bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure Evolution and Creep Rupture Behavior of Modified 9Cr-1Mo Steel Welded Joint
Authors: Ren Facai , Tang Xiaoying , Xu Jinsha , Si Jun , Yuan Yiwen
Published: October 2020

Microstructure evolution and creep rupture behavior of modified 9Cr-1Mo steel welded joint used for steam cooler in high pressure heater system were systematically studied in this paper. Creep tests were carried out using uniaxial creep specimens machined from the normalized and tempered plate at 818K and 838K with the stresses ranging from 150 to 225MPa. The curve of stress vs. rupture time was achieved to evaluate the creep rupture life of modified 9Cr-1Mo steel welded joint. The creep data were analyzed in terms of Norton’s power law, Monkman-Grant relation and modified Monkman-Grant relation. Microstructure before and after creep exposure were analyzed by optical microscope, scanning electron microscope and transmission electron microscope, to further explain the rupture mechanisms of modified 9Cr-1Mo steel welded joint.
Consideration of Wind Loads in Fitness for Service Assessment of Storage Tanks
Authors: van Zyl Gys , Long Stewart
Published: October 2020

Wind actions are important to consider when performing fitness for service assessment on storage tanks with damage. Tank design codes typically have rules where a design wind velocity is used to determine required dimensions and spacing of wind girders, and a uniform wind pressure is used to evaluate tank anchorage for uplift and overturning due to wind actions. These rules are of little use in a fitness for service assessment of localized damage, as the actual distribution of wind pressure on the wall and roof of a cylindrical tank is far from constant, and a better evaluation of the wind pressure distribution is desired when performing a level 3 fitness for service assessment. API 579/ASME FFS-1 provides no direct guidance relating to the application of wind loading but refers to the American Society of Civil Engineers Standard ASCE/SEI 7. Other international codes relating to wind loads, such as Eurocode EN-1991-1-4 and Australia/New Zealand Standard AS/NZS 1170.2 also contain guidance for the evaluation of wind actions on cylindrical tanks. This paper will present a review of these international codes by comparing their guidance for wind actions on cylindrical tanks, with specific emphasis on how this may affect a level 3 fitness for service assessment of a damaged storage tank.
Gas Supply Reliability Analysis of a Natural Gas Pipeline System Considering the Effects of Demand Side Management
Authors: Li Yichen , Gong Jing , Yu Weichao , Huang Weihe , Wen Kai
Published: October 2020

At present, China has a developing natural gas market, and ensuring the security of gas supply is an issue of high concern. Gas supply reliability, the natural gas pipeline system’s ability to satisfy the market demand, is determined by both supply side and demand side, and is usually adopted by the researches to measure the security of gas supply. In the previous study, the demand side is usually simplified by using load duration curve (LDC) to describe the demand, which neglects the effect of demand side management. The simplification leads to the inaccurate and unreasonable assessment of the gas supply reliability, especially in high demand situation. To overcome this deficiency and achieve a more reasonable result of gas supply reliability, this paper extends the previous study on demand side by proposing a novel method of management on natural gas demand side, and the effects of demand side management on gas supply reliability is analyzed. The management includes natural gas prediction models for different types of users, the user classification rule, and the demand adjustment model based on user classification. Firstly, An autoregressive integrated moving average (ARIMA) model and a support vector machine (SVM) model are applied to predict the natural gas demand for different types of users, such as urban gas distributor (including residential customer, commercial customer, small industrial customer), power plant, large industrial customer, and Compressed Natural Gas (CNG) station. Then, the user classification rule is built based on users’ attribute and impact of supplied gas’s interruption or reduction. Natural gas users are classified into four levels. (1) Demand Fully Satisfied; (2) Demand Slightly Reduced; (3) Demand Reduced; (4) Demand Interrupted. The user classification rule also provides the demand reduction range of different users. Moreover, the optimization model of demand adjustment is built, and the objective of the model is to maximize the amount of gas supply for each user based on the classification rule. The constraints of the model are determined by the classification rule, including the demand reduction range of different users. Finally, the improved method of gas supply reliability assessment is developed, and is applied to the case study of our previous study derived from a realistic natural gas pipeline system operated by PetroChina to analyze the effects of demand side management on natural gas pipeline system’s gas supply reliability.
Correlation Between Thermal Desorption Spectrum Features and Creep Damage
Authors: Zhou Yu , Fan Zhichao , Chen Xuedong , Jiang Huifeng , Jazaeri Hedieh , Bouchard Peter John
Published: October 2020

The analysis of the spectrum features of thermal desorption spectroscopy (TDS) using the desorption-rate profile against temperature is widely applied to investigate the hydrogen kinetics including diffusion and trapping in metallic materials, which is related to hydrogen embrittlement. Recently the TDS spectrum features such as the peak magnitude and the peak area have been used for qualitative assessment of creep damage, although there is still a lack of theoretical understanding on the correlation between TDS spectrum features and creep damage. In this paper, creep voids inducing creep damage are considered as the only kind of hydrogen traps in steels. The relationships between the TDS spectrum features and creep damage of ferritic steels are investigated through parameter analysis of the modified McNabb-Foster model together with the Oriani assumption, which can describe hydrogen evolution during thermal desorption. It is found that the peak area of TDS spectrum is independent of the trap binding energy, and it is proportional to the trap density, demonstrating that it could be a good indicator for creep damage. The creep damage can be characterized as a power-law function of the peak area of TDS spectrum, indicating TDS as a promising semi-destructive characterization method for creep damage of metallic steels.
Passive Control Techniques for Seismic Protection of Chemical Plants
Authors: Minagawa Keisuke , Paolacci Fabrizio
Published: October 2020

Seismic damage of chemical plant facilities (pressure vessels, piping, storage tanks, etc..) can causes human and economic losses as well as heavy environmental damages. Therefore, it is of paramount importance to reduce such a consequences. The passive control techniques (PCT) as dampers or base isolation can represent an effective technique to mitigate the major damage caused by earthquakes. Viscous dampers, tuned mass dampers and base isolators are well-known passive control devices successfully applied to civil structures, as demonstrated during the last big events as Northridge earthquake in 1994, the Kobe earthquake in 1995, the Great East Japan earthquake in 2011. The scarce application to major hazard industrial facilities as chemical plants poses some questions, including the selection of suitable devices, their real applicability and effectiveness, because of the strict requirements of chemical plant equipment in terms of safety and business continuity. Therefore, this study aim at analyzing the possible applications of the most renew passive control techniques for seismic protection for chemical plant components. In this respect, a complete review of typical seismic damage of industrial (chemical) facilities and the investigation of the applicability of PCT as mitigation strategy is offered for all possible structural typologies of units presents in a plant.
Further Evidence of Margin for Environmental Effects, Termed Fen-Threshold, in the ASME Section III Design Fatigue Curve for Austenitic Stainless Steels Through the Interaction Between the PWR Environment and Surface Finish
Authors: McLennan Alec , Morley Andrew , Cuvilliez Sam
Published: October 2020

Fatigue rules within the ASME Boiler and Pressure Vessel Code have undergone significant change over the past decade, especially with the inclusion of Code Case N-792-1 as an acceptable method to describe the effects of BWR and PWR environments on the fatigue life of components. The incorporation of the environmental effects into the fatigue calculations is performed using an environmental factor, Fen, which attempts to describe the difference in fatigue life of polished specimens between air and high-temperature water environments. The Fen depends on parameters such as the temperature, dissolved oxygen and strain rate.

The deleterious effects on fatigue life of a wide range of other factors are not accounted for by the standard constant amplitude testing, performed on small polished specimens that was used to develop the mean air curve. These factors are accounted for in the design curve, which is defined by adjusting the mean air fatigue curve with transference factors.

Evidence, obtained in recent years, now suggests that the assumed deleterious effect of surface finish on fatigue life may be excessive. Therefore, the combination of the air design fatigue curve and Fen results in overly-conservative estimates for fatigue life in high temperature water environments. Approaches have been developed to quantify the scale of this excess-conservatism and define this as a margin within the design fatigue curve that can be used to offset Fen. In the ASME framework this is termed Fen-Threshold.

This paper presents further evidence in support of the approach by extending the database of test results to 316-type steels and extending the range of environmental and loading conditions. The additional stainless steel data demonstrates that the size of the margin is insensitive to strain amplitude over an extended range of strain amplitudes. Furthermore, the analysis indicates that in conditions where the environmental effect is low (less than the value of Fen-Threshold) the margin remains great enough to offset the entire Fen, returning such sites to an assessment against the air design curve.

This paper also presents an extension of the research program to nickel based alloys through testing of Alloy 600. The intent is to investigate whether there is evidence of similar excessive conservatism that can be translated into an equivalent margin for environmental effects in nickel-based alloys.
Hydrogen Effects on Fatigue Life of Welded Austenitic Stainless Steels Evaluated With Hole-Drilled Tubular Specimens
Authors: Kagay B. , San Marchi C. , Pericoli V. , Foulk J.
Published: October 2020

Limited fatigue data exists for small-volume welded austenitic stainless steel components typically employed in hydrogen infrastructure due to the difficulty of testing these components with conventional specimen designs. To assess the fatigue performance of orbital tube welds of austenitic stainless steels, a hole-drilled tubular specimen was designed to produce a stress concentration in the center of the orbital weld. Fatigue life testing was performed on welded and non-welded 316L stainless steel hole-drilled tubular specimens, and the effects of hydrogen were evaluated by testing specimens with no added hydrogen and with internal hydrogen introduced through gaseous precharging. When accounting for the differences in flow stress caused by microstructural variations and the presence of internal hydrogen, the total fatigue life and fatigue crack initiation life of the welded and non-welded tubes were comparable and were reduced by internal hydrogen. In addition, the fatigue life results produced with the hole drilled tubular specimens were consistent with fatigue life data from circumferentially notched stainless steel specimens that have a similar elastic stress concentration factor. To better understand the mechanics of this specimen geometry, mechanics modeling was performed to compare the stress and strain distributions that develop at the stress concentration in the hole-drilled tubular and circumferentially notched specimens during fatigue cycling.
A Review of Temperature Reduction Methods in Codes and Standards for Pipe Supports
Authors: Mayes Alex , Wiseman Phillip , Gawande Kshitij P.
Published: October 2020

American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section III, Division 1, Subsection NF, Subparagraph NF-3121.11 does not require that thermal stresses in supports be evaluated. Historically, pipe support engineers have not been concerned with thermal stresses of pipe and component supports, but determining material temperature limits and allowable stresses have been a major role in designing and analyzing supports. Thus, heat transfer is often investigated in finding the temperature of pipe supports and parts of pipe supports that are not in direct contact with pipe or pipe components. There are also other Codes and standards that permit a reduction of temperature away from the outer surface of pipe or pipe components. In some but not all cases, Codes and standards explicitly address reduction of temperature for applications of utilizing thermal insulation. Additionally, the temperature distribution is established by specific geometrical parameters and their respective equations for employment by the pipe support engineer. These reductions are explored by utilizing fundamentals of heat transfer. Additionally, steady-state and transient thermal Finite Element Analyses (FEA) are used to establish computational models of simple geometric bodies in a range of atmospheric conditions. The effects of insulation on the thermal distribution are also represented through closed form solutions and FEA. The results of these analyses allow for assessment of, and recommendations for, the treatment of temperature reduction in Codes and standards.
Welded Attachments and Hydrostatic Pressure Testing Rules for Diffusion Bonded Heat Exchangers
Authors: Aakre Shaun R. , Jentz Ian W.
Published: October 2020

The mission of the U.S. Department of Energy (DOE), Office of Nuclear Energy is to advance nuclear power in order to meet the nation’s energy, environmental, and energy security needs. Advanced high temperature reactor systems will require compact heat exchangers (CHX) for the next generation of nuclear reactor plant designs. A necessary step for achieving this objective is to ensure that the ASME Boiler and Pressure Vessel Code, Section III, Division 5 has rules for the construction of CHXs for nuclear service.

Construction of Alloy 800H diffusion bonded Printed Circuit Heat Exchangers (PCHEs) involves multiple controlled welding processes. The primary diffusion bonding process creates a uniformly bonded PCHE body featuring a microchannel core. Secondary welding processes are needed to attach headers and nozzles to the PCHE body, forming a complete CHX. The quality of these welding processes is ensured by following the appropriate ASME Section IX weld qualification procedures.

Experience in constructing both 316L and 800H PCHEs has given a set of acceptable attachment weld configurations and procedures. Headers were attached to the diffusion bonded block surface using full penetration welds, as required by Class A design. The integrity of these attachment welds was demonstrated through hydrostatic pressure testing.
Check Valves in Nuclear Power Plants: ASME OM Code Requirements and Industry Compliance
Authors: Ezekoye L. Ike , Rain Mark , Thygesen Theodore E.
Published: October 2020

Nuclear power plants use lots of valves in different applications. Each valve type has specific tasks to perform. The vast majority of safety related valves are monitored during plant operation to ensure they are operable and can be relied upon to do their design functions. Unfortunately, check valves do not fall in the category of valves that can be readily monitored because of how they are designed; usually with all operating components internal to the pressure boundary. Since they are not easily monitored externally, plant operators typically disassemble and inspect them to assess the internal conditions and determine what actions to take, which can be either repair, replace, or use as found. However, not all check valves get inspected for a number of reasons resulting in some valves running to failure. In this paper, the authors present actions the nuclear industry has used to comply with ASME OM Code requirements (8) on check valves and US NRC regulatory activities in this area. The paper also covers the role the nuclear industry and other organizations have played to improve check valve reliability.
Buckling Test of Thin-Walled Metallic Cylindrical Shells Under Locally Distributed Axial Compression Loads
Authors: Jiao Peng , Chen Zhiping , Ma He , Zhang Delin , Wu Jihang , Ge Peng , Gu Yanan
Published: October 2020

Thin-walled cylindrical shell structure not only shows the highly efficient load carrying capacity but also is vulnerable to buckling instability failure. In practical application, these structures are more easily subjected to locally distributed axial compression load, which is a more common non-uniform loading case. However, until now, the buckling behaviors of thin-walled cylindrical shells under this kind of loading case are still unclear, and there are also few relevant buckling experiments. In order to fill this research gap as well as reveal the relevant failure mechanism of thin-walled cylindrical shell structures, in this paper buckling tests of thin-walled metallic cylindrical shell structures under non-uniform axial compression loads are successfully performed. In this regard, the design and characteristics of two cylindrical shell test specimens subjected to different pattern of non-uniform compression loads are mainly introduced. Meanwhile, as the important parts for conducting this buckling experiment, the axial compression buckling test rig as well as the real-time acquisition measurement system is also presented in details. Results indicate that locally distributed axial compression loads play a pivotal role in the buckling behaviors of thin-walled cylindrical shell, not matter from the point of view of load carrying capacity, shell deformation process or failure mode. The experiments carried out in this work can be served as a benchmark for related numerical simulation afterwards. Furthermore, the obtained test results can also provide some guides for the design and application of thin-walled cylindrical shell in actual engineering.
Applicability of Formula of the Irradiation Assisted Stress Corrosion Cracking Rates for Neutron-Irradiated Type 316L Stainless Steels to Various Types of Stainless Steels Under Boiling Water Reactor Condition
Authors: Koshiishi Masato , Seto Hitoshi , Tanaka Shigeaki , Obata Ryoji
Published: October 2020

The Hashimoto-Koshiishi model is the predictive mechanistic model for crack growth rates (CGRs) of stress corrosion cracking (SCC). The simplified formula of the Hashimoto-Koshiishi model was developed for the calculation of CGRs of irradiated Type 316L stainless steels (SSs). This study evaluated the applicability of the developed formula to various types of stainless steels by analyzing experimental data of CGRs. The developed formula was determined to be applicable for Type 304L SSs and 316NG SSs as well as Type 316L SSs. On the other hand, the formula was unsuitable for irradiated Type 304 SSs because the mechanical properties and the Cr concentrations at the grain boundaries of Type 304 SSs were different from these quantities for Type 316L SSs.
Long-Term Durability of Pitch-Based High Modulus Carbon Fiber Reinforced Plastics
Authors: Kobayashi Satoshi , Osada Toshiko
Published: October 2020

Static tensile and tensile-tensile fatigue were conducted on PITCH-based high modulus carbon fiber reinforced plastics (CFRP). PAN-based intermediate and high modulus CFRP were also tested for comparison.. Unidirectional laminates were prepared with wet panel method. The damage mode for high modulus CFRP was fiber breakage for both static and fatigue loading, whereas splitting was dominant for intermediate modulus CFRP. The slope of the S-N curve was larger for the intermediate modulus CFRP than that for the high modulus CFRP. This is attributed to the lower failure strain of the high modulus carbon fibers. That is, the larger strain on intermediate modulus CFRP at lower stress level comparing with high modulus CFRP caused severer matrix damages during fatigue loading. This results indicated the higher durability of high modulus CFRP. Residual strength measurement were conducted on the un-broken PITCH-based CFRP up to 1,000,000 cycles with acoustic emission measurements. The Kaiser effect was not satisfied for the specimen with lower residual strength at the stress level of the fatigue test. In addition, gradual acoustic emissions with longer duration and rise time were measured before final fracture in the static tests. These results indicated the possibility to detect the microscopic damage monitoring for the CFRP with acoustic emission measurement focusing on the duration of the acoustic wave.
Using Machine Learning Tools for Forecasting Natural Gas Market Demand
Authors: Yang Kai , Hou Lei
Published: October 2020

Providing reliable and accurate forecasts of natural gas consumption can keep supply and demand of natural gas pipelines in balance, which can increase profits and reduce supply risks. In order to accurately predict the short-term load demand of different gas nodes in the natural gas pipeline network, a hybrid optimization strategy of integrated genetic optimization algorithm and support vector machine are proposed. Factors such as holidays, date types and weather were taken into account to build a natural gas daily load prediction model based on GA-SVM was established. A natural gas pipeline network in China includes three gas supply nodes of different user type gas is forecasted, and a variety of error evaluation method, the GA-SVM evaluation index compared with other prediction methods, and through different data set partition is discussed in the periods of peak gas and gas resources in the GA — the applicability of the SVM prediction model, the ends of a natural gas pipeline network in China includes four gas supply nodes of different user type gas is forecasted, and a variety of error evaluation method, the GA-SVM evaluation index compared with other prediction methods, The applicability of the method is also discussed by dividing different data sets. By predicting the gas load forecast of the three nodes, the results show that GA-SVM hybrid prediction model has high prediction accuracy compared with other single models, and the three gas nodes MAPE of GA-SVM is respectively 3.66%, 5.17% and 3.43%. Through further analysis, even with the data samples reduced, the winter gas peak of gas prediction can still maintain good prediction effects. The research shows that the GA-SVM model has high accuracy and strong applicability in predicting gas consumption at different nodes of the natural gas pipeline network. This study can provide a research basis for analysis of gas supply uncertainty and further gas supply reliability evaluation of pipeline network.
Experimental Study on the Effect of Core Support Frame on Seismic Behavior of Fast Reactor Core
Authors: Matsubara Shinichiro , Iwasaki Akihisa , Harada Hidenori , Yamamoto Tomohiko
Published: October 2020

The fast reactor core is composed of hundreds of core elements that self-stand on the lower support plate, and core elements does not have support to constrain vertical displacement in order to avoid effects such as thermal elongation. When an earthquake occurs, the group vibration behavior including the rising of core elements in the vertical direction, the collision with adjacent core elements in the horizontal direction, and the fluid structure interaction is observed. The three dimensional core group vibration analysis code (REVIAN-3D) for evaluating these has been constructed.

In this study, to grasp and estimate the group vibration behavior with and without a core former under the earthquake motion, seismic experiment of hexagonal multi bundle model using core element mock-up was conducted. These test results show that the presence of the core former decrease the horizontal displacements and increases core compaction. And the test results are used for the verification data of the analysis code REVIAN-3D.[1]
Study on Design Approach for Tall Pressure Vessels With Intermediate Support in Consideration of Bottom Structure Flexibility
Authors: Sasaki Shunsuke , Nanjo Takanori , Miyashita Toshikazu , Kataoka Shunji , Uno Yoshiaki
Published: October 2020

The skirt and shell thicknesses of vertical tall pressure vessels are sometimes much increased in FPSO (Floating Production, Storage and Offloading) due to ship motion acceleration. In that case, intermediate support is used as an additional support from steel structure surrounding the vessels. By theoretical calculation, Nanjo et.al. introduced dimensionless parameter N that can represent stiffness of pressure vessel and acceleration load with the assumption of structure drift at intermediate support [1]. The authors proposed N-chart to investigate the necessity and effective elevation of intermediate support by using the parameter N. The flexibility of steel structure on the bottom affects the function of intermediate support (e.g. increasing reaction force at intermediate support, effect on bottom skirt calculation); however, the flexibility is not included in the parameter N. In this paper, an additional factor for the flexibility was studied and introduced by structural analysis. A model with flexibility of structure supporting the bottom skirt was used for the analysis. The variable flexibility of steel structure was applied to the bottom of the model to study the impact of bottom structure flexibility on the pressure vessel design. The analysis result was compared with the bottom fixed model without structure flexibility to study an additional factor. Finally, appropriate design approach for tall pressure vessels with intermediate supports was proposed.
Study on Vibration Mitigation of Connected Cabinets Storing Electronics Subjected to Seismic Input Using Elasto-Plastic Damper
Authors: Shintani Atsuhiko , Yoshida Takuma , Nakagawa Chihiro , Ito Tomohiro
Published: October 2020

This paper deals with the motion of coupled cabinets containing electronics subjected to seismic input. In power plants, chemical plants, etc., several rectangular cabinets containing important electronics are always lined up in the control center. These electronics are necessary for the control of the entire plant; thus, when they are damaged, the entire plant cannot be controlled, and a serious accident may occur. These cabinets are frequently put directly on the floor. Thus, it is perceived that in the worst case, cabinets may turn over by rocking motion during earthquakes and electronics may break. Moreover, even when the cabinets do not overturn, there is a concern about a large acceleration applied to the internal electronics due to the seismic waves. Hence, the need to develop methods that can reduce rocking motion and prevent electronics damage simultaneously.

First, we consider the single cabinet with electronics. The cabinet is modeled as a rotating rigid body around its corner. The internal electronics are modeled as a rigid body moving in the translational direction in the cabinet. This system is referred to as single system. We input a seismic wave to the single system and investigate the rocking angle of the cabinet and the acceleration of the electronics in the cabinet.

Consequently, we consider the adjacent cabinets connected by an elasto-plastic damper containing electronics. The cabinets are modeled as rotating rigid bodies. The internal electronics are modeled as rigid bodies moving in the translational direction in the cabinets. The whole system is known as a connected system. The elasto-plastic damper has bilinear hysteretic characteristics and can absorb the energy of earthquake inputs. We input the same seismic wave to the connected system to obtain the rocking angle of cabinets and the acceleration of electronics in the connected system. In these simulations, it is assumed that cabinets do not collide with each other. Then, we investigate the effect of the parameters of the elasto-plastic damper suppressing the rocking angle of the cabinets and the acceleration of electronics.

Finally, we compare the maximum rocking angle and the maximum acceleration of the single system with that of the connected system and consider an ideal method to reduce the rocking angle and the acceleration simultaneously.
Proposal of Simulation Materials Test Technique and Their Constitutive Equations for Structural Tests and Analyses Simulating Severe Accident Conditions
Authors: Hashidate Ryuta , Kato Shoichi , Onizawa Takashi , Wakai Takashi , Kasahara Naoto
Published: October 2020

Nuclear structure’s integrity must be confirmed under severe accident conditions. However, performing structure tests using actual steels is very difficult and expensive. Therefore, the authors conducted structure tests using the lead alloy to evaluate the structure integrity under severe accident conditions. Because the strength of the lead alloy is considerably less than that of actual steels, structure tests can be conducted under low-pressure, low-temperature conditions. To quantitatively correlate the structural response of the lead alloy to that of actual steels, finite-element analyses (FEAs) must be performed. Because the inelastic constitutive equations, namely, inelastic stress–strain relationship equation, creep rupture equation, and creep strain equation, are required to perform the inelastic FEA, the authors introduced material tests using the lead alloy and, subsequently, proposed the inelastic constitutive equations based on the material test results in a previously conducted PVP conference. However, the proposed inelastic constitutive equations could not successfully express the material characteristic of the lead alloy because of large variations observed in the material tests of the lead alloy. Furthermore, the authors observed that the material characteristic of the lead alloy could be stabilized by aging. In this study, we propose the improved inelastic constitutive equations of the lead alloy on the basis of test results newly obtained from a series of material test performed using aged alloy.
A Method for Measuring Combined Stress of Small Bore Piping Around Weld in Field Using Strain Gauge Holder
Authors: Takahama Tsunemichi
Published: October 2020

This paper proposes using the strain gauge holder which has 12 elements of strain gauge in order to measure the 2 directional bending stresses and the torsional stress synchronously around the weld in small bore piping. The paper also provides the actual measured dynamic stresses around the welds in real fields including combined stress by the strain gauge holder. The measured stresses are shown on a time axis, on a frequency axis, on an X-Y display like Lissajous figure, and on an X-Y-Z 3D display.

It was confirmed that the strain gauge holder was able to be installed within 20 minutes, to be used on 180°C piping, and to be reused in real fields because it was not necessary to adhere the strain gauges on the piping.

The measured strains obtained by using the strain gauge holder can provide useful information of the piping system to decide whether the reinforcements are necessary, to enhance the accuracy of the design and calculation, and to improve the validity of fatigue evaluation.

It is planned in future to develop a methodology of fatigue evaluation based on the measured stresses obtained by using the strain gauge holder.
Fracture Toughness Tests on Western RPV Steels Using Small Scale Specimen Technique
Authors: Obermeier Florian , Altstadt Eberhard , Hein Hieronymus , Das Aniruddh
Published: October 2020

In order to ensure continued safe operation of European nuclear reactors, it is necessary to solve specific issues that arise from irradiation induced reactor pressure vessel (RPV) embrittlement under long term operation. This requires an extension of the RPV surveillance programs to cover longer operation times than originally planned. The limited availability of surveillance materials poses a challenge for the feasibility of such programs. Among others, the use of the small specimen technology is a promising option to overcome the lack of materials. For example, a number of not less than 16 sub-sized 0.16 C(T) specimens (4 mm thickness) can be manufactured from two tested Charpy sized (10 mm × 10 mm × 55 mm) specimens, allowing a reliable determination of the reference temperature T0. Such Charpy sized fracture mechanics specimens are currently widely used in the RPV surveillance programs.

To establish the methodology for fracture mechanics testing of irradiated and unirradiated RPV steels using sub-sized specimens, a joined R&D project was launched partly financed by the German Federal Ministry for Economic Affairs and Energy. Moreover the following points shall be addressed:

• Manufacturing, pre-cracking procedure, measurement of the crack opening displacement and load line displacement under hot cell conditions

• Demonstration of the transferability of fracture mechanics data

The purpose is to demonstrate that the results measured on sub-sized specimens can safely be used in the safety assessment of RPVs. In addition, the results will establish a basis to assess results from international projects regarding sub-sized fracture mechanics specimens.
Assessment of Compact Heat Exchanger Design Following Elastic Perfectly Plastic Methodology
Authors: Shaw Avinash , Mahajan Heramb P. , Hassan Tasnim
Published: October 2020

Compact Heat Exchangers (CHXs) have a large number of miniature channels inside their core, which makes them highly thermal efficient and thus, prime utile for Next Generation Nuclear Plant (NGNP) applications. The fabrication of a CHX involves diffusion, brazed or welded bonding of plates to form CHX block with a channeled core. The elevated temperature and transient conditions of NGNP operation may induce excessive strain and creep-fatigue failure in channel ligaments. The primary objective of this study is to evaluate the design of CHX for application to NGNPs, following the ASME Code Elastic Perfectly Plastic (EPP) Analysis criteria in a draft ASME Code Section III, Division 5 and using the currently available Division 5 Code Cases (N-861 and N-862). As global analysis considering channels in the core is computationally intensive, a new analysis method is evaluated. In this method, the global analysis is performed by representing the channeled core by an elastic orthotropic material core. Subsequently, at the local level, EPP analysis is performed using models that include the channels, with thermal and pressure loading conditions. An ASME Draft Code Case is under development for the construction of CHXs. The analysis results are used to assess proposed stress limits and classification for load controlled stresses. For strain limits, the analysis results are evaluated using Code Cases N-861 and N-862 against the strain limit and creep-fatigue damage using the channel level submodel analysis. The applicability of the new analysis method, and use of the analysis results for evaluation against ASME proposed limits for various regions of the CHX are presented and discussed.
Effect of Material and Lubrication Conditions on the Underhead Frictional Response in High Strength Socket-Head Screws
Authors: Croccolo Dario , De Agostinis Massimiliano , Fini Stefano , Olmi Giorgio , Robusto Francesco , Vincenzi Nicolò
Published: October 2020

The present paper investigates the influence of several design parameters on the frictional response at the underhead in a bolted joint, involving high strength socket-head screws: M8 class 14.9 with black oxidization coating. The experimentation deals with different underhead materials (Steel, Aluminium), lubrication conditions (dry, lubricated) and repeated tightening operations. The awareness of the actual friction coefficients, depending on the current operating parameters, is a useful tool, to support the most proper design of a bolted joint. The experimental campaign has been run by a testing rig for friction coefficient estimation, complying with the recommendations by International Standard ISO 16047 and the automotive Standard VW01131-1 in order to consider the effect of the tightening speed normally adopted in the automotive field. The axial preload generated upon tightening induces a high pressure on the remarkably small underhead surface of the utilized high strength socket-head screws and is therefore likely to affect the tribological response. Consequently, some differences may be expected with respect to the tribological behavior of screws belonging to lower strength grades. This is particularly true, when tightening is done without bearing lubrication, and through several repeated assembly-disassembly operations. The collected data have been processed by the tools of ANOVA and F-Test, in order to assess the significance of each factor, as well as related interactions.
Fracture Mechanics Integrity Assessment of Stud Bolts Subjected to Cathodic Protection
Authors: de Castro Mario A. L. , Alves Fabio , Karpanan Kumarswamy , Venkatesh Anand
Published: October 2020

Exposure of metallic parts to cathodic protection (CP) in sea water leads to production and diffusion of atomic Hydrogen into the metal matrix. Absorption of atomic Hydrogen into the metal could lead to hydrogen embrittlement (HE).

In order to study the influence of stresses related to HE, FEA and Fracture Mechanics (FM) assessments were performed on a stud bolt threaded geometry. Effects of manufacturing tolerances, interface between nut and stud bolt and a defect in the form of a semi-circular crack placed in highest stress location of a thread root were also considered. Investigations of stress profiles when tension or bending are applied in test samples for measurement of HE threshold were also done, aiming at showing gaps on ASTM F1624-12 [1].

Tolerance assessment shows a relative maximum increase of 260% of nominal linearized membrane plus bending (NLMB) stresses regarding the nut runout [2] and for the proprietary nut geometry, such relative increase drops to 126% of NLMB stresses. Highest Hydrogen concentrations could be observed in the neighborhood of the first loaded thread root. FEA of cracked geometry shows that Hydrogen concentration could increase by around 283% around the crack tip, when compared to stud bolt in unloaded condition. Integrity assessment according to API 579-1 [3] or BS 7910 [4] and tests conducted according to ASTM F1624-12 [1] show less conservative results.
Estimation of Bending Stresses in Piping Systems Subjected to Transient Pressure
Authors: Taghva Maral , Damkilde Lars
Published: October 2020

Modifications in aged process plants may subject piping systems to fluid transient scenarios, which are not considered in the primary design calculations. Due to lack of strict requirements in ASME B31.3 the effect of this phenomenon is often excluded from piping structural integrity reassessments.

Therefore, the consequences, such as severe pipe motion or even rupture failure, are discovered after modifications are completed and the system starts to function under new operational conditions. The motivation for this study emanated from several observations in offshore oil and gas piping systems, yet the results could be utilized in structural integrity assessments of any piping system subjected to pressure waves.

This paper describes how to provide an approximate solution to determine maximum bending stresses in piping structures subjected to wave impulse loads without using rigorous approaches to calculate the dynamic response. This paper proposes to consider the effect of load duration in quasi-static analysis to achieve more credible results. The proposed method recommends application of lower dynamic load factors than commonly practiced values advised by design codes, for short duration loads such as shock waves. By presenting a real-life example, the results of improved and commonly practiced quasi-static analysis are compared with the site observations as well as dynamic analysis results. It is illustrated that modified quasi-static solution shows agreement with both dynamic analysis and physical behavior of the system.

The contents of this study are particularly useful in structural strength re-assessments where the practicing engineer is interested in an approximated solution indicating if the design criteria is satisfied.
Application of Low Heat Input Gas Metal Arc Welding for Corrosion Resistant Weld Overlays
Authors: Babyak Timothy , DeCenso Vincent , Alexandrov Boian , Penso Jorge
Published: October 2020

Preventing failure due to corrosion poses a challenge to the oil and gas industry. A cost-effective way to prevent such failures is the application of corrosion-resistant nickel-based weld overlays using arc welding processes. Previous research performed at The Ohio State University indicates low heat input GMAW processes, such as cold metal transfer (CMT), produce weld overlays which corrode up to ten times slower than overlays produced with cold wire GTAW [1, 2], with up to ten times higher deposition rates [3]. However, formation of lack of fusion and lack of penetration defects has been a major concern related to the widespread application of low heat input GMAW processes in the industry. In this study, optimal windows of CMT welding parameters for producing defect-free welds were established using a design of experiment approach. CMT weld overlays were compared with hot wire (HW)-GTAW overlays currently used in industry with respect to bead characteristics, microstructure, and process capability. As compared with the HW-GTAW process, the CMT process produced weld overlays with up to four times lower dilution, seven times smaller interdendritic arm spacing, and four times higher deposition rates. Additionally, average heat affected zone and fusion boundary hardness values in the CMT overlays were below 248 HV0.1 and may not require the post weld heat treatment specified by NACE MR0175.
Flaw Design for d-c EP Monitoring of Crack Initiation and Growth During Full-Size Pipe Experiments
Authors: Hong J. K. , Brongers M. , Kalyanam S. , Hioe Y. , Wilkowski G. , Zeng Y. , Hallai J. F.
Published: October 2020

A design for flaw placement in a full-scale pipe test was developed to both detect crack initiation and measure crack growth rate upon internal pressurization of a pipe exposed to a sulfide stress cracking (SSC) environment. The objective of this work was to model different sizes of longitudinally oriented, inside diameter (ID) surface flaws and lay them out on the pipe in such a manner that (1) the flaws experience their target stress intensity factor (K) value at a chosen value of internal pressure, (2) the stress interaction between flaws is minimized, and (3) the flaw layout is optimized for detecting both crack initiation and growth using a direct-current (d-c) electric potential (EP) technique.

The approach to the flaw design and layout used finite element analysis (FEA) modeling and consisted of optimizing K-profiles. First, the K-profiles were optimized by designing curved-bottom flaws such that the target K along the flaw front occurred along most of the flaw length. Then, stress interactions between the flaws were checked to confirm minimum interactions were achieved and that the proposed flaw layout around the pipe circumference was acceptable. In addition, the FE models were used to predict strains on the pipe outside surface. Finally, global (single large current supply), local (individual small current supplies) and hybrid (individual medium-sized current supplies at larger distance) approaches to the d-c EP measurements were evaluated to select which methodology would be most appropriate to detect both crack initiation and growth of the flaws. The results of the analysis show that optimizing all these design factors provides a solid basis for achieving experimental success.
Asset Integrity Management and Fitness-for-Service Assessment of a Pipe Elbow With Metal Loss
Authors: Thorwald Greg , Brendecke Devon , Webb Stephen
Published: October 2020

The objective of this paper is to describe the inspection process and examine a piping elbow found to have metal loss within the context of Asset Integrity Management (AIM). During the last five years, Industry 4.0 technology involving mobile tablet and cloud technology has merged with the proven concepts of AIM enterprise systems. Before this shift, inspectors, engineers, and managers relied on unreliable and time-consuming methods. New technologies allow inspectors and mangers to think, react, and communicate quickly and proactively when integrity threats are discovered.

A piping elbow was identified at a thickness monitoring location (TML) within a larger system due to existing internal corrosion and/or erosion. Since the metal loss is internal, an external visual examination was not sufficient to monitor the metal loss. External ultrasonic (UT) inspection was used to measure the thickness at multiple points on a grid pattern drawn on the elbow’s external surface. The thickness measurements provide the data needed for a local metal loss assessment.

An AIM program was used to assess the risks, aid in inspection, and develop an assessment for ascertaining the degradation pattern. With a heightened understanding of the asset’s degradation pattern, the risk to the asset is reassessed continuously until it has been reduced to an acceptable level as defined by the stake holders.
Effect of Cladding-Induced Stresses on Crack Driving Force in the Fracture Analysis of Pressure Vessels
Authors: Emslie Julian , White Josh , Pellereau Ben , Wood Andrew
Published: October 2020

The inner surfaces of ferritic steel pressure vessels are often coated with a weld-deposited layer of austenitic cladding for the purpose of corrosion resistance.

UK practice of assessing the defect tolerance by postulating defects in components leads to the requirement for a fracture assessment that includes cladding. Section XI requires that the cladding be considered in the fracture analysis, including cladding-induced stresses in the KI evaluation; these stresses largely arise due to the different coefficients of thermal expansion of the cladding and base material, and can also be known as cladding residual stresses.

It is thought that in some assessments of clad pressure vessels, the cladding residual stress is either not included, or assumed to be of a significantly reduced magnitude — due to it decreasing at typical operating temperatures and/or being relaxed by prior overloads such as a hydrostatic test.

This paper describes finite element analysis to determine the effect of cladding residual stress, comparing J values for loading with and without cladding stresses. Comparisons are also made with J-estimations using the R6 fracture assessment procedure. It is argued that cladding-induced stresses would not contribute to ductile failure as they would be reduced by prior loading, with remaining residual stresses being overcome under large plasticity before failure, due to their secondary nature. Further, it may be misleading to include them in an R6 assessment when using simplified approaches, as their contribution can be exaggerated through pessimistic calculations of the V factor.