Tubesheet Thickness Research Articles

Lightweight Reseach of Tube Sheet for Spiral Wound Heat Exchanger Based on ANSYS

Abstract Tube sheet is the key pressure-bearing part in the spiral wound heat exchanger, and the high-strength and light-weight tube sheet structure is of great engineering significance for the development of a large-scale heat exchanger. In order to further realize the lightweight of the spiral-wound heat exchanger, this paper analyzes the influence of the thickness of the heat exchanger tube sheet on its strength based on the Ansys software and proposes the optimization design method of the tube sheet based on the strength safety factor F, which solves the problem that the software cannot take the stress linearization result as the state variable in the optimization calculation. The optimization results show that the thickness of the tube sheet is reduced by 40%. At this time, the stress strength at the connection between the tube sheet and the head and the center of the tube sheet first exceeds the design bearing capacity, indicating that the strength conditions of the two places are the controlling factors of the thickness. The results are important for the lightweight design of heat exchanger tube plate and material saving.

Adhesive reinforced friction stir welded thermoplastic tube-to-tubesheet hybrid joints

Thermoplastic materials are gaining popularity, because of their anti-fouling and chemically inert properties, for use in industrial applications that involve heating and cooling of highly reactive fluids. The current work studies the effect of adhesive reinforcement and radial clearance (RC) on developing friction stir welding (FSW)-based thermoplastic tube-to-tubesheet hybrid joints (TTHJs), which has applications in the thermoplastic heat exchanger and piping industries. The workpieces (sheets and tubes) made of carbon black reinforced high-density polyethylene were used. First, the effect of FSW parameters on the tube pull-out behavior was studied. The fractographic investigations (macroscopic and SEM) suggest that the FSW joints can fail in a brittle, ductile, or mixed manner, depending on the FSW conditions used. The FSW technique provides better load bearing capacity (326 N (0.0 RC), 517 N (0.5 mm RC)) compared to adhesive joints (226 N (0.0 RC), 206 N (0.5 mm RC)). For 0.0 RC, the adhesive reinforcement increased the load bearing capacity by 15.6 %. On the contrary, for 0.5 mm RC, the adhesive reinforcement negatively impacted the load bearing capacity and reduced it by 40.6 %. The FSW technique with 0.5 mm RC provides a higher leak path of 77 % remaining tubesheet thickness (> tube thickness) compared to that of 46.6 % (< tube thickness) achieved at 0.0 RC. However, the adhesive reinforcement can enhance the leak path of 0.0 RC FSW joints to around 100 % remaining tubesheet thickness (> tube thickness) by introducing the adhesive material at the tube-sheet interface.

Friction stir welding of tube-to-tubesheets for thermoplastic shell and tube heat exchangers

Recently, there is a real demand for thermoplastic shell-and-tube heat exchangers because of their antifouling and chemically inert properties. A novel non-conventional joining technique is developed for creating efficient thermoplastic tube-to-tubesheet joints (TTJs) using the friction stir welding (FSW) process. The carbon black reinforced high-density polyethylene sheet and tube materials are used. A highly ductile joint with a maximum strength of 517 N (42 % greater than adhesives), and a maximum leak path of 3 mm (77 % of remaining tubesheet thickness) was achieved using FSW. The proposed technique was found promising and reliable for developing TTJs for thermoplastic shell-and-tube heat exchangers.

Tube bundle buckling analysis with support effects on tubesheet in heat exchangers

Tubesheet strength calculation is important work in design of heat exchangers. The thickness of the tubesheet depends on the two major factors: loads and structure. The former includes fluid pressure and metal thermal gradient. The later involves tubes bundle located at inner perforated area of tubesheet and constraints applied by flanges or shells at the outer ring of tubesheet. As an elastic foundation, tubes bundle is one of critical factors in calculation of tubesheet system. The effect and current problems of tubes bundle support is reviewed in this paper. Analysis and experiments show that current single tube buckling criterion used in the strength design of the tubesheet may lead to an inaccurate calculation of the tubesheet thickness since this criterion is conservative for a long tube or aggressive for a short tube. A more reasonable and safe criterion for considering the tube bundle support is proposed in this paper which could make the tubesheet thinner and thus, decrease the cost of the heat exchangers. In addition, the idea proposed in this paper may be helpful to develop a new standard for the strength design of the tubesheet or even the tubesheet system.

Optimization and Standardization of Flanged and Flued Expansion Joint Design

Flanged and flued type expansion joint (thick wall expansion bellow) used as an integral part of many shell and tube heat exchanger where process conditions produce differential expansion between shell and tubes. It provides flexibility for thermal expansion and also functions as a pressure retaining part. Design of expansion joints is usually based on trial and error method in which initial geometry must be assumed, and accordingly maximum stresses and spring rate are be calculated. Inadequate selection of geometry leads to higher tubesheet and bellow thickness, which increases cost of equipment. This paper presents standardization and optimum design approach of flange and flued expansion bellow fulfilling ASME VIII-1 and TEMA standard requirement. Methodology to define expansion bellow geometry is developed, and geometry dimensions are tabulated for expansion bellow diameter from 300 to 2000 mm and thickness from 6 to 30 mm. Each defined geometry is analyzed using finite element method, and maximum von Mises stresses are calculated for bellow axial displacement from 0.5 to 1.5 mm and internal pressure from 0.1 to 6.5 MPa. Spring rate is also calculated for each defined geometry for consideration in tubesheet calculation. Accordingly, optimum design methodology is developed, tested, and compared with existing design. Results depicted that proposed standardization approach and design methodology will optimize expansion bellow and tubesheet thickness and will also save considerable time in finalization of heat exchanger design.

Research on Light-Weight of the High Pressure Heater Tubesheet

The tubesheet is the main component of the high pressure heater, and the rationality of its design directly affects the safety and stability of the system. The light-weight of the tubesheet is conducive to resource saving, avoiding large temperature difference stress caused by excessive tubesheet thickness, and further improving parameters under the prior conditions. Therefore, the light-weight of the tubesheet has become the focus of tubesheet design research. It introduced the research of tubesheet light-weight technology from three aspects of the standard, design and material, and summarized the current research status of related literature at home and abroad. There are several problems in theoretical research and engineering application in the classification of tubesheet light-weight, including complex failure mode, experimental verification difficulties, long data accumulation, etc. It provides a direction for the in-depth study of tubesheet light-weight.

Mathematical Modelling for Thermal and Mechanical Design of Shell and Tube Type Gas Cooler Used in Transcritical CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Refrigeration System

This paper is about Mathematical Modelling for Thermal and Mechanical Design of Shell and Tube type Gas Cooler used in Transcritical CO2 Refrigeration system. Transcritical refrigeration system refers to system whose condenser temperature is above critical temperature of refrigerant. To achieve it, the condenser in conventional refrigeration system is replaced by Gas Cooler where Refrigerant vapour is cooled sensibly without condensation. The gas cooler is used for cooling of refrigerant by using water as coolant. The temperature of refrigerant vapour coming out of compressor in transcritical system is more as compared to conventional refrigerant system. So gas cooler can be effectively used for heating of water. This paper describes a mathematical model that can be used in predicting the heat transfer performance of a shell and tube type Gas Cooler used in transcritical CO2 refrigeration system. The model uses Kern Method of Heat exchanger design. Given the fluid inlet and outlet temperatures flow rates of fluid & fluid properties the model determines (a) the necessary heat transfer surface area, (b) Outside and inside heat transfer coefficient, (c) overall heat transfer coefficient, (d) Pressure drop on shell and tube side, (e) It also determines mechanical design parameters such as shell O. D, Shell thickness, Tube sheet thickness, Flange thickness.

Structural Analysis and Optimization of Transition Section of Convex Tube Sheet

The convex tube sheet which is used in heat recovery boiler consists of three parts: the high temperature tube sheet, the low temperature tube sheet and the transition section.Three-dimensional finite element model of convex tube sheet in new type of heat recovery boiler is established in this paper. Using the ANSYS Workbench software, thermal stress of the convex tube sheet is analyzed. The temperature fields and thermal stress distribution of convex tube sheet are obtained, and its structure strength is checked. The effects of the high temperature tube sheet thickness, low temperature tube sheet thickness and transition section thickness on the maximum equivalent stress of the convex tube sheet are analyzed. The results show that: temperature of most parts of convex tube sheet is close to the tube side fluid temperature, and the large temperature gradient only existed in the thinner regions of shell side of convex tube sheet; temperature distribution shows obvious skin effect. At the transition section, the temperature along the thickness direction is more evenly distributed, with little change in temperature gradient; larger thermal stress mainly concentrated at tube layout area which close to the shell side of the high temperature tube sheet and the connecting parts of transition section and low temperature tube sheet in the tube side. Through checking the strength intensity, convex tube sheet structural strength meets the requirements.The transition section thickness are optimized. The optimum thickness of the transition section analyzed in this paper is 31mm.

A Proposed General Method of Stress Analysis for Tubesheet of Heat Exchanger

The stress analysis method for fixed tubesheet (TS) heat exchangers (HEX) in pressure vessel codes such as ASME VIII-1, EN13445, and GB151 all assume a geometric and loading plane of symmetry at the midway between the two TSs so that only half of the unit or one TS is need to be considered. In this study, the midplane symmetry assumption is discarded. More common situations are considered such as unequal TS thickness, different edge conditions, pressure drop, and dead weight on two TSs. Based on the classical thin plate and shell theoretical solution, an analytical method of stress analysis for TS is presented. The proposed method is suitable for different types of HEX due to fewer assumptions employed in this study. Analysis shows that floating and U-tube HEX are the two special cases of the proposed method. Theoretical comparison shows that ASME method can be obtained from the special case of the simplified mechanical model of the proposed method. Typical geometries and loading are considered, and the proposed method is used to check the adequacy of design. Predictions are compared with the results obtained from axisymmetric finite element analysis (FEA) and current ASME method. Comparison results indicate that predictions given by this paper agree well with FEA while ASME results are not correct or not accurate.

Sensitivity study of APR-1400 steam generator primary head stay cylinder and tube sheet thickness

The steam generator is a type of heat exchanger which produces steam to drive the turbine generator. For the APR-1400, Doosan Heavy Industries & Construction manufactures a vertical type of steam generator that has a horizontal tube sheet with a central support design, called a stay cylinder. In this design, the stay cylinder limits tube sheet deformation and effectively reduces thickness of tube sheet and increases structural integrity. A concentric hole in the stay cylinder facilitates welding to the primary head and to the tube sheet. In this study, the APR-1400 steam generator tube sheet thickness parameters were investigated within the constraint of maintaining the overall deformation of the tube sheet in comparison to the current design. A parametric evaluation to reduce the thickness of the steam generator tube sheet is performed by varying the inner diameter of the stay cylinder and the thickness of the tube sheet. The solutions are developed based on two-dimensional finite element analyses. The effect of a reduction of the tube sheet is beneficial in the manufacturing of steam generator by using less material and reducing manufacturing time and allowing easier assembly process of U-tube bundles to the tube sheet.

Light-Weight Design of the Tubesheet of a High Pressure U-Tube Heat Exchanger Based on Finite Element Analysis

Based on Chinese code GB151 for the design of shell-and-tube heat exchangers, the tubesheets are usually very heavy. The reason is attributed to the oversimplified mechanical model for the calculation of the tubesheet thickness especially the insufficient consideration of the tube support to the tubesheet. In this paper, a 3-D finite element model was established for a U-tube heat exchanger consisting of tubesheet, tube-channel, part of shell and tubes. A static stress analysis was performed under tube-side pressure loading. Optimal computation or light-weight design was carried out for minimum thickness of the tubesheet with the precondition of strength requirements conforming to the design-by-analysis code JB4732-1995. It is found that with the optimization design, the thickness of the tubesheet could be decreased by 31%, meaning that by using finite element method together with the code of design-by-analysis the thickness of the tubesheet can be significantly reduced.

Analytical Modeling of the Strength of Tubesheets for Steam Surface Condensers

A tubesheet is one of the most important components in the design of a steam surface condenser. In this work, an analytical method to determine the strength of a tubesheet is established based on a beam-strip model. The validation of this beam-strip model is confirmed through a finite-element method (FEM) with the same boundary conditions and mechanical properties of the tubesheet. Effects of various parameters that affect the strength of the tubesheet are analyzed, including the tubesheet thickness, applied loading, fixity type, and length of the unperforated zone. The modeling results show that the most significant factor influencing the maximum stress that the tubesheet can bear is the tubesheet thickness, while other parameters have a weaker impact. From an engineering point of view, the beam-strip model is a useful method for the design of tubesheet.

Study on Effective Elastic Constants of Homogenization Tube Sheet

The expressions of the effective elastic constants of composite material with cylindrical inclusions are derived based on M-T method, and it can be used in discussing the approximate range of effective elastic constant of air. Moreover, it is possible to homogenize tube-sheet by making use of the expression. The numerical result obtained is in good agreement with effective elastic constant adopted by the ASME code. It demonstrates that the approach is effective and accurate. At the last, the relationship between effective elastic and thickness of the tube-sheet is discussed.

Effects of Tube Stiffness and Tubesheet Thickness on the Thermal Stress of the Tubes and Tubesheet

In this paper, numerical simulation was carried out for the tube bundle of a float-head heat exchanger with concentration on the effects of tube stiffness and tubesheet thickness on the thermal stress of the tubes and tubesheet. It is found that decreasing the tube stiffness by using corrugated tubes can reduce the axial thermal stress at the tubes and, thus, decrease the possibility of strength failure of the connection between the tubes and tubesheet. Decreasing the tubesheet thickness can reduce the thermal stress at the tubesheet, which is meaningful for the heat exchangers with large temperature difference between the shell-side fluid and tube-side fluid and under small pressures.

Ratcheting Assessment of a Fixed Tube Sheet Heat Exchanger Subject to In Phase Pressure and Temperature Cycles

An investigation of the cyclic elastic-plastic response of an Olefin plant heat exchanger subject to cyclic thermal and pressure loading is presented. Design by analysis procedures for assessment of shakedown and ratcheting are considered, based on elastic and inelastic analysis methods. The heat exchanger tube sheet thickness is nonstandard as it is considerably less than that required by conventional design by formula rules. Ratcheting assessment performed using elastic stress analysis and stress linearization indicates that shakedown occurs under the specified loading when the nonlinear component of the through thickness stress is categorized as peak stress. In practice, the presence of the peak stress will cause local reverse plasticity or plastic shakedown in the component. In nonlinear analysis with an elastic–perfectly plastic material model the vessel exhibits incremental plastic strain accumulation for 10 full load cycles, with no indication that the configuration will adapt to steady state elastic or plastic action, i.e., elastic shakedown or plastic shakedown. However, the strain increments are small and would not lead to the development of a global plastic collapse or gross plastic deformation during the specified life of the vessel. Cyclic analysis based on a strain hardening material model indicates that the vessel will adapt to plastic shakedown after 6 load cycles. This indicates that the stress categorization and linearization assumptions made in the elastic analysis are valid for this configuration.

Cracking simulation of a tubesheet under different loadings

For shell-and-tube heat exchangers, tubesheet cracking is a major failure form. Owing to complicated structures, loadings and environments, mechanisms for the crack nucleation and propagation often puzzle engineers and as a result, it is hard to take effective measures to prevent this kind of failure from happening again. In this paper, three dimensional finite element models were established to investigate a real tubesheet cracking with the emphasis on the driving forces for the crack propagation from a fracture mechanics point of view. Three different loadings, namely residual expansion stress, crack face pressure and transverse pressure, and three crack growth patterns were considered. In order to obtain the residual stresses, the hydraulic expanding process of tube-to-tubesheet joint was simulated. Residual contact pressures between the tube and tubesheet and the induced residual stress distributions in the tubesheet were computed. The possibility for crack propagation in the tubesheet under the action of the different loadings was investigated in terms of the strain energy density factor. Results show that surface crack propagation may be driven by all the three loadings especially the transverse pressure. But when surface cracks come into the interior of the tubesheet along the thickness, as acted along the whole tubesheet thickness, the residual expansion stress would play key roles in crack propagation.

On the Design Approach of Double-Tubesheets

Double-tubesheets are used in heat exchangers where strict tightness is required. In this paper, finite element analysis models were established to simulate the double-tubesheets. Stresses and deformations in the tubesheets induced by pressure load were calculated and formulated. Results showed that the tube supports to the tubesheet are much stronger than considered in the commonly used heat exchanger design codes. If the design is based on accurate stress analysis using finite element method, the tubesheet thickness of heat exchangers could be significantly reduced. The two tubesheets strengthen each other especially when their spacing is short.

Numerical simulation of thermal stress in tube-sheet of heat transfer equipment

The thermal stress induced by temperature difference in the tube-sheet of heat transfer equipment was studied in the paper. Finite element method (FEM) was used to compute the temperature and the stress fields. The effect of the tube-sheet thickness on the thermal stress has been discussed in terms of the results by FEM. Some measures to reduce or eliminate the thermal stress in the tube sheet are suggested. A new design of the structure of the flexible tube sheet was proposed.

Expanded, and Welded-and-Expanded Tube-to-Tubesheet Joints

This paper discusses some practical aspects of expanded and welded-and-expanded tube-to-tubesheet joints. It reviews elastic-plastic tube expanding theory, which it uses as the basis for setting pressures for uniform-pressure expanding and for estimating residual interfacial stress at the tube-hole interface. It addresses uniform-pressure-expanded tube joint strength and the problem of correlating of roller-expanded joint strength with wall reduction and rolling torque. It advocates two-stage expanding: 1) applying just sufficient pressure or torque to create firm tube-hole contact over substantially the tubesheet thickness; and 2) re-expanding at full pressure or torque. It points out the advantages of segregating heats of tubing and mapping the tube-heat locations. It recommends non-TEMA Standard (and non-HEI Power Plant Standard) grooves for grooved-hole joints made by roller-expanding, when the tubes are thin-walled, high-strength, low-elastic-modulus, and for joints made by uniform-pressure expanding [1, 2]. It states what to examine when considering grooves for small-diameter tubes. It reviews tube-to-tubesheet welding requirements and discusses welding before and after expanding. It suggests TEMA revise its standards to define strength and seal welds and urges the ASME Boiler and Pressure Vessel Code Committee (the Code Committee) to incorporate the TEMA definition in Section VIII of the ASME Boiler and Pressure Vessel Code (the Code) [3]. It makes recommendations for pressure and leak-testing. The work shows why welded-and-expanded joints should be full-strength expanded and why expansion length should equal the tubesheet thickness minus 1/8 in. (approximately 3 mm) rather than the lengths the TEMA and HEI Standards permit.

French rules for the design of fixed-tubesheet heat exchangers

Since 1981 new rules have been applied in France (CODAP) for heat exchanger mechanical design, which have been elaborated under the responsibility of the author. The purpose of this paper is to present the rules relative to the fixed-tubesheet heat exchangers and compare them with the rules provided by the Tubular Exchanger Manufacturing Association (TEMA). The tubesheet is replaced by an equivalent solid plate for which the effective elastic constants are given by original curves depending on the ligament efficiency and on the ratio of tubesheet thickness to tube pitch. The connection of the tubesheet with the shell and the head is simulated by considering the tubesheet as being elastically clamped at its periphery: this allows one to treat, in a continuous way, simply supported and clamped tubesheets and to avoid arbitrary choices by the designer between those two extreme cases. The method enables the calculation of the maximum stresses in the tube-sheet, tubes, shell and head, which are limited to allowable stresses established according to the stress category concept of ASME VIII, division 2. These rules lead generally to thinner tubesheets than those arising from TEMA whilst still providing more overall safety due to a better representation of the tubesheet behaviour.