Abstract During a gas pipeline rupture event, the crack propagation velocity can exceed 300 m/s and the crack can run for several hundreds of metres before arresting. The current model to predict arrest pressure is the Battelle Two Curve Method (BTCM) using the Charpy V-notch energy to characterize propagation toughness. It has been shown that this model can give non-conservative predictions for high-strength pipe steels. Hence, the Crack Tip Opening Angle (CTOA) has been introduced as a promising parameter to describe crack propagation. The objective of the current work was to study the crack propagation process in pipe by Finite Element Analysis (FEA) techniques to gain a better understanding of crack driving force and factors influencing CTOA. Implicit FEM simulations of dynamic crack propagation in pipes with diameters ranging from 355 mm to 1219 mm with a wall thickness of about 19 mm were performed using material properties representative of either X65 or X80 pipeline steel. The specification of a critical CTOA and the nodal release algorithm in the software WARP3D were employed to propagate the crack up to about two metres in the simulations. For a given critical CTOA, pipe diameter, and pipe thickness a set of simulations was performed where the initial applied gas pressure varied from as low as 4 MPa up to 60 MPa (which corresponds to about 80% of the yield strength of the material). The CTOA values used in the simulations ranged from 5° to 20° and corresponded to CTOA measurements obtained in concurrent work from Drop Weight Tear Tests performed on pipe steels. To accurately predict crack velocity, it was important to apply a flap loading profile near the crack front representative of the gas pressure response during pipe rupture. Comparison of the crack propagation response was carried out between a constant pressure profile just behind the crack front and a pressure profile that varied with circumference a round the pipe. The influence of soil pressure on the flap loading response was also considered in the models. The predicted pressure versus crack velocity profiles and the arrest pressure can then be subsequently used to predict the arrest length for a given CTOA.

Abstract In this study, we performed fracture toughness testing of ten Eurofer97 steel variants using precracked miniature multi-notch bend bar (M4CVN) specimens based on the Master Curve method in the ASTM E1921 standard. Additional Vickers microhardness and room temperature tensile testing complemented the fracture toughness testing. Compared with standard Eurofer97, the ten variants didn’t show a comprehensive improvement of mechanical properties. The Master Curve method was found to yield a reasonable prediction of fracture toughness results obtained from M4CVN specimens with most valid fracture toughness data within the 2% and 98% tolerance boundaries of the Master Curve. The three-parameter Weibull distribution with Weibull exponent b = 4 also yielded excellent prediction of the relationship between fracture toughness results K Jc and the cumulative probability for failure p f for one steel variant.

Abstract The heat affected zone (HAZ) of 2.25Cr-1Mo-0.25V welded joint is a critical part for the safety of hydrogenation reactors. Hydrogen has a significant effect on the HAZ, studying hydrogen diffusion characteristics, such as: hydrogen flux and the effective hydrogen diffusivity has a remarkable value in investigating the hydrogen-induced material degradation mechanisms. In this work, an electrochemical permeation method was applied to study the hydrogen diffusion characteristics of HAZ. Then, the metallographic microscope and a software “Image J” were used to analyze the density of grain boundaries of HAZ. The effect of the post–weld heat treatment (PWHT, i.e. annealing) on the hydrogen diffusion characteristics of HAZ was also been investigated. The results show that after PWHT, the effective hydrogen diffusivity of HAZ increases from 1.63 × 10 −7 cm 2 ·s −1 to 3.68 × 10 −7 cm 2 ·s −1 , the hydrogen concentration decreases from 1.92 × 10 −4 mol·cm −3 to 1.09 × 10 −4 mol·cm −3 , and the hydrogen trap density decreases from 3.00 × 10 26 m −3 to 0.76 × 10 26 m −3 . Thus, PWHT can significantly reduce density of grain boundaries, thereby reducing the hydrogen trap density, enhancing the hydrogen diffusivity and reducing the hydrogen concentration.

Abstract This paper discusses four different ultrasonic guided wave standards. Three of them are China’s national standards or industry standards: GB/T 31211-2014 “Nondestructive Testing Ultrasound Guided Wave Detection”, GB/T 28704-2012“Non-destructive testing—Test method for ultrasonic guided wave testing based on magnetostrictive effects”, and DL/T 1452-2015 “Thermal Power Pipeline Ultrasound Guided Wave Detection”. The another one is ASTM E2929:“Standard Practice for Guided Wave Testing of Above Ground Steel Piping with Magnetostrictive Transfusion”. Through six aspects in this article, including testing application scope, preliminary requirements, standard specimen and comparative specimen, distant amplitude curve and time gain curve, the existing difference between China and America is obvious and diversity. It is necessary to explore the underlying reasons for the connection of Chinese code and international code in the field of Non-destructive testing. During the standardization, anyone of the standard should be actually compared on the presentation of chart, and the verification and comparison of results, and lists the similarities and differences of each part based on GB31211. This paper provides reference for China to integrate with foreign standards in the field of ultrasonic guided wave detection of pressure vessel and pipelines.

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

Abstract Thermal ageing of cast duplex stainless steel components is a concern for long-term operation of EDF nuclear power plants. The thermal ageing embrittlement results from the microstructural evolution of the ferrite phase (spinodal decomposition), and can reduce the fracture toughness properties of the steel. In addition, it is necessary to consider manufacturing quality and the possible occurrence of casting defects such as shrinkage cavities. In a context of life extension, it is important to assess the safety margins to crack initiation and crack propagation instability. One major input of the assessment methodology is the toughness value of the thermally aged component. Recent work conducted at EDF R&D to improve the accuracy and the conservativeness of the toughness prediction has led to the development of new prediction formulae. The toughness prediction relies on three steps: • estimation of the Charpy impact test values at 20 and 320°C using the chemical composition of the steel and the aging conditions (temperature and duration), • estimation of the J-R curve at 20 and 320°C - defined by a power law J = CΔa n - thanks to correlations between n and C and the Charpy impact test values, • estimation of the J-R curve at any temperature between 20 and 320°C thanks to interpolation formulae. The paper presents the experimental data used to develop the formulae, the formulae themselves and some elements of validation.

Abstract In petroleum industry, hydrogen is used in many assets. With temperature and pressure, hydrogen can damage materials. This damage is called High Temperature Hydrogen Attack (HTHA) and is a time dependent degradation mechanism that can affect the integrity of steels used for pressure containment operating above about 400°F (204°C). HTHA has caused major accidents in Petroleum Industry. API RP 941 [1] currently provides guidance for steel selection (and so susceptibility to attack) in relation to temperature and ppH2 via Nelson curves. In the last edition, 4 stages of degradation for both base metal and weld metal are described. In the past, only stage III was detectable by the combination of different Ultrasonic methods which were known as AUBT – Advanced Ultrasonic Backscatter Technique. But, capability of detection was limited to defects above 500–1000μm, correspondent to small fissures. So, it was impossible to detect early stage of degradation as steel grain size (around 50μm). For several years, performances of non-destructive techniques have rapidly increased and new advanced ultrasonic technologies are available such as: - Phased Array Ultrasonic Techniques (PAUT) - Time Of Flight Diffraction (TOFD) - Total Focusing Method (TFM) This paper describes latest techniques and results obtained by Total and French Welding Institute in laboratory, and discuss the efficiency of the methods, over real HTHA degradation blocks. An overview of TFM is also proposed by CEA who work on innovating development to increase the performance of this technique.

Abstract Seismic risk evaluation of coupled systems of industrial plants often needs the implementation of complex finite element models to consider their multicomponent nature. These models typically rely on significant computational resources. Moreover, the relationships between seismic action, system response and relevant damage levels are often characterized by a high level of nonlinearity, thus requiring a solid background of experimental data. Furthermore, fragility analyses depend on the adoption of a significant number of seismic waveforms generally not available when the analysis is site-specific. To propose a methodology able to manage these issues, we present a possible approach for a seismic reliability analysis of a coupled tank-piping system. The novelty of this approach lies in the adoption of artificial accelerograms, FE models and experimental hybrid simulations to evaluate a surrogate meta-model of our system. First, to obtain the necessary input for a stochastic ground motion model able to generate synthetic ground motions, a disaggregation analysis of the seismic hazard is performed. Hereafter, we reduce the space of parameters of the stochastic ground motion model by means of a global sensitivity analysis upon the seismic response of our system. Hence, we generate a large set of synthetic ground motions and select, among them, a few signals for experimental hybrid simulations. In detail, the hybrid simulator is composed by a numerical substructure to predict the sliding response of a steel tank, and a physical substructure made of a realistic piping network. Furthermore, we use these experimental results to calibrate a refined ANSYS FEM. More precisely, we focus on tensile hoop strains in elbow pipes as a leading cause for leakage, monitoring them with strain gauges. Thus, we present the procedure to evaluate a numerical Kriging meta-model of the coupled system based on both experimental and finite element model results. This model will be adopted in a future development to carry out a seismic fragility analysis.

Abstract For steel frame infrastructure facilities like thermal power plants, storage facilities or port facilities, the more advanced seismic performance is needed which not only prevent major damages against assumed design ground motions but also result in the “desirable failure mode” that concerns the recovery works or prevent from resulting in catastrophic failure mode, even under severe ground motions beyond design assumptions in which occurrence of some damages in structures are inevitable. “Seismic structures which can control the locations of failure of structural members inside structures” is one of the examples of this seismic performance. By adding this performance to steel frame structures at the stage of seismic design, the high resilience structures which concern recovery works after earthquakes can be realized. In this research, a basic study on the seismic performance which controls the locations of fractures of steel frame members by adjusting the cross sections of each structural member was carried out. The analytical studies about the design procedure to realize this seismic performance were conducted. Then, by conducting the shaking table tests for simple steel frame structures and confirming the location of fractures under dynamic loads, the possibility of this seismic performance was discussed experimentally.

Abstract Steel storage tanks are critical components of an industrial installation due to their high seismic vulnerability and containment of hazardous materials. Failure of a which, may lead to loss of containment (LOC) triggering domino effects such as explosion, environmental pollution, loss of functionality and disruption of business. Past earthquakes have demonstrated different type of failure modes in steel storage tanks. Although there are plenty of studies related to different failure modes like elephant foot buckling or tank uplifting, there are very few efforts on the sliding behavior of tank. Large displacements caused by the tank sliding can lead to pipe detachment and release of hazardous material which might cause damage propagation. Consequently, this damage state is very important for the Quantitative Seismic Risk Assessment of industrial plants. In order to enumerate the sliding displacement of unanchored steel storage tanks, a simplified numerical model realized with OpenSees platform is proposed. The friction model used in OpenSees is calibrated with the results obtained from ABAQUS FE model. Sliding response of tanks with different D/H ratio is analyzed using the simplified model. Fragility curves for the tank sliding damage state are analytically evaluated for different D/H ratio of the tank using the “cloud method”. Finally, a parametric study is conducted in order to comprehend the influence of different parameters on the sliding behavior such as friction coefficient, tank filling level and the influence of the vertical component of ground motions.

Abstract Nuclear power plant spent fuels are initially stored in the spent fuel pool. Then, the water cooled fuels are transferred in a concrete or steel cask and transported outside of the Fuel Handling Building (FHB) or the Reactor Building (RB) for long term on site storage. The spent fuel casks are typically stored on a slab-on-grade pad. The slab-on-grade pad is designed according to the U.S. Nuclear Regulatory Commission NUREG-1536 and NUREG-1567. The two Standard Review Plans provide guidance to the regulators for the review of cask storage system license application. The ISFSI pad analysis and design have to consider various loading conditions, such as earthquake and tornado loadings as well as normal operating loading conditions. Seismic analysis of the ISFSI pad requires considering interaction between the pad and the supporting soil. Various cask loading configurations on the pad also have to be considered. Due to the lack of specific guidelines, many ISFSI pad designs show overly conservative reinforcement. This study provides guidelines and procedure for the design of the ISFSI pad that are typically used in the nuclear industry. It is considered that the guidelines and practices described in this study help design engineers understand general guidance provided in the NRC Standard Review Plans.

Abstract The seismic vulnerability of aboveground steel storage tanks has been dramatically proved during the latest seismic events, which demonstrates the need for reliable numerical models for vulnerability and risk assessments of storage facilities. While for anchored aboveground tanks, simplified models are nowadays available and mostly used for the seismic vulnerability assessment, in the case of unanchored tanks, the scientific community is still working on numerical models capable of reliably predicting the nonlinearity due to uplift and sliding mechanisms. In this paper, a surrogate model based on a Kriging approach is proposed for a case study of an unanchored tank, whose calibration is performed on a three-dimensional finite element (3D FE) model using a reliable design of experiments (DOE) method. The verification of the 3D FE model is also done through a shaking table campaign. The outcomes show the effectiveness of the proposed model to build fragility curves at a low computational cost of the critical damage state of the tank, i.e., the plastic rotation of the shell-to-bottom joint.

Abstract In Japan, the Design Fatigue Curve (DFC) Phase 1 and Phase 2 subcommittees, which are a part of the Atomic Energy Research Committee of the Japan Welding Engineering Society, have proposed new design fatigue curves and fatigue analysis methods for carbon, low-alloy, and austenitic stainless steels. To confirm the validity of the proposed design fatigue curves, a Japanese utility collaborative project was launched, and the authors conducted fully reversed four-point bending fatigue tests for large-scale specimens of carbon steel and low-alloy steel plates. Subsequently, in a previous paper (PVP2018-84456), the authors reported that the fatigue lives determined by the best-fit curve proposed by the DFC subcommittee corresponded to those of approximately 1.5–7.0-mm-deep crack initiation in large-scale specimens. In this study, the fatigue crack initiation and propagation behavior observed in large-scale specimens was investigated by using a plastic replica and beach mark method. Similar to the case of small-sized specimens, in the large-scale specimens, multiple fatigue cracks initiated at an early stage of testing, and propagated with coalescence to penetrate the specimen width. However, no fatigue cracks were detected at the design fatigue life. Approximately 100-μm-long cracks were observed, albeit only after the specimen was subjected to a number of cycles that corresponded to approximately 3.5 times the design fatigue life. According to NUREG/CR-6909 Rev.1, the crack depths in small-sized round bar specimens at the fatigue lives, which are defined by 25%-stress-drop cycles, are reported to be approximately 3 mm. The results of the large-scale tests indicated that regardless of the specimen size, nearly the same phenomenon occurred on the specimen surface until approximately 3–4-mm-deep crack initiated. The size effect was mainly caused by the stress gradient. The finite element analysis indicated that the stress gradient in the large-scale specimen was gentle owing to the large thickness of the specimen, and the stress in the vicinity of the surface was considered to be uniform. In conclusion, the size effect was not apparent. As the same conclusion can be applied to considerably larger actual components, designers do not need to consider the size effect when designing pressure vessels or piping by using the design fatigue curve determined based on small-sized specimens.

Abstract Based on the world wide fatigue test database, The Design Fatigue Curve (DFC) Phase 1 and 2 subcommittees established in The Japan Welding Engineering Society (JWES) have been developed new design fatigue curves which are applied for the nuclear component materials, in air environment. The effects of the design factor, such as mean stress, size effect and surface finish, etc. on the fatigue curves are also discussed with the fatigue database in order to construct fatigue evaluation method for the new design fatigue curves. The subcommittees also have studied the applicability of newly developed fatigue evaluation method to the nuclear component materials. This paper reports the fatigue test results of machined finished small-scale test specimens which are used for the verification of proposed fatigue evaluation method. The materials subjected to the fatigue tests are austenitic stainless steel SUS316LTP, low-alloy steels SQV2A and SCM435H, and carbon steel STPT370. Specimens finished with lathe machining are subjected to the tests. The planed maximum height roughness of the specimen are 25 and 100 μm. The fatigue test results show that the surface finish effect on the fatigue strength in the high cycle region of the austenitic stainless steel can be negligible. On the other hand, fatigue strength of the carbon steel and low alloy steel is decreased as increasing the surface roughness of the specimen. Especially, decrease of fatigue strength for the specimens with more than 100 μm maximum height roughness is larger than that of conventional estimation. It is presumed that severe roughness introduced by lathe machining tends to behave as notches and increase the stress concentration at the specimen surface, and resulted in unexpected decrease of fatigue strength.

Abstract The carbide precipitation of 2.25Cr-1Mo-0.25V steel is studied during the head-fabrication heat treatment process using gold replica technique, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Shapes, structures and sizes of carbides before and after heat treatment are analyzed. The dissolution of strip-shaped carbides and the precipitation of granular carbides are confirmed. Amorphous films at the boundaries of carbides are observed by high-resolution transmission electron microscope (HRTEM), which is formed due to the electron irradiation under TEM.

Abstract In order to develop new design fatigue curves for carbon steels & low alloy steels and austenitic stainless steels and a new design fatigue evaluation method that are rational and have clear design basis, Design Fatigue Curve (DFC) Phase 1 subcommittee and Phase 2 subcommittee were established in the Atomic Energy Research Committee in the Japan Welding Engineering Society. The study on design fatigue curves was actively performed in the subcommittees. In the subcommittees, domestic and foreign fatigue data of small test specimens in air were collected and a comprehensive fatigue database was constructed. Using this fatigue database, the accurate best-fit curves of carbon steels & low alloy steels and austenitic stainless steels were developed by applying tensile strength to a parameter of the curve. Regarding design factors on design fatigue curves, data scatter, mean stress correction, surface finishing effect, size effect and variable loading effect were investigated and each design factor was decided to be individually considered on the design fatigue curves. A Japanese utility project performed large scale fatigue tests using austenitic stainless steel piping and low-alloy-steel flat plates as well as fatigue tests using small specimens to obtain not only basic data but also fatigue data of mean stress effect and surface finishing effect. Those test results were provided to the subcommittee and utilized the above studies. In the last PVP Conference, the large scale fatigue tests using austenitic stainless steel piping were discussed for the best-fit curve of austenitic stainless steel (PVP2018-84436). In this paper, further studies are performed based on fatigue crack growth of the large scale fatigue tests using austenitic stainless steel piping. From the obtained crack growth data of the tested piping, the number of cycles at 3-mm-deep crack depth and through-wall crack of piping compares with the best-fit curve developed by the DFC1 subcommittee with considering the confidence lower bounds to survey the fatigue life of piping, and size effect for fatigue lives is discussed. The relations between the fatigue crack growths and the number of cycles and the aspect ratios are surveyed including mean stress effect.

Abstract Quenched and tempered high strength steel 07MnMoVR provides an excellent combination of strength and toughness potentially providing significant cost savings in petrochemical industry. Exposure to fire will subject steel to thermal conditions that may alter the material’s microstructure and properties. The extent of the fire damage and the potential reusability of the components can be evaluated by fitness-for-service (FFS) assessment after a fire event. According to API 579-1/ASME FFS-1, metallurgical investigation and mechanical testing are the chief means for the assessment of fire damage. This paper presents the details of an experimental investigation on the post-fire metallographic structure and hardness of 07MnMoVR steel. Metallographic analyses and hardness testing were performed on coupons exposed to elevated temperatures varying from 550°C to 850°C for half an hour to 8 hours and then naturally cooled in air or cooled by water. The results show that the microstructure of as-received 07MnMoVR steel consisted of tempered sorbite and bainite. With increasing heat exposure temperature, bainite disappeared gradually. The recovery and recrystallization of ferrite began to occur after heat exposure at 650°C for 5hrs. When the heat exposure temperature exceeded 750°C, the effects of duration time and cooling rate on microstructure were both significant. A linear correlation is indicated by fitting the ultimate tensile strength and hardness. Due to the drastically degradation of impact toughness of 07MnMoVR steel after heat exposure exceeded 650°C, it is suggested that the removal and testing of material samples shall be utilized to evaluate the fire damage of components, besides replication or in-situ field metallography and hardness testing. This study can provide basis data and guidelines for the fitness-for-service assessment of 07MnMoVR steel suffered from a fire event.

Abstract Industrial steel piping components are often subjected to severe cyclic loading conditions which introduce large inelastic strains and can lead to low-cycle fatigue. Modeling of their structural response requires the simulation of material behavior under strong repeated loading, associated with large strain amplitudes of alternate sign. Accurate numerical predictions of low-cycle fatigue depend strongly on the selection of cyclic-plasticity model in terms of its ability to predict accurately strain at critical location and its accumulation (referred to as “ratcheting”). It also depends on the efficient numerical integration of the material model within a finite element environment. In the context of von Mises metal plasticity, the implementation of an implicit numerical integration scheme for predicting the cyclic response of piping components is presented herein, suitable for large-scale structural computations. The constitutive model is formulated explicitly for shell-type (plane-stress) components, suitable for efficient analysis of piping components whereas the numerical scheme has been developed in a unified manner, allowing for the consideration of a wide range of hardening rules, which are capable of describing accurately strain ratcheting. The numerical scheme is implemented in a general-purpose finite element software as a material-user subroutine, with the purpose of analyzing a set of large-scale physical experiments on elbow specimens undergoing constant-amplitude in-plane cyclic bending. The accuracy of three advanced constitutive models in predicting the elbow response, in terms of both global structural response and local strain amplitude/accumulation, is validated by direct comparison of numerical results with experimental data, highlighting some key issues associated with the accurate simulation of multiaxial ratcheting phenomena. The very good comparison between numerical and experimental results, indicates that the present numerical methodology and, in particular, its implementation into a finite element environment, can be used for the reliable prediction of mechanical response of industrial piping elbows, under severe inelastic repeated loading.

Abstract Large scale storage of hydrogen is one of the key factors in hydrogen energy development. High-pressure hydrogen storage technology is widely used in hydrogen storage. It has advantages of easy operating, quick charge and discharge, simple equipment structure and low cost. The multi-layered steel vessel (MLSV) was developed for stationary hydrogen storage, which was flexible in design, safe in operation and convenient in fabrication. MLSV has been used in several hydrogen refueling stations in China. With the construction of hydrogen refueling stations accelerated, the vessel was required to be larger, lighter and cheaper. First, the basic structure of the MLSV was presented. Second, two light-weight methods were proposed and compared, including reducing the safety factor and increasing the strength of the steel band. Finally, the stress in the cylindrical shell of the MLSV using light-weight design were compared with the previous one. In addition, a MLSV using the light-weight method of reducing safety factor has been designed and fabricated, which can store 211 kg gaseous hydrogen at 50MPa.

Abstract The increasing energy demand has spurred the exploration and production of oil and natural gas in dangerous and hostiles areas. Therefore, accurate calculation of fracture toughness is essential for fitness-for-service (FFS) analyses of critical engineering structures, such as the piping system used in the offshore industry. Regarding the oil and gas exploration in Brazil, 68% of the total area has already been explored, with 71% of that explored area having been developed in recent years. Oil and gas companies have preferentially chosen Crack-tip Opening Displacement (CTOD) due to the vast data of fracture toughness obtained in the past. Moreover, the professionals involved in this area are more familiarly with this parameter since it is easy of understanding because it involves physically crack flank deformation. Different methods to measure CTOD are available in the literature, such as the plastic hinge model, J-integral conversion and double clip gage method (DCGM). Experimentally, DCGM has been widely used to calculate in offshore pipelines. Discrepancies between experimental and numerical measures have been reported. Motivated by the explanation above, this work aims to propose new numerical analyses to evaluate the CTOD using the DCGM using non-linear finite element analyses. New and improved equations are developed to take into accounting knifes position.