Investigation of a Shell and Tube Exchanger in Process Gas Heating Service

The design requirements for a large shell and tube vertical heat exchanger (to be used in a sulfur recovery tail gas treatment unit) included startup, shutdown and upset conditions that would subject the exchanger to significant temperature changes. The exchanger was designed to the requirement of the ASME Boiler and Pressure Vessel Section VIII Division 1 [1]. A detailed analysis of the thermal profiles and related stresses was performed to confirm the use of a flexible tube sheet design. The heat exchanger uses high pressure superheated steam on the shell side to heat a low pressure process gas on the tube side. The heat exchanger was sized and thermally rated, using commercially available analysis software. The proposed design was analyzed by Finite Element methods that included both thermal and stress analysis. These evaluations confirmed that a flexible tube sheet design was satisfactory when using specific dimensions.

Elastic-Plastic Analysis of an Elbow With Axial Part-Through Internal Crack at Crown Under In-Plane Bending

Piping elbows under bending moment are vulnerable to cracking at crown. The structural integrity assessment requires evaluation of J-integral. The J-integral values for elbows with axial part-through internal crack at crown under in-plane bending moment are limited in open literature. This paper presents the J-integral results of a thick and thin, 90-degree, long radius elbow subjected to in-plane opening bending moment based on number of finite element analyses covering different crack configurations. The non-linear elastic-plastic finite element analyses were performed using WARP3D software. Both geometrical and material nonlinearity were considered in the study. The geometry considered were for Rm/t = 5, and 12 with ratio of crack depth to wall thickness, a/t = 0.15, 0.25, 0.5 and 0.75 and ratio of crack length to crack depth, 2c/a = 6, 8, 10 and 12.

Multi-Objective Optimal Design of Sandwich Composite Laminates Using Simulated Annealing and FEM

Multi-objective optimal design of sandwich composite laminates consisting of high stiffness and expensive surface layers and low-stiffness and inexpensive core layer is addressed in this paper. The object is to determine ply angles and number of surface layers and core thickness in such way that natural frequency is maximized with minimal material cost and weight. A simulated annealing algorithm with finite element method is used for simultaneous cost and weight minimization and frequency maximization. The proposed procedure is applied to Graphite-Epoxy/Glass-Epoxy and Graphite-epoxy/Aluminum sandwich laminates and results are obtained for various boundary conditions and aspect ratios. Results show that this technique is useful in designing of effective, competitive and light composite structures.

Selecting the Optimum Bolt Assembly Stress: Influence of Flange Type on Flange Load Limit

In previous papers, practical limits on the maximum applied load for standard ASME B16.5 and B16.47 carbon steel, weld neck pipe flanges were examined. A new code equation for the tangential (hoop) stress at the small end of the hub for a weld neck flange was developed to facilitate calculation of the limits using elastic analysis. The results were verified against elastic-plastic Finite Element Analysis (FEA). In this paper, the work is extended to include other flange configurations, including loose ring flanges, slip-on flanges and flat plate flanges. This paper is a continuation of the papers presented during PVP 2006 and PVP 2007 (Brown [1, 2]) and it extends the scope of the proposed methodology for determining flange stress limits in determining the maximum allowable bolt load for any given flange size and configuration.

Crack Initiation Process for Semi-Circular Notched Plate in Fatigue Test at Elevated Temperature

Crack initiation and propagation process of fatigue test in semi-circular notched plates at elevated temperature were observed by the CCD video camera. Test specimens are made of SUS304 stainless steel, and temperature is kept to be 550°C, and geometry of semi-circular notched plate specimens are changed by diameter size of the circular hole. Photographs in all cycles were recorded to investigate crack initiation process in structural components having stress concentration and obtain number of cycle of crack initiation (Nc). The test results were compared with predictions by Stress Redistribution Locus (SRL) method and Neuber’s rule’s method.

Fatigue Evaluation in Mixing Zones: Comparison of Different Criteria of Fatigue

The distribution of unsteady temperatures in the wall of the 6" FATHER mixing tee mock-up is calculated for a loading configuration: The results seem realistic even if they are not still very accurate (see paper PVP2005-71592 [11]). On this basis, thermal stresses are evaluated for elastic and elastic-plastic material behavior. Then, different types of fatigue criteria are used to evaluate the fatigue damage. The paper develops a brief description of the criteria, the corresponding fatigue damage evaluation and attempts to explain the differences.

Stochastic Damage Growth Analysis Using EFGM

A stochastic meshless method is presented for solving boundary-value problems in damage mechanics under elastic-plastic conditions that involves random material properties. Material is assumed to have an initial damage, which follows a lognormal filed. An isotropic unified damage law, formulated by Lemaitre is used in this study. A meshless formulation based on element free Galerkin method (EFGM) is developed to predict stochastic structural response. A scaled matrix approach is used for applying the essential boundary conditions in EFGM. The proposed method is based on perturbation technique. First order perturbation technique for damage growth in an elastic plastic analysis is formulated. Newton-Raphson algorithm is used to solve for material nonlinearity. A numerical example is solved to study the effect of random initial damage in the structural response and further damage growth. Monte Carlo technique is used to validate the proposed method.

Illustration of the WPS Benefit Through Batman Test Series: Tests on Large Specimens Under WPS Loading Configurations

A study combining modelling and a series of experiments on large specimens submitted to a thermal shock or isothermal cooling has been performed in CEA-Saclay in order to show the WPS benefit on large scale specimen. The test series, named BATMAN, was made on 18MND5 ferritic steel bars, containing a short or large fatigue pre-crack. For the two performed tests (fast thermal shock creating a gradient across the thickness of the bar or for the gradual uniform cooling), the effect of “Warm Pre-Stressing” was confirmed. In both cases, no propagation was observed during the thermal transient. Fracture occurred under low temperature conditions, at the end of the test when the tensile load was increased. The failure loads then recorded were substantially higher than during pre-stressing. To illustrate the benefit of the WPS effect, numerical interpretations were performed using either global approach or local approach criteria. The capability of models to predict the WPS effect was clearly shown.

Investigation on the Strength of Ultra High Pressure Vessel Cylinder With Self-Protective Flat Steel Ribbons Wound

A unique type of self-protective Ultra-High Pressure Vessel (UHPV) cylinder with helically wound Flat Steel Ribbons (FSR) is proposed. The shielding properties of its self-protection in the hoop and axial directions of a FSR cylinder in the case of fracture failure, as well as quick-actuating of the tooth-locked end closure of this new vessel structure are both expounded. Based on its axial strength, a formula of the ultimate load-carrying capability of FSR layers is derived. The shielding function and self-protective capability of FSR layers to the UHPV cylinder are analyzed quantitatively in detail, and a design criterion is also defined. According to the formula and the design criterion defined in this paper, the predicted ultimate load-carrying capability of the FSR layers is 48.3% higher than that in previous references. Results from burst tests of 6 model vessels show that the brittle failure morphology of UHPV cylinders are changed with FSR layers and the potential hazard of failure of the UHPV is reduced. In addition, the cross fracture of the UHPV cylinder is shielded effectively and the derived formulation on the ultimate load-carrying capability of FSR layers is reasonable. UHPV cylinders designed according to the formula and the criterion can use much fewer FSR layers with the same shielding capability.

Environmental Fatigue Test of CF8M With a Small Autoclave Simulating PWR Conditions

To develop a fatigue design curve of cast stainless steel CF8M used in primary piping material of nuclear power plants, low-cycle fatigue tests have been conducted by Korea Electric Power Research Institute (KEPRI). A small autoclave simulated the environment of a pressurized water reactor (PWR), 15 MPa and 315 °C. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitudes at 0.04%/s strain rate. A small autoclave of 1 liter and cylindrical solid fatigue specimens were used for the strain-controlled low cycle environmental fatigue tests to make the experiments convenient. However, it was difficult to install displacement measuring instruments at the target length of the specimens inside the autoclave. To mitigate the difficulty displacement data measured at the shoulders of the specimen were calibrated based on the data relation of the target and shoulder length of the specimen during hot air test conditions. KEPRI developed a test procedure to perform low cycle environmental fatigue tests in the small autoclave. The procedure corrects the cyclic strain hardening effect by performing additional tests in high temperature air condition. KEPRI verified that the corrected test result agreed well with that of finite element method analysis. The process of correcting environmental fatigue data would be useful for producing reliable fatigue curves using a small autoclave simulating the operating conditions of a PWR.