bluuebunny/crossref_metadata_2025 huggingface dataset:
Modification to Shield Tank Overpressure Protection in a CANDU Reactor for Beyond Design Basis Event
Authors: Huang Michael , Khan Khurram , Etedali-Zadeh Ali , Tse Jefferson , Li Bing
Published: November 2019

The Shield Tank and End Shield Cooling System in the CANDU reactor contains a large volume of light water surrounding the Calandria and circulates water to remove heat that arises from the reactor core and Moderator. In a beyond design basis event that results in a severe event, progression in the absence of mitigating cooling actions could result in a large heat load being transferred to the water inside the shield tank from the calandria wall causing shield tank failure due to over pressurization. Following the 2011 events at Fukushima Daiichi Nuclear Power Plant, the adequacy of system pressure relief was assessed against severe events. Emergency mitigating equipment tie-ins for water make-up will likely limit the core damage state and prevent the need to protect the shield tank. However, Shield Tank Overpressure Protection (STOP) has been installed against severe event conditions pursuant to the CANDU defense-in-depth safety philosophy. A larger open vent line has been installed at some CANDU units on the top of the shield tank outside containment. This design routes the vent piping high enough to preclude any venting under any operational configuration and discharges back into the containment through an existing spare penetration. Vent piping is designed as Nuclear Class 2 in accordance with ASME BPVC Section III. Assessment of stresses in the modification piping was also completed for BDBEs including for a lower probability seismic event, steam venting and corresponding higher pressure and temperature conditions.
Simple Pd-Ag-H EAM Potentials for Hydrogen Storage Applications
Authors: Fuller Robert , Hijazi Iyad
Published: November 2019

The palladium–hydrogen system has attracted a vast amount of research interest. Palladium’s ability to absorb hydrogen at room temperature is reversible, and therefore suitable for many applications, including fuel cells, hydrogen storage, and nuclear radiation adsorption. Alloying palladium with silver can increase its performance in many applications as well as substantially lowering the materials cost. Palladium silver alloys can offer increased H diffusivity and a less pronounced miscibility gap with much improved mechanical properties over pure palladium. However, the relative insolubility of hydrogen in silver necessitates proper alloying of Pd-Ag to obtain the best combination of properties. Atomic simulations are useful in the evaluation of palladium-silver hydride systems as changes in composition can be more easily explored than with experiments. In this work we introduce fully analytical Embedded Atom Method (EAM) potentials for the Pd-Ag-H system, with fewer fitting parameters than previously developed EAM models. The central atom method is used, without the need for time-consuming molecular dynamics simulations during the fitting procedure.
Overview of Revisions to the ASME Boiler and Pressure Vessel Code Section VIII Division 3 for the 2019 Edition and Near Future
Authors: Maslowski Adam P. , Mital Gregory , Peters Daniel , Subramanian Kannan
Published: November 2019

This paper provides an overview of the significant revisions to the upcoming 2019 edition of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Section VIII Division 3, Alternative Rules for Construction of High Pressure Vessels, as well as potential changes to future editions under consideration of the Subgroup on High Pressure Vessels (SG-HPV).
Identification of Key Factors of Fire Risk of Oil Depot Based on Fuzzy Clustering Algorithm
Authors: Xie Shuyi , Dong Shaohua , Zhang Guangyu
Published: November 2019

With the rapid development of the national economy, the demand for oil is increasing. In order to meet the increasing energy demand, China has established a number of oil depot in recent years, whose largest capacity reaching up to tens of millions of cubic meters. Due to the flammable and explosive nature of the stored medium, the risk of fire in the oil depot area has increased dramatically as the tank capacity of the storage tank area has increased. The intensification of the oil depot and the development of large-scale oil storage tanks have brought convenience to the national oil depot, but also brought many catastrophic consequences. In recent years, there have been many fires and explosions in the oil depot, causing major casualties and property losses, which seriously endangered the ecological environment and public safety.

Based on the constructed oil depot fire risk index system, the fuzzy C-means algorithm (FCM) and fuzzy maximum support tree clustering algorithm is introduced. Through the two fuzzy clustering mathematical models, key factors in the established index system are identified. Firstly, the expert scoring method is used to evaluate the indicators in the oil depot fire risk index system, and the importance degree evaluation matrix of oil depot fire risk factors is constructed through the fuzzy analysis of expert comments. Then, the fuzzy C-means algorithm (FCM) and the fuzzy clustering tree algorithm are used to cluster the various risk indicators, and the key factors of the oil depot fire risk are identified. Through the comparative analysis and cross-validation of the results of the two fuzzy clustering methods, the accuracy of the recognition results is ensured. Finally, using an oil depot as a case study, it is found that passive fire prevention capability and emergency rescue capability are key factors that need to be paid attention to in the oil depot fire risk index.

The fuzzy clustering algorithm used in this paper can digitize the subjective comments of experts, thus reducing the influence of human subjective factors. In addition, by using two fuzzy clustering algorithms to analyze and verify the key factors of the oil depot fire risk, the reliability of the clustering results is guaranteed. The identification of key factors can enable managers to predict high-risk factors in advance in the fire risk prevention and control process of the oil depot, so as to adopt corresponding preventive measures to minimize the fire risk in the oil depot, and ensure the safety of the operation of the oil depot.
Fabrication and Mechanical Aspects of Using FeCrAl for Light Water Reactor Fuel Cladding
Authors: Rebak Raul B. , Huang Shenyan , Schuster Michael , Buresh Steve J. , Dolley Evan J.
Published: November 2019

General Electric (GE) is working with the US Department of Energy (DOE) to develop advanced technology fuel (ATF) for light water reactors (LWR) that will have enhanced tolerance to failure under severe accident conditions. The development of materials for the current fuel is aimed at Generation III LWR but findings may be extended to future Generation IV reactors. One of the concepts pursued by GE is to use iron-chromium-aluminum (FeCrAl) or IronClad for the cladding due to its outstanding resistance to reaction with air and steam at temperatures higher than 1000°C. Ferritic FeCrAl alloys have been used for almost nine decades in the industry, but never in nuclear applications, therefore its fabrication and mechanical aspects for nuclear use needs to be evaluated. Results show that billets of FeCrAl can be produced via traditional melting and using powder metallurgy, and these billets can later be processed to high strength full length cladding tubes having less than half a millimeter wall thickness. The tubes can be joined to the caps via several welding processes.
Experimental Study on Cryogenic Ratcheting of Pre-Strain Austenitic Stainless Steel SS304
Authors: Li Leilei , Gao Bingjun , Dong Junhua , Chen Xu
Published: November 2019

Austenitic stainless steel SS304 is often used as the inner container of the Liquefied Natural Gas (LNG) semitrailer tank. Due to excellent cryogenic ductility and strain-hardening effect, pre-strain of austenitic stainless steel is practicable and conducive to achieve lightweight design of this kind of transporting vehicle. In the present work, we focus on the cryogenic ratcheting of pre-strain austenitic stainless steel SS304. The SS304 specimens were cut from as received plates and butt welded plates which are all pre-strained 8% and 12%. With CARE electronic universal testing machine, ratcheting experiments are performed at both ambient temperature and 110K with different mean stresses and stress amplitudes. Ratcheting strains increase with the mean stress and stress amplitude under cryogenic temperature, but much smaller than that at ambient temperature. And it would quickly get shakedown after ratcheting in a few cycles due to the rapid γ-α′ phase transformation under cryogenic temperature. The cryogenic ratcheting strain generally reduces with the pre-strain amount for both parent material specimens and welded specimens. Compared with parent material specimens, weld specimens yield much smaller cryogenic ratcheting strain due to the hardening effect of welding induced initial ferrite with less slipping system.
Variable Loading Sequence Effect for Thermal Fatigue at a Mixing Tee
Authors: Miyoshi Koji , Kamaya Masayuki
Published: November 2019

Mixing flow causes fluctuations in fluid temperature near the pipe wall and may result in fatigue crack initiation. In a previous study, the authors reported the characteristics of the thermal stress to cause thermal fatigue at a mixing tee. A large stress fluctuation was caused by movement of the hot spot, at which the pipe wall was heated by hot flow from the branch pipe. According to a general procedure, fatigue damage is calculated by the linear damage accumulation rule. However, it has been reported that Miner’s rule does not always predict the fatigue life conservatively for variable stress amplitude. In this study, we investigated the change in fatigue life due to variable strain around the hot spot. The time histories of the strain around the hot spot were estimated by finite element analysis (FEA) for which the temperature condition was determined by wall temperature measured in a mock-up test. Strain-controlled fatigue tests were conducted using smooth cylindrical specimens made of stainless steel. The fatigue damage at failure of the specimen was calculated using Miner’s rule. The calculated fatigue damage around the hot spot became less than unity and the minimum value was 0.18. Therefore, Miner’s rule predicted non-conservative fatigue life. In addition, the calculated fatigue damage inside the hot spot was larger than those outside the hot spot and at the position of maximum stress fluctuation. Fatigue tests using strain with periodic overload were also conducted in order to investigate the effect of the loading history on fatigue life. It was shown that the strain with periodic overload reduced the fatigue life. The calculated fatigue damage for the strain at the maximum position of stress fluctuation range seemed to be smaller than those at other positions. This implies that the fatigue life can be estimated conservatively from the viewpoint of the loading sequence effect by calculating the fatigue damage using Miner’s rule for the strain at the maximum position of stress fluctuation range.
Direct Analysis of Post-Shakedown Quantities With the STPZ Considering Multi-Parameter Loading
Authors: Vollrath Bastian , Hübel Hartwig
Published: November 2019

If a structure is subjected to cyclic loading, strain, displacements etc. may accumulate cycle by cycle due to a ratcheting mechanism. Design Codes frequently require strain limits to be satisfied at the end of the specified lifetime of the structure. Usually, this is requested to be done considering all load sets pairwise. However, this leads to the fact that ratcheting cannot be detected, if it occurs only because of multi-parameter loading. Ordinary incremental step-by-step calculations can easily exceed time and hardware resources. This is particularly true for travelling loads, where many load steps are required for one load cycle. As an alternative, the Simplified Theory of Plastic Zones (STPZ) is used in the present paper. Being a direct method, effects from load history are disregarded. The elastic-plastic behavior in the state of either elastic or plastic shakedown is estimated on the basis of purely elastic analyses. Two kinds of linear elastic analyses are to be performed, fictitious elastic analyses for each set of loading, and a number of modified elastic analyses. Few of these analyses are usually sufficient to obtain reasonable estimates of the post-shakedown quantities. Trilinear material behavior is adopted along with kinematic hardening, a Mises yield surface and an associated flow law. The modified elastic analyses are performed making use of modified elastic parameters (Young’s modulus and Poisson’s ratio) in the plastic zone and applying suitably defined initial strains. The results obtained can be improved iteratively. The theory of the method is briefly explained and its application is shown using an example with multi-parameter loading.
Hot Cell Pulsed Laser Welding of Neutron Irradiated Type 304 Stainless Steel With a Maximum Damage Dose of 28 DPA
Authors: Freyer Paula D. , Tatman Jonathan K. , Garner Frank A. , Frederick Greg J. , Sutton Benjamin J.
Published: November 2019

Radiation-induced degradation of reactor pressure vessels and internals is a concern to the aging nuclear fleet and welding solutions will be required if repair of these irradiated components is deemed necessary. However, the weldability of highly irradiated austenitic materials is significantly diminished due to the presence of irradiation induced helium in the material matrix. Helium-induced weld cracking is a complex phenomenon that is related to the concentration of helium, the heat input from the welding process, and stresses generated during cooling of the weld. During conventional high heat input welding methods such as gas tungsten arc welding, helium bubbles can coalesce and grow on base metal grain boundaries within the heat-affected zone which subsequently causes intergranular cracking.

The objective of this work was to obtain weldability data by characterizing welds made on highly activated, neutron irradiated Type 304 stainless steel containing both radiation-induced helium and microstructural damage such as void swelling. All irradiated materials welding was performed inside a Westinghouse hot cell utilizing a pulsed Nd:YAG laser with welds made on three rectangular samples of highly activated Type 304 stainless steel. The rectangular samples were cut and milled in-cell from sections previously obtained from two neutron reflector hex blocks.

The hex blocks are U.S. Department of Energy owned material and were irradiated for approximately 13 years in the EBR-II sodium cooled fast reactor from 1982 until 1995. The three samples selected for welding have nominal damage doses of approximately 0.4, 11, and 28 dpa with corresponding estimated helium contents of 0.2, 3 and 8 appm helium, respectively.

A number of different weld parameter sets were utilized and included variations of travel speed, wire feed speed and lens-to-work distances. The parameter sets allowed for a range of effective weld heat input levels to be compared. Single pass and multiple pass as well as wire fed and autogenous welds were made. This paper presents the results from post-weld evaluations performed on the three welded irradiated samples, focusing on the reduced tendency for cracks to form adjacent to the weld as a function of weld parameters, lens-to-work distance and helium content.
Quantitative Analysis of the Cause-Effect Relationship of Incidents Occurred in Tank Farm Based on the Method of Logistic Regression
Authors: Wu Xingguang , Hou Lei , Wu Zhuang
Published: November 2019

A large number of incidents occurred in the petrochemical industry due to the continuous accumulation and frequent transfer of dangerous substances. For these historical incident data, a lot of efforts have been made to analyze how and why incidents occurred by use of descriptive statistics, while scarce work was done to in-depth explore the performance characteristics of the causal factors related to different types of incidents. This paper focuses on the relative importance of different causal factors for different types of incidents. A total of 1144 incidents related to tank farms of China during the period 1960–2018 were collected and classified with regard to the intuitive consequences of incidents (fire & explosion, material loss, quality variations, equipment damage and personnel harm) and whether the domino effect was involved (domino incidents and non-domino incidents). The causal factors were classified into five major categories and subdivided into fifteen subcategories. The interaction analysis of each factor with the specific consequence type was performed. The method of logistic regression was used to quantify the relative probability of different causal factors for different types of incidents and to determine which factors have a significant effect on triggering the domino incidents. It is found that human factors and organization/management factors were more common causal factors to lead to different consequences, and the same causal factor has distinct effects on the probability of occurrence for different types of incidents. The results highlight the more critical risk factors for each type of incident and the method can be applied to provide guidance on incident prevention and safety protection.
Modification and Extension of Screening Criteria for Fatigue Analysis
Authors: Shen Jun , Lu Mingwan , Wang Zhenyu , Peng Heng , Liu Yinghua
Published: November 2019

ASME Code VIII-2-2017 and previous versions provided three screening criteria for fatigue analysis. From Edition 2004 to 2017, the design factor for material allowable stress decreased and the considered range of permissible cyclic number for design fatigue curve extended. However, screening criterion are almost unchanged except one restriction: If the specified number of cycles is greater than 106, then the screening criteria are not applicable and a fatigue analysis is required. In this paper, percentage limit of the design pressure in Method A is modified and the specified number of cycles is extended. Some revision suggestions are also proposed to broaden the applicable range of the screening criterion.
A Novel Heat Input Equation for Analysis Welding Thermal Distribution and Welding Residual Stress
Authors: Ma Linwei , Zheng Xiaotao , Wang Wei , Lin Wei , Xu Jianmin , Yu Jiuyang
Published: November 2019

In the numerical simulation of welding residual stress (WRS), the thermal fields distribution of the weld beads during welding process is the basic data to calculate the residual stress due to thermal expansion and extraction. Different welding heat input control method had been proposed and used in the WRS finite element method (FEM) analysis, such as input based on theory, input controlled by temperature monitoring point and so on. Some disadvantages like less calculating efficiency, unexpected temperature variation have been found in these methods. Based on the study of the FEM result of temperature distribution through the weld butter field by using constant unit heat input, the heat transfer activities of each weld bead were researched. And a novel heat input fitted equation was proposed to describe the suitable heat input data for each weld bead of the welding process. More reliable and uniform melting temperature of weld beads with different location could be achieved. And the welding residual stresses from different welding thermal field of theory method, temperature monitoring point method, and novel heat input equation method are compared with the measured WRS results. The results show that the WRS achieved from the novel heat input equations is close to the measured result and has more computational efficiency. The uncertain WRS data used for probability safety assessment were also proposed based on the FEM results with the novel heat input equation method.
Effect of Flow Approach Angle on Acoustic Resonance Excitation of In-Line Tube Bundles in Cross-Flow
Authors: Alziadeh Mohammed , Mohany Atef , Hassan Marwan
Published: November 2019

This paper presents preliminary experimental results on the influence of the flow approach angle on the acoustic resonance excitation of in-line tube bundles in cross-flow. The pitch-to-diameter ratio (P/D) of the in-line tube bundles investigated is P/D = 1.733. The flow approach angle was investigated by physically rotating the tube bundle clockwise relative to the flow direction. The tube bundles are capable of rotating with increments of 5° up to an angle of 45°. For brevity, only the results for the 0° and 30° orientation will be presented herein. For the 0° orientation, two Strouhal frequencies (St1 = 0.437 and St2 = 0.252) were observed. However, only one of these frequencies (St1 = 0.437) was capable of exciting resonance. During resonance, a peak sound pressure level (SPL) of 170 dB was achieved. The Strouhal frequencies and peak SPL agrees well with what has been presented in the literature. For the 30° orientation, only one Strouhal frequency (St1 = 0.98) was measured. At this orientation, the lock-in phenomenon occurred at a much lower flow velocity compared to the 0° orientation with a peak SPL reaching 153 dB. Jumps in the lock-in frequency were observed at the 30° orientation. This phenomenon is associated with two reasons. The first reason is a partial lock-in with an acoustic resonant mode, due to the acoustic energy not being fully trapped within the tube bundle. The second reason is related to the changes in the apparent speed of sound resulting in variations in the acoustic cross-mode frequency depending on where the excitation source is emanating from within the tube bundle. A brief summary of the results is presented in this paper.
Influence of Roughness of Inner Surface of Simple Mechanical Testing Method to Evaluate Influence of High Pressure Hydrogen Gas
Authors: Ogata Toshio , Ono Yoshinori
Published: November 2019

In order to standardize the simple testing method to evaluate mechanical properties using hollow-type specimen in the high pressure hydrogen gas, influences of the hole and inner surface roughness on the relative reduction of area (RRA) and other properties in slow strain rate tensile (SSRT) tests were investigated on different surface finished specimens at 105 MPa hydrogen gas for SUS316L and JIS SNCM439 steels.

There is no influence of the hole and the inner pressure for the yield strength and the tensile strength. The RRA slightly increased in less roughness specimens. So, the axially polished finish for the hollow specimen will be proposed to the standard testing procedures of the SSRT test with this method to evaluate mechanical properties in the high pressure hydrogen gas.
Effect of Plastic Deformation on Hydrogen Embrittlement Sensitivity and Strength of 2.25Cr1Mo0.25V Steel by Synchronous Hydrogen Charging
Authors: Li Qing , Hu Yuqi , Cheng Guangxu , Zhang Zaoxiao , Liang Xiaowu
Published: November 2019

The hydrogenation reactor is an important equipment in petrochemical industry, and it has been produced by many processes such as plate rolling and welding. It served in high temperature, high pressure in hydrogen environment, and faced the risk of hydrogen embrittlement in the stages of operation and downtime cooling. Moreover, plastic deformation is inevitable in the manufacturing process of hydrogenation reactor, and influence mechanical properties and hydrogen resistance of materials. 2.25Cr1Mo0.25V is widely used in the hydrogenation reactor, so it is important to discuss how the plastic deformation affect hydrogen embrittlement sensitivity.

In this paper, the effect of plastic deformation on hydrogen embrittlement sensitivity and strength of 2.25Cr1Mo0.25V steel was investigated by slow strain rate tensile test coupled with electrochemical hydrogen pre-charging and synchronous charging experimental method. The experimental method was better than the common method which performs tensile test after hydrogen charging. Results show that hydrogen embrittlement sensitivity increases with the growth of plastic deformation. When the plastic deformation reached the necking area, the hydrogen embrittlement sensitivity decreases with the growth of plastic deformation. In addition, hydrogen significantly reduced the breaking strength of this steel, while the plastic deformation only increased the yield strength of this steel. The fracture morphology of tensile specimens indicated that the hydrogen embrittlement caused by electrochemical charging was very obvious, and the trend of hydrogen embrittlement degree of the fracture was basically consistent with the result of mechanical experiment. The mechanical properties and fracture micro-morphology of specimens without hydrogen and specimens with electrochemically irreversible hydrogen were compared, it can be obtained that the effect of electrochemically irreversible hydrogen on mechanical properties was negligible.
A New Methodology for CTOD Estimation Using Double Clip Gauge in Pipeline Steels
Authors: Silvestre Marcus N. , Sarzosa Diego F. B.
Published: November 2019

The increasing energy demand has spurred the exploration and production of oil and natural gas in dangerous and hostiles areas. Therefore, accurate calculation of fracture toughness is essential for fitness-for-service (FFS) analyses of critical engineering structures, such as the piping system used in the offshore industry. Regarding the oil and gas exploration in Brazil, 68% of the total area has already been explored, with 71% of that explored area having been developed in recent years. Oil and gas companies have preferentially chosen Crack-tip Opening Displacement (CTOD) due to the vast data of fracture toughness obtained in the past. Moreover, the professionals involved in this area are more familiarly with this parameter since it is easy of understanding because it involves physically crack flank deformation. Different methods to measure CTOD are available in the literature, such as the plastic hinge model, J-integral conversion and double clip gage method (DCGM). Experimentally, DCGM has been widely used to calculate in offshore pipelines. Discrepancies between experimental and numerical measures have been reported. Motivated by the explanation above, this work aims to propose new numerical analyses to evaluate the CTOD using the DCGM using non-linear finite element analyses. New and improved equations are developed to take into accounting knifes position.
Effects of In-Plane and Out-of-Plane Constraint on Fracture Toughness in Austenitic Stainless Steel
Authors: Palmer Iain , Mokhtarishirazabad Mehdi , Moffat Andrew , Mostafavi Mahmoud
Published: November 2019

An improved understanding of the failure behaviour of safety critical component could result in substantial benefits for industry; these include a reduction in design constraints resulting in optimised and cheaper designs, reduced risk and therefore cost. Yet surprisingly, there is little information in design and assessment codes on the behaviour of thin sections. The aim of this paper is to investigate the fracture of thin sections, with reduced out-of-plane plastic constraint, by using a unified measure of constraint. A range of single edge notched bend specimen made of stainless steel 316L were tested. The specimens had a combination of in-plane and out-of-plane constraint levels achieved through different crack lengths and thicknesses. FEA simulations of the tested specimens were conducted to estimate the crack tip stress and strain fields for each, in order to determine Rice and Tracey contour values. Using critical values of Rice and Tracey parameter and a critical area (normalised by thickness) enclosed by this parameter, toughness scaling values for low constraint specimens are calculated.
Measuring the Effectiveness of Metal Weld Overlay Repairs Through Bulge Depth and Bulge Sharpness Analysis
Authors: Araque Egler , Love Darren , Park Stephen , Rutt Daryl , Clark Rick
Published: November 2019

Weld overlay is a repair method that has been used over the last 10 years to limit the growth of bulges and to extend the remaining life of delayed coking drums. Different refinery operators have used varied approaches, ranging from localized patches on specific regions of concern, to bands along circumferential welds, to large sections of structural repair that completely cover a bulged area. The authors have observed the evolution of regions repaired with internal weld overlay on 18 drums over periods of 5 and 8 years. A comparison of bulge sharpness and bulge depth on a year-over-year basis is presented to measure the effectiveness of metal weld overlay and how the overlay impacts continued distortion of the vessel. Furthermore, factors such as the taper ratio in the transition zones, and the distance between the peak of a bulged area and the edges of the weld overlay, are presented as key parameters that affect the likelihood of cracks developing along the transition zones at the upper and lower edges of the repair.
Suppression of Low Energy Natural Modes of Pipe for Mitigation of Turbulence Induced Vibration
Authors: Seena Abu , Lee Donghyung , Kim Juyoul
Published: November 2019

Turbulence induced vibrations are most commonly encountered in industrial piping’s. Several guidelines are available for knowhow and its mitigation in piping designs and acceptable limits of vibration beyond which fatigue failure may occur in pipes. In present paper, it has been emphasized to predict potential turbulence induced vibrations at Design Stage rather than to have the expensive trouble-shooting solutions after the fabrication of system. The detailed review of currently available methods for assessing flow-induced vibrations in piping systems, including current limitations in existing codes and guidelines are discussed. These limitations are centered on the empirical approach currently taken in codes and guidelines. In present paper, a rational approach has been proposed in which the turbulent kinetic energy of the fluid flow is compared against the kinetic energy required to vibrate the pipe beyond its allowable level of vibration. The proposed method has been accessed using a documented case study. The parameters needed to evaluate the relative energies of vibration to turbulent kinetic energy of the fluid flow can be determined from FEA software, which make the present approach practically feasible for the mitigation at design stage.
Spiral Winding Technology for PTFE Gaskets
Authors: Girão Carlos D. , Veiga Jose C. , Valle André C. , Garcia André F.
Published: November 2019

PTFE is used in a variety of applications that goes from wiring in aerospace to non-stick coating in cookware. Some of the PTFE properties, such as high chemical stability and good conformability, makes it excellent for use as a gasket material, especially with aggressive media, pharma and food applications.

The scope of this paper is to present an innovative PTFE gasket manufacturing method for sealing aggressive media. The patented technology represents a unique production process that improves reliability, reduces cost and material waste when compared to traditional production methods. The gasket can be tailored to meet specific needs making it possible for customizations such as radial density variations, assorted colors compositions according to the gasket region and properties, or even use of distinctive fillers along its radius. Comparative data are reported among the developed technology and traditional processes.
Phase-Locked PIV Measurements of Vortex Shedding Characteristics Downstream of Straight Circular Finned Cylinders During Acoustic Resonance
Authors: Islam Rashid , Shaaban Mahmoud , Mohany Atef
Published: November 2019

Excitation of acoustic resonance by flow perturbation downstream of cylinders can result in hazardous levels of acoustic pressure. Previous studies have shown that straight finned cylinders are susceptible to flow-excited acoustic resonance. In this work, the excitation of acoustic resonance by flow around finned cylinders of different fin parameters including the spacing between the fins, the thickness of the fin, and the height of the fin is investigated. All the investigated finned cylinders have the same equivalent diameter. Phase-locked particle image velocimetry (PIV) measurements are carried out during acoustic resonance to characterize the flow field downstream of the cylinders and identify the influence of the fins on the flow structures at the peak of resonance excitation. Results show that straight circular fins excite acoustic resonance at lower velocities and result in higher sound pressure level compared with a single bare cylinder of the same effective diameter. This behaviour is due to the effect of fin parameters on the strength and the formation length of vortices shed during the acoustic cycle. A brief summary of the results is presented in this paper.
Effects of Local Wall Thinning With Crack on Stress Intensity Factor for Pipes Subject to Combined Pressure and Bending
Authors: Tao Joy (Xiaoya) , Zhu Lei
Published: November 2019

At ageing power plants, local thinning of pipework or vessel is unavoidable due to erosion/corrosion or other reasons such as flow accelerated corrosion (FAC) — one of the common degradation mechanisms in pipework of nuclear power plant. Local thinning reduces the structure strength, resulting in crack initiation from the corrosion pit or welding defect when subject to cyclic loading. General practice is to use the minimum thickness of the thinned area to calculate both limit load and stress intensity factor (SIF) in performing Engineering Critical Assessment (ECA) using Failure Assessment Diagram (FAD). Using the minimum thickness is normally overly conservative as it assumes that thinning occurs grossly instead of locally, leading to unnecessary early repair/replacement and cost. Performing cracked body finite element analysis (FEA) can provide accurate values of limit load and SIF, but it is time consuming and impractical for daily maintenance and emergent support. To minimise the conservatisms and provide a guidance for the assessment of locally thinned pipework or vessel using existing handbook solutions, a study was carried out by the authors on the effect of local thinning on limit loads. The study demonstrates that local thinning has significant effect on limit load if the thinning ratio of thinning depth to original thickness is larger than 25%. It concluded that the limit load solutions given in handbooks (such as R6 or the net section method) are overly conservative if using the minimum local thickness and non-conservative if using the nominal thickness.

This paper discusses the effect of local thinning on SIFs of internal/external defects using cracked body finite element method (FEM). The results are compared with R6 weight function SIF solutions for a cylinder. A modified R6 SIF solution is proposed to count for the effect of local thinning profile. Along with the previous published paper on limit load it provides comprehensive understanding and guidance for fracture assessment of the local thinned pipework and vessel.
Bolt Strength in Sectional Body Construction of Valves
Authors: Shitolé Bhaskar
Published: November 2019

ASME B16.34-2017 Section 6.4.2 provides requirements for valves with bolted body joints and threaded body joints. The section states that valves with bodies of sectional construction such that bolted or threaded body joints are subject to piping mechanical loads in addition to the pressure rating for which the valve is designed, shall satisfy the following requirements. For bolted joints, the requirement is a simple formula where the product of pressure rating class designation and ratio of area bounded by the effective outside periphery of a gasket or O-ring or other seal-effective periphery and total effective bolt tensile stress area are less than a certain constant. For bolts of strength less than 137.9 MPa, the value of constant reduces as a multiple of 50.76 times the bolt tensile strength in MPa required or provided in a sectional construction. Section 6.4.3 cautions that the minimum requirements of ASME B16.34 may fall short in scenarios due to valve design, special gaskets, high temperature service, creep characteristics etc. This paper reviews and studies this ASME B16.34 requirement which was triggered by failure of a valve with section body construction in the field. Traditionally valves have been considered as rigid bodies when analyzing a piping system for stresses, support loads, terminal point loads and deflections. The rigid modelling assumes the strength of the valve is much higher than an equivalent straight length of pipe. Some computer programs have a provision that permits modeling the valve as a multiple like 3- or 4-times pipe section modulus. This paper compares the strength of piping and valves based on inherent valve body thickness, body sectional bolting provided and strength of the equivalent piping flanges. The paper makes conclusions for the user to be aware of so that pre-emptive actions can be taken when using valves with sectional body construction.
Development of the External Pressure Charts for 2¼Cr-1Mo and Mod.9Cr-1Mo Steel at Elevated Temperature Design
Authors: Ando Masanori , Okajima Satoshi , Imo Kazumichi
Published: November 2019

For the required thickness estimation against buckling in the elevated temperature design, the external pressure chart for two kinds of ferritic steel, 2 1/4Cr-1Mo and Mod.9Cr-1Mo steel, was developed. On the basis of the guideline described in the ASME BPVC Section II, Part D, Mandatory Appendix 3 with mechanical and physical properties provided in the JSME fast reactor code, the external pressure charts for each material were constructed. The minimum stress-strain curve for evaluating the external pressure chart was applied the stress-strain equation with design yield strength, Sy, provided by the JSME fast reactor code. As a result, three external pressure charts with digital values were proposed for elevated temperature design. Moreover, the rationalization effect from the current alternative was evaluated by the sample problem. This proposal resolves two issues. One is alternative use of chart for lower strength material over the 150 °C. The other is the external pressure chart above 480°C for which ferritic steels are not available.
Seismic Evaluation Method of Piping Systems by Inelastic Response Spectrum Analysis: Part 1 — Response Analysis
Authors: Tamura Ichiro , Sakai Michiya , Matsuura Shinichi , Shimazu Ryuya , Tamashiro Hiroaki , Mabuchi Soichi
Published: November 2019

An inelastic response-spectrum-analysis method for multi-degree-of-freedom systems was proposed. The method has lower analysis loads and good outlook given by the inelastic response spectrum like the elastic response-spectrum-analysis method, and is not an equivalent-linearization method. We propose a seismic evaluation method of piping systems to conduct seismic design using the inelastic response-spectrum-analysis. In this paper, the inelastic analysis method of piping systems for the seismic evaluation method is proposed and applied to a benchmark analysis problem of a piping system vibration test. The analysis result is compared with the vibration test result of the piping system. They are consistent and applicability of the analysis to the piping system was confirmed.
Effects of Extreme Hydrogen Environments on the Fracture and Fatigue Behavior of Additively Manufactured Stainless Steels
Authors: Smith Thale R. , San Marchi Chris , Sugar Joshua D. , Balch Dorian K.
Published: November 2019

Additive manufacturing (AM) offers the potential for increased design flexibility in the low volume production of complex engineering components for hydrogen service. However, the suitability of AM materials for such extreme service environments remains to be evaluated. This work examines the effects of internal and external hydrogen on AM type 304L austenitic stainless steels fabricated via directed-energy deposition (DED) and powder bed fusion (PBF) processes. Under ambient test conditions, AM materials with minimal manufacturing defects exhibit excellent combinations of tensile strength, tensile ductility, and fatigue resistance. To probe the effects of extreme hydrogen environments on the AM materials, tensile and fatigue tests were performed after thermal-precharging in high pressure gaseous hydrogen (internal H) or in high pressure gaseous hydrogen (external H). Hydrogen appears to have a comparable influence on the AM 304L as in wrought materials, although the micromechanisms of tensile fracture and fatigue crack growth appear distinct. Specifically, microstructural characterization implicates the unique solidification microstructure of AM materials in the propagation of cracks under conditions of tensile fracture with hydrogen. These results highlight the need to establish comprehensive microstructure-property relationships for AM materials to ensure their suitability for use in extreme hydrogen environments.
Application of Probabilistic Fracture Mechanics Methodology for Japanese Reactor Pressure Vessels Using PASCAL4
Authors: Lu Kai , Katsuyama Jinya , Li Yinsheng , Yoshimura Shinobu
Published: November 2019

Probabilistic fracture mechanics (PFM) methodology, which represents the influence parameters in their inherent probabilistic distributions, is deemed to be promising in the structural integrity assessment of pressure-boundary components in nuclear power plants. To strengthen the applicability of PFM methodology in Japan, Japan Atomic Energy Agency has developed a PFM analysis code called PASCAL4 (PFM Analysis of Structural Components in Aging LWRs, Version 4) which can be used to evaluate the failure frequency of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock events. PASCAL4 is expected to make a significant contribution to the probabilistic integrity assessment of Japanese RPVs. In this study, PFM analyses are performed for a Japanese model RPV using PASCAL4, and the effects of non-destructive examination and neutron fluence mitigation on failure frequency of RPV are quantitatively evaluated. From the analysis results, it is concluded that PASCAL4 is useful for the structural integrity assessment of RPVs and can enhance the applicability of PFM methodology.
Effect of Thermal Aging on the Deformation and Failure Behaviors of Cast Austenitic Stainless Steels Under Excessive Cyclic Loads
Authors: Kim Jin Weon , Kim Sang Eon , Kim Yun Jae
Published: November 2019

This study conducts failure tests using a simulated specimen to investigate the effect of thermal aging on the deformation and failure behaviors of system, structure, and components (SSCs) of nuclear power plants (NPPs) made of cast austenitic stainless steels (CASSs) under excessive seismic loads. Both unaged and thermally aged CF8A CASSs were used for the experiment, and the large cyclic loads in the form of displacement-control and load-control were applied at a quasi-static displacement rate. Displacement-controlled tests were performed at room temperature (RT) and 316°C and load-controlled tests were performed at RT. The results show that the deformation behaviors of aged CF8A CASS under both types of cyclic load are almost the same as those of unaged CF8A CASS. The thermal aging slightly promotes the failure of CF8A CASS under displacement-controlled cyclic loads, but the failure of specimen still occurs under the cyclic load levels several times higher than the load of the design basis earthquake. Under load-controlled cyclic loads, thermal aging retards the failure of CF8A CASS. Consequently, the thermal aging has no apparent negative effect on the deformation and failure behaviors of CASSs under large cyclic loads, even if it considerably changes the strength, ductility, and fracture toughness of CASSs.
Application Examples of ASME Code Case N-513 Implementation
Authors: McGill Robert O. , Cipolla Russell C. , Houston Eric J. , Janowiak Ronald J.
Published: November 2019

Code Case N-513 provides evaluation rules and criteria for temporary acceptance of flaws, including through-wall flaws, in moderate energy piping. The application of the Code Case is restricted to Class 2 and 3 systems, so that safety issues regarding short-term system operation are minimized. The first version of the Code Case was published in 1997. Since then, there have been five revisions to the Code Case that have been published by ASME. The Code Case has been used numerous times by utilities to avoid unscheduled shutdowns without impacting plant safety.

Recent revisions of Code Case N-513 continue to expand its scope to piping components including elbows, reducers, branch tees and gate valve body ends. This paper provides three application examples of the Code Case implementation based on US plant operating experience. Specifically, detailed evaluations of through-wall leakage in straight pipe, a piping elbow and gate valve body end are provided. These examples will help facilitate Code Case implementation by future users.
Material Characterization on the Nickel-Based Alloy 600/82 NeT-TG6 Benchmark Weldments
Authors: Akrivos Vasileios , Smith Mike C.
Published: November 2019

The NeT-TG6 project examines the behaviour of a three-pass slot-welded benchmark made from Alloy 600 base material and Alloy 82 weld metal. This paper reports the material characterization studies conducted as part of the extensive round-robin activities performed to characterise the residual stress state in the TG6 benchmark using both measurement and simulation. An additional three slot specimen with one, two and three pass welds was manufactured to allow extensive characterization studies and comparison with the actual NeT-TG6 specimen, which contains only a single three-pass weld. Optical metallography and chemical composition studies examined the variability of the chemical composition and microstructure between parent material and weld metal with varying levels of dilution and differing thermo-mechanical behaviour. Micro indentation measurements were used to acquire hardness maps of the welded samples and reveal the impact of thermo-mechanical cyclic history. Electron microscopy and in particular electron back scattered diffraction (EBSD) was used to estimate the grain size variation, and, in the deformed parent and each weld bead, to assess the accumulation of plastic deformation.
Effect of Residual Stress on High Temperature Hydrogen Attack for Pressure Vessels
Authors: Honma Yuta , Hashi Kunihiko
Published: November 2019

Nelson curve for carbon steel without post welding heat treatment (PWHT) was reconsidered in Annex F of API PR941 8th Edition because a lot of hydrogen damage cases of carbon steel for pressure vessels and pipes with weld joint were reported. However the mechanism of the damage initiation has not been extensively studied. For these reason, the purpose of this study was to clarify effect of residual stress on high temperature hydrogen attack (HTHA) and examine the mechanism in terms of microstructure.

The specimens that were simulated welding residual stress by four point bending tool were exposed to high temperature and high pressure hydrogen gas to investigate relationship between damage initiation and condition of temperature and pressure. The frequency of damage occurred by residual stress under high temperature and low hydrogen pressure conditions was higher than that under low temperature and high pressure condition. The damage occurred on boundary of ferrite and pearlite. The grain reference orientation deviation (GROD) map obtained from EBSD measurement indicated the concentration of strain on the boundary generated by plastic deformation. Thus, the damage is most likely initiated by concentration of hydrogen on ferrite-pearlite boundary at which welding strain accumulated. Moreover the damage susceptibility of ferrite-pearlite structure was higher than that of bainite structure. The microstructures in base metal is ferrite-pearlite, but that in heat affected zone is bainite by reheating and cooling at welding. Hence, the base metal has higher damage susceptibility than HAZ.