ASME Code Research Articles

Proposed Material Properties, Allowable Stresses, and Design Curves of Diffusion Bonded Alloy 800H for the ASME Code Section III Division 5

AbstractIncreased interest in compact heat exchangers (CHXs) to serve as intermediate heat exchangers of very high temperature reactors resulted in significant research and development on their design, analysis, and construction. Printed circuit heat exchangers are a type of CHXs with high thermal efficiency and compactness achieved through diffusion bonding a stack of etched plates with millimeter scaled channels. The diffusion bonding process changes the microstructural and mechanical properties of the wrought metal plates. The current nonnuclear design code ASME section VIII, division 1 captures the material property change through a “joint efficiency factor.” However, the current nuclear design code ASME section III, division 5 does not address or support the diffusion bonded material properties. Hence, there is a need to develop allowable stresses, isochronous curves, and fatigue life curves for various diffusion bonded alloys. In this study, Alloy 800H material was selected to establish the diffusion bonded material properties under tension, creep, fatigue, and creep-fatigue loads at elevated temperatures in the range 550–760 °C. A set of tests on diffusion bonded Alloy 800H (DB 800H) were performed and the acquired data are used in developing allowable stresses Sy, Su, Sr, Sm, St, Smt, So, isochronous curves and fatigue life curves according to the ASME section III, division 5 requirements. This paper also presents detailed procedures used in developing the ASME code section III division 5 design provisions for diffusion bonded Alloy 800H.

Creep-fatigue damage analysis of a large horizontal molten-salt storage tank

Abstract Molten-salt storage tank is the key equipment of solar-thermal storage system. In this paper, creep-fatigue analysis and evaluation were performed on a large horizontal molten-salt storage tank according to ASME Code Case 2843, and influence of the structural form for opening reinforcement was investigated. Results found that increasing the thickness of the tube was not very helpful for the equipment to pass creep-fatigue damage assessment; On the other hand, the integral reinforced structure was effective to meet the requirement of creep-fatigue damage assessment. For the horizontal molten-salt storage tank studied here, the creep damage was dominant compared to the fatigue damage.

Can solar tower plants withstand the operational flexibility of combined cycle plants?

The aim of this work is to investigate the level of reliability of a 100 MWe solar tower plant operating as a load-following plant using actual operational data of combined cycle power plants. Despite the low cost, the steam generator has been identified as the main cause of unavailability of solar tower plants due to fatigue failures of tube-to-tubesheet joints, which can lead to steam/water leakage into the heat transfer fluid circuit, putting the plant performance at risk. A methodology based on the ASME code and EN standards is proposed to predict the fatigue failures of critical welded points of the steam generator, such as tube-to-tubesheet joints and other T-joints. The results show that the forced outages due to failures of the steam generator lead to an energy penalty that ranges over 230–453 GWh over the plant lifetime. The associated annual degradation rate ranges over 0.123–0.244%. Three tube leakage repair strategies are compared: tube-to-tubesheet weld crack repair, tube plugging and tube plugging with steam generator replacement. The latter strategy was shown to be the best practice because the lowest levelized cost of energy was obtained. In addition, the design of heat exchangers with a minimum of 20% extra area is highly recommended to not compromise the plant operation due to tube plugging. Last, the load-following operation of the solar tower plant increases the levelized cost of energy by approximately 1.6% in the case of tube repair and approximately 0.8% in the case of tube plugging with steam generator replacement.

Verification of Long-term Creep Rupture Properties and Microstructure Stability of Ni based Alloy 45Ni-24Fe-23Cr-7W-Ti Parent Metal and Weldment

ABSTRACT To clarify the long-term creep rupture strength and microstructure stability of Ni-based alloy HR6W (45Ni-24Fe-23Cr-7W-Ti, ASME Code Case 2684), creep tests were conducted up to about 70,000h and 117,000h for the weldment and parent metal respectively, and the microstructure of crept specimens was experimentally investigated. The weldment showed comparable strength with the parent metal. The metallurgical microstructure characterization and quantitative evaluation on the precipitation behavior indicated the precipitation strengthening of Laves phase, M23C6 carbide and αCr phase in the HAZ (Heat Affected Zone) and parent metal contributing to the long-term creep rupture strength stability of weldment. Satisfactory microstructural stability was proven without distinct degradation during long-term creep at 700°C up to around 117,000h. Furthermore, the internal pressure creep test of circumferential weldment was performed to verify the damage and failure morphology of actual components under the multiaxial loading

Allowable Cracks Related to Penetration for Part-Through Cracks in Pipes Subjected to Bending Stresses

Abstract Fully plastic collapse stresses for circumferentially part-through cracked pipes subjected to bending stresses are estimated by limit load criteria provided by the ASME Code Section XI. Allowable crack depths were determined by using the limit load criteria and that are tabulated in the ASME Code Section XI for different plant service-level conditions. On the other hand, crack penetration bending stresses for part-through cracked pipes were estimated by using the local approach of limit load criteria. By using these criteria, the study presented in this paper obtained allowable crack depths at penetration for circumferentially part-through cracked pipes. Comparing the allowable crack depths obtained by both methods for each service level, it is evident that the allowable crack depths at penetration calculated by the local approach of limit load criteria are almost always smaller than those at fully plastic collapse stresses calculated by the limit load criteria. It was found that the allowable crack depths provided by the ASME Code Section XI are less conservative for crack penetrations.

Development of a software for calculation of optimised pressure vessels according to ASME X

The methodology for calculating pressure vessels made of composites is included at the Secion X of the ASME Code. These vessels are more common in aerospatial engineering, or in medical gas industry, but lately are being introduced in automotive, naval, energy and petrochemical industries. The development of a software tool to calculate pressure vessels according to ASME Code sec. X is proposed. Technically, the goal is to develop a software tool to aid in and speed up the process of designing pressure vessels according to the ASME Code Sec. X. With this software, and considering the entered data (diametres, lengths, design pressures, design temperatures, etc…), dimensions and final laminates of a pressure vessel can be obtained in order not to surpass the failure criteria for the considered composite.

Activity of HPI Subcommittee on High Pressure Vessel and ASME Code Committee

Activity of HPI Subcommittee on High Pressure Vessel and ASME Code Committee

Discussion on failure criteria of orthogonally biaxial stress field

Some components which constitute a part of the boundary in nuclear plants are very important from the viewpoint of protection of radioactive material propagation. Especially, it is a serious matter if the function as the boundary is maintained or not in the case of severe accident (SA). In this paper the characteristics of FLD (Forming Limit Diagram) as the failure criteria is studied compared with the rule of ASME Code and the applicability to the boundaries of structures is discussed. Furthermore, the prospect of the application of FLSC (Forming Limit Stress Curve) to structural components including loading hysteresis is referred.

Analysis of Elbow Stress Intensification Factors for Piping System

In order to study the stress intensification effect of pipe elbow in the secondary stress check, the U-shaped pipeline commonly used in engineering was taken as the research object. The experiment platform for analysing pipe elbow stress was established, and the maximum stress with the displacement load was measured and compared with the results of the finite element analysis results and ASME B31.3 Code. On this basis, a correction formula calculating the Stress Intensification Factor (SIF) of elbows was proposed, and the influence of the wall thickness and the bend radius on the elbow stress distribution was studied. The results showed that pipeline displacement significantly affects stress for pipe bends, the stress of the elbow increased with in-plane displacement load. To ensure structural integrity for reliable working conditions for piping components, pipe displacement needs to be considered when designing bends. On this basis, a modified formula for calculating the SIF of in-plane elbow is proposed. Compared with the ASME code formula, this formula is closer to the actual stress value of the elbow due to considers the influence of pipe displacement on elbow stress. The stress value of the elbow obtained by finite element analysis essentially in agreement with the experimental value, and the average error is less than 5.16%. With simultaneous increase in bend radius and wall thickness there is a reduction in SIF. When either of the above parameters is increased on, and keeping others constant the SIF decreases. The influence of pipeline displacement on SIF is more for short bend radius and its effect decreases with increased bend radius.

A Practical Analysis Framework for Assessment of Printed Circuit Heat Exchangers in High-Temperature Nuclear Service

Abstract Printed circuit heat exchangers (PCHEs) have high thermal efficiency because of the numerous minuscule channels. These minuscule channels result in a high thermal exchange area per unit volume, making PCHE a top contender for an intermediate heat exchanger (IHX) in high-temperature reactors. Thousands of minuscule channels make finite element analysis of the PCHE computationally infeasible. A two-dimensional analysis is usually performed for the PCHE core, which cannot simulate the local channel level responses reasonably because of the absence of global constraint influence. At present, there is no analysis technique available in the ASME Code or literature that is computationally efficient and suitable for engineers to estimate PCHE local responses. A novel but practical two-step analysis framework is proposed for performing PCHE analysis. In the first step, the channeled core is replaced by orthotropic solids with similar stiffness to simulate the global thermomechanical elastic responses of the PCHE. In the second step, local submodel analysis with detailed channel geometry and loading is performed using the elastic-perfectly plastic (EPP) material model. The proposed two-step analysis technique provides a unique capability to estimate the channel corner responses to be used for PCHE performance assessment. This study first developed a methodology for calculating the elastic orthotropic properties of the PCHE core. Next, the two-step analysis is performed for a realistic size PCHE core, and different issues observed in the results are scrutinized and resolved. Finally, a practical finite element analysis framework for PCHEs in high-temperature nuclear service is recommended.

Finite element analysis of high-pressure grinding rolls for crack prediction to determine safe working conditions

High Pressure Grinding Rolls - HPGR is a relatively new technology first implemented in Europe into Cement Industry and later incorporated into Mineral industry in the late 20th century as replacement to conventional mills like rod and ball mills due to the higher efficiencies offered by them in comminuting the material fed to the mill. These are heavy duty machines designed to operate for 60–100 thousand hours, hence making millions of revolutions in their lifetime at the operating speed of 14–17 RPM sustaining thousands of Kilo-Newtons of force. As a result these machines are very expensive and bulky which makes their failure and other serious damages a very expensive affair. Hence, it is necessary to make sure they are designed and operated properly so as to avoid serious breakdowns without compromising. One such HPGR was found to be failing at half of its designed lifetime. This paper covers the detailed Finite Element Simulation done on Ansys Workbench 2019 R2 which is validated through numerical calculations of shaft design under combined and fluctuating load according to ASME code standards. The design shortcomings are found out and minimum strength required for the roll and shaft assembly is proposed.

Example of stress evaluation for a pipe subjected to impeded thermal expansion according to ASME code

Example of stress evaluation for a pipe subjected to impeded thermal expansion according to ASME code

Evaluation method of fatigue life for weld joints with defects in the horizontal restraint components of main steam pipelines

Horizontal restraint components are mainly used in nuclear power plants to limit the horizontal displacement of the “super pipelines”, such as the main steam pipelines and main water supply pipelines. Horizontal restraint components are very important for ensuring the safety of the second loop of nuclear power plants under unexpected conditions. However, because the size of the horizontal restraint components are quite large, and the pipelines are complicated, defects or cracks easily occur in the weld joints connected with the components and pipelines. The fatigue crack growth in the weld joints is one of the important reasons of the fatigue failure for the horizontal restraint components. Therefore, investigating the fatigue crack growth of the weld joints is significant to accurately predict the service life of the horizontal restraint components. In this paper, multiple cracks were found in the weld joints of horizontal restraint components in a nuclear power plant. In order to evaluate the fatigue life of the weld joints, fatigue crack growth tests were carried out under different temperature. The material parameters, C and n, of the Paris Equation for the weld joints were obtained and compared with those for the base metal (ferrite steel) in the ASME code. Results showed that the results show that the fatigue crack growth rate of the weld joints in the room temperature is lower first and then higher than that of the material in the high temperature weld joints and the base metal at room temperature, but the fatigue crack growth rate of the weld joints in the high temperature is always higher than that of the base metal at room temperature. The fatigue life of the horizontal restraint components calculated by the Paris Equation from the experiments is quite different compared with the fatigue life calculated from the base metal (ferrite steel) in the ASME code at room temperature.

Welder learning curves behaviour: “focus on welding productivity with the TIG process of marine platforms stainless steel pipes”

PurposeThe purpose of the study is to analyse the feasibility of using the potential and exponential curve models to assess the learning of a group of welders, when welding stainless steel piping with the tungsten inert gas process.Design/methodology/approachThe welding productivity data grouped according to the requirements of the ASME SECTION IX code is organised into two groups: average productivity and baseline productivity. When processing the adjustment to the two models, the Excel software Solver tool was used. The criteria for assessing the quality of the fit were: least squared method, Spearman's correlation coefficient and graphical method. The impact of the variation coefficient on the average productivity and the amplitude (difference between the minimum and maximum productivity) was also evaluated on the baseline productivity.FindingsThe curves elaborated based on the average productivity presented better quality of adjustment than those constructed from the baseline productivity. The potential and exponential models presented similar adjustment conditions, with the second having a slightly superior performance. There were no productivity gains due to learning in the studied time interval. The grouping of the average daily productivity data based on the diameter range established in the ASME code section IX presented satisfactory results, enabling its use by the industry.Originality/valueThere is no news of work on piping welding with this focus. The proposal to group the productivity data according to the degree of difficulty of execution established by the ASME code section IX, widely used in the industry, is a significant contribution to monitoring the evolution of learning. In the same way, the results allow to adopt the average productivity determined from the first 20 days of realisation of a project, as a reasonable indicator to estimate the future performance of the work, helping to correct deadlines during the realisation of a project.

An ergonomic welding torch reduces physical load response and improves welding quality in novices: a pilot study

Objectives. This crossover pilot study aimed to compare the physical load response of an ergonomically improved welding torch versus a conventional torch. Methods. Ten inexperienced volunteers performed an experimental augmented virtual welding trial at chest height (ASME code 1G) and overhead (ASME code 4G) with both welding torches in random order. Skeletal muscle load and fatigue were assessed by surface electromyography and changes in isometric peak force. The sensation of pain, perceived exertion and welding execution quality were defined as further outcome parameters. Results. The muscle load response in three out of eight muscles was lower in favour of the ergonomic welding torch, which went along with a lower sensation of pain and a higher working accuracy. Conclusions. An ergonomically improved welding torch reduces the acute physical load response and sensation of pain, which ultimately allows performing better, and might contribute to prevention of musculoskeletal diseases in the long term.

ASME Code Rules and ASTM Standards Integration for Ceramic Composite Core Materials and Components1

Fiber-reinforced ceramic matrix composites have many desirable properties for high-temperature nuclear applications, including excellent thermal and mechanical properties and reasonable to outstanding radiation resistance. Over the last 20 years, the use of ceramic composite materials has already expanded in many commercial nonnuclear industries as fabrication and application technologies mature. The new ASME design and construction rules under Section III, Subsection HH, Subpart B lay out the requirements and criteria for materials, design, machining and installation, inspection, examination, testing, and the marking procedure for ceramic composite core components, which is similar to the established graphite code under Section III, Subsection HH, Subpart A. Moreover, the general requirements listed in Section III, Subsection HA, Subpart B are also expanded to include ceramic composite materials. The code rules rely heavily on the development and publication of standards for composite specification, classification, and testing of mechanical, thermal, and other properties. These test methods are developed in the American Society for Testing and Materials Committee C28 on Advanced Ceramics with a current focus on ceramic composite tubes. Details of the composites code, design methodology, and similarities to the graphite code, as well as guidance for the development of specifications for ceramic composites for nuclear application and recent standard developments, are discussed. The next step is to “close the gap” to support licensing aspects by validating the code with benchmarking data.

Design optimization of a closure head for a PWR reactor pressure vessel

In this paper, design optimization of the closure head for PWR reactor pressure vessel has been performed. The RPV closure head mainly consist of hemispherical head with openings for CRDM and QUICKLOC nozzles, and head flange with holes for closure studs. Thickness of the head and height of the flange have been optimized by employing response surface optimization methodology through design of experiments technique. The effect of thickness of head and height of flange on the stress intensity distribution of the closure head in the presence of openings were studied in order to explore the best design under the guidelines of the ASME code. The under-designing (compromise of the Tresca yield criterion) and over-designing (compromise of the fracture toughness) of the closure head are controlled in a novel way through detailed stress analysis.

Reaching New Heights

Abstract The history of the ASME A17 elevator safety code is intertwined with the ability to build ever-taller skyscrapers. One key landmark, the Empire State Building, may have been impossible without the contribution of ASME code committee members.

Reaching New Heights

Abstract The history of the ASME A17 elevator safety code is intertwined with the ability to build ever-taller skyscrapers. One key landmark, the Empire State Building, may have been impossible without the contribution of ASME code committee members.

Fatigue reliability design and assessment of reactor pressure vessel structures: Concepts and validation

Traditional design approaches using safety factors are intended to account for uncertainties due to the lack of available data in engineering practice. However, the direct use of safety factor to represent uncertainties often causes conservative results, and it is not intuitive to describe the reliability of these structures through safety factor. To deal with the issue, this research revisits the initial consideration and intent of the safety factor for static strength and adjustment factor for fatigue design curve in the ASME code. Three conversion models applying to reactor pressure vessel (RPV) materials are proposed on basis of the stress–strength, load–life and strength–damage interference theories, which elaborate the relationship between safety/adjustment factors and structural reliability. The dispersion of strength and fatigue life is quantified, and then implemented to elaborate safety and adjustment factors with reliability respectively, which verifies the validity of safety assessment methods in the ASME code. Moreover, the safety/adjustment factor design under required reliability level is achieved, has the advantages of intuitiveness and convenience, which provides a reference for the reliability and safety design of RPV.