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.

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.

Development of Leak-Before-Break Assessment Method for Japan Sodium Cooled Fast Reactor Pipe—Part 1 Crack Opening Displacement Assessment of Thin Wall Pipes Made of Modified 9Cr-1Mo Steel

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Takashi Wakai ◽  
Hideo Machida ◽  
Manabu Arakawa ◽  
Shinji Yoshida ◽  
Yasuhiro Enuma
Keyword(s):  
Crack Opening Displacement ◽  
Fast Reactor ◽  
Work Hardening ◽  
Crack Opening ◽  
Assessment Method ◽  
Leak Rate ◽  
Thin Wall ◽  
Opening Displacement ◽  
Leak Before Break ◽  
Small Work

This was carried out to establish crack opening displacement (COD) evaluation methods used in leak-before-break (LBB) assessment of sodium pipes of the Japan sodium cooled fast reactor (JSFR). For sodium pipes of JSFR, the continuous leak monitoring will be adopted as an alternative to a volumetric test of the weld joints under conditions that satisfy LBB. The sodium pipes are made of ASME Gr.91 (modified 9Cr-1Mo steel). Thickness of the pipes is small, because the internal pressure is very low. Modified 9Cr-1Mo steel has a relatively large yield stress and small work hardening coefficient comparing to the austenitic stainless steels which are currently used in the conventional plants. In order to assess the LBB behavior of the sodium pipes made of modified 9Cr-1Mo steel, the coolant leak rate from a through-wall crack must be estimated properly. Since the leak rate is strongly related to the COD, an appropriate COD assessment method must be established to perform LBB assessment. However, COD assessment method applicable for JSFR sodium pipes—thin wall and small work hardening material—has not been proposed yet. Thus, a COD assessment method applicable to thin walled large diameter pipe made of modified 9Cr-1Mo steel was proposed in this study. In this method, COD was calculated by classifying the components of COD; elastic, local plastic, and fully plastic. In addition, the verification of this method was performed by comparing with the results of a series of four-point bending tests at elevated temperature using thin wall modified 9Cr-1Mo steel pipe containing a circumferential through-wall crack. As a result, COD values calculated by the proposed method were in a good agreement with the experimental results for the uniform pipe without a weld. In the case that the crack was machined in the weld metal or heat affected zone (HAZ), the proposed method predicted relatively larger COD than the experimental results. The causes of such discrepancies were discussed by comparing with the results of finite element analyses. Based on these examinations, the rational leak rate evaluation method in LBB assessment was proposed.

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