ML20086E336
| ML20086E336 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 04/16/1974 |
| From: | Walker R PUBLIC SERVICE CO. OF COLORADO |
| To: | Knuth D US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20086E328 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8312060460 | |
| Download: ML20086E336 (8) | |
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4 PUBLIC SERVICE COMPANY OF COLORADO P. O.
SOM S40.
D E N V E M.
COLORAOO OORO1 April 16, 1974 Dr. Donald Knuth Directorate Regulatory Operations Office of Regulations Washington, D.C. 20545
Subject:
Deficiency Report 10 CFR 50 Heat Exchanger Corrosion, Service Water System Ref:
Interim Report Filed March 8, 1973 Final Report Filed October 18, 1973
Dear Mr. Knuth:
Pursuant to the reporting requirements of 10 CFR 50, Part 50.55, we are submitting herein the twenty (20) copies of our follow-up report concerning the heat exchanger corrosion problems in the service water system at our Fort St. Vrain Nuclear Generating Station. This report is filed as a follow-up to the reports referenced above, and to provide additional information resulting from subsequent developments.
It is felt that our heat exchanger retubing work and surveillance -
plans will result in a satisfactory correction to the problem.
We will keep the local Directorate abreast of all significant developments.
We trust this report will provide you with sufficient information to evaluate the deficiency reported, and will fulfill the reporting requirements of 10 CFR 50.
Very truly yours,
.D W R. F. Walker Vice President Engineering and Planning Electric Department RFW/JHR Attachment h(
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E. Morris Howard, Directorate, Region IV f)'zlpl f
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8312060460 740516 PDR ADOCK 05000267
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DEFICIENCY REPORT 10 CFR 50 PART 50.55 i
FACILITY:
Fort St. Vrain Nuclear Generating Station
SUBJECT:
Heat Exchanger Corrosion, Service Water System REPORT DATE: April 16, 1974 L
REFERENCE:
Interim Report, Above Subject, Filed March 8, 1973 Final Report, Above Subject, Filed October 18, 1973 i
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9 1.0 SCOPE This report is filed as a follow-up to the reports referenced l
above, and to provide additional information resulting from sub-sequent developments.
It is the intent of this report to update the report of October, 1973,-presenting the current status of solutions to the heat exchanger corrosion problem, and to outline our program of future surveillance and testing.
2.0 GENERAL DESCRIPTION Implementation of the new Nalco chemical treatment program was begun in June, 1973. This program utilized the following Nalco Chemical Company products:
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- 1) Nalco 7351 (polyol-ester, polyphosphate, copper. corrosion inhibitor) at a control concentration of 18 ppm polyol-ester and 3 ppm polyphosphate.
- 2) Nalco 30B4 (liquid zine) at a control level of 4-1/2 - 5 ppm.
- 3) Nalco 344 (dispersant) at a control level-of 30 ppm.
- 4) pH control range of 7.5-8.2.
Evaluation of this program indicated less than satisfactory results-based upon visual examination of the System 46 heat exchangers during the retubing program. The tube surfaces had a considerable amount of iron deposits and the corrosion which we first observed back in February,1973, was continuing.
In September,1973, Stearns-Roger Corporation submitted a study of our service water system corrosion problems. This study included the following recommendations:
- 1) Retest all service water make-up wells for iron, after thorough pumping.
If iron content remains above 1.0 ppm, avoid using certain wells or install iron removal equipment.
- 2) Have the entire service water system cleaned by a recognized, reliable chemical. cleaning contractor.
l 3)
Immediately after the chemical cleaning, operate with an. elevated concentration of' corrosion inhibitor -- either_a zine polyphosphate, zine organic, or all organic material.
Feed rates, concentrations,
-l pH level as recommended by the' plant chemical. supplier.
4)
Resume normal service water system operation to water treatment.
chemical supplier's recommendation, and' install new coupons in-the i
test heat exchangers.
On October 17,.1973, the service water make-up wells.were tested for
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iron content.- The iron content of the wells varied from 0.05 ppm to 0.10 ppa after one (1) hour of operation.
In no case did the iron content of the water exceed 1.0 ppa, the limit beyond which iron removal equipment would be required.
The chemical cleaning of the entire service water system was begun on November 26, 1973, in conjunction with Stearns-Roger and Dow Industrial Service, and completed during the first week in December, 1973. The Dow chemical cleaning program consisted of:
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- 1) Low Temperature Scale Remover (LTSR).
- 2) Dow A-178 inhibitor to control corrosion.
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- 3) Citric acid for pH control.
This program resulted in the removal of a large quantity of iron oxide as Fe2 3 O
Following chemical cleaning, the Nalco treatment program as outlined previously was resumed with slightly higher chemical treatment concen-trations for the first few days.
During and after the chemical cleaning several leaks occurred in the service water system heat exchangers. These leaks were most noticeable in both of the System 47 exchangers and in two (2) of the System 21 exchangers.
3.0 IMMEDIATE ACTION TAKEN Work was inanediately undertaken to hydrostatically test and. plug leaking heat exchanger tubes so that the overall plant testing program could continue.
After examination of the leaking heat exchangers it was concluded that plugging of individual tubes was only a temporary solution, and that plans-would have to be formulated for retubing all of the affected heat exchangers. This was to include.(in addition to the four (4) System 46 heat exchangers) six (6) System 21 heat exchangers and two (2). System 47 heat exchangers.
4.0 EVALUATION AND STATUS OF SOLUTIONS Based upon General Atomic Company's recommendation, and upon visual inspection of the two (2) recubed System 46 heat exchangers which had been in service for several months,-it was decided to use the Sandvik 3RE60 stainless steel for recubing all affected heat exchangers.
Further, it was decided to change all tie rods, nuts, impingement plates and baffles from carbon steel to 304 stainless steel. Stearns-Roger Corporation performed. the-~ stress, thermal,-hydraulic and seismic,
analysis-for the materia 1' changes on the System 21 and System 46. heat exchangers; and Genera 1' Atomic Company performed this~ analysis work on.
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the System 47 heat exchangers. The System 21 and System 46 heat S
exchanger retubing work is being performed by Stearns-Roger Corporation utilizing refurbished original tube sheets. The System 47 heat exchanger recubing work is being performed by General Atomic Co,pany with new tube sheets.
During the course of our recubing activities a problem developed with the Sandvik tube material.
It was discovered that some of the new tubes purchased from Sandvik were not the specified 3RE60 material.
The evaluation and disposition of this problem is covered-in Attach-ment "A" of this report.
The current schedule for the recubing activities for the various heat exchangers is as follows:
Exchanger Service Scheduled In-Service Date E-2101 Back-up Bearing Water 5-30-74
- E-2106 Back-up Bearing Water 4-30-74
- E-2104 Bearing Water
' 4-19-74
- E-2104S Bearing Water 3-8-74
- E-2105 Bearing Water 5-3-74
- E-2105S Bearing Water 3-8-74
- E-4601 PCRV Cooling Water 4-16-74
- E-4602 PCRV Cooling Water 9-28-73
- E-4603 PCRV Cooling Water 7-6-73 E-4604 PCRV Cooling Water 5-30-74
- E-4701 Purification Water 4-26-74
- E-4702 Purification Water-5-10-74
- Presently retubed, but not yet in service.
- Presently retubed and in service.
5.0 LONG-TERM PLANS AND SURVEILLANCE Proposals from various other chemical treatment suppliers have been reviewed in an' effort to establish a more effective chemical treatment program. It has been concluded that, short of a chromate type treat--
ment, those proposals reviewed do not appear to differ greatly from the Nalco treatment program.- However. in' order to obtain quantitative data regarding long-term service water'syatem corrosion rates, the 4
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following program will be undertakant
- 1) Since the location of present corrosion test coupons in the service water system may, or may not, be indicative of corrosion rates throughout the system, test coupons are going to be installed at.seven (7) locations throughout the service water system. At each of the seven (7) locations the capability-to install five (5) coupons will be provided. The five (5) coupon insertion points at each of the seven (7) locations will be utilized as follows:
a) 30-day vendor coupon.
1 b) 30-day PSC coupon.
c) 90-day vendor coupon.
d) 90-day PSC coupon.
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e) Spare point.
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- 2) The majority of the carbon steel in the service water system is ASTM A-106 Gr. B.
Due to the fact that the 1010 mild steel coupons which have previously been installed in' conjunction with our test i
heat exchangers anay, or may not, be representative of system.
corrosion rates, A-106 carbon steel coupons have been orde' red and j
will be installed in the seven-(7) locations throughout the service 4.
water system, l-
- 3) A short length of flanged pipe will be' installed in a convenient.
point in the service water system to determine the effectiveness' of j
our chemical treatment program from this point in time.- This section of pipe can be removed for inspection when deemed necessary.
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- 4) A new Sandvik 3RE60 stainless steel tube' and a. carbon steel tube will be installed in our-test heat exchanger. ~ Corrosion rates will' be evaluated qualitatively, and, if possible, quantitatively at the end of 90 days.
It is anticipated that the foregoing programs will be implemented during May, 1974. After this program has been in effect-for a period of 90 days, an. evaluation of the present Nalco chemical treatment-will be' performed.
If results are satis-factory,' this chemical treatment program will be continued. - If the '
results indicate that the service water system corrosion rate is un-
. satisfactory, another chemica1' treatment supplier's product will be -
tested.
6.0 CONCLUSION
_The retubing of the twelve affected heat exchangers will provide the~
necessary heat exchanger. reliability and-effectiveness.
The extensive y
continuous monitoring program afforded by the installation of corrosion.
test coupons should provide the necessary information to evaluate the long-term corrosion. rate in the service water system..
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MTER-DEPA ENT MEMO-PUBLIC SERVICE COM Y OF COLORADO DArr April 17, 1974 To J. H. Readerm_ Resident Engineer Fort St. Vrain OEPARTMENT OR 08 VISION FROM L. McInrov. Supervisor Quality Assurance, Engineering DEPARTMENT OR DIVISION ATrN.
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Systems 21 and 47 Heat Exchangers - Non-Conforming Retubing Materials.
Purpose and Summary The purpose of this report is to summarize the circumstances concerning the detection and resolution of non-conforming tubing material which was slated for use in the retubing of the following heat exchangers:
System 21 System 47 E-2104, E-2104S, E-2105, E-4701 E-2105S, E2101 & E-2106 E-4702 The report will also show that the proper material, Sandvik 3RE60, was in fact utilized for the retubing.
Discussion It was determined at an early stage in the retubing project, by both General Atomic (GA) and Public Service Company's metallurgical consultant, that the four (4) innermost rows of bent heat exchanger tubes would require stress relieving in the bend areas. This stress relieving would be by the resistance annealing process and would be performed by the Swan Manufacturing Company of Rockaway, New Jersey.
It was also determined that the resistance annealed clamp connection area would require additional annealing by the induction method. The induction annealing was to be performed by GA in San Diego and would include tubes for both GA's use in the rebuilding of the System 47 exchangers and also those tubes for use by Stearns-Roger for rebuilding the System 21 exchangers.
It was during the induction annealing process that the non-conforming tubing was discovered. The non-conformity was detected by GA personnel when unusual meter indications were observed with the annealing equipment.
As a result of this finding, an investigation was conducted to assure that all of the non-conforming material had been located and rejected.
Since the Sandvik 3RE60 material exhibits ferromagnetic properties, tests were conducted, on all of the material received from Sandvik, to determine if the tubes were magnetic or non-magnetic. The test methods were as follows:
a) A Severn gage with a 1% ferrite coupon was used to test all material not already installed in the partially assembled tube bundles.
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b) A Magnetic Analysis Corporation Metal Test Model 966 was employed to test all tubes installed in the bundles and not accessible to the Severn gage test.
The two test methods were also cross-checked against each other to verify the results.
The investigation revealed a total of six (6) tubes, later determined to be 316ELC, and isolated the non-conformity to Heat No. 770925, one of 17 heats received from Sandvik.
Sandvik explained that the mix-up took place during the early develop-ment of 3RE60 in late 1969. They believe that the mix-up occurred as the tubes entered and left the production cycle several times as adjustments to the processing technique were being made.
In response to PSC's inquiry regarding the possibility of the other non-conforming, magnetic material being contained in the order, Sandvik advised that they do not manufacture ferritic tubing, other than 3RE60, in this size (3/4" 0.D.,.065" wall) and that the possibility of there being other non-conforming material in the order was not possible.
Sandvik further noted that the incident occurred prior to the AEC audit which found their QA program to be in conformance with 10CFR50, Appendix B.
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Conclusion Sandvik has replaced the non-conforming tubes with fully tested material and it is now believed that the disposition of the incident is satisfactorily resolved.
9 L. McInroy
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