ML20155C030

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Forwards Addl Info Re Fall 1987 Intergranular Stress Corrosion Cracking Insp Per Request
ML20155C030
Person / Time
Site: Quad Cities Constellation icon.png
Issue date: 05/31/1988
From: Johnson I
COMMONWEALTH EDISON CO.
To: Murley T
Office of Nuclear Reactor Regulation
Shared Package
ML20155C033 List:
References
NUDOCS 8806140057
Download: ML20155C030 (19)
v • d • e


Text

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_ Commonwealth Edison

  • One Fird Nabonal Plaza Chicago, Illinois

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,, Address Reply to: Post Offc; Box 7C

% Chicago,lilinois 60690 0767 May 31, 1988 Mr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Quad Cities Station Unit 1 .

Response to Request for Additional Information (RAI) Regarding Fall 1987 Unit 1 Intergranular Stress Corrosion Cracking (IGSCC) Inspection NRC Docket No. 50-254

Reference:

Letter from T.M. Ross to L.D. Butterfield dated April 13, 1988.

Dear Mr. Murley:

In the above referenced letter, members of your staff requested additional information pertaining to the completed Quad cities Unit 1 Fall 1987 Intergranular Stress Corrosion Cracking (IGSCC) Inspection. Attached, please find the responses to the eight RAI items. We are also providing a copy of a NUTECH Engineer's report entitled "Evaluation and Disposition of Flaws at Quad Cities Nuclear Power Plant Unit 1 (1987 Outage)", Revision 1 dated May 1988.

We believe these documents address the concerns raised by your staff in their review of the results of the completed IGSCC Unit 1 Fall 1987 inspection.

Please direct any questions you may have regarding this matter to this office.

~Ve y truly your .

.m I. M. Johns Nuclear Licensing Ad. istrator 1m Attachment j cc: T. Ross - WRR (w/Att.)

NRC Resident Inspector - Quad (w/Att.) )

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Item 1: During ';he Unit 1 refueling outage in the Fall of 1987, all but four (04) large bore ( ) 12" n.p.s) recirculation welds were ultrasonically examined due to cracking found in the expanded sample welds. The four recirculation weld that were not examined this outage were: 02 AD-S6, 02 AS-S3, 02BD-S2 and 02BD-S6. These welds were previously examined during the refueling outage in the Winter of 1986 (January 1986) by examiners qualified at the EPRI NDE Center af ter September 1985, and they were found free of flaw indications.

Since the aforementioned welds were examined in 1986 to the same inspection standards used today, Commonwealth Edison (CECO) feels that the 1986 inspection results are accurate and representat.fve of the current wolds condition, especially af ter only one operacing cycle.

Re-examination of these four welds at this time (in 1987) wou3d, therefore, provide little safety benerits. It would, however, incur additional unnecessary radiation exposure to inspecting personnel, and it could also affect the unit start-up scheduled for December 21, 1987.

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s Item 2: As a mitigation for IGSCC, the IHSI process was applied to selected susceptible austenitic stainless steel piping welds in the recirculation, shutdown cooling and residual heat removal systems at the Quad Cities Unit 1 between April 12, ard May 8,1984. A total of 88 welds were treated by Nutech Engineers . Five welds were deleted from the original 93 weld IHSI program: four because a pre-IHSI ultrasonic (UT) examination revealed flaws which required wold overlay repair, and one because the configuration was not conducive to IHSI.

During the Fall 1987 UT examinations of the austenitic stainless steel piping, new IGSCC-like flaw indications were observed in a total of eight welds previously IHSI treated in 1984. Reviews of the IHSI heat treatment records and the construction radiographs of these joints were performed at that time. Results of this records review are discussed.

To date, the IHSI review has focused on those welds where Nutech Engineers has issued nonconformance reports (NCRs) following the IHSI heat treatments. A total of five NCRs were prepared involving four welds. Two of the welds producing NCRs, wolds 02D-F6 and 02K-F2, were observed each to have one thermocouple which slightly exceeded the maximum prescribed OD temperature of 575-degrees C per the EPRI IHSI criteria. (The maximum temperatures were 595-degrees C for 020-F6 and 577 degrees C for 02K-F2 respectively.) The slight temperature excursion was found in the NCR to have no detrimental IHSI heat treatment effo.t. This independent review concurs with that conclusion. Two large diameter welds, welds 02BS-SS and 028-S10, were observed to have through wall temperature gradients which were below the EPRI guideline of 275-degrees C (495-degrees F) . One weld, wold 02BS-SS, was found to produce a through-wall temperature gradient of 487-degrees F (later corrected to 504-degrees F) and the other weld, weld 028-S10, produced a through-wall temperature gradient of 466-degrees F. Additional analysis performed by Nutoch and others has confirmed that these temperature gradients should be sufficient to produce compressive ID residual stresses.

More recent experimental evidence suggests that in large diameter pipes, the ID surface may not be placed into compression unless the temperature gradient is significantly larger than that prescribed by the EPRI criterion. In addition, a preexisting condition such as postweld grirdirs which can produce a cold worked layer, surface abuse and unfavorable tensile residual stress on the ID surface, can further reduce the ID crack initiation mitigation l effectiveness of the IHSI heat treatment. Consequently, when )

grindire is present, the ID surface may remain in tension, even I following a successful IHSI treatment. However, the through thickness residual stress benefit of the IHSI treatment remains, i The IHSI treatment for the two large diameter welds identified in the NCR's is acceptable by analysis and meets the EPRI residual stress guidelines.

The question which remains is whether the EPRI guidelines are stringent enough for large diameter welds and for welds in which postweld grinding has occurred. The answer to that question is ,

outside the scope of this investigation. i l

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The NRC has asked in Question 2 for Commonwealth Edison to discuss the industry-wide experience in applying the IHSI process to mitigate IGSCC. Commonwealth Edison believes that it does not have the in-house capability to reply to this portion of the question. >

It is understood, however, that EPRI is currently investigating the industry-wide performance of IHSI treated welds. In addition, laboratory studies of degraded pipe followed by an IHSI heat treatment have been completed and a final report is about to be released by EPRI.

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Item 3.a.: The contractor providirs Inservice Inspection services for the Fall 1987 refueling outage was General Electric Co. (G.E.). Most of the ultrasonic examination data were manually collected and analyzed.

Some examination data were recorded automatically by means of the GE's SMART UT system. The automated examination usually was supplemented by localized manual examination. In general, automated inspection system was used on overlaid welds, wolds in high radiation field and welds with knowa flaw (s).

Item 3.b. All level II and III ultrasonic testing personnel and equipment employed for IGSCC inspection were qualified at the EPRI NDE Center for detection, sizing and/or overlaid weld examination in accordance with the applicable "NRC/EPRI/BWROG Coondination Plan".

Specifically, all IGSCC detection examiners (Level II and III) were qualified at the NDE Center af ter September of 1985.

Item 3.c. Procedures used for IGSCC UT were:

e NDT-C-2, rev. 15: CECO's procedure for inspection of piping welds, e NDT-C-40, rev . 0: CECO's procedure for inipoction of Inconel 182 buttered welds, o NDT-C-37, rev. 0: CECO's procedure for inspection of overlaid welds.

o UT-46, rev 4: GE's procedure for inspection of piping welds using the automated SMART UT system.

Techniques used for IGSCC UT were:

  • Flaw detection: 450 or 600 shear wave,600 or 700 refracted longitudial wave and/or W9Y-7010 creepire wave.
  • Flaw sizing: 450 or 600 shear wave, 600 or 700 refracted longitudinal wave, WSY-70 ID creeping, SLIC-40 and/or OD creeping wave.
  • Examination or re-examination of overlaid welds: 600 or 700 refracted longitudim1 wave and/or OD creeping wave. For examination of new overlaid welds, a 00 longitudinal wave was also used to detect possible lack of bonding.

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Item 3.d.: Limitations of UT examination for each weld are tabulated in the following table:

System Site Weld I.D. Weld Configuration Limitation 4

Recirculation 28" 02AS-F2 Safe End-Pipe Safe end OD geometry 28" 02AS-F8 Pipe-Valve Valve OD geometry 28" 02AS-F9 Valve-Elbow Valve OD geocetry 28" 02AS-F14 Pipe-Elbow Elbow is made of cast stainless steel 28" 02AD-S2 Pipe-Tee Tee OD geometry 28" 02AD-F8 Elbow-Valve Valve OD geometry 28" 02AD-F9 Valve-Pipe Valw OD3eometry 28" 02AD-F12 Pipe-Pump Pump OD geometry 28" 02BS-F2 Safe End-Pipe Safe end OD geometry 28" 02BS-F6 Tee-Valve Valve OD geometry 28" 0285-F7 Valve-Pipe Valve OD geometry 28" 02B5-55 Pipe-Tee Tee OD geometry 28" 02BS-512 Elbow-Pipe .Weldelets in area 28" 02BS-F14 Pipe-Elbow Elbow made of cast stainless steel 28" 02BD-Fl Tee-Cross Cross Ou geometry 28" 02BD-F8 Elbow-Valve Valve 00 geometry 28" 02BD-F9 Valve-Pipe Valve 00 geometry 28" 02BD-F12 Pipe-Pump Pump OD geometry 22" 02-F1 Pipe-Valve Valve OD geometry 22" 02-F2 Pipe-Valve Valve OD geometry 22" 02A-F1 Valve-Pipe Valve OD geometry 22" 02A-F5 Pipe-Cross Cross OD geometry 22" 02A-52 Pipe-Sweepolet Sweepolet OD geometry 22" 02A-S3 Pipe-Cross Cross OD geometry 22" 02A-54 Cross-Reducer Cross OD geometry 22" 02A-56 Pipe-Sweepolet Sweepolet OD geometry 22" 02A-57 Pipe-Sweepolet Sweepolet 00 geometry 22" 02A-58 Pipe-Sweepolet Sweepolet OD geometry 22" 028-F1 Valve-Pipe Valve 03 geometry 22" 028-FS Pipe-Cross Cross OD geometry 22" 028-S2 Pipe-Sweepolet Sweepolet OD geometry 0317N/6/cle

_.____________.a____________________________ _ _ _ . , _ _ _ _ _ _ ~ _ _ . - . _ _ = . _ . . - _ , - - - ~._u._ _ _ . , _ _ _ _ . ________o

___ _ _ . _ _ _ _ __ m- _ _ - . _ __ _ _ .

Item 3.d.: Limitations of UT examination for each weld are tabulated in the following tzble: ,

System Size Weld I.D. Weld Configuration Limitat'on 22" 028-53 Pipe-Sweepolet Sweepolet OD geometry 22" 028-54 Pipe-Sweepolet Sweepolet OD geometry 22" 028-56 Cross-Reducer Cross OD geometry 22" 028-59 Pipe-Sweepolet Sweepolet OD geometry and adjacent overlaid weld 12" 02C-F6 Sweepolet-Pipe Sweepolet OD geometry 12" 02D-F6 Sweepolet-Pipe Sweepolet OD geometry 12" 02E-F6 Sweepolet-Pipe Sweapolet OD geometry 12" 02F-F6 Pipe-Reducer Ceducer OD geouetry ,

12" 02G-F6 Sweepolet-Pipe Reducer OD geometry 12" 02H-F6 Sweepolet-Pipe Sweepolet OD geometry 12" 02K-F6 Sweepolet-Pipe Sweepolet OD geometry 12" 02L-F6 Pipe-Reducer Reducer OD geometry 12" 02M-F7 Sweepolet-Pipe Sweepolet OD geometry 4" 02AB-510A Pipe-Sweepolet Sweepolet OD geometry 4" 02AD-55 Pipe-Sweepolet Sweepolet OD geometry J 4" 02BD-55 Pipe-Swepolet Sweepolet OD geometry 4" l-195-75-1All Sweepolet-Pipe Sweepolet CD geometry 4" 1407-77-1A Sweepolet-Pipe Sweepolet OD geometry RHR-LPCI 16" 10AD-F1 Tee-Pipe Tee OD geometry 16" 10AD-F4 Elbow-Valve Valve OD geometry 16" 10AD-F5 Valve-Pipe Valve 00 geometry 16" 10AD-F12 Pipe-Valve Valve 00 geometry 16" 10AD-F13 Valve-Pipe Valve OD geometry 16" 10BD-F1 Tee-Pipe Tee OD geometry 16" 10BD-F5 Elbow-Valve Valve OD geometry 16" 10BD-F6 Valve-Pipe Valve OD geometry 16" 10BD-Fl5 Pipe-Valve Valve OD geometry.

16" 10BD-F16 Valve-Pipe . Valve OD geometry RHR-SDC 20" 105-F1 Tee-Pipe Tee OD geometry 20" 105-F5 Pipe-Valve Valve OD geometry 0317N/7/cle

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Item 3.d.: Limitations of UT examinaticn for each weld are tabulated in the following ttblo: .'

System Size Weld I.D. Weld Configuration Limitation Core Spray 10" 14A-F4ER Pipe (Buttered)-Pipe *djacent sockolet weld on the downstream pipe side 10" 14A-F6 Pipe-Valve Valve OD geometry 10" 14A-F7 Valve- Elbow Valve 00 geometry 10' 14A-518 Penetration-Elbow Intradose region 10" l 149- F7 Valve-Elbow Valve 00 geometry 10" 148-F12 Elbow-Valve Valve 00 geometry 10" 148-F13 Valve-Pipe Valve OD geometry 10" 148-F16 Penetration-Pipe Penetration OD geometry 0317N/8/cle

Item 4.a: IHSI Treated Helds - A total of eight recirculation system welds which were IHSI treated in 1984, exhibited evidence of IGSCC-like indications in the UT examination performed at the Fall 1987 outage. These eight welds are identified and the location and extent of the flaw indications for each are detailed in the December 4, 1987 report (Section II-Inspection Results). Five of the joints identified in the table are 12 inch diameter shop welded joints. All five joints were observed to contain axial flaw indications during the 1987 UT examination and were repaired using a standard design weld overlay repair. THe other three remaining joints were large diameter (22 and 28 inch) welds. The presence of new IGSCC or growth of IGSCC in each of these welds following IHSI is discussed.

12 inch Diameter Riser Helds All five 12 inch diameter welds identified as having IGSCC-like indications during the Fall 1987 outage contained only axial indications. Experience with IHSI treatment of laboratory and plant piping, as well as supporting analysec, indicates that IHSI should be effective for this size weld. A review of the NCR's for the Quad Cities Unit 1 treatment revealed no evidence of problems with the IHSI treatment of these joints. The IHSI treatment records were also reviewed for these joints and the treatments were uell within the EPRI guidelines.

Review of the construction radiographs revealed very "wide welds (i.e. wide roots and crowns). The as-welded residual stress distributions from such welding practices are anticipated to be ,

conducive to the initiation of axially-oriented IGSCC flaws.

Additionally, other factors, such as the existence of the weld crown and the increased training requirements on UT examiners were considered. The evaluation of the limited number of axial flaws in '

all five welds and the existence of the weld reinforcement, leads to the conclusion that these axial flaws may have been "missed" in prior examinations.

Finally, the likelihood of postweld grinding in shop welds may create conditions where incipient IGSCC was present prior to IHSI and the IHSI process application in fact retarded crack growth.

Large Diameter Recirculation System Helds  ;

A total of three large diameter recirculation system welds  !

exhibited the presence of either new or growth of IGSCC-like l indications during the 1987 UT examination. They include: l

  • 02B-F1, a 22 inch diameter valve-to-pipe weld;
  • 02BS-85, a 28 inch diameter pipe-to-tee weld; and
  • 02BS-S9, a 28 inch diameter pipe-to-elbow weld.  ;

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A review of the IHSI heat treatment records and the construction radiographs was performed as ' part of this investigation. The results of these reviews are presented as follows:

Railograph Review-t A review of the original construction radiographs revealed that significant evidence of post weld ID grinding had occurred in each

+ of the three welds examined. The 22 inch diameter joint, 020-F1, appeared to be post weld ground over essentially the entire ID surface. Only slight evidence of the weld root or counterbore was present. This observation is somewhat surprising since this is a field weld where access to the ID is available only through the cross-tie valve.

The 28 inch diamete" pipe to tee weld which exhibited IGSCC-like indications for the first time this outage, weld 02BS-SS, appeared to be heavily 10 post weld ground. No evid6nce of weld root or counterbore was visible on the construction radiographs. This condition is not unexpected for this class of welds as ID access is readily available to large diameter shop welds following welding.

These welds are of ten post wold ground in order to improve inspection quality of the construction radiographs and for preservice and inservice UT.

The third large diameter weld examined was the 28 inch pipe to elbow weld, weld 02BS-S9, which contained reported IGSCC prior to the IHSI treatment in 1984. This weld exhibited new indications during the Fall 1987 outage and increased length and depth of the prior indications. The construction radiograph review revealed extensive regions of post weld grinding, accompanying regions where the weld root and counterbore appeared to be unaf fected. A more detailed review of the construction radiographs attempting to correlate the grinding with the IGSCC indications was attempted and is described below, i

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IHSI Record Review -

A review of the ISHI treatment records for the three large diameter wolds indicated that one of the treatments was performed in a manner which was consistent with the EPRI guidelines, one weld appeared to be marginally treated due to coil and component configurativ.1 problems, and one joint was improperly heat treated due to insufficient heating coil length. The IHSI heat treatment results are summarized below for each of these welds. The IHSI heat treatment record for the pipe to cross tie valve (weld 028-F1) revealed that the heating zone for the heat treatment was significantly less than that required for a successful heat treatment. This is due to the fact that the coil was centered over the joint to be treated and the heat treatment was performed so as to minimize heating of the cast stainless steel valve side of the joint. Consequently, approximately one-half of the coil was shorted out (on the valve side) during the heat treatmen.. This reduced heating zone and coil length produces a less effective IHSI treatment. Whereas all other IHSI treatn,ent parameters appeared to meet the EPRI guidelines, the reduced heating zone length undermined the IHSI effectiveness for this joint.

Review of the IHSI heat treatment record for the pipe to tee joint (weld 020S-SS), indicat( that the heat treatment was extremely difficult to perform successfully due to the configuration of the tee in the vicinity of the joint, the significant differences in thickness between the tee and the pipe, and the decision of the IHSI contractor to center the coil over the joint. Consequently, the weld only barely achieved the minimum acceptable temperature for successful heat treatment, even assuming high flow velocity in the line. Consequently, it is believed that this joint, which meeting the EPRI guidelines, may be a marginally heat treated joint, from a crack initiation prevention perspective. However, the IHSI process application was performed in a manner which has been demonstrated to be beneficial in retarding crack growth.

A review of the IHSI heat treatment records for the 28 inch diameter pipe to elbow joint, wold 02BS-S9, indicates that the IHSI treatment was performed without incident and appears to be within the EPRI guidelines for a successful IHSI treatment. Based upon this heat treatment records review, this joint appears to have received a successful heat treatment. The intermittent post wold grinding of weld 02BS-S9, combined with the UT reports of pre and post IHSI cracking in this joint, prompted and attempt to correlate the observed IGSCC-like UT calls with grindire locations in the ,

joint. The correlation revealed that all new indications observed in the current 1987 inspections haya occurred in post weld ground regions, with one small possible exception, whereas the UT indications identified prior to the IHSI treatment in 1984, occurred in regions where root and counterbore are present. The excellent correlation of the new UT IGSCC-like indications with the grinding locations supports the hypothesis that the IHSI treatment residual stress and surface abuse caused by post weld grinding.

Item 4.b. Wold Overlay Repaired Welds The details of the weld overlay examinations, the comparisons of the current examinations (three) with those performed in 1985 and the resolution of any flaws were addressed in detail on pages 13 and 14 of the December 4, 1987 report transmitted to the NRC. No additional information is available.

Item 5: The assumed flaw in the finite element model (figure 5.3-1) is on the pipe side of the original weld, Please refer to revision 1 of the attached NUTECH's report, item 3.3 page 3.4, for additional details.

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Item 6: The corrections in Table 5.2-1 and 5.2-2 result in Weld- 02G-S3 having a final overlay repair thickness slightly below a NUREG-0313,' Revision 2 "standard" overlay thickness. As shown in attached NUTECH Drawing CEC 073.0133 and its associated Weld Overlay Data Sheet, the surface conditioning grinding of Weld 02G-S3 resulted in a final overlay thickness (0.229") below NUTECH's requested full-structural (standard) thickness (0.24"). Due to'the heavy outage duration pressures caused by unplanned overlays during the Quad Cities Unit 1 1987 outage, this overlay was left as-is eventhough it was clearly below NUTECH's requested design thickness. During the rush to support an expedited final repor t submittal date, the data entry errors made in Tables 5.2-1 and-5.2-2 hid the fact that Wold 02G-S3 did not meet "standard" overlay criteria.

As stated in Section 5.2 of the revised flaw disposition report, the decision to leave the overlay is appropriate for the following reasons:

a. The predicted flaw depth ratio of 0.77 can be shown to meet "stanJard overlay repair thickness criteria using the alternate flaw evaluation requirements of ASME Section XI Paragraph IWV-3642,
b. Because only 0.03" of additional thickness is required to meet the arbitrary maximum allowable flaw depth ratio of 0.75 in Table IWB-3641-1, the man-REM exposure that would be expended to build up, surface condition, and reinspect the overlay cannot be justified, and
c. Because the predicted flaw depth ratio is based upon the assumption that an IGSCC indication could eventually propagate through the 0.15" thick low delta ferrite first layer, but actual observed circumferential flaws have not been detected in the outer 25% of the origir.al pipe wall and axial flaws have not been detected in the overlay, the inspection frequency associated with a "standard" overlay in NUREG-0313, Revision 2 Category E is sufficient, ,

It should also be noted that NUTECH's requested design thickness for weld 02G-S3 of 0.24" provides a "standard" thickness over a low delta ferrite first layer with a "normal" average thickness of 0.10" instead of the actual first layer thickness of 0.15". As demomnstrated by the first layer thicknesses for Welds 02C-S4, 02F-S4, and 028-S7 in Table 5.2-1, 0.10" is a reasonable assumptior.-

for a first layer thickness, but did not provide for a conservative "standard" thickness for Weld 02G-S3 in spite of the 0.229" thickness provided by the welding contractor.

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ApptriouAG AliNDid Mb W6 CEC 087.0tM nsAtur/Ma>. faca'0022 AGA I. pu/y

4 Item 7: In 1983 and 1984, the manual ultrasonic (Ur) examination of some large diameter shop wolds in the recirculation system at both Dresden Unit 3 and Quad Citios Units 1 and 2: rovealed UT1 signals which were interpreted as 'intergranular stress corrosion cracking I (IGSCC). The flaw characterizations associated with these signals were relatively long circumferential flaws with depths of 10 to 20% through-wall. In order to evaluate these.UT- reflectors, the~ "ID creeping wave" technique was'used. This technique did.not confirm the presence of IGSCC in several of these weldments. In order to resolve the apparent disagreement', metallurgical plug samples- : (approximately 1-1/4 inch diameter) were removed from the welds and metallographically examined. .The inside surface of these weldments 

                                                                  ~

were visually examined using a boroscope.and radiographed. prior to being repaired. These additional examinations confirmed that there was no IGSCC present. The metallographic examinations did reveal though that the welds were "backwelded," that is root of the weld was welded from the inside of the pipe. The fabrication sequences is illustrated as follows: e The weld joint was fit-up and welded in the normal manner from the outside of the component. I , m 

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            . The. weld root was excavated from the component 10.

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  • The excavation was then re-welded from the inside and ground in preparation for examination.

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REGION A j k

4 

                         ' The "corner" created in Region A of the above sketch provides the .

conditions necessary to produce an ultrasonic reflector Jor signal (similar to a crack -tip) in a region of the weldment (heat' affected zone).where IGSCC is commonly -seen during typical shear wave examinations. Since 1983, ultrasonic examinations' have continued to identify the signals from welds believed. to have this geometric condition. - No significant changes have beenfobserved in the 'large majority of 

                          . these weldments, thereby evidencing the geometric nature of the ultrasonic signals. Recent automated ultrasonic examinations have evaluated the signals from these locations as geometric reflectors.

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