ML20137E447
| ML20137E447 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 11/19/1985 |
| From: | MISSISSIPPI POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML20137E425 | List: |
| References | |
| 85-M-017, 85-M-17, TAC-60165, NUDOCS 8511270258 | |
| Download: ML20137E447 (48) | |
Text
{{#Wiki_filter:_ 5 METALLURGICAL EVALUATION of RECIRCULATION PIPING CENTER CROSS SURFACE CRACKING FOLLOWING IHSI GRAND GULF NUCLEAR STATION - UNIT 1 INTERIM REPORT Mechanical Section r Nuclear Plant Engineering Report No.: 85-M-017 Prepared By: / M r/ / /9 /Me/ h6' Responsible Engineer N Date Reviewed By: wg N f / / Y ] ht.' A [
~% E neering Supervisor ~' Date Reviewed By: / ! J Principal Engineer Date Approved By: / in Ii)hD Dire 6 tor of Nuclear Plant Engineering
-Date 0511270250 851120 6 DR ADOCK 0500
- e. NMEREP 159 IHSI COVER SHEET
;%/
(4 TABLE OF CONTENTS Page. List of Figures
~1.0 sBackground........................................................ 1 2.0:: Field Observation and Actions..................................... 2
-2.1. GGNS - Unit 1 Crosses........................................ 2
. 2.= 1.1. Loop "A" Cross........................................ 3 2.1.2 _ Loop B Cross.......................................... 4 2.'2 oGGNS - Unit 2-Crosses........................................ 4 2.3 Summary of Fie1d
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Observations................................ 5 3.0 Metallurgical Evaluation.......................................... 6 3.1 Chemical Analysis............................................ 6 3.2 Meta 11ography................................................ 7 3.3: Fractography.............................~................... 11 3.4 Summary.of Metallurgical Observations....................... 11 13.5 Apparent-Cause.............................................. 12 3.5.1 Scenario A........................................... 14 s
.3.5.2 Scenario B........................................... 16 4.0 IHSI Residual Stress and Fracture Mechanic Analysis.............. 20 4 '.~ 1 ~ Summary of Residual Stress / Fracture Mechanic Analysis....... 22 15.0 Conclusions...................................................... 22 6.0 Appendices 6.1 Overview of GGNS IHSI 6.2 0verview of ISI Related to IHSI 6.3 Reduction of I. D. Compressive Stress by O. D. Grinding - , _J14 MISC 85111905 11
.9 :. - - q. s: L
-List of Figures-Figure
- 1. -Map of U. T. Indications - Loop A Cross 2 . . -- A . Unused Cross #1 - Met. Samples B. Unused Cross #2 - Met. Samples
- 3. Sample Group.#1 4.. Sample Group #2 S. Sections from Sample C
- 7. Microsection Through Sample C
- 8. . Subsurface Defects in Sample B
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- 9. Subsurface Defect.in Sample C 10'. Surface in Sample E
- 11. Near. Surface Defect in Sample G V 12. SI2i Micrographs of Subsurface Defects
- 13. SEM - Tranverse Section Through Sample E
-14. SEM - Tranverse Section Through Sample G
- 15. SEM ' Micrograph of G. B. Constituent
- 16. X-Ray Energy Spectra
- 17. SEM Fractograph and X-Ray Energy Spectra - Exposed _ Crack Surface
- 18. Auger Spectrcscopy Results
- 19. Auger Spectroscopy Specturm
- 20. Analysis of 0. D. Residual Tensile Stress Following.IHSI
- 21. Plot of O. D. Residual Tensile Stress Following IHSI Table 1 ' Critical and Allovable Flaw Size r.
I LJ14 MISC 85111905 - 2
Pzgs I of 23
1.0. BACKGROUND
On October 24, 25 and 26, 1985, Induction Heating Stress Improvement (IHSI) of the welds connecting the Loop "A" cross to the recirculation header, recirculation pump discharge pipe and the cross cap were performed by NUTECH. The IESI procedures utilized by NUTECH were in accordance with the Electric Power Research Institute (EPRI) IHSI guidelines and all the IHSI process parameters were within the EPRI prescribed range. The IHSI pro-cedure called for LP examination of the thermocouple locations after the IHSI treatment. During the LP examinations, linear indications on the cross body outside surface were found. These indications were in a cir-cumferential band starting at the weld prep edge and extending approx-imately 7" axially and are shown in Figure 1. In order to determine the cause for appearance of these indications, a metallurgical evaluation was undertaken. The samples for these evaluations were obtained from the two unused SA403-WP304 crosses from GGNS-Unit 2 that had been fabricated to the same design and from the same material as the GCNS-Unit 1 crosses. One of the unused GCNS-Unit 2 crosses had been used to develop the IHSI technique and coil for the IHSI treatment of the cross cap (X-cap) (the 24" pipe cap welded to the upper 24" inlet of the cross). This cross was also examined using the same LP technique and procedure and revealed indications similar to those in the CGNS-Unit I crosses. Sample locations for metallurgical evaluations were marked in an area showing LP indications and an area well removed from the IHSI affected area. Metallurgical samples were also obtained from the second unused J14 MISC 85111904 - 1
S Pags 2 of 23 GGNS-Unit 2. cross and the samples were from the sixteen inch (16") nozzle region and an area corresponding to the1 region which was away from the IHSI, Affected' region in the unused cross #1. Locations of metallurgical samples for both crosses are shown in Figure 2.
~
The original billet material for the GGNS recirculation crosses was made by g Colt Cruicible Industries id shipped to. Taylor Forge, Chicago. At Taylor Forge, Chicago the billet was forged into four (4) seamless tubes
-(SA182F304) of dimensions 26 1/2" OD x 3.0" wall x 38" long. This forged tubing was then shipped to Taylor Forge, Woodstock, Tennessee division for hot working to a 24"x24"x16"x16" cross. The final fabrication involved a plug _ pulling technique at 1900*F (max) to form the 16" OD nozzles. Final inspection involved liquid penetrant (LP) testing at the Taylor Forge, Woodstock shop prior to shipment. Two of the crosses were installed at GGNS-Unit 1 and the other two were were retained ~1n-storage after the GGNS-Unit 2 design was changed to use the 316K piping material. Based upon the available documentat' ion, MP&L has determined that all four crosses were fabricated from the same Colt Cruicible heat of material, heat number 623058.
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2.0 FIELD OBSERVATIONS AND ACTIONS
-2.1 GGNS-Unit 1 Crosses I
J14 MISC 85111904 - 2
' Pega 3 of 23 2.1.1. Loop "A" Cross During the initial LP exam'ination of the cross body,-the indications-were found to be contained in two
.circumferential bands extending about seven (7) inches from
~
each of the twenty-four (24) inch diameter girth welds cnt the cross. Figure 1 provides a map of the indications. These two areas were ground to reduce the density of indice.tions and indication lengths to meet the ASME Section III Subsection NB acceptance criteria for two (2) inch thick forgings under an ASME Section XI repair program. Subsequent to the experiment on the GGNS Unit-2' crosses (described in Section 2.2), the areas of the loop "A" cross which had not initially shown any LP indications were r.urface conditioned using a soft-backed sanding disc. .The LP examination conducted following the surface conditioning revealed that the entire outside surface of the cross exhibited. indications similar to those seen in the original two bands. These-additional areas were ground under the ASME Section XI repair program. Currently, the number of indications exceeding the ASME Section III acceptance criteria'has been reduced to a number where the indications are being removed, or reduced in length to meet the acceptance criteria, on an individual indication basis using a die grinder and round-nosed carbide burrs. J14 MISC 85111904 - 3
m 1 .,.-.
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'2.1.2 ' Loop "B" Cross
- - :.: +
'The Loop "B"_ cross was subjected.to the same sequence of examinations, and generally showed indications similar to
, n the' Loop "A" cross. The remedial actions for:the, Loop'"B" cross were the same as-for the Loop."A" cross. The only general diffdrence was that the indications on the. Loop "B" cross appeared ~to be significantly shallower than'the-Loop-
~
"A" cross' indications. All work on the Loop "B" cross is
.l now complete.
l
< 2.2 GCNS-2 Unused Crosses I" examinations of Unused Cross #1 (IHSI, treated at X-cap) showed indications in the IHSI area similar to those found on the GGNS-Unit l'
' crosses. Some minor. indications were found in, regions removed from the
.IHSI area.. The indications were similar in. pattern but were not as.
~
dense'as chose on GGNS-Unit 1 'A' cross. Unused cross #2 was utilized to perform an experiment to demonstrate'that: (1)' the metallurgical' findings that the grain boundary defects were shallow in that they extended only to a depth of 25"_ to 0.30" deep; and (2) that thece '
' grain boundary defects were subsurface and would be revealed by light
- grinding or by the application'of tensile' stresses..
J14 MISC 85111904
?.*_
Psgs 5 of 23 The experiment and the findings are presented below: Step I. The as-is surface was subjected to LP examination in three areas. This examination did not reveal any indications. Step II. The previously examined areas in Step I, were lightly sanded and reexamined using LP technique. This time in.two of the three areas the indications were revealed and appeared to be randomly oriented. The other area did not reveal any indications. Step III. The two areas with indications were ground down by about 0.25" and reexamined by LP technique. The indications were almost removed and where they existed they were below ASME Code allowable of 3/16". In-the tapered area between the 0.25" ground surface to the lightly sanded as is surface the indications, as might be expected, were visible. 2.3 Summary of Field Observations (1) Indications on crosses subjected to an IHSI treatment exhibit a circumferential pattern. (2) Indications on the spare cross not subjected to IHSI were revealed only after light sanding of the surface and exhibited a random orientation. J14 MISC 85111904 - 5
\\
- Pcg2 6 of 23 (3) From the orientation and the appearance of these indications, (i.e., on the outside surface near IHSI treated areas and sub-surface in areas either unaffected by or untreated by IHSI),
demonstrates that the subsurface grain boundary defects were opened to the surface during the IHSI treatment. (4) The indications were resolved within approximately 0.25" of the outside surface confirming the measurements made in the metallurgical investigations. 3.0 METALLURGICAL EVALUATION 3.1 Chemical Analysis Bulk product chemical analysis of the cross material was performed to verify ASTM A403-WP304 specification requirements and to confirm original CMTR chemical analysis. The results from the sample labeled "A" of the cross, ASTM requirements and CHTR analysis are presented below: C Mn Si Cr Ni Mo P S Sample A1 0.06 1.61 0.35 18.29 9.22 0.21 0.027 0.007 ASTM A 403 0.08 2.00 1.00 18.0- 8.00- - 0.045 0.030 WP 304 Max. Max. Max. 20.0 11.00 - Max. Max. CMTR Colt Crucible Industries Heat 623058 0.07 1.72 0.42 18.48 9.16 0.18 0.029 0.005 J14 MISC 85111904 - 6
Pcgo 7 of 23 3.2 Meta 11ography Meta 11ographic sections were taken from Samples B and C of unused cross #1 samples (Figure 3) and E and G of unused cross #2 samples (Figure 4) to establish the nature of the crack indications in unused cross #1 at.d the microstructural features of the Type 304 material of both crosses. The sections were examined on the optical metallograph and in the scanning electron microscope (SEM) in the as-polished condition and after etching. Sampic Group No. 1 (Unused Cross #1) (IHSI Treated at X-cap) Sections through the locations of the externally visible crack indications revealed considerable network cracking at the outside surface. The general morphology of the cracking is illustrated in Figures 5 and 6 and details are shown in Figure 8. The pertinent features of the cracking are as follows: 4 (1) The cracks were completely intergranular and relatively wide open. (2) Surface connected segments and disconnected segments were present in each section. (3) Certain segments followed highly irregular paths (Locations 1 and 2 in Figure 6). (4) Certain crack segments and junctions of crack segments exhibited an abnormal grain boundary constituent [ Figure 7 (b) and (c)]. J14 MISC 85111904 - 7
1' Paga 8 of-23
.- (5) The max'i mum observed depth of cracking was'0.25 inch..
Two sections were taken through the outside surfaces of Samples B and-iC at locations where there were no surface' crack indications. As shown in Figures 8 and 9, numerous-subsurface crack segments were-observed'in these sections. The microetructural character of these
~
crack segments was generally similar to those of the surface connected cracks described above..
'The segments were all intergranular and a similar grain boundary constituent was present at some locations.
At the location of the surface connected cracks it is.possible that the separate segments connect to the main cracks in planes other than the polished section. However, the presence of numerous disco'nnected subsurface segments at some locations,- together with the irregular path of some segments and the abnormal. grain bou'ndary constituent, suggests that the cracking was associated with some type of pre-existing microstructural defect.
. Sample Group No. 2 (Unused Cross #2 (Non IHSI Treated))
Meta 11ographic secitons from Sample E and G of Group No. 2 were examined. Numerous microstructural defects were present in all sections-taken at or through the outside surface of these samples.
-~J14 MISC 85111904 - 8
-Page 9 of 23 Selected examples of these defects are shown in Figures 10 through
- 14. The pertinent features of these defects are as follows:
(1)' All of the defects were located at grain boundaries. (2) Although there were no visual or penetrant crack indications on the surfaces of these samples, numerous defects were present immediately below the surface (Figures 10, 11 and 12). Note that the defects in these figures are viewed in a direction normal to the original outside surfaces of the sample. (3) In sections taken normal to the outside surface defects were
' observed to e depth of approximately 0.3 inch (Figures 13 and 14).
'(4) Certain of the defects contained what was initially identified as a two-phase grain boundary constituent such as observed in Samples B and C of Sample Group No. 1. Some of the tight defects appeared to contain some type of single-phase constituent while many appeared open and empty.
(5) The defects in these samples were of a size and orientation similar to the disconnected-segments in Samples B and C (Group No. 1, Unused Cross No. 1) and exhibited microstructural features
~ essentially identical to the cracking.
J14 MISC 85111904 - 9 L
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'Pcga'10 of 23 Energy dispersive x-ray spectroscopy (EDS) was employed to provide a preliminary qualitative analysis of the grain boundary constituents. The character of what was initially identified as
'the'two-phase constituents is shownlin Figures 15 and 16. As noted,'the' uniform gray phase is chromium-rich compared to base-metal [ compare (a) and -(b) with (c) ~ in Figure 16]. These results suggest that the Cr-rich phase is a chromium-iron-oxide
- and that the iron-rich phase.is a Fe-Cr metallic phase.
Qualitative EDS analyses were also performed at locations where tight-defects appeared to contain a single-phase material.
~
Generally. these indicated chromium enhancement relative to base metal with Fe/Cr ratios varying from 0.9 to 2.0 as compared to 2.2 for base metal. - Subsequent Auger Spectroscopy confirmed that.the uniform grey phase was-a chromium-rich iron / chromium oxide surrounding
" islands" of chromium depleted base metal. (See Figures 18 and 19).
- 0xygen is not detectable by EDS.
- J14 MISC 85111904 - 10
S d*4 Pigs 11'of 23
-4 /
3.3: Fractography ,
- A 1/4-inch thick specimen containing one of the visible defect
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indications was cut.from the outside surface of Sample C.. The specimen was rb'oken open in bending to expose'thd crack surface
~
..and examined in the SEM. Fractographs from the exposed surface
,are shown in Figures 17 (a)_and (b). The intergranular nature of the surface is~ apparent in~(a) and an adherent, granular surface-
. deposit is apparent in-(b). An x-ray" energy spectrum obtained from the crack surface is shown in Figure;17 (c).' The Fe/Cr peak
- height ' ratio for the - surface is' lower (Cr-rich) than for base
-metal suggesting the presence of a chromium oxide.'
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'4 3.4 Summary of Metallurgical Observations The principal observations.made to date are as'follows:.
'(1) Numerous grain boundary defects were present in all' +
+ ..
A
~
samples examined (Unused-Cross #1 and' Unused Cross #2).o
, (2) 'The defects observed'in both crosses were essentially '
5, h identical in nature. An abnormal grain boundary , constituent was present in many of(the defects. _0ther: defects appeared open. Preliminaryandrsub$equentanalyses
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> . i, - - indicate;that certain g' rain boundary defects contained he
' iron-chromium oxides.
;J14 MISC 85111904 - 11
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'3). The. grain boundary defects appear to be mill process (billet or piercing stage) related rather than being IHSI induced.- These grain boun'dary defects-were then opened to the surface during IHSI treatment.
f(4) The maximum depth of linear cracking observed in sample Group No.-1 wasO.25 inch. In both crosses, the grain boundary defects were' observed to be confined'to the outer ja ~0.3-inch region. (5) There were no cracks or defects at the inside surface.(ID) of any of the samples evaluated in Sample Groups 1 and 2. This was verified metallographically and by bend tests conducted on metallographic specimens. l ~ #l All of,the metallographic data obtained to date indicates that
- a. the root cause for the observed surface cracks is preexisting grain boundary defects. Apparently, the application of IHSI provides-the necessary driving force to open the defects to the material surface.
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$3.5' Apparent Cause y-W f
At this time the exact " Root Cause" has not been completely-y determined, however, it has been determined that the grain t U boundary defects were present in the seamless tube (26 1/2" OD x y
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3.0" vall x 38" long preform) prior to Taylor Forge, Woodstock,
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O Tenn.-Division performing.the final pulling of the sixteen (16)
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inch outlet nozzles.' This conclusion is based upon the following. ,
. facts:
t( The cross material exhibits a' uniform large grain size-
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microstructure (thruthethib$nessofthewall)inallareas examined.except where.the sixteen,(16) inch outlets were 3. hot-workedandnormalrecryhtallizationofthegrain'
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-2) The grain boundary defects exist only onlthe outside surface g of.the$ cross. Normal mill practices require that for, forged.
seamless tubes (pipe) that the Inside Diameter (ID) is 1 ' s . 1 machined to remove the normal "as-forged" rough surface. N A
- 3) There'is no evidence of any " contamination" in the grain boundaries \whichcouldhavecomefromforginglubricants, 3
1 ' acid cleaning: baths or low melting point materials.-
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Taylor Forge, Woodstock, Tenn. Division performed no-other L.. 3
- , ;. 1 work than pulling the. sixteen inch (16") nozzles on.the
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%i q,. - ; .. 3. ., r crosses which.would have ; induced the ' grain boundary defects
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. intheareaAdistantfromwherethesixteeninch(16")
p_ ' ' .'s . , nozzles were pulled.
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9 i-The metallurgical evaluation results and a review of literature
~for standard forging practices for'austenitic stainless steels
indicates that one of the two following scenarios is the most
#\ - probable cause.for the observed grain boundary defects. The
. final determination of the most probable ~cause is dependent upon a review of the shop travelers from the Taylor Forge' Chicago facility where the preform was fabricated. EPRI is assisting MP&L in obtaining these shop travelers and the. final determination
- is expected to be made in the near, future.
-i 3.5.1 Scenario A (1) ~The rectangular billet was first upset in a cylindrical die to produce a solid cylinder.
(2) A mandrell was used to pierce-a hole ant cause the metal to flow in the annalus between the die and s the mandrel. Thus, a forged tubing is obtained. The piercing temperature is around 2200-2250*F.. (3) During the upsetting process to produce a solid cylinder it is believed that the billet surface was not adequately lubricated. Glass is commonly used as a lubricant in upsetting and piercing operations. Inadequate lubrication will permit excessive friction between the die wall and the J14 MISC 85111904 - 14
- <; ;y ~ l Paga 15 of 23
- a. s metal being worked during the piercing operation, because of the metal flow along the inadequately lubricated interface between the die wall and the metal.
(4) The excessive friction at the piercing temperature imposes severe shear strains in the metal at the immediate vicinity of the die wall. Since at elevated temperatures grain boundary strength is lower than the strength of the grain, the bound-aries will separate under the load. (5) This is a skin effect and the frictional forces rapidly dissipate as one moves away from the die wall. Thus, this phenomenon is only evidenced in the skin immediately below the outside surface. (6) As the piercing mandrell travels deeper, more metal flow occurs and since there is a reservoir of lubricant on the top. surface, metal flow is facilitated causing the grain separations to weld - shut. However, since the operation is not per-formed under controlled atmosphere, it is highly; i conceivable that when the grain boundary separates it would rapidly oxidize. The defective grain boundaries can thus become subsurface and retain their intergranular-nature. J14 MISC 85111904 1-
. ; ? V' . .
~ Pcg2 16'of 23
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f (7) The positive evidence of oxides on'the grain-boundary < facets, coupled with the absence of- other deletrious elements (e.g., Cu,-Pb, P, S, etc.)- supports the postulation that the'ob' served grain boundary' defects were induced during the piercing operation.- 3.5.2 Scenario "B"' All the metallographic observations and microanalysis activities are' consistent with'the-phenomena of internal oxidation of the forging
" preform" used to fabricate-the-cross as the root cause'of.the grain boundary condition. Internal oxidation is characterized by preferential oxidation of-.a material's grain boundaries, rather.
.than bulk surface oxidation. The microstructure observations.of grain boundary oxidation and
' dispersed oxides in the base metal matrix are-symptomatic of this mechanism.
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J14 MISC 85111904' '.16
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.Prg2 17 of 23.
Internal oxidation can be caused by several means, including:
< - Heating of a materialLin'an atmosphere with a relatively low oxidizing potential, (higher-oxidizing potential atmospheres promote bulk surface oxidation).or
- Heating of a material with an oxide scale.
1 I Larger grain sizes promote internal' oxidation due to the lower grain boundary energy, making the grain boundary act as a " conduit"~for oxygen. The presence of the grain boundary oxides only on the outside surface of the cross body, combined with the dispersed oxide at prior austenite. grain-boundaries in the mechanically worked arms of the cross,' requires that the condition was present prior to the forging of the arms from the tubular preform. Had these oxides also been present on the forged inner surface of the arms, the J14 MISC 85111904'- 171
r- + o Pego 18 of 23 4 condition could have been present on both the inner and outer surfaces of the preform and removed from the inner surface of the body during machining. Since no such oxidation could be observed in an as-forged inner surface of the arm, it is concluded that the condition was present only on the outer surface of the preform prior to cross production. The uniformity of the grain boundary condition dictates that the condition is caused by a gas / metal or liquid / metal reaction. This would mean the same condition existed on the inner surface of the rough forged preform. It was noted that the final preform had a vall thickness dimension of "3.000 inches", which would indicate the requirement for a machining operation. This machining operation would have been performed on the inner surface. It is therefore concluded that the preform "as-received" by Taylor Forge (Memphis) contained the observed grain boundary condition, though only on the outer surface. J14 MISC 85111904 - 18
+
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Paga 19 of 23,
;The-thermal treatments associated.with preheating &
a
-for. forging the arms of the cross and solution heat treatmentioft the finished cross. contributed
.to the progressive oxidation of the grain boundary
,~ into the grain',Iin.effect " widening" 'the appearance of.the. grain boundary oxide.
- Considering the postulated steps in the fabrication process-to produce the forging preform
?
gives.a-good insight into the exact steps at which the condition was introduced.. Steps - Preform Fabrication
-o Billet
. o- Heat'for Pierce (or other mechanical work) o Deformation
'(The heat / deform cycle may have been repeated)-
~ o' Descale (clean) o . Rough ~ Machine
- o. Solution Heat Treatment (1900*F minimum per SA182) o ~ Final Machine o: Examine o -Ship.as SA182 F304 material to Taylor' Forge (Memphis) to forge arms, etc. to produce cross-I J14 MISC 85111904~ 19
V ; -- Peg 2 20 of 23 s Since the_very'large' grain size is uniform throughout the 24-inch body ofLthe~ cross and internal oxidation is promoted by this large grain
~
size, it is reasonable to assume that this excessive grain growth _ occurred as a result of a thermal excursion in the range of 2000*F,
- most likely 2100*F. -Additionally, this grain. growth would have had to occur prior to the internal oxidation, since the oxidation would have served to " pin" the grain boundaries (i.e., prevent grain growth by a second phase material in the grain boundaries).
The most likely course of events was that grain growth was the result of a' temperature excursion during the heating cycle (s) associated with the piercing operation. This is possible due to controller malfunction, operator error, or inadequate process controls. Since this metal' deformation was performed above the recrystallization temperature, no grain refinement would be expected during deformation. The subsequent solution heat treatment operation-provides the large grain size, since the. furnace atmosphere control would tend to be toward the'1ess oxidizing regime to avoid scaling. 4.0 IHSI RESIDUAL STRESS AND FRACTURE MECHANICS ANALYSIS Nutech has performed an analysis to determine the residual stresses in the cross after IHSI. The analysis has confirmed that compressive stresses are present on the ID of the cross in the vicinity of the IHSI treated welds and that this stress diminishes with distance from the IHSI treated area, J14 MISC 85111904 - 20
Prga 21 of 23 The analysis has also shown that tensile stresses exist on the Outer Surface (OD) of the cross in the region of the treatment and that these-stresses diminish with distance from the' treated area (Figure 20 and 21). Blind hole drilling performed by Southwest Research Institute on the IHSI treated trial cross confirms that tensile stresses do exist on the OD and that compressive stresses exist on the ID. It appears that the grain boundary defects opened up to the surface in areas where the calculated residual tensile stress was about 20-25 kai (Figure 20). GE performed a fracture mechanics analysis to determine ASME Code , acceptable crack sizes (Table 1). The GE analysis has shown that: (1) Based on maximum operating stresses and for a factor of safety of 3, a 360' circumferential crack of a depth equal to 75% of the wall thickness is acceptable. (2) Based on maximum operating stresses and for a factor of safety of 3, a 10" axial through-wall crack is acceptable. (3) Based on the size of the existing indications, and the allowable flaw size, the incremental growth is negligible. It is, therefore, concluded that continued operation is justified for the life of the plant. J14 MISC 85111904 - 21
r. I e P::ga 22 of 23 4.1 Summary of Residual Stress and Fracture Mechanical Analysis .
- 1. - After implementation of IHSI compressive stresses are present on the inside surface and tensile stresses are present on the outside surface in the vicinity of the IHSI treated areas,_and that these stresses diminish with distance from the treated area.
- 2. The grain boundary defects opened up to the surface in areas where residual tensile stresses reached 20-25 ksi.
- 3. The incremental growth of existing indications is negligible.
Therefore, continued operation is justified for the life of the plant.
5.0 CONCLUSION
S (1) The indications found on the GGNS-Unit 1 crosses are shallow near surface grain boundary defects induced during the preform fabrication operation. (2)' The maximum observed depth of penetration of the grain boundary from the outside surface is 0.30". (3) The grain boundary defects were not caused by IGSCC. (4) IHSI treatment has been shown to have opened the near surface grain boundary defect to the surface. J14 MISC 85111904 - 22
'[T ~ [. :
p. 18' Pcga 23 of 23 (5) Fracture Mechanics analysis has concluded that ASME Code. safety margins are maintained with any remaining indications on the GGNS-y Unit-1 crosses. (6) The incremental growth of any' remaining indications is negligible.
'Therefore.. continued operation-is justified for the life of the plant.
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- J14 MISC 85111904 - 23 ,
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Appendix 1 Overview of GGNS Unit-1 IHSI Scope: Twenty-four (24) welds and two (2) twenty-four (24) inch forged pipe caps (welded to upper 24-inch outlet on crosses). l
' Results:
.o All twenty-four (24) welds treated in accordance with EPRI IHSI requirements and acceptance criteria.
o One cross cap treated in accordance with EPRI IHSI requirements and acceptance criteria. o One cross cap treated in accordance with EPRI IHSI requirements and accepted by analysis. Comments: The only unusual or unexpected event was the identification of cracks on the bodies of the crosses following the completion of IHSI. F e
- J14 MISC 85111906 - 1
- L.
,u -
. Appendix 2 Overview of-ISI Activities Related to IHSI Scope: Pre ~and Post'IHSI Ultrasonic Inspection of IHSI treated welds and cross' caps to detect any exiting IGSCC.
Results:
- o. All welds and cross caps examined by newly recertified examiners.
o No IGSCC was detected. l-9 J14 MISC 85111907 - 1
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Appendix 3 Overview of Changes in ID Stress Level Due to OD Grinding (IHSI ID Compressive Stress) b
, <s:
-In removing or. reducing the lengths ofLthe liquid penetrant gj-
. indications on the outside~ surface of the cross body,'the magnitude of the
-residual compressive stress on the inside surface of.the cross body is also reduced. .However, it should be noted that the grinding being performed is located several inches away.from tl.e welds where the IHSI was applied as a mitigation for IGSCC and that the' grinding is being performed on the '
' thicker section of the cross body, not in the weld prep transition area.
Nutech has' performed an analysis showing the changes in the level of residual stress in the cross body and near the weld root and H.A.Z. These results indicate that while there has been a reduction in the residual compressive stress on the weld ID, significant compressive stresses are _ , stilltpresent on the weld ID. The effect of the IHSI treatment for mitigation of IGSCC has not been lost. The weld ID is in a compressive stress field in excess of 10 KSI. J14 MISC 85111908 - 1 E .
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lO : : 270 275 220 265 290 295 Sco Sc6 310 516 S20 826 360 SS6 Siv ELeMEWTG "UppSF c.olL I CROGG OUTGIDS GURPNe BL5 MENT MdMPER-PIGUP5 S.I - REGIDdAL GTFt5nGE6 09 di?S66 0J T 5F sdPFAds i /-?-~5.c '41 FFecePdC5 F/.Gt. .21 l l-Revision o l p, i Precared By/Date JAT[li-6-86 _ ,, g l Checked By /Date d'VillO3 I ,o c. TABLE 1 CRITICAL AND ALLOWABLE FLAW SIZES CRACK TYPE CRITICAL FLAW SIZE ALLOWABLE FLAW SIZE
- AXIAL 35.7 INCHES 10.3 INCHES THROUGH-WALL CIRCUMFERENTIAL 90% 75%
(360* PART THROUGH CRACK) ,u Determined using a factor of safety of 3. { l l}}