bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Analysis and Optimum Design of the Heat Transport System at Molten Salt Reactor
Authors: Zhang Xiaochun , Wang Xiao , Gong Wei , Fu Yuan
Published: November 2015

The heat transport system of thorium-based molten salt reactor (TMSR) consist of the primary and secondary salt loop system, main salt pump system, heat exchanger system and salt drain tanks system. As an innovative reactor, the design temperature can go up to 700°C (1292°F) in TMSR. At first a sufficient flexible system should be considered for the heat transport system to accommodate the movements of the components as they expand under the high temperature. Then pipe supports need to be well designed to transfer the load from piping to the supporting structures. To evaluate the structural integrity, the structural analysis is carried out by using a 3-dimentional structural model. The calculated results provide the theoretical and practical guidance value for the optimum design of pipeline layout in TMSR.
Estimation of Stress-Free State From Hardness Ratio for Evaluation of Residual Stress Using Instrumented Indentation Testing (IIT)
Authors: Kim Jong-Hyoung , Ahn Hee-Jun , Jeon Seung-Won , Lee June Sang , Choi Min-Jae , Kim Kwang-Ho , Ro Dongseong , Kwon Dongil
Published: November 2015

As welding residual stress is a primary factor in serious failure or fracture of plants, many testing methods such as X-ray diffraction, hole-drilling, and saw-cutting are used to evaluate this welding residual stress. Instrumented Indentation Testing (IIT) is an attractive testing method for evaluating welding residual stress because it is nondestructive and can be used in-field. The material properties can be obtained by Instrumented Indentation Testing in field using attachments like magnetic device or chain device. In general, the principle of evaluation of residual stress with IIT is based on comparing the load-depth curves obtained from stress-free state and stressed state which are same material. However, as the mechanical properties of welds are altered during welding process, it is difficult to obtain the load-depth curve for stress-free state of welds. In this research, in order to estimate the load-depth curve for the stress-free state, we consider the relation between k value of Kick’s law which is related to the slope of the load-depth curve and the hardness value which is independent of residual stress state. The relation between maximum load and maximum indentation depth which is k value of Kick’s law is similar to the concept of hardness and as a result, the ratio of k value between two materials is almost equal to the ratio of their hardness values. To validate this research, we compare the load-depth curve of stress-free material with the load-depth curve which is estimated from hardness ratio.
Failure Experiments on Pipes With Local Wall Thinning Subjected to Multi-Axial Loads
Authors: Li Yinsheng , Hasegawa Kunio , Miura Naoki , Hoshino Katsuaki
Published: November 2015

Piping lines in nuclear power plants may experience multi-axial loads including tensile force, bending and torsion moments during operation. There is a lack of guidance for failure evaluation under the multi-axial loads including torsion moment. ASME B&PV Code Section XI Working Group is currently developing fully plastic failure evaluation procedures for pressurized piping items containing local wall thinning subjected to multi-axial loads. A failure estimation method for locally wall thinned pipes subjected to multi-axial loads including torsion moment has been proposed through numerical analyses. In this study, in order to investigate the failure behavior of the pipes with local wall thinning subjected to multi-axial loads including the torsion, failure experiments were performed on 20 mm diameter carbon steel pipes with a local wall thinning. Based on the experimental results, the proposed failure estimation method is confirmed to be applicable to pipes with local wall thinning.
Applicability of Miniature C(T) Specimens for the Master Curve Evaluation of RPV Weld Metal
Authors: Yamamoto Masato , Miura Naoki
Published: November 2015

The Master Curve approach for the fracture toughness evaluation is expected to be a powerful tool to ensure the reliability of long term used reactor pressure vessel (RPV) steels. In order to get sufficient number of data for the Master Curve approach coexistent with the present surveillance program for RPVs, the utilization of miniature specimens that can be taken from the broken halves of the surveillance Charpy specimens is important. CRIEPI has developed the test technique for the miniature C(T) specimens, whose dimensions are 4 × 10 × 9.6 mm, and has verified the basic applicability of the Master Curve approach by means of the miniature C(T) for the determination of the fracture toughness of typical Japanese RPV steel base metals [1]. A series of round robin tests on RPV steel base metals [2–4] demonstrated that the miniature C(T) specimen can be used for the determination of the reference temperature (To) with no specific difficulties in test techniques.

The present paper addresses the applicability of the fracture toughness evaluation by the miniature C(T) specimens on a RPV weld metal with multi-layer weld bead structure. The distribution of the fracture toughness and the trend in fracture toughness change with temperature were confirmed to show a good agreement with the assumption of the Master Curve method [5]. Fracture surface of the specimens were in cleavage fracture mode regardless of the difference in fracture toughness level. The relevance of the specimen size correction in the Master Curve method was confirmed. The difference of To values were only in a few degrees Celsius between the data obtained with 0.5 inch-thickness C(T) specimens and the miniature C(T) specimens. The effect of local loss of constraint nearby the specimen side surface was examined by comparing with the datasets from the specimens with and without side grooves. The difference of To was only 3 degree centigrade and no remarkable effect of side grooving could be seen. From overall examination results, it was concluded that the miniature C(T) specimen can be used for the Master Curve evaluation of tested PRV weld metal.
Friction Stir Seal Welding (FSSW) Tube-Tubesheet Joints Made of Steel
Authors: Shuaib Abdel Rahman , Al-Badour Fadi , Merah Nesar
Published: November 2015

This paper demonstrates the feasibility of successful seal welding process of tube-tubesheet joints using the relatively new friction stir welding (FSW) process. The purpose of the reported study is to develop the process parameters and to test the feasibility of friction stir welding ASTM 179 seamless cold-drawn carbon steel tube into an ASTM A516 Grade 70 tubesheet. All welds were performed in position control on a fully instrumented experimental friction stir welder using a water-cooled tool holder and a shroud for argon shielding gas. A proprietary tungsten-rhenium pin tool with a 1.54 mm pin length and shoulder diameter of 4.9 mm was used to perform the seal weld between the roller expanded tube and tubesheet. A steel plug was employed during each weld in order to maintain support for the weld throughout the circumference of the weld.

Sound welds were achieved in the FSW of ASTM 179 seamless cold-drawn carbon steel tube into an ASTM A516 Grade 70 tubesheet. Welding was improved by avoiding tool contact with the tube plug or the flash of the previous weld. Though a root void has been observed, which is typical of partial penetration butt welds, it is believed that the weld would still achieve a hermetic seal. Tool wear features of the W-Re pin has also been documented.
Assessment of Two Phase Critical Flow Models and Implementation in Fast Transient Fluid Dynamics Software
Authors: Lafon Philippe , Essadki Mohamed , Bartosiewicz Yann , Seynhaeve Jean-Marie
Published: November 2015

The discharge of a subcooled liquid or a liquid-vapor mixture at high temperature and pressure can occur in many industrial situations. This paper is focused on the analysis of critical flow models that are already available in the fast transient dynamics software EUROPLEXUS, or that are being implemented as new break boundary conditions. The results of the Moody, Fauske, Flinta, Henry-Fauske and DEM models are presented and compared with the Super Moby Dick experimental results. The best results are obtained for the DEM. Then preliminary results concerning the implementation of the DEM model as a break boundary condition in EUROPLEXUS are given.
Uncertainty Characterization of the CrCOD Circumferential Crack Opening Displacement Module for xLPR
Authors: Olson Richard , Scott Paul
Published: November 2015

The US NRC/EPRI xLPR (eXtremely Low Probability of Rupture) probabilistic pipe fracture analysis program uses deterministic modules as the foundation for the calculation of the probability of pipe leak or rupture as a consequence of active degradation mechanisms, vibration or seismic loading. The circumferential crack opening displacement module, CrCOD, estimates crack opening displacement (COD) at the inside pipe surface, at the mid-wall thickness location, and at the outside pipe surface using a combined tension/crack face pressure/bending GE/EPRI-like solution. Each module has an uncertainty beyond the uncertainty of the xLPR data inputs. This paper documents the uncertainty for CrCOD.

Using 36 pipe fracture experiments, including: base metal, similar metal weld, and dissimilar metal weld experiments; bend only and pressure and bend loading; static and dynamic load histories; cracks that range from short to long, the uncertainty of the CrCOD methodology is characterized. Module uncertainty is presented in terms mean fit and standard deviation between prediction and experimental values.
Validation of Stress Intensity Factor Solutions in xLPR Version 2.0 Code
Authors: Shim Do-Jun , Wallace Jay , Kalyanam Sureshkumar , Benson Michael
Published: November 2015

As part of the xLPR (Extremely Low Probability of Rupture) project, the stress intensity factor (SIF) solutions required for crack growth calculations were updated. This involved extension of existing solutions and development of new solutions as well. For surface cracks, the Universal Weight Function Method (UWFM) was implemented to handle complex stress distributions. In addition, a crack transition model was developed to more accurately capture the surface to through-wall crack transition. Finally, solutions for idealized through-wall cracks were extended to various pipe sizes and longer crack lengths.

In this paper, the SIF (K) solutions in xLPR Version 2.0 were validated against existing experimental data. The SIF modules in the xLPR code were used to simulate fatigue crack growth of circumferential cracks in pipes under bending up to wall penetration and to through-wall crack transition stage until idealized through-wall cracks were formed. The predicted fatigue crack growth results (mainly crack shape evolution) using the xLPR K-solutions provided good agreement with experimental data.
Anticipated Improved Performance of Advanced Steel Cladding Under Long Term Dry Storage of Spent Fuel
Authors: Rebak Raul B. , Huang Shenyan
Published: November 2015

In current light water reactors the nuclear fuel rods are dependent on zirconium alloys cladding. Used fuel bundles are generally stored in water pools for approximately twenty years and then they may be transferred to a dry casket for an interim storage until reprocessing or the final disposition in a permanent nuclear waste repository. The delay in opening a permanent repository in the US says that the used fuel bundles would need to be stored in dry casks for unanticipated extended periods (maybe 100 years). Under dry storage several mechanisms were identified for the degradation of zirconium based cladding. The vulnerabilities of zirconium alloys would limit their subsequent fuel retrievability and transportation after the long term storage. As part of the DOE Accident Tolerant Fuel (ATF), advanced ferritic steels such as Fe-Cr-Al alloys are being investigated to replace the zirconium alloy cladding. Previous performance in storage of austenitic stainless steel cladding suggests that the proposed ATF ferritic steels would perform well under long term storage in dry casks.
Parametric Investigation of the Flow-Excited Acoustic Resonance From Multiple In-Line Cylinders in Cross-Flow
Authors: Shaaban Mahmoud , Mohany Atef
Published: November 2015

In this paper, the flow-excited acoustic resonance of an in-line row of cylinders ranging from one to five is investigated. Cylinders of three different diameters of 12.7 mm, 19.1 mm, and 25.4 mm are tested in cross flow with flow speeds up to 160 m/s. Two different tube lengths of 76.2 mm and 127 mm are used to investigate the effect of the cylinder’s aspect ratio at a given diameter on the excitation mechanism of acoustic resonance. A fixed spacing ratio of L/D = 2 is used for all cases. For more than one cylinder of the larger diameter, the self-excitation of resonance occurs at two discrete flow velocity regions that are generally wider than the case of a single cylinder. A larger diameter does not only trigger the excitation of the pre-coincidence resonance region, but also increases the normalized acoustic pressure of this pre-coincidence resonance. On the contrary, the cylinder’s aspect ratio does not have a similar effect on the pre-coincidence and coincidence resonance regions. Therefore, it is important that the effect of diameter should be included in formulas predicting the occurrence of resonance for in-line tube bundles. In addition, the Strouhal number related to the coincidence resonance decreases with the increase in the number of cylinders. The coincidence resonance is related to the vortex shedding in the wake of the last cylinder, while the pre-coincidence resonance is related to the shear layer in the gap between successive cylinders.
Load Data Evaluation, Stress Analysis and Cycle Counting for the Qualified Thermal Fatigue Assessment of a NPP Component
Authors: Rudolph Jürgen , Maneschy José Eduardo , Cisternas Miguel , Freire José Luiz F. , Costa Felippe M. S. , Silva Bruno , Paiva Vitor E. L. , Suanno Rodolfo
Published: November 2015

Qualified fatigue assessment based on realistic input data constitutes an essential part of an ageing management strategy for Nuclear Power Plants. In this context and as a continuation of a previous paper PVP2014-28716 the requirements of load data evaluation, stress analysis and cycle counting are detailed based on a real world example from a Brazilian Nuclear Power Plant. One essential prerequisite of any fatigue assessment approach is the availability of realistic load data. In the present analysis, selected operational plant data from the period 2003 to 2012 are used. One further prerequisite is the accurate component stress analysis based on a transient thermal-mechanical Finite Element Analyses.

As an example, a highly loaded nozzle from the Chemical & Volume Control System (CVCS) is chosen to be analyzed. The influences on the fatigue assessment caused by the load-time histories, the stress analysis approaches and the cycle counting method are discussed in detail. The considered operational time period from 2003 to 2012 with respective selected plant data gives a consolidated background. It is one essential aim of the study to show the influence of the load-data input and the (design code conforming) stress analysis method on the resulting calculated cumulative usage factors (CUFs). In the present paper, the stress analysis employs the finite element method. Simplified elastic-plastic (application of ke plasticity factors) procedures are used in order to identify the margins and influences of design and actual loading histories on the resulting CUFs.

The paper concludes with a comprehensive picture including quantification and discussion of the different influencing parameters on the resulting CUFs. This reveals margins in the fatigue design process and solutions of coping with the design code requirements.
Methodological Features of WWER RPV Metal Critical Temperature of Brittleness Prediction on the Base of the Data Scatter and the Chemical Composition
Authors: Orynyak Igor , Zarazovskii Maksym , Radchenko Sergii
Published: November 2015

For WWER-1000 reactor pressure vessel (RPV) the metal embrittlement monitoring is performed with the usage of the radiation and the temperature surveillance specimens (SS) sets. For the fracture toughness curve indexing the critical temperature of brittleness (CTB) is used, CTB is obtained by the processing of Charpy impact energy data.

Modern codes that regulate WWER RPVs CTB prediction are based on the CTB shift ideology. According to this ideology the CTB is defined as the initial CTB value plus CTB shift due to the radiation, plus CTB shift due to the thermal ageing, plus certain margin. This margin includes the scatter of CTB in the initial state, scatter of CTB shift due to the radiation and scatter of CTB shift due to the thermal ageing.

A tendency of modern WWER RPV integrity assessment codes to provide conservatism with: choosing the CTB in the initial state for the CTB shifts determination; choosing the CTB in the initial state for the CTB determination; taking into account the scatter of CTB in the initial state, scatter of CTB shift due to the radiation and scatter of CTB shift due to the thermal ageing, leads to huge predictive values of CTB and to formal unfulfillment of brittle fracture criterion for RPVs.

This paper demonstrates that the usage of actual CTB data and their scatter (obtained directly from Charpy V-notched impact tests) instead of the shift ideology can be the one of the possible ways of adequate CTB prediction.

The CTB database for welds is created on the base of the results of WWER-1000 RPV surveillance program of all Ukrainian NPPs.

The article presents the results of the thermal aged Charpy V-notched SS tests. The thermal aging has been shown to be practically absent. The CTB thermal shift values, which were obtained in some laboratories, are caused by the CTB scattering in initial and thermal aged states only.

According to the processing results of the irradiated SS tests data, the chromium, manganese and silicon have been found to have the greatest impact on the CTB value.

The CTB dependence on the neutron fluence and chemical composition of WWER-1000 RPV beltline welds has been obtained. A new methodology of CTB curve prediction for WWER-1000 RPV welds is developed. This methodology is expected to be the basis in the modern Ukrainian normative of RPV integrity assessment since it reduces the unreasonably high conservatism inherent to the RPV project, to a more reasonable level.
3-Dimensional Finite Element T-Stress Calculation for Reactor Pressure Vessel Nozzle Blend Radius Semi-Elliptical Surface Cracks
Authors: Qin Minghao , Tang Shu , Ku Francis , Sommerville Daniel V. , Gustin Hal
Published: November 2015

T-stress is used as an indicator of the condition of crack tip constraint. In current fracture mechanics engineering applications in the U.S. nuclear industry, T-stress generally has been ignored during the calculation of applied stress intensity factors (SIF). Consideration of this crack tip constraint component could affect the evaluation of material fracture behavior, under either plane strain or plane stress or plane strain and plane stress combination. When the T-stress shows that the condition of crack front constraint is not plane strain, incorporation of T-stress may allow reduction of unnecessary conservatisms in such calculations. Under this condition, the allowable stress intensity factor is modified by increasing it above the KIc value, and it potentially increases the predicted allowable flaw sizes.

In this paper, T-stress has been calculated using 3-D finite element analyses (FEA) with a typical semi-elliptical crack in a reactor pressure vessel (RPV) nozzle blend radius. Both thermal and internal pressure load cases are considered.

To verify this finite element analysis approach, this method is applied to comparable literature models. The FEA results are consistent with closed-form solutions for T-stress calculation.
Limit Load Solution and Crack Driving Force Estimation Scheme for Embedded Flaws in Pipeline Girth Welds
Authors: Pépin Aurélien , Tkaczyk Tomasz , O’Dowd Noel , Nikbin Kamran
Published: November 2015

The acceptability of flaws in a subsea rigid pipeline is usually sanctioned based on the results of an engineering criticality assessment (ECA), carried out considering all loads seen by the pipeline from fabrication to the end of service life. Reel-lay is an efficient installation method, frequently used for installing subsea pipelines. Unlike surface breaking flaws, embedded flaws are not directly assessed in a reeling ECA because the available assessment solutions are too conservative. A work around approach is often used, whereby acceptable surface breaking flaw sizes are deemed acceptable beneath the surface, provided that the embedment depth is equal to or greater than half of the flaw height. However, the results of more recent research work suggest that this approach could be non-conservative in some cases.

In this work, a parametric finite-element (FE) study was carried out to assess the effect of the embedment depth, the crack length and the crack height on the load required to cause collapse of the shorter ligament of an embedded flaw. Subsequently, a closed form limit load solution was developed, and compared against available solutions for pipes subjected to tension. A J-based crack driving force (CDF) estimation scheme was developed for a selected material behaviour. Finally, recommendations were made for the direct reeling ECA of subsea pipelines with embedded flaws.
Determination of Path-Independent J-Integral for Cracks in Residual Stress Fields Using Finite Element Method
Authors: Zhu Xian-Kui
Published: November 2015

“Hot” residual stresses exist in metal welds due to welding thermal stresses, and “cold” residual stresses occur in mechanical damaged metallic pipes due to large plastic deformation. For a crack in ether a hot or cold residual stress field, residual stresses might have a strong effect on the crack-tip field and the fracture parameter, J-integral. To consider the effect of residual stresses and to ensure the path-independence of J, different correction methods have been developed over the years. Recently, the finite element analysis (FEA) commercial software ABAQUS adopted one of correction methods for determining the residual stress corrected J-integral.

This paper intends to evaluate this new function of ABAQUS and to see if the residual stress corrected J-integral is path-independent. A brief review is first given to the J-integral definition, the conditions of J-integral path-independence or dependence, and the modifications of J-integral to consider the residual stress effect. A modified single edge-notched bend (SENB) specimen is then adopted, and a FEA numerical procedure is developed and used in the numerical tests to evaluate the path-independence of the residual stress corrected J-integral using ABAQUS. Detailed elastic-plastic FEA calculations are carried out for the modified SENB specimen in three-point bending. The residual stress field, crack-tip field, and J-integral with and without consideration of the residual stress effect are determined and discussed.
A New Material Failure Criterion for Numerical Simulation of Burst Pressure of Corrosion Defects in Pipelines
Authors: Zhu Xian-Kui
Published: November 2015

Accurate burst pressure prediction of corroded pipelines is critical to safety design, integrity assessment and operation management. This paper evaluates five corrosion assessment methods: three flow stress-based ASME B31G, Modified B31G, and RSTRENG, and two ultimate tensile stress (UTS)-based LPC and PCORRC. The UTS-based methods were developed using the elastic-plastic finite element analyses (FEA) and an assumed material failure criterion, i.e., the Mises equivalent stress equals to the true UTS of the material. However, recent numerical investigations showed that the assumed Mises stress-based failure criterion is not valid generally, and may depend on the material hardening response. Thus the UTS-based methods may be inaccurate.

In order to improve the UTS-based corrosion assessment methods, this paper investigates a general stress-based material failure criterion, and proposes a new Mises stress-based criterion that depends on the material strain hardening exponent. This new criterion is then applied to determine burst pressures of corrosion defects in the FEA simulations. With the FEA predicted burst pressures, an improved burst pressure prediction model is developed. It is shown that the proposed material failure criterion can determine more accurate burst pressures, and the improved corrosion model predicts burst pressures agreeing well with experimental data.
Streamwise Dynamics of a Tube Array Subjected to Two-Phase Cross-Flows
Authors: Olala Stephen , Mureithi Njuki W.
Published: November 2015

Nuclear steam generator tubes in two-phase cross-flow may vibrate due to excitations that emanate from various sources. Of these excitation mechanisms, fluidelastic instability is the most dominant cause of tube failures in the short-term. These failures, other than leading to unscheduled plant shutdowns, may result in leakage of radioactive materials that may ultimately cause accidents and economic loss.

Very limited work has been dedicated to investigating purely streamwise fluidelastic instability in tube arrays. However, recent observations of tube failure caused by streamwise or in-plane instability confirm the importance of streamwise fluidelastic instability analysis.

In the present study, we present detailed dynamic cross-coupling force and phase measurement results for a central cluster of tubes in a rotated triangular tube array of Pitch-to-Diameter ratio (P/D)=1.5 subjected to air-water two-phase cross-flow, for homogeneous void fractions of 0% and 60%. The measured dynamic forces together with previously measured quasi-steady forces are necessary to estimate the time delay which is an important input for the quasi-steady fluidelastic instability model.
A Method of Ultrasonic Phased Array Inspection of Middle-High Pressure Plastic Pipe Reinforced by Cross Helically Wound Steel Wires Electro-Fusion Joint
Authors: Miao Xiaoming , Shi Jianfeng , Zheng Jinyang
Published: November 2015

With strong bearing capacity, good corrosion resistance, excellent wear resistance, light weight and easy transportation and installation, Plastic pipe reinforced by cross helically wound steel wires (PSP) is widely used in oil industry, coal chemical industry, slurry transportation engineering, and sea (river) bottom water projects. Due to the PSP at middle-high pressure, an effective and reliable method of connection between pipes is particularly important. Heat-fusion weld and electro-fusion weld are usually used in middle-high PSP connections, or adding steel plate reinforcement at present. The pipe welded-joint failure is the main failure mode at service stage, causing the damage of pipelines and fluid leakage. Ultrasonic phased array inspection, which is one of the non-destructive inspection methods, is mainly used in pipe welded-joints inspection. A higher attenuation coefficient of polyolefin materials and the interference of steel mesh skeleton among PSP can cause great impact to the ultrasonic inspection; It’s worse if a steel plate is added. In order to put forward a kind of method can better detect the connection joint, this paper examines a new method of ultrasonic phased array inspection in PSP welded-joints based on customized probe, focus law and scanning mode which overcomes the difficulties found in other usual non-destructive inspection measures.
Effects of External and Internal Hydrogen on Tensile Properties of Austenitic Stainless Steels Containing Additive Elements
Authors: Itoga Hisatake , Matsunaga Hisao , Yamabe Junichiro , Matsuoka Saburo
Published: November 2015

Effect of hydrogen on the slow strain rate tensile (SSRT) properties of five types of austenitic stainless steels, which contain small amounts of additive elements (e.g., nitrogen, niobium, vanadium and titanium), was studied. Some specimens were charged by exposing them to 100 MPa hydrogen gas at 543 K for 200 hours. The SSRT tests were carried out under various combinations of specimens and test atmospheres as follows: (i) non-charged specimens tested in air at room temperature (RT), (ii) non-charged specimens tested in 0.1 MPa nitrogen gas at 193 K, (iii) hydrogen-charged specimens tested in air at RT, (iv) hydrogen-charged specimens tested in 0.1 MPa nitrogen gas at 193 K, and (v) non-charged specimens tested in 115 MPa hydrogen gas at RT. In the tests without hydrogen (i.e., cases (i) and (ii)), the reduction of area (RA) was nearly constant in all the materials, regardless of test temperature. In contrast, in the tests of internal hydrogen (cases (iii) and (iv)), RA was much smaller at 193 K than at RT in all the materials. It was revealed that the susceptibility of the materials to hydrogen embrittlement (HE) can successfully be estimated in terms of the nickel equivalent, which represents the stability of austenite phase. The result suggested that the nickel equivalent can be used for evaluating the material compatibility of austenitic stainless steels for hydrogen service.
Evaluation of SCC Crack Growth Rate in BWR Water Based on Elastic-Plastic Fracture Mechanics Parameters
Authors: Takanashi Masahiro , Itabashi Yu , Hirano Takashi
Published: November 2015

This paper presents an applicability of elastic-plastic fracture mechanics parameters for evaluating a crack growth rate of stress corrosion cracking (SCC). Currently linear fracture mechanical approaches have been applied for the SCC crack growth evaluation, even though some cracks due to SCC are found in plastic deformation zones near welding where linear fracture mechanics is no longer applicable. In this paper, the authors have proposed an elastic-plastic parameter “equivalent stress intensity factor KJ” for evaluating the SCC crack growth rate based on the J-integral value, which is valid in both elastic and plastic stress fields. In order to verify the applicability of the evaluation by KJ, SCC crack growth tests were carried out in a simulated boiling water reactor (BWR) water. When the SCC crack growth rate was evaluated by the stress intensity factor K, no linear relationship between the K values and the crack growth rates was observed in the high K-value region, where a small-scale yielding condition was not met. The crack growth rates increased exponentially according to increasing the stress intensity factor to exceed the linear relationship. On the other hand, when the crack growth rate was evaluated by the elastic-plastic parameter KJ, a linear correlation between the KJ values and the crack growth rates was confirmed regardless the specimen size and the stress condition. This result suggests that by applying the elastic-plastic parameter KJ, the SCC crack growth rates in a wider range could be estimated easily with using a smaller specimen.
Thermal Annealing of Reactor Pressure Vessels
Authors: Sokolov Mikhail A. , Server William L. , Nanstad Randy K.
Published: November 2015

Some of the current fleet of nuclear power plants is poised to reach their end of life and will require an operating life time extension. Therefore, the main structural components, including the reactor pressure vessel (RPV), will be subject to higher neutron exposures than originally planned. These longer operating times raise serious concerns regarding our ability to manage the reliability of RPV steels at such high doses. Thermal annealing is the only option that can, to some degree, recover irradiated beltline region transition temperature shift and recover upper shelf energy properties lost during radiation exposure and extend RPV service life. This paper reviews the experience accumulated internationally with development and implementation of thermal annealing to RPV and potential perspectives for carrying out thermal annealing on US nuclear power plant RPVs.
Weld Residual Stress (WRS) Modeling of Layered Pressure Vessels (LPV) and Fracture Assessment
Authors: Brust F. W. , Punch E. , Kurth E.
Published: November 2015

NASA has numerous non-code layered pressure vessel (LPV) tanks that hold various gases at pressure. Since replacement costs of the tanks would be high an assessment of the pressure vessels’ capabilities for continued use is desired. Layered tanks typically consists of an inner liner/shell (often about 12.5 mm thick) with different layers of thinner shells surrounding the inner liner each with thickness of about 6.25-mm. The layers serve as crack arrestors for crack growth through the thickness. The number of thinner layers required depends on the thickness required for the complete vessel. All cylindrical layers are welded longitudinally with staggered welds so that the weld heat affected zones do not overlap. The built-up shells are then circumferentially welded together or welded to a header (or nozzle) to complete the tank construction. This paper presents computational weld residual stress (WRS) modeling results of two representative layered tanks; (i) a small 4-layer tank and (ii) a large 14-layer tank. Contact between the layers must be considered which led to some convergence difficulties that were overcome. These predictions are compared with the corresponding monolithic tanks (non-layered) of the same size and thickness along with comparing to some compiled API-579 [1] WRS solutions. In general, the WRS fields in layered tanks are quite different from those in corresponding monolithic tanks and the effect of layering is necessary to include in the modeling. In addition, since the toughness of some aged tanks can be low the effect WRS on cracks may important. This is examined by introducing cracks into the tanks at locations where cracking may occur using the finite element alternating method (FEAM). Comments about the effect of WRS fields on fracture are also made.
Alternative Characterization Rules for Quasi-Laminar Flaws Based on 3D X-FEM Calculations
Authors: Lacroix Valéry , Dulieu Pierre , Bogaert Anne-Sophie
Published: November 2015

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected, mainly in the lower and upper core shells of the RPVs.

In the frame of the Structural Integrity demonstration of these RPVs according to ASME XI principles, ASME XI IWB-3300 article requires combining closely spaced flaws in order to account for their mechanical interactions. However, it appeared early that the characterization rules were adapted neither to quasi-laminar flaws nor to such densities of flaws.

Therefore, an alternative methodology to derive characterization rules for quasi-laminar flaws has been developed, implemented and validated.

This work, based on 2D eXtended Finite Element Method (X-FEM) calculations and presented during ASME PVP 2014, has led to the proposed ASME Code Case N-848 “Alternative characterization rules for quasi-laminar flaws – Section XI, Division I”.

This 2D approach, even though better suited to quasi-laminar flaws, results however in very conservative proximity rules.

Therefore, it appeared that more realistic — although still conservative — proximity rules based on 3D X-FEM calculations could be developed.
Optimization of Polymer Composite Pipe Under Consideration of Hybridization
Authors: Häußler Michael , Schatz Markus , Baier Horst , Mertiny Pierre
Published: November 2015

Filament-wound fiber-reinforced polymer composite piping has excellent corrosion resistance and high specific properties, which makes it an attractive choice for various industries. Another attractive aspect of composite piping is the ability to select fiber architectures and material systems to meet design specification and maximize performance while minimizing material usage. The present contribution describes an optimization approach that is aimed at providing design recommendations for multi-material composite piping with multiple fiber orientations.
Development of Fitness-for-Service Standard for Pressure Equipment With Metal Loss Based on Reliability
Authors: Kaida Takuyo , Sakai Shinsuke
Published: November 2015

Concern about probabilistic approach for Fitness-For-Service (FFS) assessment has been growing over the last several years. The FFS assessment based on reliability helps to make a rational decision as to whether to run or repair the equipment. High Pressure Institute of Japan (HPI) formed a committee to develop a HPI FFS standard that can be used for pressure equipment with metal loss. This new standard provides an assessment procedure to evaluate structural integrity of components with metal loss based on reliability. This paper introduces the assessment procedure which is standardized and under preparation for publication, and the technical backgrounds. The standard provides information about limit state of pressure equipment, probabilistic properties of basic variables and target reliability. Probabilistic approach can be applied easily to metal loss assessment by using the standard.
Negative Load Ratio Fatigue Crack Growth Rate Testing on Austenitic Stainless Steel in a Simulated Primary Water Environment
Authors: Platts Norman , Tice David R. , Zhang Wenzhong
Published: November 2015

Light water reactor coolant environments are known to significantly enhance the fatigue crack growth rate of austenitic stainless steels. However, most available data in these high temperature pressurized water environments have been derived using specimens tested at positive load ratios, whilst many plant transients involve significant compressive as well as tensile stresses. The extent to which the compressive loading impacts on the environmental enhancement of fatigue crack growth and more importantly on the processes leading to retardation of those enhanced rates is therefore unclear, potentially leading to excessive conservatism in current assessment methodologies.

A test methodology using corner cracked tensile specimens has been developed which provides significant advantages over more conventional specimen geometries in terms of autoclave testing at negative load ratios. Finite element analysis of the specimen geometry has been performed to generate effective stress intensity factors, Keff, for specimens loaded in fully reverse loading. Test data generated in both air and water are compared to conventional compact tension specimen data to validate the test methodology.
Study of Fatigue Initiation of Austenitic Stainless Steel in a High Temperature Water Environment and in Air Using Blunt Notch Compact Tension Specimens
Authors: Platts Norman , Tice David R. , Nicholls Jennifer
Published: November 2015

Fatigue life assessment procedures for components exposed to high temperature pressurised water environments are typically based on NUREG/CR-6909 or broadly similar codes (e.g. proposed ASME code case N-792). The effects of a high temperature water environment on the fatigue life are accounted for by simply adjusting the fatigue life in ambient temperature air by an environmental factor (FEN). This adjustment assumes that the environment affects both initiation (nucleation) and propagation equally, which is potentially over-conservative. Blunt notch compact tension (CT) specimens (along with direct current potential drop (DCPD) crack detection) have been proposed as a means of determining the “true” fatigue initiation life, enabling the relative impact of the environment on initiation and growth to be characterised and the level of conservatism in the FEN approach assessed.

The current work uses a combination of finite element analysis and fatigue testing in both air and water to assess the feasibility of blunt notch CT testing to detect initiation and to quantify the environmental impact. This work indicates significant difficulties with the blunt notch CT test methodology both in terms of quantifying the applicable strain and in terms of detection of the very early stages of initiation which preclude the quantitative application of the technique to study true initiation. Qualitatively, the results suggest that there is still a significant impact of the high temperature water environment on the earliest detectable stages of crack growth in austenitic stainless steels; however the earliest defects detectible by DCPD techniques still involve a significant contribution from short crack growth. Nevertheless, the technique provides a valuable insight into initiation and residual life of components subjected to through wall strain gradients.
Guided Wave Damage Detection in Power-Plant-Tubes by Using Magnetostrictive Transducer Arrays
Authors: Guo Peng , Li Hongyuan , Tian Zhenhua , Xu Hong
Published: November 2015

This paper presents an efficient damage detection technique for power-plant-tubes by using guided waves and magnetostrictive transducer arrays. Particularly, our detection technique focuses on the small diameter and thick wall power-plant-tubes, such as superheater tubes, reheater tubes and water wall tubes. Firstly, the damage effects on guided waves in small diameter and thick wall tubes were studied by using three-dimensional finite element method. The wave reflections and mode conversions induced by damage were investigated. Secondly, based on T (0, 1)-F (n, 2) modes, magnetostrictive transducers were designed for guided wave generation and sensing in small diameter and thick wall tubes. The designed magnetostrictive transducers can effectively generate and measure guided waves, especially the non-dispersive torsional T (0, 1) wave mode. Finally, a magnetostrictive transducer array was developed for damage detection in small diameter and thick wall tubes. Through a virtual focusing array imaging algorithm, intensity images were constructed, which can show both the location and size of damage.
Design of an Experiment to Measure the Thermal Accommodation Coefficient Between Helium and Stainless-Steel in Concentric Cylinders
Authors: Green Rachel , Nacer Mustafa-Hadj , Greiner Miles
Published: November 2015

Heat transfer through a 1 mm gap between two concentric cylinders representing the gap between a fuel support basket and a canister is experimentally and numerically investigated. The objective of this work is to study rarefied gas heat transfer in a simple geometry, and to measure the thermal accommodation coefficient at the interface between stainless steel and rarefied helium. The thermal accommodation coefficient is used to characterize the interaction between gas molecules and wall at the molecular level. It is important to determine its value with precision for better determination of heat transfer at low pressure. The experimental procedure consists of measuring the temperature difference between the inner and outer cylinders as the pressure is decreased in the gap. By knowing the heat flux across the gap the thermal accommodation coefficient can be extracted from the theoretical expression relating the temperature difference to the radial heat flux. Three-dimensional simulations using the ANSYS/Fluent commercial code are conducted to assess on the design of the experimental apparatus. These simulations confirmed that the apparatus design is effective to study the heat transfer across rarefied gas and to determine the thermal accommodation coefficient for helium on stainless steel surface.
Update on European Standards and Guidelines for Managing the Integrity of Bolted Joints
Authors: Noble Robert
Published: November 2015

A number of standards and guidelines associated with integrity of bolted joints were updated or introduced in 2013 and 2015 will see the release of “The Energy Institute Guidelines for the Management of Integrity of Bolted Joints in pressurized systems.” The first guidelines were introduced in 2002 in response to a drive to reduce Hydrocarbon leakage in the UK Offshore Industry; the third edition sees the industry once again targeting Hydrocarbon Leak Reduction. This paper will give an overview of the Guidelines — and discuss the key changes on the previous versions and alignment with ASME PCC-1-2013 and ASME PCC-2-2011. Ongoing work is in progress on European Standards: July 2013 saw the publication of the harmonized calculation standard. En1591-1. Late 2013 saw the training and competence standard EN1591-4 published and this standard is now being implemented. A guide and sample calculations to EN1591-1 are being worked on under EN1591-6. The paper will discuss other developments in Europe with the aim of complementing and harmonizing with the work of ASME.
Calculation of Maximum Allowable Bending Moment on Pipe Flange Connection for Leak Tightness Design
Authors: Nagata Satoshi
Published: November 2015

This paper proposes a method to calculate the maximum allowable bending moment on pipe flange connections for leak tightness design of piping systems in process plants. The method evaluates the gasket stress reduction due to the bending moment as well as internal pressure based on the load factor of the bolted-gasketed pipe flange connection and the equivalent axial force. It determines the critical load combination of pressure and bending moment causing leakage. The calculated maximum allowable bending moment has shown fairly good agreement with experimental results with reasonable conservativeness. The paper also shows the advantage of the proposed method against the conventional methods such as the equivalent pressure method, NC-3658.3 method, B31.8 method, and so on.
Technical Basis for Code Case N-809 on Reference Fatigue Crack Growth Curves for Austenitic Stainless Steels in Pressurized Water Reactor Environments
Authors: Cipolla Russell C. , Bamford Warren H.
Published: November 2015

Reference fatigue crack growth curves for austenitic stainless steels in pressurized water reactor environments have been proposed for Section XI flaw evaluation applications. The reference curves are dependent on temperature, loading rate, mean stress, and cyclic stress range, which are all contained in the model. This paper presents the technical basis for the curves, which is based on various research and industry sources. The reference curves for unirradiated material are implemented through Code Case N-809. Applications for N-809 include analytical evaluations for flaw growth to Appendix C and Appendix L of ASME Section XI where environmental effects are important in establishing the service life and inspection interval for austenitic stainless steel piping and components.
Application of Elastic-Plastic Finite Element Analysis to Determine the Ultimate Load of Components
Authors: Reinhardt Wolf
Published: November 2015

An assessment of pressure retaining components based on ultimate load (or plastic instability load) is used in Section VIII Div. 2 and Section III Appendix F of the ASME Boiler and Pressure Vessel Code, as well as in various fitness-for-service standards and guidelines. The ultimate load analysis strives for a realistic prediction of the plastic behavior of a component up to the highest load or load combination that the component can support. The high level of applied load may cause significant deformations in the component, and for an accurate assessment the analysis must consider the effect of these deformations on the material as well as on equilibrium and the state of stress. This paper discusses briefly the basis of ultimate load analysis and considerations in performing such analysis with finite element analysis. The main focus is to validate the analysis approach by demonstrating close agreement between finite element analysis and analytical solutions and the results of component tests.