bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Bolt Tightening Sequences on the Mechanical Behaviors of Gasketed Flange Joint
Authors: Chang Chia-Lung , Huang Jung Xian
Published: November 2019

During tightening bolts on the flange joint, a load is applied on each bolt. The deformation and stress on joint parts vary with magnitude and location of applying bolt forces. Therefore, sequence of tightening bolts has effects on the deformation and accumulated stress on joint parts. Finite element method is used to model the flange joint and to simulate effects of bolt tightening sequence on the deformation and stress on joint parts. The model includes bolts, nuts, raised face flanges, and gasket. Contact conditions are set on contact surfaces between contact parts. 3D elements are used to build the model. In order to prevent leaks, the bolt load and gasket pressure should be uniform. The accumulated stress of bolts and gasket are calculated. The deformation of gasket and flange are also simulated. The model is used to simulate the stress and deformation of flange joint generated by various bolt tightening sequences. The optimal tightening sequence is selected by that the variation of accumulated stress on gasket is the least.
Experimental and Simulation Study on Effective Hydrogen Diffusivity of Cold-Worked Type-304 Austenitic Stainless Steel
Authors: Sezgin Jean-Gabriel , Takatori Daichi , Yamabe Junichiro
Published: November 2019

This study presents some measurements of the effective hydrogen diffusivity in a cold-rolled, Type-304 stainless steel. Steel plates rolled under various cold working (CW) ratios were prepared. Disk specimens, referred to as LT and SL specimens, were sampled from the plates to determine the diffusivity. The rolling direction is perpendicular to the thickness direction for LT specimens and parallel for the SL specimens. Fraction and distribution of α′ phase islands resulting from strain-induced martensite were characterized by electromagnetic induction (EMI) method and electron backscatter diffraction (EBSD) analysis, respectively. The diffusivity of the LT and SL specimens exposed to high-pressure hydrogen gas was determined experimentally through desorption methods. Hydrogen permeation tests for LT and SL specimens were simulated using the finite element method (FEM) by considering a model material containing an inhomogeneous distribution of α′ phase islands. The EMI measurements established that the fraction of the α′ phase increases with the CW ratio. The phase maps from the EBSD analysis revealed an important difference in α′ phase distribution on planes perpendicular and parallel to the rolling direction (LT and SL planes). For CW = 60%, the diffusivity of the SL specimen was five times larger as compared to the LT specimen, although the fraction of the α′ phase is equal. The simulation of the permeation tests also showed a strong difference in the diffusivity between both specimens, and therefore supports the experimental results. Both experiments and simulations suggested that the anisotropic nature of the effective hydrogen diffusivity (in LT and SL specimens) could be attributed to the inhomogeneous distribution of the α′ phase islands in the cold-rolled material.
Enhancement of Uplift Displacement of Tanks due to Out-of-Round Deformation of Cylindrical Shell
Authors: Miyauchi Yoshiyuki , Taniguchi Tomoyo , Nakashima Teruhiro , Hongu Junichi , Okui Daisuke
Published: November 2019

Two unanchored vinyl chloride scale tank models, whose diameter, height and thickness of their shell and base were 860 mm, 400 mm and 0.5 mm respectively, were set on a shaking table for experiencing the horizontal motion. These scale tank models satisfy law of similarity to have an equivalent strain under the action of loads.

The first scale tank model has no stiffeners on its cylindrical shell that allows out-of-round deformation of the cylindrical shell during the shaking table test. To understand effects of the out-of-round deformation of the cylindrical shell on the tank uplift, the sweeping test is carried out. The Operational Modal Analysis clarifies that the out-of-round deformation of the cylindrical shell enhances the uplift displacement by denting a part of cylindrical shell.

The second scale tank model has the multi-stage stiffeners on its cylindrical shell to prevent its out-of-round deformation during the shaking table test. The primary purpose of the second test is to verify applicability of the explicit finite element analysis for analyzing the tank rocking motion. The time history of the uplift displacement of the tank base during a seismic excitation is measured and compared with that computed by the explicit finite element analysis. The comparison shows that the explicit finite element analysis adequately reproduces the tank rocking behavior.
Wet Coated Thin Barrier Films to Prevent Hydrogen Embrittlement on SUS304 Stainless Steel
Authors: Kawami Kazuyoshi , An Bai , Iijima Takashi , Fukuyama Seiji , Imaoka Mutsuharu , Tamai Hiroyasu , Tamura Motonori , Kinoshita Atsushi , Tanaka Toshiyuki
Published: November 2019

Hydrogen barrier coating is a promising technology for preventing hydrogen embrittlement in metals. In this study, characterizations of hydrogen barrier films coated on surfaces of austenitic stainless steel, SUS304 of the Japanese Industrial Standard (JIS), by wet coating processes applied electro-polishing and chemical oxidation method are carried out using cross-sectional transmission electron microscopy (TEM) analyses, and then slow strain rate tensile (SSRT) tests are performed in 1.1MPa hydrogen and nitrogen gases at room temperature. The hydrogen barrier films show 200–300nm total thickness of compositionally modulated Chromium oxide dense layer. The SSRT results reveal that both the elongation and reduction of area are decreased in hydrogen gas compared with those in nitrogen gas for the non barrier-coated specimens but no significant differences appear for the barrier-coated specimens. The fracture surface of the non barrier-coated specimen shows quasi-cleavagy cracking in hydrogen gas while that of the barrier-coated specimen shows only ductile dimple fracture in hydrogen gas, indicating that the coated films effectively prevent the hydrogen embrittlement of SUS304 stainless steel in hydrogen.
Study on Effects of Non-Isothermal Condition and Strain Holding on Environmentally Assisted Fatigue in PWR Primary Water Environment (Step III)
Authors: Takagoshi Daiki , Asada Seiji , Nomura Yuichirou , Stevens Gary , Ahluwalia Kawaljit
Published: November 2019

To further understand the environmentally assisted fatigue (EAF) behavior of Type 316 austenitic stainless steels (SS) in a pressurized water reactor (PWR) primary water environment, the influence of non-isothermal transient conditions was investigated using hollow, small-scale fatigue specimens. In our previous study (Step I: PVP2016-63798), isothermal and non-isothermal EAF tests were performed. The non-isothermal transient conditions for the fatigue tests investigated transients that consisted of both in-phase and out-of-phase temperature and strain variations. The result of this test series showed longer fatigue lives than those predicted using the modified rate approach and the EAF multiplier (Fen) presented in the draft of NUREG/CR-6909, Revision 1.

In our follow-on study (Step II: PVP2017-66233), one extra non-isothermal test was performed and application of the Weighted Stress Intensity Factor (K) Rate (WKR) method was discussed.

In the latest Step III testing, an extra non-isothermal test with periodic beachmarking has been performed. This paper discusses, based on the completion of all EAF tests performed in Steps I – III of this project, the effects of non-isothermal conditions and recommendations which are made for treatment of non-isothermal conditions in EAF assessments.
Development of New Design Fatigue Curves in Japan: Discussion of Fatigue Crack Growth Based on Fatigue Test Data With Large Scale Piping
Authors: Bodai Masaru , Fukuta Yuichi , Asada Seiji , Hayashi Kentaro
Published: November 2019

In order to develop new design fatigue curves for carbon steels & low alloy steels and austenitic stainless steels and a new design fatigue evaluation method that are rational and have clear design basis, Design Fatigue Curve (DFC) Phase 1 subcommittee and Phase 2 subcommittee were established in the Atomic Energy Research Committee in the Japan Welding Engineering Society. The study on design fatigue curves was actively performed in the subcommittees.

In the subcommittees, domestic and foreign fatigue data of small test specimens in air were collected and a comprehensive fatigue database was constructed. Using this fatigue database, the accurate best-fit curves of carbon steels & low alloy steels and austenitic stainless steels were developed by applying tensile strength to a parameter of the curve.

Regarding design factors on design fatigue curves, data scatter, mean stress correction, surface finishing effect, size effect and variable loading effect were investigated and each design factor was decided to be individually considered on the design fatigue curves.

A Japanese utility project performed large scale fatigue tests using austenitic stainless steel piping and low-alloy-steel flat plates as well as fatigue tests using small specimens to obtain not only basic data but also fatigue data of mean stress effect and surface finishing effect. Those test results were provided to the subcommittee and utilized the above studies.

In the last PVP Conference, the large scale fatigue tests using austenitic stainless steel piping were discussed for the best-fit curve of austenitic stainless steel (PVP2018-84436).

In this paper, further studies are performed based on fatigue crack growth of the large scale fatigue tests using austenitic stainless steel piping. From the obtained crack growth data of the tested piping, the number of cycles at 3-mm-deep crack depth and through-wall crack of piping compares with the best-fit curve developed by the DFC1 subcommittee with considering the confidence lower bounds to survey the fatigue life of piping, and size effect for fatigue lives is discussed. The relations between the fatigue crack growths and the number of cycles and the aspect ratios are surveyed including mean stress effect.
Particular Fatigue Resistance of Stabilized Stainless Steel: Endurance Limit, Strength and Ductility of Fatigued Steel
Authors: Solin Jussi , Alhainen Jouni , Arilahti Esko , Seppänen Tommi , Mayinger Wolfgang
Published: November 2019

Comprehensive experimental research on fatigue performance of niobium stabilized (type 347) X6CrNiNb1810mod steel has revealed particular features of cyclic performance. This paper reports and discusses on the endurance limit behavior studied by strain controlled HCF tests at room and elevated temperatures. In contrast to carbon steels, stainless steels can tolerate notable amounts of plastic strain and display broad hysteresis loops at and below endurance limit. Together with pronounced secondary hardening, this results to abrupt endurance limit behavior. The modified Miner rule with S-N–curves extrapolated to low amplitudes is generally applicable for carbon steels, but not for stainless. Effectiveness of the endurance limit even with variable amplitude straining was shown for 347 type steel. Extrapolation of ε-N curves beyond a few million cycles is conservative. An increase of temperature decreases, but does not vanish the endurance limit.

Another peculiar feature of the studied stainless steel is its superior ductility, which is not affected by partial fatigue ‘damage’. Five LCF tests at 325°C and 0.22 ≤ εa ≤ 0.5% were interrupted beyond the half-life condition (N/N25 ≥ 0.5) at 0.5 ≤ CUF ≤ 0.9. Cyclic straining was directly followed by monotonic pulling to fracture. Surprisingly low correlation between tensile properties and fatigue usage was observed. The ultimate tensile strength was preserved within 10 MPa (2.5%) in all cases. Yield strength and elongation remained practically unchanged by pre-fatigue.

This paper provides new experimental results. They are discussed together with earlier observations on the same steel extracted from a pipe, which has been manufactured for use in primary loop of a German NPP.
Real-Time Eddy Current Imaging and Flaw Detection Under Tube Support Plate by Cylinder-Type Magnetic Camera
Authors: Kim Sejin , Lee Hoyong , Lee Jinyi
Published: November 2019

In this study, a novel method is proposed to detect flaws directly under tube support plate (TSP) of heat exchanger tube using a cylinder-type magnetic camera (CMC). The CMC measures and images magnetic flux density changes occurring around a defect by applying a time-varying magnetic field to a metallic object through magnetic sensors which are arrayed in a matrix. If there is a flaw directly under the TSP, the magnetic flux density is concentrated in the TSP due to its higher permeability. Accordingly, flaws directly under the TSP are difficult to be detected. In order to solve this problem, the principle that the magnetic flux density distribution around the TSP is uniform in the circumferential direction is used. When the magnetic flux density signals obtained at the position where the TSP is placed are set as reference signals and the signals obtained by rotating the sensor probe in the circumferential direction are compared with the reference signals, it is possible to detect the flaw signals from which the TSP signals are removed. If the flaw is formed in the circumferential direction, the flaw can be detected by moving the sensor probe in the axial direction and comparing the signals with the reference signals. The proposed method to detect flaws directly under the TSP was verified using an artificially flawed heat exchanger tube (HXT) test specimen made of titanium alloy.
Retrofitting Non-Ductile RC Frames for Seismic Resistance Using Post-Installed Shear Walls
Authors: Chiu Chien-Kuo , Hsiao Fu-Pei , Liao Wen-I , Quacoo Samuel Jonathan , Ho Chin-En , Gu Zi-En
Published: November 2019

Reinforced Concrete (RC) frame structures that were designed and built according to older standards can be damaged during destructive earthquakes as a result of insufficient lateral strength and/or deformation capacity. Such structures must be retrofitted to satisfy the current requirements and to survive future earthquakes. Owing to its high lateral strength and stiffness capacity of an RC wall, the post-installation of an RC wall in a non-ductile frame for retrofit is a widely used retrofitting technique. However, for frame structures with low-strength concrete, the typically used connected construction method on the interface between existing and new concrete may be not able to provide effective force transfer, and may cause unexpected brittle failure in the retrofitted structure. Such unexpected brittle failure may reduce the seismic capacity of the structure and threaten its safety. Therefore, in this experimental investigation, two retrofitting methods that use a post-installed RC wall are proposed to improve the load transfer mechanism on the interface. The first involves a wall with diagonal rebar and boundary spirals, and the second involves a wall with an additional inner frame. A typical traditional retrofitting specimen was constructed and tested for comparison. Reversed cyclic loading is used to test the seismic capacity of the specimens. Finally, post-embedded piezoceramic-based sensors were used to monitor the structural health and detect damage in one of specimens during the test. The experimental results demonstrate the effectiveness of the piezoceramic-based approach to structural health monitoring and the ability of the method to detect damage in shear governed RC structures under seismic loading.
Testing of a Non-Cylindrical Vacuum Vessel
Authors: Reich Alton , Chew Geoffrey , May Douglas
Published: November 2019

Most vacuum vessels are bodies of revolution that are cylindrical or spherical. A square vacuum vessel was developed for a specialized application that needed to be suitable for repeated, rapid sealing and unsealing, and operation at mild vacuum (∼0.5 bara). This paper discusses the challenges that we faced in fabrication and testing of the vacuum vessel. The vacuum vessel was initially tested in a test rig. A second set of challenges was encountered when the vessel was tested mounted in the system. It captures the lessons learned from fabrication, rework, and modifications that were necessary to get the vessel to pass leakage testing.
ASME XI–RSE-M: General Comparison of Flaw Evaluation Rules
Authors: Faidy Claude
Published: November 2019

After a short review of the 2 Codes in term of flaw evaluation, this paper will compare Scope, Standards, Methods, Material Properties, Structural Factors of 2 major International In-service Codes: ASME Boiler and Pressure Vessel Codes – Section XI – “Rules for In-service Inspection of Nuclear Facility Components”, 2017 Edition and RSE-M “In-Service Inspection Rules for Mechanical Components of PWR Nuclear Island”, 2017 Edition.

The cracked components are evaluated by dedicated engineering methods: comparison of fracture mechanic parameters (K/ Kcp, J, C*...) with material properties (toughness KIC, JIC, J resistance curve...) associated to structural factors for margins evaluation.

The comparison will consider mainly Appendices A, C of ASME Section XI and Appendix 5 of RSE-M (Appendices 5.0 to 5.8).

To conclude, the paper will discuss gaps, needs, ongoing and future developments of both Codes, like Warm-pre stressing, Master Curve, Leak Before Break....
Seismic Evaluation Methods for Fire Protection Sprinkler Piping Systems in Buildings
Authors: Lin Fan-Ru , Chai Juin-Fu , Tsai Yung-An , Yeh Chang-Chen , Chang Kuo-Chun
Published: November 2019

Based on recent earthquakes experiences in Taiwan, losses do not necessarily result from damages of building structures but non-structural components. For instance, the leakage of the fire protection sprinkler systems in hospitals during small earthquakes could results in shortage of medical function and fire protection, and malfunction and repairs of medical equipment. The break of sprinkler systems caused by strong earthquakes could even harm the life safety. Taking a medium-scale hospital as an example, this research aims to conduct a simplified seismic evaluation method to improve seismic performance of the fire protection sprinkler system in critical buildings. The content of this research is summarized below:

1. Numerical analysis of the sample sprinkler piping system: a detailed numerical model of the fire protection sprinkler system in the sample hospital was established with SAP2000 v.20 software. Proper parameters to simulate the threaded joint of piping and the gap between adjacent partition walls or ceiling systems were proposed and verified by the results of component tests and shaking table tests. Ambient vibration tests in the sample hospital were conducted with velocimeters to clarify the structural characteristics of the building structure and the sprinkler piping system.

2. Fragility analysis of sprinkler piping systems: seismic fragility curves the fire protection sprinkler system in the sample hospital were conducted according to a mount of detailed analysis results and verified by the real damage state under Jiaxian earthquake. The effects of engineering demand parameters and categories of ground motion on fragility results are discussed for three types of failure modes.

3. Simplified seismic evaluation method for sprinkler piping systems: according to the results of shaking table tests and detailed analysis, a reliable simplified evaluation method was established to predict seismic behavior of typical sprinkler piping systems in hospitals by the information obtained from in-situ survey. The conservative level and accuracy of simplified evaluation results were verified by comparing the results of fragility analysis of numerical model and simplified evaluation.
Temperature Dependence of Fatigue Crack Growth in Low-Carbon Steel Under Gaseous Hydrogen
Authors: Takakuwa Osamu , Ogawa Yuhei , Okazaki Saburo , Matsunaga Hisao , Matsuoka Saburo
Published: November 2019

In order to elucidate the temperature dependence of hydrogen-assisted fatigue crack growth (HAFCG), the fatigue crack growth (FCG) test was performed on low-carbon steel JIS-SM490B according to ASTM E647 using compact tension (CT) specimen under 0.7 MPa (≈ 0.1 ksi) hydrogen-gas at room temperature (RT: 298 K (≈ 77 °F)) and 423 K (≈ 302 °F) at stress intensity factor range of ΔK = 30 MPa m1/2 (≈ 27 ksi in1/2). Electron backscatter diffraction (EBSD) observation was performed on the mid-thick section of CT specimen in order to investigate change in plasticity around the crack wake in gaseous hydrogen environment and how it changes due to temperature elevation. The obtained results showed the higher temperature, the lower intense of HAFCG as reported in our previous article. Plasticity around the crack wake became less in gaseous hydrogen environment, especially tested at 298 K. The propensity of the results obtained at higher temperature (423 K) can be separated into two cases: (i) intense plasticity occurs like tested in air, (ii) crack propagates straighter accompanying less plasticity like tested in gaseous hydrogen environment at 298 K. This implies macroscopic FCG rate is determined by combination of microscopic FCG rate in the case (i) and case (ii).
Basic Design Rules for Lines in Pulsating Flow Service
Authors: Eijgenhuijsen Menno , Masand Girish
Published: November 2019

To avoid unacceptable vibration of suction and discharge piping for reciprocating pumps and compressors, acoustic and mechanical response analyses are to be carried out. These analyses are generally provided by the suppliers of such equipment. This paper explains the fundamentals behind an acoustic and mechanical response analysis and provides a simple set of consolidated design and engineering rules. The paper encourages application of these rules while developing the equipment and piping layout as well as pipe support configuration. The aim of these rules is to minimize the chance for the ultimate supplier’s detailed acoustic & mechanical response analysis to recommend significant changes to the design in a late stage of a project. Specific emphasis is placed on how the support stiffness affects the natural frequency of the piping system and a practical methodology is provided to account for this in pipe support span calculations. This paper also describes the process information that needs to be submitted to the supplier to conduct a meaningful acoustic as well as mechanical response analysis. Acknowledging requirements for lines in pulsating service at a late stage in the project, not providing the supplier with the required process information or a piping and support configuration that is not ‘mature’ enough will most likely result in significant delay and cost.
Vibration Assessment of Thermowells
Authors: Prasad Piyush , Poddar Sudhanshu , Casey Finlay
Published: November 2019

ASME PTC 19.3 2016 code does not provide clear guideline on how to deal with the vibration problems of existing thermowells that are currently in operation and may be operating near inline or transverse vibration zone.

While the code allows passing through the in-line vibration zone, it prohibits operation completely in transverse vibration due to lock-in phenomenon. Once lock-in occurs, the thermowell gets into resonance and in the absence of adequate damping in the system, the thermowell vibration amplitude would keep on building with every cycle till eventual failure. It was identified that several operating assets had thermowells operating in the prohibited zone as per ASME PTC 19.3 and were facing a greater process safety risk.

Damping though difficult to predict, plays very crucial role in amplitude when thermowell is operated in critical zone i.e. within 20% of natural frequency. Hence it is very important to estimate the damping factor. ASME PTC 19.3 2016 have suggested conservative damping factor (ζ) of 0.0005 based on the lab studies. The test set-up assumes the piping system as rigid component, whereas, in the field piping systems are flexible. Using a conservative damping in the stress calculations leads to a high fictitious stress indicating failure of the thermowell.

In the present paper, a method is suggested to quantify the damping in the system by utilizing actual site vibration measurement of thermowell in the finite element analysis and thus a more realistic assessment of the stresses in the thermowell can be made. This assessment presented a much larger damping present in the system than ASME suggested and led asset to continue operate the plant with no risk of unplanned downtime as well as technical integrity of equipment. The results are presented for one sample thermowells.
Various Strength Properties of Aluminum Alloys in High-Pressure Hydrogen Gas Environment
Authors: Matsuoka Saburo , Iijima Takashi , Yoshida Satoko , Yamabe Junichiro , Matsunaga Hisao
Published: November 2019

Three types of strength tests, slow strain rate tensile (SSRT), fatigue life, and fatigue crack growth (FCG) tests, were performed using six types of aluminum alloys, 5083-O, 6061-T6, 6066-T6, 7N01-T5, 7N01-T6, and 7075-T6, in air and 115 MPa hydrogen gas at room temperature. All the strength properties of every material were not deteriorated in 115 MPa hydrogen gas. In all the materials, FCG rates were lower in 115 MPa hydrogen gas than in air. This was considered to be due to a lack of water- or oxygen-adsorbed film at crack tip in hydrogen gas. In 5083-O, 6061-T6 and 6066-T6, relative reduction in area (RRA) were remarkably higher in 115 MPa hydrogen gas than in air. These differences were attributed to a hydrostatic pressure produced in 115 MPa hydrogen gas. In contrast, in 7N01-T5, 7N01-T6 and 7075-T6, the values of RRA in 115 MPa hydrogen gas were nearly the same as those in air. Observation of fractured specimens inferred that the degree of such a hydrogen-induced improvement was determined by the fracture mode (e.g. cup-and-cone or shear fracture), which is dominated by the microstructure morphology.
The Fundamental Mechanical Characteristics Evaluation for Bolted Pipe Flange Connections With RTJ Gaskets Under Internal Pressure
Authors: Nakade Kenshiro , Sato Koji , Sawa Toshiyuki
Published: November 2019

Bolted pipe flange connections with metallic flat gaskets or ring type joint (RTJ) gaskets are used under higher pressure and higher temperature. However, a sealing mechanism is not known and a design method is not established how to determine bolt preload for preventing leakage from the connection with metallic gaskets. In addition, the characteristics of the connection are not known when oval and octagonal gaskets are used. In previous paper, when the contact stress of metallic flat gasket reaches the stress at plastic deformation inflection point, the leak rate is decreased rapidly. However, the leak rate could be measured up to 1.0 × 10−5 Pa · m3/s level. The objectives of the paper are to measure the leak rate of the metallic flat gasket of which the contact stress is over the stress at plastic deformation inflection point, and to measure the leak rate of 1.0 × 10−9∼10 Pa · m3/s level in the flat metallic gasket in the platen tests and the connection with RTJ gaskets. In addition, the characteristics of the connection are examined when oval and octagonal gaskets are used. As a result, it is found that the leak rate for the metallic flat gasket can be measured around 1.0 × 10−9∼10 Pa · m3/s in the platen tests when the contact stress of aluminum gasket reaches the stress at plastic deformation inflection point and more while the leak rate of SUS 304 flat gasket is around 1.0 × 10−7∼8 Pa · m3/s even if the contact stress is over 1.3 times of the stress at plastic deformation inflection point. In addition, the sealing characteristics of the connection with oval gasket are shown to be better than that with octagonal gasket. From a laser microscope observation, it is found that the contact area of oval gasket in the connection is smaller than that of octagonal gasket in the connection.
The Variability in Weld Residual Stress
Authors: Cathcart H. , Horne G. , Moffat A.
Published: November 2019

Residual stresses resulting from welds are a key consideration in the design and assessment of piping and pressure vessels. As welding is a variable process, the resulting variability in weld residual stress should be accounted for in design and assessment. This paper investigates the variability in residual stress resulting from flux cored arc welds by performing residual stress measurements on a set of nominally identical welds between 25mm plates of grade DH36 steel. The welds were produced in two environments to assess the impact on residual stress variability: a well-controlled laboratory environment and a less controlled factory environment.

The results showed significant variability in the residual stresses between the welds, with standard deviations up to 25% of the peak value in some locations near the weld center. The welds were two sided and higher variability was measured in the side performed second, with the variability in heat applied appearing to be a key driver of the residual stress variability. A difference was observed between the standard deviations of residual stress in the factory and laboratory samples, with the laboratory samples showing less residual stress variability. Whilst the small number of samples measured prevents firm quantitative conclusions being drawn about the potential differences in residual stress variability between production environments the results do suggest that there is value in further study.
A Critical Review of Recent Fatigue Crack Growth Data in Relation to ASME Code Case N-809
Authors: Mann Jonathan , Currie Chris , Tice David , Platts Norman
Published: November 2019

ASME Code Case N-809 provides Fatigue Crack Growth (FCG) expressions for austenitic stainless steels operating in a primary water environment within a Pressurised Water Reactor (PWR). The code case currently contains different expressions for nominally low-carbon (304L, 316L) and conventional (304, 316) grades.

Since the original work that provided the technical basis for N-809 was completed, an increased amount of FCG data has become available through industry testing, particularly for low-carbon stainless steels. A large database is now available that contains significantly more data than the one used in the original development of the code case. The data cover a wider range of testing conditions (temperature, loading rate, and mean stress) and represent a more diverse population of material types, including multiple heats.

In this paper, the N-809 laws are re-analysed in terms of these new data, with a focus on each of the environmental dependencies that are currently included in the law. In particular, alternative R-ratio expressions from the literature are shown to provide an improved description of the effect of R-ratio for nominally low-carbon materials. The statistical distribution of FCG rates and the treatment of partially retarded data are also investigated as part of the derivation of revised descriptions of best-fit and bounding FCG rates.

The analysis highlights a small amount of potential non-conservatism in the current N-809 description of best-fit FCG rates at higher R-ratios. The current description of upper-bounding behaviour is shown to still be valid, however significant over-conservatism exists at lower R-ratios.
Level Three Assessment of Local Thin Areas in Pipelines Using Web-Enabled FEA
Authors: Brown Donald L. , Spring Daniel W. , Panzarella Charles
Published: November 2019

The fitness-for-service procedures for local thin areas in pipelines trade complexity for conservatism, with more complex procedures being less conservative. In this paper, we outline a procedure for automating the advanced Level 3 assessment procedure outlined in API 579-1/ASME FFS-1 for local thin areas. The outlined procedure is bundled into a web-enabled, industrial trade tool where the minimum data requirements are the same as those for a Level 2 assessment. The procedure can be applied to an entire in-line inspection scan of UT thickness readings and, after calculation, can identify hotspots of local damage. By reducing the inputs to those of a Level 2 assessment procedure, the Level 3 procedure presents as an attractive alternative to the current Level 2 approaches.
Investigation of the Seismic Risk of Industrial Pipe Rack - Piping Systems Accounting for Soil-Structure Interaction
Authors: Karagiannakis George , Di Sarno Luigi
Published: November 2019

Earthquake events have shown that industrial pipe racks lack of a completed design framework that encompasses contemporarily a number of uncertainties such as modelling, seismic action, design and analysis procedures as well as soil conditions. That being said, the seismic behaviour of piping systems has not been assessed up to par recognizing the potential effects of nonbuilding – nonstructural components interaction as well as soil conditions that constitute a decisive parameter particularly for structures that lie on alluvial deposits. In the present work, after reviewing European and American standards and technical literature upon design parameters, the seismic reliability analysis of two pipe rack – piping systems in decoupled and coupled case considering near- and far-field records as well as soil deformability is addressed. As it is illustrated, the classic nonlinear static analysis may overestimate the resistance of racks, common limit states of interstorey drift ratio cannot be applied and the behaviour factor selection may be unjustifiable. Also, soil-structure interaction affects detrimentally the response both of rack and piping system as depicted by the fragility functions.
Study on Active Vibration Control of Seismic Isolation Structure With Variable Gain Using Spectrum Monitoring
Authors: Fujiwara Ukyo , Miura Nanako , Sone Akira
Published: November 2019

In this research, the seismic isolation structure which can switch the active control gains by the characteristics of the earthquake is proposed. As the number of high-rise buildings in urban areas in has increased in recent years, damage due to long-period earthquakes is expected to increase. In this paper, the focus is on the area of velocity response spectrum as an index of long-period earthquake. Then we design the time varying weighting coefficient from the area of the velocity response spectrum obtained from the seismic wave. The long periodicity of the earthquake is judged from the area of the velocity response spectrum calculated from the seismic wave arriving from moment to moment. In addition, we aim to improve the performance of the control system by inputting appropriate control power. We also aimed for energy saving of control by not performing control input within the range where the earthquake does not have a long period. We proposed a method of switching control using time varying weighting factor, designed time varying weighting factor, and confirmed its effectiveness by performing time history response analysis on actual seismic waves.
Review of Ferrite Number (FN) Requirements and Proposed Changes to Code Case N-504-4 and Nonmandatory Appendix Q
Authors: McCracken Steven L. , Segletes David
Published: November 2019

ASME Section XI Nonmandatory Appendix Q and Code Case N-504-4 are routinely used to install full structural weld overlays in the nuclear power industry for repair or mitigation of stress corrosion cracking in austenitic stainless steel weldments. Both Appendix Q and N-504-4 specify a Ferrite Number (FN) and carbon content requirement for the stainless steel weld metal used for the weld overlay to ensure acceptable resistance to stress corrosion cracking. The Ferrite Number (FN) is used in the ASME Code for establishing the delta ferrite content in the deposited weld metal.

Field experience indicates there is often confusion and differing opinion concerning how the Ferrite Number and carbon content requirements of Appendix Q and N-504-4 are satisfied. This is in part due to unavailability of the original technical basis for these requirements. This paper provides a background for the delta ferrite and carbon content requirements, information on influence of delta ferrite and carbon content on stress corrosion cracking and U.S. Nuclear Regulatory Commission (NRC) guidance on the issue. Finally, this paper details a proposed revision of Nonmandatory Appendix Q and N-504-4 to clarify the FN and carbon content requirements.
A Unified Engineering Inelastic Model for 316H Stainless Steel
Authors: Phan V.-T. , Messner M. C. , Sham T.-L.
Published: November 2019

Section III, Division 5 of the ASME Boiler & Pressure Vessel Code provides rules for designing high temperature nuclear components using inelastic analysis. However, the current Code does not provide guidance on suitable inelastic constitutive models to use with this design method nor does it provide Code qualified constitutive models for any of the high temperature Class A materials. This paper describes the development of an inelastic constitutive model for 316H steel, suitable for use with the Division 5 design procedures. The model captures the average response of all Code permissible 316 material as described by a large set of experimental data collected from the literature. The model uses a unified model to describe creep and rate dependent plasticity at high temperature that accounts for the experimentally-observed coupling of these deformation mechanisms. The goal is to incorporate the inelastic model developed here for 316H along with similar models for the other Class A, high temperature materials into Section III, Division 5 to facilitate the use of the design by inelastic analysis method.
Study of the Fracture Toughness in Electron Beam Welds
Authors: Mokhtarishirazabad Mehdi , Simpson Chris , Horne Graeme , Kabra Saurabh , Truman Chris , Moffat Andrew , Mostafavi Mahmoud
Published: November 2019

High energy welding technologies, such as electron beam, have a number of potential benefits including: faster process time, smaller heat affected zone and potentially favourable weld residual stresses. Therefore, they are good candidates for manufacturing complex components for the next generation of nuclear power plants. However, before electron beam can be deployed on a wide scale, further work is required in a number of areas, including how these welds are treated in structural integrity assessments. As an example, the full extent of the effects of complex residual stress (RS) fields, arising from high energy welding technology, on the fracture behaviour of components has not been fully investigated. This understanding is essential for defect tolerance calculations using integrity assessment procedures. In this study, the fracture toughness of austenitic stainless steel 316L plates with various thicknesses (6mm to 25mm), joined by electron beam welding, is evaluated. Residual stresses were measured using non-destructive diffraction and mechanical relief methods (contour method). This is to examine the effect of welding residual stresses on the resistance of the welded component to fracture.
Impact of Including Spiral Wound Bead Width in Gasket Area
Authors: Worden Kathryn , Ruffin Mark
Published: November 2019

Bolted joint and gasket designers currently calculate spiral wound gasket stress in one of three ways. The differences lie in gasket area determination. The first is the historical Boiler & Pressure Vessel Code calculation method of using an effective sealing width which is half or less of the full dimensional width. Found to be inadequate for creating consistently acceptable sealing performance, those promoting and affecting lower leaks rates and emissions opt to use a gasket’s full width to determine gasket area and stress.

The full width of a spiral wound gasket is currently being determined in two different ways among industry participants. Most use the dimensioned outer diameter which includes the bead of winding wire that does not contact the flange surface. Some exclude the width of the bead. Inclusion or exclusion of the bead has a significant impact on gasket seating stress for sealing elements of narrow width as the width of the bead represents a large percentage of the overall dimensions.

In this paper, all three methods will be discussed focusing on gasket stresses for NPS calculated from the preferred method of full width comparing the inclusion and exclusion of the bead width.
TDFAD Analysis of Creep Crack Initiation in 0.5CMV/2.25CrMoV Steel Weldments
Authors: Ejaz M. , Davies C. M.
Published: November 2019

The time dependent failure assessment diagram (TDFAD) is a convenient methodology to simultaneously assess whether a component is likely to fail by brittle, ductile or creep fracture, plastic collapse or creep rupture. In this work, creep toughness data, Kmatc, have been derived from experimental creep crack growth (CCG) tests on compact tension fracture mechanics specimens made of a weldment consisting of 0.5CMV parent material, 2.25CrMo, where the starter crack was located in the heat affected zone (HAZ). Time dependent failure assessment diagrams (TDFADs) are then constructed for each material condition and creep crack initiation (CCI) time predictions were obtained for the CCG tests performed on the weldment samples using both a TDFAD based on either parent and weld material data. The TDFAD based on the weld data provided the most conservative prediction of CCI times thus is recommended for use for weldment samples.
Inclined Surge Line Design Considerations for Analysis and Monitoring
Authors: Oakman Jamie , Gray Mark , Leber Benjamin , Salac Matthew
Published: November 2019

Thermal stratification can occur in pressurizer surge lines when flow rates are low and large temperature differences between the pressurizer fluid and reactor coolant loop fluid exist. NRC Bulletin 88-11 requires that utilities address this issue with respect to the licensing basis. Additionally, significant fatigue usage can develop due to insurges and outsurges from the pressurizer that occur when the temperature difference (ΔT) is large. An important aspect of the surge line fatigue analysis is determination of global pipe moment loads due to insurges, outsurges, and related stratification effects.

The Westinghouse AP1000® plant surge line is designed to limit the global effects of stratification using a surge line geometry that is inclined more than that of the previous generation plants. However, this design provides unique challenges to the analytical solution in comparison to the mostly horizontal geometries in previous PWR designs. The main challenge is due to the location of the stratified fluid hot/cold interface. The horizontal geometry has historically allowed conservative (based on analytical testing) treatment of the stratified interface profile. The inclined geometry requires consideration of positional changes, as the stratified interface moves through the line due to flow changes. Because of this, iterative calculations were required to predict global piping moment loads through the transient histories based on the movement of the stratified interface. Software was developed to solve a series of correlative equations representing moment loads due to pipe temperatures and stratification ΔT within discretized portions of the surge line throughout each transient. The correlative equations, which are based on the matrix solution of piping analysis load cases, predict the global pipe moment loads to a high degree of precision.

The surge line is also a significant location in the online fatigue monitoring program implemented at the sites. The complexity of the design analysis that is reflected in the monitoring model requires a more detailed accounting for the location of the stratification interface, the effect on prediction of moment loadings for controlling locations, and the effect on local stresses at the monitoring locations. This paper describes the approach used to address all of these factors in the design evaluation and subsequent fatigue monitoring application.
Further Work on Analyzing Accuracy and Overall Performance of Torque Tools for Assembling Bolted Flanged Joints
Authors: Rodery Clay D. , Hamilton Scott , Ferguson Neil
Published: November 2019

Over the past two years, the accuracy and repeatability of equipment used to assemble bolted flanged joints have been studied, and progress has been reported in past papers. One of the findings has been that pneumatic torque wrenches demonstrated a broader plus/minus range on bolt stress from the targeted value (e.g., lack of accuracy) than manual or hydraulic torque wrenches. What was notable, however, was that the repeatability of the bolt stress that was achieved did remain consistent with the other types of torque wrenches. Since the repeatability has been shown to be consistent, attention has turned to investigating and determining the reason for the perceived lack of accuracy. One aspect that might account for this is the calibration of the pneumatic torque wrenches.

This paper outlines and documents the research that has recently taken place to identify the parameters that are key elements in improving the accuracy of pneumatic torque wrenches that might form the basis of development of a standard for calibration of powered torqueing equipment.
Study of Simplified Assembly Patterns With Load-Based Feedback and Preemptive Elastic Interaction Compensation
Authors: Richardson Jordan
Published: November 2019

A total of 12 flange assemblies, spanning both class 300 and 600 were instrumented with ultrasonic transducers and observed following differing assembly patterns to gain insight into the BFJ elastic interactions. Each flange assembly was additionally tested to multiple load targets to monitor the overall sensitivity of interaction to load. Analytical work following the data collection led to the development of a simplified installation method and sequencing that dramatically reduces the work effort required to effectively close a joint while being independent of fastener condition or tool selection. The range of validity for the simplified method is further extended with linear multivariate solving techniques and accelerated joint “snugging” to promote joint stiffness. Limits on the acceptable load achievement was set to < 5% error on the average load and < 10% normalized standard deviation to be considered acceptable when targeting Appendix-O calculated loads of ASME PCC-1. Validation of the proposed method was undertaken by the University of Houston at the Bechtel WATC facility with support of Carber Engineering which included full size pressure testing following joint assembly. The observations made from the 60+ full size trials then served to validate FEA work towards the analysis of the remaining sizes of class 300/600 from 4″ to 24″.