bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Elastic-Plastic Methods to Delayed Coker Drum Design
Authors: Aumuller John J. , Xia Zihui , Ju Feng
Published: May 2012

Coke drums are pressure vessels that are used in oil sands and conventional refinery processing industries for the thermal cracking of reduced bitumen to recover additional, saleable gas and liquid product streams. The drums are constructed to the requirements of ASME VIII Division 1 although they are in a low cycle thermal-mechanical service environment. Recent practice has been to introduce design by analysis considerations from ASME VIII Division 2 even though service temperatures of the actual equipment exceed the design limits of the Code. In this paper, simplified elastic-plastic analysis models are developed for assessment of the stress and strain levels in coke drums during specific operational phases. One model is applied for determination of the local stress caused by differences in the coefficients of thermal expansion between the clad liner and base materials. Because clad construction is used throughout the vessel, the impact is extensive. Consideration is given to the general stresses induced by the cyclical, progressive dilation and contraction action of the drum shell caused by axial thermal gradients. Another model estimates hot and cold spot formation and the development of localized stress / strain distributions in coke drums. The resulting thermal stresses include the local stress from suppression of differential expansion between clad and base material, thermal bending stresses and local thermal stresses from hot and cold spot formation. It is found that the evaluation of these loads on drum cracking aligns with industry survey results. Better understanding of these loads has impact on materials selection and fabrication procedures for new drums and repair of existing drums. Operational considerations can also be identified to help improve drum reliability.
Investigation of Bulging Behavior of Coke Drum: Feasible Study on Causes of Bulging
Authors: Ohata Mitsuru , Kawai Nana , Tagawa Tetsuya , Minami Fumiyoshi , Yamamoto Toshiya , Arii Kazuaki , Niimoto Shinta
Published: May 2012

Coke drums undergo cyclic operations typically in the temperature range from ambient temperature to about 500°C (930°F). During quenching, the coke drum is inevitably subjected to a rapid drop in temperature because cooling water is injected directly into the coke drum through the bottom inlet nozzle. The temperature profile on the shell surface is no more uneven in quenching, and can vary in each cycle of quenching operation. Such complicate thermal profile induces large strains in the shell portion of the coke drum, and eventually causes damage like bulging or cracking. This study makes investigations into the bulging behavior of the coke drum by the thermal elastic-plastic FE-analysis. In this work, a feasible study is conducted on potential causes of bulging. As factors inducing a heterogeneous plasticity in the shell structure of the coke drum, the strength overmatch of welds and the uneven temperature field in quenching as well as quenching conditions are focused.
Forces on Piping Bends due to Propagating Detonations
Authors: Ligon Thomas C. , Gross David J. , Shepherd Joseph E.
Published: May 2012

This paper reports the results of experiments, analytical models, and finite element simulations on the structural response of piping systems to internal detonation loading. Of particular interest are the interaction of detonations with 90° bends and the creation of forces that lead to axial and bending structural response of the piping system. The piping systems were fabricated using 304 stainless steel, 2-in. (50 mm) diameter schedule 40 commercial pipe with a nominal wall thickness of 0.154-in. (3.8 mm) and welded construction to ASME B31.3 standards. The piping was supported using custom brackets or cantilever beams fastened to steel plates that were bolted to the laboratory walls. Nearly-ideal detonations were used in a 30/70 H2-N2O mixture at 1 atm initial pressure and 300 K. The detonation speeds were close (within 1%) to the Chapman-Jouguet velocity and detonation cell sizes much smaller than the tube diameter. Pressure, displacement, acceleration and hoop, longitudinal, and support strains were measured using a high-speed (1 MHz) digital data acquisition system and calibrated signal conditioners. Detonation propagation through a bend generates a longitudinal stress wave in the piping that can be observed on the strain gauges and is predicted by both analytical models and finite element simulations. The peak magnitude of the bend force is approximately twice that due to the pressure alone since the peak momentum flux of the flow behind the detonation front is comparable to the pressure in the front. With relatively simple models, quantitative predictions of the bend forces can be made for the purposes of design or safety analysis of piping systems with internal detonations.
Comparison of Creep-Fatigue Fitness for Service Assessment Methods for Ferritic-Austenitic Dissimilar Welds
Authors: Penso Jorge A. , Hazime Radwan , Nungesser Stephen , Benatar Avraham
Published: May 2012

The metallurgical characteristics of the damage observed in both service and laboratory test samples indicate that creep rupture is the dominant failure mode for Dissimilar Metal Welds (DMW) in some high temperature service conditions. However, it has also been observed that temperature cycling contributes significantly to damage and can cause failure even when primary stress levels are relatively low. Therefore, a creep-fatigue assessment procedure is required as part of a remaining life calculation. API 579-1/ASME FFS-1 2007 Fitness-For-Service standard includes a compendium of consensus methods for reliable assessment of the structural integrity of equipment containing identified flaws or damage. Part 10 of this document includes a method for protection against failure from creep-fatigue. In the assessment of DMW, a creep-fatigue interaction equation is provided to evaluate damage caused by thermal mismatch, sustained primary stresses, and cyclic secondary loads. In this work, alternative methods based on the ductility exhaustion with creep-fatigue interaction R5 V2/3 and R5 V6 are compared to the API 579-1/ASME FFS-1 standard method. The validity of an elastic FEA with linear material behavior is evaluated based on comparing results from FEA with nonlinear material behavior. A 2.25Cr 1Mo to SS 347 dissimilar joint welded with alloy 625 in a hydroprocessing heat exchanger nozzle joint was selected for the analysis. A Finite Element (FEA) model is used to estimate the sustained and cyclic primary and secondary stresses and strains for this weld. The model includes details of the geometry, material properties, boundary conditions, and loads. The results from the FEA are post-processed using the fatigue methods described above. Lastly, a sensitivity study based on operating temperature is performed. The results of this work indicate that the predictions of the number of cycles and time in service to crack initiation and creep failure are not significantly different between various methods. However, the results of the R5 V2/3 method using linear elastic FEA become invalid at higher temperatures because of significant stress redistribution. The temperature sensitivity analysis clearly showed that the life of the weld is strongly influenced by the service temperature for this type of joint.
Guidelines for Repair Welding of Pressure Equipment in Refineries and Chemical Plants: Part 6—Material Degradation and Repair Welding
Authors: Kiso Tomoaki , Kayano Rinzo , Nagashima Eiki , Hara Yasuhiro
Published: May 2012

It has been recognized that repair welding plays an important role in the long term, safe operation of pressure equipment. In 2009, the Japan Welding Engineering Society (JWES) published guidelines for repair welding of pressure equipment, to meet the great need for the safe operation and proper maintenance of aging plants. This paper addresses the key points of repair welding for damaged materials, based on JWES’s guidelines. The various factors to be considered before implementing repair welding and typical methods of repair welding for the major damage mechanisms are summarized.
Validation of Fabricability for ITER TF Coil Structures
Authors: Chida Yutaka , Iguchi Masahide , Nakajima Hideo , Oosemochi Koichi , Niimi Kenichiro , Tokai Daisuke
Published: May 2012

The ITER superconducting magnet system consists of 18 Troidal Field (TF) coils, 6 Central Solenoid (CS) modules, 6 Poloidal Field (PF) coils and 18 Correction coils. The Japan Atomic Energy Agency (JAEA), acting as the Japan Domestic Energy Agency (JADA) in the ITER project, is responsible for the procurement of 9 TF coil winding packs (WP), structures for 19 TF coils, (including one spare), and assembly of the WP and the coil structures for 9TF coils [1]. TF coil structures, which support large electromagnetic force generated in TF coils under the cryogenic temperature (about 4K), are the mega welding structures composed of coil case and support structures made of heavy thickness high strength and high toughness stainless steel. JAEA started the study on welding trials for the materials to be used since 2008 and have been demonstrating of full scale mock-up model fabrication for main sub-components since 2010. This paper introduces the results on welding trials and status of full scale mock-up model fabrication before fabricating actual products. Enough weld joint performance was obtained with the base metal of JJ1 (FMJJ1 specified by JSME (The Japan Society of Mechanical Engineers) Code [2] and is developed in Japan) and SS316LN (FM316LN specified by JSME Code), and also their combination using JJ1 filler wire (FMYJJ1 specified by JSME Code and is developed in Japan) by narrow gap GTAW process. Welding deformation such as angular distortion between outer plate and side plates of U-shape segment could be controlled and minimized by using effective restraint jig in trial manufacturing of 1m long leg. Validity of welding technology and manufacturing design are confirmed during full scale mock-up model fabrication. And also investigations such as UT (ultrasonic test) and effective welding process for rationalization have been performed.
The Creep-Fatigue Evaluation Method for Intermediate Hold Conditions: Proposal and Validation
Authors: Okajima Satoshi , Kawasaki Nobuchika , Kato Shoichi , Kasahara Naoto
Published: May 2012

In this paper, for the application to the Japan Sodium-cooled Fast Reactor, JSFR, the creep-fatigue damage evaluation method is improved to consider the intermediate holding condition. The improved method is validated through both of the uni-axial and the structure model creep-fatigue tests. In these validations, the target material is 316FR steel, which is planned to use for the reactor vessel. The reactor vessel portion near the liquid sodium surface is one of the most probable points where the creep-fatigue damage is considerable. Because of the relaxation of the temperature gradient, the steady operation stress on the portion near the liquid sodium surface is less than the maximum stress in the transient. In the conventional method, in order to evaluate the creep damage conservatively, the maximum tensile value in the thermal stress transient cycle is used as the initial stress. The improved method evaluates the creep damage using the lower initial stress than the conventional method, while it has the rational margin. For the validation of the improved method, uni-axial creep-fatigue tests and structure model tests are carried out. A series of uni-axial creep-fatigue tests was carried out in the following conditions: 600 degree C testing temperature, 1% total strain range, 1 hour holding time, vacuum or air environments, and the various holding position. While the test environment affects the fatigue damage, it didn’t have significant effect on the creep damage. In the cases with high holding position, the creep damages were evaluated based on the given initial stress with high precision. In the other cases, by the assumption of the steady-stress existence, the rational margin is given for the evaluation. Furthermore, in the design stage, the evaluated creep-fatigue damage has enough margins derived from the conservative evaluation of the initial stress. The structural tests modeled the movement of the liquid sodium surface in the start-up and the shut-down stages, and the relaxation of the temperature gradient in the operation stage. In these tests, the temperature distribution was given by coolant water and an external high-frequency heating coil for the cylindrical specimen, and moved in the axial direction. In addition, the primary stress, which was caused by the weight of the reactor vessel, was given by the screw jack. As a result, using the strain range evaluated by the elastic analysis, the improved method evaluated the crack initiation life due to the creep-fatigue damage with the sufficient safety margin. In the case when the strain range was evaluated by the elastic-plastic analysis, the method predicted the crack initiation life with the good precision. While the evaluation of the crack penetration life was possible, further examination was desired for the precision improvement.
Research on Quantitative Method and 3D Finite Element Analysis of Tank Bottom Corrosion Defect Leakage Magnetic Field
Authors: Dai Guang , Li Wei , Yang Zhijun , Wang Yali
Published: May 2012

According to the principle of magnetic flux leakage testing and the finite element numerical simulation, 3D finite element model (FEM) for MFL testing of tank bottom was established. Through simulative analysis, influence law between defect size and defect magnetic flux leakage field and the relationship curve of defect leakage magnetic field change with its size was obtained. The result showed that: When the length vary with sequence, the peak valley length of defects leakage magnetic signal increase with the increase of defect length, the relationship curve between each other is approximate linear; When the depth vary with sequence, the relationship between peak valley height of defects leakage magnetic signal and defect depth is also approximate linear, but this relationship was different with different length; When the width vary with sequence, on the defect symmetry plane, the peak of magnetic flux density along the width direction corresponded with the defect edge, and the length of the two peaks were equal to the width of the defect. According to simulation data and theory of regression analysis linear regression equation and relation surface between defect length depth and the characteristic quantity of its signal was established, quantitative method of defects signal was also proposed. Then experimental study was carried out in the Laboratory, the result show that the quantitative size was consistent with the actual defect size.
Guidelines for Repair Welding of Pressure Equipment in Refineries and Chemical Plants: Part 2—Repair Welding Method
Authors: Shiga Keisuke , Hirai Yukio , Yasushi Ogayu
Published: May 2012

It has been recognized that repair welding plays an important role of in the long term, safe operation of pressure equipment. In 2009, the Japan Welding Engineering Society (JWES) published guidelines for repair welding of pressure equipment, to meet the great need for the safe operation and proper maintenance of aging plants. This paper gives brief descriptions of three types of repair welding method, “Flaw excavation and repair welding”, “Butt-welded insert plates”, and “External fillet welded patches”, which welding methods are based on Chemical Plant Welding Research Committee of JWES.
LES Analysis of Temperature Fluctuations at T-Junctions for Prediction of Thermal Loading
Authors: Qian Shaoxiang , Kasahara Naoto
Published: May 2012

T-junctions are widely used for fluid mixing in nuclear power and chemical and refinery plants. Temperature fluctuations generated by the mixing of hot and cold fluids at a T-junction can cause high cycle thermal fatigue (HCTF) failure. Japan Society of Mechanical Engineers (JSME) published ‘Guideline for Evaluation of High Cycle Thermal Fatigue of a Pipe (JSME S017, 2003)’ which results in a very conservative evaluation. CFD/FEM coupling analysis is considered as a useful tool for the more rational evaluation of HCTF. The present paper aims at the validation of CFD simulations to establish a more rational method of evaluating thermal loading, prior to performing CFD/FEM coupling analysis. It is very important to choose the proper turbulence model for the analysis of unsteady phenomena such as the highly fluctuating flow and temperature fields at a T-junction. Here, large eddy simulation (LES) turbulence models suitable for the simulation of the unsteady phenomena were investigated. LES sub-grid scale (SGS) models used include standard Smagorinsky model (SM) and dynamic Smagorinsky model (DSM). The effects of numerical schemes for the calculation of the convective term in the energy equation on the simulation results were also investigated. LES analyses of the flow and temperature fields at a T-junction were carried out using the above SGS turbulence models. For the sake of comparison, the simulation conditions are the same as those of the WATLON experiments conducted at Japan Atomic Energy Agency (JAEA) in the literature. All of the simulation results show the flow pattern of the wall jet with the strong flow and temperature fluctuations, which is the same as that observed in the experiment. The simulation results indicate the numerical schemes have great effect on the temperature distribution and the temperature fluctuation intensity (TFI). The 1st-order upwind differencing (1UD) significantly underestimates the TFI for each LES model, although it exhibits a good numerical stability. On the other hand, the hybrid scheme, which is mainly the 2nd-order central differencing (2CD) blended with a small fraction of 1UD, can better predict the TFI for each LES model. Furthermore, the DSM model gives a prediction closer to the experimental results than the SM model while using the same numerical scheme. In this study, an important finding is that a combination of the DSM model and the hybrid scheme with a large blending factor can provide a prediction agreeing very well with the experimental results.
Ductile Crack Initiation Behavior of Prestrained Steels
Authors: Yamada Takehisa , Yamashita Yoichi
Published: May 2012

Ductile crack initiation behaviors were experimentally and analytically investigated using compressively prestrained notched round bar specimen (lower stress triaxiality condition) and four point bend specimen (higher stress triaxiality condition). The materials used were SM400B and HT780. It was observed that ductile crack initiation of notched round bar specimen occurred at the center of specimen and was caused by coalescence of micro voids. Ductile limit curves, which are the relationships between equivalent plastic strain and stress triaxiality factor at ductile crack initiation, were obtained using FE-analyses and experimental results. Ductile crack initiation of four point bend specimens as cracked specimens could be evaluated using ductile crack initiation limit curves obtained from notched round bar specimens if the positions of void nucleation at crack tip are properly considered. It has been found that ductile crack initiation limits can be evaluated using ductile limit curves under both low and high constraint conditions (stress triaxiality conditions.
Pressure Coefficient Distribution Over Tube Surfaces of Tube Bundle Subjected in Two-Phase Flow
Authors: Sim W. G.
Published: May 2012

Two-phase cross flow exists in many shell- and tube heat exchangers such as condensers, evaporators and nuclear steam generators. During the last two decades, research devoted to two-phase flow induced vibrations has increased, mainly driven by the nuclear industry. Flow-induced vibration excitation forces can cause excessive vibration which will result in long-term fretting-wear or fatigue. To avoid potential tube failures in heat exchangers, it is required for designer to have guidelines that incorporate flow-induced vibration excitation forces. The phenomenon of the vibration of tubes in two-phase flow is very complex and depends on factors which are nonexistent in single-phase flows. To understand the fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Pressure distributions generated by two-phase flow over tube surfaces yield more general information than the local velocity distribution. The pressure coefficient distribution obtained by experimental test has been evaluated.
Design of a Large Diameter Steel Reinforced Plastic Pipe
Authors: Shi Jun , Rao Jing , Shi Jianfeng , Xu Ping , Shao Taiqing , Shao Hanzeng , Chen Defu , Li Guangzhong , He Xiaolian
Published: May 2012

A steel reinforced plastic pipe (PSP), which is composed of two layers of high density polyethylene (HDPE) matrix and a high strength steel wire mesh skeleton, has wide applications in many industrial areas, such as gas and petroleum transportation, etc. In order to achieve higher efficency and lower costs, a large diameter PSP has been developed. However, requirements of the large diameter PSP in safety and economy are much higher, compared with those small diameter PSPs, and some potential problems should be taken into account. In this paper, relevant structural parameters of the large diameter PSP are determined, based on a previously proposed model, and a short-term burst test is carried out. The experiment results agree with the theoretical results quite well. Subsequently, the resistance of vertical pressure and uniform external pressure are evaluated by using experiment investigation and finite element method, respectively. And corresponding results indicate the large diameter PSP with determined structural parameters is qualified to use.
A Method of Crack Detection in the Turbine Blade Using Digital Holographic Microscopy (DHM)
Authors: Tada Naoya , Hamada Seiichi , Teramae Tetsuo , Yoshino Shin , Suzuki Takehiko
Published: May 2012

The authors proposed an NDE method of detecting the crack developed in the turbine blade by means of digital holographic microscopy (DHM). UT procedures sometimes have limitations in particular cases of in-service-inspections such as the detection and sizing of a creep crack developed in the air-cooled casting blade of the combined cycle gas turbine. The local displacement at the blade surface near the crack during a mechanical loading is different from that of a non-cracked blade. This small different can be detected by DHM. The authors discussed whether this difference affected by the mechanical load between the cracked blade and the non-cracked is detectable by means of DHM or not. In this paper, the authors verified the practical validity of the proposed NDE method using the finite element analyses.
Effect of the Out-of-Plane Constraint on Creep Crack Growth Property of Cr-Mo-V Type Steel
Authors: Tan Jian-Ping , Wang Guo-Zhen , Xuan Fu-Zhen , Tu Shan-Tung , Wang Zheng-Dong
Published: May 2012

In order to establish an accurate integrity assessment of structures containing defects at high temperature, it is necessary to clarify the constraint effect on creep crack growth (CCG) property. However, the effect of the out-of-plane creep constraint induced by the specimen thicknesses has been little studied. In this study, the CCG properties and fracture mechanism of Cr-Mo-V type steel at 566°C were investigated by using the compact tension specimens with different thicknesses. The results show that the data of the CCG rate da/dt versus C* lie within a relatively tight scatter band on log-log scale for the specimens with different thicknesses at higher values of C*. In addition, the differences of CCG rate becomes large with C* decreasing. It means that the effect of out-of-plane constraint on CCG rate is dependent on the load level (C*). The reason for the similar CCG rate is that the creep damage and fracture mechanism of void growth at grain boundary ahead of crack tips in the specimens with different thicknesses does not essentially change. The size rc of the creep damage and fracture process zone in front of crack tips is related to the specimen thickness, and the damage rate fields over the process zone are similar for the specimens with different thicknesses. The deformation near the crack tip obscures the constraint effect. Based on a reference stress field under plane strain state and the creep process zone rc, in-plane and out-of-plane constraint parameter Rd and Td were defined and the creep crack-tip constraint effect induced by specimen thickness were quantitatively examined. The factors of creep time and load level (C*) influencing the constraint effect were analyzed.
Study on the Microstructure of 20 Steel With Strain Aging
Authors: Li Mengli , Wang Weiqiang , Li Aiju
Published: May 2012

20 steel thick-wall high-pressure pipes are widely used in chemical industry in China, but brittle fracture accidents of them happen frequently in recent years. The strain aging steel pipes in this research were artificially made in the laboratory and naturally occurred in fabrication or service. The microstructure of strain aging in samples taken from the unused pipes and the accident pipes caused directly or mainly by strain aging were observed with optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that: (1)uniform ferrite and pearlite with uniform lamellar structure can be achieved with normalizing; lamellar pearlite fractures and distorts while a large number of dislocation cells, micro-holes or cracks appear in material after strain aging; and broken distorted pearlite changes to uniform spherical structure after stress relieving; (2) both the samples taken from unused and accident pipes which strain aging artificially in the laboratory and naturally in fabrication or service have the same characteristics as following: the basic changes of microstructure after strain aging cannot be observed with optical microscopy, but can be observed with scanning electron microscopy and transmission electron microscopy.
A Remaining Life Assessment for Shell-to-Skirt Juncture of Coke Drum With Crack-Like Flaws
Authors: Oka Masaaki , Ambarita Himsar , Daimaruya Masashi , Fujiki Hiroyuki , Kobayashi Hidetoshi
Published: May 2012

Coke drums are subjected to severe cyclic thermal and mechanical loads, thus their operational life is much shorter than other the conventional pressure equipments in oil refineries. Information developed from surveys indicates that one of major typical locations of failure due to thermal fatigue in coke drums is the shell-to-skirt juncture area. At the outer surface of the upper part of the skirt, there are two peak strains in every cycle which are tensile in the beginning of the filling stage and compressive in the cooling stage. The objective of the present paper is to develop a remaining life assessment method for shell-to-skirt juncture of coke drum with cracks propagated during cyclic operation. A coke drum currently in service with inside diameter of 8.55 m, height of 34.9 m, shell thickness varies from 28.5 mm to 34 mm, and skirt thickness of 24 mm is taken into analyses. In order to get the actual operational characteristics of the coke drum, temperatures and strains on the coke drum have been measured for 100 cycles. The selected operational temperatures will be employed as thermal boundary conditions for analyses. Propagations of 2 mm initial cracks depth at the inner surface of the upper part of the skirt, underneath the juncture as shown in Fig-3, is simulated on the basis of linear elastic fracture mechanics (LEFM). The relations of crack size with the number of operation cycles are plotted.
Progress Towards the Revision of BS 7910
Authors: Hadley Isabel
Published: May 2012

BS 7910, the UK procedure for the assessment of flaws in metallic structures, is being revised with a view to publication in 2012. Like the existing procedure, the new procedure will address all major failure/damage mechanisms, namely fracture, fatigue, creep and corrosion, and is intended to be used across a range of industry sectors and component types. There are several major proposed changes, which draw mainly on the existing BS 7910 procedures, the UK nuclear industry’s R6 document and the European FITNET procedure. The most far-reaching changes are in Section 7 (fracture) and related annexes. Here, the modifications include: • a re-structuring of the fracture assessment procedures from their present form (Levels 1–3) to a new hierarchy based on Options 1–3, which are more compatible with the current R6 and FITNET approaches, • revised treatment of flaw interaction, • a new annex (Annex N) permitting analysis under conditions of reduced crack tip constraint, • a new annex (I) addressing analysis of weld strength mismatch, • a revised residual stress compendium (Annex Q). As part of the revision, all annexes will be reviewed and edited where necessary, and a new annex on non-destructive examination (NDE) will be included for the first time. In view of the fact that many of the major changes concern the fracture assessment clauses, this paper presents a case study based on the analysis of a fully-circumferential flaw in a pipeline girth weld. The basic assessment Options (1 and 2) given in the new procedure are used to analyse the flaw, and three more advanced techniques (constraint-based assessment, assessment using an idealised residual stress distribution and analysis based on weld strength mismatch) are also applied.
Aeroacoustic Source Identification in Gas Transport Pipe System
Authors: Golliard Joachim , Di´ez Ne´stor Gonza´lez , Nakibog˘lu Gu¨nes¸ , Hirschberg Avraham , Belfroid Stefan
Published: May 2012

Whistling due to Flow-Induced Pulsations can occur in gas transport and gas export pipe systems with low Mach number flow. These flow-induced pulsations can lead to piping vibration or acoustic fatigue of piping elements. The study presents a simple numerical pulsation source identification method applied to restriction orifices. In case of whistling, small acoustic perturbations incident on some pipe elements such as restriction orifices and T-junctions are amplified by the shear layer flow at certain frequencies, propagate downstream and upstream of the elements, and are reflected by the ends of the piping or by large section changes. The element acts as an acoustic amplifier for the incident acoustic energy at certain frequencies. The source identification method, earlier presented by Martinez-Lera et al [1] for the aeroacoustic source identification of T-junctions and improved by Nakiboglu et al [2] for circumferential cavities in corrugated pipes, combines incompressible numerical simulations with vortex sound theory. It is applied here to restriction orifices, commonly used in industrial pipe systems as measuring devices, to induce a pressure drop, or to reduce low frequency pulsations. Incompressible, laminar CFD simulations are used for the source identification instead of fully compressible LES. These simplifications enable much less CPU intensive computations, but require extra post processing. A particularly sensitive point is the estimation of the pressure drop due to the potential flow. This is estimated with a simulation made on a straight, empty pipe of same characteristics. This method is applied to restriction orifices in this paper, and the specific points for this particular geometry are reviewed. The results are compared to the experimental and numerical results of Testud et al [3] and Lacombe et al [4]. The application of the method to the source identification of whistling restriction orifices predicts whistling at Strouhal numbers similar to earlier experimental and numerical studies, with limited computational effort.
Damage Caused by Dynamic/Cyclic Loading of Detonation Chamber
Authors: Takashima Yasuhito , Ohata Mitsuru , Tagawa Tetsuya , Simoens Bart , Lefebvre Michel H. , Nickell Robert E. , Koide Kenji , Kitamura Ryusuke , Hayashi Koichi , Asahina Joseph K. , Minami Fumiyoshi
Published: May 2012

The plastic damage caused by multiple dynamic loading and its influence on the ductility and toughness of 3.5%Ni-steel (SA203E) and C-steel (SA516M) were examined for the discussion of integrity design of detonation chambers. V-notched specimens and hourglass specimens were welded on 1/7-scale model of a 1-ton explosive class detonation chamber and subjected to 30 detonation shots. It has been indicated that 30 detonation shots caused pre-strain in the specimens. The ductility was reduced by the pre-strain. The Charpy impact toughness was affected as well in a lower temperature. It has been noted that the damage is developed with fatigue crack growth at notch root of the V-notched specimen.
Study on Skirt-to-Shell Attachment of Coke Drum by Evaluation of Fatigue Strength of Weld Metal
Authors: Sasaki Yasuhiko , Niimoto Shinta
Published: May 2012

A skirt-to-shell attachment of a coke drum experience severe thermal cyclic stresses, which cause failures due to low cycle fatigue. Various skirt attachment designs, therefore, have been proposed and implemented. A design where the skirt is attached by a weld build-up is most commonly used. A design where the skirt is attached to the drum shell by utilizing an integral machined plate or forging has been utilized in several projects. One of the advantages of the integral skirt attachment is that a large inner radius can be formed which allows reducing stress concentration compared with the weld build-up design. This advantage can be confirmed easily by FE-analysis in recent years [1] [2] [3]. Another major advantage of the integral skirt attachment is that the area of highest stress intensity is located at the base metal section, not at the weld metal or the heat affected zone which are generally thought to have lower fatigue strength. The fatigue design curve from ASME Section VIII Division 2 [9] is based on fatigue tests for the base metal. It is necessary to reveal differences of fatigue strength among these metals. This paper describes a comparison of fatigue strength of three metals: i) base metal ii) weld metal iii) heat affected zone provided by the low cycle fatigue test for 1 1/4Cr-1/2Mo materials. Our results indicate that the fatigue life of the base metal is about twice as long as that of the weld metal and about three times as long as the heat affected zone. Accordingly, the integral skirt attachment is more resistant to cracking than its welded counterpart from a fatigue strength viewpoint.
Crack Tip Behaviour in Residual Stress Field: Finite Element Modelling and Neutron Diffraction Measurements
Authors: Dai H. , Kelleher J. F. , Withers P. J.
Published: May 2012

Simple analyses of fracture and fatigue often make use of the stress intensity at a crack tip or the J-integral surrounding it. However, there is no universally accepted method of including the effect of residual stress in these values, even though the qualitative effect of residual stress on crack growth is well known. In this work, we create a cracked compact tension C(T) specimen with a residual stress field that affects the crack tip behaviour, in particular by altering the level of expected crack closure. Neutron diffraction measurements under in situ applied loading reveal strain distributions consistent with an increased level of closure when the crack tip is in a state of compressive residual stress. Through finite element modelling of the samples studied, we show that the residual stress in these samples redistributes as the crack grows, which changes the level of crack closure for any given crack length and applied load. As crack closure is often considered in fatigue analysis by deriving an ‘effective’ stress intensity based on the applied load needed to overcome the closure and open the crack, the model is used to compare this approach with numerical calculations of the J-integral for different crack lengths.
Effect of Mechanical Parameter Selection in Quantitative Estimation of the Growth of Environmentally Assisted Cracks at Flaws in Light Water Reactor Components With Complex Mechanical Condition
Authors: Xue He , Gong Xiaoyan , Zhao Lingyan , Lu Zhanpeng , Shoji Tetsuo
Published: May 2012

To simplify the experimental process, most experiments carried out to make quantitative predictions of environmentally assisted cracking (EAC) growth rate of stainless steel or nickel based alloy are based on standard specimen in a simulated high temperature water environment in laboratories. In the other hand, the mechanical state and geometrical shape of the flaws in the components of light water reactors (LWRs) are usually more complex than the cracks in standard specimens. It is well known that the mechanical factor near to the crack tip is one of the most important factors affecting EAC growth rate in high-temperature aqueous environments. Based on an EAC experiment with a mock-up pipe specimen with two inner axial cracks and a numerical simulation by the elastic-plastic finite element method (EPFEM), it is analyzed that the effect of the different mechanical parameter selection in describing mechanical state close to the tip of EAC on quantitative estimation of EAC growth rate at flaws in nuclear pressure vessels and piping in this study. And the study is expected to form a bridge between predicting EAC growth rate in the stainless steel or nickel based alloy and evaluating EAC growth in key structural components in LWRs.
Evaluation of Local Thinning Shape by LDI for Seismic Safety Evaluation of Piping System
Authors: Morita Ryo , Inada Fumio , Sakai Michiya , Matsuura Shin-ichi , Onishi Shigenobu , Kugimoto Mitsuo
Published: May 2012

For seismic safety evaluation of piping system with local thinning surface by liquid droplet impingement erosion (LDI), hybrid seismic tests were conducted to the piping with a locally-thinned elbow. In this paper, a method for predicting the thinning shape by LDI on the elbow is developed. To determine the thinning shape by LDI, droplet behavior at the elbow is calculated for various flow conditions and geometries. With the calculation of the collision point and velocity for each droplet, collision frequency and average collision velocity on the elbow are estimated. Then, the thinning shape on the elbow is determined with the relationship between the flow conditions and thinning rate. Finally, the evaluated thinning shape is compared with an actual LDI case for the validation of the method.
Failure Probability Assessment of Piping Systems Affected by SCC and Pipe Wall Thinning for LBB Analysis
Authors: Chitose Hiromasa , Machida Hideo , Saito Itaru
Published: May 2012

This paper provides failure probability assessment results for piping systems affected by stress corrosion cracking (SCC) and pipe wall thinning in nuclear power plants. On the basis of the results, considerations for applying the leak-before-break (LBB) concept in actual plants are presented. The failure probability for SCC satisfies the target failure probability even if conservative conditions are assumed. Moreover, for pipe wall thinning analysis, pre-service inspection is important for satisfying the target failure probability because the initial wall thickness affects the accuracy of the wall thinning rate. The pipe wall thinning analysis revealed that the failure probability is higher than the target probability if the bending stress in the pipe is large.
Low Cycle Fatigue Behaviors of Elbow With Local Wall Thinning Under Combined Bending and Internal Pressure
Authors: Takahashi Koji , Matsuo Kazuya , Sato Kyohei , Ando Kotoji , Urabe Yoshio , Kasai Naoya
Published: May 2012

Low-cycle fatigue tests were conducted using elbow specimens with local wall thinning in order to investigate the influences of position of local wall thinning on the low-cycle fatigue behaviors of elbows. Local wall thinning was machined on the inside of the elbow in order to simulate metal loss from erosion corrosion. The local wall thinning was located in three different areas. The elbow specimens were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. In addition, three-dimensional elastic-plastic analyses were also carried out using the finite element method. As a result, the crack penetration area and the crack growth direction were successfully predicted by the analyses.
Improvement of Contact Strength of Si3N4/SiC by Combination of Shot Peening and Self-Crack Healing
Authors: Takahashi Koji
Published: May 2012

In this study the combination effects of shot peening (SP) and crack-healing on the contact strength of ceramics were examined. Si3N4/SiC composite ceramics with high crack-healing ability were used and the specimens were subjected to shot peening with several peening pressures and shot diameters. Then, some specimens subjected to SP were heat-treated in air to heal surface cracks introduced by shot peening. Sphere indentation tests were carried out on the specimens and investigated the Weibull distribution of the contact strength. As a result, it is found that the combination of shot peening and crack-healing is effective to increase contact strength and decrease the scatter of the contact strength.
Modelling the Interpass Temperature Effect on Residual Stress in Low Transformation Temperature Stainless Steel Welds
Authors: Dai H. , Moat R. J. , Withers P. J.
Published: May 2012

Weld residual stresses often have serious implications for the integrity of engineering structures (distortion, stress-corrosion cracking, hydrogen-induced cracking). Previously, it has been demonstrated by the authors that the use of a stainless steel welding consumable with a low martensite start temperature in single-pass welding can lead to lower (potentially harmful) tensile residual stresses or even compressive stress within the fusion zone and heat affected zones compared to non-transforming austenitic fillers. However, such effects may not carry over to multi-pass welding if the filler transforms fully on cooling from the first pass. In this paper finite element modelling is used to examine the use of interpass hold temperatures on the residual stresses introduced using such weld fillers in multi-pass welding of 304L stainless steel plate. Four levels of interpass temperature have been studied. The model has also been verified against experimental data obtained using the contour method for two welded plates having two different inter-pass temperatures. It is demonstrated that interpass hold temperatures above, or around, the transformation temperature can have very significant effects, allowing residual stress management of the resulting welded joint.
Specimen Geometry Effects on Creep Crack Initiation and Growth in Parent Materials and Weldments
Authors: Davies Catrin M. , Wimpory Robert C. , Dean David W. , Nikbin Kamran M.
Published: May 2012

High temperature crack growth in weldments is of great practical concern in high temperature plant components. Cracking typically occurs in the heat affected zone (HAZ) and often propagates into adjacent parent material (PM). Recently, the importance of constraint effects on creep crack growth behaviour has been recognised and creep crack growth testing on a range of specimen geometries has been performed. Experimental crack growth testing has been performed at 550 °C on a range of fracture specimens using sections taken from a non-stress-relieved 316 steel weldment. These specimens include the compact tension, C(T), middle tension, M(T) and circumferentially cracked bar, CCB, geometries. Results are presented from two long-term creep crack growth (CCG) tests performed on M(T) weldment specimens and these are compared with available data on C(T) and CCB weldment specimens together with both long and short term tests on parent material for a range of specimen geometries. The creep crack initiation (CCI) and growth (CCG) behaviour from these tests has been analysed in terms of the C* parameter. As high levels of residual stress exist in non-stress-relieved weldments, the residual stresses remaining in the weldment specimens have therefore been quantified using the neutron diffraction technique. Long-term (low-load) tests are required on PM specimen to observe specimen constraint effects in 316 steel at 550 °C. When interpreted in terms of the C* parameter the CCG behavior of PM and Weldment materials follow the same trendline on low constraint geometries. However, significant difference is observed in the CCG behavior of PM and weldments on the high constraint C(T) geometry. Long term tests on C(T) specimen weldments are required to confirm the results found.
Cold Stretching of Cryogenic Pressure Vessels From Austenitic Stainless Steels
Authors: Zheng Jinyang , Guo Abin , Miao Cunjian , Xu Ping , Yang Jian , Ye Jianjun , Ma Li , Wu Linlin , Yang Guoyi
Published: May 2012

Austenitic stainless steel (ASS) exhibits considerable work-hardening upon deformation while retaining the characteristics of the material. The high rate of austenite deformation hardening was utilized by cold stretching (CS) of cryogenic pressure vessels. A few percent deformation will give the vessel a considerable and homogeneous yield strength improvement, and the wall thickness may be greatly reduced. The authors have conducted extensive experimental and numerical studies on CS of cryogenic pressure vessels from ASS. A summary of our work as well as a brief introduction of the history, standards, safety, and advantages of CS are given in this paper. What should be further investigated, such as fatigue properties of cold stretched ASS especially under cryogenic temperature, design of cold stretched transportable cryogenic vessels based on life, are also presented.
Creep Damage Assessment Procedure for Weldment Parts of P91 Boiler Piping in USC Plants: Part II—Validation of a Creep Damage Assessment Method Based on Void Growth Simulation
Authors: Ogata Takashi , Sakai Takayuki , Yaguchi Masatsugu , Hoshino Katsuaki
Published: May 2012

Clarification of creep damage mechanisms and establishment of remaining life prediction methods of weldment parts of P91 boiler pipings are important subjects to maintain reliable operation of boilers in thermal power plants. In order to develop a creep damage assessment method of weldment parts of P91 pipings, internal pressure creep tests were conducted on P91 steel longitudinally welded tubes and a previously proposed void growth simulation method is applied to predict void growth behavior. Failure occurred at the heat affected zone without significant deformation. It was found from observation of creep damage interrupted specimens that initiation of creep voids concentrated at the mid-thickness region rather than the surface. It was suggested that triaxial stress states caused acceleration of creep damage evolution in the heat affected zone resulting in internal failure of the tube specimens. Void growth behavior in the heat affected zone was well predicted by the previously proposed void growth simulation method. The void growth prediction method is applied to predict creep damage induced by void initiation and growth in a weldment part of an actual P91 pipe. From comparison of void number density between measurement for a weldment part of a retired elbow pipe and prediction by the simulation, good agreement is obtained indicating the void growth simulation method can be applied to creep damage assessment of weldment parts in actual boiler piping.