ML19345G508
| ML19345G508 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 03/31/1981 |
| From: | Towsley H DAIRYLAND POWER COOPERATIVE |
| To: | James Shea Office of Nuclear Reactor Regulation |
| References | |
| LAC-7440, NUDOCS 8104070407 | |
| Download: ML19345G508 (3) | |
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In reply, please
'.9, pp refer to LAC-7440 A
Director of Nuclear Reactor Regulation ATTN:
Mr. James J. Shea, Project Manager Operating Reactors Branch No. 5 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C.
20555
SUBJECT:
(1)
LACBWR Forced Circulation Piping Corrosion Program.
(2)
LACBWR Reactor Vessel Lamination
Dear Mr. Shea:
A portion of piping in each of the forced circulation loops, not behind the biological shield walls, is of low-alloy steel.
The alloy steel is made to ASTM Specification A335, Type P-ll (lh Cr-h Mo).
The low alloy piping is between loop isolation valves and this section of piping contains the forced circulation pump.
A program was established in 1967 to investigate the corrosion rate of this low-alloy piping.
The program consisted of two phases:
(1) evaluation of corrosion specimens placed in 8-inch nozzles out of the main stream of the piping, stagnant conditions, and (2) wall thickness measurements at selected points in the piping system, flow-ing conditions.
The intent of the two phases is to provide infor-mation on corrosion rates of the material in stagnant and flowing water.
Data has been taken twice on the corrosion specimens.
Corrosion rates have been calculated-in accordance with procedures given in ASTM G-1, " Standard Recommended Practice for Preparing, Cleaning and Evaluating-Corrosion. Test Specimens" using 27,055 hours6.365741e-4 days <br />0.0153 hours <br />9.093915e-5 weeks <br />2.09275e-5 months <br /> as the time of exposure.
After the coupons were removed, they were transported to SwRI where they were cleaned, weighed, and examined.
Corrosion rates were calculated on the basis of weight loss from the following formula given in ASTM'G-1:
(534,000) (original Wt. - Final Wt.)
Corrosion Rate (mpy)
=
(Density) (Area) (Time)
Wei<3 t is~in grams, h
where:
3 Density is in grams /cm,
2 Area is in inches, and Time is in hours.
f N f'G 1 s q8 1810,4070 @ 7
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Mr. James J.
Shea, Project Manager LAC-7440 Operating Reacters Branch No. 5 March 31, 1981 Criginal and final weights, weight icsses, areas of speci= ens exposed to the LACEWR environ = tnt, and calculated cerrosion rates for the ten speci= ens re=cved frc= the 13 1 cop were done.
The average calculated rate is 0.221 =py; cur accuracy in weighing and =easuring the coupons is less than the accuracy i= plied in this rate, but we can say with certainty that the average corrcsien rate of these coupons was between 0.2 and 0.3 =py.
This is an insignifi-cant general corrosion rate.
The appearance of the coupens was very good.
A s=coth black exide was present on the coupons when they were re=cved; after removal of the oxide the steel underneath was also found to be s=coth and free frc= localized corrosion.
Sc=e pitting was present in creviced areas under spacers used to separate coupens.
These pits were judged to be between 5 and 10 =ils deep.
The overall conclusion is that A-335, P-11 steel has excellent general ccrrosion resistance in the LACEWR enviren=ent, but is mildly suscept-ible to pitting in crevices.
Wall thickness =easurements on the icw-alley piping were taken at two places in each loop - a straight pipe secticn en each pu=p dis-charge, and en a suction elbow in each loop.
The =easure=ents have been done 5 ti=es by ultrasonic =eans at each 5 of cutside circu=-
ference at each 1ccation.
The results showed that general corrosien was negligible- (less than 3 mils), and localized corresien was less than 80 mils.
Although systematic error of the instru=entation established 80 =ils as the threshold of accuracy, localized corrosien probably has a much icwer value.
This uncertainty is due to syste.-
atic error facters in ultrasenic thickness =easure=ent which were not recognized when the prcgram was initia*ed.
Measure =ent data frc=
1968 and 1973 were reduced and cc= pared statistically to de=cnstrate that carbon steel-pipe corrosion is not a matter for c;.rrent concern.
The last wall thickness =easure=ent was done in 1975.
An ultrasonic examination of the nozzles to reacter prese ne vessel welds in 1970 disclosed a laminar flaw located -adjacent (beneeth)
Recirculation Outlec Nozzle No. 1, and also adjacent to a 1cngitudinal i
. vessel weld.
The riaw = cst likely develcped as a result of the fabri-cation stresses during the manufacturing process.
Because the vessel stress analysis did not necessarily consider all the types of Icadings t
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which might be present in the direction of the thickness of the plate,
.a planned program for periodic inspection of this flaw has been done.
There have been six exa=inations, the last in 1979.
Analysis of the exa=ination data has revealed that the la=inar con-dition has not changed nor are there any indications of vertical cc=ponents developing.
No significant changes have occurred since the criginal scanr.ing in March 1970.
...ms.
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Mr. James J. Shea, Project Manager LAC-7440 Operating Reactors Branch No. 5 March 31, 1981 If you have any questions regarding this letter or if you need additional information, please let us know.
Very truly yours, DAIRYJAND POWER COOPERATIVE f( &&Jb*A
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H. A. Towsley LACBWR QA Supervisor HAT:af-cc:
R. Shimshak J. Taylor i
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