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Revision as of 15:10, 27 February 2020
| ML19322B868 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/31/1970 |
| From: | BABCOCK & WILCOX CO. |
| To: | |
| References | |
| BAW-1363, NUDOCS 7912060699 | |
| Download: ML19322B868 (42) | |
Text
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Decembe r 19 3 3 8 Analysis and Resolution of Dve-Penetrant D Indications in Submerged Arc Weld Cladding of Reactor Coolant System Straight Pipmg Duke Power Company Oconce Unit 1 L U D D
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B AW- 1363 December 1970 3 3 9 . Analysis and Resolution of Dye-Penetrant Indications in Submerged Arc Weld Cladding of Reactor Coolant System Straight Piping Duke Power Company Oconee Unit 1 5 3 3 , l 5 I I I g BABCOCK & WII4OX 3 Nuclear Power Generation Department Components Engineering Barberton, Ohio Babcock & Wilcox I
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5 CONTENTS
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- 1. INTRODuCT10N............................. 1 II. DESCRIPTION OF STRAIGHT PIPING PROBLEM . . . . . 2
- m. m vESuc AuON -o PmDmOS . . . . . . . . . . . . . . . . . s A. Investigation of Manufacturing Aspects . . . . . . . . . . . 5 D. Investigation of Oconee Umt 1 Problem and De finition of P roble m. . . . . . . . . . . . . . . . . . . . 7 C. Investigation of Manufacturing Mstory . . . . . . . . . . . 9 D. La bo ra to ry Exarninaticns . . . . . . . . . . . . . . . . . . . . 10 E. Dis cus sion of Inve s tigation . . . . . . . . . . . . . . . . . . . 13 IV. CONCLUSION OF INVESTIGATION ............... 16 A. Corrective Action to Oconee 1 Coolant System . . . . . . 16 B. Corrective Action to Manufat.:uring Processes and Quality Control Improvements . . . . . . . . . . . . . . 17 V. S U M MAR Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 APPENDIXES I. NDT Procedure for Dye-Penetrant Inspection of the Weld-Deposited Cladding in the Coolant Piping System of Oconee Unit 1. . . . . . . . . . . . 1-1 II. Fabrication Procedure for the ModiGeation of the B - 67 As s e mbly in M t. Ve r non . . . . . . . . . . II- 1 E
I Table List of Tables I. Dye-Penetrant Examination of Reactor Coolant Piping . . . 3 II. Chemical Analysis of Five Representative Areas in the 20-Inch-14ng Section of Excess Material Removed From the B-67 Straight Inlet Pipe at Mt. Vernon . . . . . . . 20 I I - 111 - BaM & h1
7 . ..-. . -. hl I. INTRODUCTION
- f. In the course of t.ie paping system modificati instali uon ut a replacement cool.a. pump ons incidental to the the s:raight section of the B-67 clad pipi. Oconee Unit 1, Dae rowe r.
( the Mt. Vernon Works of Babcock k Wil ng assembly was returned to { of this rework a routine dye penetrant coxexaminati for rework. In the course tions in the cladding. on revealed some indica-I grinding and replaced by welding in Mt. VernonThe affec i In order to assure that the balance Unit I piping system did not show a simila ng inof thethe claddi Oconee r I spection of all of the cladding in the Oconee Unit Icondition, a complete rein-was initiated. cooling piping system This report is addressed specifically to the w i tion to the cladding on the straight secti ork done with rela-the investigation and findings of theopr blons of the coolant piping system;
; ing and non-centructive testing; and th em with respect to manufactur-respect to processes. the Oconee I coolant system straighte corrective actions take An accompanying report, pipe and manufacturing relating to cladding on the elbows of the coolantBAW-1364, addresse system piping.
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II. DESCRIPTION OF STRAIGHT PIPING PROBLEM 1 Straight sections of the 28-in, and 36-in. main coolant piping for l Duke Power Company's Oconce Unit I were fabricated by cladding l carbon steel with austenitic stainless steel by a multiple elec: rode sub-merged arc process. Following complete installation of the B-67 assem-bli main coolant piping, a straight section of the B-t>7 28 ~n. return coolant piping was removed to permit installation of the Westinghouse replacement reactor coolant pump, and was returned to the shop for re wo rk. Micro-fissures, as defined in section III of this report, and fre-quently referred to as fissures, were found in the cladding of the B-67 assembly during the course of routine shop inspection. Complete dye-penetrant inspection of all other remaining arc-weld-clad piping in Unit 1, carried out as a result of the B-67 inspection findings, revealed small amount of micro-fissuring in one other assembly, B-57. The remaining ten assemblies showed no eddence of fissures. As discussed in section III-D of this report, laboratory tests on excess material determined that the cladding was not embrittled, that it was completely 1 satisfactory for its intended service and that all of the B-67 fissures were removed by grinding or replacement after identification by dye-penetrant examination. A complete record of the results of the re-examination by dye-penetrant procedures of the Oconee Unit I weld metal cladding of the l reactor coolant system piping is listed below. l J l I 1 1 I 1 ! Babcock & Wilcox
I Table 1. Dye-Penetrant Examination of Reactor Coolant Tipe Cladding Inspection Completion
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As sembly Re sults Da *.e A-57 PT-OK 9/4/70 B-67 PT - Reject 9/4/70
$ Linear Fissuring 3 in Vertical Run B-45 PT-OK 9/4/70 B-41 PT-OK 9/14/70 A-67 PT-OK 9/9/70 B-46 PT-OK 9/11/70 A-33 PT-OK 9/12/70 I A-32 A-24-1 (A leop)
PT-OK PT-OK 9/12/70 9/14/70 A-24-2 (B Loop) PT-OK I B-40 PT-OK 9/14/70 9/14/70 B-37 PT - Reject 9/16/70 Linear Indications 1 in Vertical Run I e All straig'nt pipe All the Liquid Penetrant Inspection performed at Duke Power Corppany was witnessed by Duke Power Inspectors. For the df e-pene-trant inspection and weld repair procedures utilized in connectiors with sho,3 and site work, see Appendixes I and II. I To summarize this report, the following assemblies required corrective action:
,As s embly Results B-67 Removed and shipped to Mt. Vernon for repai rs B-57 1 area 12" x 18" linea r indications blend ground I and PT'd clear on 9/16/70 at the job site.
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+F See Figure 3. Reactor Coolant Loop Isometric for further clarifi-cation of assemblies and location of individual components. Segments of A-57 B-67, A-67 and B-57 were cut out of the coolant system as "
typically shown on Figure 3 and returned to Mount Vernon for rework. The segments were snortened to permit the installation of a leger pump suction nozzle associated with the Westinghouse reactor coolant pump. In addition, assemblies B-40, B-41, B-45 and B-46 were modified at the job site as typically shown on Figure 3. The segments were modi-fled to meet new system angular configuration of the pu.np discharge - associated with the reactor coolant piping changeover. M M l i - i e l l l 4 Babcock & Wilcox
-.-n !I III. INVESTIGATION AND FINDINGS A. Investigation of Manufacturing Aspects Straight run main coolant piping for the Duke Power Compar.y's Unit I reactor coolant system at Oconee was fabricated oy cladding carbon steel pipe with austenitic stainless steel weld metal. The base material for this pipe is in accordance with A106 Grade C, ard was quenched and tempered to enhance its toughness prior to cladding.
Cladding was done with the submerged are welding process which deposits a single layer of stainlet 5 steel over*ay. The require- ' rnents for chemical analysis of the deposited cladding were 17% mini- , mum chromium, 7% minimum nickel, and 0.08% maximum carbon. All cladding for Oconee Unit I was done at BL*X's Barbe rton Works. The first four assemblies (B-67. A-57. B-45, and B-41) were completed and shipped to the const.uction site from the Barberton Wo rks . Pipe manufacturing operations were later moved to the Mount Vernon Works and the remaining eight piping assemblies (A-67 B-57, B-40, B-46, A-32, A-33, A-24-I and A-24-2), for Oconec Unit I were shipped from the re. The significant difference in fabrication methods between me two plants is that final dye-penetrant inspection of the submerged ar-cladding on *he Barberton-shipped assemblies was performed prior to post weld stress relief heat treatment rather than afterward. This was not in accordance with the requirements of the BLW internal specifica-tion which stated that final non-destructive testing should follow heat treatment of piping co nponcats. The stress relief heat treatment had been shifted to a later sequence in the manufacturing process and the dye-penetrant inspection sequence was not shifted in a parallel manner. Both Quality Control Engineering and Process Engineering personnel have since been instructed to assure in the future that all process se-quences for c'. adding operations are carefully reviewed for conformance I with specification in order to prevent a reoccurrence of this problem. Post-weld heat treatments greatly facilitate the detection of micro-fis-sures by dye-penetrant inspe: tion. It was recognized that stririgent control standards had to be set up and maintained in order to assure uniform high quality in the M & EN
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l l caau de r .;t. The pmca dure employed for cladding this pipe had been j l successfully employed for cladding many reac'.or vessel shell course. I made of A302 Grade B low alloy steel and was requalified for the A-106 l Grade C material. The welding parameters were the same for the two applications. Standard quality control practices employed to essure j production of satisfactory cladding include: )
- 1. Use of a thoroughly developed and testing welding pro- l cedure which is identical for both base metals.
- 2. Qualification of the procedure and all operators in accor-dance with the ASME Code.
- 3. Qualification of each combination of heat of filler wire and tot of welding flux by making test plates using the production weld-ing procedure and making chemical analyses of these to assure that the alloying material in the weld deposit complies with the specificatio i.
- 4. Chemical analysis of chips removed from every fifth production weld bead. Chips are analyzed for carbon, chromium, and nickel to assure the procedure is under control and in accordance with s pe cification. Since the routine chemical analysis check involves only carbon, chromium, and nickel, a meani'agful calculation of the ferrite content is not possible. The Schaeffler calculatiens are used only where a complete analysis is available such as in the course of Procedure Qualification Developments and are not s tilized as a Quality Control technique in production.
- 5. Periodic checks of the ferrite content of the weld metal during the cladding operation. This is done with a Severn Ferrite Detector which is considered to provide a general indication of clad quality, subject to confirmation by chemical analfsis.
In view of the extensive non-destructive testing of the cladding in the course of fabrication, no additional testing by the liquid ! penetrant method .vas planned for the pipe cladding during installation at Oconee except for small areas adjacent to back cladding of circle seams used to join assemblies. No indications were reported from this examination.
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B. Investigation of Oconee Unit 1 Problem and Definition ~of Problem
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return coolant piping assembly was rernoved from each 'oop as discussed in section II of this report (A-57 B-67, B-57, A-67) at a loc. tion just below the main pumps and returned to B&W - Mount Vernon Plant for re wo rk. One of the requirements of the pipe modification program was to flame cut twenty inches of excess material from each pipe sec-I tion (A-57 B-67, B-57, A-67) returr.ed to Mount Vernon. During the course of preparing the remaining pipe of the B-67 assembly for weld- l ing to another section, dye-penetrant inspection of the internal cladding adjacent to the weld preparation revealed the presence of small randomly oriented linear indications defined as micro-fissures (see section III-D of tids report). Further penetrant inspection revealed general surface fissuring throughc.ut the B-67 vertical run, but similar 100% inspection showed that no fissures were present in the other three I return coolant pipe sections, ( A-57, B-57, A-67) seturned to Mount Vernon for rework.
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It was determined from the processing that only four assem-blies (B-67, A-57. B-45, and B-41) had been shipped directly from Barberton to Oconee Urdt 1 and nor.e of these were liquid penetrant inspected after stress rellel. At Mount Vernon the fabrication sequence required 12 quid penetrant inspection of the cladding after post weld stress relief heat treatment. This change was incorporated on all piping assemblies shipped from the e. . I On the basis of the fissures found on the B-67 assembly, shipped from Barberton, it was decided to perform a 100% liquid pene-trant inspection on all the Barberton shipped straight main coolant pipe i at Oconee Unit 1. The remaining portion of the B-67 return coolant pipe which was stil; attached to ti.e retura coolant elbow on the lower head of the stean generator contained the same type of fissures as were noted on the eight foot length which had been shipped to Mount Vernon for rework. No other fissures were found in any of the remain-ing assemblies shipped from Barberton. I t
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l [ ! u c; In addition, 10% of the surface of each straight pipe assembly shipped to Oconee Unit I from Mount Vernon was subjected to liquid { h penetrant inspection. During the si:c ins pection of the B-57 assembly, d m which is similar in configuration to the B 67 assembly but en the other r j steam gene rator, micro-fissures were rounti in .12** Y. !?" = = aMut h a foot below the cut edge. Figure 3 shows the general location of the indications. These fissures were similar to those found in the B-67 y
, pipe, but on a smaller scale. Since 10% inspection revealed a small j area containing fissures, all Mount Vernon roipped piping, both 28-and 36-in. diameter pipe were also subjected to 100% luspection by the dye-penetrant method. No new indications were disclosed.
Thorough surface preparation and 100% liquid penetrant in-H spection of the straight main coolant piping on Oconee Unit 1 showed H that ten of the twelve assemblies were free of indications. The B-67 g assembly contained fissures through its entire length, the B-57 assem- [ bly was free of indications except for one 12-in. by 18-in, area.
] As previously stated, the linear indications resulting from e the dye-penetrant inspection were restricted to the surface of the clad-a ding. The 1- 1/ 2 fta of defects in the B-57 pipe were removed at the site by grinding an average of 1/64 in, to 1/16 in. of material from the surface with the maximum depth of localized probing being g
1/8 in. The depth of grinding was determined by actual measurement [ using a straight edge and rule and the cladding thickness remaining in
@ the ground areas was confirmed with the Eddy Current Instrument as p
W a c ce ptabic. 2.1 The fissures in the upper portion of the B-67 straight pipe K run were repaired while the piece was still at Mount Vernon being 1 modified as discussed in section II of this report and as described in j detail in the Process Documents, Appendix II. These fissures were
; removed by machining 1/8 in of material from the surface, leaving saund cladding. After performing a liquid penetrant inspection to verify ) removal of all indications, the inside surface was overlayed with stain-u less steel using the submerged are process, and ground for surface
( 2 requirements. The pipe section was then subjected to a post weld stress relief heat treatment. Inspection after heat treatment by the liquid penetrant and ultrasonic test methods showed clad to be free of fissures. It was returned to the Oconee site for re-installation. 1 Ra W 4 N M b I -
O The lower poruc. on o. ........ _. ... , which remained attached to the steam generator lower head outlet elbow 1 q also contained fissu.-e s in the clad. Rather than attempt repair of this section in the field. this pipe section was r< moved and a sound duplicate section f.om another unit was substituted. C. Invesugciou u.~ ;.I ..d .f 9; Mia'arv - Mount Vernon and Bsrbercon All processing has been reviewea to assure that fabrication and inspection is in accordance with the applicable specifications and codes. It is emphasized that Mount Vesnon processing hs i always i specified penetrant testing after stress relief heat treatment. BLW has examined all records 3= rtaining to the pipe fabrica- ) I tion, paying particular attention to heat treatn.ent records. No omis-sions or temperature excursions beyond the specified range were found. Records indicate that all compon:nts have been examined by the appro-priate non-destructive t st after post-weld stress relief heat treatment at Mount Vernon. , Indications found in the submerged are deposited cladding of two return coolant piping assemblies installed in Oconee Unit I are defined in section III-D of this report as inter-granular micro-fissures l that were formed during solidificat2on of the weld metal. Fissures in l 1 a and were I the B-57 assembly occurred in an area of less than 1-1/2 ft removed by light grinding. More extensive microficouring was detected , 1 1 i in the B-67 assembly and a portion was repaired in the shop. I The microfissures occurred during weld metal solidification ; when the submerged arc welding flux was not uniformly enriched with , chromium. The resulting cladding had patches with insufficiert de'.ta ferrite to resist fissuring during weld metal solidtfication. Similar indications had been infrequently noted during pipe fabrication and cor-rected at that time. i J Corrective acticn at the flux mam.facturer's plant was insti-I tuted as soon as the problem was noted in the shops. No furt%r dif-1 t ficulties have been experienced. The fisaures in the B-67 pi;,ing covered a wide area. They f
- were missed in the shop because they were very small and tight, and 1 1
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I . 9 Babcock & Wilcor
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had not been subjected to a post weld heat treatment prior to the liquid penetrant inspection. Had the cladding been heat treated prior to liquid penetrant testing, the fissures would have been found. Fissures in piping shipped from hit. Vernon were caught in the shop and corrected prior to aldpr.w n6, since hit. Vernon Engineering changed the processing to require penetrant inspection after heat treatment. "Ihe small area of minor fissuring in the B-57 assembly was not disclosed in the shop because of human error. Extensive retraining of dye-penetrant opera-tors on actual samples removed from the scrapped pipe is being con-tinue d. Careful grinding and dye-penetrant inspection of all pipe in Oconee Unit I clad by the automatic submerged are process has been completed. The nominal cladding thickness as specified to be 1/4 in. and in order to assure that the cladding thickness in the areas that were ground in the course of corrective work would still meet minimum clad-ding thickness requirements, the entire clad surface was subjected to an Eddy Current testing program to clearly establish that the minimum cladding thickness of 1/8 in was not violated. A special instrument had been designed and built by B&W for this type of analysis and was utilized for the work. D Laboratory Examinations After discovering and reporting the existence of small linear indicatiens on the surface of the two straight runs of piping, B&W decided to confirm their opinion that the indications were micro-fissures formed during solidification of the submerged arc weld metal. Since the twenty inches of excess length that was removed from the B-67 assembly dur-ing modification at hit. Vernon contained indications of the same type and severity as those that were present in the remainder of the pipe,
; portions of this excess material was used to provide test specimens for metallographic examination, side bend tests, ferrite checks, and chem-ical analysis. Samplea were not removed from the B-57 piping at Oconee since the indications were similar in nature and it was not considered necessary to cause the major field repair that would result from remov-
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ing a sample. Following are the details of these tests performed on the scrap portion of the B-67 pipe. The results obtained and their com- ) parison with similar tests conducted on other piping are noted. Babcock & Wilcox
- l. Ferrite Check:,
Use of the Severn Ferrite Indicator showed that the stainless steel cladding in the 20 inches of excess pipe had a delta fer-rite content I-1/2 to 2-1/25 Although the clad thickneaa on the sample tested was 1/4 inch, there was found to be some magnetic inGuence from the carbon steel backing material. When the steel backing was cut away, tne ferrite reading on the cladding alone was less than 1-1/25 Similar ferrite checks on the B-67 pipe remaining at Oconee, which had scatterec nssuring along the entire length, sho wed values ranging from 2-1/2% to 105 The worst fissuring was in the areas showing 2-1/2% ferrite. I The ferrite content of the B-57 return coolant piping was checked in the field after this problem was discovered, and was found to be 5% in the 12 ir. by 18 in. area that contained the fissures. The surro+mding areas, which had no indications, showed a ferrite content of 10~. to 15% based upon the Severn Indicator. It should be noted that delta ferrite checks are random partial checks and were made periodically during cladding of the piping. Acceptance standards were 2-1/2% rmnimum if additional chemical j analysis of production cladding were made; otherwise the acceptance sta: trds were 5% minimum fe rrite. As long as the welding flux has ! the proper homogeneity such spot checking constitutes a satisfactory Quality Control procedure. When the welding Gux is not uniform as was the case here, a satisfactory weld metal cladding cannnt be con-sistently achieved.
- 2. Side Bend Tests:
A portion of the 20 in excess length section of the B-67 l pipe was prepared for side bend tests in accordance with all of the re- 1 quirements and dimensions of section IX of the ASME Boiler and Pres-sure Vessel Code. The samples were taken from the 20 in. excess length as shown in Figure 4. The area selected for bending contained indications representative of those present in the remainder of the B-67 piping. Fissures present on the face of the specimen were ground away to provide a meaningful test of the cladding ductility. Testing of the 3 specimen in accordance with ASME Code requirements produced no tears i g EEM l
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or fissures, demonstrating adequate ductility of the pr., duction cladding in the area of indications.
- 3. Metallographic Examination:
Figure I shows photomicrographs of etched and unetched cross sections of typical fissures removed from the same piece of ex-cess length previously discussed. The location of the sample for rnetal-lographic examination was immediately adjacent to the area where the ferrite was checked by Severn Indicator and found to be less than 1-1/2%. Metallographic examination, as shown in Figure 1. confirms the low ferrite content of the cladding in this area. It is clear that the indications are typical rnicro-fissuring caused by insufficient delta ferrite and are therefore defined as such. These photographs should be compared with those shown in Figure 2, the latter illustrating a normal submerged arc weld made by the same procedure, with sufficient delta ferrite. The uncorrected Severn Ferrite Indicator reading of the sample illus-trated in Figure 2 shows it to contain 9% to 10% ferrite.
- 4. Chemical Analysis:
1 Chemical aralyses of five representative areas in the l 20 inches of excess lengtl. removed from the B-67 pipe are shown in Table II. This analysis confirms the results obtained from both the Severn ferrite check and the metallographic examination which had indicated that the ferrite content was less than 1-i/2% in the area of fis s uring. The calculated level of ferrite in this area of the cladding, based upon the Schaeffler diagram, ranges from 0 to 2% The low ferrite content of this weld metal results in part from the unusually high carbon content of 0.089 to 0.097% in this portion of the cladding. Carbon will reduce the ferrite content of the weld metal very rapidly; for example, carbon is 30 times as effective 'l as the same percentage . nickel. This effect is demonstrated both by the Severn gauge data as well as by the Schaeffler Calculations. It i should be noted that the chrome and nickel contents of this portion of ; the cladding are on the high side in spite of the high carbon level. This i l occurs as a result of the previously discussed flux inhomogeneity which I changed the weld penetration, thus resulting in greater dilution with the i Babcock 8 Wilcox ! l 4 1 e
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base metal while maintaining more than sufficient chromium and nickel in the weld. The adequate ferrite level (5%+) in the balance of the weld cladding provides assurance that this condition prevailed only in the pipe welded with the improperly made flux. Preliminary samples taken from the cladding of the B-67 assembly indicated chromium values of 17.43%,17.5%, 17.95% and 18.02 %. The corresponding nickel contents were 8.58%, 8.64 %, 8.71% and 8.68%. Carbon values were also out of specificatior. (O. 111 %, 0.205 %, 0.120% and 0.102%). Since the samples were removed with c. c..arbide burr, the high carbon content can be attributed to sample contamination. The lack of homogeneity of the welding flux is directly responsible for the erratic chromium and nickel values obtained from these samples. E. Discussion of Investigations Two questions are raised by the disclosure of microfissures in the submerged arc cladding. The first, why did the fissures occur in a process that had been so thoroughly developed, qualified, and field tested? Second, why were the indications not detected during normal shop inspection? BLW is certain that these fissures are not something new or une xplaina ble . B&W has known since the early forties that certain analyses of austenitic stainless stects may be subject to intergranular microfissuring during solidification from the liquid under restraint. This is corrected by adjusting the chemistry to provide a two phase structure of austenite plus a few percent by volume of delta ferrite. I The delta ferrite breaks up the continuous grain boundary network found in the purely austenitic stainless steel, significantly increasing the grain boundary length and reducing its thickness. Grain boundary thick-ness reduction is beneficial because it reduces the weakening effect of low melting point constituents at the grain boundary that may cause intergranular microfissuring during solidification of the weld metal. The welding development and qualification program, the filler metal testing procedure, and the production quality control procedures were specifically designed to incorporate this technology and prevent weld I mic rofis s uring. l I I Babcock 3 Wilcox
_______ _ ,- ',.--.-n-.-,.---,-m._, Some submerged are cladding done early in 1968 employed flux which had not been manufactured in such a way as to insure homog-encous chromium enrichment. Techniques of blending and addition of sodium silicate binder were not in accordance with previous or subse-quent practice. This led to small areas in the clad deposit which had sufficient chromium for corrosion resistance, but an insufficient amount to maintain the beneficial delta ferrite at the level required to preclude mic rofis suring. This infrequent lack of homogeneity was not disclosed in the flux qualification teets or in process tests. Corrective action for this deficiency was instituted as soon as the problem was identified. By this time, the cladding for Oconee Unit I was essentially complete as far as the weld cladding was con-l cerned. ! Corrective action consisted of an elaborate blending schedule l
- at the flux mamw.turers plant and an irsprovement in their method of adding sodium silicate binder. BbW is ms,intaining a surveillance of the operation to preclude further difficulties.
Some minor indications were noted during normal shop inspection and were easily corrected. By coincidence, the only piping shipped to Ocer ce Unit I with a larFe number of undetected fissures in the straight leagths was the B-67 assembly. This was one of four assemblies fabricated and shipped from Barberton; these assemblies did not receive the originally scheduled post weld stress relief heat treatment prior to liquid penetrant inspection of the cladding. As can l be seen by the typical photomicrographs shown at 100X and 500X mag- ) nification in Figure 1 and Figure 2, even after stress relief the micro- ! fissures remain exceedingly tight. Prior to stress relief, they could l
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be too tight for meaningful interpretation by the dye-penetrant inspection. ' Thermal strains imposed by the differential expansion characteristics l between the overlay and the steel base material would tend to open the l fissures curing subsequent heat treatment. The pipe, however, received l no further dye-penetrant inspection until the rework operation and the disclosure of the indications at Mt. Vernon. The above analysis does not explain the presence of a small patch of fissures in the B-57 piping which was shipped from the Mt. Vernon Plant. There, the manufacturing sequence was changed to BaM & hX
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I I j require liquid penetrant inspection of cladding after the strean relief heat treatment. l The fissures in this pipe were apparently even tighter and most were removed after grinding about 1/32 in. from the surface . These fissures were missed during liquid penetrant inspection because of operator error.
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IV. CONCLUSION OF INVEST
- CATION
, A. Corrective Action to Reactor Coolant System i As pointed out in section II, straight pipe cladding in assem-blies B-67 and B-57 required repairs. The action taken in ca. h case is as follows: , j
- 1. B-67 Assembly - Replacement and Repair
- a. An 8-ft section of pipe was removed by the following method:
(1) Made a cut 12 in. below the Bingham pump suc-tion nozzle. (2) Made second cut 8 ft below first cut.
- b. This 8-ft section was shipped back to Mt. Vernon.
- c. The section was then cut in Mt. Vernon to a length of 5 ft 2-3/8 in.
- d. At that time, indications were found. One-eighth inch of cladding was machined out and nine remaining local indications were ground out. A layer of cladding was then deposited using the sin-gle-wire submerged-arc welding proces s. A preliminary dye-penetrant examination disclosed no indications.
- e. The piece was stress-relieved after final assembly in Mt. Vernon and again examined by dye-penetrant procedures. No indications were found.
- f. A type-316 alloy stainless steel transition 14 in. long and a type-316 alloy stainless steel safe end 17-1/4 in. long were welded to the 5-ft 2-3/8-in. carbon steel piece forming a piece approximately 7 ft 10 in. long.
- g. Due to indications found in the remaining straight piping at Oconee in the B-67 assembly, it was determined that this pip-ing should be removed. A 16-ft (approximately) section was removed and replaced with an acceptable substitute.
- h. Accordingly, the new 16-ft section of clad carbon steel pipe was welded to the approximately 7-ft 10-in. piece in Mt.
Vernon. This new 16-ft piece was made up of two pieces taken from
- 16 Rahenck 3, Wi)COX
, - - ,,, -- , - - , , ~ - . . , -
l l spare material. Two carbon -steel-to-ca rbon-steel welds were made. , This required re-stress-relieving the assembly.
- i. Prior to stress-relieving, the 316 stainless steel transition piece and safe end were cut off.
J. After stress-relieving, this 316 stainless steel piece was rewelded forming a piece 23 ft 10-13/16 in. long. This piece was then shipped to Oconee. t ( k. This 23-ft 10-13/16-in. piece was welded into the pip-ing system between the Westinghouse pump suction nozzle and the 90-degree elbow leading from the steam generator. l
- 2. B-57 Assembly - Repair This assembly had only one small area 12 by 18 in., which l was ground clear at Oconee. The deepest penetration was 0.121 in. deep.
Cladding thickness was checked, following grinding and determined to be I/8 in. thick or greater. B. Corrective Action to Manufacturing Processes 5 and Quality Control Improvements l The occurrence of a manufacturing pro'alem such as the one u described here usually represents financial as well as schedular losses i l to the manufacturer and the customer, but it also provides a lesson that can prevent similar occurrences in the future if properly heeded. The effectiveness of the lesson is best evaluated by the quality and extent of , ( the corrective action instituted to avoid repetition of the problem. The following corrective action has been taken by B&W: 1
- 1. B&W has instituted a program where the clad surface of
)
the piping will be dye-checked after every major operation to ensure i freedom from this type of indication in the end product and ensure de- ) l tection and correction of the problem at the earliest possible time in the manufacturing process.
- 2. Mt. Vernon has effected a very intensive operator train-ing program for using the dye-penetrant technique. The men see about I 80 hours of classroom and practical demonstration work as part of the B&W training program, and, in addition to that, are qualified dye-g - 1, - -~
.,,___ _ _ _ _ _ _ _ . _ _ _ _ _ _ . _ _ - . - - - - - - - - - - - " ' - - - " ' - - - - - - " - - ~~
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. . . - ~ c ,.n n -. n penetrant inspectors in strict accordance with the provisions of section J Appendix IX of the ASME Code. Qualification is in sccordance with m provisions of SNT-TCIA, which is the standard upon which the ASME Code relies. This involves another 10-30 hours of intensive training.
Actual samples of unacceptable production work, such as those discussed herein, are used as visual aids. I
- 3. The flux manufacturing operation is being closely mom-tored to ensure homogeneous enrichment of the material with chromium and nickel. Corrective action in this area was initiated more than two years ago.
RM&h
I I V. SUM MARY B&W's actions towards the solution of this problem will succeed in completely eliminating the micro-fissure from the current Oconee Unit 1 straight pipe as well as from piping supplied for all fut re jobs. The very careful training eif SkW operators, together with better con-trol of the manufacturing processes, should guarantee sound cladding in future components, and certainly the thorough examination and cor-rective work conducted at the Oconee Unit 1 job site provides adequate assurance that the problem there has been solved. In this connection, it is imp:,rtant to recognize that the cladding of this straight pipe is not considered part of the struc'ure in terms of the piping's ability to with-stand operating stresses. From a design point of view, the carbon steel l carries the entire load. Thus, tha cladding does not contribute to the integrity of the pressure boundary but rather provides a surface protec-I tion for the carbon steel. The extensive investigations, surface examinations, and field re-work as discussed throughout this report make possible the final con-clusions that the reactor coolant system integrity has not been jecpar-dized in any way and that the reactor coolant system is 1007. sound for operation with respect to the investigations and repairs reported here. I I . I I : 1 I I RnM & Wik
-.-.,--,..mm,-
7 4^ Table II. Chemical Analysis of Five Representative Areas in the 20-Inch-I.ong Section of Excess Material Removed From the B-67 Straight Inlet Pipe at Mt. Vernon l l
% by weight !
Area Carbon"I I Chromium Nickel 1 0.093 18.45 8.99 2 097 18.14 8.87 3 .092 18.07 8.92 4 094 18.02 8.89 5 0.089 18.50 8.94 N The carbon content is in excess of the maxi-mum of 0.08% carbon allowed by the specifi-ca tion. There is no logical explanation for this discrepancy. All QC records indicate that 0.08% carbon was not exceeded in the shop. Rahendr & Wilcox l l
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B l D D I I I I B ATTACHMENTS I I I I I I I I Babcock & Wdcox I I M
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I B l l i I , i i I I D APPENDIX I ) NDT P-
- for Dye-Penetrant Inspection D of the .gosited Cladding in the Coolant
_ jang System of Oconee Unit 1 i l I I-1 Babcock & WilCOX
e THE BAECOCK & WILCOX CC.v.1..d ' POWER GENERATION LIVISION QUALITY CONTROL SPECIFICATICN PPS 9179 7. ISSUED SUBJECT DYE PENETRANT INSPECTION AND SPEC. NO. ..' 12-2-63 ACCEPTANCE STANDARDS FOR WELDS S-102C "[
- 1. SCOPE: This specification shall govern the dye penetrant method of inspection and h. "
acceptance standards for welds. The dye penetrant inspection. described herein shall be used for the detection of surface flaws, suel as cracks or porosity in welds made in accordance with the following codes and regulations: . A. ASME Boller and Pressure Vessel Code B. MIL-STD-278 C. Coast Guard Regulation CG-115 .' D. American Welding Society Codes .
- 2. PREPARATION OF SURFACES:
2.1 The weld surfaces to be tested and the adjacent surfaces within one inch shall be cleaned to insure they are free of loose film, slag, dirt, grease, embedd ed , sand, etc. The surfaces may be inspected without surface preparation or con- S, . ditioning except as noted above, but the surface finish shall permit proper t' l interpretation of inspection results. Shot, sand, grit, and vapor blastic g 3 I shall not be performed on surfaces prior to liquid penetrant inspection. f;. i 2.2 There shall be no extraneous matter that would obscure surface openicgs or q otherwise interfere with the tests. In all caerse, ih.) surface to be exa nined g shall be cleaned with acetone before application of the dye. The drying of .-. the test surfaces shall be accomplished by normal evaporation; blottin g with g ' paper towels or clean, lint-free cloth; or usingt circulating air. The saini-mum drying time shall be five minutes. It is important in the drying.spera- 7 t tion that no contaminating materials such as oil from air nozzles or 1! nt from . cloths be introduced onto the surface, since they may cause irreleva st indica- j tions. 7 4-
- 3. APPROVED DYES CLEANERS. AND DEVELOPERS:
3.1 The following penetrant, developers, and cleaners produced by the Magnailux $ Corporation that are listed in Group I of Military specification MIL-1 -25135 ]g may be used in combination with one another, but shall not be used ii con- ' junction with any other manufacturer's materials. Combination No.1 is pre-ferred and shall be used whenever possible, r q-EEV. NO. REV, SY REVISION SFEC. NO. 5 JL:11 S-102C t REVISICU DATE PAGE NO. $~ 2 67 Revised Paragraph 8 1 of 5 .
f THE EAECOCK & WILCOX COMPANY PO*4ER GENERATION DIVISION QUALITY CCNTROL SPECIFICATICN PDS 9179 I D SUBM *
- DYE PENETRANT INSPECTION AND 12-2-63 ACCEPTANCE STANDARDS FOR WELDS S-102C Combination No.1 Combination No. 2 B
Penetrant SKL-HF SKL-HF Developer S KD-S SKD-NF Cleaner SKC-S SKC-NF The SKD-S and SKC-S materials, though not on the Qualified Products List for Specification MIL-I-25135, have been approved for use by authorized Governm ent agencies. Materials made by other companies are acceptable provided they are qualified on approved test plates using the procedures of this specification. m 3. 2 All penetrant materials shall be qualified by demonstrating the adecuacy of the materials to detect known defects in standard and approved test plates.
- 3. 3 Each batch of materials shall have been tested for residual amounts of total halogen and total sulfur exclusive of carrying licuids or gases. The residu amount of each shall not exceed 1 percent by weight.
- 4. APPLICATION OF PENETRANT l>YE:
4.1 All sur faces to be tested shall be thoroughly and uniformly coated with the penetrant dye. The dye shall be applied to the weld and to the base material for 1/2" on each side of the line of fusion whenever possible. The dye may be applied by brushing, swabbing, dipping, or spraying. 1
- 4. 2 The surfaces shall remain wetted with the penetrant for a minirnum of 15 min- '
utes and a maximum of 20 minutes. On special applications, the maximum tim, limit may be increased when permitted by Quality Control and the customer. 1 Any Comp 12te drying of penetrant during the penetration time shall require ' recleaning of the surfaces and a repeat of the test. The work piece and the penetrant shall be at a temperature between SOF and 100F during the dye pene-trant operation.
- 4. 3 After the penetrant dye has been on the surface to be inspected for the pre-scribed amount of time, all excess dye shall be removed by the following steps:
A. Remove all possible penetrant dye with a clean, dry, lint-free cloth or absorbent paper. I EEV. NO. 5 REV BY JL:11 REVISION SPE C. NO. S102C REVISION TATE - PAGE NO. l Z 67 Revised Paragraph 8 2 of 5 1 I i
/ THE PAECCCK & WILCOX COMPANY ' POWER GENERATION C4 TISION ;4 QUALITY CONTROL SPECIFICATION t PDS 9179 g ISSUED SUBJECT SPEC. NO. 'g DYE PENETRANT INSPECTION AND . 12-2-63 ACCEPTANCE STANDARDS FOR WELDS S-102C B. Finish cleaning the surface with lint-free cloths that have been dampe - with the approved cleaner. Flushing of the surface with a cleaning solu-tion for the purpose of removing excess penetrant shall be prohibited. 4.4 The drying of surfaces after removal of the excess penetrant shall be accomp-lished by normal evaporation or by blotting with clean lint-free cloths ar absorbent paper. Forced air circulation in excess of normal vnetilation shall be prohibited.
- 5. APPLICATION OF PENETRANT DYE DEVELOPER: -
4 5.1 The penetrant dye developer shall be thoroughly 'igitated and shall be applied } to the surface within 15 minutes after the preceding operations have been com- ' pleted. Normally, the developer shall be apnlied by spraying. The developer may be applied by dipping, swabbing. or brushing when spraying is not possible. ;_ When applying the developer by swabbing or brushin or brushing out of the developer shall be prohibited.g, intentional swabbing out(' -
- 5. 2 The developer shall dry for seven minutes before interpretation and the interpretation should be completed within 30 minutes. However, evaluation g may continue after the 30 minute period has elapsed provided indications &
remain within applicable acceptance starxiards. Surfaces which are evaluated ^ after 30 minutes and have indications exceeding the acceptance standards [ shall be c1 caned and reinspected by the technique described in the preceding *
^
paragraphs except that interpretation shall be started after the developer has dried for seven minutes and shall be completed within 30 minutes. [ g-A INTtCRPRETATION OF R ESULTS: 7 u.1 Precaution shall be taken to prevent any object from touching the dry devel-oper film as it is very friable and easily damaged. When questionable ? results are obtained, the surfaces shall be reinspected. 4 J.
- 6. 2 Indications and defects in the surface shall be identified as red stains y against the white developer. A thin r-d line may indicate a fine crack or f a cold shut. Scattered red dots may indicate porosity in the material and h a line of dots may indicate a tightly closed crack. M
- 7. LIGHTING IN THE TEST AREA:
6 7.1 The area in which the inspection is performed shall be adequately illuminated $ J for proper evaluation. EEV. NO. REV. BY REVISION S PE C. NO. b 5 JiL:11 S-102C E REVISION DATE PAGE NO. 2 67 Revised Paragraph 8 3 of 5
THE BABCOCK & WILCOX CCMPANY POWER GENERATION DIVISION m QUALITY CCNTROL SPECIFICATION J PDS 9179 ISSUED SUBJECT DY E PENETRANT INSPECTION AND *
- 12-2-63 ACCEPTANCE STANDARDS FOR WELDS S-102C
- 8. ACCEPTANCE STANDARDS: Welds, base materials, and weld edge pre-parations chall meet the minimum quality requirements of this specification.
M 8.1 All indications revealed by liquid penetrant inspections are not necessarily M defects, and nonrelevant indicationr, are sometimes encountered. liowever, all indications in the weld craters or in the line of fusion between base material ar.d weld metal shall be treated as defects. All indications
]LE believed to be nonrelevant shall be explored by surface conditioning and reinspected or shall be reinspected by other non-destructive methods. If $ reir.spection reveals any indications they shall be considered defects and W shall be evaluated to the acceptance standards as specified in Para. 8. 2.
8.1.1 Linear defects are those defects in which the length is greater than three times the width. 8.1. 2 Rounded defects are those defects which are circular or elliptical with the length less than three times the width.
- 8. 2 WC d metal including cladding and adjacent base materials, including 1/2" on each side of the weld, shall be free of the following indications:
8.2.1 All cracks and linear defects.
- 8. 2. 2 .\11 rounded indications with dimensions greater than 3/16 inch.
8.2.3 Four or more rounded indications in line, regardless of size, separated by 1/16" or less, as measured from edge to edge. H 8.2.4 Ten or more rounded indications, regardless of size, located in any six square inches of surface whose minor dimension is no less than one inch with these dimensions taken in the least favorable location relative to the indications being evaluated.
- 8. 3 Weld Edce Preparation - Base Material (Cross-Section Inspection): Liquid penetrant inspection shali be used to evaluate cracks, laminations, and similar discontinuities.
- 8. 3.1 The test surface shall be free of all cracks, and nonlaminar defects.
I REV. NO. 5 RU. BY JL:11 REVISION SPEC. NO, S-102C REVIgIglgTE PAGE NO. g , Revised Paragraph 8 4 of 5 i
THE BABCOCK & WILCOX COMPANY PCWER GENERATICN DIVISION QUALITY CONTROL SPECIFICATION PDS 9179 IS M D SUBJECT DYE PENETRANT INSPECTION AND SPEC. 10. 12-2-63 ACCEPTANCE STANDARDS FOR WELDS S-102C 8.3.2 Dircontinuities which are parallel to the surface, such as luninar type indications, shall be acceptable as specified below: Max. Total Indication Max. Length of any Base Material Thickness Length in 3" Single Indication 1/4" or below 1/16" 1/16" Above 1/ 4" to and incl.1/2" 1/8" 1/8" Above 1/2" to and incl.1" 1/ 2" 1/4" Above 1" to and incl. 2" 3/4" 1/2" Above 2" to 4" 1-1/ 4" 1" 4" and over 1-1/ 2" 1" 8.3.3 Repairs on Weld Edge Preparation of Base Material: Only such indica-tions need removal and repair as to render the base material accept-able to the limits specified in Paragraph 8. 3. 2. Indications which have been probed to a depth of 3/8" from the surface of the weld edge i preparation and have not been removed, amy be sealed by welding.
- 9. FINAL CLEANING: When the inspection is concluded, the penetrart material l shall be removed as soon as possible with acetone or other approg ed solvents. l
- 10. SAFETY PRECAUTIONS: )
10.1 Repeated or prolonged contact of penetrant dye or developer with the skin shall be avoided since these liquids are skin irritants. . I
- 10. 2 The solutions us-d in dye penetrant inspections shall be used in well venti-lated areas, since they are highly volatile, i
10.3 Dye penetrant solutions have low flash points and shall not be heated or i exposed to open flames and hot surfaces. It is recommended that "No l l Smoking" signs be posted in areas where penetrants are used. EEV NO. REV. BY REVISION SPEC. No.
$ JL:11 S-102C PAGE NO. I REVIST0"i4DATE
'2 - 67 Revised Paragraph 8 5 of 5 l i
1 i
B B B B B B B i S g APPENDIX U e Fabrication Procedure for the Modification of the D-67 Asaembly in Mt. Vernon I I - I I I I I I . .. . . .
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l i l Note: The following fabrication procedure applies only to one l partial section of the vertical straight piping in the B-67 assembly that was reclad in Mt. Vernon; therefore, all dye-penetrant examination described in the following process is of a preliminary nature and an additional Quality Control measure. Final dye-penetrant examination was conducted after a stress-relieving heat treatment in the course of subsequent fabrication. The remainder of the modification work was done in accordance with standard manufacturing procedures and pro-ceases. II-2 Babcock & Wikox
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*o c 215-203-50-1 I "o- ~U 00 Receive and inspect, check fcr any da-age (1.0) that might have occurred d:1 ring shipsent.
10 set up on engine lathe, part off stainless steel safe end at 2' 3 3/4" frcrs centerline of MK-58 nozzle. Face to 2' 31/2" frcrs centerline of MK-58 nozzle and fom weld prep per Detail "F" on Drawing 1516!*7E. Reposition: Part off carten end of pipe to an o.A. length of 5' 2 5/8". Face to an o.A. length of 5' 2 3/S" and fem veld prep per Detail "If' cc sane drawing. 20 Blend grinEl if required to remove tool marks. oo Inspect c:achining. (0.6)
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N.' OPERAT1011 MMMMI.DETAL C 21 -203-50 1 ao - "5'- 30 M.T. weld prep en carba end of pipe. S-102 3 I LO Re=ove defects. I 50 Reinspect as required. I 00 Inspect and chart catitle=. 5 00 Repair veld. V-52 70 Blent grind repairs. I I i
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lC215-203-50-1 l 00 Inspect grinding. 80 M.T. repaired areas. 3-102 B 90 P.T. edge of cladding at carbcn end of pipe. S-102 J P.T. weld prep cc S.S. end of pipe. N IE: P.E. action is ret. tired if any defects exist in ed6e of c1=44trg.
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C215-?01- %-1 101 Set up on I.D. grinter and grini to remove { all defective < 1 ming ' 1 00 Inspect grinding. 102 Re.nspect I.D. curface with P.T. as required. I 103 Iayout thf. folicwing aress and iniicate ah inecoel fcr easy it'.entift:stien. I Iayout 6" dia. ctale arcand n 11 nozzle. Iayout 12" dia. circle around E 58 nozzle. I Iayout 6" wide aras ceasuring frcus stainless steel end of pipe, (360*). Identify these (3) areas as incocel. 00 Inspect laycuts. I U3l
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5wo0l OPERATMil DESCRIPT10N.DETA!1. c215-203-50-1 NO ", r"4! - l 104 Set up and sub are clad I.D. Of pipe with (1) layer cf S.S. clad. Use sirgle wire deposit. W-52-4 D0 noT clad (3) areas marked inconel. 00 Inspect claddirg. 105 !!.M.A. cle.d (3) rc=ainirs areas with ineccel. W-52-4 Tie in with stainless steel. OO Inspect for sufficient claddirg. 1 05 Take chip sa=ples frcn S.S. claddirg.
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