ML20235N433

Review of Evaluations Performed for Nonconformance in Main Steam Line for Steam Generator 12

ML20235N433
Person / Time
Site:	Calvert Cliffs
Issue date:	09/30/1987
From:	Houstrup J ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML20235N256	List: ML20235N253 ML20235N316 ML20235N369 ML20235N433
References
NUDOCS 8710060518
Download: ML20235N433 (10)

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A Review of the Evaluations Performed For a Non-Conformance in the Main Steam Line For the Number 12 Steam Generator by John P. Houstrup Combustion Engineering, Inc.

for Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant Lusby, MD September, 1987 O g79,30 Dt g P 05000317 PDR

Table of Contents

1. Discussion'of the Problem

2. Probable.Cause-

3. ' Conclusions

4. Discussion of Technical Reviews

5. . References l

1. Discussion of the Problem .

During a voluntary inspection of piping components in Unit 1 of the Calvert Cliffs Nuclear Power Plant, an area of a pipe wall was discovered to be less than the minimum thickness required for general design by the Piping Design Code, USAS B31.1, (1967). The area is in the main steam line for steam generator 12 and is located in the base metal of the horizontal run just downstream from the second elbow af ter the flow restrictor. The area of non-conformance is approximately 1/2 inch in axial length along the pipe and 24 inches in circumferential length, located immediately adjacent to the weld of the pipe run to the second elbow. A graphical representation of this area is shown in Figure 1 of Reference 3. The pipe is 34 inches in diameter with a i design pressure of 1000 psi and design temperature of 580*F, i and fabricated of ASTM A-155 KCF70 grade 1 (welded A-515 grade 70 plate) material. The required minimum wall is 0.950 inches, the average as measured wall is 1.08 inches and the smallest measured wall thickness is 0.86 inches.

2. Probable Cause It is this reviewers opinion that this area of reduced wall thickness is a result of the initial fabrication and was not operationally induced. The area is adjacent to a field weld. It is probable that this thin-walled pipe was slightly bent or dented in handling and was ground locally on the I.D. in the field for weld fit up. A pictorial of this is shown in Figure 1. This kind of fabrication action would result in the shape of the thin area observed and would result in a fabrication non-conformance rather than a flaw. This opinion is substantiated by the original weld 1

radiographs that show a slightly darker band in this region, and by the OD contours as plotted on Sheet 8 of Reference 1.

I i

t 781^J Weso 20'!!

Fust THicwess 3

1 -

I A

EL 00 60 JgpJ y  ?!PY NALL gy ,g g, f,dALL

_b L lbATPKIAL fROVAJD AwAv foe fir-Up Figure 1 Probable Configuration

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3. Conclusions A review of the evaluations performed to demonstrate the adequacy of this pipe and the results of the NDE used to establish the existing as-built geometry leads to the conclusion that this pipe in its present configuration meets the requirements of the original Construction Code, USAS B31.1 (1967), with the additional analysis provided in Reference 3. The NDE showed no evidence of cracks or flaws, only the local thin area. Thus, considering this area as an original fabrication non-conformance, Reference 3, if accepted by the ANI and the Regulatory authorities, provides full justification and the problem is solved. If it is

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mandated that this area be considered as a flaw, Reference 2 (modified to show compliance with IWB-3612 rather than IWB-3611) and Reference 3 demonstrate full compliance with IWB-3610 (a) and (b) of ASME B&PV Code Section XI, 1983 with S-83 Addenda. This again completes the problem except for additional future examinations as required by Section XI.

4. Discussion of Technical Reviews (a) BG&E Calculation M-86-10 dated 12-9-86 (Reference 1).

This calculation established the basic requirements for the pipe and uses a novel reinforcement approach to justify the reduced thickness. The concept of local reinforcing would be valid for some shapes of reduced wall thickness, but does not apply to this long narrow area and has been rejected by the NRC.

(b) SWRI Report 17-4772-861, " Thin Walled Pipe Integrity Assessment - A Fracture Evaluation" dated March, 1987 (Reference 2)

i This is a fracture mechanics evaluation of the reduced wall area assuming it as a circumferential crack. The methods used are those of Appendix A, IWB-3610(a) and IWB-3611 of the ASME B&PV Code Section XI, 1983 with S-83 Addenda. A lower bound material toughness of K73 = KIc = 100 ksi 7b bI was assumed and crack growth over the life of the plant was determined to be small (0.045 inches in the remaining 30 years). The critical crack depth was determined to be 4.29 l inches, or through wall. A pressure of 1693 psi was used.

l A simplified limit load evaluation considering a 360*

l l circumferential crack showed that a remaining ligament of 0.405 inch or less (0.675 crack depth) is necessary for plastic collapse, using the methods of IBW-3640 for austenitic piping. (Note: this is not completely l applicable and IWB-3640 is not included in the 83 Edition, S-83 Addenda of Section XI).

This evaluation used only membrane loadings (pipe bending was not included, nor can Appendix A methods accommodate them), used a very high pressure of 1693 psi, a high membrane correction factor, M , f 1.65 (should be 1.1), and m

applied Appendix A to a thin-walled pipe. Appendix A was developed for ferritic vessels 4 inch and greater in thickness. It's use in this case (Class 2 thin-walled pipe) would be permitted - IWC-3000 (Class 2) refers back to IWB-3000; IWB-3620 (ferritic components less than 4 inches thick) refers back to IWB-3610, the paragraph used.

However, the potential for ductile flaw growth in ferritic piping is not included, nor are the effects of gross pipe bending. The results should be conservative.

An application of the currently being developed IWB-3650 criteria for ferritic piping, shown in Addendum 1, using LEFM techniques and including pipe bending, yields a K7 =

35.6 ksi tIin that is compared with an allowable of 135.9

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ksiyinasrequiredforthismaterialusingminimum properties. Thus, even if this thin area is considered as a crack, both flaw evaluations conservatively justify continued operation for the remaining life of the plant.

(c) SWRI Report 17-4772-861, " Stress Analysis of Thin Pipe i Region in No. 12 Steam Generator Main Steam Line",

dated February, 1987 (Reference 3)

This is a finite element stress analysis of a section of straight pipe and a full elbow with a reduced thickness area at the joint simulating the actual area. The results demonstrate that the primary local membrane stresses for pressure and dead weight loadings meet the stress allowables of USAS B31.1 (1967), even in the reduced thickness areas.

The sophisticated approach used (as opposed to the simple thickness formula) is permitted by 331tl as stated in the Forward:

... a designer who is capable of a more rigorous analysis than is specified in the Code may justify a

'less conservative design, and still satisfy the basic intent of the Code."

and in the

Introduction:

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"It is intended that a designer capable of applying more complete and rigorous analysis to special or unusual problems shall have the latitude in the i development of such designs and the evaluation of complex or combined stresses."  !

This reviewer agrees with the conclusion stated in the summary that the reduced section of the pipe meets the original design requirements of the Construction Code 1.

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[(USAS B31.1(1967)] for primary loadings. Although not evaluated in the referenced report, the expansion bending and membrane stresses (axial in the pipe and normal to the reduced section) are low (see P e in Addendum 1) at this location and the total combined axial stress should be less than S, a conservative approach to B31.1.

5. References

1. BG&E Calculation M-86-10 dated 12-9-86 by W. C. Holston.

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2. SWRI Report 17-4772-861, " Thin Walled Pipe Integrity i Assessment - A Fracture Evaluation" dated March, 1987.

3. SWRI Report 17-4772-861, " Stress Analysis of Thin Pipe Region in No. 12 Steam Generator Main Steam Line", dated February, 1987.

4. USAS B31.1 Code for Pressure Piping (1967)

5. ASME B&PV Code Section XI, " Inservice Inspection of Nuclear Power Plant Components", 1983 Edition, Summer 83 Addenda.

s a

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Addendum 1 Application of Currently Being Developed IWB-3650 and Appendix "Z" for Flaw Evaluation of Ferritic Piping.

The most conservative approach (LEFM) will be used. This will demonstrate the validity of the Reference 2 results.

Pipe -

A-155 KCF70 Class 1 (A-515 Grade 70 plate) 34" O.D. 1.08 wall Flaw -

24" long, 0.276 deep circumferential on I.D.

l in base metal Loadings P = 1000 psi P

m = 7.57 ksi P3 = 1.70 ksi E' = 30,800 ksi T>500'F P

e = 3.85 ksi (on upper shelf)

/, Material Category 1 2

Use J IC = 600 in#/in 6' = 27.1 ksi Y

L-IWB-3650 Criteria for acceptance

'K ,5.(J 7 IC E'/1000)0.5 Appendix "Z" Z-7300 l

K7 = (SF) 17 a (P,F,+(Pb+ )F3 b l

F, = .1.10 + ( [ .15 2 41 + 16. 77 2 ( X 6 /fr) . 8 5 5 - 14.944 (X9/;r)]

I F

b=1.10+((.09967+5.0057(Xe/W).565 - 2.8329 (XG/#)]

x=(= 5 g = .2546 A= 24 100.028

= *2399

?f F,= 1.30' Fb = 1.29 Ky = 35.60 ksi y in (SF)'= 2.77 (J 1c E'/1000)0.5 135.94 ksi %

=

35.60 < 135.94 , /, flaw acceptable i

JP068

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