ML19326B549
| ML19326B549 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/15/1975 |
| From: | Murchison M BECHTEL GROUP, INC. |
| To: | |
| Shared Package | |
| ML19326B551 | List: |
| References | |
| NUDOCS 8004160338 | |
| Download: ML19326B549 (99) | |
Text
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g;/d so s/s 2 3?a INVESTIGATION OF PIPE LEAKAGE,
REACTOR BUILDING SPRAY SYSTEM PIPING,
ARKANSAS NUCLEAR ONE, UNIT 1 FINAL REPORT August 15,1975 p 313d cteksto g g gel p,! '.
PREPARED BY MATERIALS, FABRICATION AND QUALITY CONTROL SERVICES DEPARTMENT SCIENTIFIC DEVELOPMENT OPERATIOLS BECHTEL CORPORATION SAN FRANCISCO, CALIFORNIA
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DATE:
August 15, 1975 PROJECT NO:
6600, Arkansas Nuclear One, Unit 1 9
SPECIFICATION & P.O. NO:
6600-M101 TITLE:
4 Investigation of Pipe Leakage, Reactor Building Spray System Line i
Final Report e
CLIENT:
Arkansas Power. II t Company PREPARED FOR:
E. H. Smith, Project Engineer BY:
M. L. Murchison, Engineering Specialist Materials, Fabrication & Quality Control Se rv ic e s APPROVED BY:
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R. C. Bertossa Metallurgical Engineering Manager Materials, Fabrication & Quality Control Servieps j,2,[ __ j APPROVED BY:
W. R. Smith, Sr.
Manager Materials Fabrication & Quality Control Services
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TABLE OF CONTENTS
_Section g
1 INTRODUCTION l-1 2
SUMMARY
OF FINDINCE 2-1 3
RECOMMENDATIONS 3-1 4
MATERIALS 4-1 5
CENERAL DISCUSSION 5-1 6
DETAILED RESULTS 6-1 Appendix A A-1 l
Appendix 3 B-1 Bibliography e'
LIST OF.1LLUSTRATIONS i
- Page Figure 6-1 Pictorial View of Crack No.1 in its Entirety.
6-3 through 6-21 6-2 Pictorial View of Crack No. 2 in its Entirety.
6-23 through 6-27
~
6-3 Pictorial View of Crack No. 3 in its Entirety.
6-29 through 6-3o 6-49 6-4 Photograph of Stress-Corrosion Bending Fixtures Complete with Specimens.
6-50 6-5 Photograph of Stress-Corrosion Specimens in Exposure.
3 6-52 6-6 Photograph of Stress-Corrosion Container Showing Yellow Jrystals from Decomposition of Sodium Thiosulfate.
6 6-7 Examples of Shop Welds, S-2, S-3, and S-4, Selected at Random from the Crossover Loop.
6-8 A Comparison of Appearances of a Shop Weld and a Field 6-56 Weld from the Crossover of Unit 1.
6-9 Corrosion Pits In and Along the Root of Field Weld, FW-6A.
6-57 6-10 Corrosion Pits on the Ingide Surface and Cracks in the RAZ 6-5d of Shop Weld SW-F.
6-11 Cracks and Corrosion Pits on the Inside Surface of Shop Weld, 6-59 SW-F.
6-12 Corrosion Pits on the Incide Surface of Shop Weld, S-2.
6-60 6-13 Corrosion Pits and Cryscalline Deposit on the Inside Surf ace 6-61 of Shop Weld, S-4.
6-14 Prints from X-ray Radiogrcphs Showing Indications in the HAZ 6-62 of Shop Weld, S-3.
6-15 Cracks in the HAZ Which Did Not Show Indications in Radiographs.
6-63 6-64 6-16 Photomacrographs Showing Cracks in Shop Weld, SW-F.
6-17 Outside Surface Profile of SW-F Showing Sharp Crain Boundary 6-65 Pene t rat ici.
6-66 6-18 Photomacrograph Comparing Field Weld FW-6A with Shop Weld S-3.
A-1 Isometric Number 5-85-6 A-2 Isometric Number S-BS-3 A-3 Isometric Number S-BS-8 A Isometric Number 5-BS-104 A-5 Isometric Number 27-CA-102 A-6 Isometric Number 5-B5-2 A-7 Isometric Number 7-DH-9 A-8.
Isometric Number 7-DH-11 i s.
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LIST OF TABLES Table Page n
4-1 Chemical Analyses of Type 304 Stainless Steel Heat No. 800201 4-1 6-1 Analytical Results of Sample No. 2, Unit 1 Crossover Pipe Water 6-38 a
6-2 Analytical Chemical Referee Results - Seven Laboratories 6-40 6-3 Chemical Analysis for Impurities of Sodium Thiosulfate Pentshydrate 6-41 Crystals from Unit 1 8*
6-4 Summary of Results of T sts of 44 Specimens on 304 Stainless Steel 6-42 Pipe Per ASTM-A262, Practice A 6-5 Results of ASTM-A262 Practice A and Practice E Tests on Welded 6-45 Pipe Specimens - Series No. 1 6-6 Results of ASTM-A262 Practice A and Practice E Tests on Welded 6-43 Pipe Specimens - Series No. 2 6-7 Results of Stress Corrosion Testing of Welded Pipe Specimens in 5-53 Sodium Thiosulfate Solutions.
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Section 1 INTRODUCTION O
9 On November 8,1974, a leak was discovered in a Reac:or Building Spray System pipo of Arkansas Nuclear One, Unit One (hereafter. referred to as Unit 1). The p,lant was shut down following the hot functional test of the primary coolant drain line, and was going into the decay heat mode at the time the leak was detected. The leak was located adjacent to a weld (HCB-6-1). A segment of the systep, including the leak, was replaced and the plant returned to operation. On Novecber 412th, a second leak was detected adjacent to a new weld made in the original pipe as part of the repair of the first leak. Also on November 12th, a third leak developed in a different part of the system (HCB-6-4). All of the failed piping is located in the Auxiliary Building, floor elevation 317 feet, Area 4. Failures 3 and 2 may be '. cated on Isometric Drawing No. 5-BS-6 and failure 3 on Isometric brawing No.
5-BS-7. Failures 1,2, and 3 were sent to the San Francisco Material's Fabrication and Quality Control Services (MF&QCS) laboratory for analysis. Three* additional leaks found in the system were sent for examination to the Southwest Research Institute of San Antonio, Texas.
A total of 11 f ailures (leaks or part-through cracks) were investigated either by the Bechtel MF&QCS Department or by the Southwest Research Institute. A list-ing of these failures follows:
ITEM INVESTICATOR Leaks't,2, and 3-MF&QCS Leaks 4.5, and 6 Southwest Research FW-5 (Radiographic indication)
Southwest Research FW-6A (Represertative field weld)
HF6QCS and Southwest SW-F (Representative shop weld)
MF60CS and Southwest Shop welds S-2 and S-3 selected MF&QCS at random from the crossover, Unit 1 All of the leaks occurred in 10-inch Schedule 10 Type 304 stainless steel pipe manufactured to ASTM-A358 by Supplier No. I from one heat of steel, Heat No.
800201. The temperature of the system is estimated not to exceed 150 F. (The names of pipe suppliers, fabricators, steelmakers, and analytical laboratories involved in this investigation are not given in this report and may be obtained from the Of fice of the Manager, Nuclear Services, Arkansas Power and Light Caspany.)
An interim report was issued on December 5,1974 listing intergranular stress-assisted corrosion cracking as the mode of failure for leaks 1,2, and 3.
1-1 i
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- e Section 2
SUMMARY
OF FINDINGS The following list briefly describes the major investigational failure fi di r
for the Reactor Buildang Spray System Line.
n ngs ing Spray System was found to be stress-assisted corrosi s
u 2.
The conditions producing the stress-assisted corrosion cracking were:
stresses produced by welding (always present); sensitization in the heat affect d sones near welc produred by welding heat; and, one or more corrodents.
e 3.
high carbon contentContributary factors in the stress assisted corrosion cracking were:
of the piping material at the ment by the pipe manufacturer. sensitization of the piping material due to the still a treat-4.
The corrodents are believed to be chloride ions and/or ions of su x
es.
5.
The failures all occurred in one heat of material, Heat No.
near the. pump suction crossover piping.
800201 in or 6
oxides probably from sodium thiosulfate. Sampling of the crossover piping wate u ur 7.
and no abnormal metallurgical conditions were produced in t e sound There appears to be no difference between the examined field and sho c ed zones.
Unit I with regard to susceptibility to intergranular stress-assisted corrosi p welds from cracking.
on 8
The piping material, Heat No. 600201, cation, ASTM-A358. The base caterial passed the Practice A and Practice F tes met the requirements of the specifi-of ASTM-A262.
s 9.
Specimens.of six heats of piping material from Unit MF6QCS with only Heat No.
showing evidence of partial sI were examiaed by 800201 delivered." One other heat examined by S'iR1 showed evidence of sensiti ensitization "as zation.
10.
Laboratory investigations by MF&QCS indicate that c acking susceptibility is enhanced by:
stress-assisted corrosion and, sensitization of the base metal prior to welding.high c excess welding heat; 11.
Corrosion testing in the MF5QCS laboratory indicates that affected zones of austenitic stainless stects are susceptible to intergran l sensitized heat-u ar 2-1
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f ailure in a dilute solution ->f sodium thiosulf ate (and decomposition products) and chloride ions. A concentrated solution of sodium thiosulfate alone did not cause as severe intergranular damage. "[his concentrated solution was not treated with sodien hydroxide to enhance the stability of sodium thiosulfate as required i
in Unit I storage.
12.
Studies in the field indicate that radiography is preferred over ultrasonic examination for detection of stress-assisted corrosion cracking.
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f Section 3 RECOMMENDATIONS 1.
Every precaution must be taken to keep from exposing og contqcting austeritic stainless steels, whether in construction or ic operation, with corrosive media such as chlorides or solfur bearing compounds.
Note:
8 The following recommendations are made for procurement and handling of systenitic stainless steels for any required replacement material.
2.
All future unstabilized austenitic stainless steel materials should be 5.urchased to a specification calling for cooling from solution h'est treating temperatures to below 800 F within a maximu. ti=c of three minutes.
3.
Shop and field welding should, be controlled so as to minimize the time the materials are in the temperature range of 1400 to 800 F.
4 k'here design conditions permit, type 304L austenitic stainless steel base material should be used. This grade has a maximum carbon content of 0.03 k' hen design considerations will not permit Type 304L stainless steel to percent.
be used, Type 304 stainless steel should be selected within a carbon content range of 0.05 percent maximus.
3-1
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Section 4 MATr: RIALS All 10-inch schedule 10 pipe sections containing leaks were purchased to ASTM-A358, TP-304, class I. The pipe was produced by Supplier No. I from ASTM-A240 strip produced by Steelmaker No. 1. The pipe subassemblies were manufactured by Fabricator No.1. The ladle chemical analysis by Steelmaker No.1, and check analyses by Supplier No. I and Bechtel are given in Table 4-1. The tensile results on the plate are:
%Elong in 2" i
ASTM-A358 Specification 75,000 min 30,000 min.
40 min.
Supplier No. 1 Certification 65,600 31,500 65 The pipe was cooled from the solution annealing temperature in still air, pra-ducing a microstructure containing carbide precipitation at mid-wall thickness.
The carbide precipitation measured approximately 40 percent encirclenent at mid-thickness but only 10 percent near the surface. The material, Heat No. 300201, passed Practices A and E of ASTM-A262.
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TABLE 4-1 CHEMICAL ANALYSIS OF TP-304 Ht. 200201 Steelmaker No. I Supplier ho.!
A-240 Required I.adle Chetk hethe el Chet 4 El e ment we. 2 (1)
Acalysis wt. %
Analysis wt. 2 Analysis wt.1 i2)
Carbon 0.08 0.080 0.0 57 0.075 9
- % ganese 2.00 1.45 1.53 1.49 Phosphorus 0.045 0.019 0.0!!
0.016 Seal fur 0.030 0.005 0.012 0.008 4
Sit 6on 1.00 0.63 0. 39 0.65 Nic kel 8.00-10.50 9.17 S.89 9.43 e
Chromius 18.00-20.00 18.43 18.29 18.38 Molybdenuts 0.390 d.39 Cobalt 0.05 0.09
' Cesium (3) 0.001 1.attthanum ( 3 )
0.0003 s Cerium (3) 0.003
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Nitrogen 0.026 vanadium (4) 0.015 Copper (4) 0.0d Calcius (4) 0.003
( I)
Sacimum (unless r.w.4 specified).
(2)
Ch,.ical analysis a.* Laboratory No. 8.
( 3)
R. vst e<'
by 3et h:t! as check on deoxidat ion prac tice.
(4)
Ee-r u.intitaties amission spectrographic analysis.
4-2
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Sectioa 5 GENERAL DISCUSSION
+
Metallographic examinations reveal.d that the cracking in Unit I piping near circumferential wells was intergranular in nature and that the cracks were in the weld heat affected zone (HAZ) just outside the area where the carbide precipitation appeared to be the greatest. All of the cracks appeared to have originated at the inside wall ei the pipe and ranged in length from one to abuut two inches at the outside surf ace. The cracks were branching and irregular in direction, but were generally parallel to the weld. In addition,- the pipe material away from the weld area exhibited varying degrees of intergranular carbide precipitation' ranging from arproximately 10 percent on the cuter surfaces to as much as 40 percent near the cs ater. This same condition of sensitization was found in other piping manu-factured by Supplier No.1, whose piping is also located at other power plant sites where Bechtel is involved. (Heat No. 830201 was the only heat from Unit 1 examined by MF6QCS which shows partial sensitization.) The type of cracking found in. this investigatian is generally identifie3 as intergrar.ular stress-assisted corrosion cracking (ICSACC).
Three primary conditlans are normally associated with intergranular stress-assisted corrosion cracking:
Stress Sensitized natorial Corrosive media Other facters may contribute to the fa!!.re on a secondary basis.
5.1 STRESS Residual stresses free welding are unavoidable and are present to the degree necessary to cause this type of cracking, it is assumed that the stress compon-ent present for IGSALC was introduced by welding because the crccking obcerved has all been parallel with and along the circumferential welds in the HAZ.
5.2
+ SENSITIZED MATERIAL The piping 26terial is ASTM-A358, TP-304 By the specification, "all pipe shall be furnished ii. the heat-treated condition. The heat treatment procedure shall consist of heating the material to a minimum of 1900 F and quenching it in water or rapidly cooltar by other means." Extensive microstructural exeminat ion of the cracked pipe Sections revealed continuous precipitation in the HAZ Jue to welding and some. partial sensitization of the base metal as a result of the still air c>>t ing practice used by Supplier No. 1. However, the sensitizat ioa nf the base j
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- 1 metal was heast.st at mid-thickness and this wauld have no ef fect on the subse-quea.,ortace react'ans if it did not entend to the surface in some areas, escept that any sensitization in the s,se metal is additive to that normally produceJ an f
.the heat affected zone during weldin3
.The examination also revealed the presence of a continuous network of intergran-ular attack on both the ID and OD surfaces of the piping. The attack was on the order of 0.001 to 0.0025 inches deep and was probably caused by pickling after heat treatment. Ti.e fact that the attack on the outside and inside surfaces is of the same depth is significant as it indicates that this attack existed prior to installation of the piping and was not caused by the service environment. This' type of intergranular attack is believed to hasten cracking of sensitized stain-less steels and also to provide retention of corrodents from the pickling solution.
The pipe material, with the carbon con ^ent at the maximum permitted and with the t
varying degree uf sensitization in the base metal and the attack on the pickled surfaces, is not believed to be the entire cause of the failures. These conditions, however, resulted in a material most sensitive to intergranular failure yet within the range of the ASTM-A358 Specification, depending upon the interpretation af th.-
words " rapid cooling."
e 5.3 CORROStVE HEDIA Probably the most significant factor in producing stress-assisted corrosion crack-ing in the pump suction ~ system was the presence of a corrodent which is the factor least defined in this investigation. The water of the pump suction loop was sampled on December 13, 1974, one day after the discovery of Leak No.5, and presumably the water was in contact with the pipe at the time of this leak discovery. However, i
it is highly enlikely that the water sampled in December w;= the same water in j
contact with the pipe at the time of Leaks I through 4 The sequence of events e
normally followed with the discovery of a leak is: (1) To valve off the portion of the system af fected; (2) drain the pipe; (3) repair the leak; and, (4) replace the water from the water storage system. The water in the system at the time of Leaks 1 through 4 la therefore unidentified. Tne water sampled, which was found by analysis to oe high in ions of sulfur oxides, e " have been present in the pipe at the time of leak No. 5, but there is no assurante was present at the time of initial crack formatian. that water of this analysis Though the corrodert chemistry was not well defined, there is ample evidence the ' water in contact with the af fected pipe was corrosive.
that 5.3.1 The presence of corrosion pits in the heat-af fected zone of the pioe is evidence of the presence of one or more corrodents in the water. Chemicals krown to cause pitting in austenitic stainless steels include the chloride ion, sodiun thiosulfate, and hydrogen sulfide which is a possible decomposition product of sodium thiosultate.
5.3.2 The preseace of a large ame unt uf sulfur cocpounds in the sampled water confirms that chemicals other than those intended to be present found their wae into the. system.
5.1.3 T'ae fact that, to date, cracking has only occurred in Heat No. 80020: i, the pamp suction and crossover loop, indicates that cond it ions were d i t fer-from those in other portions of the Building Sprey and Decay !!est ent systems that also contain pipe from Heat No. 800:01.
5-2
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ological activity, or in acid, neutral 'or slightly alkaline conditions. Under slightly stkaline conditions sodium thiosulfate can decompose as follows: Na2S203 + H20+H2S
+ Na2SO4. 9ulfidic environments are known as corrosive environments causing inter-granular stress-assisted corrosion crackin: of sensitized stainless steels.
Note:
Refer to Bibliography for list 'of technical literature involving stress-assisted corrosion cracking.
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k' Section 6 DETAILED RESL'LTS The investi ation determined the mode of failure and defined as far as possible 2
the f actors involved which may have had some influence on the mode of failure.
6.1 LABORATORY INVESTICATION - FAILURE MODE Pipe sections containing leaks numbered 1,2, and 3 were sent ta San Francisco for metallurgical examination. T%e investigations included visual observations; microstructural examinations; scanning ele-tron microscopic examination of fracture surfaces; mechanical testing; chemical analyses of the pipe material; analysis of the crossover water sample and the sodium thiosulfate crystalr; and testing for intergranular corrosion susceptibility to ASTM A 262, Practices A and E.
The results of the failure mode investigaticas are suemarized here without re fe rence to specific photomacrographs or photomicrographs. A pictorial review of the three cracks is presented in Figures 6-1, 6-2, and 6-3. The photomacrographs and photomicro-graphs are supported by consentary.
6.2 VISUAL OBSERVATIONS The surface areas of the three pipe sections in which leaks occurred, were exam-ined visually at a magnifiestion of 30%. The three sections contained cracks par-allel to the circumferential butt welds. Ine cracks were approximately 1/4 iacn f rom the root of the weld. All cracks were within the HAZ. The cracks were longer, with wider openings on the ID surfaces, indicating that they originatad on these surfaces. Three additional cracks U: pipe No. 3 originated on tha ID surface and did not penetrate all the way through the wall. Examinations at 30% of both 10 and 00 surfaces of tne pipe revealed a " dried cud-cracked" appearance. ac crack ::o.
1, the pipe had been deformed to match the adjacent pipe fitting. The cracked portiar.
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of the pipe was found in contact with a wall nenetration sleeve, and scratches were found in the contact surface. Visual examination of all three pipe sections revealed
- a. similar'ity of location (in HAZ), orientatinn (parallel to weld), appearance (intergranular), and origin (ID surface) of the cracks.
The cracks on t e pipe perimeters are locatet as follows:
Looking into the pipe from the ci cumferential butt weld side, crack No. I was located at 12:00 o' clock; crack No. 2, at 7:00 o' clock; and, cracks on pipe No. 3 were located at 1:00 o' clock, 5:00 o' clock, 7:00 o' clock sad 4:00 o' clock. Those at 5:00, 7:00 and 9:00 o' clock did not penetrate the well.
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The following figures 6-1A through 6-1S are a pictorial review of Failure No. l.
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Electrolytic etching in 10% oxalic acid.
These pictures indicate the pipe was solution treated after seam welding.
6-12
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Figure 1-lN.
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E12ctrolytic etching in oxalic acid.
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6-21
Figuro 6-2 The following figures 6-2A through 6-2E are a pictorial e
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4 The follawing figures 6-Ja through 6-3H are a pictociqi review of Failure No. 3.
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3. -w J i 6.) MICKt%!Nt*t:fL'NAL ASALYSIS Cross secti..nm of all cracks and nipe base net.it away from the circumferent i.el f welJs were esamined metallurgically at earnificat ions up to 1500X. Th.* r.sults were very similar for all three pipe sectionn esami. sed. I A) g The cracks originated on the ID surf aces sad progressed through th. pip ** thickness le an intertranular manner. There <as no evidence of transaranuiar or mixed mode cracking. b) The cracking occurred in the heat-af fected zone just outside the aro.e where cont inuous carbide precipitation was heaviest; however, cont inuous grain boundary carbide precipitation was present in the cracked area, a c) The cracking was branched with secondary cracking. e u D d) Tne welds appaared sound with no objectionable features. No cracking was found in any of the welds. s e) The longitudinal welds on all pipe sections appear to have been sJIHr idn* treat ed af ter planishing. There was no evidence of a neat-af fleted gone near these welds. f) The base metal of all pipe from the cracked sections contained carbi.to precipitation at the grain boundaries, indicating an inadeqqate cooling rate from th* solut ion heat-treating temperature. The carbide precipigation was heavier in '.he center of the pipe thickness than at either surfste. 3) The pipe ctoss section was characterized by mixed grain size; snali cr ina (0.1 mm) ar the center and large grains (0.3 mm) toward the surf ace. At the auriace was a zone of re:rystallized grains. h) On both the ID and 00 surfaces throughout the pipe lengths, there NJs J i network of intergranular attack. This intergranular attack (including grain b.sund-ary oxidation at the tip of tr.e attack) catended to a depth of 0.001 to 0.Lv2 ** inch. This attack appeared to have bc.*n caused by pickling subsequent to 'i.*at treating. 6.4 FitACT0 GRAPHIC ANALYSIS Tne fracture surface of crack No. I was examineJ on a scanning electron aicrosec p.. This examination also showed the intergstr.uiar -ode of tracture. The f r.act ure features were snarp, indicating the fracture -as accoe. aniaJ by very lit's-cor-rosion whic?. is a characteristic of intergranolar strees-assiste.d corrosion erackins (ICSACC). 6.5 CHEMICAL ANALYSIS, PIPE BASE. METAL I 4 sample f rom the pipe containing crack No. I was subjected to chemicit analysin to the specification requirements. The analysis indicated all of the specitie.itiae requirements for chemistry were met, although the carbon content is near tS* m.sams.s permitted. The resulta are given in Table 4-l. 6.6 m*4TER ANALYSIS A water sanple (approximately one gallon) was taken from the crossover line af tor Building Spray Loop which had been valved off following the discovery Jf a l e a ** 6-31
tu roi.e. -uve r s,ines Specie (1) Laboratory Laboratory. Laboratory Laboratory Laboratory 1.a!.o rat o ry 1.aboratory _ No L N o. 2 No l No.4 N o. 's No.6 N c. 7 _ __ u s Fluoride ton
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Lead 0.1 Total Sulfur 930 900 1100 - Chromium 0.05 Total Dissolved Solids, 7910 Total Solids 13425 9 pli 6.7 Specific Conductance hiicro hilIO/ Chi 4600 2890 3250 3000 i 1) llesults in parts per millic.n unless.otherwise indicated. i 4 3) Less than
. ~... on De <=ber 12, 1974.
- .. sample was taken on December 13, 1974 The sanpline was witnessud by a Bechtel MF&QCS representative. The water was drawn from a driin time at the point wh!re the crossover line connects to tne main line. Tne water was subjected to chemical analyses by seven dif ferent licensed laboratories all usinz standard analytical sethods given in " Standard.wethods for the Examina t ion of Vater ar.J wastewater",13th Edition, 1971. The resulta reported by these labor-atories are'given in Table 6-1.
It will be nottd the wide variations in values w-re reported for ento, rid; and. the sulfur products. The ciloride ranged from 0.7 ppo to 550 ppo. The range in sulfur product s is likewise considerable, though the total sulfur reported was an the fairly narrow range of 930 - 1100 ppe. An investigation in the hechtel Scientific Development Sturry Laboratory (identified as Laboratory No. 7; revealed that analysis of chloride is ditficult in the presence of large amounts of reducing sulfur ions such as sulfite and thiosulfate. These ions require a vigorous oxidation to remove this interference, otherwise a false hign analysis for chlori e will result. l In order to verify the high or low chloride results, e'ich of the seven Icboratories analyzed samples prepared by MT&QCS with known amounts of chloride and thiosal tate. These solutions were prepared using analytical reagent grade chemicals and n.3: illed I water. The results are given in Table 6-2 and indicate that laboratories that originalt,. reported low chloride results have adequate methods for the removal af 8' interfering ions in the analysis of chloride. It was concluded t;iat the water removed from the crossover pipe contains 2 ppe ar less of caloride cnd a total sulfur content of approximately 1000 ppm. The water had essentially a neutral pH (6.7) and specific conductance of 3000 micro cho/cm. 6.7 SODIUM THICsULFATE CRYSTALS - AMALYSIS Sodium thiosulfate pentahydrate c..tals furnished by Ar. kansas Power and Light Conpany were analyzed for chloride ion. The specification for the sodium thiosulfare s crystals limits chloride as sodius chloride to 0.2 percent (2000 ppm) an an i murity. Analyses were obtained from three licensed laboratories. The results are given in Table 6-3 and rar.;e f rom 10 ppe to 2800 pps as sodium chloride. The law value of lass than 10 ppt was confirmed by the Slurry Laboratory which analyzed a 30 ercent solution c of the sodium th;osulfate crystals and reported a result of less than 3 ppm. Tnese resuits indicate that the sodium thiosulfate crystals used in Unit I could not be a significant source of chlorides. 6.8 LABORATORY INVESTIGATION - SENSITIZATION / CORR 0 DENT PARAMETERS This phase of the laboratory investigation was conductec to determine the relative inf tsence on stress assisted corrosion cracking of prise partial sensitization and we' ding heat treat parameters. ASTM A252, Practice A was used to measure the degree of sensit ization and Practice E was used to provide a measurement of muscept-iblity to intergranular corrosion mechanisms. 6.8.1 Unit I Sampling for Deeree of Sensitization . Ten pipe specimens representing six dif ferent heats installed in Unit I were o tsin d for analysis by Practices A and C, per ASTM-A262. These pipe specimens were sriesced following a pipe surface condition survey in the field, and covered a br.saJ snectrum of heat numbers, pipe sizes, and surf ace conditions. All of this pipe w:s mtiof act-ured by Supplier No. 1. Complete data on these specimens are containc.1 in Tast.' e 4 1socetric drawings detailing the locations of all of the trepan ted specim. u are 11 Appendix A of this report. The trepanned specimea nu-bers correspond to the 'in plant" inspect ion locat ion numbers given in Table J of the Soc'.hwest Research leract. 6-39 -Q- -G 4
TABLE 6-2 RESULTS OF REFEREE SAMPLE ANALYSES (1) WITH KNOWN CHLORIDE ADDITIONS (3) Sample Sample Sample Sample Sample D No.2 A B C Cl-Content < 1 ppm 366 ppa ll.3 ppm 139 ppa LABORATORY (ppm) Cl-Cl-Cl-Cl-No. I 130 < 1 325 125 110 No. 2 180 $72 575 550 128 No. 3 ( 0.7 < 0.7 338 8.5 142 No. 4 (2 41 335 7 135 ) I No. 5 48 <1 360 2 140 No. 6 850 1600 2149 1749 300 (2). No. 7 2 400(384) 14(17) (1) Sacples A, B, and C utre nrepared f rom analytical reagent grade chemicals to give 1* Boric Acid and 0.5* Sodium Thiosulfate Pent-ahydrate. Sample D contains 1% Boric Acid and no Sodium Thio-sulfate. (2) Ihe number in parentheses are chloride additions to these samples. The:e samples were made at a different time from the others. (3) Sample No. 2 is from the crossover piping of Unic 1. O I 6-40 9
.4 = s ......cu TABLE 6-3 RESULTS OF ANALYSIS OF CitLORIDE IN SODIUM THIOSULFATE PENTAltYDRATE CRYSTALS FROM ARKANSAS POWER AND LIGHT LABORATORY CHLORIDE ION, WT. PERCENT No. 1 0.17 e No. 3 0.05 No. 5 0.0010 ) ) (1) No. 7 0.0010 e (1) ,Sased upon analysis of T-9 so'lution from AP&L containing 30 percent sodium thi.> sulfate pentahydrate. i 6-41 .o ',
m 2 TAitLE 6-4 A
SUMMARY
OF METALL0 GRAPHIC EXAMINATION OF 4", SPECIMENS FROM SUPPLIER NO. I PER ASTM A202, PRACTICE A % CRAIN BOUNDARY CAMB1DE ENVELOPE Pickli.ne ~ .smen Heat Pipe Size Carbon OD OD ID ID M.tx. ser Number Inch Wt. % 0-0.010 'O.010-0.025 Center 0-0.010** 0.010"0.025 Depth %NSAS. UNIT I ~ .ked s 800201 to x.165 0.08 10 10 40 10 10 0.0025 800201 10 x.165 0.08 0 0 20 0 0 0.0020 800201 10 x.165 0.08 0 5 30 0 5 0.001 8050929 10 x 165
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0 0 0 0 0.001 800201 10 x.165 0.08 0 5 30 0 5 0.002 7T2004 6 x.134 0.05 0 0 0 0 0 0.001 7T2004 i x.134 0.03 0 0 0 0 0 0.001 2P4063 4 x.120 0.055 0 0 0 2 6 0 0.001 M-4359 4 x.120 NA 0 0 0 0 0 0.001 4348 4 x.120 NA 0 0 0 0 0 0.001 0 7T-2004 6 x.134 0.05 0 0 0 ,0 0 0.001 ER PIPE 14519 24 x 3/8. 0.063 0 0 10 0 0 0.001 71709 12 x.180 0.057 0 80 0 5 0.0006 72174 6 x.134 0.066 0 10 90 0 5 0.001 82619 14 - .2 50 0.065 0 5 70 0 0 0.0006 230254 6x.134 0.060 0 0 30 0 0 0.0009 321081 10 x.250 0.068 0 0' 5 0 0 0.0012 800208 6 x.134 0.080 5 5 40 0 5 0.000o 800413 8 x.148 0.050 0 0 0 0 0 0.00u9 8044473 6 x.134 0.064 0 0 0 0 0 0.0006 0 8050153 12 x.250 0.050 5 to 90 5 10 'O.0006 1 3082471 12 x.250 0.057 0 0 0 0 0 0.0000 2 7T1852 10 x.165 0.056 0 0 0 0 0 0.0005 3 7T1972 6 x.134 0.055 0 0 5 0 0 0.0005 4 9T3029 8 x.148 0.042 0 0 0 0 0 0.0006 5 207812 5 N.A. 0 0 5 0 0 0.0009 7T2544 8 x.134 H.A. 0 0 0 0 0 0.0008 72275 8 x.134 N.A. 0 10 10 0 5 0.0006 335874 10 x.250 d.A. 0 5 5 0 0 0.001 71778 10 x.165 0.07 0 10 95 0 10 0.0006 8044361 10 x.165 N.A. 0 0 0 0 0 0.001 308384 10 x.165 N.A. 0 5 90 0 5 0.000s 19219 10 x.165 N.A. 0 5 95 0 5 0.001 71804 10 x.165 N.A. 0 5 90 0 5 0.000s 9T2977 10 x.165 N.A. 0 0 0 0 0 0.001 0 9T2977 10 x.165 N.A. 0 0 0 0 0 0.001 1-7T2600 14 x.250 N.A. 0 0 95 0 0 0.001 71778 10 x.155 0.07 0 0 95 0 5 0.001 71683 6 x.134 0.0 74 0 10 98* O 10 0.001 F61086 18 x.250 0.05 0 5 90 0 5 0.001 9T3029 8 x.250 0.042 0 5 30 0 5 0.001 l F61086 18 x.250 0.05 0 15 40 0 15 n.001 9T 3209.. 8 x.250 0.042 0 0 5 0 0 0.001 71778 10 x.165 0.07 5 15 95 0 10 0.001 71778 10 x.165 0.07 0 20 95 5 20 0.001 ' Reject per Prac t ice A =. -.... : i.u. 6-42 a
v In addition to the specimens from Unit 1, thirty-four spetimens from thin-w.illed piping, representing 27 dif ferent heats of Type 304 stainless steel manuf ac ture.1 by Supplier No. I and installed in other power plants where Bechtel is involved, were also subjetted to Practices A and E. The test results for the+e heats are given in Table 6-4 listed under "Other Pipe." 'A review of the data in Table 6-4 indicates the following: 1. A wide range of sensitization was produced in Type 30'e stai.ilens steel pipe when solution heat-treated using the still air tooling practite, ranging from nil at the sur' fate to approximately 95 per cent toward the center; 2. In general, heats containing lower percentages of..arbon produte less sensitization. ~ 3. There appears to be no correlation between degree of sensitization and the dep:h of surface etching from pickling. 5 4. Only une heat, Heat Number 71683, which was manuf actured by Supplier No. I and installed in another power plant, failed the Practice A staeening test. 5. Thin walled Type 304 stainless steel pipe manufactured by Supplidr No. 1, but not installed in Unit I, is senritized to about the ame degree as that in J Unit 1. 6. All specimens tested passed Practice E of ASTM-A262. 6.8.2 Sensitization as a Function of Heat Treatment and 'a'elding Effect on Cracking Susceptibility Two series of laboratory tests vete cor. ducted to determine how heat treat tool-ing practice and welding variables af fected the degrec of sensitization in Type 304 stainless steel and its subsequent sensitivity to intergranuls.r tracking. The degree of sensitization was evaluated by Prat tice 'A (metallograp. tic examination after etching with oxtlic acid) and the sensitivity to intergranelar tracking by Practice E (bend testing af ter 24 hours exposure to boiling aridified toppe-sulfate plus copper metal solution). Variables in the tests included: (1) ta'rbon content; (2) welding heat input; and, (3) tooling rate from solut ion annealing temperature. The solution annealing was conducted at 1950 F for 30 minutes. The welding'was performed using Bechtel procedure P8-T-Ag (CTAd). The welding c urrent was maintainad in the 60 - 70 ampere range. The maximum interpass temperature used was 350 F. The following materials were used in the first series of tests: 1. 10-i nc's schedule 10 pipe, HT 800201 Type 304 austenitic staint-,s steel from Unit 1,40.075 percent carbon content manufactured by Supplier No. 1. Speti-mens were taken from two pipe sectinns, the spools containing t racks number 2 and 3. 2. 10-inch schedule 10 pipe Type 304L austenit it st ainless steel, 0.029 percent carbon content, manufac tured by Supplier No. 2. Heat No. 2i0576. 3. 10-inch sched sie 10 pipe. Type 304 austenitic staialess steel. Heat No. unknown, AST>l A-312. 0.07 percent carbon manufactured by Supplier No. 3. 6-43 w~ m < m-.-w% y--,-
l The Londitions of Series No. I testing and results are given in Table 6-5. The results inditate that prior sensitization of the Type 304 base material produc es a heat-af fec ted zone on welding more sensitive to tracking than a prior complately solution annealed structure; that 3 pass welding of Type 304 stainless steel produt'es 4.more track-sensitive strutture than 2 pass welding; and that low tarbon Type 304L is not sensitive to cooling rate and welding variables as measured by these tests. A second series of tests was conducted on three 8-inth schedule 10. Type 304 stainless steel pipe samples purchased from three suppliers, plus a welded 10-inch schedule 10 pipe section from Heat No. 800201, Unit 1; and another 10-inth schedule 10 Type 304 stainless steel pipe sample manufactured by the Supplier No. 1. The 8-inch pipe samples were manuf actured by : (1) Supplier No. 1, Heat No. 35476-04, (2) Supplier No. 3. Heat No. 2405'30; (3) and, Supplier No. 4, Heat No. 31139. The details of these tests and the results are given in Table 6-6. These results confirm the previous results on the tests in series 1 that 3 pass welding produces a more crack-sensitive microstructure in Type 304 austenitic stair.less steel than does 2 pass welding. (Note: The use of 2 and 3 pass welding techniques in the labor-atory is not meant to simulate production welding. This means was used in a labor-atory stuJy of the total heat input to the HAZ. The number of welding passes used 8' in field or shop welding is to a large extent controlled by the pipe fit-up require-ments.) However, the results also indicate that thare are probably other lesser f actors which influence heat-af fected zone sensitization in addition to priar sensit-ization. The two series of tests indicate that, in general, resistance to intergranular stress-assisted corrosion cracking is improved by: (1) lowering the carbon content in austenitic staioless steels; (2) by reducing the time that the veld heat-af fec ted zone is in the sensiti=3ng tecperature range; and, (3) by using a. properly solution treated material with a microstructure free from carbides prior to welding. o.8.3 Stress Corrosion Test,s A series of stress corrosion tests were conducted in solutions containing crystals of sodium thiosulfate pentahydrate obtained from Arkansas Power and Light Company. The tests were conducted in solutions of one and twenty percent sodium thiosulfate pentahydrate at a te=perature range of 150 F - 170 F. The one percent solution contained 300 ppm of added thloride. Bent beam specimens were placed in fixtures and exposed to the corrodent in total iceersion. Specimens approximately 1/2 inch x 4 inch were cut from welded and unwelded Type 304 stainless steel pipe purchased to ASTM.-A358. Some of the pipe was procured for this program. Other pipe from Unit I was also used for a specimen source. All spetimens were cut from the longitudinal direction of the pipe. All specimens (except one) were pickled, prior to testing, in a solut ion of 20 percent nitric ac id and two percent hydrofluoric ac id. The speci-mens were placed in a three point bending fixture and bent beyond the yield paint. The spec imens were bent to stress the root of the weld or the ID surfaces of base metal specimens. See Figure 6-4 for photograph of bending fixtures complete with speti-mens. The fixtures were placed in glass containers equipped with reflux tondensars. Figure 6-5 is a photograph of the two corrosion setups. The solutions were heated with hot plates. Seventeen specimens were exposed to tne solution sontaining one percent sodium thiosulfate pentahydrate plus 300 ppm added chloride, and ten speti-mens were exposed to the twenty percent thiosulf ate aclut ion. Exposures in these environments lasted for -32 days. 6-44
-unw w w, TABLE 6-5 THE RESULTS OF ASTM A262 PRACTICE E TEST ON THREE 10" DIAMETER SCHEDULE 10 TYPE.304 PIPE SP2CIME.'s SLMIES NO. A ee Specimen Test Heat Treatment Microstructure Specimen Resul t s Source No. Temp. Cooling Rate Pract ice A** Ided No. Pract ice E Ut:IT 1 Crack No. 3 pipe 1 As received 304 0.0752 C (still air cooled) 10,10,40,10,10 No No crac ks HT 800201 e a i ASTM A358 2 1950F Still air cool 0,0,0,0,0 No 32 No cracks 3 1950F Water quenched 0,0,0,0,0 No ", 34 No tracks 4 1950F Cooled between 10,10,70,16,5 No 33 Cracks o.4 methanis-bricks at 450F/hr ally polished side 3 & cut side (cross-section) but not j as-received surfat. 5 1950F Furnace cooled 100,100,100,100, at 330F/hr 60 No 35 Severe tratking when bent 45 degrees 6 As received kelded 36-37 HAZ-small t rac ks 7 1950F Water quenched Velded 18-39 RAZ-no t rat ks A As received 2 pass 329 HAZ-small t rac ks weld (f.b.)* RAZ-t rac ks on t ut side only (r.b.) 9 As received 3 pass 331 HAZ-snall trasks weld (f.b.) HAZ-small t ras ks (r.b.) 10 1950F Fan air cool 2 pass 333 RAZ-small t rac ks weld (r.b.) HAZ-bordestine ( f.b. ) 11 1950F Fan air cool 3 pass 3 34 HAZ-small trasks weld (r.b.) HAZ-small tratks
== ( f.b. ) 6-45
~ -, - -. e..,......... TAMLE 6-5 (continued) i i 3 No. 2 pipe 12 As received Field 232 HAZ no cracks (r.b. ' 0751 C (still air cooled) Weld HAZ-no cracks (f.b. (bath of the above 8201 J58 specimens show er No. 1 cracks on cut sido. cross sections) 13 As received 2 pass 225 NAZ-scrall cracks weld (r.b.) HAZ-no cracks (f.b. 14 As received 3 pass 227 HAZ-nocracks(r.b.l weld HAZ-small cracks (f.b.) 15 1950F Water quenched 3 pass 230 HAZ-no cracks (r.h. weld HAZ-no cracks ( f.b. - ' LIER NO. 2 16 As received. 0,0,0,0,0 No M1 Not tested i . HT 240576 _ (water quenched) !$/0.029 C 1 A358 17 1950F Scill air cooled 0,0,0,0,0 No M2 No cracks 18 Water quenched 0,0,0,0,0 No M4 No cracks 19 Slow cooled (450F/hr) 0,2,5,2,0 No M3 No cracks 20 Furnace cooled (330F/hr) 0,5,5,5,0 No MS No cracks 21 As received Welded M6-M7 KAZ-no cr acks (r.b. & f.b.) 22 1950F Furnace cooled Weided M8-M9 HAZ-no cracks (r.b. & f.b. ) ___ LER NO. 3 23 As received 0,0,0,0,0 No K1 Not tested f un-known (water quent.hed) i C \\-312 24 1950F Still air cooled 0,0,0,0,0 No K2 No cracks 25 Ware quenched 0,0,0,0,0 No K4 No cracks 26 Slow c'ooled (450F/hr) 5,15,40,5,2 No K3 No cracks 27 Furnace cooled (330F/hr) 30,90,100,40,5 No K5 Bordertine 28 1950F Slowly cooled Wclded K8-K9 HAZ-no cracks (450F/hr) (r.b. & f.b.) 29 As received 3 pass K12 HAZ-no cracks weld (r.b. & E.b.) ): 6-46 6 e
. ~ ~ " ~. - ~ - . -,. ~... - ..e.-..-..- TABLE 6-5 (Cont inued) 30 1950F Furnace cooled-3 pass (11 HAZ-cracks on tut 2 weld sides only (r.b. & f.b.) 31 Furnace cooled No KID Edge and side cracks o.ily = =-...... _.
- f.b. : face bend; r.b.: root bend s
- The numbers indicate Z grain boundary ditching at C - 0.01", 0.01 - 0.02",
mid-thickness. 0.02" - 0.01", and 0.01" - 0" from either surface. e 6 G l l l 6-47 -e,
~ ~., mm .. m -. s... TA81.E 6-6 RESULTS OF ASTM-A262 PRACTICE A AND PRACTICE E TESTS ON WELDED TYPE 304 STAINLESS STEEL Pit'E SAMPLE'. SERIES NO. 2 frlc~EEEe E Base Metal ~ Base Metal Number Resufis ~~~~~ n Conditioning Microstructure Weld Number Shallow Deep before Waldina Practice A* Passes Tests Cracks Cracks y .c No. I As received .0.0,0,0,0 2 10 1 7 (still air e s '6-04 cooled) 3. 10 _0 10 'j. -dule 10 ) y i 55 8 s a i
- r No. 1 As received 0,10,95,10,0 2
5 0 0 (still air t 3 5 0 0 '8 cooled) iedule 10 1950F, W.Q. 0,0,0,0,0 2 5 1 0 g 158 3 5 t 2 i
- r No. 1 As received 10,10,40,10,10 3
3 1 2 Field Weld, i l01 Unit 1 (still air 158 cooled) tr No. 3 As received 0,20,40,20,0 2 5 2 0 i30 (water quenched) tdule 10 3 5 2 2 ) 158 tr No. 4 As received 0,0,0,0,0 2 5 2 0 19 (water-quenched) .Jule 10 3 5 3 0 15 8
- NumbJr indicates *. grain boundary ditching at 0.000 - 0.010*
O.025 - 0.010" t 0.010 - 0.025" 0.310 - 0.000" from either surfate i Mid thickness i. L-48 .i 9
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L u...,...:.+. N W 'M. e r.. ~.~r$ i h1 o. h. g-. 'x,C ~ r ..4 . A'aX} Figure 6-4 Corrosion specimens in fixtures. The fixture on the right was for the l percent sodium thiosulfate exposure. The fixture on the left was for ti.e 20 percent sodium thiosulfate exposure 6-49
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Sf[.f'I. ~ ::g*. 'j, l}, g -... a y2.. ..r-Jp +.: a t, g..... u,. . r. g_ _. 1 Figure 6-5. A photograph of the corrosion set-ups. 4 e .4 -a 6-50 l I i .. -.. ~ ~..., l O
-+ w -w 9sur y Though both solutions were approximately n-utral in pH at the beginneng of the tests, decomposition of the thiosulfate was apparent almost immediately. The detoopos iton was evident by the depo'sition of a yellow substante (probably ele-mental sul fur) and by the evolut ion of sul fur dioxide gas (by odor). Figure 6-6 is a photograph of the container. with 20 pertent Sodium thiosul fate showing the yellow trystals presumed to be sulfur from the decomposition of the sodium thiosul f ate. The pH of both solutions dropped to the 4 to 5 pH range by the end of the te4* s. Table 6-7 tontains a description of the specimens that were exposed and the results of the exposures. The spet imens were examined af ter the exposures with the ai f of a binoc ular sitrost ope at 30X. Some tracks were visible at this magni fic at ion. All of the spec imens were then bent 180 degrees similar to the bending in Prac t ic e E to determine if intergranular torrosion had escurred. All of the welded spec imens in the one percent thiosulfate (with 300 ppa added thloride) exposure showed t rat king in the heat-affected zone after bending. Three of the specimfhs fr8m the 26 persent sodium thiosulfate exposure showed any evidente of intergranular strac k on the sur-faces. s The results of the initial exposures of Type 304 stainless steel welded and un-welded spec imens to sodium thiosul fate under slightly ac idic (nndit ions were indi-tative of the susceptibility of the heat-atfected cones of welds 8to intergranular attack by sodium thiosulfate and/or its decomposition products. The exposure to one percent sodium thiosulfate with 300 pps added chloride resulted in'intercranular attack. Exposure to the more concentrated solut ion (10 percent sodium t5iosulfate) did not give as severe an attack. The 20 partent sodium thiosul fate solut ion. sire nearly represents the composition of the solution of the sodium thiosul f ate storaga tank and piping system, but was not treated to give the alkalinity required to prevent decomposition of the sodium thiosul fate. The sodium thiosulfate at the plant is treated with sodium hydroxide to give an sikaline condition (pH 9.6) to enhance the stability of the solution. 6.9 SOLUTION TREATING METHODS BY PIPE MANUFACTUREP.S The failed Unit I pipe was cooled in still air from the solution treating tempers-ture at the time of manufacture. We understand that is is this manuf ac turer's recular practice for cooling thin walled pipe (less than 1/2 inch thick) f rom tha salution heat treating temperature. A survey was conducted to determine the heat treating practices of other manufacturers who supplied thin-wall Type 304 stainless steel pipe to Unit 1. Five manufacturers replied to the survey, all indicating water quenching as their regular practice in the time period involved. These replies were not confirced by plant visit s. Three manuf ac turers sent samples representina their practices. These samples were 1-1/2 inthes diameter x 0.145 inth-thin k; 2 inches diametcr x 0.218 inth-thick; and 8 inches diameter x 0.148 inth-thi(k. Or.l y the 2-inch diameter x 0.218 inch-thick saeple showed a so all amount of carbide precipitat ion at midthic kness. All samples were water quenched from the solat ion treating temperature. 6.10 EVALUATION OF SHOP WELDS FROM CN1f 1 One-half of a typis al shop weld and one-hal f of a typical field weld were rec eived from Unit I for additional evaluation. The other half of each weld was sent to South-west Research Institute for a similar evaluation. In addition, three other s5ap welds, selected at random from the crossover line, were sent to San Francisco by MFSQC3 per-6-51
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.n. 1 Ahl t..- / ltLSPl,th OF CORROSibN TESTING IN 'Sulall'M Ih i!' SULF A l t. !;ol.18 81'sN5
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SPECIMEN DESCRIPTibt. TESTING AFh.d LFP95 E'_ TEST' SOLUTION A; 11 N'a25201 SH2O + 500 ppm Nat! 1. Crack Us. 2 Pipe with weld f rom l'ait I, Ht. No. M00201, Cracks Supplier No. 1 2.' Field Weld - 6A, l'esit I, Ht. Ms. 800201, Supplier No. I Cra6ks .l. HL. No. 72275, Supplier No. 1 - 2 pass welded to Cra6ks Ht. No. 35470-04, Supplier No. I 4. Ht. No. 35476-04, Supplier No. 1, Parent Matal No Cracks 4 5. Ht. No. 35476-04, Supplier No. 1 - 3 pass welded to Cra6ks Ht. No. 31139, Supplier No. 4 6. Ht. No. 35476-04, Supplier No. 1 - 3 pass welded to Cr.(ks 88 Ht. No. 240530, Supplier No. 3 7. Crack No. 2 pipe, Ht. No. 800201, Supplier No. 1. Parent Metal No Cracks 8. Same as 7 Cra6ks 9. Same as 5' Cretks 10. Ht. No. 35476-04, Supplier No. 1 - 2 pass welded to Cra.ks 4t. No. 31139, Supplier No. 4 Same as 2 Cracks 12. Ht. No. 35476-04, Supplier No. 1 - 2 pass valded to Cracks Ht. No. 240530, Supplier No. 3 13. Same as 7 No Cracks 14 Same as 5 Cracks 15. Ht. No. 35476-04, SHT40, Soplier No. 1 - 3 pcss welded to Cracks Ht. No. 7,2275, Supplier No. I 16. Same as 1 Cracks 1 17. Ht. No. 35476-04, SHr.0 S..pplier No. 1. Parent Metal No Cratka i list SOLUTION B; 29% Na2S203 $H2O 18. Same.is 5 cr wks 19. Same as 2 No Cracks 20. Same as 12 Crask$ 21. Same as 2 4.1 Crr.ks 22. Same as 3 L. Cra.k< 23. _Same as 6 Na Crnk. 24. Same as 15 N.,
- r.n L.
25. Sama as ! Cru k4 26. Same as,10 N Crisks 27. Same as 7 No Crake
~ j l ~ sonnel at the site. All of these welds were suppasedly " good" welds, that is, they did n9t show indicat ions in radiographic examination in November.1974. These welds were received in San Francisco in May,1975. These welds were all from the crossover and pump suction loop that had the previously cracked pipe. The pipe sections of all welds were from liest No. 800201, the same heat in Giich the other' i tracks otturred. For the purpose of identification, the hal f ring field weld was numbered FW-6A and the half ring shop weld was numbered SW-F. The three additional shop welded specimens, selected at random, were numbered S-2 S-3, an'd S-4. The other halves of field weld FW-6A and shop weld SW-F were examined at the Southwest Research Institute. All five welded sections were visually examined up to 30X. All welds and heat-sf fected zones had exhibited corrosion pits on the inside surfaces. In addition, the field weld FW-6A, the shop weld SW-F, and the shop weld S-3 showed evidence of cracks in the heat-af fected zones of the pipe sections approximately 1/3 to 1/4 inch from the welds. These cracks were much wider on the insida surfaces than on the exterior surfaces and appeared visually very similar to the ones examined previously. Figures 6-7 through 6-13 are photographs detailing the appearante of these welded specimens showing the corrosion pits and cracks. Two shop welds, S-2 and S-3, and one field weld FW-6A, were subjected to radio-graphic examination which revealed indic 4tions in RAZ of shop weld S-3 and tonfirmed the tracking in FW-6A. From the radiographs the indications appeared to encompass approximately half of the pipe circumference. Liquid penetrant examinati6n revealed that the track was approximately half the circumference on the ID surface, but penatrated to the CD surface for only approximately one inch. On comparing the. radiographs of S-2 and S-3 with the liquid penetrant indications on the 10 surfaces, it became apparent that the radiographic examination did not reveal the total extent of the intergra?ular damage. This is illustrated in Figures 6-14 and 6-15. Figure 6-14 shows prints from radiographs showing crack indications in the heat-affetted zone of shop weld S-3. Part (c) of Figure 6-14 shows a print of an area which does not show an indication readily seen in Figure 6-15. The pipe cactions were bent 30 degrees to open up the cracks for photographic purposes. In this area the intergranular trac ks were tight and did not penetrate to the OD surface. The radiograph of shop weld S-2 did not reveal any indication at all. However, liquid penetrant inspection revealed a small crack approximately 1/2 inon long in the RAZ of the inside surface of the pipe section. Radiography is basically a volumetric NDE process and the above observation may indicate that it has less than perfest capability to resolve very tight intergranular cracking or tery small and shallow tracking. Metallographic examination of all four cracked pipes indic ted the same type of cracking as previously noted in leaks 1, 2, and 3; intergranular cracking in the heat-af fected zone, approximately 1/4-inch from the weld and originat ing on the j IP surfaces. Figure 6-16 illustrates the cracking and the pitting characteristic'of all four of the welds. Figure 6-17 shows the outside surface profile of SW-F showing ] the sharp grdin boundary penetration so characteristic of Heat No. 800201. An exami-nation of many heats indic ates that grain boundary attack during pickling is not unusual. The maximum depth of pickling attack noted in Heat No. 800201, however,is approxicately twice that of any other heat examined. The profile of shop weld S-3 is typical of the four shop welds examined and may be compared to the profile of field weld FW-6A in Figure 6-18. There is practically no di f ference in the degree of sensitizat ion of the HA7. hetween the e
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& ~~ R I e 'e (a) Etched in oxalle acid 4X UW50MW-1'V e 3s O;.?,.,.,.. -.. x.,l 2. 1: b f$?.1'bhh. d,.'5O$isDJh:h l V [IN?!$Yldhs '^2*. ::.h;;'Q:ts 4 _ QM*. (b) As polished 12X Shop Weld S'.'/-F Figure 6-16.Macrographs showing the crack marked by the arrows in 1. - tre 10. (b) shows the section through the pit marked by the white vrow in Figure 11 (c). 6-64 l
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~.__ 1 .w shop weld and the' field weld indicating about an equal degree of susceptibility { co stress-assisted corrosion cracking for shop and field welds. 6.11 FIELD INSFECTION A random sampling of areas adjacent to 46 welds in the Reactor Building Spray Systes pipe was accomplished by ultrasonic and raciographic methods. Of thcse areas, five showed crack-like indications in the radiogriphs. It was concluded that ultrasonic testing is not a satisfactory method of examining pipe for this type of defect aad that radiography wa's the more satisfactoty (although not completely satisfactory) method of examination. Pipe sections with these indications were sent to Southwest Research Institute for examination. 6.12 OUTSIDE CONSULTANTS Southwest Research Institute of San Antonio, Texas was retained to assist in thia 8 investigation. Mr. Herman Burgherd, Jr., was assigned as Project Engineer. Mr. Burghard assisted in the original laboratory-investigation of the pipe failures reported in Abnormal Occurrence Report No. 59-313/74-llA and in the pipe surf ace survey at Arkansas Nuclear One, Unit 1. In addition, Southwest Research conducted en an independent investigation in the San Antasio Laboratcry of the following: 6.12.1 A metallurgical evaluation af the five indications found by MF&QCS in radio-graphic examination of 46 areas near welds in the Reactor Buildics Spray System pipe in Unit 1. 6.12.2 Metallographic exasinations by the procedures of Practice A, ASTM-A262 of 10 trepanned disk samples of pipe from Unit 1 (half of each sample was examined by MF&QCS and the results are reported in Table 6-4 of this report). 6.12.3 A metallurgical examination of oce-half of a shop weld and one-half of a field weld from the crossover line of Unit 1. The other half of each weid was exami-ned by MF&QCS and the results are included i= this report. 6.12.4 A report of the investigation at Southwest Research was prepared end is included as an Appendix to this report. The principal conclusions of Southwest Research Institute are: 6.12.5 The tailures occurred by intergranular stress-corrosion cracking, 6.12.6 Chloride contamination appears to have contributed to the failures, but is i not the sole cause. 6.12.7 The high carbon content and large grain size of Heat No. 809201 are likely to have enhanced its susceptibility to intergranulse stress-corrosion cracking. 6.12.8 There is no direct evidence that tne partially sensitized structure of Heat No. 800201 is, in itself, a contribut'ng fa: tor to cracking. 6.12.9 The failures are attributed to the ce=ulative influence of a combination of several factors. a) High carbon content of Heat No. 600201. b) Residual welding ar
- fit up stresses, c)
Chloride contamination. 6-67 .A',
I d) Degree of sensitization in RAZ associated with welding procedure. e) Oxygen content of water and stagnant conditions. Each factor alone probably is an insufficient condition to cause cracking. ( 6.12.10 There is no evidance that cracking is likely to occur in*cther piping with lower carbon content and normal structure. 6.13 CONCLUSIONS The principal conclusions of Southwest Research Institute are in general agreement with the findings of Mr&QCS. Tha lt electron microprobe analyuis of chloride ions in and near the cracked suffices is an important addition to the MF&QCS findings since they have determined that chlorides were de(instely present. 6 h 4 N 9 6-68
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' <e@ w BIBL10CRAPHY J. D. Harston and J. C. Sectly, Stress Corrosion of Type 304 1. Steel in H2SO4/ Nacl Environstnts at Room Temperature. Corrosion, 25, 493 (December 1969). 2. C. T. Ward, D. L. Mathis, and P. W. Staehle, Research in Progress. e Intergranular Attack of Sensit ed Austenitic Stainless Steel by W.ser i Containing Fluoride lans, Cotrosion, 25, 394 (September 1969). l 3. L. R. Scharf stein and W. F. Brindley, Chloride Stress Corrosion Cracking of Austenitic Stainless Steel - Effect of Temperature and pH, Corrosion, p588t,-(December 1958). 4. H. C. Burghard, H. B. Norris and R. D. WVlie Examination of Upper Liquid Level Line from Elk River Reactor, USAEC Reprit O'*3I-1228-P9-16 (27 February 1960). 5. W. E. Berry, E. L White and W. K. Boyd, Stress Corrosion Cracking of Sensitized Stainless in Oxyger.erated High Temperature Water, Corrosion 29, 451 (December 1973). 6. Fundamentals of Analvtical C'eoistry - Skoog and West; Holt, Rinehart a and Winscon, P 467 (1903). 7. J. J. Heller and C. R. Prescott, Cracking of Stainless Steels in Wet Sulfidic Environments in Refinery Units, Materials Protection Vol. 4,
- 14. (September 1965).
8. A. J. Brophy, Stress Corrosion Cracking of Austenitic Stainless Steels in Refinery Environments, Materials Protection. (May 1974). C. H. Saman*, Stress Corrosion Cracking Susceptibility of Staieless 9. Steels and Nickel-Base Alloys in Polythicaic Acids and Acid Copper ) Stilfate Solut ion, Corrosion. Vol. 29, ( Argust 1964). l i l i l . _. ~.... 1}}