ML18093B523
| ML18093B523 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 03/17/1989 |
| From: | Miller L Public Service Enterprise Group |
| To: | Russell W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| 89-01, 89-1, NLR-N89049, NUDOCS 8903280211 | |
| Download: ML18093B523 (29) | |
Text
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Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge. New Jersey 08038 Nuclear Department
- w. T. Russell, Administrator NRC Region I 475 Allendale Road King of Prussia, PA 19406 Gentlemen:
SPECIAL REPORT 311/89-01 SALEM GENERATING STATION UNIT NO. 2 DOCKET NO. 50-272 March 17, 1989 NLR-N89049 This special report is being provided as committed to in our Request for Discretionary Enforcement dated March 3, 1989. -The Request for Discre~ionary Enforcement involved Technical Specification 3.6.2.1, Containment Spray and was necessitated by a through-wall leak on the Unit 2 No. 21 spray header line.
The attached (Attachment 1) report describes *the corrective actions taken, the to-date results of our investigation into the root cause and future corrective actions.
The result of future examinations will be provided when they become available.
If you desire, PSE&G will present the results of our investigations at your convenience.
Should you have any questions on this*transmittal, please do not hesitate to contact us.
Attachments 8903280211 890317 PDR ADOCK 05000272 S
PNU The Energy People Sincerely,.,
- fu~
L. K. Miller General Manager *-
Salem Operations
W. T. Russell NLR-N89049 c
Mr. J. c. Stone Licensing Project Manager Ms. K. Halvey Gibson Senior Resident Inspector
- 1?1Doaumen.a~ant:.¥8'.i-"BTf~
Mr. Kent Tosch, Chief 2
New Jersey Department of Environmental Protection Division of Environmental Quality Bureau of Nuclear Engineering CN 415 Trenton, NJ 086.25 3/17 /89
I ATTACHMENT 1 Immediate Corrective Action The 21 containment spray train was tagged out of service and the header isolated inside containment by removal of a spool piece and installation of a blind flange.
An approxbmate.ly 38 11 long, 8 11 diameter pipe section with approximately 10 bend was removed from the 21 containment spray header.
This piping was radiographed and a field replication study as described in was performed onsite.
Three portions of the removed pipe (both ends and a middle section) were sent to Westinghouse for metallurgical analysis.
A new spool piece was cold bent from a 20 foot section of pipe to the required dimensions.
During the bending process *a gouge was created on-one end of-the 20 foot long pipe~
Measurements were taken of the actual wall thickness after bending and were found acceptable by engineering analysis.
However, this end was not used in the field. "The other end of the 20 foot pipe was also bent to the required dimensions and this end was installed in the field* using slip-on flanges.
The installation was carried out with the applicable code being the ASME Boiler and Pressure Vessel Code,Section XI, 1983 edition and Addendum, Summer 1983.
The change package was reviewed by the NRC Resident Inspector at Salem.
The installation was hydro tested at 1.25 x design pressure and no leaks were found.
The 21 spray header was declared operable on March a, 1989.
A photograph of the repaired section of pipe is attached.
Additional examinations of the 11, 12, 21 and 22 containment spray trains were performed to identify any additional areas of concern.
Examinations.consisted of field walkdowns for the 11, 12, 21 and 22 headers and NDE examinations of the 21 and 22 headers as described later.
Field walkdowns were performed to identify any visible leakage or discolored areas indicative of heating.
No further leakage was observed.
Additionally, chloride swipes were performed on selected areas of the spray neaders.
This examination identified some areas where surf ace chloride levels were out of specification.
These areas were cleaned and brought to acceptable levels.
The metallurgical examinations found that the surface. chlorides.. were not. a... contributor. to. the. f orma ti on. of. the.
cracks*~
Discolored** areas* were'* identified" on** the* Unit** 2,
- 22***
containment spray header (1 location) and the Unit 2, 21.
containment spray header (2 additional locations).
These areas were examined by liquid penetrant and no defects were identified.
Additional field sensitization determinations will.be performed on suspect areas.
NDE consisted.of* the following examinations:
Ultrasonic (UT) examination of the_21 & 22 containment spray header was initially employed for the detection of discontinuities such as those associated with the leak on the 21 NLR-N89049
2 -
spray header.
Several indications were observed in the area of the leak.
Two additional areas of discoloration on the 21 spray header and one on the 22 spray header were observed and were subsequently examined.
Random ultrasonic reflectors from the inside surface between nine and three o'clock were observed in all of the areas.
A visual examination of the cut out section of the pipe with the leak failed to confirm the source of the UT reflectors.
NOTE:
Ultrasonic testing did detect a linear indication associated with the through wall leak.-
This linear indication was later confirmed by radiog~aphy.
.. *~*~
Based-on the facts available at that time, a decision was made to examine the discolored areas on 21 and 22 CS Headers with liquid penetrant {PT) and gamma radiography {RT).
It was determined that manual ultrasonics was not the best tool to be used for the detection of small linear indications on large sections of thin wall piping.
The following areas were examined by NDE:
{see Sketch 1)
Spool Piece 2CS60 Arc II B" 21 Header PT,RT, UT Spool Piece 2CS61
-21 Header PT,RT Upstream of hanger 2P-CSH-305 22 Header PT,UT Spool Piece 2CS.60 Cut out Section 21 Header UT,RT The results of the PT and R'll-examinations are summarized as follows:
Penetrant -
The three areas revealed no linear indications.
The area upstream of hanger 2P-CSH-305 on 22 header had random rounded indications in a band one-half inch wide along the inside radius of the formed pipe.
Radiography -
Spool Piece 2CS60 Arc 11B11 21 Header -
no relevant indications were observed.
Spool.. *Piece* 2CS61: 21 *Header. -': a*
one-half inch long. l.inear indication was.
observed in the axial plane.
The indication is sharp and distinct and differs in appearance from the radiograph of the leak which appears somewhat broad and diffused.
Several rounded indications were observed in the long seam weld.
This area was later hydro-tested with no leaks observed.
Spool Piece 2CS60 Cut Out Section 21 Header
{area containing leak) - three linear indications were observed, two were running circumferentially
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and measured 5/16 11 and 1/2" in length.
The third indication was running axially and measured 5/16 11 in length.. All three indications appeared somewhat broad and diffused.
Additional radiographs were taken down the length of the cut out section revealing several linear broad and diffused indications also running circumferentially.
Area upstream of hanger 2P-CSH-305 22 Header remains to be radiographed.
Indications found during these examinations will be subject to future examinations as detailed below.
Root cause Investigation As stated previously, portions of the removed section.of pipe were examined onsite by Maplewood Laboratory.
Results of their examinations are J:'.)'rovided in Attachment 2.
Additional sections (Sketch 2) were sent to Westinghouse for further testing.
These results are presented in Attachment 3.
The results indicate that the cracks were internally initiated in a localized, sensitized area and were due to intergranular stress corrosion cracking caused by stagnant borated water.
Corrective Actions Future corrective actions that are currently planned are as follows:
- 1.
As stated previously, Header 22 has a section of pipe which may have been heated during plant construction.
This area will be examined by RT at the next outage of sufficient duration.
- 2.
Any indications found during previous or future NDE examinations will be examined by Maplewood Labs to determine whether.the area of pipe in indication area is sensitized.
- 3.
Piping in the penetration area will be added to weekly rounds by Operations.. personnel. to.. identify leaks. from s.erv:ice water..
piping* onto "Containment* spray* and* sa*fety*inj*ect:ion** piping~
Any leakage will be cleaned up in accordance with current station administrative procedures.
- 4.
Procedure changes are being made to require fluid samples be taken from piping in the penetration area arid from piping inside containment.
These samples will be analyzed for chlorides.
Any out-of~specification chemistry will require flushing the piping to meet applicable specifications.
The procedure change will be in effect by April -1989.
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- 1.
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CONTAINMENT B'-2-CS-6il~,_____.
21CSHDR CONTAINMENT SERVICE WATER
- PIPES. ABOVE**,
22CSHDR DISCOLORED BEND REPLACED PIPE AREA TEST CONE CTI ON 21CS52 2CS60 8~2-CS-60ARCB 2P-CSH-305 DISCOLORED AREA 22CSS FROM RHR 8'-2-CS-73 SKETCH I AUXILIARY BUILDING FROM RHR AUXILIARY BUILDING
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SECTIONS SENT TO WESTINGHOLJS*E
- 4) PS~G RESEARCH AND TESTING LABORATORY REPORT To the Technical Manager -
March 10, 1989 Salem Technical Department -
PSE&G Report No. 72428 FIELD REPLICATION AND LABORATORY EXAMINATION. OF NO. 2 UNIT CONTAINMENT SPRAY PIPE SPOOL PIECE, SALEM GENERATING STATION Requested by P. J. Ott, March 4, 1989 Analysis Conducted by R. T. Heeren INTRODUCTION A field replication study was made on an 8 inch diameter, schedule 10, containment spray pipe spool piece removed from No. 2 Unit at Elevation 95 feet.
It was reported that the approximate 38 inGh long spool piece had developed a pin hole leak in service and had been removed and sent to the Hot Shop for examination.
The spool piece had a 10" bend.
The Laboratory was requested by the Inspection Services engineer to determine the condition of the austenitic stainless steel spool piece material in a suspect pinhole failure area, and to look for material sensitization (carbide precipitation at the grain boundaries).
The spool piece examined by replication was identified by the 11Station 11 as 11 Containment Spray Pipe Spool Piece in Hot Shop".
SUMMARY
I.
The* containment <spray pipe spool piece examined** at* an outer bend surface area by field microscope and replication showed almost no carbide precipitation in the grain boundaries of the austenitic stainless steel material.
Hence the area examined. is not considered sensitized.. There was. no evidence of crack~ng or intergranular corrosion, however some surface roughness in a few spots was noted that progressed deeper than the polished surface.
These anomalies could be sugges-tive of corrosion pitting.
L.-4*2
Technical Mgr.
Salem Tech. Dept.
SUMMARY
(cont'd.)
2 -
March 10, 1989 Report No.. 72428 Since the internal surface of the pipe could not be examined
- it could not be established if the anomaly found was due to internal surface through wall corrosion or cracking or merely an external surface anomaly.
- 2.
The microstructure showed slip bands that resulted from cold working in the bend area during manufacture.
- 3.
The pinhole type through the wall failure was not found in the microstructure of the area examined.
TEST PROCEDURES AND RESULTS A.
Visual Examination:
Visual examination was made on the 8 inch diameter 38 inch long spool piece located in the Salem Hot Shop.
- The overall outside surface was gray in color with some surface rough-ness.
~he i~ternal surface of the*spool*piece was not examined, as the ends were plugged because of reported contamination.
The spool piece contained a slight 10 degree bend in the center of its length where the spot for metal-lurgical examination was chosen.
It was reported that the area chosen for microstudy contained a pinhole type failure.
B.
Microstudy and Replication:
For field microscopic examination and replication, the Metallurgy Procedure Met-8, Rev. 1, "Preparation Of Metals For Metallographic Examination In The Field", dated June 2, 1988, and Prociedure Met-15 "Preparation of Metals for
~etallographic Examination By The Replication Method, dated June 16,
- 1988" was used.;..
- The. *procedures*. used mechan.ical.
- po1ishing and etching to prepare the surface to be examined.
Field microscopic examination of the prepared surface.at 100 to 400X magnification showed no evidence of excessive carbide precipitates at the grain boundaries.
There was no evidence of cracking or intergranular corrosion.
The microstructure contained slip bands that resulted from cold working during manufacture.
)
Technical Mgr.
Salem Tech. Dept.
3 -
TEST PROCEDURES AND RESULTS (cont'd.)
March 10, 1989 Report No. 72428 Two replicas, (No. 154 and 155) were made* on the prepared surf ace and processed for a record and further study at the Laboratory.
Microstudy of the replicas showed that the austenitic stainless steel was not sensitized (no excessive precipitation of carbide particles at the grain boundaries).
(Figure 1, top).
The few carbide particles that were found at the grain boundaries were not considered s'ignificant (Figure 1, bottom).
The microstructure contained slip bands in the grains and pit type anomalies or surface roughness (Figure 2).
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Materials Division RTH:mth 3510H c
R. F. Brandt Metallurgist
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Replica 154 Photo No. 5725 Mag. lOOX Replicaticiti photo showing austenitic stainless.steel microstructbr~*~~
spool piece.
Note material does not show excessive precipitation of carbide particles at grain boundaries.
Replica 154 Photo No. 5726 Mag. 400X Higher magnif ica-tion photo showing an area of some limited.. carbide precipitation at the grain boundaries (arrows).
This was the worst condition found.
Report No. 72428
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Figure 2
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Replica 155 Photo No. 5727 Mag. lOOX Replication photo showing slip bands in the grains resulting from cold working during manufacture.
Note some surface roughness at the center.
Report No. 72428
NATO Letter MI-MNA-063 ATTACHMENT 3 METALLURGICAL FAILURE ANALYSIS OF A LEAKING CONTAINMENT SPRAY LINE FROM SALEM UNIT 2 C. M. Pezze March 1989 Work Performed Under Shop Order SEFP:...138...
WESTINGHOUSE ELECTRIC CORPORATION Nuclear and Advanced Technology Division P.O. Box 2728 Pittsburgh, Pennsylvania 15230-2728 I I I
1.0 INTRODUCTION
Public Service Electric and Gas Company personnel detected a leak at the Salem Unit 2 site on the number 21 containment spray line during a routine su.rveillance of the pumps.
The leak was detected by the presence of local boric acid crystal buildup on the outside diameter of the line.
The 8 inch outside diameter Schedule 10 pipe was manufactured in accordance with ASTM A312 type 304.
The section containing the leak was removed and replaced.
In an attempt to determine the root ca.use of the leak, the pipe section removed was submitted to Westinghouse Nuclear and Advanced Technology Division (NATD) for failure 'analysis investigation.
This report describes the techn~gues employed and the results obtained from the failure analysis investigation.
The evaluations included visual examination, light optical macrophotography, radiography, metallography, scanning electron fractography, hardness measurements and chemistry evaluations.
The final section of the report provides recommendations for mitigation of the leaking containment spray line.
2.0 METALLURGICAL EVALUATIONS AND RESULTS This section describes the techniques employed in the failure analysis of the leaking containment spray line.
The steps performed during the investigation are discussed and the results presented.
The samples submitted from Salem Unit 2 consisted of two longitudinal sections of the 8 inch outside diameter pipe labeled Al and A2, and one half of a longitudinal section labeled B2, and a small rectangular section labeled Bl.
~he samples labeled Al and A2 were.halves of the same section of pipe.
PSE&G personnel reported that the leak was located on one of the sections labeled Al and A2, therefore the examinations were centered' around these two sections.
The inside diameter surface of the Al and A2 pipe sections contained an isolated concentric area containing a heavy oxide with an orange color, an area containing black colored oxide and finally an area containing a shiny metal surface (see figure 2-1).
The outside diameter sections Al and A2 contained an area that appeared as though it was polished or ground.
This area corresponded to the inside diameter area that contained the orange colored oxide.
In. an.attempt, ta.. locate.. the. leak location(s),.. the.Al... and.. A2... pipe.. sections.
were* subjected* tc radiographic* examination~. The examinations** were conducted utilizing a Seifert Isovolt 320 X-ray machine.
The radiographic examination revealed two circumferentially oriented cracks separated by approximately 1/4 inch and located approximately 5 inches from the top of the edge (the edge containing the heavy oxide) and approximately centered on the A-2 pipe section.
Metallographic examinations were conducted on section Al-2 from the orange colored oxide area on Al, on section A2-2 from the leak location on A2, and on section A2-l from the shiny metal area away from the leak location on A2 (see figure 2-2).
The samples were mounted, polished and etched in a solution comprised of glycerol, acetone, nitric acid and hydrochloric acid.
The samples were examined under the light microscope in.both the as-polished and etched condition.
The examination of section Al-2 rravealed an annealed austenitic stainless steel microstructure.
The examination of sections A2-1 and A2-2 revealed a cold worked austenitic stainless steel microstructure.
The course grained structure of the annealed austenitic stainless steel microstructure had an ASTM grain size of 1 and the other sections, including the microstructure in the leak area, had a much finer ASTM grain size of 4 (see figure 2-3).
The examinations in the leak area revealed very tight intergranular cracking_ (see figure 2-4).
The metallographic mounts were then subjected to an electrolytic oxalic etch in accordance with ASTM-A-262 practice A.
The results of this examination revealed a heavily sensitized mic-rostructure in the leak area, a small amount of sensitization in the area away from the leak, and no sensitization in the area of the orange colored oxide (see figure 2-5).
One of the cracks in the leak area was opened and fractographic examination was performed on the freshly opened fracture face by scanning electron microscopy (SEM) techniques.
The SEM examination revealed an intergranular fracture (see figures 2-6 and 2-7).
In an attempt to identify contaminating species which may have contributed to the failure, the fracture face was subjected to energy dispersive X-ray spectographic (EDS) analysis.
The results of the examinations revealed iron, nickel.and chromium~
Rockwell B hardness measurements were attempted on the outside diameter surface of Al and A2.
The radius of the pipe proved to be too large such that intimate contact between the hardness tester and pipe could not be maintained.
Therefore Knoop hardness measurements were conducted on each of the metallographic mounts and converted into Rockwell B.
As expected, the results listed in table 2-1 indicate that -the coarse grained microstructure in section Al-2 had a slightly lower hardness than_ sections A2-1 and A2-2.
Quantitative chemical analysis was performed on the pipe base material.
The metals analysis was accomplished utilizing inductive coupled plasma spectrometry and.. the. sulphur. analysis.. waa accomplished. utiliz.ing.
combustion/titration*** techniquei:r.;
- The* results** listed* in. table* 2-2 *indicate**
that the pipe is within the specified chemical composition for an ASTM A312 type 304 material. I I
TABLE 2-1 HARDNESS MEASUREMENT RESULTS Section Al-2 (coarse grains)
A2-1 (fine grains)
A2-2 (fine grains)
- Rockwell B 74.9 79.7 76.9
- NOTE:
The values listed are the average of five measurements. *
)
ASTM A312 type 304 Al-5 c
TABLE 2-2 CHEMISTRY EVALUATION RESULTS Chemical Composition, wt. \\
Mn P
S Si Ni 0.08 max 2.00 max 0.04 max 0.03 max 0.75 max 8-11 0.058 2.00 0.021 0.026 0.47 10.08 I I Cr 18-20 18.79
3.0 DISCUSSION The results of the visual examination revealed a heavy oxide with an orange layer on top of a black layer on the inside.diameter surface of sections Al and A2 of the containment spray line.
This heavy oxide was in a localized patch and the outside diameter surface had a polished or ground appearance in the same area.
Heating the 304 stainless steel would cause a heavy black oxide, magnetite, to form on the surfaces.
As the magnetite is exposed to a moist oxygenated environment, it will slowly transform to hematite which is an orange colored oxide.
The polished or ground outside diameter surface appe~rance is indicative of removal of oxide.
This data seems to indicate that the pipe was heated locally (flame washing) prior to being put into service.
Additional evidence of the localized heating on the pipe is the coarse grained, softer, annealed austenitic microstructure (see figure 2-3 *(a)) in this location..
This microstructure **is. the" result of the 304 stainless steel being held at an elevated temperature 0
(<1040 C).
The metallographic examination of the leak area (see figure 2-4) revealed an intergranular through-wall crack.
In the vicinity of tlee leak there were a number of incipient intergranular cracks that initiated at the inside diameter surf.ace and propagated towards the outside diameter.
The sensitized microstructure (see figure 2-5 (b)) is common in 304 stainless steels that are exposed temperatures in a critical range (550° to 850°C) *. This condition, carbide precipitation at the grain boundaries and subsequent chromium depletion nearby, result. in a microstructure.
particularly susceptible to intergranular cracking in a stagnant borated water environment.
Additiona~ evidence of th~ intergranular fracture.
morphology is provided in the scanning electron fractographs (see figures 2-6 and 2-7).
The fractography indicated.that the crack penetrated the outside diameter at only a* few locations.
The metallographic and fractographic results indicate that the cracking initiated at the inside diameter and propagated to the outside diameter.
The chemistry evaluation results (see table 2-2) indicate that the spray containment line was within the specified limits of a ASTM A312 type 304 material.
It is well understood that austenitic stainless steels that contain more than 0.03 weight percent carbide precipitation along the grain 0
0 temperatures from about 550 to 850 c.
contained 0.058 weight percent carbon chromium carbide.. precipitation *.
4.0 CONCLUSION
S carbon become susceptible to chromium boundaries when they are exposed to The spray containment line and therefore was susceptible to Based on the results of the evaluations performed it.is concluded that the leak on the number 21 containment spray line resulted from IGSCC that initiated on. insid,a diameter surface of the line. and propagated to the outside diameter.
IGSCC susceptibility in austenitic stainless steels is
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- influenced by the environment, stress and microstructure.
It is understood that the containment spray line contains a stagnant borated water environment and is primarily at ambient temperature.
Laboratory data and service experience, as stated in NRC I.E. bulletin 79-17, indicate that this stagnant borated water environment coupled with a sensitized microstructure is highly susceptible to IGSCC.
The specific chemical species known to promote IGSCC on sensitized austenitic stainless steels include oxygen, chloride and sulfide.
It is important to note that chloride and sulfide levels within the specified limits in the presence of an oxygen saturated fluid can promote IGSCC on sensitized austenitic material.
The sensitized microstructure most likely occurred during the localized heating of pipe.
The localized heating induced a temperature gradient in the pipe such that some portion was in the sensitizing range 0
0 (550 to 850 C) which promoted carbide precipitation.at the grain boundaries.
5.0 RECOMMENDATIONS Essentially the factors which contributed to the IGS~C of the containment spray line are the sensitized austenitic stainless steel microstructure and*
the stagnant borated water environment.
The unique aspect of this containment spray line leak is that the sensitized region is not in the vicinity of the weld but rather in some unknown base metal area.
It is recorrunended that some effort to locate similar suspect lines be considered.*
The following are recorrunended techniques to find suspect lines:
- 1.
Perfqrm walkdown,of pipe lines looking for suspect areas that may have been heated. *suspect are~e will include patches of black oxide. or patches of polished/ground surfaces particularly in the vicinity of elbows.
- 2.
Perform field metallography in the center of and some distance away from the suspect area.
compare the grain size of the microstructures present.
- 3.
Perform.field hardness measurements in the center of and some distance away from the sus;Pect area.
At least five measurements per area is recommended.
A softened area has most likely been annealed.
Once a suspect area has been confirmed to be locally heated, i.e. a sof.tened coarse grained.structure:,:: then.it, is,.recommended*,. that. some* form.*. of..
nondes.truc.ti.ve examination.,. either.. radiographic. or ultrasonic.inspection,.
be performed on the line in an attempt to identify cracks.
Recorrnnendations.for mitigation of the IGSCC potential in the future include eliminating the susceptible material and the environment.
The sensitized austenitic stainless steel microstructure and the environment can be eliminated by:
- 1.
Avoiding localized heating (flame washing) during fabrication.
- 2.
Utilizing a steel with a reduced carbon content (below 0.03 weight percent) such as type 304L.
}*
Implementation of periodic chemistry analysis of water in the system
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FIGURE 2-1 ~crophotographs i11ustrati*9 the inside diameter surface condition; (al sectio
~-1 (not* red color is from pT) and lb) section ~-2.
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FIGURE 2-1 cont.
~-7" Orange Oxide-~-r-Al-3 (METALLOGRAPHY)
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(CHEf4ISTRY)
Weld A2-2 (METALLOGRAPHY)
Orange Oxide 1-:::~~L_---A 2-3
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- FRACTOGRAPHY) 9-1--r---A 2-1 (METALLOGRAPHY)
Section A2 FIGURE 2-2 Sche_matic illustration of sectioning sequence used on A-1 and A-2.
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(a) lOOX (b) lOOX FIGURE 2-3 Light optical micrographs illustrating the microstructures at various locations on the pipe; (a) Microstructure at Al-2, and (b) Microstructure at A2-2.
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FIGURE 2-4 Light optical micrograph illustrating the intergranular through-wall crack on section A2-2.
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Light optical ~icrographs illustrating the structures following an electrolyitc oxalic etch; (a) Al-2, (b) A2-2 and (c) A2-1.
- FIGURE 2-6 Scanning electron fractograph illustrating the fracture morphology seen on the_ freshly opened crack.
FIGURE 2-7 Scanning electron fractograph illustrating the fracture morphology seen on the freshly opened crack (Area 1 of figure 2~6)..