The stress corrosion cracking of tube-to-tubesheet joints is one of the major faults causing heat exchanger failure. After the expansion process, the stresses are developed in a plastically deformed tube around the tube-to-tubesheet joint. These residual stressed joints, exposed to tube and shell side fluids, are the main crack initiation sites. Adequate contact pressure at the tube-to-tubesheet interface is required to produce a quality joint. Insufficient tube-to-tubesheet contact pressure leads to insufficient joint strength. Therefore, a study on the residual stress and contact pressure that have a great significance on the quality of the tube-to-tubesheet joint is highly demanded. In this research, a 2D axisymmetric numerical analysis is performed to study the effect of the presence of grooves in the tubesheet and the expansion pressure length on the distribution of contact pressure and stress during loading and unloading of 400 MPa expansion pressure. The results show that the maximum contact pressure is independent of the expansion pressure length. However, the presence of grooves significantly increased the maximum contact pressure. It is proven that the presence of grooves in the tubesheet is distinguishable from the maximum contact pressure and residual von mises equivalent stress. The tube pull-out strength increases with the expansion pressure and the number of grooves. In conclusion, the presence of the grooves affects the tube-to-tubesheet joints.

In the steam generator, anti-vibration bars are often provided to support the tube bundle. Due to the non-linearity of the support, the fluid-solid coupling simulation of large-scale tube bundles supported by the anti-vibration bars will bring great trouble. In order to solve this problem, this paper conducts experiments on the heat exchange tube based on the turbulent power spectrum to generate the excitation force. By changing the support form, the force of the lift and the direction of the drag and the ratio of the force, the excitation of the heat exchanger tube is researched. The results of the displacement response, the contact force and friction force distribution, and the contact angle distribution provide reference for the subsequent model simplification. Experiments show that the contact rate increases with the increase of the excitation force, and the contact force and the friction force increase with the increase of the excitation force. When the heat exchange tube contacts with the anti-vibration bars, the contact angle is mostly less than 45°, more than 50% of the contact angle is less than 45°. The work rate of the tube at the edge is greater than the work rate of the tube in the center.

The mission of the U.S. Department of Energy (DOE), Office of Nuclear Energy is to advance nuclear power in order to meet the nation’s energy, environmental, and energy security needs. Advanced high temperature reactor systems will require compact heat exchangers (CHX) for the next generation of nuclear reactor plant designs. A necessary step for achieving this objective is to ensure that the ASME Boiler and Pressure Vessel Code, Section III, Division 5 has rules for the construction of CHXs for nuclear service. Given their high thermal efficiency and compactness, expanding the use of Alloy 800H diffusion bonded Printed Circuit Heat Exchangers (PCHEs) beyond their current application in Section VIII, Division 1 to the high temperature nuclear applications is of interest. The research being completed under the Department of Energy project is focused on preparing a draft Code Case for consideration by the ASME Code Committees for high temperature nuclear components which must meet the requirements of Section III, Division 5, Subsection HB (Class A), Subpart B. Acceptance of a Code Case by the ASME Code Committees to use PCHEs in nuclear service requires a broad understanding of PCHE failure mechanisms. At the highest level, the ASME Code requirements prevent failures of structures and pressure boundaries. Historically, the approach is a process of understanding the known failure modes, such as overload failures, plastic collapse, progressive distortion (ratcheting) and fatigue, and then establishing rules for construction to preclude those failure modes in components. For Division 5 applications, attention to differential thermal expansion, creep life, and creep-fatigue must also be considered. Failure from these loadings is manifest within PCHEs both within the internal micro-channel geometry, and at substantially larger solid header and nozzle attachments. To address the adequacy of the PCHE, a Failure Mode Effects Analysis (FMEA) has been performed for standard etched channel PCHEs. This FMEA is linked to the proposed rules in the code case for compact heat exchangers in Section III, Division 5 Class A applications. The PCHE FMEA covers all design failures addressed by Section III.

High thermal efficiency of Compact Heat Exchangers (CHX) makes them distinctly utile for application to Next Generation Nuclear Plants (NGNPs). The high temperature application and transient conditions of NGNP operation induce stresses in CHX. These induced stresses can be categorized under different classifications based on their cause and location. ASME Sec. III Div. 5 has different analysis methodologies based on failure modes, failure criteria to be assessed, and constitutive relationship considered. The primary objective of this study is to provide a description of the classification of stresses in CHX. Further, evaluation of CHX design is conducted according to simplified analysis methodologies in ASME Sec. III Div. 5: Elastic and Simplified Inelastic Analysis. These simplified analyses are performed following the submodeling technique. At the global level, the channeled core is replaced by an elastic orthotropic core for analysis. At the local level, the stresses and strains for critical regions are determined following the simplified analysis methods. The load controlled stresses are checked against HBB-3220 of ASME Sec. III Div. 5. For the Elastic Analysis Method, strains in critical sections in CHX are checked for thermomechanical cycle against the HBB-T-1320 of ASME Sec. III Div. 5 criteria. For Simplified Inelastic Analysis, critical sections are analyzed for strain limits following HBB-T-1330 of ASME Sec. III Div. 5. The analyses outcomes are compared and results are discussed.

Compact heat exchangers (CHX) fabricated using the diffusion bonding process will be useful in the design and operation of Generation IV nuclear power plants. The NDE challenges posed by diffusion-bonded compact heat exchangers (DBHE) are quite different from those of their more familiar shell-and-tube cousins. The examination scope encompasses three parts: the welds joining the headers to the CHX body; the body’s solid perimeter, serving as the pressure boundary; and the channeled interior. Current investigations are in support of a Section III Code Case including CHX fabrication rules and post-fabrication nondestructive evaluation (NDE) requirements to ensure adequate initial quality. In-service examination methodologies are also considered to inform code developers, regulators, and vendors exploring use of CHX in advanced reactor designs. The welds joining the headers to the CHX body likely will be full-penetration set-on welds of conventional design. Standard fabrication examinations, namely visual, dye penetrant and hydrostatic examinations will likely suffice. Additional methods should be specified for the purpose of ensuring that the weld stresses have not caused degradation or separation of individual layers within the adjacent diffusion-bonded core. The channeled core of the CHX is geometrically complex and does not allow application of traditional NDE methods from the outside. Radiography permits imaging of small demonstration scale components. Meanwhile, identifying bond failures within larger components may require embedded strain sensors. A theory for employing strain sensors to detect failures within the core is introduced here along with early experimental results. The diffusion-bonded solid perimeter should be examined to ensure that any presence of bonding failures is allowable. Ultrasonic examination results are presented, obtained from test blocks containing simulated bond failures and from high-pressure CHX used during lab studies.

Calibrating inelastic models for high temperature materials used in advanced reactor heat exchangers is a critical aspect in accurately predicting their deformation behavior under different loading conditions, and thus determining the corresponding failure times. The experimental data against which these models are calibrated often contains a wide degree of variability caused by heat-to-heat material property variations and general experimental uncertainty. Most often, model calibration is done against mean of these experimental data without considering this variability. In this work we aim to capture the bounds of the viscoplastic parameter uncertainties that enclose this observed scatter in the experimental data using Bayesian Markov Chain Monte Carlo (MCMC) methods. Bayesian inference provides a probabilistic framework that allows to coherently quantify parameter uncertainties based on some prior parameter distributions and the available data. To perform the statistical Bayesian MCMC analysis, a pre-calibrated model, fitted against mean of the experimental data, is used as an initial guess for the prior distribution and bounds, while further sampling is done using Meteropolis–Hastings algorithm for four Markov chains in tandem, to finally obtain the posterior distribution of the model parameters. Since different inelastic parameters are sensitive to different tests, data from multiple experimental conditions (tensile, and creep) are combined to capture the bounds in all the parameters. The developed statistical model reasonably captures the scatter observed in the experimental data. Quantifying uncertainty in inelastic models will improve high temperature engineering design practice and lead to safer, more effective component designs.

Pressurized equipments maybe deform partially or wholly, and the mechanical properties of the construction material would be degraded due to a fire event. Fitness for service assessment can help to minimize reconstruction costs and allow safe resumption of unit operation as fast as possible. A propylene heat exchanger was exposed to overheating for about 3 hours due to a fire accident five or six meters far away. A fitness for service assessment was conducted according to API 579-1/ASME FFS-1. The material of the propylene heat exchanger is 09MnNiDR. The possible damage was examined by dimensional checks, hardness testing, in-situ field metallography, ultrasonic testing and magnetic particle testing. The heat exposure temperature of the propylene heat exchanger during the fire accident was estimated through the comparison between the results of in-situ field metallography examination and heat exposure simulation experiments. The heat exposure zones were identified based on the results of visual inspection and conjectural heat exposure temperature. The level 2 assessment was adopted to evaluate the heat exposure zones of V and VI. The approximate ultimate tensile strengths for the shell and the eastern head were converted from the hardness testing results. The caculated MAWP of the shell side is higher than the design pressure of the heat exchanger. The finite element method was adopted to evaluate the influence of the bulge in the upper part of the shell. The analytical results showed that the bulge had no significant effect on the operation of the heat exchanger before next inspection.

The mission of the U.S. Department of Energy (DOE), Office of Nuclear Energy is to advance nuclear power in order to meet the nation’s energy, environmental, and energy security needs. Advanced high temperature reactor systems will require compact heat exchangers (CHX) for the next generation of nuclear reactor plant designs. A necessary step for achieving this objective is to ensure that the ASME Boiler and Pressure Vessel Code, Section III, Division 5 has rules for the construction of CHXs for nuclear service. Construction of Alloy 800H diffusion bonded Printed Circuit Heat Exchangers (PCHEs) involves multiple controlled welding processes. The primary diffusion bonding process creates a uniformly bonded PCHE body featuring a microchannel core. Secondary welding processes are needed to attach headers and nozzles to the PCHE body, forming a complete CHX. The quality of these welding processes is ensured by following the appropriate ASME Section IX weld qualification procedures. Experience in constructing both 316L and 800H PCHEs has given a set of acceptable attachment weld configurations and procedures. Headers were attached to the diffusion bonded block surface using full penetration welds, as required by Class A design. The integrity of these attachment welds was demonstrated through hydrostatic pressure testing.

Heat exchanger is a device that transfers heat between hot and cold fluids. Due to the different size and type, the actual heat transfer performance is usually not the same as the design value. Meanwhile, various heat exchangers using new types of heat transfer elements have emerged, bringing the difficulty to obtain the heat transfer performance by only theoretical calculation. Therefore, studying test methods and developing test standards for heat exchangers have become the research focus in many countries. In this paper, the basic principles of various performance test methods are firstly introduced, including Wilson plot method, equal Reynolds number method and nonlinear fitting method. Then the restrictions on the use of these methods and the factors affecting the test results are analyzed. Finally, the Chinese codes and standards of performance testing for heat exchangers are listed, including JB/T 10379-2002, GB/T 27698-2011 and TSG R0010-2019. The test methods used in GB/T 27698 are described in detail. The results show that GB 27698 mainly focus on the specification of testing systems and procedures and can test heat transfer performance of almost all types of heat exchangers in industry under different heat transfer modes. However, there are lack of formulas and methods for calculating uncertainty of testing results.

There is increased interest in the application of compact heat exchangers (CHXs) for nuclear service given their high thermal efficiency and compactness. CHXs are fabricated by joining a stack of etched plates with dense microchannels through diffusion bonding. Diffusion bonding material has basic mechanical properties that differ from a base material, requiring appropriate mechanical properties and allowable stresses for design. Existing nuclear code ASME Section III, Division 5 does not address diffusion bonded materials . Hence, there is a need to develop material properties and allowable stresses of diffusion bonded materials and weldments. In this paper, one candidate material, Alloy 800H, was selected for diffusion bonding trials. Preliminary results obtained from a series of tensile and creep tests suggest that the diffusion bonded material is weaker than the base metal 800H. These experimental data are used in determining recommended allowable stresses of the diffusion bonded 800H material. In this paper, tables of the strength reduction factors for various allowable stresses which includes Smt, So, St, Sy and Su for diffusion bonded Alloy 800H are presented. These reduction factors are applicable to CHX design. The Larson Miller Parameter (LMP) is used to extrapolate short term creep tests to longer creep life and lower temperatures, and estimate the onset of tertiary creep strain.

Compact Heat Exchangers (CHXs) have a large number of miniature channels inside their core, which makes them highly thermal efficient and thus, prime utile for Next Generation Nuclear Plant (NGNP) applications. The fabrication of a CHX involves diffusion, brazed or welded bonding of plates to form CHX block with a channeled core. The elevated temperature and transient conditions of NGNP operation may induce excessive strain and creep-fatigue failure in channel ligaments. The primary objective of this study is to evaluate the design of CHX for application to NGNPs, following the ASME Code Elastic Perfectly Plastic (EPP) Analysis criteria in a draft ASME Code Section III, Division 5 and using the currently available Division 5 Code Cases (N-861 and N-862). As global analysis considering channels in the core is computationally intensive, a new analysis method is evaluated. In this method, the global analysis is performed by representing the channeled core by an elastic orthotropic material core. Subsequently, at the local level, EPP analysis is performed using models that include the channels, with thermal and pressure loading conditions. An ASME Draft Code Case is under development for the construction of CHXs. The analysis results are used to assess proposed stress limits and classification for load controlled stresses. For strain limits, the analysis results are evaluated using Code Cases N-861 and N-862 against the strain limit and creep-fatigue damage using the channel level submodel analysis. The applicability of the new analysis method, and use of the analysis results for evaluation against ASME proposed limits for various regions of the CHX are presented and discussed.

Compact heat exchangers have high compactness and efficiency, which is achieved by joining a stack of chemically etched channeled plates through diffusion bonding. In the diffusion bonding process, compressive stress is applied on plates at elevated temperatures for a specified period. These conditions lead to atomic diffusion, which results in the joining of all plates into a monolithic block. The diffusion bonding temperatures are above recrystallization temperatures, which changes the mechanical and microstructural properties of the bonded metal. Hence, diffusion bonded material needs mechanical and microstructural property evaluation. In this study, Alloy 800H is selected to study the influence of the diffusion bonding process on mechanical and microstructure properties of base metal. A series of tensile, fatigue, creep, and creep-fatigue experiments are conducted on base metal 800H (BM 800H) and diffusion bonded 800H (DB 800H) to explore the mechanical properties. Microstructure evolution during diffusion bonding is studied and presented in the paper. The mechanical and microstructural observations indicated ductile fracture at room temperature and brittle failure with bond delamination at elevated temperatures. The microstructure evolution during diffusion bonding is studied through tensile, fatigue, creep and creep-fatigue tests, and the implied root causes for the mechanical property changes are investigated. Efforts are made to correlate the microstructure change with mechanical property change in DB 800H.

In the finite element analysis of large-scale heat exchangers, the tightness analysis of tube-to-tubesheet joints of heat exchanger is classified into a highly nonlinear problem due to the existence of contact between tube and tubesheet, and there are a large number of tubes in the heat exchanger. These all make it difficult to analyze the tube-to-tubesheet joints in detail with the full model method. The traditional local model method simplifies the problem in a certain extent, but its boundary condition is different from the actual situation, which will result in an inaccurate result. In this paper, the sub model method is introduced into the tightness analysis of tube-to-tubesheet joints of the heat exchanger. Taking a U-tube heat exchanger as an example, the traditional local model method and the sub model method are used to analyze the tightness of tube-to-tubesheet joints respectively. The residual contact pressure of the seal ring on the contact surface of tube-to-tubesheet joints is taken as the criterion to evaluate the tightness of the joint. Variations of the residual contact pressure obtained by the two methods are comparatively studied. It is found that the traditional local model method is not conservative enough compared with the sub model method, and the sub model method can simulate more real boundary condition and obtain tightness conditions of the joint in different locations,which is a more effective analysis method. In addition, it is found that the choice of cutting boundary of the sub model has certain influence on the analysis results.

In order to improve the safety, reliability, and life of diverse structures, the development of effective methodologies for structural health monitoring is critical. Among damage detection techniques, guided ultrasonic Lamb waves are particularly suitable for damage detection applications for plate-like and shell-like structures, such as aircraft wing-box structures, heat exchanger tubing, stiffened panels, and nuclear steam generator tubing, due to their sensitivity to damage. Computational models can play a critical role to study wave propagation for monitoring structural health and develop a technique to detect structural damage. Due to complexity of guided wave behavior, efficient and accurate computation tools are essential to study the mechanisms that account for coupling, dispersion, and interaction with damage. In this study, a numerical technique is presented for guided waves propagation in metallic structure by employing co-simulation using ABAQUS Standard module and ABAQUS Explicit module simultaneously to simulate transient wave propagation from an PZT actuator into a metallic plate. The present co-simulation analysis couples multiphysics (piezoelectric) analysis with transient dynamics (wave propagation) analysis. A numerical test is conducted using a PZT actuator for exciting planar Lamb waves and a sensor for acquiring wave signals. The signals achieved from defected and pristine models by FEA are then compared to identify and detect damage in the structure.

Nubbins are predominately machined into a heat exchanger flange to create a high stress point to produce a tighter seal. Traditionally the gasket used when a nubbin is present is a Double Metal Jacket (DMJ), which consists of a metal jacket with a soft internal sealing material e.g. Graphite, PTFE. The metal jacket is commonly soft iron, carbon steel or a 300-series austenitic stainless steel. This paper will compare the performance of a DMJ and Kammprofile gasket, performance being – leakage and temperature cycling and the affect the nubbin has on the gasket after testing.

The use of stainless steel (SS) tubes in boiling applications must consider the potential risk of chloride stress corrosion cracking (SCC). Most steam generating tube bundles are carbon steel or low alloy steels, but occasionally, higher alloys are needed for the process side corrosion resistance. The use of SS tubes for these cases has had both successes and failures. SS has performed very well in other water and steam services, such as condensing, steam superheating, and boiler feed water (BFW) preheating applications, but for steam generating (i.e. boiling services) the experience has been mixed. Similar failures have also occurred in various process services which are being heated and contain water. The boiling of the water can lead to SCC. Some of the variables that can affect the risk of SCC for SS tube bundles in boiling services include: chloride concentration, tube wall temperature, exchanger design (i.e. kettle, thermosiphons, etc.), vertical vs. horizontal tubes, full vaporization vs. partial vaporization, recirculation rate, and BFW blow down rate. If SS materials are being considered, the risk of SCC can be determined by analyzing these variables as described in this paper. Where the risk of SCC cannot be avoided, an alternate, resistant tube material should be selected. The material options for various services are presented herein.

Compact and thermally efficient, Printed Circuit Heat Exchangers (PCHEs) are favored for use in next generation nuclear power plants. Containing thousands of small working fluid channels distributed in a solid 316H or 800H block, PCHEs can handle high pressures and operating temperatures required by generation IV nuclear plants. Advanced nuclear reactors will require the certification of a nuclear service PCHE design by construction codes, such as BPVC Sec-3. Compliance with this standard requires Creep fatigue and ratcheting analyses be performed for expected loading service transients. Realizing this analysis in PCHEs requires a simplified and flexible modeling approach that can be run over dozens of transients for multiple heat exchanger geometries. The Rich Environment Heatex-changer Transient (REHT) model is being developed to provide a full PCHE model needed to properly resolve Sec-3 loading conditions without the complexity inherent in resolving all facets of the PCHE geometry. This work introduces the thermohydraulic model that is the core of the REHT model. An example problem modeling an experimental scaled PCHE is presented. The ability of the REHT model to simulate fluid flow through a directional varying microchannel core of two heat exchanging streams is demonstrated. The REHT model resolves PCHE thermohydraulics using simple model definitions and minimum computational overhead, making it an ideal design tool.

Printed circuit heat exchangers (PCHEs) are used in a number of novel nuclear reactor designs. In order to use a PCHE as a primary coolant confinement unit in the United States, the stress and strain must be modeled under realistic service loads, and shown to remain within limits imposed by ASME standards. Due to the complex geometry and multi-length scale features, direct simulation of the stress and strain in a utility scale PCHE is not practical because of the large number of degrees of freedom. This work presents an algorithm to model damage to the core region of a PCHE using planar 2D formulation and realistic service loads. We compare how closely the results from three different planar formulations match the results of a corresponding 3D model. We also explore other ways of reducing the size of the numerical model required to accurately simulate the stress and strain in the core region of a PCHE. Finally, we perform strain-limits evaluation on a core region of a PCHE using fully temperature coupled, elastic perfectly plastic material properties, and realistic service loads, obtained from plant dynamics code of sodium cooled fast reactor coupled with a supercritical CO 2 Brayton cycle. For our analyses, we used CSIMSOFT Trelis: a commercial meshing software, Multi Object Oriented Solver Environment (MOOSE): an open source finite elements solver, and Paraview: an open source post processing tool. Our methodology is presented and discussed in sufficient detail so that the work can be reproduced by others.

Hybrid Friction Diffusion Bonding (HFDB) is a solid-state welding process that proved its capability of producing sound tube-tubesheet joints, but with limitations on tube thickness (up to 1mm) and tube-tubesheet materials. In the petrochemical industry, there is a great demand for the use of carbon steel shell and tube heat exchangers. To investigate the feasibility of HFDB techniques in joining thicker tube (i.e 2.1 mm) on tubesheet joint, a three-dimensional thermo-mechanical finite element model (FEM) was developed and solved using ABAQUS (commercial finite element analysis (FEA) software). The model was used to predict the temperature distribution and developed stresses during and after welding. The model considered temperature dependent material properties while Johnson-cook model was used to govern material plastic flow behavior. In this paper,19 mm (¾ in) ASTM 179 cold-drawn carbon steel tube into an ASTM A516 Grade 70 tubesheet joints was simulated. Results are validated based on temperature measurements, which was found in good agreement with experimental results. The developed model can be used to optimize processing parameters (i.e. tool rotational speed, dwell time “holding time”, and forging force.. etc) and study their effect on material flow and developed stresses.

The existing Class A metallic materials qualified for ASME Section III, Division 5 rules for high temperature nuclear reactors, are not optimized for corrosion resistance when exposed to corrosive reactor coolants such as molten salts, and molten lead and lead-bismuth eutectic. Introducing new corrosion-resistant materials into the Code would be a lengthy and expensive process for long design lifetimes, requiring long-term creep test data. A near-term alternative solution might be to allow designers to clad the existing Class A materials with thin layer of some corrosion-resistant material. However, the current ASME Section III, Division 5 rules provide no guidance on evaluating cladded components against the Code creep-fatigue or strain limits requirements. This necessitates the development of design rules for cladded components that do not require long-term testing of clad materials. Depending on the difference in mechanical properties, the influence of clad on the long term response of the structural system can be significant or negligible. This work focuses on developing design rules for cladded components with a clad material that does not accumulate significant inelastic deformation compared to the base material. This work proposes to treat such clad materials as linear elastic. Sample calculations including finite element analyses of a representative molten salt reactor heat exchanger tube without and with clad were performed to verify the proposed approach. Finally, a complete set of design rules for components with noncompliant clad material is proposed.