ML19329E504
| ML19329E504 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 02/07/1973 |
| From: | Birkle A CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML19329E498 | List: |
| References | |
| NUDOCS 8006160301 | |
| Download: ML19329E504 (2) | |
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e To WEKessler, GO-lGTA Faos AJBirkle, HH-930 s
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February 7, 1973
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POV!8f SussecT Midland Plant
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Company xs Steam Generator Veld Records INTERNAL CORRESPCNDENCC Birk 18-73 cc The Babcock & Wilcox Co=pany Topical Report (EAW-lh02) was reviewed to ascertain if there was adequate data available to fulfill the intent of the docu=entation require =ents of the ASMI Boiler and Pressure Vessel Code,Section III (1968). Welding electrodes used with the manual =etal are veld-ing process to repair veld, veld pad buildups and veld so=e nos le attach =ent velds on steam generators for B&W nuclear steam systems had unsatisfactory documentation of =echanical properties. This discrepancy was noted initially on my July 1h,1972 QA audit at Barberton on the Midland steam generators.
In one case both the che=ical and =echanical property documentation was =iss-ing but this batch of electrodes; ie, Type 7018 - lot nu=ber 51052A, was not used for the Midland steam generator fabrication. Further= ore, the Type 8015 and 11018 types were not involved on the Midland steam generator, Units 1 and 2.
The Type 7015 electrode which was involved has, based on data on Th lots of B&W =anufactured velding electrodes, s =ini=u= Charpy V-notch energy absorption of h5 ft-lbs at 10F. Although this value is entirely adequate, the typical values ranged fren 80 to 110 ft-lbs at +10F vith a nor=al distribution of values both higher and lover than these values. The =ini=um energy absorp-tion required by the ASME 3 oiler and Pressure Vessel Code is 20 or 30 ft-lbs at +kOF depending on the electrode type. At te=peratures in excess of +10F it is known that the fracture toughness increases rapidly so it can be reasonably expected that at the operating te=perature and pressure ve vill have values v'aich are substantially higher than the h5 ft-lb =inimum obtained from that one lot of velding electrode 3&W tested at +10F.
The tensile strength of all of the 73 lots of velding electrodes exceeded to the required =ini=um.
The
" carbon equivalent" of the veld deposit frca the actual velding electrodes used for the velding on the Midland steam generators was shown through correla-tion with the lots of electrodes with known che=istry and tensile properties to exceed the =ini=u= required tensile stre=gth. This =ethod of correlation using " carbon equivalents" has been shown to be technically Ecceptable if all other parameters such as veld heat input, joint configuration, etc, para eters are duplicated closely.
In a check vith Barberton personnel I have been assured that they hold these para =eters to tights limits so their laboratory tensile and Charpy V-notch test results vill indeed be indicative of actual shop velds. In a subsequent QA audit at 3arberton I will reviev velding pro-
'cedures to verify that velding electrode qualification velding para =eters do simulate actual repair velds.
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T g WEKessler, GO-107A Midland Plant 2
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Steam Generator Veld Records
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February 7, 1973 On Unit 2 the 7018 velding electrode was used in addition to the 7015 type already discussed.
For this filler tetal type the SW Co=rany has 11 lots of Type 7013 velding electrodes where the tensile, Charpy V-notch,
'f and chenistr-f is knovn. " Carbon equivalents" of the lot nu bers 818-026931 and 1078h show that the tensile strength of the electrode lots used en the Midland Unit 1 steam generator is above the 70,000 usi minimum required.
These 11 lots of S pe 7018 velding electrodes with kncvn chemistry, tensile f
strength, and Charpy V-notch properties the Charpy V-notch energy absorption at h0F exceeds the 20 ft-lb required by the AS'!E Boiler and Pressure Vessel Code by a large =argin. The lovest value of the known S pe 7018 Charpy V-f notch energy absoretion is h3 ft-lbs at +10? vith typical values which exceed 100 ft-lbs consistantly.
From the viewpoint of experiencing a failure due to rapid fracture of the Midland steam generators I have used linear elastic fracture techanics calculations to show that the lack of documentation of the 7015 and 7018 velding electrodes vill not adversely affect the safety of the plant.
The 43 and h5 ft-lb Charpy V-notch energy absorption values at +10? (the minicus values obtained from the velding electrodes with known mechanical properties) are approximately equivalent to a critical stress intensity factor of 180 K siVinch which, at the yield strength of the caterial, results in a flav size for failure which exceeds one-half the vall thickness.
At higher te=pera-tures than +10? this calculated critical flav size for failure vill increase rapidly to a still larger value because ferritic stee'.i undergo a transition in fracture toughness with a change in te=perature. At service stresses which are much lover than the yield-strength of the material (AST'4 516, Grade 70) used in the comparison and at the operating te=perature flaws required to cause failure would correspondingly be greatly in excess of one-half the thick-ness, and a leak-before-break criteria would be valid.
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