bluuebunny/crossref_metadata_2025 huggingface dataset:
NTD ASI, Section IV: Evaluation of Residual Lifetime of Components and Piping in WWER Type NPPs
Authors: Brumovsky Milan
Published: October 2018

VERLIFE – “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs during Operation” was initiated and co-ordinated by the Czech and was developed within the 5th Framework Program of the European Union in 2003 and later upgraded within the 6th Framework Program “COVERS – Safety of WWER NPPs” of the European Union in 2008. This Procedure had to fill the gap in original Soviet/Russian Codes and Rules for Nuclear Power Plants (NPPs) with WWER (Water-Water-Energetic-Reactor = PWR type) type reactors, as those codes were developed only for design and manufacture and were not changed since their second edition in 1989.

VERLIFE Procedure is based on these Russian codes but incorporates also new developments in research, mainly in fracture mechanics, and also some principal approaches used in PWR codes.

Last upgrading and principal extending of this VERLIFE Procedure was realized within the 3-years IAEA project (in close co-operation with another project of the 6th Framework Program of the European Union “NULIFE – Plant Life Management of NPPs”) that started in 2009 with final approval and editing in 2013.

As all versions of the VERLIFE procedure were coordinated by the Czech and first version was based on the Czech version of the NTD ASI, there have been simultaneously incorporated into the Czech NTD ASI (Normative Technical Documentation of the Czech Association of Mechanical Engineers) guidelines that are accepted by the Czech State Office for Nuclear Safety for the use in evaluation of Czech NPPs.

This document has several parts: Section IV – “Evaluation of Residual Lifetime of Components and Piping in WWER type NPPs” deals with the evaluation during NPP operation. Main part of the document is divided into four main parts:

- Evaluation of resistance of components and piping against non-ductile failure

- Evaluation of resistance of component and piping against fatigue damage,

- Evaluation of resistance of components and piping against corrosion-mechanical damage

- Evaluation of residual lifetime of components and piping with defects found during in-service inspections

Additionally, several appendices are included for detailed description of individual parts of evaluation, e.g.

- Determination of neutron fluences in reactor pressure vessel and internals

- Determination of degradation of materials during operation

- Requirements for evaluation of pressurized thermal shock regimes

- Evaluation of corrosion-errosion effects in piping

- Environmental fatigue evaluation

- Evaluation of reactor pressure vessel failure probability

Finally, the following appendices dealing with components integrity have been included:

- Lifetime of reactor pressure vessel internals

- Leak-before-break concept for WWER piping

- No-break-zone for WWER piping

The paper will describe structure and main principles of this Section IV.
Evaluation of Reactor Internals Integrity and Lifetime According to the NTD ASI
Authors: Brumovsky Milan
Published: October 2018

Reactor internals are components that are no typical pressure boundary but they are nevertheless very important as they hold fuel elements and all reactor control system elements and thus must ensure their safe and reliable operation during the whole reactor life under all operating and even beyond bases regimes.

In principle, reactor internals can be replaced but their weight, quantity of very high activated material and cost such possibility practically excluded.

Thus, evaluation of the reactor internals condition and prediction of their behavior during the whole or even extended lifetime is of high importance. Reactor internals are subjected to very high neutron irradiation that could initiated not only stress corrosion (irradiation assisted) cracking but also large embrittlement and changes in dimensions (swelling and creep).

VERLIFE – “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs during Operation” was initiated and co-ordinated by the Czech and was developed within the 5th Framework Program of the European Union in 2003 and later upgraded within the 6th Framework Program “COVERS – Safety of WWER NPPs” of the European Union in 2008. This Procedure had to fill the gap in original Soviet/Russian Codes and Rules for Nuclear Power Plants (NPPs) with WWER (Water-Water-Energetic-Reactor = PWR type) type reactors, as those codes were developed only for design and manufacture and were not changed since their second edition in 1989.

VERLIFE Procedure is based on these Russian codes but incorporates also new developments in research, mainly in fracture mechanics, and also some principal approaches used in PWR codes.

Within the last upgrading and principal extending of this VERLIFE Procedure was developed within the 3-years IAEA project (in close co-operation with another project of the 6th Framework Program of the European Union “NULIFE – Plant Life Management of NPPs”) that started in 2009 with final approval and editing in 2013”) a part dealing with the evaluation of reactor internals lifetime was elaborated..

This IAEA VERLIFE procedure for internals has been implemented into the existing Normative Technical Documentation (NTD) ASI (Czech Association of Mechanical Engineers), Section IV – Evaluation of Residual Lifetime of Components and Piping in WWER type NPPs.

Main damaging mechanisms that should be taken into account in reactor internals and the procedure are described in detail with necessary formulae for materials of internals:

- Radiation hardening

- Radiation embrittlement

- Radiation swelling

- Radiation creep

- Swelling under stress effect

- Swelling inducing embrittlement

- Irradiated assisted stress corrosion cracking

- Transformation austenite-ferrite

and also the method for evaluation of the resistance against non-ductile failure of postulated defect.

The paper will describe these main principles and also more detailed information on the procedure for evaluation of reactor internals will be given.
Interlaboratory Study for Small Punch Testing Preliminary Results
Authors: Brumovsky Milan , Kopriva Radim
Published: October 2018

Small punch test specimens are widely used for a long time as they are simple to produce and requires only a small volume of material. This fact is advantageous especially for high activity materials but also for assessment of operational damage in components materials when component integrity and strength may not be affected. In the same time, no test standard exists and several different specimen types and test procedures have been developed in different place.

Thus, to unify this activity, considerable attention has been paid since 2012 to the standardization of small punch test technique within the American Society of Testing and Materials (ASTM). In 2016 a large InterLaboratory Study has been launched within the ASTM subcommittee E10.02 - Behavior and Use of Nuclear Structural Materials, involving 12 laboratories and 6 evaluated structural materials from the nuclear and non-nuclear power plant components.

Paper describes the current status of ASTM standardization, results of the InterLaboratory Study, first analysis of the results with respect to some important test parameters, lessons learned and open questions remaining to be solved for the successful completion of the standardization process.
A Modified Microstructure-Based Creep Damage Model for Considering Prior Low Cycle Fatigue Damage Effects
Authors: Zhang Wei , Wang Xiaowei , Gong Jianming
Published: October 2018

A modified continuum damage mechanics (CDM) model was proposed to predict the creep behavior of P92 steel with prior low cycle fatigue (LCF) damage. In order to investigate the damage mechanisms of prior LCF, microstructural observations of P92 steel after various prior LCF and subsequent creep exposures were performed. Results show that the key creep degradation is associated with the martensite lath recovery. Based on the physics of microstructural evolutions, three state variable formulas which represent damage mechanisms related to martensite lath recovery were employed to account for the prior LCF damage. The three state variable formulas which describe the damage evolution with prior LCF cycles were coupled with Hayhurst CDM model. The main advantage of the modified CDM creep model lies in its ability to directly predict creep behavior with different levels of prior LCF damage. The only parameter needed to be known for the prediction is the martensite lath width after prior LCF. Comparison of the predicted and experimental results shows that the proposed model can give a reasonable prediction for creep behavior. Moreover, this model also shows good predictive ability at different strain amplitudes of prior LCF.
Prediction of Transient Hydrodynamic Loads on the PWR Steam Generator Tubes at a Main Feed Water Line Break Accident
Authors: Jo Jong Chull , Jeong Jae Jun , Yun Byong Jo
Published: October 2018

A computational fluid dynamics (CFD) analysis was performed to predict the transient hydrodynamic loads exerted on the steam generator tubes and the thrust forces on the broken pipe (which is equal to the impingement forces on target structures in the expanding fluid jet path) during a main feed water line break (FWLB) accident at a pressurized water reactor (PWR) power plant. To address a possible severe case of the transient hydrodynamic loads, the break was assumed to occur at the circumferential weld line between the feed water nozzle and the main feed water pipe so that the compressed sub-cooled water would be discharged through the short broken pipe. Thus, a sub-cooled liquid flashing flow through the broken short feed pipe was simulated numerically. Typical results of the prediction were illustrated and discussed. In addition, the present simulation in terms of the transient mass flow rates during the blowdown following the MFLB was compared to other previous calculations. Based on the discussions, the present simulation is considered to be physically plausible and more realistic than other previous predictions.
Experimental and Numerical Investigations on the Failure Behavior of Pressurized Components Containing Crack Fields
Authors: Gauder Patrick , Schuler Xaver , Seidenfuss Michael
Published: October 2018

During the 2012 outage of the Belgian nuclear power plants (NPP) Doel 3 and Tihange 2 non-destructive testing (NDT) measurements revealed a high quantity of indications in the upper and lower core shells of the reactor pressure vessels (RPV). A root cause analysis leads to the most likely hypothesis that the indications are hydrogen flakes in segregated zones of the RPV ferritic base material. The laminar and quasi-laminar orientation (0° – 15° inclination to the pressure retaining surface) of the hydrogen flakes, the interaction of several adjacent flakes and the mechanical loading conditions lead to a mixed-mode behavior at the crack tips.

In the framework of an ongoing research project, experimental and numerical investigations are conducted with the aim to describe the failure behavior of such complex crack configurations. The experiments are carried out using two ferritic materials. One is a non-irradiated representative RPV steel (SA 508 Class 2) and the second material is a special lower bound melt of a modified 22NiMoCr3-7 steel (FKS test melt KS 07 C) containing hydrogen flakes. A material characterization is done for both materials including tensile specimens, notched round bars, shear-, torsion- and compact-tension-shear (CTS) - specimens to investigate different stress states. Furthermore, flat tensile specimens with eroded artificial crack fields are used to investigate the interaction between the cracks in different arranged crack fields. Numerical simulations are carried out with extended micromechanical based damage mechanics models. For the description of ductile failure an enhanced Rousselier model is used and an enhanced Beremin model to calculate the probability of cleavage fracture. To account the sensitivity for low stress triaxiality damage by shear loading, the Rousselier model was enhanced with a term to account for damage evolution by shear. The Beremin model will be enhanced with a term to account for different levels of triaxiality. For the numerical simulations in the transition region of ductile-to-brittle failure a coupled damage mechanics model (enhanced Rousselier and Beremin) will be used. In this paper, the current status of the ongoing research project and first results are presented.
Modeling Automatic Detection of Critical Regions in Composite Pressure Vessel Subjected to High Pressure
Authors: Macri Michael F. , Littlefield Andrew G. , Root Joshua B. , Smith Lucas B.
Published: October 2018

Composites can undergo micro damage leading to variations of the mechanical properties. The micro damage can be the result of high internal pressures and/or exposure to physical trauma. Modeling techniques, such as homogenization, are effective outside of these critical regions. However they break down in regions where the micro damage is occurring. To account for this, an algorithm has been developed to detect and implement a multiscale method on elements that observe a critical strain. The remaining model uses the homogenization method to simulate the composite. The elements surrounding the multiscale elements are adapted to act as a transition from multiscale to the homogenization. The multiscale approach is based on the partition of unity paradigm, allowing macro-scale computations to be performed with the micro-structural features explicitly considered. The model has been validated by comparing it to experimental results of a composite overwrapped steel tube section subjected to high internal pressures.
Fracture Failure Analysis of 304 Stainless Steel Elbow
Authors: Wang Yian , Xie Guoshan , Song Libin , He Meng , Zhuang Fakun , Li Xiaopeng
Published: October 2018

A cracking incident of a 304 stainless steel elbow serving in the synthesis gas purification device occurred during running. In order to get an understanding of the failure mechanism, a failure analysis was performed on the cracked elbow in this paper. The chemical composition, mechanical properties of strength, toughness and hardness, hydrogen content were identified and determined. The metallographical structure was observed and analyzed by optical microscope (OM) and X-Ray Diffraction (XRD), while the fracture morphology was observed by scanning electron microscope (SEM). The results showed that the chemical composition of the cracked elbow meet the requirements for China standard, while comparing with GB/T 14976-2012 standards, the strength and elongation of the leaked elbow are higher and lower respectively, and the hardness of the leaked elbow was higher than quality certificate documents that of HB ⩽ 187. Large quantities of martensite and δ-ferrite were observed in elbow, which indicated that the elbow was not well solid solution heat treated required by specification (1050°C,30min). The fracture morphology presents typical brittle fracture. The hydrogen content of cracked elbow was significant higher than that of other 304 stainless steel elbow serving in the environment without hydrogen. It is acknowledged that martensite showed higher sensitivity of hydrogen embrittlement compared with austenite. Furthermore, the operating temperature of cracked elbow was in the range of high hydrogen embrittlement sensitivity. Depending on the metallographical structure, strength, service environment, hydrogen content and fracture morphology, it can be concluded that hydrogen induced delayed cracking was the dominant mechanism of the failure.
Effective Portion of Sample Taken From USC Boiler Pipes to Consider Heat-to-Heat Variation of Creep
Authors: Yaguchi Masatsugu , Tomobe Masato , Komazaki Shin-ichi , Kumada Akihiro
Published: October 2018

One of authors proposed a creep life assessment method for USC boiler pipes that can consider heat-to-heat variations of the creep property of each welded joint, where the creep property of the welded joint is estimated from that of each base metal. In the method, it is assumed that the creep property of each base metal in actual pipes is approximately constant in the thickness direction of the pipes, and test results with small samples cut from base metals at the outer surface of pipes are useful for representing the creep properties of the pipes. In this work, the assumption was examined for five pipes of Grade 91 steel, which had been used for longer than 100,000 h at USC power stations. The microstructure, chemical composition, hardness, void density and remaining creep life were investigated in detail in the thickness direction of the pipes. No difference was observed for these items, except in an area less than about 0.2 mm from the outer surface of the pipes, which means that the assumption in the assessment method is valid except in this area. Therefore, it is suggested that an effective portion of the sample taken from USC boiler pipes to consider heat-to-heat variations of the creep properties of base metals is the material excluding the area less than about 1.0 mm from the outer surface of the pipes.
Development of Lightweight Design and Manufacture of Heavy-Duty Pressure Vessels in China
Authors: Chen Xuedong , Fan Zhichao , Chen Yongdong , Zhang Xiaohu , Cui Jun , Zheng Jinyang , Shou Binan
Published: October 2018

In recent years, with the gradual expansion of units scale for energy industries such as oil refining, chemical and natural gas, etc. in China, pressure vessels are developing toward the large and heavy direction with the maximum wall thickness reaching hundreds of millimeters and weight exceeding one thousand tons. It not only causes huge material consumption, difficulty in manufacture and processing (even beyond current capability), but probably also lead to new failure modes and mechanisms, and significant safety risks thereby. Therefore, the lightweight design and manufacture under the premise of inherent safety has become an urgent need to break through the bottleneck of manufacturing capability and realize the material and energy conservation. In this paper, the progress of lightweight design and manufacturing technology of heavy-duty pressure vessels in recent years in China is introduced from the aspects of adjustment of material allowable strength, application of high strength steel and matching of strength and toughness, cold stretch of austenitic stainless steel, structure optimization design with multi-parameter coupling, and application of composite materials. Application cases in the construction of pressure equipments such as large hydrogenating reactors, low-temperature ethylene spherical tanks, austenitic stainless steel cryogenic vessels, butyl octanol heat exchangers, etc. are also included. Finally, some suggestions on the future research are proposed including composite pressure vessels in cryogenic environment, materials genome and additive manufacturing technologies for pressure vessels.
Effect of Pre-Heat Treatment on Hydrogen Concentration Behavior of y-Grooved Weld Joint Based on a Coupled Analysis of Heat Transfer-Thermal Stress-Hydrogen Diffusion
Authors: Ozeki Go , Yokobori A. Toshimitsu , Ohmi Toshihito , Kasuya Tadashi , Ishikawa Nobuyuki , Minamoto Satoshi , Enoki Manabu
Published: October 2018

Hydrogen induced cracking occurs at the welded position of the structure due to concentration of hydrogen during cooling process of welding. In order to prevent the hydrogen induced cracking, Pre-Heat Treatment (PHT) is conducted. However, since PHT takes high cost, it is important to find out the suitable PHT condition based on computational mechanics. One of authors has been proposed α multiplication method which magnifies the hydrogen driving term in the diffusion equation to find out detailed behaviors of hydrogen concentration around a local stress field.

In this study, in order to clarify the effect of PHT on hydrogen diffusion and concentration behaviors, a coupled analysis of heat transfer – thermal stress – hydrogen diffusion combining with α multiplication method was conducted for the model of y-grooved weld joint under various PHT conditions.

This analytical method is as follows. At first, heat transfer analysis was conducted by finite difference method (FDM). And, temperature at each grid obtained by heat transfer analysis was interpolated to each node for thermal stress analysis by the finite element method (FEM). Then, thermal stress was calculated for each node using the interpolated temperature. After that, thermal stress obtained by this analysis was interpolated to each grid point for analysis of hydrogen diffusion by FDM. Using the interpolated thermal stress, stress driven hydrogen diffusion analysis was performed. By conducting sequentially these calculations mentioned above, hydrogen diffusion and concentration behaviors during cooling process were analyzed. The temperature of weld metal was 1500°C. And at initial state, hydrogen was introduced in weld metal. Thermal stress analysis was conducted under plane strain condition.

As a result, hydrogen diffusion and concentration behaviour at weld joint during cooling process was found to be typical at the site of maximum hydrostatic stress and to be affected not only the gradient of hydrostatic stress but also the gradient of diffusion coefficient induced by temperature distribution.
A Normalized Stress of Pull-Out Action on Bolted Joints Under Eccentric Load
Authors: Imura Makoto , Koyama Takayuki , Iizuka Motonobu , Suzuki Takayuki
Published: October 2018

Our objective is to evaluate precisely a life-cycle of bolted joints under an eccentric load against a bolt axis. Many approaches to achieve the objective based on a lot of theories and practices have been proposed so far [1–12]. As we can refer from their approaches, the opening of the structural interface between clamped plates of bolted joints occurs by the eccentric load, which is over a bolt preload, and then the opening gradually propagates as the eccentric load increases. In the case, nonlinearity appears remarkably on the tensional and bending stress of bolts in the axial direction. In addition to the above, the axial bolt stress larger than expected occurs due to the principle of leverage depending on the load position and the bolted joints layout in the early phase of the pull-out action. Accordingly, the stress evaluation of bolted joints under the eccentric load is very important in order to ensure the safety of industrial machines.

If dimensionless quantities of the bolt stress are found out considering the influence of the structural opening and the load eccentricity, we can have a few advantages as follows. First, bolt stress evaluations can be conducted by easily converting the dimensionless quantities of the bolt stress to the physical dimension quantities in a lot of cases where the bolt preload and the load eccentricity are different. Second, the number of times of verification tests can be reduced.

We are developing a lot of industrial machines which have bolted joints used under eccentric load. In such development [13], bolt stress analyses are usually conducted under the combinations of the following conditions: (i) tapped thread joints, (ii) thin clamped plates than the bolt diameter, (iii) large eccentric loads, (iv) permitting the opening of the structural interface. Therefore, we propose a concept of a normalized bolt stress considering the effect of the structural opening and the load eccentricity. We validated this concept through theoretical studies, finite element analyses, and experiments under the direct load and the centrifugal load.

As a result, the dimensionless quantities of the bolt stress caused by the bolt preload and a lever ratio of bolted joints under combined conditions was determined in this study. We can easily evaluate the bolt stress by simple conversions in a lot of cases in which the bolt preload and the load eccentricity differ.
Study on Characteristics of Wall Temperature Fluctuation at a Mixing Tee With an Upstream Elbow
Authors: Miyoshi Koji , Nakamura Akira
Published: October 2018

The characteristics of wall temperature fluctuation at the mixing tee with an upstream elbow were investigated and compared to those of the case without the elbow. The elbow of 90 degrees was installed in the inlet of the horizontal main pipe. The inlet flow velocities in the main and branch pipes were set to about 1.0 m/s and 0.7 m/s, respectively, to produce a wall jet pattern where the jet from the branch pipe was bent by the main pipe flow and made to flow along the pipe wall. A total of 148 thermocouples were installed near the pipe inner surface to measure the temperature distribution in the mixing tee. The upstream elbow decreased the temperature fluctuation intensity and the temperature fluctuation range at the inner surface. On the other hand, the distribution profiles and the dominant frequencies of temperature fluctuations were similar. The temperature fluctuation was also caused by the movement of a hot spot in the circumferential direction for both cases with and without the upstream elbow. The reduction of the movement of the hot spot in the circumferential direction decreased the temperature fluctuation for the case with the upstream elbow.
Microstructure and Tensile Properties of a 1.25Cr-0.5Mo Main Steam Pipe After Long-Term Service
Authors: Yang Bin , Jiang Wen-Chun , Sun Wen-Qi , Zhao Yan-Ling , Zhang Wei-Ya
Published: October 2018

Metallographic tests, micro-hardness tests and tensile tests were conducted for a 1.25Cr-0.5Mo main steam pipe weldment served for more than 26 years. The results were compared with those for virgin material. Microstructural evolution of 1.25Cr-0.5Mo base metal was investigated. Degradation in micro-hardness and tensile properties were also studied. In addition, the tensile properties of subzones in the ex-service weldment were characterized by using miniature specimens. The results show that obvious microstructural changes including carbide coarsening, increasing inter lamella spacing and grain boundary precipitates take place after long-term service. Degradation in micro-hardness is not obvious. However, the effects of long term service on tensile deformation behavior, ultimate tensile strength and yield stress are remarkable. Based on the yield stress of micro-specimens, the order of different subzones is: WM > HAZ > BM, which is consistent with the order of different subzones based on micro-hardness. However, the ultimate tensile strength and fracture strain of HAZ are lower than BM. Brittle failures can happen more easily for HAZ due to its high yield ratio.
Hydrogen Diffusion Concentration Behaviors for Square Groove Weld Joint
Authors: Ohmi Toshihito , Yokobori A. Toshimitsu , Ozeki Go , Kasuya Tadashi , Ishikawa Nobuyuki , Minamoto Satoshi , Enoki Manabu
Published: October 2018

Hydrogen induced cracking occurs at the welded position of the structure due to concentration of hydrogen during cooling process of welding. A square groove weld joint is one of typical one in engineering field. Hydrogen embrittlement cracking is sometimes caused during cooling process of a weld joint. For such case, hydrogen diffusion and concentration behaviour is a significant factor. One of authors has been proposed α multiplication method which magnifies the hydrogen driving term in the diffusion equation to find out detailed behaviours of hydrogen concentration around a local stress field. In this paper, to clarify hydrogen diffusion behaviour in the square groove weld joint, a coupled analysis of heat transfer – thermal stress – hydrogen diffusion combining with α multiplication method was conducted. From these results, it was found out that for the case of a square groove weld joint, since thermal stress was not highly localized for the case of using usual value of thermal expansion coefficient of steel, hydrogen concentration behaviour is not typical. However, if thermal stress is highly localized, hydrogen was found to be localized in the side of HAZ (heat affected zone) at the interface of WM (weld metal) and HAZ and is much more typical near the outer surface side of weld joint. Hydrogen diffusion and concentration behaviours were also found to be dominated not only by local thermal stress gradient, ∇σ but also by diffusion coefficient gradient, ∇D caused by temperature difference during cooling process. In this paper, effects of these factors on hydrogen concentration were investigated based on a coupled analysis of heat transfer – thermal stress – hydrogen diffusion combining with α multiplication method.
Formable Duplex Stainless Steel for High Pressure GPHE Applications
Authors: Groth Anders , Sun Chang-Ching , He Hailan , Guan Li , Schedin Erik
Published: October 2018

The high-pressure applications of traditional Gasket Plate Heat Exchangers (GPHE) are limited by the sheet material, gasket material and the design of the GPHE. The newly developed stainless steel grade UNS S82031 (EN 1.4637) is a duplex stainless steel grade with improved formability compared to other duplex stainless steel grades. It can be used in forming intensive applications, such as in typical chevron corrugated-plate heat exchangers. Compared to the standard austenitic stainless steel grades typically used, the new duplex stainless steel increases the application performance of GPHE applications, such as maintaining higher working pressures.

In this paper, the properties and material behavior of UNS S82031 is compared with the standard austenitic stainless steel UNS S30400 (EN 1.4301) in a pressure test at different working pressures. The pressure test is used to evaluate the performance of the selected material for a GPHE application. The experimental test results are compared with Finite Element (FE) simulation of the same pressure test, to achieve a deeper understanding of the results. The results show that plates made of UNS S82031 can withstand significantly higher working pressures than UNS S30400 for the same PHE-design, proving the new duplex stainless steel UNS S82031 is more suitable for high pressure GPHE applications.
Failure Analysis of Ring Hoop Tension Test (RHTT) Specimen Under Different Loading Conditions
Authors: El-Bagory Tarek M. A. A. , Younan Maher Y. A. , Alarifi Ibrahim M.
Published: October 2018

The thermo-mechanical history during manufacturing of plastic pipes affects their resulting material mechanical behavior. Therefore, it is necessary to demonstrate a study of the mechanical behavior of ring tensile test specimens cut from pipe to obtain proper design data during evaluations of the final product from the polymeric pipe material. Ring hoop tension test (RHTT) is one of the most important methods that can be used to measure transverse tensile properties accurately for pressure pipes. Two types of tensile ring specimens are tested; single ring hoop tensile test specimen with one configuration of Dumb-bell-shaped (DBS) specimen in the transverse direction of the pipe ring specimen and double ring hoop tensile test with two configurations of DBS cut in the collinear direction from the pipe ring specimen. RHTT specimens are cut from the pipe in circumferential (transverse) directions with similar dimensions. The material of the investigated pipe is high-density polyethylene (HDPE), which is commonly used in natural gas piping systems. The pipe has internal rated pressure Pi = 1.6 MPa, standard dimension ratio, SDR = 11 and external diameter, Do = 90±0.5mm. All the dimensions RHTT specimens are taken according to ASTM D 2290-12 and ASTM D 638-10 standards. The ring hoop tensile tests are conducted on specimens cut out from the pipe with thickness 9.5±0.2 mm at different crosshead speeds (VC.H = 10–1000 mm/min), and loading angle, θ equal 0° at ambient environmental temperature, Ta = 20 °C to investigate the mechanical properties of RHTT specimens. The results are compared with those obtained for DBS specimens taken along the axial pipe direction [1]. This shows the effect of DBS specimen orientation (longitudinal and circumferential) on the mechanical properties of HDPE pipe material at different crosshead speeds. The tensile testing fixture is designed specially on specified design criteria in order to test the RHTT specimen in the transverse direction. The main purpose of the design of test fixture is that it prevents the bending effect and stress concentration due to rotation of half disks during the tensile test. In order to avoid this rotation, the half disks are fixed, and their sharp ends are smoothed (rounded). The present experimental work reveals that the crosshead speeds, specimen orientation of DBS and configuration of DBS for RHTT specimens have a significant effect on the resulting mechanical behavior of HDPE pipe material.
Stress Evaluation Method by Frequency Response Function for Elbow Pipes Under Thermal Stratification
Authors: Alrakan Salman , Kuribayashi Hiroshi , Kasahara Naoto
Published: October 2018

In nuclear reactors, piping components are susceptible to thermal fatigue damage. This is due to the fluid temperature change along these pipelines that can generate repeated thermal loads. One of these loads is thermal stratification.

Thermal stratification generates an oscillating stratified layer, which induce cyclic thermal stresses leading to fatigue damage. To evaluate thermal fatigue by thermal stratification, a frequency response function for straight pipes was developed. However, this function cannot evaluate elbow pipes under thermal stratification. Here, thermal stress generates due to bending moment that is generated by the horizontal portion unlike straight pipes. Furthermore, the elbow pipe can give rise to stress intensifications which can affect the peak stress values within the elbow.

To understand the stress generation mechanism, Finite element analyses were performed. The study focused on the effect the frequency of the fluid oscillation on the stress generation mechanism. Based on the clarified mechanism, the frequency response function was improved to correspond to the thermal stratification at elbow pipes. Applicability of this function was validated through agreement with finite element simulation.
Investigation of Fluid Diffusion Properties From Various Flaw Geometries of Piping
Authors: Watanabe Shun , Morita Ryo , Uchiyama Yuta
Published: October 2018

Light water reactors in Japan are expected to restart sequentially after given permission in condition to meet the new regulatory requirements imposed on the regulatory follow-up actions against the Fukushima nuclear power plant accident. Since several safety related systems were added to the plants through the process of the new regulatory requirements, the numbers of components to be inspected, which is already a large amount, will increase even more after the restart in Japan. Effective measure will be required to command maintenance activities by reasonably assigning limited resource. The authors had planned a research project aiming optimization of maintenance considering influence of fluid leakage behavior, for example, diffusion area, flow rate, flow impingement pressure and all, with pipe failure, mainly targeting less-safety related piping and components. And the experimental equipment which has the ability to evaluate the fluid leakage behavior from crack, pinhole and break were constructed. In this paper, fundamental data about fluid diffusion properties of low energy water is mentioned.
Toughness Requirement of Chinese Pressure Vessel Steel 07MnNiMoDR Based on Fracture Mechanics Assessment Method
Authors: Gui Lele , Xu Tong , Sun Yonghui , Shang Xuexin
Published: October 2018

07MnNiMoDR is a widely used quenched and tempered high strength steel in fabrication of low-temperature pressure vessels in China. It can be used at/above −50°C according to the current design specification of GB 150. Some data show that this provision severely underestimates the performance of this material at low temperature, while others indicate that it overestimates the cryogenic performance of this material. In the paper, a series of tests including uniaxial tension tests, impact test and fracture toughness tests were carried out at low temperature to investigate the properties of 07MnNiMoDR with different thickness specimens. Fracture mechanics assessment procedures in API 579-1/ASME FFS-1 (Fitness-For-Service) is adopted to evaluate the low temperature design curve of 07MnNiMoDR, and the fracture toughness is obtained by master curve method (MC method) in the transition region. The results show that 07MnNiMoDR can be classified between exemption curve B and D in current edition of ASME Section VIII, Division 2.
Application of the Enhanced Reference Stress Method to Fatigue Propagation of a Surface Crack in a Plate Subjected to Cyclic Bending
Authors: Yamasaki Ippei , Fujioka Terutaka , Shindo Yasuhiro , Kaneko Yusuke
Published: October 2018

This paper describes an experimental validation of the enhanced reference stress method to calculate fatigue J-integral ranges, which are effective in predicting the fatigue crack propagation rate under low–cycle fatigue loadings. Although J-integral type fracture mechanics parameters can be calculated via elastic–plastic finite element analysis (FEA) of the crack geometry, performing such an analysis is costly and requires a high–end computer. A simplified method for estimating the elastic–plastic J-integral is therefore desired. Herein, several representative simplified methods for estimating the elastic–plastic J-integral were applied to crack propagation prediction and compared with each other. The experiments referred to was a previously performed cyclic bending tests using wide–plate specimens containing a semielliptical surface crack. Limit load correction factors to improve the accuracy of the reference stress method were estimated by performing an elastic–plastic FEA. The predicted crack propagation behaviors were compared against the test results.
A Novel Approach for Assessment of Pressurised Equipment for Slow Depressurisation During Fire
Authors: Ebrahimi Kaveh , Mofrad Saeid Rahimi , Millet Barry , Kirkpatrick Kenneth , Miller George
Published: October 2018

Majority of modern design codes and regulations for pressurised equipment mandate that pressurised equipment are equipped with depressurising facilities so that in the event of an over-pressurising scenario or during emergency shut-downs the equipment can be safely depressurised.

In the process industry, depressurisation calculations are usually done in accordance with the requirements of API 521 standard. For equipment with a wall thickness greater than 25mm, this standard recommends that depressurising facilities are designed to reduce the pressure of a vapour containing system exposed to external pool fire from the initial internal pressure to the final safe pressure within 15 minutes. There are cases where the depressurising time is even further shortened from 15 minutes by design engineers, e.g. for LPG applications or jet fire scenario.

Once depressurisation facilities are sized for the fire-case, depressurising calculations are carried out in order to determine the minimum metal temperatures at coincident pressures reached in the equipment in a non-fire depressurising scenario (called cold-case). This will enable design engineers to analyse equipment for potential brittle fracture of equipment during cold-case depressurisation.

Whilst the above mentioned methodology is usually adequate for majority of applications, there may be occasions that achieving API 521 recommended fire-case depressurisation time would require a large depressurising valve. This can potentially cause:

• Significantly fast depressurising (and subsequent auto-refrigeration) in the cold-case leading to very low metal temperatures and the need for costly materials, particularly in cold climate environments;

• Damage to equipment internals due to high depressurising rate;

• Overloading the existing flare network in a brown field project.

Increasing the depressurising time can alleviate the operational and/or economic issues arising from rapid depressurisations. However, slower-than-usual depressurisation increases the risk of rupture during fire-case, as equipment will be subject to heat for a longer period of time whilst still pressurised.

This paper describes a methodology and identifies the necessary steps for assessment of pressurised equipment for slow depressurisations. The method is based on the provisions in the latest editions of API 521, API 579-1/ASME FFS-1 and Finite Element Analysis (FEA). A sample high pressure vessel is analysed in this paper for both cold and fire depressurisation.
Design and Validation of a Filament Wound Composite Rocket Motor Case
Authors: Özaslan Emre , Acar Bülent , Yetgin Ali
Published: October 2018

Filament wound composite structures are widely used in aerospace applications such as motor case of rockets owing to their high stiffness/weight ratio and high strength. However, design and analysis of a filament wound structure is so complex due to the anisotropic nature of the composite material. Variation of the winding angle through the rocket motor case axis and through the thickness, which is also a function of winding angle are the main challenges to the realistic modeling of a filament wound composite rocket motor case. In this study, finite element analysis of a filament wound rocket motor case with unequal dome openings was performed. The finite element model was compared with manufactured motor case in terms of winding angle and thickness to ensure the exact modeling. The finite element analysis was compared with burst tests in terms of fiber direction strain distribution through the outer surface of the motor case to verify analysis. The weak regions of the motor case were determined with finite element analysis to be transition region from cylinder to dome which is subjected to significant bending because of the stiffness difference between these regions. Then, some design improvements were proposed to increase the mechanic performance of motor case. Significant improvement was succeeded in terms of mechanic performance. Important aspects of designing and analyzing a filament wound composite rocket motor case were addressed for designers.
Estimation of the Reference Temperature, T0, by Means of the Small Punch Testing Technique
Authors: Andrés David , Lacalle Roberto , Cicero Sergio , Álvarez Jose A. , Pinzón Manuel
Published: October 2018

The extension of the operation period of nuclear plants requires an accurate characterisation of the vessel materials, in order to monitor their embrittlement due to neutron irradiation. This need poses a challenge, since the availability of specimens inside the vessels to characterise their evolution is rather scarce. Therefore, innovative techniques have to be applied, in order to reduce the number of tests and the volume of the specimens. In this paper, the Master Curve approach has been employed, combined with the use of small punch notched specimens. The Master Curve methodology allows to evaluate the embrittlement of the material using a single parameter: the reference temperature, T0. This parameter has been estimated for several steels by means of modified small punch specimens, which are characterised by their reduced dimensions: only 10 × 10 × 0.5 mm. The obtained results have been compared with those obtained by means of conventional testing and a methodology to estimate T0 by means of small punch tests together with the Master Curve has been proposed.
Fatigue Performance of Preloaded Ultra High Strength Threaded Fasteners
Authors: Nassar Sayed A. , Li Tianwu
Published: October 2018

This experimental study investigates the high cycle fatigue (HCF) performance of preloaded ultra-high strength (UHS) threaded fasteners. Every sample is subjected to a cyclic uniaxial stress additional to a mean stress, which is arbitrarily set as half of the static tensile strength. Experimental results of UHS fasteners (Classes 14.9 and 15.9) and commercially available (CA) fasteners (Class 10.9) are analyzed: S-N curves are constructed following the ASTM standards and compared after normalization. Results indicate that the normalized fatigue strength of UHS threaded fasteners is lower than that of CA threaded fasteners. For each class, the experimental S-N curves are compared with the estimation obtained using Marin equation adjusted by mean stress criteria. It is concluded that the estimation by Marin equation did not show acceptable consistency to experimental data.
The Effect of Specimen Thickness on Low Temperature Gaseous Carburization of 316L Austenitic Stainless Steel
Authors: Jiang Yong , Zhang Peng-peng , Gong Jianming
Published: October 2018

In this present paper, the effect of specimen thickness on carburized layer thickness and surface residual stress of low temperature gaseous carburized AISI316L austenitic stainless steel was investigated by using specimen with thicknesses from ∼0.1 to ∼3 mm. After 15 and 30 hrs Low Temperature Gaseous Carburization (LTGC) treatment, the carburized layer thickness, surface residual stress and surface morphology were studied by optical microscope (OM), X-ray residual stress analyzer and scanning electron microscope (SEM). The results show that the specimen original thickness has no effect on the thickness of carburized layer. Surface compressive residual stresses are constant as about −1.6 and −2.1 GPa when the specimen thicknesses are not less than 0.485 mm for 15 hrs and 0.926 mm for 30 hrs LTGC treatment respectively. With the reduction of specimen thicknesses from 0.485 to 0.081 mm for 15 hrs LTGC treatment and 0.926 to 0.082 mm for 30 hrs LTGC treatment, the compressive residual stresses declined and finally reached about +0.4 and +1.0 GPa, respectively. Surface inter-granular cracking occurred on 0.082 mm specimen after 30 hrs LTGC treatment.
Development of Small Diameter and Thin-Walled Tube Docking Girth Joint Ultrasonic Testing Probe and Block
Authors: Zhou Lu-yun , Fu Ming-hai , Xu Wei-pu
Published: October 2018

Due to the Small diameter and thin walled tube docking girth joint ultrasonic testing has the problems of: dead zone is often greater than the wall thickness; large curvature of the pipeline causes ultrasonic scattering, greatly reduces the sensitivity; pipe weld root’s is not welded and so on. In this paper, the prepared small-bore and sheet steel tube docking girth joint ultrasonic testing probe has sufficient sensitivity, is less than 2.5mm of initial pulse width, short front (≤ 5mm), high resolution, less clutter, less surface wave components, At the same time, the test block was designed and used for the testing of probe’s related technical indicators, the test block can meet the focus probe’s performance and scanning sensitivity calibration. Combined with the field detection and compared with the radiographic testing, the ultrasonic testing obtain good result. It is suitable for the ultrasonic quantitative testing of the joint ring weld of thin wall pipe.