Socket Weld Integrity

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<p> Socket weld integrity in nuclear piping under fatigue loading conditionYoung Hwan Choi, Sun Yeong Choi * .. ** Mr. Sodsai Lamtharn Assoc. Prof. Dr. Monsak Pimsarn (CVCS) (PSS) / ASME boiler and pressure vessel (B &amp; PV) Code Sec. III 1/16 1.09 x t1 t1 1.09 x t1 0.75 x t1 </p> <p> 3 ASME Code 3 , P=0 15.51 T=25 T=288 (1) ASME operation and maintenance (OM) code (2) CVCS PSS (3) ASME OM Code / P=0 T=25 P= 15.5 T = 288 (4) 1.09 x t1 0.75 x t1 Abstract The purpose of this paper is to evaluate the integrity of socket weld in nuclear piping under the fatigue loading. The integrity of socket weld is regarded as a safety concern in nuclear power plants because many failures have been world-widely reported in the socket weld. Recently, socket weld failures in the chemical and volume control system (CVCS) and the primary sampling system (PSS) were reported in Korean nuclear power plants. The root</p> <p>causes of the socket weld failures were known as the fatigue due to the pressure and/or temperature loading transients and the vibration during the plant operation. The ASME boiler and pressure vessel (B &amp; PV) Code Sec. III requires 1/16 in. gap between the pipe and fitting in the socket weld with the weld leg size of 1.09t1, where t1 is the pipe wall thickness. Many failure cases, however, showed that the gap requirement was not satisfied. In addition, industry has demanded the reduction of weld leg size from 1.09t1 to 0.75t1. In this paper, the socket weld integrity under the fatigue loading was evaluated using three-dimensional finite element analysis considering the requirements in the ASME Code. Three types of loading conditions such as the deflection due to vibration, the pressure transient ranging from P = 0 to 15.51 MPa, and the thermal transient ranging from T=25 to 288 oC were considered. The results are as follows; (1) the socket weld is susceptible to the vibration where the vibration levels exceed the requirement in the ASME operation and maintenance (OM) code. (2) The effect of pressure or temperature transient load on socket weld in CVCS and PSS is not significant owing to the low frequency of transient during plant operation. (3) No gap is very risky to the socket weld integrity for the systems having the vibration condition to exceed the requirement specified in the ASME OM Code and/or the transient loading condition from P = 0 and T=25 oC to P = 15.51 MPa and T = 288 oC. (4) The reduction of the weld leg size from 1.09t1 to 0.75t1 may induce detrimental effect on the socket weld integrity.</p> <p>-----------------------------------------------------------------------------------------------------------------------------------------------* ** </p> <p>1</p> <p>1. ASME B &amp; PV Code Sec. III (ASME, 2001a) [1] 2 (NPS) ASME classes 1 2 4 ASME classes 2 (NPPs) (ASME, 2001a) [1] 40,000 (PWR) 1000 (OECD/NEA, 2002 [5]; EPRI, 1998 [4]; USNRC, 1998 [6]; Choi and Choi, 2003 [3]; USNRC, 1980a, b [7], [8]; USNRC, 1989 [9]) OPDE (OECD Piping Failure Data Exchange) (.0.a) 1970 2001 108 2399 (OECD/NEA, 2002) [5] 6 (Choi and Choi, 2003) [3] 1. , , , ASME Code Sec. III 1/16 (g) 1.09 x t1 (WL) t1 1. </p> <p>2</p> <p> ASME (NDE) (MT) (PT) (RT) </p> <p> 1/16 (NDE) (RT) 2. </p> <p> 1. </p> <p> 1999 2003 6 1. 2003 </p> <p>3</p> <p>, , , , , , (CA) (ISI) (Choi and Choi, 2003) [3] (CVCS) WH 3-loop (PSS) (KSNP) , (TF), (NPS) 3/8 2 304SS 316SS 1. (Choi and Choi, 2003) [3]</p> <p>CVCS : ;PSS : ;TWC : ;</p> <p>4 CA : ;WH : Westinghouse;KSNP : </p> <p>2.1 (CVCS) (CVCS) 5 3 0.043-0.09 1 (Tech. Spec.) (CVCS) (CVCS) 110 30 ASME Code OM Part 3 ( allow) (Vallow) (ASME, 2001b) [2] allow Vallow 18 20 ASME Code OM Part 3 6.1 1.5 </p> <p>5</p> <p> 2-3 2.2-2.4 (TWC) 2%-48% (CVCS) 4.86E05/Rx-Yr 9.04E-05/Rx-Yr 3/4 2 (Choi and Choi, 2003) [3] 2.2 316 (316SS) 3/8 0.01 4 14% O/H (TF) </p> <p>6</p> <p> 20 (YGN 3 and 4, 1995) [10] P=0 T=25 P=15.51 T=288 P T (Tech. Spec.) 3 (PSS) (PSS) 2.54E-04/Rx-Yr (Choi and Choi, 2003) [3] 3. (FEM) 3.1 (FEM) ABAQUS 20-nodes isoparmetric brick reduced integration element (C3D20R in ABAQUS) 2. </p> <p>7</p> <p> 2. B 1. element node 4321 19,932 2 1. (ri) 21.41 , (t1) 8.738 , (L1) 310.5 , (t2) 23.70 , (L2) 86.00 , i=16.00 (WL) 9.525 , (g) 1.588 (1/16 ), (d) 1.016 , 25 3.2 </p> <p>8</p> <p> 3. 1 A D 1. 3. 2 ( B) ( C) (MT) (RT) 3.3 3 (1) (2) P=0 P=15.51 (3) T=25 T=288 3.3.1 </p> <p> 3. 1 1.</p> <p>9</p> <p> 4. (K) Kref=289 MPa mm</p> <p> (d) 1. (K) 4. (d) K Kref </p> <p> 289 MPa mm ( K) K 135.3 MPa mm 0.73 WH 3-loop (CVCS) C ASME Code Sec. XI da/dN = Co( K)n (1) n=3.3 Co R (Kmin/Kmax) </p> <p>10</p> <p>Co = (1+1.8R) x 10[ -10.009+8.12E-4T-1.13E-6T x T+1.02E-9T x T x T ] (2) R R Kmin/Kmax T (oF) (da/dN) K 135.3MPa mm 4.05E-07 </p> <p> 8.25 (9.525 ) (CVCS) 33 ASME Code OM (ASME, 2001b) [2] ASME Code OM 3.3.2 5. (15.51 ) 535.4 MPa mm K 535.4 MPa mm </p> <p>11 5. (K) Kref=289 MPa mm</p> <p> R (CVCS) R 0.394 0.818 K 535.4 MPa mm K = 135.3 MPa mm 0 (15.51 ) (PSS) (da/dN) (1) K 2.33E-05 409,040 (9.525 ) (CVCS) (PSS) 3.3.3 6. T=0, 100, 200 263 (288 ) K 4.07E-05 233,890 </p> <p>12</p> <p> 6. (K) Kref=289 MPa mm</p> <p> 542.9 MPa mm (da/dN) (1) (9.525 ) (CVCS) (PSS) 3.4 ASME Code 1/16 (g=0) 7. </p> <p>13</p> <p> 7. K K 273.4 MPa mm (da/dN) (1) K 4.73E06 17 (9.525 ) (CVCS) (CVCS) 33 ASME Code OM (ASME, 2001b) [2] 8.25 1/16 3.3.1 7.</p> <p> 7. (K) Kref=289 MPa mm </p> <p> 8. (g) g=0 1.5875 (1/16 ) 1.588 (1/16 ) </p> <p>14</p> <p> 0.069 T=263 2 (288 ) 1182.7 MPamm</p> <p>1811.6 MPa mm P=0 T=25 P=15.51 T=288 (da/dN) 2.18E-05 </p> <p> 8. (K) Kref=289 MPa mm </p> <p> 4370 (9.525 mm) 7.3 </p> <p>15</p> <p> ASME Code OM P=0 T=25 P=15.51 T=288 (RT) 3.5 1.25 x t1 1989 0.75 x t1 1992 ASME Code Sec. III t1 1.09 x t1 ASME Code Case N316 9. Kopen K K K WL=0.75 x t1 1.5 WL=1.09 x t1 0.75 x t1 1.09 x t1 1.5 K 0.75 x t1 (6.554 ) 273.4 MPa mm </p> <p>(da/dN) (1) K 4.72E-06 </p> <p>16</p> <p> 9. (K) Kref=289 MPa mm</p> <p> 11.7 (6.554 ) (CVCS) 33 (ASME, 2001b) [2] 1.09 x t1 0.75 x t1 4) 6 (CVCS) (PSS) ASME Code Sec. III 3 3 , P=0 P=15.51 T=25 T=288 </p> <p>17</p> <p> (1) ASME Operation and Maintenance (OM) code (2) (CVCS) (PSS) (3) ASME OM Code P=0 T=25 P=15.51 T=288 (4) 1.09 x t1 0.75 x t1 [1] ASME, 2001a. ASME Boiler and Pressure Vessel Code Sec. III NB. [2] ASME, 2001b. ASME Code OM, Requirements for Pre-operational and Initial Start-Up Vibration Testing of Nuclear Power Plants, ASME Boiler and Pressure Vessel Code Operation and Maintenance (OM) Part 3. [3] Choi, S.Y., Choi, Y.H., 2003. Piping failure analysis for the Korean nuclear</p> <p>18</p> <p>power piping including the effect of in-service inspection. APCNDT, Jeju. [4] EPRI, 1998. Reactor Piping Failures at US Commercial LWRs : 19611997, EPRI TR-110102. [5] OECD/NEA, 2002. OECD Piping Failure Data Exchange (OPDE) Project. [6] USNRC, 1998. Rate of Initiating Events at U.S. Nuclear Power Plants : 19871995 NUREG/CR-5250. [7] USNRC, 1980a. Pipe Cracking Experience in LWR, NUREG-0679. [8] USNRC, 1980b. Investigation and Evaluation of Cracking Incidents in Piping in PWR, NUREG-0691. [9] USNRC, 1989. Erosion/Corrosion-Induced Pipe Wall Thinning in US NPPs, NUREG-1344. [10] YGN 3 and 4, 1995. Operation Procedure for Primary Sampling System, YongKwang Units 3 and 4. KAERI KINS</p> <p>19</p>

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