bluuebunny/crossref_metadata_2025_split huggingface dataset:
Considering Hydrotest Pressure Loading in the Calculation of MAWP of a Pressure Vessel
Authors: Nawandar Suresh K. 
Published: October 2021

Abstract
As defined in UG-98 of the Code, the Maximum Allowable Working Pressure (MAWP), is the maximum pressure permissible at the top of the vessel in its normal operating position. It is the least of the values calculated for each of the vessel part adjusted for the static head and by including the effect of any combination of loadings listed in UG-22 of the Code.
Conventional method of calculating the MAWP is to consider only the main pressure parts viz., the shells and the heads and the significant UG-22 loading viz., the wind and the seismic. Once the MAWP is determined, the rest of the vessel design is completed considering this value of MAWP as design pressure combined with any other applicable UG-22 loading. At the end, the vessel is verified for its adequacy to the test condition.
It is noted that, the MAWP obtained through this method is often higher than the design pressure thus leading to the overdesign of the vessel. Moreover, higher MAWP results in higher test pressure, which might have a considerable impact of its own on the design of the vessel.
The objective of this paper is to propose a design approach in which the test pressure itself is included as one of the governing loads in the determination of the MAWP so that the impact on vessel design, as explained above, is minimized.
Natural Frequency of Oval-Type Vibration of an Aboveground Storage Tank Installed With Wind Girders
Authors: Yoshida Shoichi 
Published: October 2021

Abstract
The current seismic design codes of aboveground storage tanks (ASTs) for oil storage are conducted based on the beam-type vibration with circumferential wave number m = 1. The oval-type vibration with m ≥ 2 in which shell plate vibrates like a petal shape occurs in ASTs. The causes are local mass/stiffness, initial imperfections or nonlinear strong vibration. The initial stress due to hydrostatic pressure was reported to increase the natural frequency in high m range by several studies. The circumferential tensile stress on shell plates due to hydrostatic pressure increases the stiffness and as a result, the natural frequency is also increased. Wind girders are installed to the shell plates of ASTs for the prevention of buckling due to wind pressure. The wind girder which is a ring stiffener increases the stiffness of the shell plate. In this paper, the natural frequency of the oval-type vibration in a large-sized AST is analyzed and the effect of the wind girder on natural frequency is studied. The method is the free vibration analysis of axisymmetric shell finite element method considering vibration coupled with fluid motion.
Post-Test Analysis of a Large Scale Mock-Up Test Performed in the European Project ATLAS+
Authors: Nicak Tomas , Rempel Alexey 
Published: October 2021

Abstract
The safety and reliability of all systems has to be maintained throughout the lifetime of a nuclear power plant (NPP). This requires a systematic ageing management procedure for justifying their safe long term operation. One fundamental part in this process is to demonstrate the integrity of the nuclear power plant components. The European project ATLAS+ aims to develop and validate advanced methods of structural integrity assessment applicable in the ageing and lifetime management of primary circuit components.
To support development and validation of those methods a large scale test programme was developed with the aim to investigate fracture behavior of relevant piping material at the component level.
Three of the planned large scale experiments focus on the fracture behavior of flawed ferritic pipe segments made of material WB 36 (15 NiCuMoNb 5); this material is representative of secondary feedwater lines installed in German NPPs.
In order to improve understanding of test results post-test simulations and fractographic examination of all large scale tests are planned, some of them have been already performed.
In this paper the post-test simulation of the mock-up FP2 (ferritic pipe with outer semi-elliptical circumferential crack) is presented and discussed. This mock-up was selected because it experienced an unexpected brittle fracture during the test, which occurred after limited ductile crack propagation.
To investigate both the ductile and the brittle crack propagation phases of the test detailed ductile tearing analysis and brittle fracture assessment have been performed. In addition, relevant results of fractographic examination of the mock-up FP2 are presented and discussed.
A Study on Residual Stresses on Autofrettaged LDPE Tubing Including the Bauschinger Effect and Strain Aging
Authors: Nyquist Taylor , Warren Kraig 
Published: October 2021

Abstract
This paper compares and discusses the change to the residual stresses and strains on four tubes of SA-723 Gr 1 Cl 2 (Timken HS 220) tubing material that were autofrettaged at different Overstrain ratios (20% and 40%). The four tubes were autofrettaged with strain gages to obtain actual OD strain. The effect on the residual stress and strain of the material is reviewed after a single autofrettage and after a low temperature heat treat followed by a second autofrettage. The low temperature heat treat was performed on two of the four tubes to create comparable data. Any strain aging effect from the low temperature heat treat is examined on the measured residual stress and strains. The effect and possible benefits of strain aging and re-autofrettage on tubes with different Overstrain ratios is discussed. To obtain the residual stress values in the tube wall after the autofrettage cycles, the sample tube pieces were tested by X-ray diffraction. The actual residual stresses after autofrettage were then compared with the calculated theoretical residual stresses including Bauschinger effect correction factors from ASME Section VIII Div. 3 KD-5. The residual stress and strain data between one and two rounds of autofrettage is also studied to see if the Bauschinger effect is present.
Structural Integrity Assessment of Refractory Lined Component With Thermal Hot Spot Subjected to Steam Cooling
Authors: Yoo Eui Jong , Choi Capjoo 
Published: October 2021

Abstract
The refractory lined components could be damaged during operation due to various causes such as thermal expansion and contraction from changes of the temperature in service fluids, vibration caused by internal flow, or improper refractory construction. The damaged refractory causes thermal hot spot because a hot service fluid contacts to the inside surface of the component directly and this situation leads temperature increases in the skin of the component. This temperature increases from thermal hot spot does not causes immediate failure of the component, but creep phenomenon can cause structural rupture in the long term. As one of the countermeasures against thermal hot spot, the steam cooling is used as a field practice of maintenance works to reduce elevated temperature by spraying steam onto the area of thermal hot spot. However, when steam cooling is applied, it is designed and installed based on experiences without performing proper engineering. After steam cooling is applied, it is observed that thermal hot spot is locally cooled only in the area where the steam touches, which also raises concerns about unexpected damage due to local temperature gradient from localized cooling. This paper provides the evaluation of structural integrity of an actual case of thermal hot spot subjected to steam cooling in the FCC unit and discusses the appropriate steam cooling method as a countermeasure for thermal hot spot to ensure more effective structural integrity.
Valve Failures and Suggested Remedies
Authors: Ezekoye L. Ike , Josodipuro Irawan 
Published: October 2021

Abstract
Valves are one of the most used products in the power industry. The subject of valves is broad. They come in various configurations to meet end-user requirements. Because of their uniqueness, valves are designed to meet specific industry standards such as the American Petroleum Institute (API), the American Society of Mechanical Engineers, the Manufacturers Standardization Society, the British Standards Institute, the International Organization for Standardization, and many others. Compliance with these standards assures the valve end-users that their purchased valves will provide them with long term service. In most cases they do. However, there is no guarantee that newly installed valves in plants will last forever as nothing mechanical lasts forever. In this paper, the authors present survey results where the newly installed valves did not last long in service and where they did. In another survey, the authors will show some examples of valves that failed in service and what actions were taken to address the failures. Additionally, the authors will present examples of installed valves that provided long term services and the reasons for their good performance. Finally, the paper will cover remedies that valve end-users should consider adopting to ensure that their valves will provide long term service in operation.
Study on the Predictive Evaluation Method for Loads Acting on Roof and Sidewall of Cylindrical Tank in Nonlinear Sloshing Based on Simplified Equations
Authors: Ikesue Shunichi , Morita Hideyuki , Ishii Hidekazu , Sago Hiromi , Yokoi Shinobu , Yamamoto Tomohiko 
Published: October 2021

Abstract
When a cylindrical tank installed on the ground, such as an oil tank or a liquid storage tank, receives strong seismic waves, including a long-period component, motion of free liquid surface inside a tank called sloshing may occur. If high-amplitude sloshing occurs and waves of free liquid surface collide with tank roof, it may lead to accidents such as damage to tank roof or outflow of internal liquid. There is also a possibility that tank sidewall may be damaged due to fluid force generated by high liquid surface level of sloshing.
When sloshing wave height is small, liquid surface level and velocity can be calculated based on the linear velocity potential theory. When sloshing wave height increases, sloshing becomes nonlinear, and the difference between actual value and calculated value based on the linear velocity potential theory increases. Sloshing loads acting on roof and sidewall should be evaluated in consideration of nonlinear sloshing. In the previous study, simplified equations of nonlinear liquid surface shape and nonlinear liquid surface velocity distribution were proposed, as input parameters of evaluating sloshing loads.
In this paper, a new method is proposed for nonlinear sloshing condition of cylindrical tanks, which can evaluate the vertical load acting on roof and the horizontal load acting on sidewall. In the proposed method, new pressure models modified from existing models are combined with simplified equations of nonlinear liquid surface shape and nonlinear liquid surface velocity distribution proposed in the previous study. A long calculation time as CFD analysis is not needed, because the proposed method is consisted of simplified equations.
Designing and Optimising Duplex/Superduplex Compact Flanges to Negate HISC in Subsea Applications
Authors: Lutkiewicz Przemyslaw 
Published: October 2021

Abstract
Hydrogen Induced Stress Cracking (HISC) is a phenomena related with metals, with potentially severe consequences when utilizing Duplex / Super Duplex stainless steels in subsea equipment exposed to Cathodic Protection (CP). In general, the three conditions need to be present: hydrogen source (CP), susceptible material (Duplex/Super Duplex stainless steel) and high stresses/strains. The third one can be related with loads, calculation promises and parts design in general (for example risers). The designing rules to minimize the risk of HISC failure are still in development and the latest state of art is presented in DNVGL-RP-F112 June 2018 edition. The Compact Flange (CF) is much lighter and more robust connection than standard ASME or API types as the CF design methodology is based on plastic capacity which is presented in the ISO-27509 code. However, ISO standardization covers only topside applications (with IX seal ring type), pressure class range up to CL2500 and simplified face angles methodology. The ISO-27509 flanges are not HISC proven. Therefore, to deal with HISC requirements and subsea conditions the SPO-S (Subsea) flange series with HX seal ring type was defined and type approved by DNVGL based on extensive FEA documentation, testing and field experience. The SPO-S range has, currently, only HISC compliant designs for the 5K, 7.5K, 10K and 15K flange ranges. For the projects where the Duplex / Super Duplex flanges are used subsea with CP, consideration for HISC still must be addressed. For such cases, the process is not straight forward and often many FEA rounds are needed depending on the engineer’s experience and project related restrictions. The process is time consuming and every decision reflects many aspects to finalize the design. Genetic Algorithms (GA) are a good optimization tools to use in such situations, because at the end, the engineer will only get few design propositions to choose from, and the process itself, is highly automated. In the following paper the results for HISC optimized CF flange connection will be presented and compared with standard ISO-27509 flange design. The GA optimization steps and designing process will also be presented in the same example. Commercial FEA code ANSYS will be used for calculations based on parametrical model and GA implemented by APDL scripting. The following optimization method is already in use for HISC related projects.
Research on Characterization Method of Pressure Equipment Accident
Authors: Fang Zhou , Huan Zhibo , Wang Zhe , Fu Junjie , Shi Puan , Liu Qia , Wu Gang 
Published: October 2021

Abstract
The description of pressure equipment accidents has always been expressed in large paragraphs. It was difficult for readers to grasp the contents of the whole accident and analyze the objective laws of the accident. The representation method based on chart can show the accident context of pressure equipment intuitively and clearly, so that readers can quickly grasp the causes and consequences and development law of the accident. In this paper, the research framework of pressure equipment accident characterization method was established. Three characterization methods: fault tree, fishbone diagram and radar chart were used to analyze a typical pressure equipment accident. The advantages and disadvantages and application scope of the three characterization methods were obtained by comparing the analysis process and results. The results show that fault tree and fishbone diagram can not represent the weight of each factor, but radar chart method can do it directly. Radar chart method is suitable to analyze the primary and secondary causes of pressure equipment accidents. Since the radar chart has never been used in the accident analysis of pressure equipment before, a new characterization method of pressure equipment accident was established based on radar chart in this paper.
Modified Response Spectrum Accounting for Seismic Load Categorization as Primary or Secondary in Multi-Modal Piping Systems
Authors: Labbé Pierre , Nguyen Thuong-Anh 
Published: October 2021

Abstract
This paper presents practical implementation of a theoretical approach that was introduced at PVP 2020 conference. Analysis of the seismically induced ductility demand in elastic-plastic oscillators of variable frequencies and hardening slope is carried out by running time response analyses. The input motion consists of 1000 stochastic process samples of central frequency fc. Oscillators of natural frequencies, f0, (0.1 fc ≤ f0 ≤ 10 fc) are submitted to a wide range of ductility demand, up to 20. It turns out that seismic loads should be regarded as secondary for flexible oscillators (f0 &lt; fc) and primary for very stiff oscillators (f &gt; fcut, cut-off frequency of the input motion), with intermediate situations. On this basis, we derive a strongly f0/fc dependent evaluation of the seismically induced inertial stresses primary part. In the frame of the conventional linear modal analysis method, practical implementation consists of reducing the input response spectrum: spectral ordinates are minimized in the low frequency domain by a factor that depends on the ductile capacity and hardening slope, unchanged at the ZPA frequency and vary linearly in the medium frequency domain. This approach is tested against nonlinear time-response analysis of a multimodal piping system.
A New Stress-Intensity Factor Solution for an External Surface Crack in Spheres
Authors: Sobotka James C. , Lee Yi-Der , Cardinal Joseph W. , McClung R. Craig 
Published: October 2021

Abstract
This paper describes a new stress-intensity factor (SIF) solution for an external surface crack in a sphere that expands capabilities previously available for this common pressure vessel geometry. The SIF solution employs the weight function (WF) methodology that enables rapid calculations of SIF values. The WF methodology determines SIF values from the nonlinear stress variations computed for the uncracked geometry, e.g., from service stresses and/or residual stresses. The current approach supports two degrees of freedom that denote the two crack tips located normal to the surface and the surface of the sphere. The geometric formulation of this solution enforces an elliptical crack front, maintains normality of the crack front with the free surface, and supports two degrees of freedom for fatigue crack growth from an internal crack tip and a surface crack tip. The new SIF solution accommodates spherical geometries with an exterior diameter greater than or equal to four times the thickness. This WF SIF solution has been combined with stress variations common for spherical pressure vessels: uniform internal pressure on the interior surface, uniform tension on the crack plane, and uniform bending on the crack plane.
This paper provides a complete overview of this solution. We present for the first time the geometric formulation of the crack front that enables the new functionality and set the geometric limits of the solution, e.g., the maximum size and shape of the crack front. The paper discusses the bivariant WF formulation used to define the SIF solution and details the finite element analyses employed to calibrate terms in the WF formulation. A summary of preliminary verification efforts demonstrates the credibility of this solution against independent results from finite element analyses. We also compare results of this new solution against independent SIFs computed by finite element analyses, legacy SIF solutions, API 579, and FITNET. These comparisons indicate that the new WF solution compares favorably with results from finite element analyses. This paper summarizes ongoing efforts to improve and extend this solution, including formal verification and development of an internal surface crack model. Finally, we discuss the capabilities of this solution’s implementation in NASGRO® v10.0.
Crack Propagation Calculation for Axial Cracks in Hollow Cylinders Subjected to Thermal Shock
Authors: Mora M. Diego F. , Niffenegger Markus 
Published: October 2021

Abstract
The core region of the RPV can be considered a hollow circular cylinder disregarding the geometrical details due to nozzles. This contribution investigates the prediction capabilities for crack initiation, crack growth and arrest by means of a rather simple method based on the closed-weight function formula for the stress intensity factor (SIF) for axial cracks in hollow cylinders subjected to thermal shock. The method is explained together with some illustrative examples for real low allow steel used in nuclear applications. In order to obtain the temperature and stress distribution in the cylinder during the thermal shock, a finite element (FE) model is defined to obtain the uncoupled solution of these two fields needed for the closed-weight function. Since the material exhibits a ductile-brittle transition fracture behavior, the temperature-dependent fracture toughness for initiation and for arrest are described using the ASME model. The solution for the SIF is based on linear elastic fracture mechanics (LEFM) and therefore only elastic material is assumed and the crack can propagate in brittle manner. The crack initiates propagation if the SIF value at the crack tip reaches the fracture toughness (for initiation) and propagates unstably in mode I unless the fracture arrest toughness is reached. The quality of the solution is checked by comparing the obtained solution for a “stationary” crack with the calculated extended finite element method (XFEM) solution for the same loading transient. The results show that for some geometries of the cylinder, the crack stops and in some other cases the crack propagates until the cylinder fails. The combined closed-weight function-initiation-growth-arrest (WFF-IGA) algorithm does not require expensive computational resources and gives fast reliable results. The WFF-IGA method provides a powerful and economical way to predict the crack propagation and arrest of the initial crack. This is an advantage when an optimization of the structure is needed.
Study on Fracture Behavior and Assessment for Dissimilar Metal Weld of Low Alloy Steel and Ni-Base Alloy Weld Using a BWR Reactor Pressure Vessel Material
Authors: Hayashi Takahiro , Ogawa Takuya , Yoshida Shuichi , Itatani Masao , Hattori Yasuhiro , Yamaoka Tetsushi , Tanaka Shigeaki , Saito Toshiyuki 
Published: October 2021

Abstract
Cases of stress corrosion cracking (SCC) in Ni-base alloy weld metals welded to low alloy steel (LAS) of reactor pressure vessel (RPV) components have led to discussions on the possibility of SCC propagating into the RPV. However, the fracture behavior and the assessment methodology have not been sufficiently studied for such dissimilar metal weld (DMW) components where embrittlement due to neutron irradiation damage is negligible and the operating temperature is above the upper shelf temperature range.
In this study, the fracture mode of the DMW of LAS and Ni-base alloy weld was investigated by using a large, heavy forged steel part, called the bottom head ring, of a RPV, manufactured for a recent BWR. In addition to fracture toughness tests with compact tension specimens, fracture tests using plates cut from a DMW material with a semi-elliptical surface crack were conducted. The initial crack tip locations were designed and controlled to be in the heat affected zone (HAZ) in LAS, at varying distances from the weld fusion line. All the mechanical tests conducted showed highly ductile fracture behaviors and properties; the evaluated elastic-plastic fracture toughness was more than 400 kJ/m2 in the fracture toughness tests. The fracture loads evaluated using the elastic-plastic fracture mechanics (EPFM) methodology showed fairly good agreement with the maximum loads in the fracture test. The results confirmed that the fracture assessment methodology based on EPFM is reasonably applicable to the DMW of RPV components where the operating temperature is above the upper shelf temperature range and the embrittlement is not a concerned mechanism of degradation.