on Each Side of Weld at 45*, 8X 7-4 24 Beginning of Crack "A", 128X 7-5 25 Tip of Crack "A", 128X 7-6 26 Cracking on Pipe Side of ICAC-F-19 at 45' 7-7 27 Tip of Crack "C", 128X 7-8 28 Crack Penetration into Weld, Okalic Acid Etch, 128X 7-9 29 Crack Penetration into Weld, Kalling's Etch, 128X 7-9 v 30 Crack Penetration into Weld, Kalling's Etch, 500X 7-10 31 Pipe Side of Scal-F-19 at 360*, 8X 7-11 32 Opening of Crack on Pipe Side of ICAC-F-19 at 360* 7-12 4 33 Tip of Crack at 360* 7-13 34 Cracks in Safe End at 260*, 8X 7-14 35 Safe End at 260*, 128X 7-15 36 Shallow Transgraular Crack, Pipe Side of ICAC-F-19, 2" Away from Weld, 8X 7-16 37 Same as Figure 36, 128X 7-17 38 Shallow Transgranular Crack on Safe End Side of 4 ICAC-F-19, 2.5" Away from Weld, 8X 7-18 39 Same as Figure 38, 128X 7-19 40 Pipe Side at 332*, 100X 7-20 41 Safe End at 259*, Crack Tip, 55X 7-21 42 St ~e End at 259*, 300X 7-21 43 Pipe Side of ICAJ-3 at 11:00, 8X 7-24 vii/viii

NEDE-25400 ILLUSTRATIONS (Continued) Figure Title Page 44 Opening of Crack at 11:00, 128X 7-25 ( 45 Tip of Crack at 11:00, 128X 7-26 46 Pipe Side of ICAJ-3 at 1:00, 8X 7-27 47 Beginning of Crack "B", 128X 7-28 48 Tip of Crack "B", 128X 7-29 49 Elbow Side of ICAJ-11 at 4:00, 8X 7-30 50 Crack Penetration into Weld, Kallings Etch, 330X 7-31 51 Closeup of Region "A", 100X 7-32 52 Pipe Side of ICAJ-U at 1:30, 8X 7-32 53 Pipe Side of ICAJ-ll, 250X 7-34 54 Pipe Side of SCAJ-2 at 33", 8X 7-35 55 Beginning of Crack at 33", 128X 7-35 56 Pipe Side of Weld at 37", I.O. Surface Is Plane of Polish, 8X 7-36 57 Crosn Section of Faint Circumferential Indication on Machined Area of Pipe Surface, 3" from Weld 23" Location, 330X 7-37 s ix/x

NEDE-25400 ACKNOWLEDGEMENTS The timely response of G. R. Lundeen and R. D. Sanchez in providing metallography is greatly appreciated, as is the helpful background information supplied by B. M. Gordon. 6 xi/xii

NEDE-25400 1. INTRODUCTION In December 1980 Northeast Utilities reported a series of Type 304 Stainless steel pipe cracks at Millstone 1. Cracking was reported in the Isolation Con-denser, Shutdown Cooling, and LPCI systems. A total of four sections of piping from the isolation condenser and shutdown cooling systems were sent to the Vallecitos Nuclear Center (VNC) for failure analysis. Work was begun in January 1981 on a section of 12 inch pipe welded to an iso-lation condenser safe-end. Up to 270 of cracking had been reported in the weld heat affected zone. In early March three additional sections of piping were received. Two of the sections were from the 14 inch Class 1 portion of the isolation condenser supply line, between the reactor vessel and the dry-well. Both sections had reported ultrasonic (U.T.) indications; on one sec-tion these indications had been verified by dye penetrant examination. Also included was a section from the 14 inch shutdown cooling "A" line with a reported spot U. T. indication. The purpose of this report is to characterize the piping cracks and determine their cause. l-1/1-2

NEDE-25400 2 OBSERVATIONS AND CONCLUSIONS 2.1 PIPE TO ISOLATION CONDENSER SAFE-END WELD ICAC-F-19 1. Circumferential Intergranular Stress Corrosion Cracking (IGSCC) of unprecedented extent for large diameter piping (360 on the safe-end side) was found in the weld heat affected zone (HAZ). 2. Shallow Transgranular Stress Corrosion Cracking (TGSCC), characteristic of chloride stress corrosion cracking, was found near the weld fusion line in essentially annealed material, and in base material (away from the weld) on both the pipe and safe-end sides. 3. It is believed that the cracking occurred as a result of chloride contamination. 2.2 ISOLATION CONDENSER SUPPLY LINE WELDS ICAJ-3,11 1. Circumferential IGSCC was found in the weld HAZ. 2. A shallow TGSCC crack was found in weld metal on Section ICAJ-ll. 3. The weld heat affected zones were highly sensitized. 4. Analysis of scrapings from the I.D. of Section ICAJ-ll revealed a low concentration of chlorides, below acceptable levels for as-received Type 304 stainless steel. 5. Chlorides may have assisted initiation of the observed cracking. 2.3 SHUTDOWN COOLING "A" LINE WELD SCAJ-2 1. Longitudinal IGSCC was found at three locations in the pipe side weld HAZ. 2. The heat affected zone was highly sensitized. 2-1

NEDE-25400 3. Analysis of scrapings from the section I.D. revealed a low concentration of chlorides, below acceptable levels. 4. Chlorides are not believed to have assisted crack initiation. 2-2

NEDE-25400 3. BACKGROUND l During startup after the first refueling outage at Millstone in September of l 1972, with the reactor at 2% power, 980 psi, and 531 F, sea water in leakage l through condenser tube leaks caused twa demineralizer beds to " break through". This was immediately reflected in high water conductivity and a plant shutdown was initiated by inserting control rods to cause the reactor to become sub-critical. With the reactor cooldown continuing at 100 F/hr, all conductivity instrumentation was reading full scale. Aporoximately 90 minutes after becom-ing sub-critical, the reactor was scrammed and cooldown was maintained with the isolation condenser. The isolation condenser remained in service for about six hours. Post incident water analysis confirmed 3.4 ppm chlorides in the condensate return line. Three to four days af ter deactivation the isolation condenser was drained. Two sub-sequent fill and drain operations rid the system of out-of-specification water, e 3-1/3-4

NEDE-25400 4. TERMINOLOGY To resolve any doubt regarding the meaning or usage of some of the terms and j abbreviations used in this report, the following list has been compiled for reference: 1. IGSCC - Intergranular Stress Corrosion Cracking. 2. TGSCC - Transgranular Stress Corrosion Cracking. 3. EPR - Electrochemical Potentiokinetic Reactivation; a quantitative measure of the degree of sensitization (grain boundary carbide pre-cipitation) in stainless steel. 4. ICAC-F The weld between the 12 inch Class 2 isolation condenser supply line and the north inlet safe-end. Sometimes this term is used to refer to the section containing the weld. 5. Pipe / Safe-end - Another name for the section containing veld ICAC-F-19. 6. ICAJ A pipe to elbow weld from the 14 inch Class 1 isolation con-denser supply line. 7. ICAJ-ll - Another pipe to elbow weld from the 14 inch Class 1 isolation condenser supply line. 8. SCAJ A pipe to elbow weld from the 14 inch Class 1 shutdown cooling "A" line. 9. HAZ - heat affected zone; a region of piping in the immediate vicinity of a weld. 4-1/4-2

NEDE-25400 5. VISUAL AND DYE PENETRANT EXAMINATIONS, AND SECTIONING PLANS 5.1 WELD ICAC-F-19, PIPE TO ISOLATION CONDENSER SAFE-END A six inch length of pipe containing weld ICAC-F-19, which joined the 12 inch isolation condenser supply line to the north inlet safe-end was received at VNC in January, 1981. Figure 1, an isometric diagram of the Class 2 isola-tion condenser supply piping, shows the location of this weld. The section consisted of four inches of safe-end and two inches of pipe. See Figure 2. The I.D. was free of oxide because it had been thoroughly cleaned prior to dye penetrant examination at Millstone. No cracks could be observed by visual examination at VNC. Dye penetrant examination, however, revealed circumferential indications in the HAZ on both the pipe and safe-end sides of the weld. See Figures 3 through 5. The circumferential indication in the safe-end HAZ covers 360. Indications in the pipe side HAZ cover 120 of the circumference, but not continuously. In addition to the circumferential indications in the weld HAZ, numerous short (3 't inch long) randomly oriented indications were observed (Figure 6). They were found on both the pipe and safe-end sides of the weld, beginning near the fusion line and continuing into the base material inches away from the weld. The distribution of these indications was not homogeneous; their concentration was much greater in some areas of the pipe / safe-end. After penetrant examination, the pipe safe-end was sectioned for metallography, EPR, and crack depth measurements. A summary of the sections removed for metal-lography is given below: M-1 0 end of 0-1 segment where crack may be in weld. M-2 Center of 0-1 segment, through cracks on each side of weld. M-3 2 end of 1-2, small indication on pipe side, 2 inch from weld. 5-1

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NED0-25400 5.2 ISOLATION CONDENSER PIPE TO ELBOW WELD ICAJ-3 A ten inch section containing pipe-to-elbow weld ICAJ-3 is shown in Figure 7. This is a section of 14 inch Type 304 stainless steel piping from the isolation l condenser supply line near the reactor vessel (Figure 8). No reference markings l were found on the as-received section so the following system of reference was used: l l The section was placed so that the inside radius of the elbow was at the top, in the 12:00 position. Looking into the pipe side, markings were made proceed-ing clockwise from the top (12:00). The longitudinal weld seams of the elbow lie at 12:00 and 6:00. No cracks were observed during visual examination at VNC. The inside surface of the section was coated with a light layer of oxide but was reasonably clean from prior dye penetrant examination at the site. After cleaning with acetone this surface was penetrant examined again at VNC. Two short circumferential indications were found in the HAZ on the elbow side of the weld at 7:30 and 12:00 (Figures 9 and 10). Short Three circumferential indications were found in the HAZ on the pipe side. (approximately 3 inches in length) indications were found at 11:00 and 1:00 (Figures 11 and 12). The indication at 1:00 has a secondary crack that forms an angle of about 30 with the main crack. The third indication measures 7 inches in length from 4:00 to 6:00. A branch, making a 60 angle with the main cir-cumferential crack, was observed at the 5:00 location. randomly oriented indications of the type observed on the pipe / safe-No short end section were found. A more thorough check was made by cleaning the inside of the pipe with a wire brush and dye penetrant examining again. No additional indications were found. The locations of metallographic and EPR samples are shown in Figure 13. M-1 is from the forked indication in the pipe side HAZ near 1:00. M-2 contains cracks on both the pipe and cibow sides of the weld at 12:00. Samples EPR 1 and 2 are from the pipe and elbow weld ilAZ respectively. 5-6

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NEDO-25400 f t AJ-3 /* Po r E 7' - a f g<n.i. d '. t ' i GEME2 Figure 13. Location of Metallographic Samples from Section ICAJ-3 The 22 to 44 inch (6-12:00) segment was halved, and the 33 to 44 inch segment, which contained the reported UT indication was cleaned with sandpaper and a wire brush. Dye penetrant examination did not reveal an indication at the location required by UT (40 inch). Axial indications, however, were found in the pipe side, starting approximately 1/16 inch from the weld at 33 and 37 inches (Figure 16). The indication at 33 inch measured 7/16 inch in length; the indi-cation at 37 inches measured 3/8 inch. No short randomly oriented indications were observed. The sectioning plan for EPR and metallography is shown below: M-3 M4 16 di EPR-3 PIPE ELBOW EPR4 33" 37' 5-11

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jd % LAu O C % ['y[ $e9ei Q Q;?Ij %b - pg{ g Q Q 3fgj%$g, ,pqpqy.. y;9-(q)y T 1"sfp_,y, n t s, s g:r.e-p.y %cu! Q go,* a ~. w y, g. ? (; uz - QJf+;ggG} of a ,. c. ,;a w cq ~ 4~ ~ y p s AJ-2 AP pg @3(" t k. >q Asci 6 a-e Figure 16. Longitudinal Indication on Pipe Side of SCAJ-2 at 33" Since dye penetrant indications were found at locations not associated with UT indications, it was decided to clean and P.T. another quarter section of the pipe / elbow. An axial indication similar to those on the 33 to 44 inch segment was found at 29 inches. Also, a faint circumferential indication was found on achined pipe surface at 23 inches, three inches from the weld (Figure 17). Metallographic sample M-5 was taken from this indication. No other indica-tions were found. 5.4 ISOLATION CONDENSER PlPE TO ELBOW WELD ICAJ-ll ICAJ-ll is a pipe-to-clbow weld from the Class 1 isolation condenser supply line near the drywell penetration (Figure 8). This section was cut very near the weld with the result that it was essentially an elbow section with only inch of pipe. The section was 2 inches long at inside radius, 8 inches long at the outside radius. The reference system is the same as that of ICAJ-3 (top 5-13

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Faint Circumferential Indication 3" from Weld on Pipe Side of inside radius is 12:00, proceed clockwise looking in from pipe side). The section was cut through the longitudinal welds at 12:00 and 6:00. The 12-3-6 segment is shown in Figure 18. The inner surface of the pipe was covered with a heavy layer of oxide. An area of four square inches was scraped to remove the surface layer for chloride analysis. Due to the difficulty of removing the oxide layer, only half (the 12-3-6 segment) of the section was cleaned and dye penetrant examined. A h inch long circumferential indication was found in the elbow near the weld fusion line (Figure 19). On the pipe side a three inch circumferential indi-cation was found between 1:00 and 2:00 (Figure 20). No short randomly criented indications of the type found on the pipe / safe-end were seen. 5-14

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kk h 9,. .o -; w - ~,, m.7. 9,.5. 3.1, 1 s v.. g >.- 4 y 9kw. s .s. s, p,. < ,3 s v .' 79 ~ - ... g - ~ .q - 5 ,3 -#c le' .4Qt,0 %. ga.4 s, -m ^ pt ..[ L,'..'~.' p-h,$.I.[. / ..w.g e. , - [p. .'. ' k ;h^".. - .l. % N,_h*, f y,b,Y'i l 4 Figure 19. Short Dye Penetrant Indication on Elbow Side of ICAJ-11 at 4:00 5-15

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o hf. h 'lW5 .41; - , Mys:, u.j;q .i 3 ~. y T9jyA w .w.2 Figure 20. Faint Dye Penetrant Indication on Pipe Side of ICAJ-ll between 1:00 and 2:00 Metallographic Samples 6 and 7, from the elbow and pipe respectively, were cut through the two above mentioned indications. EPR-5 is from the HAZ on the elbow side of the weld. EPR measurement on the pipe side of the weld would be misicading due to the effects of the Plasma Arc process used to remove the section. 5-16

NEDE-25400 6. ELECTROCHEMICAL POTENTI0 KINETIC REACTIVATION (EPR) Electrochemical Potentiokinetic Reactivation (EPR) is a quantitative measure of'the degree of sensitization in Types 304, 304L, 316, and 316L stainless steel. Sensitization (chromium depletion at the grain boundaries) can render stainless steel susceptible to IGSCC. There appears to be a correlation be-tween the degree of sensitization, measured by EPR,'and IGSCC resistance in a BWR coolant environment. EPR measurements were made on five' samples from the pipe / safe-end section. The results are given below: Location Pa (coul./cm ) Pipe Base Material 0.19 Pipe Side Weld HAZ 5.36 Safe End Weld HAZ 7.35 Safe End Base Material 1.50 2 Pipe Base Material Adjacent to Short 0.31 45 Indication i l An EPR measurement of 2.0 is the marginal degree of sensitization for cracking under high stress in oxygenated water. EPR measurements were also made on material from the HAZ of welds ICAJ-3, ICAJ-11, and SCAJ-2, with the following results: Location Pa (coul./cm ) ICAJ-3 Pipe HAZ 49.2 Elbow HAZ 17.4 ICAJ-ll Elbow HAZ 24.4 SCAJ-2 Pipe HAZ 52.2 Elbow HAZ 10.4 6-1/6-2

NEDE-25400 7. METALLOGRAPHY 7.1 SECTION ICAC-F-19 Reference points on the pipe / safe-end will be expressed as azimuths, with 0 at 0 ; 1 at 90 ; 2 at 180 ; etc. (Refer to Figures 3 through 5). Metallographic Sample M-1, from 0 is shown at low magnification (8X) in Figure 21. The. cracks are shown at higher magnification (128X) in Figure 22. Nearest the weld is a~ grossly _ branched transgranular crack that becomes intergranular at a depth of 0.035 inch. The total crack depth is 0.215 inch. Slightly further from the weld is an intergranular crack. Sample M-2 is a section through cracks on each side of-the weld at 45. Fig-ure 23 is a low magnification (8X) photograph of Sample M-2. There are two cracks on the pipe side of the weld and one on the safe-end s de. To avoid confusion, the crack in the safe-end will be referred to as "A", the crack nearest the weld on the pipe side as "B", and the longer crack in the' pipe as "C". The beginning and end, respectively of crack "A" are shown in Figures 24 and 25. This crack is intergranular and 0.170 inch deep. The cracks on the pipe side are shown in Figure 26. Crack "B", nearest the weld, is a grossly branched transgranular penetration of 0.030 inch. One of the branches appears to cross the weld fusion line. Crack "C" is intergranular and 0.185 inch in depth. It proceeds perpendicular to the inner surface of the pipe, until reaching the weld. Here it propagates along'the fusion line (Figure 27) and looks as if it is trying to penetrate the weld. Finally it enters what appears to be weld material and stops. Figures 28 and 29 show the crack after repo11shing and etching in oxalic acid and Kallings reagent, respec-tively. After repolishing, the depth of crack penetration into the weld decreased. Oxalic acid attacks ferrite and carbides, but Kallings reagent attacks only ferrite. The crack has propagated into a region depleted of fer-rite. It arrests where the ferrite content approaches that of the weld base material. The region of arrest is shown at higher magnification (500X) in Figure 30. 7-1

NEDE-25400 i.d. SUR F ACE I n /f / b. SAFE END } O.215 in, k I v a_ Figure 21. Safe End Side of ICAC-F-19 at 0, 8X A short indication in the pipe, 45 to the weld, can be seen in Figure 5, near the zero end of segment 3-0 (1 60 ). A cross section at low magnification (8X) 3 is shown in Figure 31. The crack opening and tip, respectively, are shown in Figures 32 and 33. It is completely intergranular with a depth of 0.400 inch in the plane of polish. Figure 34 shows cracks in the safe-end of 260*. As seen in the pipe at 45 and the safe-end at 0, there are two cracks: a grossly branched transgranular crack nearest the weld and an intergranular crack slightly further from the ) weld. The transgranular crack becomes intergranular at a depth of 0.040 inch (Figure 35) and appears to join the longer intergranular crack, which proceeds to a depth of 0.285 inch. As discussed previously, numerous short randomly oriented indications were found away f rom the veld IIAZ. A typical indication of this nature, from the i 7-2

l l NEDE-25400 (- f -y 3, - / \\*/.. '- Ii. h ,f [~ ,s .f.ss s ( ./, 'I [s-( y s s. \\, 1 / w v j a ,y,' v n (1 f. r _ ~N J i \\ f ' ~... y. / .\\ g,' h;.A<y D i s f-7i \\ ,t - s.., .:J ( f i e '; i s g 4.- x; x I v~, ~ s f, x v l .N-s- - 'y .f. 7 N., 0.035 ',,i p){ e s e y q g M,, n< q ,N. 4 ,s i s N s, \\ py y d ^ m. fg. e .a r ll \\ s l \\. h \\ fr ~'N .. ' *'s T - r ] ,y t '( [f '. I [ ~.., _ _ 1 r )., N. c.- -- f.^^ .,/: ~ ~ - - - v..

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[l N.. 4 'w. s . \\.s ' i-8 Figure 22. Intergranular and Transgranular Cracks on Cafe End Side at 0, 128X 7-3

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, y hg.. .r . n 2.Q / ', ' @}, y ,M:)s&]J l _ l .jtjjy(lTs f.' % ; j:[ kl _ 'y i ,y A (( m % 7'.. 'E p ., Wi x 9,-n_ f; e. 3 i 1 nib [d..i.[.Ti bkJ f.s -w,. :. m ya,L,gs! h Figure 23. Cracking on Each Side of Weld at 45,8X l i pipe side 2 inches away from the weld (Sample M-3), is shown in Figure 36. It is transgranular and heavily branched (Figure 37) with a depth of 0.035 inch. A similar indication, 2.5 inches from the weld on the safe-end side, is shown in Figures 38 and 39. It is also a branched transgranular crack, 0.030 inch deep. Sections containing cracks (pipe llAZ at 332 ; safe-end HAZ at 259 ) were removed for scanning electron microscope (SEM) analysis. The cracks were broken open to reveal their surfaces. Figure 40 shows the pipe side fracture surface near mid wall. There is evidence of secondary cracking, perpendicular to the fracture surface, characteristic of IGSCC. The safe-end fracture surface is shown in Figures 41 and 42. It is also inter-granular with some secondary cracking. The lower portion of Figure 41 shows the f racture that occurred when the sectio-was broken open. Neither the pipe or safe-end fractures show other evidence of ductility or plastic deformation. 7-4

NEDE-25400 i.d. SUR F ACE r i 'w \\a ~(, x - -n,;y-t ;. ( ,.,.,rx )> <*f-, s., t (n,. m .2 ,/ ' r / h,,~ f" 1 \\' ~ a -s \\ T / - y' i I l 1 0 . / J 7 SAFE-END 1 ) 1 Figure 24. Beginning of Crack A",128X l 7-5 i i

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I ', N.g;..,.h s ~ s, M-; . ) ~ d); ' ^ \\ i i t i e., 5 \\ Figure 28. Crack Penetration into Weld, Okalic Acid Etch, 128X f >> -r,. (.st t. r i a i s ,i ,3 .u (,,, k ,I b ! ,s 4, s r. ,3 e s 4 1' * = t ,\\. s ^ .\\. 1 I' - ss g' s J 4 e g 4 Y, 6 Figure 29. Crack Penetration into Weld, Kalling's Etch, 128X r 7-9 i

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( NEDE-25400 i.o. SUR F ACE N .$ Q/ \\ ' ! i ly 2 ^ t (. i ;<.,@,,.y ,;h l 'J .~. r-f I ,7N [ftS.' : v. , gn,.mn PIPE U, ,. ;.i?[2;Aph ((ly qjr SIDE 0.400 gj, s..t.g ;jy in. V. f t. 8/ WELD '-,3 '"$f'3 , Ja., f4:\\ ".j)., o-c. - r a 1 '.l$

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,. 19, V l d' Figure 31. Pipe Side of Scal-F-19 at 360, 8X 7-11

NEDE-25400 l I i.d. SUR F ACE z 4,}< s'j. s s ,,,/ ! ./ ,- 4 4 nj ,- { ; {},L lm) \\. < } ~ ~. ,'y ~ { b y,. .. f w-- \\ \\ w j 't / 4. ....( s s.._,,- x'l .O i i y N .,,/ l s . N,_ \\. ,X \\. ' ,/ i i. -- f- ? ,f ,..y 4,, - -.. f4 's k' .; ' :1 -., / w 'x fx - Q, (-.. N' ., ) i ,9 s N Y,.s, . t. y / ,] ~ j 'N / ~/ . s,- \\ ~,! 4 s s -\\ ts ~e ' ' s, 1:Q ~,'. Q/ . ;.. ") ^ f'. m s .s a. s i \\ ,e ,1 u,,. ~-,,'\\ I i s e 7/_,-' - x - x_ \\, ..s. .j I s ~ ~ ' ' 5., } - s.,, .j s. 3 v- ~ s 360 Figure 32. Opening of Crack on Pipe Side of ICAC-F-19 at 7-12

N EDE-25400 e ~ 'n i \\ t / \\y. - Figure 33. Tip of Crack at 360 Up to this point, the mode of cracking has been discussed, but not the cause. Reference has been made to the 1972 chloride intrusion. Chlorides can cause stress corrosion cracking in stainless steel. j Sensitized stainless steel is susceptible to IGSCC in 550*F high purity oxygen-ated water. In sensitized type 304, chlorides can; (1) lower the magnitude of stress required for IGSCC, and (2) accelerate the initiation and propagation of IGSCC. In non-sensitized Type 304, transgranular stress corrosion cracking (ICSCC) can occur in the presence of chlorides. The grossly branched transgranular cracks shown in Figures 22, 26, 35, 37 and 39 are classic examples of chloride stress corrosion cracking. They were found in material near the weld fusion line and in base material away from the weld. EPR measurements show that the base material of the pipe and safe-end is not sensitized. Also, material close to the weld fusion line is non-sensitized 7-13

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Cracks in Safe End at 260, 8X 7-14

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2 -a + 'M ^ r. d ~ l:aa e,/ s Figure 36. Shallow Transgranular Crack, Pipe Side of ICAC-F-19, 2" Away from Weld, 8X because it was heated to a temperature above the sensitization range during welding. Slightly further from the weld, the matcrial is sensitized, as verified by EPR measurements, approximately 0.25 inch from the fusion line. This explains the occurrance of pairs of transgranular and intergranular cracks in the weld HAZ (Figures 22, 26 and 35). The transgranular cracks are in essentially annealed material; the intergranular cracks are in sensitized material. Further evidence of chloride effects is given by the overall extent of crack-ing and the depth of the transgranular cracks. Never before has 360 of cir-cumferential cracking been observed in weld sensitized material. A list of crack depth by azimuth location is given in Table 7-1. Crack initiation at multiple azimuthal locations can occur in the presence of chlorides. 7-16

NEDE-25400 A 3 4_ I*;j ' t. c k ' ~ ~,i y

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r /* / ~d ' s. ]f 'e .- N. s-Figure 39. Same as Figure 38, 128X 7-19

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NEDE-25400 1 1 riW ^ 7 .. i; K n t 7. [ ENVIRONMENTAL

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CRACK LAB FRACTURE Figure 41. Safe End at 259, Crack Tip, 55X p,"i f[.'r,'. ' I A h.: -',r ., 6 -

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,c ' ,.w, t ~,.; _g '{p _. p. 7. _.y.< > ?g. Figure 42. Safe End at 259, 300X 7-21

NEDE-25400 Table 7-1 MILLSTONE ISO CONDENSER SUPPLY LINE: DEPTil 0F CRACKING IN PIPE / SAFE-END WELD ZONE Safe End Pipe Depth Depth Azimuth (in.) Thickness (in.) Thickness 0* 0.215 29 5.6 0.097 13 0.176 24 34 0.152 20 0.191 26 45 0.170 23 0.185 25 68 0.294 40 0 0 101 0.121 16 0 0 158 0.302 41 0 0 191 0.191 26 0 0 225 0.412 54 0 0 259 0.285 38 293 0.239 32 0 0 332 0.136 18 0.252 34 354 0.400 54 Average: 0.219 30% 7-22

NEDE-25400 The depths of several transgranular cracks were measured and all are between 0.030 and 0.040 inch. It is likely that they grew to this depth during the chloride intrusion; subsequent flushing of the isolation condenser rid it of chlorides. 7.2 SECTION ICAJ-3 Figure 43 shows the crack in the pipe side of the weld at 12:00. It is 0.220 inch deep in the plane of polish, and intergranular. The crack beginning and tip are shown in Figures 44 and 45, respectively. Figure 46 shows a cross section of pipe containing the ' forked portion of the in-dication shown in Figure 13. Both cracks are in the llAZ on the pipe side of the weld and are intergranular. The crack furthest from the weld, marked "A" in Figure 43, reaches a depth of 0.250 inch in the plane of polish. Crack "B" extends to a depth of 0.095 inch in this plane and is very close to the weld fusion line. It is shown at higher magnification (128X) in Fi<3ures 47 and 48. This situation is unlike that of the pipe / safe-end where tran3 granular cracks initiated next to the weld fusion line. EPR measurements (on the I.D. surface) from the pipe side llA7. of Section ICAJ-3 are much higher than those of the llAZ of the pipe / safe-end (49.2 versus 5.36, 7.35). The material immediately adja-cent to the weld fusion line of Section ICAJ-3 may be sensitized while that next to the fusion line of Section ICAC-F-19 is likely to be annealed. Although chlorides can promote IGSCC in sensitized stainless steel, they are not likely to have had an effect on Section ICAJ-3 becase no transgranular cracking was observed in non-sensitized material away from the weld. Also the extent of ICSCC was much less even though the IIAZ was highly sensitized. 7.3 SECTION ICAJ-11 The circumferential indication in the IIAZ on the elbow side of the weld at 4:00 is an intergranular crack (Figure 49) and 0.170 inch deep in the plane of polish. The crack tip (Figure 50) appears to penetrate weld metal, but actually enters two regions where the ferrite content is low. 7-23

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,X* Figure 44. Opening of Crack at 11:00, 128X 7-25

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( m-- t.; /, '.~ } - Figure 45. Tip of Crack at 11: 00, 128X 7-26

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,f 3 e \\,- i r. .e 0.250 in. ]k i 'f' V B A i.d. SURF ACE Figure 46. Pipe Side of ICAJ-3 at 1:00, 8X 7-27

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,'y t e (,, ..s 3. .,;f}t} i l 7 '5, s,W i " ^ ' ~(y'i I s ) s j s n 1 I' A, v Ld. SURF ACE Figure 47. Beginning of Crack "B", 128X 7-28

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NEDE-25400 0.170 in. ---->- .my --.,-v7,,-,.,. m. .h 3. c.- ..'.a,J < =, r, 2 y s: ss a 4 ' ~.g i i .%<~ ^E' N ,,N. N

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,.} y- . W. w,, - + [L 1 ', \\ ',., p. r-rf* h. . e-J %,' -' y\\o,.fe9"f? ~ e ,:, k;.s,i r;D g ( 'J3 i.t ',, 4:g . -N QNf w m s w. > - m + e. a:~aw&y L. Figure 49. Elbow Side of ICAJ-ll at 4:00, 8X The darkened area, marked "A" on Figure 49 is prcbably the result of an arc strike that occurred during welding. Figure 51 shows this area at higher magnification (100X). It is likely that the cracking occurred as the area re-solidified. The crack in the pipe side at 1:30 is illustrated in Figure 52. It is in weld metal, but not that of the weld root; this region is probably the result of a weld repair made to restore proper fit-up between the pipe and elbow. The gross branching (Figure 53) is characteristic of chloride TGSCC, which can occur in stainless steel weld metal. The absence of extensive transgranular (or intergranular) cracking on Section ICAJ-11 is an indication that chlorides had little effect on the observed pattern of cracking. The weld HAZ was highly sensitized and thus susceptible to IGSCC in the absence of chlorides. 7-30 ti

NEDE-25400 .y f. I I .). ? e, g 6 p: J s ( a ' i 4 /. E Figure 50. Crack Penetration into Weld, Kallings Etch, 330X 7-31

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Figure 52 Pipe Side of ICA.1-U at 1:30, 8K l-U

NEDE-25400 It may have occurred to the reader that the pipe / safe-end, which exhibits extensive chloride stress corrosion cracking, is downstream of Sections ICAJ-3 and ICAJ-11, which do not. The isolation condenser inlet, however, is filled with hot condensate, while most of the supply piping is exposed to a steam environment. 7.4 SECTION SCAJ-2 Three longitudinal indications were found on the pipe side, beginning approxi-mately 1/16 inch from the fusion line and extending up to 3/4 inch up the pipe, but not beyond the region of weld-prep machining. Figure 54 shows a cross sec-tion of pipe containing the indication found at 33 inches (using the reference system discussed earlier). It is 0.340 inch deep in the plane of polish. Fig-l ure 54 is somewhat misleading because the actual ratio of crack depth to wall thickness is much less than it appears; the cross section was cut at mid-wall to facilitate metallographic polishing. Figure 55 illustrates that the crack is intergranular. The I.D. surface of the pipe side at 37 inches is shown in Figure 56. A face polish of the crack at this location shows that its opening is intergranular. Its length is 0.725 inch. A photo micrograph (Figure 57) of a section through the faint circumferential indication on the pipe side, 3 inches from the weld shows that it is a machin-ing lap. The microstructure of the flap is highly deformed. No transgranular cracking was found on Section SCAJ-2. The pipe side HAZ which contained the intergranular cracks was highly sensitized, rendering it susceptible to IGSCC in a 550 F high purity oxygenated water environment. I 7-33

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.{ , e .x = / t. t t k i? ' ( '? I / Figure 55. Beginning of Crack at 33', 128X 7-35

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j F Figure 56. Pipe Side of Weld at 37", 1.0. Surface Is Plane of Polish, 8X 7-36

NEDE-25400 i.d. SURF ACE i I /- d, ,a %s/ ( i i i Figure 57. Cross Section of Faint Circumferential Indication on Machined Area of Pipe Surface, 3" from Weld 23" Location, 330X 1 i ) i i l l l 4 7-37/7-38

NEDE-25400 8. HARDNESS MEASUREMENTS Microhardness was measured near transgranular indications on the pipe / safe-end, and near a machining lap on the pipe side of SCAJ-2. The results are given in Table 8.1 below: Table 8-1 MICR0 HARDNESS MEASUREMENT INDICATIONS ICAC-F-19 SCAJ-2 Pipe, 3 In. Safe End Pipe 3 In. Distance From I.D. Surface (in.) Knoop Rockwell Knoop Rockwell Knoop Rockwell Edge 382 C38 0.002 390 C39 352 C35 317 30 0.003 267 23 317 31 O.004 267 23 267 23 253 B100 0.005 260 22 253 20 0.006 260 22 253 20 224 95 0.008 192 88 1 j 0.010 240 B99 228 B95 There is a layer of cold worked material extending to a depth of 0.002 to 0.003 inch beneath the I.D. surface. The hardness gradient is similar for Section SCAJ-2, which had no transgranular cracks, and Section ICAC-F-19 which was covered with them. The cold work (probably from machining) may have con-tributed to the initiation of transgranular cracks. Prior cold working can aid in the initiation of chloride stress corrosion cracking and, in the case of the pipe / safe-end, probably did so. The depth of the transgranular cracks was, however, an order of magnitude greater than the depth of the cold worked layer. 3 8-1/8-2

NEDE-25400 9. MATERIAL TEST CERTIFICATES AND CHEMICAL ANALYSIS Material test certificates obtained from northeast utilities show that all of the pipe in the isolation condenser supply and shutdown cooling lines was fabricated from the same heat. The results of chemical analysis and mechani-cal testing are given below: C Mn P S Si Cr Ni Mo Co B Ladle Analysis 0.08 1.45 0.005 0.013 0.39 18.87 10.27 -- 0.05 0.005 Check Analysis 0.08 1.52 0.011 0.008 0.41 18.85 10.40 -- 0.06 0.2% offset Yield (psi) 34,800 Tensile strength (psi) 91,000 % Elongation 60.7 % Reduction in area 75.0 Flattening Test Satisfactory Material certificates for the shutdown cooling "A" line elbows, also fabricated from the same heat, provide the following test results: C Mn P S Si Cr Ni Mo Ladle Analysis 0.048 1.47 0.022 0.014 0.76 18.63 9.48 -- Check Analysis 0.040 1.40 0.024 0.015 0.79 18.32 9.14 -- 0.2% Of fset Yield (psi) 36,000 Tensile Strength (psi) 82,500 % Elongation in 2 inches 56.0 Test certificates were not available for the isolation condenser north inlet safe-end or the isolation condenser supply line elbows, but base material from the pipe / safe-end was analyzed for carbon content by an accredited independent laboratory, with the following results: Pipe 0.062% C Safe-end 0.074% C 1he maximum allowable carbon content in Type 304 stainless steel is 0.08%. 9-1

4 NEDE-25400 i i Scrapings from the I.D's of Sections ICAJ-ll and SCAJ-2 were analyzed for chlorides. Unfortunately the I.D. surface of Section ICAC-F-19 was free of i oxide and corrosion products due to prior cleaning at Millstone. Care was taken to avoid contamination of the samples by removing the' corrosion products 2 with a clean scalpel and collecting them on clean laboratory paper. The scrap-ings were sealed in a glass container rinsed with boiling nitric acid. The results are given below: Sample Chloride Content ICAJ-ll 1.2 mg/ft. SCAJ-2 0.6 mg/ft. Test results indicate that the residual chloride content on normally processed stainless steel tubing may range from approximately 0.05 to 0.23 mg/ft. of tube surface. Tubing in storage for several weeks awaiting inspection may have a chloride content ranging from 1.30 to 3.23 mg/ft. however. Thus, the chloride content measured on Sections ICAJ-ll and SCAJ-2 cannot be con-sidered excessive. 9-2

NEDE-25400 V DISTRIBUTION R. B. Adamson V03 R. J. Brandon 889 R. A. Carnahan (5) 138 J. E. Charnley 879 J. P. Clark 744 M. Costandi 855 J. C. Cutt 138 D. E. Delwiche 138 0 J. Foster 195 G. M. Gordon 138 N. R. Hughes 138 J. N. Kass 511 J. F. Kilty (5) 881 I J. C. Lemaire 138 C. S. O'Toole 138 E. D. Sayre 777 B. Stevens (5 + 1 fiche) 126 NEBG Library (5) 328 VNC Library (2) V01 l 1/2 (

NUCLEAR ENERGY DIVISIONS e GENERAL ELECTRIC COMPANY SAN JOSE, CALIFORNIA 95125 GENER AL h ELECTRIC TECHNICAL INFORMATION EXCHANGE TITLE F*,GE AUTHOR TlE NUMBER 81NED330 R.A.Carnahan 730 DATE J.C. Cutt August 1981 TITLE GE CLASS Millstone Point 1 Isolation 77 Condenser and Shutdown Cooling GOVERNMENT CLASS System Piping Cracks REPRODUCIBLE COPY FILED AT TECHNICAL NUMBER OF PAGES SUPPORT SERVICES, R&UO, SAN JOSE, 72 CALIFORNIA 95125 (Mail Code 211)

SUMMARY

In December 1980 Northeast Utilities reported a series of Type 304 Stainless steel pipe cracks at Millstone 1. Cracking was reported in the Isolation Condenser, Shutdown Cooling, and LPCI systems. The purpose of this report is to characterize the piping cracks and determine their cause. NEDE-25400 By cutting out this rectangle and folding in ha!f, tne above information can be fitted into a standard card file. l NEDE-25400 DOCUMENT NUMBER INFORMATION PREPARED FOR SECTION Plant Materials and Mechanics Technology BUILDING AND ROOM NUMBER 1900 1139 M AIL CODE 138 NED-914 (6/77)

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SUMMARY

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