Fixed Tubesheet Heat Exchangers Research Articles

The Unified Theory of Tubesheet Design—Part III: Comparison With ASME Method and Case Study

Abstract Based on the unified theory of tubesheet (TS) design for fixed TS heat exchangers (HEXs), floating head and U-tube HEXs presented in Part I and Part II, theoretical and numerical comparisons with ASME method are performed in this paper as Part III. Theoretical comparisons show that ASME method can be obtained from the special case of the simplified mechanical model of the unified theory. Numerical Comparison results indicate that predictions given by the unified theory agree well with finite element analysis (FEA), while ASME results are not accurate or not correct. Numerical comparisons also indicate that ASME results of TS stresses are not always conservative and may lead to unsafety design.

The Unified Theory of Tubesheet Design—Part I: Theoretical Foundation

Abstract The unified theory of tubesheet (TS) design for fixed TS heat exchangers (HEXs), floating head and U-tube HEXs is developed by removing the midplane symmetry (MPS) assumption, which assumes a geometric and loading plane of symmetry at the midway between the two TSs so that only half of the HEX or one TS need be considered. The unified theory can be successfully extended to all common types of HEXs, with arbitrary combinations of TS configurations for two TSs, and with arbitrary material properties and temperature for each component due to less assumptions. The effects of unperforated annual plate, TS flange, gravitational (e.g., dead-weight of tubes, catalyst inside tubes, shell side fluid and tube side fluid) and fluid flow pressure loss, bending stiffness of the tubes, TS in-plane stretch, pressure in TS perforations as well as temperature gradient across TS are also evaluated by the unified theory. Theoretical analysis shows that the existing theories of TS design can be derived from the unified theory as special deductions. The limitations and problems faced in the existing theories and codes are systematically reviewed and solutions to these limitations and problems are also provided by the unified theory. Numerical comparisons indicate that predictions given by the unified theory agree well with finite element analysis (FEA), while ASME results are not accurate or not correct and may lead to unsafety design.

The Unified Theory of Tubesheet Design—Part II: Supplement to the Theoretical Analysis

Abstract The theoretical foundation of the unified theory of tubesheet (TS) design for fixed TS heat exchangers (HEXs), floating head, and U-tube HEXs are presented in Part I, in which only the most important equations are addressed to show the main points of the theory. The equations, conclusions, and other aspects referenced in Part I are presented or proved in this paper as Part II to supplement the theoretical analysis in Part I.

Prediction of Cycle Life of Expansion Bellows for Fixed Tube sheet Heat Exchanger

Research on determining the lifetime of an expansion bellows designed to compensate the difference in expansion between the shell and the tubes in a fixed tube sheet heat exchanger has never ceased because of its Importance in a heat exchanger. The main function of the expansion bellows is to absorb the difference in expansion between the shell and the tube bundle while resisting the axial thermal deflection and the equivalent internal pressure on the shell side. TEMA-9 [1] edition attaches great importance to the finite element method in the case of an expansion bellows because of the disadvantages of the old design methods, which lead to overestimation and stress overload in the bellows. The objective of this work is to study the damage in the most stressed zone of the expansion bellows in order to construct a numerical simulation tool of the rupture to determine the lifetime that an expansion bellows can support during the operating conditions of a fixed tube heat exchanger. In a first step, the ANSYS FEM calculation code will allow the determination of the critical zone where the Von Mises is maximum and where potential cracks can develop. In a second step, a post-processor based on the concept of Continuum Damage Mechanics and using Newton's iterative method will be applied to this critical area for the determination of the bellows critical lifetime. The maximum lifetime will be the value of the number of cycles that corresponds to the critical value of the DC damage (crack initiation).

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.

A PROCEDURE FOR TUBE COUNT DETERMINATION IN SINGLE AND MULTIPLE PASS TUBULAR HEAT EXCHANGERS

The development of a simple computational procedure that allows the precise determination of important parameters for the thermal and mechanical design of tubular heat exchangers is discussed in the present work. The design of tubular heat exchangers for a wide variety of applications can involve the use of empirical expressions and data tables for the determination of the tube bundle parameters, such as the tube count and the tube bundle outside diameter. The motivation for developing the discussed procedure resides in addressing cases for which empirical expressions are inapplicable or data table are unavailable. Initially, the shell positions in which tubes can be placed are determined based on specified tube pitch, angle of arrangement, inlet and outlet nozzle diameters and tube bundle-to-shell clearance. The maximum number of tubes for the given configuration is obtained from the tube position searching procedure. A sorting algorithm, based on the tube distance to the shell center, is used to appropriately place a specified number of tubes within the heat exchanger cross section. Results for a single- and multiple-pass fixed-tubesheet heat exchangers are presented and compared with available tube count tables.

A PROCEDURE FOR TUBE COUNT DETERMINATION IN SINGLE AND MULTIPLE PASS TUBULAR HEAT EXCHANGERS

The development of a simple computational procedure that allows the precise determination of important parameters for the thermal and mechanical design of tubular heat exchangers is discussed in the present work. The design of tubular heat exchangers for a wide variety of applications can involve the use of empirical expressions and data tables for the determination of the tube bundle parameters, such as the tube count and the tube bundle outside diameter. The motivation for developing the discussed procedure resides in addressing cases for which empirical expressions are inapplicable or data table are unavailable. Initially, the shell positions in which tubes can be placed are determined based on specified tube pitch, angle of arrangement, inlet and outlet nozzle diameters and tube bundle-to-shell clearance. The maximum number of tubes for the given configuration is obtained from the tube position searching procedure. A sorting algorithm, based on the tube distance to the shell center, is used to appropriately place a specified number of tubes within the heat exchanger cross section. Results for a single- and multiple-pass fixed-tubesheet heat exchangers are presented and compared with available tube count tables.

A computer program for designing of shell-and-tube heat exchangers

In a computer-based design, many thousands of alternative exchanger configurations may be examined. Computer codes for design are organized to vary systematically the exchanger parameters such as, shell diameter, baffle spacing, number of tube-side pass to identify configurations that satisfy the specified heat transfer and pressure drops. A computer-based design model was made for preliminary design of shell-and-tube heat exchangers with single-phase fluid flow both on shell and tube side. The program covers segmentally baffled U-tube, and fixed tube sheet heat exchangers one-pass and two-pass for tube-side flow. The program determines the overall dimensions of the shell, the tube bundle, and optimum heat transfer surface area required to meet the specified heat transfer duty by calculating minimum or allowable shell-side pressure drop.

고정 튜브시트를 갖는 수평형 열교환기의 등가 모델링을 이용한 튜브 건전성 평가

고정 튜브시트를 갖는 수평형 열교환기의 등가 모델링을 이용한 튜브 건전성 평가

A program for the design of a heat exchanger as per TEMA standards

A program has been developed for the mechanical design of various parts of a fixed-tubesheet heat exchanger with two saddle supports. The design procedure given in TEMA and ASME VIII Section 1 standards have been followed, using a program which has been compiled in PASCAL and provides for automatic selection of nozzles and bolts for the channel head. Use of this program results in a considerable reduction in time required for the design.

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.

A Model for Fixed-Tubesheet Heat Exchanger

A model for a fixed-tubesheet heat exchanger was developed under the assumption that the outer rim of the tubesheet behaves as a circular plate. The tubesheet is conceived as made up of two parts; an inner drilled plate with uniform tube pattern and an external circular rim. Previous models assumed the outer rim to behave as a rigid plate. Under our more realistic model, a more accurate and economic design is possible. Four examples are brought to bear in order to show the procedure as well as to compare the stress distributions for a previous model assuming a rigid ring and our flexible counterpart.

Letter to the Editor commenting on “Tubesheet Thicknesses and Tube Loads for Floatinghead and Fixed-Tubesheet Heat Exchangers” (Soehrens, J. E., 1984, ASME J. Pressure Vessel Technol., 106, pp. 289–299)

Letter to the Editor commenting on “Tubesheet Thicknesses and Tube Loads for Floatinghead and Fixed-Tubesheet Heat Exchangers” (Soehrens, J. E., 1984, ASME J. Pressure Vessel Technol., 106, pp. 289–299)

Erratum: “Tubesheet Thicknesses and Tube Loads for Floatinghead and Fixed-Tubesheet Heat Exchangers” (Journal of Pressure Vessel Technology, 1984, 106, pp. 289–299)

Erratum: “Tubesheet Thicknesses and Tube Loads for Floatinghead and Fixed-Tubesheet Heat Exchangers” (Journal of Pressure Vessel Technology, 1984, 106, pp. 289–299)

Tubesheet Thicknesses and Tube Loads for Floatinghead and Fixed-Tubesheet Heat Exchangers

This paper presents procedures for computing tubesheet thicknesses and tube loads for floatinghead and fixed-tubesheet heat exchangers. It was prepared in connection with the activities of the Special Working Group on Heat Transfer Equipment of the ASME Boiler and Pressure Vessel Code Committee, for their use and consideration in the drafting of code rules for these items. The mathematical procedures are closely associated with the publications of Mr. K. A. Gardner. These are references [1 and 2] of the attached bibliography. As far as practicable, the symbols in this paper are those used by Gardner. Some differing symbols are used to be consistent with currently used Code symbols.