While establishment of appropriate policies and securing key technologies on spent nuclear fuels are state-of-the-arts in the world due to saturation of fuel pools and/or temporary facilities, the details of transportation, storage and repository are different depending on the situation in each country. Thereby, accurate integrity assessment of specific transportation casks and contained fuel assemblies as well as their breakdown effects on the public and environment are becoming more important. The purpose of this study is to carry out parametric stress analyses of spent nuclear fuel assembly in a prototypal dual purpose cask under development. As the representative postulated accident conditions, four scenarios were selected such as vertical, horizontal, corner and oblique drop from 9 m height on the ground. Then, taking into account computational cost, a simple model that considers only the equivalent mass of the fuel assembly was made for preliminary finite element analyses to determine the most dangerous drop condition and critical location. Subsequently, a detailed model that considers the acceleration of fuel assembly was made based on the preliminary analysis results and finite element analyses were carried out to calculate engineering parameters. Resulting membrane and bending stress intensities were compared with allowable design limits, of which findings will be used as technical background for development of transportation cask and management of the spent nuclear fuel integrity.

Stress Intensification Factors or SIFs allow piping to be analyzed using beam theory, with a SIF representing local effects of specific piping geometry. However, the current piping codes do not explicitly provide SIFs for collared type piping joints for use in pipe stress calculations. The objective of this paper is to describe the methodology on how a finite element analysis (FEA) was to model the behavior of collared joints, and to ultimately develop appropriate SIFs that can be used in pipe stress analyses. This paper describes a real-life analysis example on collared joints installed on a set of existing fuel transfer lines. The lines, which ranged in size from DN200 to DN350, were concrete lined carbon steel with the collars fillet welded to the carbon steel section of the piping. Test coupons cut from existing pipe-collar sections were tested in a laboratory to determine the forces required to break the collar welds. Using FEA, the same test coupons were modelled to replicate the failure tests. Multiple iterations were undertaken to determine an appropriate bi-linear stress-strain curve fit for the weld material. The curves of different weld electrode materials were considered. The curve which lead to results similar to those observed in physical testing was selected. From this, a failure stress across the weld could be determined. This stress, 435MPa was then used in subsequent models to determine the point at which the weld fails under bending loads. Multiple tests were analyzed to allow for possible effects of inclusions and voids. Finite element models of the collar geometries were constructed and non-linear analyses were undertaken using the weld strengths determined from the coupon testing data. A simple cantilever type arrangement with a point load at one end was analyzed, inducing a bending moment across the collar. The peak stress resulting from the bending moment across the collar weld at the center of the cantilevered pipe arrangement, was investigated across various pipe diameters, wall thicknesses, weld sizes and collar geometries. Based on the results, a relationship between the pipe geometry and SIF was developed. Hence a pipe stress model of the transfer lines could ultimately be developed using these SIFs to predict the behavior of the piping.

Protection against local failure is one of the integral components in the design-by-analysis requirements in ASME BPVC Section VIII, Division 2. Of the methods offered by the ASME, the Local Strain Limit procedure outlined in 5.3.3.1 is the typical calculation method. However, it has been found that relying on this procedure alone can lead to untenable utilization results if used on certain analyses with varied load paths. The flange described in this study was calculated using “design by analysis” according to Part 5 of ASME BPVC Section VIII, Division 2. The elastic-plastic stress analysis method was used. The flange was loaded with an initial bolt pre-tension and then with internal pressure. During the local failure calculation, an abnormal condition was encountered in the form of a large spike in the history curve of the ratio between plastic strain and limiting triaxial strain. An investigation found that despite being in a stress state below yield stress, some nodes had a non-zero plastic strain and high triaxiality factor. This was caused by the load sequence: first, the bolt pre-tension and then internal pressure. The flange was first bent due to the pre-tension load, and later experienced bending in the opposite direction after the internal pressure load was applied. This resulted in a relatively low stress state with a high triaxiality factor and non-zero plastic strain in certain areas, which then showed high utilization under the local failure strain limit criterion. This paper will discuss how this issue can be avoided by using the strain limit damage calculation procedure 5.3.3.2 outlined in ASME BPVC Section VIII, Division 2.

The current design by analysis for protection against collapse from buckling in ASME Section VIII, Division 2, B&PV Code [8] has three different methods. However, these is no background bases for the three methods and analyst have found that the elastic plastic collapse analysis will give overly conservative results when compared with design by rule. Therefore, this study was undertaken to resolve this concern and develop a new procedure for buckling analysis to be implemented in the ASME Section VIII, Division 2, B&PV Code, Part 5.

China is the world’s largest user of compressed natural gas vehicles, with a total of nearly 6 million compressed natural gas (CNG) vehicles. The nominal working pressure of the cylinders used in the CNG vehicles in China is 20 MPa, as a result, CNG vehicles have a short range. In order to improve the range of CNG vehicles, the development of CNG vehicles with higher pressure is promoted by the CNG vehicle industry in China nowadays. In this paper, structural design of a fully-wrapped composite CNG gas cylinder with nominal working pressure of 30 MPa are carried out. The steel liner is made of 4130X seamless steel with design wall thickness of 5.9 mm, and the outer surface of steel liner is wrapped with resin based glass fiber composite material. The fully-wrapped composite adopts mixed fiber winding mode: low-angle helical winding, high-angle helical winding and hoop winding. Stress analysis and autofrettage pressure optimization of the designed composite gas cylinder are carried out with finite element method. The results show that the designed composite gas cylinder meets the requirements of ISO 11439-2013, and the best autofrettage pressure of the gas cylinder is 52 MPa after optimizing the autofrettage pressure.

Ratcheting assessment by elastic-plastic stress analysis is presented in ASME VIII-2, paragraph 5.5.7. There are three criteria. The first one is strict in engineering design. It’s hard for most of structures to satisfy it. If the plastic strain in the structure is zero, it means that the material is not fully utilized and maybe the structure is unreasonable. Therefore, the second and third criteria are used much more. The first one and the third one can be observed directly and judged accurately by the finite element analysis results. The second one demands an elastic core in the primary-load-bearing boundary. It could be easily observed when the structure is axisymmetric, but hard to judge in the 3D structure. Okamoto in Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) has studied two thermal stress ratchet criteria: evaluating variations in the plastic strain increments and evaluating variations in the elastic core region, which can accurately assess ratcheting. Recent years, based on the criteria above, more researches have been performed by engineers not only from C-TDF but from all over the world. In this work, several two-dimensional structures and three-dimensional structures under particular load and displacement boundaries are performed by using finite element software ANSYS, aiming to compare the similarities and differences between the criteria in ASME VIII-2, 5.5.7.2 and those given by C-TDF. The assessment of these structures presented in this work will help engineers understand the realization of the criteria and methods in engineering design, especially how to utilize the results from ANSYS.

Industrial production is accompanied by a large number of physical and chemical reactions. Steam, whose heat was often used to carry out various production activities, is a common medium in industrial production. Steam pipeline has the characteristics of high temperature and high pressure. The pipeline has been in service at high temperature for a long time, which is prone to metal material degradation such as graphitization and spheroidization. Cause of the expansion of steam pipeline after heating, the natural compensation structure is generally adopted in the whole plant pipe gallery. In recent years, the accidents of steam pipeline occurred frequently, so we must pay more attention to the safety of steam pipeline. Periodic Inspection Regulation for Industrial Pressure Piping (TSG D7005-2018) explicitly requires stress analysis and checking in some cases to determine the safety of the pipeline. The traditional inspection method adopts a random sampling model which has the risk of over inspection and missing inspection. Taking a whole plant steam pipeline as an example, this paper introduced the stress check criterion of pipeline in ASMEB31.3.The model of the pipeline was established by the software, and the stress state and displacement of each node of the pipeline were calculated. According to the calculation results, a targeted inspection scheme was established and effective data support was provided for the regular inspection of steam pipeline.

Piping vibrations in process plants are rarely analyzed or anticipated correctly during the ‘design Stage’. Most of the times ‘in -depth’ analysis is not carried out during ‘design stage’ except following few good engineering practices. As a result, few pipes can show excessive vibrations during operations that fall under the ‘danger’ zone. The vibrating pipe transfers the vibrations to the steel structure and these vibrations are experienced by operating personnel causing a ‘safety hazard’. The real risk is loss of containment due to unacceptable vibrations and eventual fatigue failure of pipe and or structure. The reason resulting in vibrations can be connection of pipe with rotating equipment, the vibration of structure on which the pipe is supported, flow inside the pipe, noise level or slug / water hammer. Here, the authors present a case study of a vibrating pipe beyond the accepted limit and how the pipe vibrations which are being transferred to supporting platform are minimized. The analytical results obtained by software simulations are benchmarked against actual readings measured at the site. The paper also provides the mathematics and its application to solve a practical vibration problem. It provides a systematic approach starting from generic calculations until a detailed flow simulation. In the end, it provides guidelines to select rubber and viscous dampers. The innovative part of the case study is the usage of specially designed rubber mounds which have yet not been used for pipe vibrations.

The flare system is an indispensable safety facility in petrochemical production. The function of the flare system is to collect the tail gas emitted from the production of each device into the main pipe of the flare, lead it pass through the liquid separation tank and the water seal tank in turn, and finally to the high-altitude flare for combustion and discharge into the atmosphere. The high temperature of flare gas pipeline will cause the pipeline to expand under heat. Due to the large thermal stress caused by the thermal expansion of the pipeline, the load on the nozzle of the connected equipment will be increased, which is easy to cause safety accidents. Taking the flare system of a whole factory as an example, this paper introduced a simple discriminated method to measure the flexibility of the pipeline system. The software CAESAR II was used to establish the model of the main flare pipe and the liquid separation tank in the whole factory. The calculated stress state of the pipe system meets the requirements of ASMEB31.3, and the stress of the liquid separation tank nozzle meets the technical conditions of the manufacturer. It is hoped that this method can provide some reference for the regular inspection of pipelines.

SS316L finned tubes are becoming very popular in high-pressure gas exchangers and particularly in CO 2 cooler applications. Due to the high-pressure requirement during operation, these tubes require an accurate residual stress evaluation during the expansion process. Indeed, die expansion of SS tubes creates not only high stresses when combined with operation stresses but also micro-cracks during expansion when the expansion process is not very well controlled. This research work aims at studying the elastic-plastic behavior and estimating the residual stress states by modeling the die expansion process. The stresses and deformations of the joint are analyzed numerically using the finite element method. The expansion and contraction process is modeled considering elastic-plastic material behavior for different die sizes. The maximum longitudinal, tangential and contact stresses are evaluated to verify the critical stress state of the joint during the expansion process. The importance of the material behavior in evaluating the residual stresses using kinematic and isotropic hardening is addressed.

This paper is a report of the studies on the mechanical behaviors and leakage characteristics of pipe-socket threaded joints subjected to bending moment as well as internal pressure by means of experimental tests and finite element simulations. The paper dealt with the 3/4″ and 3″ joints, and the joints for both sizes have two different combinations of thread types in the pipe and socket, i.e. taper-taper thread combination or taper-parallel one, respectively. Experimental bending leak tests showed that the taper-taper joints could retain internal pressure under bending load up to nearly plastic collapse. The taper-parallel joints, however, could hardly keep internal pressure against bending moment even the sealing tape was applied to enhance the sealing performance. Finite element analysis was carried out to simulate those bending tests, especially to clarify the deformation and the stress distribution in the engaged threads in detail. The analysis demonstrated that the sealing performance of the joints highly depend on the contact conditions not only at the thread crest to thread root but also in between flank surfaces. A complicated leak path across the engaged threads under bending moment was identified by the simulation.

The paper presents estimated thermal expansion coefficients of 316SS and 508LAS base, 316SS filler or similar metal weld (SMW), and 316SS-508LAS dissimilar metal weld (DMW) filler and butter weld metals. These base and weld metals are typically used in nuclear reactor pressure boundary components. Accurate estimation of the expansion coefficients of these metals is essential for accurate estimation of thermal-mechanical stress in reactor pressure boundary components. In this paper we present the expansion coefficients of 316SS and 508LAS base, 316SS-SMW filler, and 316SS-508LAS DMW filler and butter weld metals. The coefficients were estimated based on our own experimental data. The corresponding expansion coefficient results and the FE validation results are presented in this paper. We anticipate that these types of results can be used as guidelines for choosing appropriate expansion coefficients for thermal-mechanical stress analysis of safety critical nuclear reactor components.

Cyclic and over-elastic loading can lead to an accumulation of plastic strains. If there is a cyclic load, which is driven by a single parameter, the lifecycle design can be very costly in terms of computational effort. If more than one cyclic load parameter is to be taken into account, which is then a multi-parameter loading, this task can become even more complex and costly. To solve this problem efficiently, different techniques are proposed. One of these techniques is based on step-by-step calculations of the strain ranges for a reduced set of loadings. Once these strain ranges are known, the accumulated state for each individual load case can be estimated using the Simplified Theory of Plastic Zones (STPZ), which requires just a few linear elastic analyses. It is shown that cyclic loads, which occur in intervals, can be replaced by interval-free calculations, which reduce the computational effort enormously. All these techniques lead to a procedure, which delivers good estimations in terms of post-shakedown quantities with very low computational effort compared to incremental step-by-step calculations. The results of the STPZ are presented by an example. A thick-walled cylinder is loaded with a constant axial force and subjected to cyclic shear and cyclic internal pressure. In general, for structures exhibiting ratcheting, hundreds or more load cycles must be analysed via step-by-step calculations until the shakedown state is reached. Using the STPZ, post-shakedown quantities, including strain ranges and accumulated strains can be estimated efficiently and the structure can be designed according to the rules of the ASME Codes. The computational effort and the quality of the results of the STPZ are compared with a step-by-step calculation.

We considered the Type2 pressure vessel (hereinafter, Type2) used in hydrogen refueling stations (hereinafter, HRS), a stational Composite Reinforced Pressure Vessel (hereinafter, CRPV) in which a metal layer made of high-strength low-alloy steel is wrapped with a carbon fiber reinforced plastic (hereinafter, CFRP) layer in the circumferential direction. Because Type2 is lightweight and has a long life, installation in HRS is expected. However, since no technical standards concerning design for safe use of Type2 for HRS currently exist, few Type2 have been installed in HRS in Japan. Based on these circumstances, we are developing a Technical Document on the safe use of Type2 (hereinafter, TD) to promote the installation of Type2 at HRS. In this paper, we introduce the current discussion on issuance of the TD as an industrial standard, focusing especially on the following: Type2 shall be considered a two-layer pressure vessel in which the CFRP layer shares the circumferential stress of the metal layer. The wall thicknesses of the metal layer and CFRP layer of Type2 are calculated by Design by Rule approach, but when necessary, Design by Analysis (stress analysis and fatigue analysis) can be applied. Design specification tests such as the burst test and hydraulic pressure cycle test using an actual Type2 should not be required. The hydrogen compatibility and fatigue life of the low-alloy steel used in the metal layer are evaluated in accordance with our previously-proposed methods [1]. In the fatigue analysis, the effect of autofrettage can be considered.

Leak-before-Break assessments require a reliable method to obtain leakage rates from narrow cracks. The ability to predict leakage accurately is crucial to the overall success of Leak-before-Break arguments as the detection capability and limiting crack size are often very small. This can make it difficult to achieve the desired margin between limiting defect size and the crack size required for detectable leakage. The resulting narrow flow paths (< 0.1mm) relative to the wall thickness (> 10mm) necessitates the use of complex thermodynamic and friction models in the leak rate calculation. A method to calculate leakage rates through complex paths was presented in PVP2015-45468 using an ordinary differential equation (ODE) for Mach number. This model was developed to account for crack opening displacements that vary non-linearly through the wall of a pipe. This situation typically arises when there is a through wall crack at a weld, where significant residual stresses are present. This paper considers an FEA model of a plate with a weld residual stress (WRS) profile applied. The WRS is prescribed with nodal displacements, and the COD is calculated from post processing of the elastic stress analysis solution. This results in a COD function in terms of the distance through the wall, which can then be used in the leak rate calculation. Comparisons are made with the R6 methodology recommended software DAFTCAT and the benefits of using the ODE method are discussed. In collaboration with Framatome, Germany, a test case based on the previous European project STYLE was considered. The test case involves a Type 316L Stainless Steel pipe with a girth weld, and the FEA model includes postulated through wall defects at the weld interface to assess crack opening displacements. This model will be used to extract crack opening displacements and calculate leak rates using various methods. Two phase flow will be considered for this test case as the pipe geometry is very relevant to PWRs.

A weld overlay (WOL) following the general guidelines of ASME Code Case N-740-2 was successfully installed in March of 2018 on a dissimilar metal weld joining the super emergency feedwater 1 piping to steam generator (SG) at the Dukovany nuclear power plant (NPP) in the Czech Republic. The repair was necessary due to stress corrosion cracking detected in the super emergency feedwater nozzle to safe-end dissimilar metal weld. This was the first WOL installed in the Czech Republic and represents a significant step towards further acceptance of this proven repair technology in Europe. The WOL repair approach was accepted by the Czech regulator, and two different inspection agencies, following successful mockup demonstrations, welding procedure qualification, nondestructive examination demonstrations and weld residual stress analyses. This paper describes the preparatory work as well as field deployment of WOLs in the Czech Republic.

In this paper we present the room temperature tensile test results for 82/182 Filler, Butter Weld and Heat-Affected-Zone in a 508 LAS − 316 SS Dissimilar Weld (DW). Also we present the associated tensile properties and material hardening model parameters; those can be used for future component level stress analysis modes. In addition, we present the finite element (FE) model of the uniaxial DW tensile-test specimens to validate the accuracy of the estimated material model parameters. Through the FE model results, we also explain the importance of various offset strain yield stress in capturing the material behavior in a mechanistic (using FE) modeling approach particularly while modeling the plasticity driven low-strain-amplitude low-cycle-fatigue damage of a structural component.

Pressurized water reactor (PWR) steam generator (SG) main steam and feedwater nozzles are classified as ASME Code, Section XI, Class 2, Category C-B, pressure retaining welds in pressure vessels. Current ASME Code requirements specify that the nozzle-to-shell welds (Item No. C2.21 & C2.32) and nozzle inner radius sections (Item C2.22) are to be examined very 10 years. An evaluation was performed to establish a technical basis for optimized inspection frequencies for these items. The work included a review of inspection history and results, a survey of components in the PWR fleet (which included both U.S. and overseas plants), selection of representative main steam and feedwater nozzle configurations and operating transients for stress analysis, evaluation of potential degradation mechanisms, and flaw tolerance evaluations consisting of probabilistic and deterministic fracture mechanics analyses. The results of multiple inspection scenarios and sensitivity studies were compared to the U.S. Nuclear Regulatory Commission (NRC) safety goal of 10 −6 failures per year.

The Nuclear Power Plant KKG in Gösgen, Switzerland was designed according to the ASME Boiler and Pressure Vessel Code. The ASME BPVC, Section III, Appendix 11 regulates the flange calculation for class 2 and 3 components, it is also used for class 1 flanges. A standard for the determination of the required gasket characteristics is not well established which leads to a lack of clarity. As a hint different y and m values for different kinds of gasket are invented in ASME BPVC Section III [1]. The KTA 3201.2[2] and KTA 3211.2[3] regulate the calculation of bolted flanged joints in German nuclear power plants. The gasket characteristics required for these calculation methods are based on DIN 28090-1[4], they can be determined experimentally. In Europe, the calculation code EN 1591-1 [5] and the gasket characteristics according to EN 13555[6] are used for flange calculations. Because these calculation algorithms provide not only a stress analysis but also a tightness proof, it would be preferable to use them also in the NPP’s in Switzerland. Additionally, for regulatory approval also the requirements of the ASME BPVC must be fullfilled. For determining the bolting up torque moment of flanges several tables for different nominal diameters of flanges using different gaskets and different combinations of bolt and flange material were established. As leading criteria for an allowable state, the gasket surface pressure, the allowable elastic stress of the bolts and the strain in the flange should be a good and conservative basis for determining allowable torque moments. The herein established tables show only a small part according to a previous paper [7] where different calculation methods for determining bolting up moments were compared to each other. In this paper the bolting-up torque moments determined with the European standard EN 1591-1 for the flange, are assessed on the strain-based acceptance criteria in ASME BPVC, Section III, Appendices EE and FF. The assessment of the torque moment of the bolts remains elastically which should lead to a more conservative insight of the behavior of the flanges.

Brittle fracture assessments (BFAs) of pressure vessels based on API 579-1/ASME FFS-1, Section 3 procedures are frequently easier and more straightforward to implement in comparison to the BFAs on piping systems. Specifically, the development of the MSOT curves. This is due to the complexities involved in the piping systems due to the branch piping interactions, end conditions of piping systems such as nozzle flexibilities at the pressure vessel connections, temperature changes in the length of piping especially when the piping is significantly long as seen in flare header piping systems. MSOT curves that are alternatively used for MAT curves provide a better picture to the plant personnel in understanding the safe operating envelope. Development of MSOT curves is an iterative process and therefore involves significant number of piping stress analyses during their development. In this paper, an approach to develop the MSOT curves is discussed with two case studies that are of relevance to olefin plants.