Tube Sheet Research Articles

Study on Mechanical Behavior of High Pressure Heater Tubesheet 20MnMoNb

20MnMoNb alloy steel is a structural steel for forgings with good mechanical properties, which is typically used in the manufacture of pressure vessel tube sheets. The mechanical properties of 20MnMoNb at different temperatures were systematically studied. It is shown that the 20MnMoNb material has the good high temperature resistance. With the increase of temperature, the yield strength and tensile strength of the material have little difference. The tensile strength is nearly 800MPa at high temperature, and the yield strength is about 643MPa, which could meet the complex working environment of the high pressure heaters. It is helpful to improve the accuracy of analytical design results and provide a data base for the revision of subsequent material standards.

The thermophysical properties and the stability of nanofluids containing carboxyl-functionalized graphene nano-platelets and multi-walled carbon nanotubes

Two structures of carbon-based materials with sp2-hybridized are carbon nanotubes and graphene arrayed in the concentric tube and two-dimensional sheet, respectively. The most important problems of graphene and carbon nanotube for use in various applications are insufficient dispersibility and their inadequate stability in different organic and aqueous solvents. The low interaction with other materials is second category problems of carbon nanostructures. Functionalization, a common method suggested by numerous researchers, can be employed to enhance this property. In this regard, the nanofluids containing graphene nanoplatelets and carboxylated multi-walled carbon nanotube were synthesized and dispersed in deionized water to prepare homogeneous samples of 0.1 and 0.2 wt%. The stability dependency of samples was investigated, for the first time, on ultrasonic time and microwave irradiation. Thermophysical properties including shear stress, viscosity, surface tension, density and stability were also measured and reported.

Weld Strength Analysis of T-Joint Segments of the Metro Crossing Passage by the Shield Method Based Sub-Model

The weld of T-joint segments is the weakest link during the excavation of a metro crossing passage tunnel with the shield method. The stress on the weld is one of the key factors and should be given special attention. This paper aims to monitor the stress and strain of the weld of the T-joint segments during the construction process of the metro crossing passage tunnel of Ningbo Metro Line 3, the world first metro crossing passage tunnel by the shield method. A finite element model of the metro crossing passage tunnel is established. The CAE (Computer Aided Engineering) simulation is conducted by the sub-model approach. The calibration analysis between test data and CAE results for the strain of the weld under several key cases is performed. Based on this, the vary regulation of the stress and strain of the weld seam at various positions of the steel tube sheet under critical working conditions is obtained. Consequently, an authentic, reliable and advanced simulation process is established, and the weld strength of the T-joint segments of such kind constructions can be well assessed and predicted.

Research on Heat Treatment Process Optimization of Welding Workstation under New Engineering Background

With the development of new engineering, more research began to transform to energy-saving technology in equipment manufacturing industry. Studies about measurement and analysis of residual stress after surfacing of Heat exchanger tube sheet & the causes of PWHT (post weld heat treatment). Results revealed that the residual stress distribution presented certain trends. PWHT have a limited impact on general trend. Strongest point of stress appears in the ends of test piece or at the surface center of test piece. To some extent, annealing time of 300 minutes is more conducive to removing the residual stress than 90minutes. Annealing temperature of 610°C has more significantly effect than 580°C. Stress of measuring point reduced on average by 40%. At 580°C to 610°C and when annealing time is from 90 minutes to 300 minutes, main cause of removing the residual stress is annealing temperature.

Electromagnetic expansion joining between tubular and flat sheet component

To join tubular and flat sheet components, this paper investigates an electromagnetic expansion joining (EMEJ) method, which combines tube expansion and electromagnetic forming (an emerging high-speed forming technique). To enable partial modification of the conductive coil, an assembly-type Bitter coil was utilized. The aluminum alloys AA6063-O and AA7075-T6 were selected for the tube and flat sheet joining targets, respectively. EMEJ tests were performed with several charging voltages: 5.7, 7.5, 9.2, and 11.1 kV. Three EMEJ mechanisms were revealed by numerical simulations: a geometrical constraint imposed by the bulging and flanging of the tube, an interference fit imposed by the residual stress, and an indenting phenomenon caused by impact with the flat sheet. Complete joining without any looseness was accomplished at charging voltages of 9.2 and 11.1 kV. Through pull-out testing, the connection strength was confirmed to be higher than the yield strength of the tube, as was predicted by the numerical simulation. As a result, the tube and flat sheet were successfully joined by EMEJ without additional connecting elements, and the feasibility of EMEJ as an advanced joining technique was verified.

Fatigue lifetime assessment on a high-pressure heater in supercritical coal-fired power plants during transient processes of operational flexibility regulation

The operational flexibility of coal-fired power plants has become a priority objective; however, the lifetime of main devices is reduced due to thermomechanical fatigue during transient processes. This study focuses on the safety of high-pressure heaters at operational flexibility measures. The dynamic characteristics of thermal parameters in the 1# HP heater were obtained and analyzed based on transient models of a coal-fired power plant. The change trends of pressure/temperature on the steam/feedwater side of the 1# HP heater at three throttling the extraction steam measures were different with that at the feedwater bypass measure. Subsequently, finite element analysis method was used, and the thermomechanical stresses under the four measures were calculated and analyzed. The time to reach the maximum mechanical stresses was shorter than that of thermal stresses. Finally, the fatigue lifetimes of the heater were estimated. The maximum fatigue damage ratio at the per load cycle was 0.0069%, and the minimal allowable number of cycle was 14413 in the upper region of the tube sheet when the extraction steams of #1, #2, and 3# HP heaters are regulated simultaneously. The study could offer data guidance to the safety and maintenance of coal-fired power plants during operational flexibility regulations.

ABOUT THE USE OF TERMS «TUBE SHEET» AND «TUBE PLATE»

Development of scientific and technical knowledge, creation of new sci- ence disciplines arise the need for a standard for technical terminology. It is a serious problem to organize a lot of new terms. The clear fixed content is the main requirement for new terminology. In this paper, authors analyzed the use of well known terms «tube sheet» and «tube plate», which duplicates one another and are used to describe similar parts. This duplication is seen in various regulatory and technical documents that governs manufacturing technology, repair and operation of shell-and-tube heat exchangers, and also equally used in modern educa- tional and scientific literature. Authors analyzed the terms used in regulatory documentation, technical documentation, and in scientific papers. This analysis was performed on domestic resources and existing regulatory documents used in the US, Great Britain and many EU countries. The analysis of the usage of «tube sheet» and «tube plate» in the scientific and technical documentation, and scientific publications shows that there is no common view among the scientific and manufacturing community on what term should be used to refer to the part description, and therefore terms are used randomly. Terminology analysis given in this paper shows that the term «tube sheet» is preferred, it has one meaning for different construction designs, it is brief and corresponds to norms and rules of Russian language, and has all the necessary and sufficient features.

Failure analysis of titanium heater tubes and stainless steel heat exchanger weld joints in nitric acid loop

A 400 l capacity nitric acid loop (NAL) test facility simulating inactive plant operating conditions was designed, constructed and evaluation of candidate materials was carried out for nuclear spent fuel reprocessing applications. Austenitic stainless steel coupons were exposed to flowing nitric acid medium at various temperatures in NAL. Assessment of critical components of NAL after 10,000 h operation revealed failure of titanium heater tubes and stainless steel heat exchanger tube sheet welds. Failure analysis and detailed characterisation of corrosion products on the failed tubes were carried out using SEM, EDX and XRD techniques. The brown colour corrosion product on titanium heater tubes comprised iron and small amounts of chromium indicating that failure of titanium tubes was due to deposition of corrosion products of stainless steel, leading to galvanic corrosion. Cracks observed on titanium heater tubes were attributed to hydrogen-induced cracking, resulting in severe degradation. Surface morphology and EDX analysis of the corrosion product on stainless steel heat exchanger tubes revealed dislodged grains from 304LSS and XRD analysis confirmed the deposit as stainless steel. Grain dropping occurred due to intergranular corrosion of 304L SS in nitric acid and deposition of the dislodged grains at the seal weld joints resulted in localised corrosion and failure. Based on the studies carried out, surface heaters instead of immersion heaters and periodic inspection and frequent removal of corrosion products from the nitric acid loop were suggested to mitigate such failures. Based on the results of the investigation, repair and refurbishment of the nitric acid loop was undertaken.

Research possibility of application of non-destructive testing method based on the Barkhausen effect for the control of heat exchange equipment, exposed to im-pulse pressure

The article deals with the issues of ensuring the reliability of operation and methods for evaluation of connections (tube attachment points in tube sheets) of heat exchangers used in various industries. It is estimated the applicability of the control method based on the Barkhausen effect to check the place of tube fastening in tube sheets. Installations are considered as heat exchangers in which the connection is derive pipe with tube sheets is obtained by using impulsed pressure sources.

Current State and Trends in the Design and Operation of Water-Cooled Condensers of Steam Turbines for Thermal and Nuclear Power Stations (Review)

A review and analysis are presented of the available foreign publications on the modern methods of design, manufacture, design calculation, and operation of water-cooled condensers for large steam turbines used in Russia and abroad. A list of the world’s leading manufacturers of condensers is presented. The adopted alternative arrangements of condensers concerning the turbine centerline and available condenser design styles are examined. The condensers for turbines manufactured by General Electric and the Leningrad Metal Works (LMZ) are compared by their design characteristics and performance indices. The arrangements of tube bundles used in designing and upgrading condensers in Russia and abroad are presented. Information is given on construction materials of condenser tubes and tube sheets as well as on the methods for tube-to-tube sheet attachment. Data on air removal equipment of the condensers are presented. The basic lines of evolution of steam jet ejectors, water-ring pumps, and hybrid air removal systems are considered. The methods of condenser heat-transfer surface cleaning adopted in Russia and abroad are compared. The data on the number of failures and the basic causes of these failure are presented. The procedures for replacement of tubes during repair or modernization of condensers and the symptoms used to determine the necessity of tube replacement are described. Information derived from the authors' investigations and a review of American publications on the potential for heat transfer enhancement in the condensers through the use of shaped tubes is given. The condenser design methods and standards applicable in Russia and abroad are assessed. The lines of improvement in the design of condensers for modern steam turbines of thermal and nuclear power stations are outlined.

The method of connecting pipes with a thin tube sheet of a shell-and-tube heat exchanger

The method of connecting pipes with a thin tube sheet of a shell-and-tube heat exchanger

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).

Micro-Galvanic Corrosion of Steam Generator Materials within Pores of Magnetite Flakes in Alkaline Solutions

In secondary coolant system of the pressurized water reactors, the reduced corrosion products such as metallic Cu and Pb particles were accumulated in the pores of the magnetite flakes and electrically contacted to the steam generator materials. The micro-galvanic corrosion behavior of steam generator materials (steam generator tube materials: Alloy 600 and Alloy 690, steam generator tube sheet materials: SA508 Gr.3) contacted to the corrosion products (magnetite, Cu, and Pb) was investigated in an alkaline solution. The steam generator materials considered in this study were all the anodic elements of the galvanic pair because their corrosion potentials were lower than those of the corrosion products. The corrosion rate of the steam generator materials was increased by the galvanic coupling with the each corrosion products, and was more accelerated with increasing the area ratio of the corrosion products to the steam generator materials. Among the corrosion products, Cu has the largest galvanic effect on steam generator materials in the pores when area ratio of cathode to anode is 10.

A Unified Analytical Method of Stress Analysis for Tubesheet—Part III: Applicable Configuration of Heat Exchanger

Based on the unified analytical (UA) method and the unified and refined analytical (URA) method of stress analysis for fixed tubesheet (TS) heat exchangers (HEXs), floating head, and U-tube HEXs, the applicable configuration of HEX which depends on the combination of the TS edge conditions is discussed in this paper. Comparison shows that the UA and the URA methods cover a wide range of HEX configurations well beyond established ASME methods.

Pulsed Eddy-Current Detection of Loose Parts in Steam Generators

Flow-induced vibration of loose parts located on steam generator (SG) tube sheets can result in SG tube damage and eventual loss of SG efficiency. Regular inspection of SG tubes at support structures can help extend SG life by detecting and monitoring flaws as well as identifying accumulation of loose parts. Application of conventional eddy-current technologies in this case, however, is limited when magnetite fouling is present or when loose parts are resting directly on the SG tube sheet. Pulsed eddy current (PEC) combined with a modified principal components analysis (MPCA) was investigated as a method of detecting and identifying a variety of loose part materials in close proximity to 15.9-mm outer diameter Alloy-800 SG tubes and surrounding steel support structures. Loose parts were found to be detectable for varying axial positions along the SG tube and when in contact with the tube sheet. When offset radially from the SG tube, 1.6-mm-diameter carbon steel parts with a strong magnetic component allowed detection up to 3.2 mm away, while nonferromagnetic stainless steel parts of the same size could only be detected up to 1.5 mm away. Signal variation in the presence of loose parts was attributed to differences in amplitude of transient response and in relaxation times for diffusion of transient magnetic fields through various materials. The ability to accurately detect and identify loose parts located in close proximity to SG tubes establishes PEC combined with MPCA as a potential candidate for SG inspection.

Failure Analysis of Authentic Stainless Steel Tubes in a Vertical Fixed Shell–Tube Heat Exchanger

The vertical fixed shell–tube heat exchanger failed to work in one chemical plant, and the leakage of the heat exchanger tubes were found after the examination. To figure out the failure mechanism of the tubes, a series of investigations were performed including the specification verification, the visual examination, the analysis of the chemical composition, metallographic, scale layer composition, and the work fluid examination. The pits and cracks were observed on the tube end, which was welded to the upper sheet. It could be classified as the pitting corrosion and stress corrosion cracking of authentic stainless steel. Due to the substandard expansion process on the tube end, the crevices between the tube end and the upper tube sheet holes were not eliminated thoroughly. The high-temperature steam, mixed with the chloride ion and salts, entered into the crevices, and the chloride ion sufficiently gathered and absorbed on the surface of the tube end. Additionally, the stress was generated on the tube end from the operating pressure and welding process. The stress condition and high-temperature chloride condition on the tube end eventually led to the pitting corrosion and stress corrosion cracking.

A Unified Analytical Method of Stress Analysis for Tubesheet—Part II: Case Study

Based on the unified analytical method of stress analysis for fixed tubesheet (TS) heat exchangers (HEX), floating head and U-tube HEX presented in Part I, numerical comparisons with ASME method are performed in this paper as Part II. Numerical comparison results indicate that predictions given by the unified method agree well with finite element analysis (FEA), while ASME results are not accurate or not correct. Therefore, it is concluded that the unified method deals with thin TS of different types of HEX in equal detail with confidence to predict design stresses.

On the Homogeneity of Microstructure and Mechanical Properties for Stream Generator Tube Sheet

On the Homogeneity of Microstructure and Mechanical Properties for Stream Generator Tube Sheet

A Unified Analytical Method of Stress Analysis for Tubesheet—Part I: Theoretical Foundation

Based on a brief review of existing tubesheet (TS) design standards and the pertinent technical literature, a unified analytical method of stress analysis for fixed TS heat exchangers (HEXs), floating head and U-tube HEXs is proposed 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 needs be considered. The unified method can be successfully extended to the situations for different TS materials, unequal TS thicknesses, different TS edge conditions, different TS temperatures, pressures drop and dead weights on two TSs. The effects of pressure in TS perforations and temperature gradient in TS thickness direction are also considered by the unified method. Theoretical comparison shows that ASME method can be obtained from the special case of the simplified mechanical model of the unified method. Numerical comparison indicates that predictions given by the unified method agree well with finite element analysis (FEA), while ASME results are not accurate or not correct.

A CFD modeling to investigate the impact of flow mal-distribution on the performance of industrial methanol synthesis reactor

A two-step configuration consisting water-cooled and gas-cooled reactors has been developed by Lurgi to produce methanol from natural gas. The gas-cooled reactor, which is a vertical shell and tube heat exchanger, is constructed by fixed tube sheets with the cold gas stream in the tube side to properly cool the reacting gas mixture in the shell side. Under the practical operating condition, increase in the temperature drop is observed. As a result of high temperature decrease occurs at the end of the reactor, formation of gas condensate is observed in the fourth year of operation. In this regard, a computational fluid dynamics (CFD) model was developed to predict the behavior of gas streams in the shell and tube sides in order to find the reasons such phenomenea. The obtained results of the developed model were validated with the real plant data and a good agreement was observed. Then, gas velocity and temperature distributions in the shell and tube sides were presented. The obtained results show that the temperature mal-distribution in the shell side is a result of non-uniform flow distribution in the shell and tube sides. Furthermore, this flow distribution non-uniformity inside the reactor comes from an improper design of the distributer inside the reactor.