Abstract 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.

Abstract The thread ring block heat exchangers, served at the high temperature and pressure, are the key equipment in the petrochemical industry. Due to the severe operational conditions and unsuitable assemble, internal leakage problem commonly occurs, especially for the seal gasket between the tube sheet and shell. Many failed gaskets are collected. Through a series of experiments including chemical composition, metallographic analysis, SEM and fracture analysis, the gasket damage and leakage causes are analyzed. For further interpretation, the gasket stress analysis is completed by the finite element method. It shows that the gasket stress is a main factor that affects the sealing performance for the thread ring block heat exchanger. Under long term operation at high temperature and pressure, the gasket stress between the tube sheet and shell becomes loose and creep. The gasket material also deteriorates with increasing time. Therefore, in order to prevent the internal leakage, the stress should be controlled in an appropriate range. And periodical inspection must be performed.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract Printed Circuit Heat Exchangers (PCHEs) are well-suited for Very High Temperature Reactors (VHTRs) due to high compactness and efficiency for heat transfer. The design of PCHE must be robust enough to withstand possible failure caused by cyclic loading during high temperature operation. The current rules in ASME Code Section III Division 5 to evaluate strain limits and creep-fatigue damage based on elastic analysis method have been deemed infeasible at temperatures above 650°C. Hence, these rules are inapplicable for temperatures ranging from 760–950°C for VHTRs. A full inelastic analysis method with complex constitutive material description as an alternative, on the other hand, is time consuming; hence impracticable. Therefore, the simplified Elastic-Perfectly Plastic (EPP) analysis methodology is used as a solution in ASME Code Section III Division 5. The current literature, however, lacks any study on the performance evaluation of PCHE through EPP analysis. To address these issues, this study initiates the pathway of EPP evaluation of an actual size PCHE starting with elastic orthotropic analysis in the global scale. Subsequently, preliminary planning for analyzing intermediate and local submodels are provided to determine channel level responses to evaluate PCHE performance against strain limits and creep-fatigue damage using Code Case-N861 and N862 respectively.

Abstract The added mass coefficient is an important parameter when calculating the flow induced vibration (FIV) in heat exchangers. The calculation method of the added mass coefficient for tube bundles in triangular and square arrays had been presented in relevant standards which like GB/T 151. Presently, concentric arrays of tube bundles are applied extensively in the heat exchangers at nuclear power plants. However, the method for calculating the added mass coefficient of tube bundles in concentric arrays has not been given in these standards. In this paper, in order to calculate the added mass coefficient of a central flexible tube surrounded by rigid tubes in concentric arrays, the fluid-structure interaction models of tube bundles has been established by ANSYS CFX. The influence of the circumferential and radial distance of the tube bundles on the added mass coefficient has been studied by calculating the natural frequency. The results are expected to provide the calculation reference for added mass coefficient of the tube bundles in concentric arrays. The coupling vibration of tube bundles in concentric arrays has been studied by the other model which is made up of all the flexible tubes, and the coupling vibration of the tube bundles is simulated by the rigid wall motion of ANSYS CFX. According to simulation results, there exists a band of amplitude peaks in the coupling vibration of the tube bundles. It is shown that as the circumferential and radial distance increases, the band of amplitude peaks becomes narrow.

Abstract A considerable amount of time and dedication have been devoted into the development of an unified non-dimensional random excitation forces (Power Spectrum Density) PSD model of tube bundles into two phase flow conditions. However, any model cannot be used for wide-range two phase flow conditions as random excitation forces depends strongly on a two phase flow regime. Therefore, we have developed a new scaling method for a two phase random excitation force PSD to be applicable for a wide-range of flow conditions. This method has been developed by focusing on the correlation between a two phase pressure loss and two phase turbulence energy. Comparisons of non-dimensional random excitation force PSDs in various conditions scaled by using the developed method, showed a good concordance between the two.

Abstract Fluidelastic instability (FEI) remains an important concern to designers of heat exchangers subjected to high flow velocities of gases, liquids or a combination of the two phases. In the present work, experimental tests are conducted to measure the quasi-steady fluid forces acting on a normal triangular tube array of P/D = 1.5 subjected to single-phase cross-flow. The quasi-steady forces together with previously measured unsteady fluid forces are used to estimate the time delay between the central tube motion and fluid forces on itself. The time delay effect for the quasi-steady fluidelastic instability model is derived in the frequency domain in the form of an equivalent Theodorsen function. The results are compared with the Theodorsen function previously obtained for the rotated triangular array. Using the time delay formulation, a stability analysis is carried out to predict the critical velocity for fluidelastic instability in a normal triangular array subjected to single-phase flow.

Abstract In this study, a novel method is proposed to detect flaws directly under tube support plate (TSP) of heat exchanger tube using a cylinder-type magnetic camera (CMC). The CMC measures and images magnetic flux density changes occurring around a defect by applying a time-varying magnetic field to a metallic object through magnetic sensors which are arrayed in a matrix. If there is a flaw directly under the TSP, the magnetic flux density is concentrated in the TSP due to its higher permeability. Accordingly, flaws directly under the TSP are difficult to be detected. In order to solve this problem, the principle that the magnetic flux density distribution around the TSP is uniform in the circumferential direction is used. When the magnetic flux density signals obtained at the position where the TSP is placed are set as reference signals and the signals obtained by rotating the sensor probe in the circumferential direction are compared with the reference signals, it is possible to detect the flaw signals from which the TSP signals are removed. If the flaw is formed in the circumferential direction, the flaw can be detected by moving the sensor probe in the axial direction and comparing the signals with the reference signals. The proposed method to detect flaws directly under the TSP was verified using an artificially flawed heat exchanger tube (HXT) test specimen made of titanium alloy.

Abstract Printed circuit heat exchangers (PCHEs) have a high heat transfer coefficient which makes them a suitable option for very high temperature reactors (VHTRs). ASME Section VIII design code provide PCHE design rules for non-nuclear applications. The PCHE design methodology for nuclear applications is yet to be established. Towards developing the ASME Section III code rules, this study started with the PCHE design as per section VIII. An experimental set up is developed to evaluate the designed PCHE for creep and creep-fatigue performances. This study performed pretest finite element analysis to estimate experimental responses and failure loads for setting up the experiments. Three dimensional isothermal analyses of the PCHE’s were conducted by using an advanced unified constitutive model to simulate the creep-fatigue interaction. The sub-modeling technique was used to analyze the channel scale response of the PCHE. Analysis results indicate that the failure may be governed by the channel corner responses, which is influenced by the creep-fatigue interaction. Analysis based creep-fatigue damage curve is plotted as per ASME code to evaluate the design of PCHEs for nuclear application.

Abstract The development of Compact Heat Exchangers (CHE) improves heat transfer efficiency with surface-to-volume ratios approaching 2500 m 2 /m 3 . In the applications such nuclear plants, CHE need to work for years in a harsh environment of high temperature up to 800 °C and high pressure up to 20 MPa. Any structural failure, i.e. cracks due to material fatigue or residual stress concentration in the CHEs, may result in safety problems and tremendous economy losses. Compared to the conventional heat exchangers, the non-destructive testing for CHE is challenging because the deformation of micrometer sized channels is hard to detect by the conventional means such as strain gauges or ultrasonic sensors. This paper presents a novel approach to detect the presence of cracks using fiber strain sensors embedded in the compact heat exchangers. The fiber sensors are proposed to install the heat exchanger with the microchannel plate stacks in the heat exchanger, measuring the strain distribution in the structure during the operation. Numerical and analytical models of CHE with and without cracks are built to learn crack size influence on strain variation. Sensors’ sensitivity to crack positions was calculated through simulation. A defect retrieval algorithm based on Tikhonov regularization is presented to achieve crack detection according to sensors’ outputs. A sample CHE section with 5x5 channels are simulated to quantitatively test the accuracy and validity of the proposed method.

Abstract 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.

Abstract 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.

A program for a high-temperature design analysis and defect assessment has been developed for an elevated temperature evaluation according to the RCC-MRx for Generation IV and fusion reactor systems. The program, called ‘HITEP_RCC-MRx,’ consists of three modules: ‘HITEP_RCC-DBA,’ which computerizes the design-by-analysis (DBA) for class 1 components such as the pressure vessel and heat exchangers according to RB-3200 procedures, ‘HITEP_RCC-PIPE,’ which computerizes the design-by-rule (DBR) analysis for class 1 piping according to RB-3600 procedures and ‘HITEP_RCC-A16,’ which computerizes high-temperature defect assessment according to the A16 procedures. It is a web-based program, and thus can operate on a smartphone as well as on a personal computer once it is connected to the URL. The program has been verified with a number of relevant example problems on DBA, Pipe, and A16. It was shown from the verification works that HITEP_RCC-MRx with the three modules conducts a design evaluation and a defect assessment in an efficient and reliable way.

A high pressure carbamate condenser (HPCC) is a shell and tube heat exchanger with low pressure steam/condensate on the shell side and high pressure carbamate solution on the tube side. The inlet channel of the exchanger is protected from the internal corrosive environment by means of an austenitic stainless steel liner. During the first internal inspection after commissioning, a bulge was observed in the liner where a pass partition plate is joined to the liner. Surface-breaking cracks were observed at the partition plate to liner welds in the bulged region. The cracks were removed by shallow grinding, but a fitness-for-service assessment was required to evaluate the suitability of the bulged liner for continued service. Due to the complexity of the geometry, a handheld 3D geometry scanner was used to accurately measure the deformed shape of the bulge. Using the measured geometry, a finite element model was developed and used to perform a level 3 fitness for service assessment. This paper will describe the assessment procedure in detail as well as the complex internal repairs that were ultimately implemented in order to restore the integrity of the equipment.

Whenever undesirable dynamic events occur within power plant, refinery, or process piping systems, specialty supports and restraints have the task of protecting the mechanical equipment and connecting piping from damaging loads and displacements. The array of components that may be affected include, but are not limited to, piping systems, pumps, valve assemblies, pressure vessels, steam generators, boilers, and heat exchangers. In particular, the dynamic events can be classified into two distinct types that originate from either internal events or external events. The internal dynamic load generating events include plant system start-up and shut-down, pressure surges or impacts from rapid valve closures such as steam and water hammer, boiler detonations, pipe rupture, and operating vibratory displacements that may be either low frequency or high frequency vibrations. The external dynamic load generating events include wind loads, earthquake, airplane impact to supporting structures and buildings, and explosions. Most of the aforementioned dynamic load generating events can be defined quite simply as impact loads, i.e., forces and moments that are applied over very short periods of time, for example, less than one second. While earthquake loads may be applied over a total time period of an hour or so, the peak loads and resulting displacements occur on a more sinusoidal basis of peak-to-peak amplitudes. One of the most common specialty restraint components utilized in the piping industry to absorb and transfer the dynamic load resulting from impact events is the hydraulic shock suppressor, otherwise known as the snubber. The snubber is a formidable solution to protecting plant piping systems and equipment from impact loading while not restricting the thermal displacements during routine operations. In the dynamic events that may be characterized by an impact type loading, snubbers provide an instantaneous, practically rigid, axial connection between the piping or other component to be secured and the surrounding structure whether it be concrete or steel (for example). In this way, the kinetic energy can be transmitted and harmlessly dissipated. In the vibratory environment, however, neither the impact load scenario nor the rapid translations are imposed upon snubbers, thereby presenting the competing intended application of the snubber to protect against impact loads versus, in many cases, the improper selection of the snubber to dampen vibratory (other than seismic) loads. The details of the hydraulic shock suppressor design are reviewed and discussed to exemplify why a case can and should be made against the use of snubbers in piping systems within an operating vibratory environment.

Printed Circuit Heat Exchangers (PCHEs) have high compactness and efficiency for heat transfer, which makes them an attractive option for the Very High Temperature Reactors (VHTRs). Design methodology of PCHE for non-nuclear service is well established in the ASME Code, Section VIII; however, ASME Code rules for PCHE nuclear services are yet to be developed. Towards developing the ASME Section III code rules for PCHE, the study started with the design of PCHE core specimens for testing following the ASME section VIII methodology. The failure responses of these PCHE specimens are investigated by using Finite Elements Analyses (FEA). Two dimensional isothermal plane strain analyses are performed using an uncoupled constitutive material model. Parametric studies by varying shape and size of semicircular channels, PCHE core size, and loading cases are performed to quantify the critical parameters which influence the PCHE failure responses under pressure creep and pressure burst loadings. Results indicate that the maximum creep strain and its location are dependent on the PCHE core size. Significant reduction in creep strains are observed at the channel sharp corners by considering a realistic semielliptical channel shape instead of a semicircular channel in the analysis.

The high-pressure applications of traditional Gasket Plate Heat Exchangers (GPHE) are limited by the sheet material, gasket material and the design of the GPHE. The newly developed stainless steel grade UNS S82031 (EN 1.4637) is a duplex stainless steel grade with improved formability compared to other duplex stainless steel grades. It can be used in forming intensive applications, such as in typical chevron corrugated-plate heat exchangers. Compared to the standard austenitic stainless steel grades typically used, the new duplex stainless steel increases the application performance of GPHE applications, such as maintaining higher working pressures. In this paper, the properties and material behavior of UNS S82031 is compared with the standard austenitic stainless steel UNS S30400 (EN 1.4301) in a pressure test at different working pressures. The pressure test is used to evaluate the performance of the selected material for a GPHE application. The experimental test results are compared with Finite Element (FE) simulation of the same pressure test, to achieve a deeper understanding of the results. The results show that plates made of UNS S82031 can withstand significantly higher working pressures than UNS S30400 for the same PHE-design, proving the new duplex stainless steel UNS S82031 is more suitable for high pressure GPHE applications.

In new design of heat exchangers with high turbulence intensity and low pressure drop in the shell side, parameters or structures beyond the standards may be adopted and failure risk due to fluid induced vibration can increase. As pitch ratio is related with some significant parameters, the range of pitch ratio determines whether the FIV calculation could be established. In this research, FIV of heat exchangers with pitch ratio beyond the standards was investigated on mechanisms such as vortex shedding, turbulent buffeting and fluid elastic instability. Both theoretical and numerical methods have been applied during the study to get parameters beyond the pitch ratio range. Parameters related to pitch ratio such as additional mass coefficient C m and damping ratio ζ were extended, and then verified by experiments. Calculating cases on several conditions were accomplished as well as comparation with literatures. The results and methods could be guidelines for the design of new type of heat exchangers and references in the amendment of relevant standards.