bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study on the Effect of Non-Idealized Crack on a 90° Elbow by Using Finite Element Analysis
Authors: Kim Jae-Hee , Kim Min-Kyu , Choi Ye-Rin , Cho Doo-Ho , Kim Moon Ki , Choi Jae-Boong
Published: October 2018

The present paper proposed the modified limit load solution related to code case N-513-4 which is currently actively researched. To apply to assessment method for an elbow in code case N-513-4, the crack should be postulated as the idealized circumferential through-wall crack (TWC). For this reason, it could be led to overestimate the results due to the assumption of real crack shape. Then, the many research which is related to an accurate solution for a straight pipe by considering realistic crack has been investigated. However, the accurate solution for the elbow with non-idealized TWC is still lacked. Therefore, based on three-dimensional finite element model, the effect of non-idealized circumferential TWC on plastic limit load was investigated under internal pressure. To do this, the finite element (FE) model and analysis procedure employed in the present numerical study were validated by comparing the present finite element analyses result with existing solutions for idealized TWC in the elbow. Then, the correction factor for calculating plastic limit load was newly proposed as a tabulated form by considering practical ranges of geometry.
Importance of Connections in High-Pressure Barricade Design
Authors: Kostecki Jodi , Edel Matthew , Montoya John
Published: October 2018

High pressure testing and operation of industrial tools and equipment can be hazardous to personnel and property in the event of an accidental mechanical failure or release of contained pressure. Hazard barricades are commonly installed around equipment to protect nearby personnel or property from projectile impacts or overpressure. The ASME Standard PCC-2 “Repair of Pressure Equipment and Piping” allows the use of hazard barricades for this purpose when a safe standoff distance cannot be satisfied, but it currently provides minimal guidance for engineered design. Other references provide guidance for preventing projectile perforation of a barricade. While perforation prevention is a key component of shield design, properly anchoring a shield and inter-connecting the shield components will make the difference between an effective barricade application and a barrier that could potentially compound the consequences of an accidental failure.

This paper investigates the importance of engineered structural connections and consideration of global structural response in the design of protective barricades. The structural models focus on impact loading of steel plates and bolted connections, and the results are directly compared to test results in terms of effective barrier response.
Effects of Non-Normal Input Distributions and Sampling Region on Monte Carlo Results
Authors: Tsembelis Konstantinos , Eom Seyun , Jin John , Cole Christopher
Published: October 2018

In order to address the risks associated with the operation of ageing pressure boundary components, many assessments incorporate probabilistic analysis tools for alleviating excessive conservatism of deterministic methodologies. In general, deterministic techniques utilize conservative bounding values for all critical parameters. Recently, various Probabilistic Fracture Mechanics (PFM) codes have been employed to identify governing parameters which could affect licensing basis margins of pressure retaining components. Moreover, these codes are used to calculate a probability of failure in order to estimate potential risks under operating and design loading conditions for the pressure retaining components experiencing plausible and active degradation mechanisms.

Probabilistic approaches typically invoke the Monte-Carlo (MC) method where a set of critical input variables are randomly distributed and inserted in deterministic computer models. Estimates of results from probabilistic assessments are then compared against various assessment criteria.

During the PVP-2016 conference, we investigated the assumption of normality of the Monte Carlo results utilizing a non-linear system function. In this paper, we extend the study by employing non-normal input distributions and investigating the effects of sampling region on the system function.
Hydrogen-Assisted Fatigue Crack Propagation in a Commercially Pure BCC Iron
Authors: Birenis Domas , Ogawa Yuhei , Matsunaga Hisao , Takakuwa Osamu , Yamabe Junichiro , Prytz Øystein , Thøgersen Annett
Published: October 2018

Hydrogen effect on fatigue performance of commercially pure BCC iron has been studied with a combination of various electron microscopy techniques. The fatigue crack growth (FCG) in gaseous hydrogen was found to consist of two regimes corresponding to a slightly accelerated regime at relatively low stress intensity factor range, ΔK, (Stage I) and the highly accelerated regime at relatively high ΔK (Stage II). These regimes were manifested by the intergranular and quasicleavage types of fractures respectively. Scanning electron microscopy (SEM) observations demonstrated an increase in plastic deformation around the crack wake in the Stage I, but considerably lower amount of plasticity around the crack path in the Stage II. Transmission electron microscopy (TEM) results identified dislocation cell structure immediately beneath the fracture surface of the Stage I sample, and dislocation tangles in the Stage II sample corresponding to fracture at high and low plastic strain amplitudes respectively.
Establishing Fracture Mechanics Based Minimum Allowable Temperatures for Low Temperature Applications of ASME B31.3 Piping
Authors: Kummari Seetha Ramudu , Macejko Brian , Shipley Kraig S. , Prueter Phillip E. , Evans Geoff , Jamal Nijat
Published: October 2018

Impact test exemption curves in ASME B31.3 [1] were adopted from ASME Section VIII Division 1 (VIII-1) [2] with subtle modifications. The VIII-1 exemption curves were generated based on early fracture mechanics methodologies and limited amount of test data with an assumption on maximum applied stress intended to correspond to the typical VIII-1 allowable stress criteria. The applicability of the exemption curves for low temperature applications of ASME B31.3 piping (such as blowdown events) is open to discussion because of potentially high longitudinal thermal expansion stresses that may exceed the VIII-1 allowable stress criteria. Additionally, unlike in VIII-1 and ASME Section VIII Division 2 (VIII-2) [3], there is no post weld heat treatment (PWHT) credit on Minimum Design Metal Temperature (MDMT) in ASME B31.3. Detailed fracture mechanics analyses have shown that PWHT can significantly reduce the risk of brittle fracture failures due to its relaxation effect on weld residual stresses, a major crack driving force.

In this paper, a fracture mechanics-based methodology for establishing Minimum Allowable Temperatures (MAT) for low temperature applications of ASME B31.3 piping is presented. A state-of-the-art fracture mechanics methodology published in Welding Research Council (WRC) Bulletin 562 [4] is used to develop step-by-step Level 1 and Level 2 procedures for establishing MAT for low temperature applications of ASME B31.3 piping. For the Level 1 methodology, MAT screening curves are developed based on a likely conservative assumption that the stresses in the piping component are at the maximum code allowable stresses in both the hoop and longitudinal directions. For the Level 2 methodology, stress ratio verses temperature reduction curves are developed to consider the effect of lower operating stresses. Similar to VIII-2 [3] toughness exemption curves, the screening curves are generated for both As-Welded and PWHT conditions. The curves can also be used for impact tested materials. The established MAT can be directly coupled to different reference flaw sizes and integrated with an inspection criteria for piping components. Two examples of establishing MAT using both the proposed Level 1 and Level 2 methodologies are presented herein.
Failure Analysis of a High Pressure Air Cooled Heat Exchanger
Authors: Volfson Boris
Published: October 2018

The paper examines the causes of failure, which led to a major burst and a fire incident in a high pressure box-type air cooled heat exchanger. The material of the header boxes was duplex steel SA-240 S32205/S31803. Design pressure – 20.8 MPa. The strength calculation was performed in accordance with ASME Section VIII Division 1, Appendix 13. Following on from the results of numerical calculations, examination and testing of samples, cut from the header boxes elements, the study demonstrates that the failure was due to the design and calculation errors, caused by the lack of precision in the ASME Section VIII Division 1, defective workmanship, and an inadequate control. The paper discusses additional requirements, which allow to avoid such failures for the future.
Effect of Constraint Induced by Specimen Geometries on Crack Growth Behavior Under Creep-Fatigue Interaction
Authors: Zhao Lei , Xu Lianyong
Published: October 2018

Creep-fatigue interaction would accelerate the crack growth behaviour and change the crack growth mode, which is different from that presenting in pure creep or fatigue regimes. In addition, the constraint ahead of crack tip affects the relationship between crack growth rate and fracture mechanics and thus affects the accuracy of the life prediction for high-temperature components containing defects. In this study, to reveal the role of constraint caused by various specimen geometries in the creep-fatigue regime, five different types of cracked specimens (including C-ring in tension CST, compact tension CT, single notch tension SENT, single notch bend SENB, middle tension MT) were employed. The crack growth and damage evolution behaviours were simulated using finite element method based on a non-linear creep-fatigue interaction damage model considering creep damage, fatigue damage and interaction damage. The expression of (Ct)avg for different specimen geometries were given. Then, the variation of crack growth behaviour with various specimen geometries under creep-fatigue conditions were analysed. CT and CST showed the highest crack growth rates, which were ten times as the lowest crack growth rates in MT. This revealed that distinctions in specimen geometry influenced the in-plane constraint level ahead of crack tip. Furthermore, a load-independent constraint parameter Q* was introduced to correlate the crack growth rate. The sequence of crack growth rate at a given value of (Ct)avg was same to the reduction of Q*, which shown a linear relation in log-log curve.
Anisotropic Materials Use in the ASME Boiler and Pressure Vessel Code
Authors: Cameron Jay
Published: October 2018

Very few materials have all their properties behave the same in all orientations of the material. The term for this behavior is anisotropy or anisotropic properties. The properties that are affected and the degree of anisotropy they exhibit, depend on the material family, the alloy, and the processing of the material. This paper will only discuss metals, and limited to those metal specifications adopted in the ASME Boiler & Pressure Vessel Code (B&PVC) Section II, Parts A and B.

The anisotropic properties of plate have been well recognized explicitly and implicitly in the B&PVC for a very long time. At issue, and the specific focus of this paper, is another wrought product form: bars. Bar, specifically round bar — also called rod, is a very useful starting material to manufacture pressure parts. The bar can be stocked at the largest feasible diameter and length, and then cost-effectively machined to whatever diameter and length is desired for the part. Due to the anisotropic properties of bar, there is a need for understanding and setting limitations for the use of such material in the B&PVC. This paper will explore the past history, current status and future directions of the Code requirements for bar.
Numerical Analysis of Bolt Elastic Interaction in Non-Gasketed Flange
Authors: Zhang Wei , Ye Yongsong , Chen Dean , Han Qingkai , Ma Yue
Published: October 2018

The joint of low pressure shaft in turbofan engine is a typical non-gasketed flange connection structure, which requires the uniform preload distribution due to high performance. But in the process of tightening, because of bolt elastic interaction, the final preload distribution could be varied. The face runout of contact surface changed the properties of the elastic interaction, which proposed new requirements of non-gasketed flange research. Thus the two bolts flange FEA model was developed to focus on the effect of bolt space, tightening step and face runout on preload change rate with actual contact. The six bolts flange FEA model was developed to make a comparison between ideal contact and actual contact. The bolt elastic interaction of actual contact was proposed, which provide the final preload distribution of different tightening patterns. And then the effect of tightening start position on final preload distribution was discussed, which could provide theoretical basis for non-gasketed joint assembly.
Determination of Residual Stress Directionality by Instrumented Indentation Testing Using Anisotropic Indenter
Authors: Choi Sungki , Kim Jong Hyoung , Lee Jun Sang , Lee Kyungyul , Choi Min-Jae , Ahn HeeJun , Kwon Dongil
Published: October 2018

Residual stress is a major factor in failure and fracture in structures or electronic components. Various testing methods are used to measure residual stress: there are saw-cutting, holedrilling, X-ray diffraction and layer-removing methods. In particular, instrumented indentation testing (IIT) has many advantages: it is a simple and non-destructive procedure that can be used for in-field testing.

In previous research, we proposed an algorithm for evaluating the magnitude and directionality of residual stress using an asymmetric Knoop indenter with long and short axes in the ratio 7.11:1. Indenting in different directions with a Knoop indenter creates different indentation load-depth curves depending on the residual stress state. In addition, the directionality of the residual stress can be expressed as a function of the load difference ratio calculated from these load-depth curves.

However, When the Knoop indentation test is performed at small indentation depths, experimental issues such as surface preparation or indentation normality can become significant as the load difference decreases. In order to solve these issues, we introduce a wedge indenter, that makes it possible to select the edge length independent of indentation depth. We can thus decrease indent size when working in a small testing area. The load difference between the stress-free and stressed state is related to the sensitivity of residual stresses, and a wedge indenter can maximize the sensitivity to residual stress. In this study, we suggest a way to use the wedge indenter and verify the model using cruciform bending specimens and finite element analysis.
Stud Bolt Thread Engagement: Implications of Applying New Construction Requirements in Post Construction Scenarios
Authors: Rodery Clay D.
Published: October 2018

In its 2016 Edition, ASME B31.3 [1] removed its long held provision for thread engagement that deemed the lack of complete engagement acceptable if the lack of engagement is not more than one thread. This change can have implications on existing piping assemblies which prompted some clarifications in ASME PCC-1 [2].

This paper reviews some of the reasons for the change, the issues around determining a specific measurable criterion of an acceptable amount of thread engagement, and proposes alternate criteria for the new construction codes to consider that are easily measurable and enforceable.
Effects of Strain Amplitude and Loading Path on Cyclic Behavior and Martensitic Transformation of 304 Stainless Steel
Authors: Li Yajing , Yu Dunji , Chen Xu
Published: October 2018

Effects of strain amplitude and loading path on cyclic deformation behavior and martensitic transformation of 304 stainless steel were experimentally investigated at room temperature. Series of symmetrical strain-control low cycle fatigue tests with strain amplitude ranging from 0.4% to 1.0% and various loading paths (uniaxial, torsional, proportional, rhombus, square and circular) with the same equivalent strain amplitude of 0.5% were carried out. Three-stage cyclic deformation behavior containing initial hardening, cyclic softening or saturation, and secondary hardening as well as near-linear relationship between α’-martensite content and number of cycles was observed during the whole life regime as for each test. Besides, a nearly linear relation between peak stress and α’-martensite content was found during secondary hardening stage. Furthermore, higher strain amplitude or non-proportionality of loading path resulted in higher cyclic stress response and α’-martensite content growth rate, defined by the slope of curves of α’-martensite content versus number of cycles.
Microstructure-Property Relationships in Powder Bed Fusion of Type 304L Austenitic Stainless Steel
Authors: San Marchi Chris , Sugar Joshua D. , Smith Thale R. , Balch Dorian K.
Published: October 2018

Additive manufacturing (AM) includes a diverse suite of innovative manufacturing processes for producing near-net shape metallic components, typically from powder or wire. Reported mechanical properties of materials produced by these processes varies significantly and can usually be correlated with the relative porosity in the materials. In this study, relatively simple test components were manufactured from type 304L austenitic stainless steel by powder bed fusion (PBF). The quality of the components depends on a host of manufacturing parameters as well as the characteristics of the feedstock. In this study, the focus is the bulk material response. Tensile properties are reported for PBF type 304L produced in similar build geometries on two different machines with independent operators. Additionally, the effect of hydrogen on the tensile properties of the AM materials is evaluated. The goal of this study is to provide a benchmark for tensile properties of PBF 304L material in the context of wrought type 304L, and to make a preliminary assessment of the effects of hydrogen on tensile properties.
Case Studies on the Use of Thermal-Mechanical Finite Element Analysis to Evaluate Weld Ring Gasket and Diaphragm Seal Designs
Authors: Prueter Phillip E. , Davis Robert C. , Rodery Clay D. , McJones Stephen F. , Brodzinski Richard P. , Havekost Josh , Feddeler Daniel E.
Published: October 2018

Weld ring type gaskets are relatively common in the refining and petrochemical industries. These gasket configurations usually consist of two steel rings, fillet-welded to each of the mating flanges with another seal weld between the lips of the two rings. These seal welds or lip seals are sometimes prone to in-service cracking that can eventually lead to leakage and costly equipment downtime. One particular design feature that can significantly influence the propensity for leakage is the shape of the weld rings; flat-lip weld rings or hollow-lip (Omega-seal) weld rings are the two most commonly used designs. The hollow-lip designs inherently offer more flexibility and can generally accommodate more differential radial thermal expansion between mating flanges.

This paper highlights a case study of a high-pressure heat exchanger where the shell side-to-tube side girth flange joint is fitted with a weld ring gasket configuration. Comparisons are made using detailed finite element analysis (FEA) that include bolt pretension and pressure-temperature loading. Sensitivity to lip seal design, temperature profile, and assumed friction coefficient between seating surfaces is also investigated. Furthermore, general commentary on flat and hollow lip weld ring gasket geometries is provided with design recommendations for different applications. In summary, the flat-lip seal weld experiences high shear stress, even with small amounts of differential temperature between flanges, which makes it prone to cracking. The added compliance of the hollow-lip seal design can minimize stresses in the seal weld, but understanding operating temperature differentials between mating flanges represents a key aspect of ensuring leak-free operation. The design of a diaphragm seal on a flat heat exchanger channel cover is also evaluated using FEA techniques, with sensitivity analysis on the size of the external fillet weld and diaphragm material specification. The analysis techniques presented in this paper offer valuable insight into establishing damage tolerant weld ring gasket and diaphragm seal designs to minimize the potential for leakage and to optimize critical gasket and bolting parameters.
Novel Use of Electromagnetic-Sensitive Nano-Additives to Develop Reversible Hot-Melt Adhesives
Authors: Brunella Valentina , Spezzati Giulia , Koricho Ermias Gebrekidan , Belingardi Giovanni , Martorana Brunetto , Bondji Ngabang Fabrice , Simioli Marco
Published: October 2018

The paper describes the use of electromagnetic-sensitive nano-particle additive for developing a reversible hot-melt adhesive for structural applications. A prototype of a lower tail gate has been manufactured by means of this innovative technology to demonstrate the potential for joining plastic components in automotive and aerospace applications. Monitoring of nanoparticles release during preparation of modified adhesives shows very low environmental impact if the mixing process is performed under a fume hood. The innovative electromagnetic bonding process can provide to the manufacturing industry new opportunities in terms of simplification of productive lay-out, more flexible design and process rapidity, in addition to significant economic benefit. The reversibility of the process would also increase the chances for part reuse and/or recycling that would otherwise be discarded.
Hardness and Microstructural Evolution of a JRQ A533 Cl.1 Steel Submitted to Thermal Annealing
Authors: Medina-Almazán A. Liliana , Ovando-Ramírez Lizandra S. , Hernández-Callejas Rogelio , Galicia-Aguilar Gonzalo
Published: October 2018

RPV steels are industrial alloys with very complicated microstructures. The characterization of the evolution of microstructural features that can affect the hardness of this type of steel can provide information on parameters that may be considered for modeling the mechanical behavior of these materials. Thermal aging at temperatures higher than the operating temperatures of nuclear reactors may provide some information that could be related to enhanced diffusion irradiation effects. Thermal aging may also provide data about the evolution of RPV steels submitted to heat treatment within the temperature domain proposed for RPV thermal annealing. We present the results of heat treatments (450°C, 500°C, and 550°C) carried out on samples of an A533B Cl.1 (JRQ) steel up to 1000 h. JRQ steel has a heterogeneous microstructure, with well-separated ferrite and bainite islands observed at high magnification. The thermal aging of JRQ steel at 450°C, 500°C, and 550°C promoted an increase in hardness in both bainite and ferrite, with the increase more significant in bainite than in ferrite. For the thermal treatment at 550°C, a maximum of the density of precipitates (per μm2) in the treatments was observed over a period of 500 h. This coincides with the depletion of the alloying elements in the bainite matrix and a decrease of HV in bainite. Copper-rich nanoprecipitates (< 6 nm in size) were observed in the samples treated at 550°C for 500 and 1000 h. The Cu content in the nanoprecipitates increases with aging time. Finally, the HV of the samples treated at 550°C for up to 500 h is a function of the Geometrically Necessary Dislocation (GND) density, which was obtained from EBSD cartographies. GND density is at the same time a function of the density of the precipitates (40–300 nm in size).
Modeling of Crack Extensions in Arc-Shaped Specimens of Hydrogen-Charged Austenitic Stainless Steels Using Cohesive Zone Model
Authors: Wu Shengjia , Sung Shin-Jang , Pan Jwo , Lam Poh-Sang , Morgan Michael J. , Korinko Paul S.
Published: October 2018

Crack extensions in arc-shaped specimens of hydrogen-charged and as-received conventionally forged (CF) 21-6-9 austenitic stainless steels are investigated by two-dimensional finite element analyses with the cohesive zone model. The material constitutive relation is first obtained from fitting the experimental tensile stress-strain data by conducting an axisymmetric finite element analysis of a round bar tensile specimen of the as-received CF steel. The material constitutive relation for the hydrogen-charged CF steel is estimated based on the experimental tensile stress-strain data of the as-received CF steel and the hydrogen-charged high-energy-rate-forged (HERF) 21-6-9 stainless steel. The cohesive zone model with the exponential traction-separation law is then adopted to simulate crack extensions in arc-shaped specimens of the hydrogen-charged and as-received CF steels. The cohesive strength of the cohesive zone model is calibrated to match the experimental load-displacement curve with the cohesive energy determined by the J-integral at the maximum load of the arc-shaped specimen. The computational results showed that the numerical predictions of the load-displacement and crack extension-displacement curves for the hydrogen-charged and as-received CF steel specimens are compared reasonably well with the experimental data.
A Thermomechanical PWR Test Facility to Investigate Thermal Shock Loading on a Small Scale Tubular Specimen
Authors: Gill Peter , Platts Norman , Currie Chris , Grieveson Eleanor
Published: October 2018

Pressurized water reactor environments are known to reduce the fatigue life of austenitic stainless steel components when compared to air environments. Laboratory testing has provided a means of quantifying this, allowing conservative plant assessments to be made. The majority of this testing has been isothermal and carried out on membrane loaded hollow or solid specimens. The geometry and loading of laboratory test specimens is significantly different to that experienced on plant, where complex strain waveforms are generally out of phase with temperature changes, and significant through wall strain gradients may be present. To address the issue of realistic loading, a test facility has been developed which can simulate thermal shock loading on a tubular specimen.

The capability of the test facility was presented at the PVP2016 conference [PVP2016-63161]. Since then the facility has evolved, with modifications made to the rig configuration and specimen geometry in order to maximize the strain amplitude from the thermal shock, including the adoption of an annular flow geometry. These modifications were designed to optimize both the heat transfer coefficient and the speed of cycling between hot and cold water in order to induce a thermal strain that can cause mechanical failure within practicable test durations. In order to calculate the magnitude of the thermal strain, detailed calculations were required both in terms of thermal hydraulics as well as stress analyses. The latest stress analysis has been combined with state of the art life prediction models to estimate the time for crack initiation.

This paper presents the results of the latest stress analysis and life prediction, including the derivation of the heat transfer coefficient for an annular flow region. The life prediction method uses best estimate strain-temperature histories from elastic-plastic finite element analysis (FEA). Heat-specific material properties have been developed during accompanying tests within the same experimental programme, and have been applied to enable cyclic hardening to be taken into account. The comparison of the prediction to an on-going test is also discussed.
Williams-Wittrick Approach Application for an Effective Search for Natural Vibration Frequencies of Pipeline Systems With Fluid-Structure Interaction
Authors: Orynyak Igor , Batura Anatolii , Dubyk Yaroslav
Published: October 2018

The approach for quick and effective search of natural vibration frequencies of multibranched beam systems with distributed mass, developed by F.W. Williams and W.H. Wittrick, is adopted for complex pipe systems with fluid-structure interaction. The general principle of the matrix composition is formulated for the case of beam systems of arbitrary complexity. The flexibility of such principle allows to extend it and to take into account the fluid free vibration. The special approach is developed to consider the fluid boundary conditions at the ends of the pipeline and a volumetric balance equation in the junctions. The formulated methods are implemented in an effective calculation procedure for the search of natural frequencies of coupled vibrations of the system with fluid-structure interaction, i.e. taking into account junction coupling as well as Poisson coupling. The procedure accuracy is demonstrated for a number of comparison examples.
Cyclic, Monotonic and Fatigue Performance of Stabilized Stainless Steel in PWR Water and Research Laboratory
Authors: Solin Jussi , Alhainen Jouni , Seppänen Tommi , Karabaki H. Ertugrul , Mayinger Wolfgang
Published: October 2018

Strain controlled LCF testing extended to 10 million cycles revealed an abrupt endurance limit enforced by secondary hardening. In elevated temperatures the ε-N curve is rotated and endurance limit is lowered, but not vanished. When very low strain rates are applied at 325°C in simulated PWR environment, fatigue life is reduced, but far less than predicted according to NUREG/CR-6909. It is possible, but not probable that the difference is due to different stainless grades studied. We assume that the test method plays a more important role.

We have repeatedly demonstrated in different tests campaigns that interruptions of straining with holds aiming to simulate steady state normal operation between fatigue relevant cycles can notably extend the fatigue endurance. Further proof is again presented in this paper. The suspected explanation is prevention of strain localization within the material microstructure and also in geometric strain concentrations. This actually suggests, that hold effects should be even more pronounced in real components.

Cyclic behavior of austenitic steels is very complex. Transferability of laboratory data to NPP operational conditions depends on test environment, temperature, strain rate and holds in many ways not considered in current fatigue assessment procedures. In addition to penalty factors, also bonus factors are needed to improve transferability. Furthermore, it seems that the load carrying capacity of fatigued stainless steel is not compromised before the crack growth phase. Tensile tests performed after fatigue tests interrupted shortly before end-of-life condition in 325°C (N ≈ 0.85 × N25) showed strength and ductility almost identical to virgin material.

This paper provides new experimental results and discusses previous observations aiming to sum up a state of the art in fatigue performance of German NPP primary loop materials.
Hidden Roles of Time and Temperature in Cyclic Behavior of Stainless Nuclear Piping
Authors: Solin Jussi , Seppänen Tommi , Mayinger Wolfgang , Karabaki H. Ertugrul
Published: October 2018

Unexpected findings on time and temperature dependent behavior have been recorded during our research on fatigue performance of niobium stabilized stainless steel.

Cyclic straining at 325°C and low strain rates resulted in higher stress responses than in higher rate tests. This effect is particular strong in PWR water environment. Subsurface bulk effect in environment is in contrast to the assumption on similar responses in air and environment, which is the foundation of the ‘companion specimen’ method where the strain in environment is measured from a parallel specimen similarly tested in air.

Our data shows that environmental effects caused by PWR water cannot be isolated as a separate issue. Environment, temperature and strain rate are factors, which interactively affect the cyclic response and fatigue performance of stainless steel in relevant temperatures and loading conditions.

The current ASME Code Section III design curve is based on different translation of the laboratory data than that made by Langer et al. The resulting effect is not as radical as caused by replacement of the original test data to a new highly scattered data base. But also the procedural changes have detectable effects and open a door for a provocative question:

“is the design curve still compatible with the code?”
Definition of Fatigue Crack Growth Thresholds for Ferritic Steels in Fitness-for-Service Codes
Authors: Hasegawa Kunio , Strnadel Bohumir
Published: October 2018

Fatigue crack growth rates are expressed as a function of the stress intensity factor ranges. The fatigue crack growth thresholds are important characteristics of fatigue crack growth assessment for the integrity of structural components. Almost all materials used in these fatigue tests are ferritic steels. As a result, the reference fatigue crack growth rates and the fatigue crack growth thresholds for ferritic steels were established as rules and they were provided by many fitness-for-service (FFS) codes. However, the thresholds are not well defined in the range of negative stress ratio. There are two types of thresholds under the negative stress ratio. That is, constant thresholds and increment of thresholds with decreasing stress ratios. The objective of this paper is to introduce the thresholds provided by FFS codes and to analyze the thresholds using crack closure. In addition, based on the experimental data, definition of the threshold is discussed to apply to FFS codes. Finally, threshold for ferritic steels under the entirely condition of stress ratio is proposed to the ASME Code Section XI.
Evaluation of Bending Limit of 9Cr-1Mo-V Steel by Master Curve and Failure Assessment Diagram Method: Evaluation of Base Metal
Authors: Oda Kazuo , Nakatani Mitsuyoshi , Tanaka Tomohiro , Abe Masamitsu , Takashima Yasuhito , Minami Fumiyoshi
Published: October 2018

We investigated the bending and rolling limit of 9Cr-1Mo-V steel plate used in pressure vessels for the purpose of improving its manufacturing efficiency. Hereafter in this report, the bending limit refers to bending by press or by roller. It includes acceptable crack size, temperature, introduced plastic strain and other factors.

When fracture toughness tests of 9Cr-1Mo-V steel plate were performed at bending temperature in production, unstable fracture rarely occurred. Since fracture probability during the bending process seems to be low, it was not possible to evaluate aspects of the degree of safety factor for brittle fracture. To estimate the bending limit at high temperature where unstable fracture rarely occurs, a method was proposed for estimating fracture probability using master curve and failure assessment diagram (FAD).

In order to verify the proposed method, loading tests simulating the bending process were performed. The bending limits obtained from the loading tests were in good agreement with the values predicted by the proposed method.

In this study, guidelines such as required toughness value and bending temperature for preventing brittle fracture during the bending process of 9Cr-1Mo-V steel plate were investigated.
Study on the Creep Property by Small Beam Specimen With Fixed Constraint
Authors: Guo-Yan Zhou , Hong-Yu Qin , Jun-Qi Wang , Shan-Tung Tu , Jian-Guo Gong
Published: October 2018

To guarantee the safe and highly efficient operation of the high temperature plants, evaluation of the material creep properties and deterioration are necessary. As for small-structure components, especially in service, the material is not sufficient to provide a standard specimen for creep tests. So, as one of the promising techniques, small specimen creep tests have been developed. Three-point bending specimen with fixed constraint (TPBSF) has been attracting scholars’ increasing interests due to its simple stress state and easily achievement of rupture data. However, the TPBSF is limited in many applications for its different constitutive equations and larger errors. In this study, on the basis of beam bending theory, the creep deformation formula of TPBSF was modified. Its feasibility and accuracy was verified by comparing with the creep test data of A7N01 aluminum alloy at 380 °C in literature. Further, based on this modified constitutive equation, finite element method was used to investigate the creep behavior of 0Cr18Ni9 at 600°C. The results show that the modified creep deformation constitutive equation correlates better with uniaxial creep. The corresponding creep parameters B and n of 0Cr18Ni9 at 600°C by TPBSF test are much closer to the experimental results by uniaxial specimen. Von Mises stress and normal stress distribute almost symmetrically along center line at the beginning. But they redistribute with increasing time and reach to a steady state with constant values.
Towards an Integrated Computational Model for Additive Manufacturing Process: Heat Source-Particle Interaction and Effective Thermal Conductivity of Powder Bed
Authors: Chen Jian , Feng Zhili
Published: October 2018

An integrated computational modeling frame work is under development for the electron beam based additive manufacturing process to establish the fundamental correlation among material properties, process parameters and thermal and mechanical performances of the final manufactured components such as residual stresses. This paper focuses on the investigation of beam-powder interaction in mesoscale, the kinetics of the powder sintering, and the effective thermal property of the powder bed as a function of powder size distribution.
Issues With Multiaxial Fatigue Assessment in the ASME Boiler and Pressure Vessel Code
Authors: Meggiolaro Marco Antonio , de Castro Jaime Tupiassú Pinho , Wu Hao
Published: October 2018

This work analyzes the applicability of the ASME Boiler and Pressure Vessel Code procedures to calculate fatigue crack initiation under multiaxial stresses and/or strains, in particular when caused by non-proportional loads that lead the principal directions at the critical point to vary with time, e.g. due to out-of-phase bending and torsion loads induced by independent sources. Classic uniaxial fatigue damage models are usually inappropriate for analyzing multiaxial loads, since they can generate highly inaccurate predictions. Moreover, it is shown that the ASME procedures can lead to non-conservative results for non-proportional load histories.
Dynamic Instability Analysis of a Spring-Loaded Pressure Safety Valve Connected to a Pipe by Using CFD Method
Authors: Zheng Feng Jie , Zong Chao Yong , Qu Fu Zheng , Sun Wei , Song Xue Guan
Published: October 2018

As the ultimate protection of a pressure system, pressure safety valves (PSV) can respond in an instable manner such as flutter and chatter which will affect service life, reliability and performance. In order to study the dynamic instability caused by multi-source forces including the flow force, the spring compressing force and the pressure wave force, a more realistic CFD model containing a PSV and different connected pipes as well as the pressure vessel is developed, in which advanced techniques in Fluent such as User Defined Function (UDF) and Dynamic Layering method are combined to allow the PSV to operate. Based on this model, the process of the valve’s opening and reclosing is monitored to examine the influence of design parameters on the dynamic instability of the PSV. Specifically, the propagation of pressure waves along the connecting pipes is successfully captured, which is of great help to explain the instability mechanism and optimize the design and setup of pressure relief systems.
Proposal of Flaw Evaluation Method for Securing Reliability of Circumferential Flawed Pipes
Authors: Machida Hideo
Published: October 2018

This paper describes the requirements for securing the reliability of pipes with a circumferential surface flaw when they are used continually without repair. In the Rules on Fitness-for-Service (the Rules on FFS) of the Japan Society of Mechanical Engineers (JSME), limitations for flaw angle and flaw depth, and the safety margin for fracture evaluation are prescribed to ensure structural integrity during the evaluation period. In addition, for continued use without repair, three successive inspections are conducted and the prediction of flaw size is reviewed. The influence of these rules on the fracture probability when applying the limit load analysis was evaluated. From these evaluations, the flaw depth limitation and improvement of the safety factor are ineffective in improving the reliability of fracture evaluation, and the most influential factor is the prediction accuracy of flaw size. To improve the prediction accuracy of flaw size, it is important to review the predicted flaw size to envelop its actual size at the end of the evaluation period using the results of successive inspections. Based on this examination, the framework of the rules of the successive inspections and flaw evaluation incorporating the revision of the flaw size at the end of the evaluation period was proposed.
Characterization of Dissimilar Welded Joints Between Austenitic and Duplex Stainless Steel Grades for Liquid Tank Applications
Authors: Ubertalli G. , Ferraris M. , Matteis P. , Di Saverio D.
Published: October 2018

Lean duplex stainless steels have similar corrosion and better mechanical properties than the austenitic grades, which ensure their extensive spreading in industrial applications as a substitute of austenitic grades. In the construction of liquid tanks, however, it is often necessary to weld such steels with a range of fittings which are commonly fabricated with austenitic stainless steel grades. Therefore, this paper examines dissimilar welded joints between LDX 2101 (or X2CrMnNiN22-5-2) lean duplex stainless steels plates and austenitic stainless steel pipes, carried out by different arc welding processes. The investigation focuses on the correlation between the welding procedures and the microstructural and mechanical properties of the welded joints.
Gasket Catastrophic Failure Modes
Authors: Brown Warren , Knight Nathan
Published: October 2018

This paper outlines how, under certain scenarios, gaskets may catastrophically blow out of pressure boundary bolted joints. Supporting the observations on industry occurrences of such failures, attempts were made to re-create one of the failure modes in a test set-up. The tests managed to highlight critical factors for blow out of Corrugated Metal with Covering Layer (CMCL) gaskets. A summary of the known industry experience with gasket blow out and the CMCL test results are included in the body of this paper. Conclusions and recommendations for considering these failure modes in both pressure boundary bolted joint design and also risk assessment are made.
Update on Allowable Limits for Corroded Pressure Boundary Bolted Joints
Authors: Brown Warren , Long Stewart
Published: October 2018

In a previous paper, guidelines for assessment of bolt and nut corrosion on pressure boundary bolted joints was developed and verified using tests on joints with spiral wound gaskets. The work has since been extended to include a wider range of gasket types, corrosion of the flange itself (in addition to the bolts and nuts) and higher pressure class joints. This paper provides a summary of the additional work performed and updated guidance on general guidance for acceptable levels of corrosion for each component in the pressure boundary bolted joint.
Application of Failure Mode and Effect Analysis on Centrifugal Pumps of Atmospheric and Vacuum Distillation Unit
Authors: Li Xiang , Dai Cheng , Gao Feng , Wang Huadong , Sun Zhimin
Published: October 2018

A failure mode and effect analysis is performed on 58 centrifugal pumps of Atmospheric and Vacuum Distillation Unit in one of the plants of SINOPEC. Firstly, the failure modes of the pumps are classified. Then, the failure causes of the pumps are analyzed. After that, the influence of the failure and the risk level are determined. Finally, the maintenance strategies to reduce risk are put forward according to the equipment failure mode and risk level, which is the basis for the maintenance of pumps. The results show that the main failure modes of the centrifugal pumps are process medium leakage, unexpected stop, vibration, damage, noise, low output and of useful medium leakage. The mean time to failures of centrifugal pumps is 14533 hours, about 20 months. Nine centrifugal pumps are in the risk of high or medium-high, which accounts for 15.52% of the total number of pumps.
Pilot Study for Uncertainty Analysis in Probabilistic Fitness-for-Service Evaluations of Zr-2.5Nb Pressure Tubes: Identification of Influential Variables
Authors: Manu Christopher , Datla Suresh , Gutkin Leonid
Published: October 2018

Canadian Nuclear Standard CSA N285.8, “Technical requirements for in-service evaluation of zirconium alloy pressure tubes in CANDU® reactors”(1), permits the use of probabilistic methods when performing assessments of the reactor core. A non-mandatory annex has been proposed for inclusion in the CSA Standard N285.8, to provide guidelines for performing uncertainty analysis in probabilistic fitness-for-service evaluations within the scope of this Standard, such as the probabilistic evaluation of leak-before-break. The proposed annex outlines the general approach to uncertainty analysis as being comprised of the following major activities: identification of influential variables, characterization of uncertainties in influential variables, and subsequent propagation of these uncertainties through the evaluation framework or code.

The application of the proposed guidelines for uncertainty analysis was exercised by performing a pilot study for one of the evaluations within the scope of the CSA Standard N285.8, the probabilistic evaluation of leak-before-break based on a postulated through-wall crack. The pilot study was performed for a representative CANDU reactor unit using the recently developed computer code P-LBB that complies with requirements of Canadian Nuclear Standard N286.7 for quality assurance of analytical, scientific, and design computer programs for nuclear power plants. This paper discusses the approach used and the results obtained in the first stage of this pilot study, the identification of influential variables.

The proposed annex considers three approaches for identifying influential variables, which may be used separately or in combination: analysis of probabilistic evaluation outputs, sensitivity analysis and expert judgment. In this pilot study, local sensitivity analysis was used to identify and rank the influential variables. For each input variable in the probabilistic evaluation of leak-before-break, the local sensitivity coefficient was determined as the relative change in the output variable associated with a relative change of a small magnitude in the input variable. Each input variable was also varied across a large range to assess the linearity of the relationship between the input variable and the output variable. All relevant input variables were ranked according to the absolute value of their sensitivity coefficients to identify the influential variables. On the basis of the results obtained, the pressure tube wall thickness was found to be the most influential variable in the probabilistic evaluation of leak-before-break based on a postulated through-wall crack, followed by the fracture toughness of Zr-2.5Nb pressure tube material and the pressure tube inner diameter. The results obtained at this stage were then used at the second stage of this pilot study, the uncertainty characterization of influential variables, as discussed in the companion paper PVP2018-85011.