ASME Code Research Articles

A probabilistic evaluation method on temperature and time-dependent stress intensity limit St in creep assessment of components at elevated temperatures

Abstract Creep is an important damage mode of components at elevated temperatures, and the temperature and time-dependent stress intensity limit St is an essential indicator in creep assessment of components. In general, the safety factors are directly applied to three criteria in stress intensity limit St in ASME code, but a quantitative evaluation on the failure probability covered in this indicator is rarely reported. Based on this, a probabilistic evaluation method on stress intensity limit St is proposed by correlating each criterion with mean creep rupture life data. The failure probability of three criteria in stress intensity limit St of 316 and 304 stainless steels is calculated, and the effect of safety factors on failure probability results is discussed. A probabilistic evaluation on stress intensity limit St is conducted. Results indicate that the stress intensity limit St presents a low failure probability or high conservativeness, and the minimum stress to creep rupture is the governing role in stress intensity limit St for cases involved. The failure probability of stress intensity limit St of 316 stainless steel is much lower than that of 304 stainless steel, attributed to the differences of creep deformation features and data scatter of the two stainless steels.

Fabrication and Performance Evaluation of Rice Polishing Machine

This paper focuses on the fabrication and performance evaluation of rice polishing machine. The motor power of the machine is 1.5 hp and rotational speed is 1440 rpm. This motor uses v-belt transmission system to drive the main shaft and blower shaft. The number of two belts are used in this transmission system. The diameter of the main shaft is 22mm. ASME code equation is used to design the main shaft for rice polishing machine. Square key is used and shear and torsional strength of the key are 58.5404MPa. Single-row deep groove ball bearing is selected for left and right bearing of main shaft. The average milling efficiency, broken efficiency and milling capacity and moisture contents for existing and modified blade were compared. The average milling capacity is 35.23 kg/h, 38.41 kg/h and 41.76 kg/h with modified blade and 30.35 kg/h, 32.20 kg/h and 34.03 kg/h with existing blade at the moisture condition of 13%, 12% and 11%, respectively. As comparison results, the modified blade of the machine has more efficient and convenience than the existing blade of the machine.

The reduced order model for creep using dynamic mode decomposition

Given the computational challenges associated with finite element methods in analyzing creep behavior in high-temperature components, this work presents an advanced method for modeling thermal creep in complex structures through a reduced order model (ROM) developed via dynamic mode decomposition (DMD). The results indicate that the ROM using DMD can predict long-term structural responses related to creep based on short-term data with high accuracy, enhancing significantly computational efficiency. The application of ROM allows for the rapid estimation of creep effects in complex structures, like monoliths in the MegaPower reactor, thereby improving the design efficiency. The eigenvalues of the creep related ROM all fall in the unit circle on the complex plane, indicating that creep is a stable development process. The DMD with improved time mode coefficient can reconstruct strain-rate related plastic deformation and cyclic visco-plastic deformation process. Additionally, we derive the necessary stress updating algorithm and consistent tangent operator matrix for the 316H unified visco-plastic constitutive equation in 2023 edition ASME code, ensuring accurate modeling of material creep behavior under high temperatures in this paper. This work provides a valuable tool for the safe design and operation of critical components in nuclear engineering and other high-temperature applications.

Applicability analysis of induction bending process to P91 piping of PGSFR by high-temperature fatigue test

The application of the induction bending process in pipe fabrication is expanding across industries, significantly reducing leakage by minimizing welded sections in curved pipes. In this study, the applicability of the induction bending process to P91 bent pipes of PGSFR was analyzed, focusing on both material fatigue tests and structural fatigue tests for induction bent pipe at high temperatures. First, both high-cycle and low-cycle fatigue tests on specimens from the bent pipe were carried out at 550 °C to confirm that the fatigue properties meet the ASME Code's fatigue requirements. Second, material constants for a Chaboche combined hardening model were identified by using the material test results and an inelastic finite element analysis of the P91 bent pipe were performed to determine the fatigue test load for structural test effectively. Lastly, a high-temperature fatigue test on the bent pipe structure was performed to assess its structural integrity and post-test non-destructive examination confirmed that no fatigue cracks developed, and thereby affirming the applicability of the P91 bent pipe.

Minimization of wire-wound pressure vessel diameter based on distortion energy theory

This paper investigates the minimization of the diameter of wire-wound pressure vessels. The study is conducted in two stages. Firstly, the stresses arising from the wire winding of the vessel and the internal pressure application are extracted based on the distortion energy theory. It is assumed that the equivalent stress within the winding area in each layer, under the internal pressure condition, equals the allowable stress of the wire, and in the cylinder area, it does not exceed the allowable stress of the cylinder. The required number of layers and the wire tension during winding (two essential unknown parameters in the industrial winding process) are determined to satisfy these assumptions. In the second stage, the diameter optimization of the vessel is studied using the Distortion Energy (DE) theory. It is found that reducing the cylinder diameter results in a decrease in the vessel diameter. The occurrence of buckling or yielding in the cylinder is a limiting constraint for reducing the cylinder diameter. For validation, the results obtained from the derived equations are compared and confirmed against finite element results and the equations provided in the ASME code. Wire-winding simulation around the cylinder uses the element birth and death technique. The agreement between the derived equations and the code equations, as well as finite element results, is excellent. In the examined case study, using the DE theory leads to a 24 % reduction in wire consumption compared to the maximum shear stress (MSS) theory. In the optimization stage, the vessel weight is further reduced by 24 %. Compared to monobloc shells, the optimized wire-wound vessel weight based on the DE theory experiences a 77 % reduction.

Path Forward: Materials Data Modernization for ASME Codes and Standards in the Artificial Intelligence Era

Abstract Development of the ASME Materials Properties Database was initiated in the early 2010s to support the ASME Codes and Standards. As information technologies advance at an accelerated pace with the artificial intelligence era on the horizon, the ASME Materials Properties Database must be further modernized from a database to a knowledgebase to ride the wave of digital information revolution and effectively support the ASME Codes and Standards in the new era. This paper is intended to provide an overview of the ASME Materials Properties Database and discuss a roadmap for its future development to facilitate understanding of and participation from different sectors of the Codes and Standards community. It first reviews the basic concepts of data, information, knowledge, database, and database system as well as the pros and cons in different types of data management and then discusses the path forward for a desired evolution of the database into a self-explanatory and machine-readable knowledgebase that is consistent with human cognitive processes for the Codes and Standards development and, furthermore, provides resources for data processing and analysis to reach an eventual goal of streamlining the Codes and Standards development from the initial inquiry, throughout data submission, analysis, …, to Codes and Standards rule establishment for final publication.

Assessment of environmental fatigue in nuclear power plants: A comparative analysis of the effects of plasticity correction

In accordance with Regulatory Guide 1.207, Rev.1, fatigue assessments must be conducted considering the influence of primary coolant environment in nuclear reactors. Environmental fatigue, resulting from corrosion in the primary coolant, is evaluated in air fatigue life assessments through the application of an environmental fatigue correction factor. This environmental fatigue correction factor depends on sulfur content, operating temperature, dissolved oxygen, and strain rate. It remains constant for sulfur content, operating temperature, and dissolved oxygen, while strain rate introduces potential errors based on the analysis method. The current fatigue evaluation procedure for air, following ASME B&PV Code Sec.III, NB-3200, employs elastic analysis with a simplified elastic-plastic correction factor(Ke). However, Ke factor is considered excessively conservative, prompting less conservative alternatives proposed by JSME, RCC-M, ASME Code Case N-779. This study applied both ASME Ke and JSME Ke for fatigue evaluations considering environmental effects. Additionally, fatigue assessments accounting for elastic-plastic effects were conducted using Neuber and Glinka methods, compared with actual experiments. The analysis systematically examined changes in fatigue life and the environmental fatigue correction factor due to plastic effects in environmental fatigue evaluations.

Applicability investigation on failure assessment diagram of ASME code section XI - Appendix H for ferritic nuclear piping

The failure assessment diagram (FAD) is a widely used tool for evaluating the fracture acceptance of structural components. In addition to linear elastic fracture mechanics, elastic-plastic fracture mechanics, and limit load analysis, the ASME Code incorporated FAD as an alternative safety evaluation method for flaws in nuclear pipes starting from 2004 edition. This paper conducts a series of finite element elastic-plastic fracture mechanics analyses to establish the specific J–based FAD curves considering various loading and geometry conditions for ferritic pipes containing various circumferential flaws. By comparing with the suggested FAD of ASME Code Section XI - Appendix H, it is found that the radius-to-thickness ratio of pipes and the flaw depth influence the applicability of FAD, but with minor effects of crack length. In addition, the effects of material properties between base metal and weld materials on FAD are also discussed. The result of this work could be a reference when applying the FAD to evaluate the flawed piping for nuclear power plants.

Modeling of creep-fatigue features of hydrogen storage bed and its parameter optimizing based on finite element method and orthogonal experimental design with artificial neural networks

Regarding the creep-fatigue behavior of hydrogen storage bed (HSB) structures under high-temperature loading and internal pressure loading under repeated hydrogen absorption and desorption process, the heat transfer characteristics and creep-fatigue life during a complete service process in HSB were calculated using Ansys Workbench and Ncode software, and the reliability of the life results calculated by finite element method were validated using ASME code. Based on orthogonal experimental design (OED) theory, an orthogonal experimental table with 4 factors and 5 levels was compiled for the four process parameters: diameter of cooling tube, thickness of cylinder wall, spacing between inner and outer layers, and heat transfer coefficient of condensate. Moreover, an optimization method based on OED coupled with BP ANNs was proposed to find the best process parameters. And the importance of each parameter was analyzed based on range analysis and analysis of variance (ANOVA) to divide the process parameters into rough optimized parameters and precise optimized parameters in this method. In order to identify the optimal process parameter combination of HSB, the maximum life and corresponding process parameter combinations were identified based on OED and the combined method, respectively. The maximum life identified by the combined method proposed in this work is increased by 10.23 % than that identified by OED, which shows the superiority of this combined method.

A kind of numerical model combined with genetic algorithm and back propagation neural network for creep-fatigue life prediction and optimization of double-layered annulus metal hydride reactor and verification of ASME-NH code

The safety and stability of metal hydride reactor (MHR) structure are significantly important for normal operations of hydrogen isotope storage and supply system. Moreover, considering that the experiments of studying the fatigue and creep properties of MHR structure are always time, money, difficulty and energy consuming. To further improve the service life of MHR as well as lower the failure risk, this paper proposes a system integration method based on ASME code validation, which combines genetic algorithm (GA) and back propagation neural network (BPNN) for rapid assessment of creep-fatigue life (CFL) and optimal design of structural parameters. First, numerical simulation is applied to perform thermal-mechanical coupled finite element analysis and verified by ASME code. Then, parametric sensitivity analysis and experimental design of parameter-based training set based on Taguchi method were performed, and response values are obtained from physical models combined with numerical simulations. Finally, a parametric optimization procedure combining BPNN and GA is developed based on the training data. In the workflow, parametric data flow is passed through the experimental design, numerical simulation, prediction and optimization processes. The results show that the proposed BPNN proxy model based on ASME code validation has good performance in predicting the life of MHR. Based on this, the life of the MHR is improved by 8% compared to the reference sample.

Stress Classification Lines for Non-Standard Y-Tee Design in Piping System

All processes fluids in the oil and gas industry are generally transferred from one point to another via complex piping networks. The process temperature and the pressure of the fluids may vary between -21 °C to 816 °C and from atmospheric, 1.013 barg to 431 barg, respectively. Under these conditions, the entire piping networks are exposed to thermal expansion and contraction resulting in mechanical bending, potentially causing mechanical failures. The most common pipe fitting used in piping networks to divide the fluid flow into two different directions would be a standard equal tee which was designed in accordance with ASME B16.9. The equal tee, however, has distinctive flexibility characteristics compared to the pipe, which is well defined in ASME B31.3. These flexibility characteristics generate a stress intensification factor (SIF) through bending moment equations for beam-type element analysis for standard equal tee components. However, due to the limitation of SIF and flexibility characteristics for the non-standard pipe fittings, the stress evaluation could not be done using beam-type element analysis. When using finite element method (FEM) analysis, generally equivalent stresses (Von Mises or Tresca) or principal stresses would be evaluated depending on the stress categorization as explained in ASME codes and standards. In this paper, a stress evaluation method for non-standard Y-tee was developed and demonstrated against ASME VIII Div. 2 Part 5 requirement. The developed SCLs line for the non-standard Y-tee fittings provides the guides for stress assessment against design stress allowable. An optimum design for non-standard Y-tee is proposed at 45° and 60° crotch radii which resulted in lower stress value at SCL lines, hence improving the structural integrity.

Correlation between reliability and safety factor based methods in characterizing uncertainty of creep rupture properties

Reliability and safety factor based methods are usually employed to characterize uncertainty of creep rupture properties, but the correlation between these two methods is rarely reported. In this work, a framework of correlation between reliability and safety factor based methods was proposed, and application of this framework in representation of minimum stress to creep rupture was reported. Effect of standard deviation on correlation results was discussed and comparisons of minimum stress to creep rupture in codes and standards were conducted. Results indicated that for a given reliability, the safety factor included in the minimum stress to creep rupture is higher at a small stress level and a high temperature. Accordingly, the minimum stress to creep rupture by reliability based method in ASME code (i.e. 95 %) is lower than that by safety factor based method in RCC-MRx code (i.e. 1.25), presenting a smaller allowable stress value and more conservative evaluation. Contrarily, a smaller safety factor is gained at a high stress level and a low temperature for a given reliability. The opposite conclusion is drawn when the reliability at a given safety factor is analyzed. In addition, the safety factor of 1.5 is larger than that at the reliability of 99 % for a wide range of stress levels, inducing an over-conservative design and excessive manufacturing costs.

Analysis of the stress field in the reactor vessel of the China Initiative Accelerator Driven System during postulated ULOF and UTOP transients

The China Initiative Accelerator Driven System (CiADS) was proposed by China Academy of Science since 2015. The subcritical reactor in CiADS is a liquid Lead Bismuth Eutectic (LBE) cooled fast reactor. When the reactor core is in operation, the LBE coolant will directly contact and corrode the inner surface of reactor vessel. Due to the high temperature, the corrosion will be more severe. If the stress on the reactor vessel exceeds the limit, the plastic deformation will occur, leading to the generation and expansion of defects and cracks, and the safety of the reactor will be affected. Therefore, evaluating the stress field of the reactor vessel under different operating conditions is a very important research project. In this paper, the finite element analysis software ADINA was applied to analyze the reactor vessel in CiADS, and the ASME Code was used as stress assessment standards. We can preliminarily prove that the stress assessments of the vessel during the postulated Unprotected Loss of Flow (ULOF) accidents satisfy the requirements of ASME Code. The limit reactivity insertion to protect the vessel from plastic deformation is 0.58$ in the postulated Unprotected Transient over Power (UTOP) accidents based on our current results. Therefore, we can preliminarily conclude that the current material selection and structural design of the reactor vessel in CiADS could survive most of the postulated transient accidents considering the stress effect.

Development of an HTS-SQUID Based Nondestructive Evaluation System for Boiler Tubes On-Site Inspection in Thermal Power Plant

In ultra-supercritical (USC) thermal power plants, Super304H (KA-SUS304J1HTB, ASME code: 2328) is widely used in the superheater and reheater tubes in boilers because of its excellent creep rupture strength under high-temperature and -pressure conditions. Thus, a degradation diagnosis of these tubes after long-term operation should be conducted using a quick and easy inspection. In this study, in order to discover the degradation of the boiler tubes for early diagnose before they rupture, a high-temperature superconductor (HTS)–superconducting quantum interference device (SQUID) with high sensitivity was used. A SQUID-based nondestructive evaluation system for the on-site inspection of boiler tubes in an USC thermal power plant was developed. Our system comprises a movable eddy current testing (ECT) probe and HTS-SQUID gradiometer. Five LED markers were set on a manually operated ECT probe for position detection using a stereo camera. Customized software was used for data acquisition through a lock-in amplifier and data visualization on a PC with a connected smart glass. Thus, the system can be used for quick inspection by time-sequence signals and detailed scanning through a two-dimensional contour map projected on the smart glass. Therefore, this study successfully introduced an HTS-SQUID-based nondestructive evaluation system for the on-site inspection of boiler tubes.

Creep Life Assessment Method for Super304H Boiler Tubes Based on HTS-SQUID Gradiometer

This paper presents a novel method for the creep life assessment of Super304H (KA-SUS304J1HTB, ASME code: 2328) boiler tubes based on a discrete-type eddy-current-testing (ECT) HTS-SQUID nondestructive evaluation (NDE) system. Six specimens were subjected to internal pressure creep tests at a stress level of 110 MPa and a temperature of 700°C. The specimens were inspected at various creep test times using our NDE system, which included an ECT probe and a HTS-SQUID gradiometer. By studying the physical characteristics and microstructures of the specimens at different test times, we found that the electrical conductivity and permeability of the specimens varied with an increasing test time. The detected signals may have been generated from creep voids and/or surface microcracks. Based on the NDE inspection results, creep life assessment curves that can be used for assessing the remaining creep life of the Super304H boiler tubes were plotted. The results confirmed the possibility of assessing the remaining creep life using our HTS-SQUID-based system in a nondestructive manner.

Generation of allowable stress for indigenously developed 304HCu Stainless steel

The 304HCu stainless steel (SS) is the candidate material for reheater and superheater tubes in Advanced Ultra Supercritical (AUSC) coal-fired power plants of India. In the present study, the creep design data have been generated for indigenously developed 304HCu SS using the creep properties (creep strain and the rupture life) and tensile properties available at the temperatures 923 K, 973 K and 1023 K. The time dependent allowable stresses were obtained for the above steel according to the stress criteria specified in ASME Section III Division 5 Subsection HB. The allowable stresses were also derived in the creep as well as non-creep regimes as per the guidelines in ASME Section IID. In both the cases, the maximum allowable stress at each temperature was dictated by the stress to cause rupture. The allowable stress determined as per Section IID was the same as that estimated according to section III.5 HB for creep exposure of 100,000 h. Further, it must be mentioned that, at the temperature range 923–1023 K, the indigenously developed 304HCu SS possess allowable stresses that are in par with the corresponding values specified in ASME code case 2328–2.

Ratcheting-fatigue behavior and life prediction of Z2CN18.10 austenitic stainless steel elbow

The ratcheting fatigue behavior of Z2CN18.10 austenitic stainless steel elbow under internal pressure and cyclic loading was studied. The evolution of axial and hoop ratcheting strains at four different positions, respectively at intrados (0°), 45°, crown (90°) and extrados (180°) on the outer surface of the elbow was discussed. It is shown that the hoop ratcheting strain of the elbow is always greater than the axial ratcheting strain. Under cyclic test with force control, the order of ultimate hoop ratcheting strain is intrados (0°)>crown (90°)> 45°> extrados (180°). Under cyclic test with displacement control, the order of ultimate hoop ratcheting strain is 45°> intrados (0°)> crown (90°)> extrados (180°). Under cyclic tests with both force and displacement control, the crown (90°) of the elbow leaked first, which is the critical point to evaluate ratcheting fatigue life. Afterward, the ratcheting fatigue life is predicted based on ASME code, and it is found that the prediction results tend to be non-conservative. Then, a modified Manson-Coffin equation considering ratcheting strain is proposed to predict fatigue life of elbow well.

An Optimum Design of Pressure Vessel by using PV-ELITE Software

bstract: The safety factor of a pressure vessel is related to both the tensile stress and yield strength for material allowance. ASME code section VIII has fully covered these two on the construction code for pressure vessel. This code section addressed mandatory and non-mandatory appendixes requirement, specific prohibition, vessel materials, design, fabrication, examination, inspection, testing, certification, and pressure relief. Mechanical design of a horizontal pressure vessel based on this standard had been done incorporating PV ELITE software. Analyses were carried out on head, shell, nozzle and saddle. The input parameters are type of material, pressure, temperature, diameter, and corrosion allowance. Analysis performed the calculations of internal and external pressure, weight of the element, allowable stresses, vessel longitudinal stress check, nozzle check and saddle check.

A whole-section failure criterion for creep life evaluation of components at elevated temperatures

High-temperature components in advanced power systems suffer multi-axial stress states due to structural discontinuity, thermal gradient and other factors, and creep life evaluation is essential for the long-term safe operation of the system. Existing codes and standards provide different creep life evaluation methods combined with single-node failure criterion, but this remarkably underestimates the actual failure life of the component. Based on this, a whole-section failure criterion for creep life evaluation of components at elevated temperatures is proposed. Creep tests of notched components with various acuity ratios are conducted. Margin differences between single-node and whole-section failure criteria are evaluated, using creep life evaluation methods in ASME and RCC-MRx codes. Results indicate that compared with single-node failure criterion, the whole-section failure criterion could remarkably reduce conservatism degree. Creep life evaluation method in ASME code is less conservative than that in RCC-MRx code for notched cases included, irrespective of the safety factor effect. The conservatism degree of creep life evaluation methods is related to specimen type and acuity ratio of notched components.

Stress Analysis of ASME Section X Flanges Using Classical Lamination Theory

AbstractThe increased usage of fiber reinforced plastic (FRP) composite pressure vessels and piping components in the past decades in the residential and industrial sectors is attributed to the FRP material resistance to corrosion and chemical attacks. FRP composite flanges are, however, known for their anisotropic behavior. In the ASME code section X, FRP composite flanges are treated using an analytical approach derived from that metallic flanges in addition to the fact that the geometries are made to fit them as much as possible and not designed independently. This is known to have caused structural flaws for certain FRP flange classes and sizes. Using a recently developed anisotropic FRP flange approach, it is proposed to identify the most critical flanges by analyzing the flange parameters such as flange ring rotation and stresses in their different parts; gasket, flange ring, hub, and shell subjected to pressure loading. The study on the strength of flanges described in ASME section X RD-620.1 table, will reveal the most critical size and class flanges and their highly stressed locations. To conduct such a study, the selected flange material is an E glass/Vinyl Ester laminate composite. The study shows that FRP flanges of classes 25 and 50 are most vulnerable and should comparatively be less loaded. The stresses are found to reach 50 MPa in the shell and 58 MPa in the flange ring while the maximum flange rotation is 0.83 deg.