Enhanced reference stress-based J and crack opening displacement estimation method for leak-before-break analysis and comparison with GE.EPRI method

2001 ◽  
Vol 24 (4) ◽  
pp. 243-254 ◽  
Author(s):  
Y.-J. Kim ◽  
N.-S. Huh ◽  
Y.-J. Kim
Keyword(s):  
Crack Opening Displacement ◽  
Crack Opening ◽  
Estimation Method ◽  
Opening Displacement ◽  
Displacement Estimation ◽  
Reference Stress ◽  
Leak Before Break

A Method of J Testing Based on Crack Opening Displacement for Circumferential Through-Wall Cracked Pipes under Combined Tension and Bending

2006 ◽  
Vol 110 ◽  
pp. 63-70
Author(s):  
Nam Su Huh ◽  
Ludwig Stumpfrock ◽  
Eberhard Roos ◽  
Yun Jae Kim ◽  
Young Jin Kim
Keyword(s):  
Crack Opening Displacement ◽  
Conventional Method ◽  
Crack Opening ◽  
Estimation Method ◽  
Combined Loading ◽  
Resistance Curve ◽  
Opening Displacement ◽  
Load Line ◽  
Load Line Displacement ◽  
Leak Before Break

Application of the leak-before-break concept to nuclear piping requires accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to combined tension and bending. One important element is determination of relevant J-resistance curve for pipes under combined loading. This paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.

scholarly journals Engineering Leak-Before-Break Analyses of Pressurized Piping: Part I- Crack Opening Displacement

2004 ◽  
Vol 47 (4) ◽  
pp. 591-599 ◽  
Author(s):  
Yun-Jae KIM ◽  
Nam-Su HUH ◽  
Young-Jin KIM ◽  
Jun-Seok YANG
Keyword(s):  
Crack Opening Displacement ◽  
Crack Opening ◽  
Opening Displacement ◽  
Leak Before Break

Estimation of Elastic Crack Opening Displacement for Thin Elbows With Circumferential Through-Wall Cracks

2015 ◽  
Author(s):  
Min-Kyu Kim ◽  
Han-Bum Surh ◽  
Min-Gu Won ◽  
Nam-Su Huh ◽  
Moon-Ki Kim ◽  
...  
Keyword(s):  
Crack Opening Displacement ◽  
Nuclear Power ◽  
Crack Opening ◽  
Three Dimensional ◽  
Opening Displacement ◽  
Dimensional Finite Element ◽  
Elastic Crack ◽  
Thin Walled ◽  
Three Dimensional Finite Element ◽  
Leak Before Break

Leak-before-break (LBB) is an important concept that could confirm design and integrity evaluation of nuclear power plant piping. For the LBB analysis, the detective leakage rate should be calculated for a through-wall cracked pipes. For this calculation, the crack opening displacement (COD) calculation is essential. Recently, sodium faster reactor (SFR) which has thin-walled pipes with Rm/t ranged 30–40 was introduced and then the investigation of these thin walled pipes and elbows has received great attention in the LBB evaluation. In this context, the three-dimensional finite element (FE) analyses for thin elbows with circumferential crack under in-plane bending are carried out to investigate the elastic COD values. Finally, the solution for elastic COD which can cover sufficiently thin elbow is successfully addressed.

Crack Opening Displacement Model for Through-Wall Axial Cracks in Cylinders

2013 ◽  
Author(s):  
Michael L. Benson ◽  
Bruce A. Young ◽  
Do-Jun Shim ◽  
Frederick W. Brust
Keyword(s):  
Internal Pressure ◽  
Crack Opening Displacement ◽  
Wall Thickness ◽  
Pipe Wall ◽  
Crack Opening ◽  
Pressure Loading ◽  
Opening Displacement ◽  
Piping Systems ◽  
Displacement Model ◽  
Leak Before Break

For piping systems, leak-before-break calculations rely on estimates of leak rates when postulated cracks grow through the pipe wall. The leak rate, in turn, depends on the crack opening dimensions. Previous work on crack opening displacement (COD) includes recent advances in COD estimates for circumferentially-oriented cracks in cylinders under tension, bending, and internal pressure loading conditions. This paper summarizes previous work in this area and reports on new solutions for COD in the case of axially-oriented cracks under internal pressure. The results reported here include COD solutions at three locations through the wall thickness for axial cracks.

Effect of Weld Induced Residual Stresses on Pipe Crack Opening Areas and Implications on Leak-Before-Break Considerations

2002 ◽  
Author(s):  
Lee Fredette ◽  
F. W. Brust
Keyword(s):  
Residual Stresses ◽  
Crack Opening Displacement ◽  
Crack Opening ◽  
Crack Size ◽  
Battelle Memorial Institute ◽  
Pipe Material ◽  
Correction Factors ◽  
Opening Displacement ◽  
Leak Before Break ◽  
Current Guidelines

The USNRC is anticipating updating their leak-before-break (LBB) procedures. One of the technical areas of concern in the existing procedures is the prediction of the crack-opening-displacements (COD) needed for estimating the postulated leakage crack size for a prescribed leakage detection capability. If cracks develop in the welded area of a pipe, as is often the case, residual stresses in the weld may cause the crack to be forced closed. Earlier studies have shown that pipe welding produces high residual stresses with a sharp stress gradient ranging from tension to compression through the thickness of the welded area of the pipe. The current guidelines are inadequate to predict crack size based on leak rates for cracks in welded areas of pipes. The current guidelines rely on the calculation of the crack-opening-displacement as related to pipe loading. Values from the current guidelines are used to predict a crack’s cross sectional area and, in turn, to determine the severity of an existing crack by monitoring in-service leakage rates. The equations currently in use are applicable to service loaded pipe material only. Residual stresses caused by cold work, welding, etc. are neglected. This study uses two and three dimensional finite element models and weld residual stress calculation software created at Battelle Memorial Institute to develop correction factors to be used with the traditional design equations. The correction factors will compensate for the effects of welding induced residual stresses on cracks in pipe welds. This study concentrates on type 316 stainless steel material properties, but the COD corrections should be equally applicable to all stainless steels, and also can be used for ferritic steels. A test matrix of pipe radius, thickness, and crack size was used to develop the equation correction factors. Pipe wall thicknesses (t) of 7.5 mm (0.295 in.), 15 mm (0.590 in.), 22.5 mm (0.886 in.), and 30 mm (1.181 in.) were studied in pipes with mean radius to thickness ratios of 5, 10, and 20. Cracks with half-lengths in radians of π/16, π/8, π/4, and π/2 were introduced in these virtual pipes. The matrix of results was used to produce correction factors for crack opening displacement equations applicable to a broad range of pipe sizes.

Estimates of J and COD for Complex-Cracked Pipes Based on FE Analyses and ERS Method

2014 ◽  
Author(s):  
Jae-Uk Jeong ◽  
Jae-Boong Choi ◽  
Nam-Su Huh ◽  
Yun-Jae Kim
Keyword(s):  
Finite Element ◽  
Crack Opening Displacement ◽  
Crack Closure ◽  
Crack Opening ◽  
Crack Depth ◽  
J Integral ◽  
Opening Displacement ◽  
Reference Stress ◽  
Estimation Scheme ◽  
Complex Crack

A complex crack can occur at the dissimilar metal weld parts of nuclear pipes due to stress corrosion cracking. The fracture behavior of such crack is different with those of a simple through-wall crack. Thus, the engineering estimation equations for predicting the fracture mechanics parameters, i.e. crack opening displacement and J-integral, should be newly provided in order to evaluate the leak-before-break of pipe including complex cracks. In the previous research, an engineering scheme using reduced thickness analogy was suggested to calculate the crack opening displacement and J-integral for complex cracked pipes. However, this method has limitations in the sense that a through-wall crack is assumed to be developed only in the circumferential direction, and the effect of crack closure cannot be considered. Another scheme for complex cracked pipes is the enhanced reference stress method considering crack closure effect by suggesting the optimized reference load for complex crack geometry. It presented the more accurate results compared to previous engineering estimation scheme. However, an elastic component of crack opening displacement and J-integral were calculated by assuming the crack shape as the simple through-wall crack due to the absence of engineering solutions for complex-cracked pipes. In this context, finite element based evaluation of fracture parameters was performed to confirm the validation of previous estimation schemes. Moreover, the variations of crack opening displacement and J-integral according to a change of surface crack depth ratio of complex crack are systematically investigated based on detailed 3-D finite element analyses. Furthermore, enhanced reference stress method considering finite element based elastic values from the complex-cracked pipe models is assessed to overcome the limitation of previous enhanced reference stress approach.

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