ML20086E359

Final Deficiency Rept Re Pcrv Cooling Water Sys HX Corrosion Problems.Test HX Installed Along W/Corrosion Coupons to Permit Monitoring & Evaluation of Svc Water Treatment.Hxs Being Retubed

ML20086E359
Person / Time
Site:	Fort Saint Vrain
Issue date:	10/18/1973
From:	Walker R PUBLIC SERVICE CO. OF COLORADO
To:	Knuth D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086E328	List: ML20086E336 ML20086E359 ML20086E445
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8312060467
Download: ML20086E359 (12)

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pubine service company *e cenoemde P.O. BOX 840 DENVER, COLORADO 80201 h

October 18, 1973 Dr. Donald Knuth Directorate Regulatory Operations Office of Regulations Washington, D. C. 20545 i

Subject:

Deficiency Report 10 CFR 50 PCRV Cooling Water System 7(EsMicie Water Corrosion)

Ref.:

Interim Report Filed March 8, 1973

Dear Dr. Knuth:

Pursuant to the reporting requirements of 10 CFR 50, Part 50 55, we are submitting herein, the twenty (20)' copies of our final report concerning th'e heat exchanger corrosion problems.

This report is filed to finalize the interim report referenced -

above, and to report additional findings resulting from follow-up action initiated by the original deficiency.

You will note from the attached report that the ultimate solution to the corrosion problem is considered to be a long term item. It is felt, however, that the problem is defined, and that our plans for resolving the problem and monitoring the effects are sufficiently defined for ultimately correcting the overall problem.

' We will keep the lomil' Directorate abreast of all significant developments.

8312060467 73051'6 PDR ADOCK 05000267

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'a' 10/1g/73 wo.cr c cer Puauc Scavice C:MPANY C F CCL.3% ADD DME I

We trust this report vill provide you with sufficient information to evaluate the deficiency reported, and vill fulfill the reporting requirements of 10 CFR 50.

Very truly yours, R hwake R. F. Walker Vice President Engineering and Planning Electric Department RW/DW:ga j

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E. Howard Morris, Directorate, Region IV l

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DEFICIENCY REPORT l.

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Facility: Fort St. Vrain Nuclear. Generating Station q

Subj$ct: PCRV Cooling Water System (Heat Exchanger Corrosion,

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Repo.rt Date:' October.9,f1973'

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Reference:

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l.0. SCOPE' This Report is filed to finalize the interim report referenced above, and to report additional information resulting from subsequent investigation. The corrosion problems as defined in the text that follows are of a long tem nature. Although it'is felt that the problem has been defined, long term surveillance and long term test programs as required to evaluate the problem in its entirety.

It is the intent of this report to address those problems that have been identified and to outline a program of future action, surveillance and testing.

2.0 GENERAL DESCRIPTION The corrosion problem was identified in February,1973, when en apparent leak in the PCRV cooling water system (System h6) vas-traced to one of rour heat exchangers (E-4601) serving the system.

These carbon oteel tubed heat exchangers are arranged with the-process fluid (PCRV Cooling Water) on the tube side 'and. service water on.the shell cide. Further investigation revealed that a considerable deposit ~ of iron oxide and/or other corrosion products-had built up on the tube surfaces on the service water side.

Subsequent inspection by our water treatment consultants indicated.

that the " Cellular Type". or. %calized Pitting T;T6" corrosion was probably the result' of one or more or.a eccin.. ion of all -

of the following:

a)

Lov flow and resulting low velocity on the shell side of the'

. exchangers, together with a very tight. tube-to-tube spacing -

- within.the ~ bundle permits thei accumulation of particulateb_.

Once an accumulationLis formed'on the:tnbe -surface ~the water.

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treatment ~ system 'can no longer function to protect. the. tube.

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b)

Hydro testing and long term lay-up without adequate protection could start the corrosion process.

c)

Inadequate water treatment for existing conditions.

d)

Overall systen cleanliness.

An immediate survey was made of all heat exchangers served by the service water system to determine if we had other -exchangers in a similar service. This survey. revealed eight (8) more exchangers; E-h701 and E-4702, Purification Cooling Water Exchangers; E-2101, E-2106, Back-Up ' Bearing Water Exchangers and E-2104, E-210hS, E-2105 and E-2105S, Normal Bearing Water Exchangers. These exchangers all had carbon steel tubes, and all were served by the service water system on the shell side of exchanger. No other ex^ hangers in c

the service water system have carbon steel tubes.

Subsequent inspection of the System h{exchangers and two (2) of the System 21 exchangers indicated the same type of corrosion'as observed in the System 46 exchangers, but the corrosion was not nearly as extensive or as advanced as that on the System 46 exchangers.

Hydro tests were conducted on these eight (8) bundles and'there was no evidence of tube failure..

The service water treatment at the' time of the' incident consisted of a phosphonate treatment, together with a sealing -inhibitor. - Chlorine-was added for. algae control and the pH vas: controlled to around 8.3 Lby adding sulphuric acid. ~ Philosphy of treatment:was to keep the stability

'index on the scaling side and then prevent scale formation by(adding

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3.0 IMMEDIATE ACTION TAKET The System h6 exchanger tubes were leaking, and the corrosion had resulted in considerable tube vastage.

It was evident that these four (b) bundles would have to be. replaced. The exchangers were needed, however, to complete the test program so the bundles were jet blasted to remove the bulk of the corrosion products, leaking tubes were plugged and the bundles. vere temporarily returned to service until new tubes and associated material could be ordered and shipped.

The System 21 exchangers had experienced some localized corrosion, but the tube vall vastage was still within acceptable limits. On this basis it was decided to chemically clean these tube bundles in place., Chemical cleaning was performed. One of the six (6) exchangers was inspected after chemical cleaning, and on the basis of this inspection it was determined that the process used for cleaning was more than adequate.

The System 47 exchangers had experienced some localized corrosion, but similar to the System 21 exchangers the tube vastage was within acceptable limits. Since these bundles were relatively small it was decided to jet blast the bundles using high pressure water. The bundles were: satis-factorily cleaned'and were returned to service.

Bypasses were insta11ed' around the System 46 exchangers and two (2) of the System 21 exchangers to_ obtairi velocitie's on' the shell side of approximately 1 FPS. Valves in the service water system serving the remaining System 21 exchangers and the System 47 exchangers were positioned to obtain m'aximum velocities.

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3.0 I!CEDIATE ACTION TAFEN - Cont'd.

A test heat exchanger as shown in Fi ure 1 was installed along E

with corrosion coupons to permit monitoring and evaluation of the service water treatment.

h.0 EVALUATION, SHORT TERM SOLUTIONS The immediate plan was to place the test heat exchanger in service and monitor the results without any change in water treatment strictly to pemit an evaluation of the velocity effects. While velocity helped somewhat it was apparent that the water treatment program was inadequate.

Corrosion, as evidenced by the mild steel test coupons continued to be a localized type corrosion with a rate of 10 to 15 mils / year.

After considerable consulation with water treatment con-sultants it was decided that the mild steel tubed heat exchangers could not be adequately protected without the use of a corrosion inhibitor. In this light the water treatment program was changed in early July employing a zine phosphate, polyol esther treatment including an a=monia quaternary as an iron dispersant, chlorine for algae control and acid for pH control (T.5 to 8.0).

In conjunction with this program a second test heat exchanger, see Figure 2, was installed. Corrosion changed from localized type corrosion with a rate of 9 mils / year early in the new treatment program to a general type corrosion of 0.6 mils / year rate as evidenced by the -last test coupon analyzed in late August,1973.

Although the corrosion rate has apparently decreased to a more than acceptable value a considerable amount of iron continues to be moved thru the system with the iron depositing out on the test heat exchanger tube surfaces in the low velocity areas. Most of

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k.0 EVALUATION, SHORT TERM SOLUTIONS - Cont 'd.

this iron i~s felt to be the result of iron build-up in the system from the previous water. treatment program, but there is also evidence that the rav vater make-up to the service water system does contain rather high concentrations of iron at times.

Concurrently with the evaluation of the water treatment program evaluations of various materials for retubing the System 46 exchangers resulted in the selection of a Sandvik 3RE60 stainless tube. - This material, ASTM-A669, is a. binary stainless alloy which.has demonstrated-very good corrosion resistance characteristics, and has also demon-strated' reasonable resistance to stress corrosion.

Samples of this -

Sandvik material have been, installed as a part of the test heat exchanger program. After approximately 60 days of exposure in the. system the coupon ~

has shown no physical evidence of corrosion attack.

Two of the System h6 exchangers have been retubed,' installed and are in service. Work is in progress retubing the remaining two System 46 exchangers.

50 IONG TERM PLAUS AND SURVEILLANCE Although there has;not been sufficient time to allow a complete water treatment program evaluation it does appear from all-pre-liminary indications Ehat a zine phosphate or similar type treatment would be adequate to bring the corrosion under control' provided that the' iron problem can be handled. On this basis the plans for, the:immediate -

-future include:

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. Pull /one 'of the System 21 'exchangers,to assess.the corrosion effects.on these 'exchangers.since the-initial chemical cleaning;..

.and to determine remaining. tube. life.

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50 IONG TERM PLANS __XJD SURVEILLANCE - Cont'd.

'b)

Considez chem cally cleaninC the entire service water system to cleanup the iron deposits.

c)

Run extensive sampling program of make-up water to determine the need for iron filtration of the raw water.

d)

Continue the zine phosphate polyol esther treatment or similar type treatment for further evaluation of corrosion problems.

Install iron filtration if required.

e)

Continue monitoring the system perfomance and corrosion rates utilizing the test heat exchanger and corrosion coupon program.

With reference to longer tem plans the following considerations will be developed as necessary and in parallel with the above shorter tem plans in the event that the short tem plans are not effective, a)

Consider various alternatives for pretreating make-up water to allow the service water system to be closed up (eliminate blow-down). This would pemit the use of chromates or other type.

corrosion inhibitors which cannot be used at the present time ~

due to environmental controls on effluent from the plant.

b)

Consider retubing the System 21 exchangers, to eliminat'e_ the carbon steel tubes, utilizing admiralty metal or a similar!

metal which has demonstrated good corrosion resistance to the '

se*vice water to date.

-c)

Consider-retubing the System NT exchangers with inconel or '

some similar highly corrosion resistant material. _(Admiralty'

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metal cannot be considered due to the high pH'.ofL the, process side water).

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• '5 0 LONG TERM PLINS AND SURVEILLANCE - Cont'd. ;

d)

Continue conitoring the effectiveness of the service water treatzcent program utilizing test heat-exchangers and corrosion

. coupons making adjustments as necessary.

6.0 CONCLUSION

It-is felt that the shorter term plans as outlined will bring the corrosion problem under control. Development of the longer term Plans should provide adequate alternatives in the event that the shorter term solutions prove to be ineffective. The continuous i

monitoring program afforded by the test heat exchangers and the coupons vill provide sufficient information to evaluate the corro-sion taking place.

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