bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximize Hyper Compressor Uptime Applying an Industry Proven Monitoring Approach
Authors: Franz Oliver , Vigants John
Published: November 2015

The high pressure (Hyper) Compressor is one of the most critical assets within a LDPE production line. Failures starting off with simple valve leakage may lead into interstage pressure variation, load increasing and loss of load reversal and finally a main bearing failure resulting into multiple days’ downtime. This paper describes some of the challenges and a proven effectively method for monitoring Hyper compressors and its individual components. Using a series of short real-life case studies, it will be illustrated how a state-of-the-art monitoring technology helps to detect impending failures at an early stage to eliminate consequential damages and avoids to be caught off-guard. One case study describes the early indication of a developing valve failure; another provides understanding how a packing failure is detected reliably. The third case study covers aspects of a safety relevant damage resulting into an automatic compressor shutdown, which otherwise would have likely resulted into significant and costly production loss. The session will be concluded with hands-on guidance on recommended Safety Protection analysis.
Failure Analysis of Pipeline With Pore Defects
Authors: Li Yan , Shuai Jian , Zhou Yan , Xu Kui
Published: November 2015

During the welding process, the pore defects may be produced in the weld body. Statistic results showed that welding defect is one of the main causes for pipeline failure. According to this factor, this paper presents a detailed description of numerical research to assess the structural condition of circumferential weld seam pipeline with pore defects. Based on elastic-plastic theory, a set of nonlinear finite element analyses of pipelines with pore defects are carried out to study the influence of different sizes and locations on failure mode. Aimed at evaluating the load bearing capacity of pipeline with pore defects, limit stress states are investigated in this paper by using the finite element analysis. By comparing the present analysis results with the relevant standards, a proposed acceptance criterion is brought out. The results presented in this paper can be used to make suggestions on welding procedure qualification and continued safe operation of pipelines.
The Effect of Soil on the Structural Response and Fatigue Life of Free Span for Submarine Pipeline
Authors: Dong Jie , Xuedong Chen , Wang Bing , Guan Weihe , Yang Tiecheng , Zhichao Fan
Published: November 2015

Free span resulting from unevenness of seabed or scour of current is a dangerous status for submarine pipeline. Fatigue failure caused by vortex induced vibration (VIV) is one of the main failure modes for free span. Because of the contact between soil and pipeline, the effect of soil must be considered for the fatigue analysis of free span. In this paper, aimed at one in-service submarine pipeline, the research on the VIV response of free span was investigated considering the effect of stiffness and damping of soil. Furthermore, fatigue damage and fatigue life of free span were evaluated based on the actual measured flow velocity data varied with time. The analysis results have provided support for the maintenance of free span for the submarine pipeline.
Creep Crack Incubation in P92 Steel at 650°C in the Presence of Structural Elastic Follow-Up
Authors: Khayatzadeh Saber , Tanner David W. J. , Smith David J.
Published: November 2015

It is customary to study the creep deformation of materials at high temperatures and the incubation and growth of creep cracks using constant load test machines. However, this highly idealised loading condition does not accurately reflect the practical circumstances that occur when operating high temperature plants. Real loading conditions often lie between load and displacement control and correspond to situations where there is elastic follow-up, with low values relating to near displacement control and high values near to load control.

This paper explains a series of experiments where pre-cracked martensitic P92 steel compact tension specimens are loaded and tested for different values of structural elastic follow-up, ranging from constant load to near fixed displacement. It is found that the degree of elastic follow-up significantly changes the time taken for creep crack incubation. This is a consequence of the relaxation of the load applied to the specimens. Elastic-plastic creep finite element simulations are used to reveal the underlying mechanical behaviour of the specimens. The simulations were confined to 2D analyses for plane stress and plane strain conditions. It is observed, that, irrespective of the initial loading and boundary conditions, the predicted mechanical response for plane stress and plane strain lies either side of the experimental results.
Optimization Calculation Method of Wall Thickness for Large Oil Storage Tank Made of High Strength Steel
Authors: Fan Haigui , Chen Zhiping , Wan Futeng
Published: November 2015

Optimization calculation method determining wall thickness for large oil storage tank made of high strength steel is investigated in this paper. Taking three oil storage tanks with different volumes of 10×104 m3, 15×104 m3 and 20×104 m3 for examples, the wall thickness calculation methods of API 650, GB 50341, JIS B 8501 and BS EN 14015 have been analyzed and compared. Results show that as the volume of oil storage tank increases, some wall thickness calculation results of the standards have been larger than the allowable value, leading to the unreasonable distribution of the wall circumferential stress. The wall thickness calculation result applying the method of API 650 is more reasonable than other standards. While for the tanks made of high strength steel, like 12MnNiVR (GB 50341), the yield ratio of the steel has reached 0.803, which is larger than the upper limit value of API 650. In order to make up the deficiency, an optimization method based on API 650 is presented, which considers the effects of yield strength, tensile strength and yield ratio on the determination of allowable stress. Taking the 20×104 m3 oil storage tank and selecting a proper welded joint efficiency, the wall thickness is calculated by the presented optimization method. The wall thickness calculation result is more reasonable and the circumferential stress distribution is more homogeneous when the safety factor of tensile strength is taken to be 2.4. Results show that the optimization method is applicable to the thickness calculation of oil storage tanks made of high strength steel.
Strength and Stability Analysis of Double-Deck Floating Roof Under Wind Load
Authors: Chen Zhiping , Huang Song , Fan Haigui
Published: November 2015

Double-deck floating roof has gained more and more popularity in large oil storage tanks. Wind load is one of the main factors that cause failure of the floating roofs. Because of complexity of structure and difficulty in theoretical calculation, wind load on double-deck floating roof has not been considered into the general design standards. An engineering calculation method based on finite element method for the strength and stability of double-deck floating roof under wind load is established. The relation between pressure distribution on floating roof and liquid height is studied when the double-deck floating roof locates at different levels. Results show that pressure difference on the roof reaches maximum when the liquid height is 100%. The finite element model of double-deck floating roof is established based on large deformation theory, the overall displacement, deformation and stress are obtained by applying pressure distribution on the roof. The first anti-sinking criterion and axial compression stability criterion of long bar are selected to verify the strength and stability of floating roofs under wind load. Results show that the engineering calculation method presented can be effectively used to analyze the strength and stability of double-deck floating roof under wind load.
A Comparison of Design by Analysis Techniques for Evaluating Nozzle-to-Shell Junctions per ASME Section VIII Division 2
Authors: Prueter Phillip E. , Brown Robert G.
Published: November 2015

Part 5 of ASME Section VIII Division 2 offers several design by analysis (DBA) techniques for evaluating pressure retaining equipment for Code compliance using detailed computational stress analysis results. These procedures can be used to check components for protection against multiple failure modes, including plastic collapse, local failure, buckling, and cyclic loading. Furthermore, these procedures provide guidance for establishing consistent loading conditions, selecting material properties, developing post-processing techniques, and comparing analysis results to the appropriate acceptance criteria for a given failure mode. In particular, this study investigates the use of these methods for evaluating nozzle-to-shell junctions subjected to internal pressure and nozzle end loads. Specifically, elastic stress analysis, limit load analysis, and elastic-plastic stress analysis are utilized to check for protection against plastic collapse, and computational results for a given load case are compared. Additionally, the twice elastic slope method for evaluating protection against plastic collapse is utilized as an alternate failure criterion to supplement elastic-plastic analysis results.

The goal of these comparisons is to highlight the difference between elastic stress checks and the non-linear analysis methodologies outlined in ASME Section VIII Division 2; particularly, the conservatism associated with employing the elastic stress criterion for nozzle end loads compared to limit load and elastic-plastic analysis methodologies is discussed. Finally, commentary on the applicability of performing the Code-mandated check for protection against ratcheting for vessels that do not operate in cyclic service is provided. The intent of this paper is to provide a broad comparison of the available DBA techniques for evaluating the acceptability of nozzle-to-shell junctions subjected to different types of loading for protection against plastic collapse. Predicted deformations and stresses are quantified for each technique using linear and non-linear, three-dimensional finite element analysis (FEA) methodologies.
Modelling of Streamwise and Transverse Fluidelastic Instability in Tube Arrays
Authors: Hassan Marwan , Weaver David S.
Published: November 2015

The development of a theoretical model for fluidelastic instability in tubes arrays is presented. Based on the simple model of Lever and Weaver, it considers a group of 7 tubes which move in both the streamwise and transverse directions. The analysis does not constrain either tube frequency or relative mode shape so that the tubes’ behaviour evolves from a perturbation naturally. No additional empirical input is required. A particular case is used to evaluate the model’s performance and the ratio of streamwise to transverse natural frequency is varied. Both streamwise and transverse fluidelastic instability are predicted and the results agree well with experimental observations.
Dynamic Effects on Fracture Toughness for Ferritic Steel in the Ductile-to-Brittle Transition
Authors: Jacquemoud C. , Delvallée-Nunio I. , Balestreri F.
Published: November 2015

Dynamic loading effects on ferritic steel toughness have been evaluated in the brittle-to-ductile transition, considering loading rates representative of object drops. To verify that the brittle-to-ductile transition curve, initially defined from static tests, tends to shift to higher temperatures due to dynamic effects even in the case of object drops, experiments on 16MND5 steel have been performed.

A three-point bending set-up and a thermal chamber have been designed in order to perform dynamic fracture tests on large Single Edge-notched Bending SE(B) specimen, at very low temperature using a drop-shock machine. In a first step, considering that the reference temperature of the material (according to the master curve concept) is −122 °C, dynamic tests at −120 °C have been performed. These tests have confirmed that the fracture mode is still brittle at this temperature, when an impact speed of 4.85 m/s is used.

Elastic-plastic or viscoplastic dynamic simulations of the tests, compared to classical static analysis, have demonstrated that the effects of inertia and viscosity on fracture toughness are negligible considering the very low values obtained on these tests at −120 °C. These results also confirm the decrease of fracture toughness due to dynamic loading compared to experimental data from static tests. A further step will be to complete this demonstration with dynamic tests at higher temperatures in the brittle-to-ductile transition.
Evaluation of Crack Growth of Ni-Base Alloys Under Long Term Cyclic Loading in BWR Environment
Authors: Itatani Masao , Ogawa Takuya
Published: November 2015

Crack growth test data of Ni-base alloys under cyclic loading in simulated boiling water reactor (BWR) environment including the effects of load rising time (tr) were evaluated in the view points of both fatigue and stress corrosion cracking (SCC). When the test data were plotted in the relationship between da/dt and Kmax, da/dt monotonically decreased with increasing tr and the stress ratio (R). For alloy 182 weld metal under short tr and/or low R, the crack growth rate assuming SCC is much lower than those of the test data. For alloy 182 under tr = 30 and 1000 s at R = 0.8, the crack growth rate assuming SCC almost coincided with test data. For heat affected zone (HAZ) of alloy 600 base metal (600HAZ), the crack growth rate assuming SCC had much different slope of da/dN-ΔK relationship compared with the test data in the tested range of tr up to 3000 s. From these observations, the contribution of SCC is relatively small and the main mechanism of crack growth is thought to be fatigue for the tested range (tr=1 to 1000 s for weld metal, tr=1 to 3000 s for base metal and R = 0.1 to 0.8). It was assured that the fatigue crack growth formula proposed by the authors accounts the effect of SCC adequately at long tr. Additionally, the applicability of the fatigue crack growth rate formula for austenitic stainless steels to the long term cyclic load was investigated and it was found that the formula can be applied to tr=30000 s.
Hydrogen Embrittlement for X-70 Pipeline Steel in High Pressure Hydrogen Gas
Authors: Baek Un Bong , Lee Hae Moon , Baek Seung Wook , Nahm Seung Hoon
Published: November 2015

The tensile properties of API 5L X70 pipeline steels have been measured in a high-pressure (10 MPa) hydrogen gas environment. Significant decreases in elongation at failure and reduction of area were observed when testing in hydrogen as compared with air, and those changes were accompanied by noticeable changes in fracture morphology. The present paper exposes the changes in mechanical properties of a grade API 5L X70 steel through numerous mechanical tests, i.e. tensile tests, notch tensile tests, fracture toughness and fatigue crack growth measurements, performed either in atmosphere or in 10 MPa pressure of hydrogen gas.
CFD Analysis of the Non-Uniform Velocity Distribution Generated by a Large Axial Flow Fan
Authors: Lu Hongliang , Xue Xiaolong , Tang Xiaoying , Geng Xuefeng , Yao Jianping
Published: November 2015

The air flow propelled by an axial flow fan is often assumed to be uniform across the tube bundle of an industrial air-cooled heat exchanger, but the fact is that the air flow is non-uniform in practice to the extent that as much as 35% performance of air-cooled heat exchangers is cut off. Besides the structure of tube bundle, the high flux and low pressure head fan with 1.5 m to 4.5 m in diameter is the primary reason of the air flow maldistribution. CFD was employed to numerically simulate the non-uniform air flow distribution produced by the fan in the radial and flow direction. One axial flow type fan with 3 blades about 2 m in diameter was investigated under the angular speed of 80, 350 revolutions per minute. Given that the uniform velocity is the default for the velocity or mass flow boundary, the boundary of the total pressure inlet and the static outlet was adopted in the present work for axial flow fan simulation. Between the rotating zone and the other zones is the fluid to fluid type interface with frozen rotor. The result showed that the air velocity rises when it comes nearer to the fan either in the upstream or in the downstream direction. The upstream flow decreases more rapidly than the downstream flow, the upstream velocity air at Z=−1.5 m is almost the same with the ambient while the downstream velocity at Z=5.8 m is still 2, 6 times larger than the ambient for 80, 350 RPM respectively. In each plane, the air flow distribution from the rotating center of the fan to the circumference is different from each other plane by the boundary conditions. And the maximum velocity locates at about the radial middle part of the blades. The hub at the central part near the fan causes the concave velocity distribution of the downstream flow. It is the driver mechanism geometry that causes the radial velocity change of the upstream flow. Finally, 3 methods involving the upstream or downstream type and the blade angle of inclination are provided to reduce the air flow non-uniformity.
Mechanism of Slow Crack Growth in Polyethylene: A Finite Element Approach
Authors: Luo Xiangpeng , Shi Jianfeng , Zheng Jinyang
Published: November 2015

Slow crack growth (SCG) is a common failure mode in underground polyethylene (PE) piping which was designed for 50-year services. It had been revealed by experiments that the SCG process is caused by continuous propagation of the craze zone at the crack tip through the bulk material. However, the mechanism of SCG failure has not been understood clearly. The eXtended Finite Element Method (XFEM) is found to be an effective tool for locally non-smooth features (voids, cracks, etc.) in solid or fluid mechanics solutions. In this paper the time-dependent property of PE was considered, a viscoelastic constitutive model was used for the bulk material. To represent the material deterioration during SCG, a damage model was developed for the craze zone. Combined with the XFEM, the process of the Pennsylvania Notched Test (PENT), which had been widely applied for characterizing resistance of SCG for PE pipes or resins, was analyzed based on the proposed finite element (FE) model containing the two constitutive models. The numerical results were then compared with the experimental data in literatures. It showed that the failure time and final notch angle were in agreement with the experimental observations. Based on the verified FE model, strain distributions along the boundary of the crack were studied and the shortcomings of this model were discussed.
Gun Barrel Refurbishing Using a Shrink-Fitted Autofrettaged Liner
Authors: Perry J. , Perl M.
Published: November 2015

During the firing of guns, the barrel undergoes two major damaging processes: wear of its inner surface, and internal cracking. Barrel’s are condemned based either on the increase of their internal diameter due to wear, or the severity of their internal cracking. The cost of replacing such a damaged gun barrel runs in the tenth of thousand of US$. Therefore, cost effective methods are sought for restoring such gun barrels. In the present analysis a new method is proposed for refurbishing vintage gun barrels by machining their inner damaged layer and replacing it by an intact, autofrettaged, shrink-fit liner that will restore the barrel to its original performance. The preliminary results demonstrate the ability of this process to mend such barrels, bringing them back to their initial Safe Maximum Pressure (SMP) and their intact conditions, rather than condemning them. Furthermore, such an alternative seems to be cost effective.
Study on Application of PFM Analysis Method to Japanese Code for RPV Integrity Assessment Under PTS Events
Authors: Osakabe Kazuya , Masaki Koichi , Katsuyama Jinya , Katsumata Genshichiro , Onizawa Kunio , Yoshimura Shinobu
Published: November 2015

A probabilistic fracture mechanics (PFM) analysis method for pressure boundary components is useful to evaluate the structural integrity in a quantitative way. This is because the uncertainties related to influence parameters can be rationally incorporated in PFM analysis. From this viewpoint, the probabilistic approach evaluating through-wall cracking frequencies (TWCFs) of reactor pressure vessels (RPVs) has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. As a study of applying PFM analysis to the integrity assessment of domestic RPVs, JAEA has been preparing input data and analysis models to calculate TWCFs using PFM analysis code PASCAL3. In this paper, activities have been introduced such as preparing input data and models for domestic RPVs, verification of PASCAL3, and formulating guideline on general procedures of PFM analysis for the purpose of utilizing PASCAL3. In addition, TWCFs for a model RPV evaluated by PASCAL3 are presented.
Monitoring Degradation in Nuclear Reactors
Authors: Brumovsky Milan , Kytka Milos
Published: November 2015

Nuclear reactor materials are affected by many stressors during their operation that result either from the nuclear reactions in the reactor core or by operation conditions (temperature, pressure) and water environment.

Generally, several different methods of monitoring damage in reactor materials are applied, depending on their type, design and conditions:

- Destructive, usually represent by surveillance specimens,

- Semi-destructive, usually performed by cutting small specimens from component surface, e.g. for small punch tests,

- Non-destructive, representing by non-destructive inspection methods applied during in-service inspections, like traditional ultrasonics, optical, dye-penetrant, eddy current etc. and also some new like automated ball indentation, thermoelectric power measurements etc.

The paper summarizes the possibility of application of these methods on main reactor components and shows some typical results and problems.
Validity of Procedure for Plastic Collapse Assessment of a Local Thin Area Near Vessel and Nozzle Intersections Subjected to Internal Pressure and External Loadings
Authors: Oyamada Kenji , Konosu Shinji , Miyashita Tetsuji , Ohno Takashi , Suzuki Hideyuki
Published: November 2015

There are numerous cases in which a volumetric flaw such as a local thin area (LTA) is found in pressure equipment such as vessels, piping, tanks, and so on. Sometimes it is found near vessel and nozzle intersection. A fitness for service (FFS) rule of such cases was desired, because plastic collapse assessment of LTA near vessel and nozzle intersection usually needed to conduct by numerical analysis such as FEA.

Recently, an FFS assessment rule of plastic collapse assessment of LTA near vessel (run-pipe) and nozzle (branch pipe) intersection subjected to internal pressure and external loadings has been developed and proposed by one of authors of this paper.

In this paper, the proposed plastic collapse assessment rule was verified with results of experiments and FEA for cylindrical vessels with an LTA near vessel and nozzle intersections subjected to internal pressure and external loadings.
Evaluation Method of Creep-Fatigue Life for 316FR Weldment
Authors: Nagae Yuji , Yamamoto Kenji , Otani Tomomi
Published: November 2015

The most important failure mode to be prevented is creep-fatigue at elevated temperatures in fast reactors. 316FR stainless steel is a candidate material for the reactor vessel and internal structures. A method to evaluate creep-fatigue life, based on the time fraction rule, has been already developed in base metal of 316FR stainless steel. Development of procedure in evaluating creep-fatigue life is also necessary for the weldment of 316FR stainless steel by similar fillers or 16-8-2 fillers. Compared between mechanical properties of weldment and those of base metal, strength-reduction factors for weldment have been evaluated. Strength-reduction factor for fatigue has been proposed. It is considered that strength-reduction factor for creep strength is not necessary. Creepfatigue life could be evaluated in the same way for weldments of similar fillers and 16-8-2 fillers, because a difference in mechanical properties between both filler metals is negligible. Creep-fatigue life by the time fraction rule using analytical relaxation curve for weldments were compared with experimental data, and a method to evaluate creep-fatigue life for the weldments of 316FR stainless steel has been proposed.
Stress Intensity Factor and Elastic COD for Circumferential Through-Wall Cracks in the Interface Between an Elbow and a Straight Pipe Under Internal Pressure
Authors: Jang Youn-Young , Huh Nam-Su , Jeong Jae-Uk , Kim Ki-Seok , Cho Woo-Yeon
Published: November 2015

Leak-Before-Break (LBB) is one of important approaches applied to nuclear piping design. In the LBB assessment, it is important to evaluate crack instability and to predict leak rate based on a fracture mechanics concept, in which an idealized straight pipes with through-wall cracks (TWCs) are generally considered in the typical LBB analysis. On the other hand, in nuclear piping system, elbows are often connected with straight pipes by welding, in which cracks could occur as well known. Hence, accurate assessment needs to be performed for cracks in weldments joining an elbow and attached straight pipe.

In the previous study, it has been revealed that crack instability of a TWC in the interface between an elbow and a straight pipe under bending moment could be different with that of a straight pipe with a TWC depending on a change of pipe thickness, radius of curvature and crack length. Especially, elbows attached to a pipe were more severe than straight pipes for relatively shorter crack length. Thus, a need of engineering solutions for cracks in the interface between an elbow and a pipe is raised for accurate LBB analysis on nuclear piping system.

In this present study, stress intensity factor (SIF) and crack opening displacement (COD) are estimated via detailed 3-dimensional finite element (FE) elastic analyses for circumferential TWCs in the interface between an elbow and a straight pipe subjected to internal pressure. The geometric variables (pipe thickness, radius of curvature and crack length) affecting SIFs and CODs were systematically considered in order to cover actual ranges of geometric variables. Also, the effect of elbow on elastic fracture parameters was investigated by comparing the present results with the results from the previous straight pipe solution. Moreover, based on the present FE results, the shape factors (F, V) used for calculating SIFs and CODs are proposed for circumferential TWCs in the interface between an elbow and a pipe. The present results can be used to perform the accurate LBB assessment for nuclear piping system including elbows welded to a straight pipe.
On the Effect of Water Film on Flow-Induced Pulsations in Closed Side Branches in Tandem Configuration
Authors: Sanna F. , Golliard J. , Belfroid S. P. C.
Published: November 2015

Previous studies demonstrate that the presence of liquid strongly influences the pressure pulsation amplitudes of flow induced pulsations. In particular, in case of annular flow (thin liquid film on the walls) the pulsations can be eliminated. The present study aims at evaluating the contribution of the liquid film to the pulsation reduction.

Experiments have been performed in a tandem configuration with two side branches upward oriented. The side branches have the same diameter as the main pipe.

A first set of experiments has been conducted with the injection point located far upstream the upstream side branch. To isolate the sole effect of the film, a second and a third set of experiments have been performed with the injection point located close upstream the T-junction with the injection such that a thin film only was generated.

In the first configuration (far upstream), the pulsation level decreases with increasing liquid rate. The reduction in amplitude compares well with the assumption of added damping in the length between the two side branches.

A similar decrease in pulsation amplitude was obtained in the second configuration. However, the amplitude reduction depends on the local liquid flow pattern at the (upstream) side branch and in particular on whether liquid bypasses the side branch or it interferes with the shear layer.

This indicates that acoustical damping is the main effect and small amounts of liquid do not significantly interfere with the shear layer.
Explicit Finite Element Analyses of Drop Tests With Thin-Walled Steel Sheet Containers for the Konrad Repository
Authors: Protz Christian , Zencker Uwe , Liebich Robert
Published: November 2015

Alternatively to experimental drop tests, the mechanical safety analyses of containers for final disposal of radioactive waste with negligible heat generation in the German Konrad repository may be carried out by numerical simulations within the safety assessment procedure. In the past, safety assessments for thin-walled steel sheet containers have been done exclusively by prototype tests and unfavorable drop scenarios were determined by engineering judgment. So far, reliable numerical simulations do not exist. Therefore, a research project was started to develop numerical simulation approaches for drop test analyses and to determine existing safety margins. Comparisons of experimental and numerical results confirm that the Finite Element (FE) model represents the general mechanical behavior of the steel sheet container sufficiently. Simulations have been used to determine an unfavorable drop scenario resulting in large deformation and damage. This paper presents the investigations carried out as well as the further development of the FE model in terms of damage mechanics.
Experimental Study on Failure Estimation Method for Circumferentially Cracked Pipes Subjected to Multi-Axial Loads
Authors: Li Yinsheng , Hasegawa Kunio , Miura Naoki , Hoshino Katsuaki
Published: November 2015

When a crack is detected in a piping line during in-service inspections, failure estimation method provided in ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the structural integrity of the cracked pipe. The failure estimation method in the current codes accounts for the bending moment and axial force due to pressure. The torsion moment is not considered.

Recently, analytical investigations have been carried out by several authors on the limit load of cracked pipes considering multi-axial loads including torsion and two failure estimation methods for multi-axial loads including torsion moment with different ranges of values have been proposed. In this study, to investigate the failure behavior of cracked pipes subjected to multi-axial loads including the torsion moment and to provide experimental support for the failure estimation methods, failure experiments were performed on 20 mm diameter stainless steel pipes with a circumferential surface crack or a through-wall crack under combined axial force and bending and torsion moments. Based on the experimental results, the proposed failure estimation methods were confirmed to be applicable to cracked pipes subjected to multi-axial loads.
An Application of Two Step Stress Classification Approach (Primary Structure Method) for Stress Classification at Cylindrical Shell–Nozzle Intersections Subjected to Internal Pressure, Radial Load and In- and Out-of-Plane Bending Moments
Authors: Bhattacharya Anindya , Bapat Sachin , Patel Hardik , Patel Shailan
Published: November 2015

Stress classification at shell and nozzle interface had always been an interesting and challenging problem for Engineers. Basic shell theory analyses shell stresses as membrane with local bending stresses developed at locations of discontinuity and load applications. Since in a shell structure, bending stresses develop to mainly maintain compatibility of deformation and membrane stresses to equilibrate the applied load, a simple stress classification will be to categorize the bending stresses as secondary stresses. This is because by definition, secondary stresses develop to maintain compatibility of deformation and primary stresses develop to maintain equilibrium with the applied load. This simplified analysis can result in errors as in real world 100% primary stress as well as 100% secondary stress is rare if not impossible [15], [16]. The widespread use of Finite Element Analysis has made this problem become even more challenging. Several researchers have addressed the problems of stress classification. References [1], [2], [3], [4], [5[, [6], [11], [12] can be consulted for additional details. In this paper the work done by Chen and Li [1], using the two step primary structure method has been used to analyse the problem of stress classification of a shell and nozzle. The spirit of the method has been retained, but several FE models have been made with some deviations from the method in ref.[1], to meaningfully arrive at primary structures.
Stress Intensification Factors for Non-Concentric Elbow Branches in Old Carbon-Steel Pipelines
Authors: Scano Lorenzo
Published: November 2015

Unreinforced branch connections manufactured using elbow ducts can be occasionally encountered during the Fitness-For-Service evaluation of very old, low-service, carbon-steel pipelines. For these peculiar components, no Stress Intensification Factors (SIFs) are usually available in the international codes and standards used by practicioners for stress analysis purposes.

In a previous work from the author [1], the SIFs for various elbow branch connections were determined via FEA and a formula was derived through a parametric analysis in order to calculate the SIF for the elbow tees using the codified SIF of the equivalent standard joints. The investigation was restricted to concentric elbow branches, i.e., tees where the elbow duct had the same principal axis of the run pipe.

In this paper the case of non-concentric elbow branches was taken into account, considering the offset between elbow and run pipes and the rotation of the curved duct in the two main meridional planes, thus bringing into focus lateral and non-planar elbow tees. The SIFs were calculated using FEA for different configurations of reducing elbow branches with diameters ranging from 2” to 10” and thicknesses from Piping Schedule 10, 40 and 80. Lateral and non-planar joints were analyzed for one reference geometry and at various offsets and rotation angles. A parametric analysis was then carried out to evaluate the offset effect on the stress intensification both on run and branch side, for in-plane and out-of-plane bending. The results showed a significant impact only on the branch side where an increase in piping offset resulted in a reduction of the dominant out-of-plane bending SIF. The original formula devised for the concentric elbow branch connections was hence modified to include this offset effect. Finally, the combined role of offset and rotation angle was parametrically analyzed for the special geometry investigated. The results demonstrated a significative increment of the SIFs for non-planar tees, both on run and branch pipes, whilst in lateral joints the major SIF increased to a maximum only on the branch side.
Comparison of Plastic Work Curvature Methods for Assessing the Collapse Load of a Structure
Authors: Seal Christopher K. , Han Jae-Jun , Ainsworth Robert A.
Published: November 2015

Plastic work methods for determining the collapse load of structures present a promising means of analysing complex geometries subjected to combined loading. Recent work has identified the curvature of a plot of plastic work as a function of the applied load as being indicative of the collapse load that is both accurate and physically based.

Several methods by which the curvature plot can be used to identify the plastic collapse load have been proposed by various authors and there is no consensus as to which method should be used. This paper presents an analysis of these and other methods and concludes with a recommendation for a robust approach that could be used in assessment.
Estimation Method for Evaluating Energy Release Rate of Circumferential Through-Wall Cracks in Dissimilar Metal Welds
Authors: Park Jeong Soon , Olson Richard
Published: November 2015

In this study, an estimation method is proposed to evaluate the energy release rate (J-integral) of a circumferential through-wall crack in a dissimilar metal (DM) weld subjected to tension and/or bending. In order to evaluate such cracks in a DM weld, the concept of a mixture ratio has been introduced, so that the existing single-material J-integral estimation method can be utilized with effective material strength properties which are the mixture of the two base metal properties with some ratio. The mixture ratio, however, is empirical, and several numerical analyses would be required to determine an appropriate value of mixture ratio. The new J-integral estimation method proposed in this study can take account of three material properties of the two base metals and a weld metal. Following the approach similar to the LBB.ENG2 method, the new method provides closed-form solutions for the J-integral by introducing an equivalent reduced thickness section replacing the cracked section in the DM weld. It is confirmed that the new method successfully degenerates to the existing one- and two-material J-estimation methods, when simulating one- and two-material crack problems. Furthermore, the maximum moments predicted by the proposed method, as a result of crack stability analyses, show good agreements with DM weld test results.
Assessing Fatigue Endurance Limit of Pitted Specimens by Means of an Integrated Fracture Mechanics Approach
Authors: Larrosa Nicolas O. , Chapetti Mirco D. , Ainsworth Robert A.
Published: November 2015

From an operator/engineering perspective, the correct assessment of the severity of corrosion defects (e.g., pits) can have enormous economic, social and environmental benefits; therefore the development of a generally applicable and simple to apply procedure for fatigue assessment of key components is recognised as a valuable tool, seeking to reduce the current overly conservative procedures whilst maintaining structural integrity. The critical condition for a crack emanating from a pit (pit-to-crack transition) to start to propagate is analysed in this paper. The pitcrack configuration is re-characterized into that of a hemispherical crack of length equal to the pit depth, and this assumption is analysed by detailed 3D FEA. A propagation threshold approach is used to estimate the fatigue resistance from intrinsic material properties. The proposed approach is validated by comparison with experimental results available in the open literature.
Numerical Analysis and Experimental Assessment of the Cylinder Temperature in a Reciprocating Compressor
Authors: Balduzzi Francesco , Tanganelli Andrea , Ferrara Giovanni , Babbini Alberto , Maleci Riccardo
Published: November 2015

Accurate evaluation of the thermal deformation is important to the analysis of reciprocating compressors since the induced deformations are responsible of the thermal stresses on the cylinder. The cylinder body experiences a non-uniform temperature distribution, with the presence of hot and cold spots, creating a bending strain on the structure. A cylinder cooling system is designed to control the uniformity of the temperature field and to reduce the fresh gas heating due to a hot cylinder body, improving the volumetric efficiency.

Due to the difficulties associated with obtaining detailed data on the heat transfer processes by experimental means, a more and more important role is played by numerical analysis in reciprocating compressor design.

This paper shows the capability of a conjugate heat transfer (CHT) simulation for a double-acting reciprocating compressor cylinder in accurately predicting both the thermal state of the compressor cylinder and the temperature field of the cooling water. The results of the three-dimensional simulations of the water-circuit flow field and the thermal conduction inside the solid metal were compared to temperature measurements collected on a dedicated test bench for both the coolant and the metal structure. Satisfactory agreement was obtained between the experimental data and the numerical computations.

In addition, three different modifications for the CHT model were introduced in order to obtain a better match with the experimental results. The suitability of using the CHT simulation as an efficient tool for replicating the actual condition of the reciprocating compressor was analyzed and discussed.
Effective Outage Planning and Implementation for Nuclear Power Plants in the UK
Authors: Reece-Barkell H. , Vorster W. J. J.
Published: November 2015

Effective outage planning and implementation is critical to the efficient and safe operation of commercial nuclear power plants in the UK. Statutory outages are necessary for refuelling, for preventive and corrective maintenance when shutdown conditions are required, and for major modification and improvement projects. Outages involve the support of many companies and individuals working together and, as such, require high levels of coordination. Planning of activities before the outage is critical to the overall success of the outage. Establishing the integrity of power plant piping and pressure vessels is a key objective as part of any outage and the methodology and processes involved are the subject of this paper.

Establishing the integrity of piping and pressure vessels requires an understanding of the specific threats, their relationship to the overall condition of the system, and the mitigating measures required to assure safe operation. Understanding the specific threats allows the engineering function of an organisation to advise on pipework and pressure vessel ‘Minimum Acceptable Thicknesses’ which can be used to assure integrity via comparison with thicknesses measured during outage inspections. Minimum Acceptable Thicknesses should be recorded in the outage management documentation so they are accessible during the outage implementation phase.

Historically a variety of different methodologies have been used to advise on Minimum Acceptable Thickness requirements including design drawing specified minimum thicknesses, design code based required thicknesses and thicknesses calculated based on Fitness for Purpose methods. It is important that a robust procedure be applied to promote consistency of approach as regards the calculation of pipework and pressure vessel Minimum Acceptable Thickness requirements across all power station assets. An additional consideration is that of ensuring that the approach adopted is consistent with high level safety case guidance, i.e., the assessment is appropriate for the failure tolerability of the plant item.

This paper provides an overview of the strategy, methodologies and processes employed to determine Minimum Acceptable Thicknesses for pipework components. These ensure that, over a specified inspection interval, were the weld/component to be defect free, it would not fail due to any of the relevant failure mechanisms, which typically are plastic collapse, creep rupture, fatigue, incremental collapse (ratcheting) or buckling.

Readers of this paper will gain a valuable insight into the statutory outage process applicable to nuclear power plants in the UK. A particular focus of this paper is on the structural integrity assessments applied in a non-traditional sense prior to, during and after the statutory outage. As well as sharing a valuable insight into the assessment methodologies this paper highlights best industrial practice.
Temperature and Rise Time Inputs to Fatigue Crack Growth Calculations for Austenitic Stainless Steels in a Pressurised Water Reactor Environment
Authors: Emslie Julian , Watson Chris , Gill Chris , Wright Keith
Published: November 2015

The draft ASME Code Case N-809 provides a Fatigue Crack Growth (FCG) law for austenitic stainless steel in a Pressurised Water Reactor (PWR) environment. This growth law explicitly considers the effect of the environment through the additional parameters of temperature and rise time applied in conjunction with a standard Paris equation. FCG calculations using this growth law have been shown to have the potential to produce significantly faster growth rates than those predicted using the current ASME XI FCG law for an air environment.

The testing on which this new FCG law is based is predominantly sawtooth loading in isothermal conditions; interpretation of the rise time and temperature variables is not straightforward when applied to PWR thermal transients which exhibit temperature and stress variations simultaneously, and the stress rate is not constant. This paper discusses temperature and rise time assumptions which may be applied with the PWR environment FCG law, and the practical implications of carrying out calculations with these additional parameters.
Ultrasonic Guided Wave Testing of Finned Tubing
Authors: Malinowski Owen M. , Lindsey Matthew S. , Van Velsor Jason K.
Published: November 2015

In the past few decades, ultrasonic guided waves have been utilized more frequently Non-Destructive Testing (NDT); most notably, in the qualitative screening of buried piping. However, only a fraction of their potential applications in NDT have been fully realized. This is due, in part, to their complex nature, as well as the high level of expertise required to understand and utilize their propagation characteristics. The mode/frequency combinations that can be generated in a particular structure depend on geometry and material properties and are represented by the so-called dispersion curves. Although extensive research has been done in ultrasonic guided wave propagation in various geometries and materials, the treatment of ultrasonic guided wave propagation in periodic structures has received little attention. In this paper, academic aspects of ultrasonic guided wave propagation in structures with periodicity in the wave vector direction are investigated, with the practical purpose of developing an ultrasonic guided wave based inspection technique for finned tubing. Theoretical, numerical, and experimental methods are employed. The results of this investigation show excellent agreement between theory, numerical modeling, and experimentation; all of which indicate that ultrasonic guided waves will propagate coherently in finned tube only if the proper wave modes and frequencies are selected. It is shown that the frequencies at which propagating wave modes exist can be predicted theoretically and numerically, and depend strongly on the fin geometry. Furthermore, the results show that these propagating wave modes are capable of screening for and identifying the axial location of damage in the tube wall, as well as separation of the fins from the tube wall. The conclusion drawn from these results is that Guided Wave Testing (GWT) is a viable inspection method for screening finned tubing.
Modeling of Hydrogen Embrittlement by a Ductile-Brittle Damage Model
Authors: Chen Qianqiang , Moumni Ziad , Angles Jean , Rouby Corinne
Published: November 2015

Hydrogen embrittlement (HE) in a martensitic steel has been investigated by tensile tests. It is shown that increasing hydrogen amount results in a transition of void coalescence cracking to a mixture of intergranular and quasi-cleavage cracking. In order to reveal the mechanisms of HE, a non-local ductile-brittle damage model has been proposed to model these tests. Modeling results show that HE is caused by a combined effect of HEDE, HELP and AIDS mechanisms.