ML20073D022

Full Structural Weld Overlay Design for Peach Bottom Unit 2 RWCU Weld 12-I-1D

ML20073D022
Person / Time
Site:	Peach Bottom
Issue date:	04/30/1991
From:	Frederickson C, Mehta H, Ranganath S GENERAL ELECTRIC CO.
To:
Shared Package
ML20073D020	List: ML20073D018 ML20073D022
References
SASR-91-26, NUDOCS 9104260122
Download: ML20073D022 (19)

Text

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SASR 91 26 DRF 137 0010 FULL STRUCTURAL VELD OVERLAY DESIGN FOR PEACH BOTTOM UNIT 2 RWCU WELD 12.I+1D April, 1991 Prepared For Philadelphia Electric Company By G.E. Nuclear Energy Prepared By: N ' W C.D. Frederickson Senior Engineer, Structural Analysis Services Verified By:

H S. Mehta

- Principal Engineer, Structural Analysis Services l

l Approved By: # "' N ^ ^^ ^ -

S. RanganatW Manager, Structural Analysis Services I

9104260122 910439 fDR ADOCK 05000277 PDR r v,

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IMPORTANT NOTICE REGARDING CONTENTS OF THIS REPORT Please Read Carefully The only undertakings of General Electric Compcny respecting information in this document are contained in the contract between the customer and General Electric Company, as identified in the purchase order for this report and nothing contained in this document shall be construed as changing the contract. The use of this information by anyone other than the customer or for any purpose ather than that for which it is intended, is not authorized; and with respect to any unauthorized use, General Electric Company makes no representation or warranty, and assumes no liability as to the completeness, accuracy, or usefulness of the information contained in this document.

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SASR 91 26 DRF 137 0010

1. INTRODUCTION During ultrasonic examination of the Reactor Water Clean Up (RWCU) piping system at Peach Bottom Unit 2 (PB2), the examiner located a circumferential indication at'the inside surface of a 4 inch schedule 80 pipe. This indication was found March 9, 1991 near the weld to a check valve (weld 12 I-1D) as shown in Figure 1. The affected pipe is made of ASTM A 376 type

-304 stainless steel. Details on the indication found are contained in the Reference 1 -report. Further UT and radiography examinations wev e used to verify the existence of the flaw and to accurately characterize the flaw geometry. The flaw was determined to have a maximum depth of 0.14 inch with a pipe wall thickness of 0.40 inch in this region. This flaw is located an-axial distance of about-0.8 inch from the weld centerline extending in length from about 1 to 3 inches clockwise from Top Dead Center (TDC).

To repair tha pipe at this location, a full structural weld overlay is designed and applied at weld 12 1 1D. This full structural weld overlay is

. designed to support the entire pressure, dead weight and seismic loadfug_in the pipe conservatively assuming that the crack exter'ds through the wall of the original pipe'for the~ entire circumference. The weld overlay is-designed-in accordance with Section XI of the ASME code to restore _the pipe to meet ASME code structural margins.

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2.

SUMMARY

The weld overlay shown on Figure 2 has been designed ~ to repair the indication in accordance with Section XI of, the ASME code. The nominal- ,

overlay,chickness is defined as 0.200 inches with a minimum thickness of 0.175 inches. The overlay must extend at least 1.5 inches past the

. indication on'the' side away from the valve to allow future UT_ measurements.

On'the valve side, the overlay should blend into the valve bevel as shown on Figure 2. The Reference- 6 GE overlay procedure may b6 used to provide guidance in developing a site specific procedure.

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SASR 91 26 DRF 137 0010

3. WELD OVERIAY PROCESS The weld overlay design consists of a continuous 360' band of veld metal deposited 'over the outside surface of the pipe directly over the crack indication. The overlay is made with high ferrite, low carbon Type ER308L stainless steel weld metal. This material has a very high toughness and is resistant to Intergrannular Stress Corrosion Cracking (IGSCC). The weld metal is deposited using an automatic Gas Tungsten Arc Welding (CTAW) technique with water cooling the inside surface of the pipe. Using this process, compressive residual stresses are created at the inside surface of the pipe which tends to arrest crack growth. The Reference 6 CE weld overlay procedure may be used to provide guidance in developing a site specific procedure for PECO.

4. WELD '0VERLAY DESIGN METHODOLOGY In designing a full structural weld overlay, the crack is conservatively assumed to extend through the original pipe wall thickness for the full circumference of the pipe. Making this assumption, the weld overlay design is independent of the size of the indication. This is conservative for the indication found which extends less than 40% through wall for less than 20%

of the circumference. Also, the crack is unlikely to grow due to the compressive residual stresses created at the inner surface of the pipe using the heat sink veld overlay process.

The weld overlay ef fectively increases the pipe wall thickness with high ferrite, low carbon Type ER308L stainless steel material that is resistant to ICSCC. Therefore, a crack growing through the wall of the pipe will not extend into the overlay. This will be confirmed by future inspections.

The overlay thickness is designed such that a factor of safety of-3.0 is maintained against not section collapse for normal and upset condition loading per Paragraph IWB-3642 of Reference 2. A facto'r of sasety of 1.5 must also be met for emergency and faulted loading, j SASR9126 WP _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - _ - - .

SASR 91 26 DRF 137 0010 4.1 Weld Overlay Thickness An iterative process is used to determine the required weld overlay thickness. An initial overlay thickness, T, is first assumed. Considering the pressure, deadweight and seismic loading on the pipe, the membrane (Pm) and bending (P b ) stresses on the uncracked, overlaid section (Section A A of Figure 3) are then calculated. The bending rtress (Pb c) in the uncracked, overlaid section of the pipe (Section A A) at the point of net section collapse of the cracked section of the overlay (Section B B) is next calculated usin5 the methodology described in Reference 3. The stress distribution shown for section B B of Figure 3 is assumed at collapse. The flow stress, og, is defined as 3 Sm as in Appendix C of Reference 2. For the membrane stress calculated previously, the neutral axis angle is determined by equation 3 of Reference 3 as 0-n ( 1 - d/t Pm/og ) / ( 2 - d/t )

The bending stress in the uncracked section (A A) at not section collapse of the cracked section (B-B) is then calculated according to equation 4 of Reference 3 as Pb c " ( 2- of / n ) ( 2 d/t ) sin (S)

The not section collapse stresses are then compared against the applied stresses to determine if factors of safety on collapse of 3 for upset loading and of 1.5 on faulted loading are achieved.

(Pm + Pb c) / (Pm + P b ) upset h3 (Pm + bP c) / (Pm + bP ) faulted it 15 If these condition are met, the assumed overlay thickness is sufficient. if these condition are not met, the assumed thickness must be-increased and the calculations repaated until the required factors of safety are achieved.

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SASR 91 26  ;

DRF 137 0010 l i 4.=2-Weld l0verlay Width

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After the; required overlay thickness has been determined, the overlay width is considered. The overlay width is sized taking into account several

. considerations. First, the overlay must extend along the length of the pipe -i i

t a distance great-enough to ensure it will envelope the extent of cracking. J For an axial crack, this overlay width must take into account the projected

growth of the. crack. For a circumferential crack, the= extent of cracking is i confined 2to a small axial region of the' pipe. GE has completed studies.into- 1 theiminimum overlay width required to. provide adequate structural- )

reinforcement of the cracked area and to assure that the stresses in the-di ' overlay will.be' reasonably uniform. These studies have shown that an-overlay width .of; 0.5 ' Mit- to each side of the indication .'is adequate ; This I

: axial distance is=also great enough to assure that the circumferential crack .

.is. fully enveloped by the overlay.

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JAnother consideration is the inspectibility . of the indication after the-overlay'.is applied. .The UT transducer must'be placed' flat on the outside 1

surface of-the overlay at some-distance-from:the~ indication.

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A -f This distance

-must beigreat-enough to locate' the1 crack tip with a 45or-'60' refracted J Lwave. - This -requirement of ten exceeds' the structural requirements for the m overlay width! described above. Finally. - the loverlay width may' 'be l dictated

!by geometric constraints if-. located near.a. tee,; valve or.other fitting.

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SASR 91 26 DRF 137 0010

5. WELD OVERLAY DESIGN As stated previously, the weld overlay is designed using an iterative approach. The thickness is adjusted until the structural margins defined by the ASME code are achieved. For this analysis, the iterations made to arrive at the final overlay thickness are not shown. Only the calculations for the final overlay thickness are included to show that the designed thickness is sufficient. The calculations for this final weld overlay thickness, summarized in Table 1, are described in detail below.

5.1 Welti Ove.rlay Thickness The minimum overlay thickness was determined to be T - 0.175 inches. For this-overlay thickness, the important dimensions and cross sectional properties are:

Pipe + Overlay Thickness, t - 0.400 + 0.175 - 0,575 inches Pipo Inner Radius, Rt - 1.850 inches Overlay Outer Thickness, Ro - 2.425 inches Nominal Radius, R - 2.138 inches Cross Sectional Area, A - 7.722 inch 2 Bending Inertia, I - 17.961 in' The actual UT measured thickness of the pipe (0.40") was used rather than the nominal thickness for a 4 inch schedule 80 pipe (0.337") because for the veld overlay desi 5n, the greater original pipe thickness conservatively leads to a greater overlay thickness.

Applied Stresses Per Reference 4, the design pressure for this piping is 1800 psig. The primary membrane stress is thus Pm - x R i 2 P/A-n (1.850 in)2 (1800 psig) / 7.722 in2 - 2506 psi SASR9126.WP _ _ _ _ _ _ - _ _ _ _ _ _ -

SASR 91 26 DRF 137 0010 The' maximum' upset condition deadweight and OBE seismic bending stresses in the original 4 inch schedule 80 pipe are also given in Reference 4 as ad - 5127 psi 1

and I

1. 0BE - 4575 psi

'The dimensions and cross sectional properties for the original 4 inch schedule 80 pipe are:

Pipe Wall Thickness, d - 0.400 inches, Pipe Inside Diameter, ID - 3.700 inches, Pipe Outside Diameter, OD - 4.500 inches, and Pipe Bending Inertia, Ip - 10.929 inch4, Again, the actual UT measured thickness of 0,40" is conservatively used instead -of the standard 4 inch schedule 80 nominal thickness of 0.337".

Because thetstrength of the weld overlay is designed in relation to the strength of the original _ pipe, the--use of the greater thickness is conservative and will lead to a. greater overlay thickness. The applied moments.can-be calculated from the resulting stresses and-the cross sectional properties as Md ." #d (I p) / (OD/2) - 24905 inch lbs and MOBE " 00BE (Ip ) / (OD/2)== 22222 inch lbs for the-deadweight and OBE seismic' loading, respectively, Using these

' applied moments, the upset condition bending stress.In the overlaid section-is determined to be Pbu _(Md+MOBE) Ro / I - (24905 + 22222)-2.425 / 17.961 - 6363 psi SASR9126.WP 6-

SASR 91 26 DRF 137 0010 For the faulted case, the SSE bending moment is conservatively assumed to equal twice the OBE moment HSSE " 2 MOBE = 44444 inch-lbs The faulted condition bending stress is then calculated as Pdt - (Md+MSSE) Ro / I '.;4905 + 44444) 2.425 / 17.961 - 9363 psi Net Section Collapse Stresses The design stress intensity for this ASTM A 376 stainless steel pipe at 550*F is given in Table I 1.2 of Reference 5 as Sm - 16950 psi The ER 30BL stainless steel weld material hat a greater strength.

Therefore, the-pipe material properties will conservatively be used. The flow stress is defined as three times the design stress intensity, or og - 3 Sm - 50850 psi For the 2506 psi membrane stress calculated above, the neutral axis angle is calculated as

$ - w( 1 0,400/0.575 2506/50850 ) / ( 2 0.400/0.575 ) - 0.6143 rad as described in Section 4.1. The bending stress in the overlaid pipe at net section collapse of the cracked section is Pb c - [ 2 (50850) / n ] ( 2 0.400/0.575 ) sin (0.614) - 24339 psi SASR9126.WP - __ _ _ _ _ _ _ _ - _-

SASR 91 26 DRF 137 0010 Factor of Safety to Net Section Collapse The ratio of net section collapse stresses in the uncracked, overlaid pipe over the applied stresses due to pressure, deadweight and an OBE seismic event, yields the factor of safety of (P m + Pb c) / (P m + Pb u) - (2506 + 24339) / (2506 + 6363) - 3.03 This factor of safety exceeds the required f actor of safety of 3.0 for normal operating and upset condition per Paragraph IWB-3642 of Reference 2.

For the faulted condition, the factor of safety is 1

i (Pm + P b c) / (Pm + Pbf) - (2506 + 24339) / (2506 + 9363) - 2.26 )

l This exceeds the required factor of safety of 1.5 for faulted conditions per IWB 3642 of Reference 2. Both of the factor of safety requirements are met.

Therefore, the minimum weld overlay thickness of 0.175 inches is sufficient.

25 mils are added to the-minimum weld overlay thickness to obtain the nominal weld overlay thickness of 0.200 inches. No maximum overlay thickness is needed.

The weld overlay repair is shown on Figure 2.

5.2 Weld overlay Width i

As described in section 4.2, the overlay must be applied for a width of at least L - 0.5 / R t - 0.5 / (2.138) (0.575) - 0.55 inches beyond the indication on each side to meet structural requirements.

However, to ensure the ability to conduct UT inspection of the indication after the overlay is made, an overlay width of 1.5 inches from the indication is recommended. The weld overlay repair is shown on Figure 2.

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SASR 91 26 DRF 137 0010 Table 1 Veld Overlay Thickness Calculation Summary i

Pipe and Flaw Dimensions: Piping Loads:

9' Pipe ID: 3.700 (in) Pressure, pt 1800 (peti Wall Thickness, de 0.400 (in) Axial Loads: Deadweight, Fdi 0 (1bst ,

Pipe 00: 4.500 (in) OBE seismic, Fs 0 (1bs) l Pipe Area, Apt 5.152 (in*2) Moments: Deadweight, Md 24905 (in.lts) i Pipe Inertia, Ip: 10.929 (in'4) OBE seismic, Ms: 22222 (inolts) 1

1) Assumed Flaw Depth, at 0.400 (in) l overlay DLmensions: Piping Stresses  ;

........................................ ................................................ I overlay Thickness, T: 0.175 (in) Membrane, Pmps 3756 (pot)  !

Min. Overlay Length, L 1.109 (in) ( Pep = (p(PI/4)ID*2+Fd+Fe) / Ap)

(L= TKt on each side of indication) Bending, Pbps 9702 (pat)

( Pbp = (Md+Me) 00 / (2 Ip) )  !

Pipe + overlay Dimensions: Pipe overlay Stresses f Wall *0vely Thickness, c 0.575 (in) Membrane, Pmos 2506 (pot)

(t=T+d) ( Pmo = (p(PI)Ria2+Fd+Fe) /A}

Pipe Inner Radius, Ri 1.850 (in) Bending, Pbo: 6363 (pet) overlay outer Radius, Ron 2.425 (in) ( Pbo = (Md+Ms) Ro / I }

Nominal Radius, Ri 2.138 (in) Factor of Safety, FS: 3.00 Cross sectional Area, At 7.722 (in*2) MIN Critical Bending stress: 24101 (p*L)

Bending Inertia, In 17.961 (in*4) ( Pbc > FS (Pmo+Pbo) - Pmo )

Material Properties: Critical Bending Stress Calculation:

-Pipe Material TP 304 SS, ASTM A-376 Neutral Axis Angle, B 0.6143 (rad)

Overlay Material Type 306L $$ ( B = PI (1.a/t-Pmo/Sf) / (2-a/t) }

Design stress, see 16950 (psi) Critical Bending stress, Pbei 24339 (psi)

Flow Stress, Sf = 3 sa 50B50 (psi) ( Pbc = 2-(sf/PI) (2-a/t) sins }

Critical Bending Stress, Pbc = 24339 (pst)

Notes: is greater than the Required

1) The pipe is conservatively assumed Critical Bending Stress of 24101 (psi) to have a 360 degree through-wall Therefore, the overlay Design crack for this full structural Thickness of T = 0.175 (in)

-overlay design. and Length of L = 1.109 iin) is sufficient.

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SASR 91 26 DRF 137 0010

6. REFERENCES

1) Indication Notification Report (INR) # PB2 91 INR 02, Prepared for Philadelphia Electric Company by EBASCO, March 11, 1991.

2) 1989 ASME Boiler and Pressure Vessel Code,Section XI.

3) S. Ranganath and H.S. Mehta, " Engineering Methods for the Assessment of Ductile Fracture Margin in Nuclear Power Plant Piping, " Elastic-Plastic Fracture: Second Symposium. Volume II. Fracture Resistance Curves and Encineerint Aeolications," 1983, (ASTM STP 803), pp. 309-330,

4) Non Conformance Report (NCR) # P 90407, Prepared for Philadelphia Electric Company by Bechtel, July 12, 1990, Sheet XVII 4.

4

5) 1989 ASME Boiler and Pressure Vessel Code,Section III.  !

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6)' G.E. Document # P50YP225, Rev. 3, " Process Specification for Weld Overlay l for Austenitic Stainless Steel Piping k* elds," July 1987.

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ATTAC!! MENT 2

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1 GE Nuclear fnergy

, SASR 91 26 DRF 137 0010 April 15, 1991 To: A.R. Diederich (PECO) cc: S. MacNichol Manager of Projects, Peach Bottom P. Tutton S. Ranganath From: C.D. Frederickson (CE)

Subject:

Full Structural Weld Overlay for PB2 RWCU Weld 12-I-1D I have reviewed the records for the full structural weld overlay completed on Weld 12-I-1D at Peach Bottom unit 2 and have concluded that the final overlay applied by Philadelphia Electric Company (PECO) meets the overlay design specified in the Reference 1 report. Also, the weld overlay process was controlled in accordance with the Reference 2 weld overlay procedure. l Specifics of the final weld overlay and the process control information are l

discussed below. '

l 1

The final weld overlay thickness ranged from a minimum of 0.270 inch to a maximum of 0,380 inch as decermined by 20 UT thickness measurements taken before and after the overlay. These measurements were taken for 0*, 90*,

180' and 270' azimuths at five axial locations ranging from 1 inch upstream to 1 inch downstream of the indication. The weld overlay thickness exceeds the nominal thickness of 0.20" given in Reference 1 for a length exceeding 0.5/Rt (0.55 inch) on each side of the indication.

The weld overlay thicknesses described above include the first weld pass.

Ferrite measurements were taken for the first weld pass with values ranging from.7.7FN to 12FN. The average ferrite measurement for this pass is 9.6FN.

These measurements meet the ferrite acceptance criteria of 5FN minimum and 8FN average given in paragraph 4.4.2 of Reference 2. Therefore, the first pass may be included in the total overlay thickness. The average of the ferrite measurements for the second, third and fourth passes are 9.5FN, 9.4Di and 9.Ini, respectively.

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SASR 91 26 DRF 137 0010 The to.tal-ove'rlay width was approximately'4 inches. The shrinkage was measured a't four-azimuths to be:

Azimuth Shrinkare (inch)

O' O.325 90' O.245 i 180' O.270--

I 270' 0,311 These shrinkage values range from 0.245" to 0.325" for a maximum variation Lof 0.08". This variation matches the distortion control guideline of i 0.02 x:4" - 0.08" for a 4 inch wide overlay as defined in paragraph 3.7.4 of. I Reference 2 to assure uniform shrinkage.  ;

- To achieve favorable compressive residual stresses-at the inside surface for '

this weld-overlay, the inside surface of'the pipe was water cooled.during the weld overlay process. The temperature of the cooling water was measured upstream of the overlay at a point between the pump-discharge and the regenerative; heat exchanger. This temperature ranged from 105 to'120*F.

- The~ ; coolant , temperature at the weld overlay region' will be'somewhat below the indicated temperatures due to heat loss .through the regenerative and non r.egenerative' heat exchangers. Pipe surface temperatures;were:also' monitored just' upstream of : the - overlay _. These surface temperatures ranged-

-from188;to 94*F. The inlet coolant : water _ temperature was thus- ~ maintained -

welltbelow thes120'F maximum-' requirement specified in paragraph 3.6.3 of-Reference .2. The flow maintained- through ' this pipe during the overlay

process.was.125 gpm (0.2793 ft /sec).

This translates to a: flow velocity of

'approximat'ely 3.7 ft/see for the-4 inch schedule 80 pipe. ~This flow rate is-t within 5% of'the-minimum flow rate recommended-inipara8raph 3.6.2 of i

? Reference 2. The water cooling techniquetwas_also verified by-conducting a

mockup. The mockup test l confirmed'that the water cooling provided during the overlay procedure wasLacceptable. Water cooling for the overlay thus- t met:the; requirements given.in the Reference-21 specification- .

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-SASR 91 26 DRF 137 0010 The 1:1 slope for the blend of the overlay to the pipe was recommended by GE. This slope provides a reasonably smooth transition, preventing significant stress concentration. A 1:1 slope was used rather than the 3:1 slope specified in Reference 2 to provide the maximum flat surface for UT measurements while maintaining the minimum overall lenSth of the overlay and thus also the least possible shrinkage.

As described in this letter, the overlay applied by PECO meets all structural requirements defined by GE in the Reference 1 report. The veld overlay process was also well controlled by PECO within .he guidelines given by the Reference 2 weld overlay procedure. All design records for this overlay are contained in DRF#137-0010, SASR# 91-26.

Sincerely,

$/$$ W72'/

C.D. Frederickson Senior Engineer, Structural Analysis Services (408) 925-2699

References:

1) G.E. Report # SASR 91 26, DRF 137-0010 " Full Structural Weld overlay Design for Peach Bottom Unit 2 RWCU Weld 12-I-1D," C.D. Frederickson, April 1991.

2) G.E. Document # P50YP225, Rev. 3, " Process Specification for Weld Overlay for Austenitic Stainless Steel Piping Welds," July 1987,

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