Simplified Development Method of FEA Code for Sloshing of Floating Roof Tanks (Lagrangian Formulation for Axisymmetric Linear Problem)

Floating roofs are widely used to prevent evaporation of content in large cylindrical aboveground oil storage tanks. The 2003 Hokkaido Earthquake caused severe damages to the floating roofs due to sloshing. These accidents became a cause to establish structural integrity of the floating roof tanks in sloshing. However, many designers do not have a solution for the sloshing of floating roof tanks except for three-dimensional FEA computer codes. The three-dimensional FEA requires a long computational time and expenses. The sloshing of floating roof tanks is a coupling vibration problem with fluid and structure. The simplified and convenient method has been desired for this solution. This paper presents a simplified development method of a FEA code in the axisymmetric linear problem. It is performed to modify an existing structural analysis code. The fluid behavior is formulated in terms of displacement as the Lagrangian approach.

Environmental Considerations for Gasket Selection and the Development of an Emissions Calculator for Gasket Materials

The choice of gasket type for flanged connections has typically been determined on the basis of temperature, pressure, and chemical nature of the contained fluid; sealability; ease of handling and installation; expected service life; comparable cost; and other factors. Of ever increasing importance is the environmental performance of the selected gasket with an emphasis on fugitive emissions reduction. All gaskets have some level of fluid leakage but this may vary significantly depending on the type selected. A practical tool using Microsoft® Excel® has been developed that can help predict anticipated fugitive emissions of gaskets for which Room Temperature Testing (ROTT) data are available. The construction and application of this tool are described and a relative comparison of tightness parameters and projected fugitive emissions for example gasket types are documented.

Account for Metal to Metal Contact Between Gasket Centering Ring and Flange Facing in Calculation Using the XP CEN\TS 1591-3 Method: Comparison With Other Analytical Method and Finite Element Analysis

The european standard EN1591-1 [1], initially published in 2001, defines a calculation method for bolted gasketed circular flanges, alternative to the TAYLOR-FORGE method, used as the basic method in most codes. In 2007, a new part, XP CEN/TS 1591-3 [2], has been added to the EN1591 series. This technical specification enables to take into account the Metal to Metal Contact (MMC), appearing inside the bolt circle on some assemblies. Due to a lack of industrial feedback and detailed validation, this document has not been raised to the standard status. In that context, under the request of its Pressure Vessel and Piping commission, CETIM has performed a study comparing this calculation method to Finite Element Analysis (FEA) on several industrial configurations. After a description of the XP CEN/TS 1591-3 calculation method, the major results obtained for spiral wound gasketed joints where MMC appears between centering ring and flange facing are presented and compared with FEA results. Moreover, results obtained with other classical analytical calculation methods as TAYLOR FORGE and EN1591-1 on the same Bolted Flange Connections (BFC) configuration are also analysed and compared to XP CEN/TS 1591-3 results.

Using Explicit Finite Element Analysis to Simulate the Structural Damage Associated With an Internal Detonation in a Heat Exchanger

Developing the realistic blast loading associated with an internal detonation occurring within a pressure vessel or heat exchanger is challenging. Unlike evaluation of external blast loading on structures due to far-field explosions, where typical overpressure-time histories can be reasonably defined based on empirical data, investigating confined detonations presents additional complications. The subsequent impulsive peak reflected overpressure from confined detonations acting on a structure can be extremely high due to the close proximity of the blast source to the vessel wall or pressure boundary. This establishes the possibility of significant structural damage for process equipment subjected to an internal detonation, even for relatively modest amounts of concentrated explosive products. This paper discusses the underlying theory of blast analysis and examines the practical application of non-linear, finite element based, explicit computational techniques for simulating the load acting on a structure due to internal and external blasts. The investigation of a recent, real-life industry failure of a heat exchanger due to a suspected internal detonation is discussed. Explicit, three-dimensional blast analysis is performed on the heat exchanger in question, and an internal detonation is simulated to reasonably replicate the considerable damage actually observed in the field. This analysis permits the determination of an approximate amount of concentrated product that caused the accidental explosion; that is, the plausible equivalent amount of explosives is back-calculated based on the predicted damage to the finite element model of the equipment in question. Computational iterations of varying charge amounts are performed and the predicted amount of permanent damage is documented so sensitivity to the hypothesized charge amount can be quantified. Furthermore, explicit blast analysis of nearby equipment is performed. In this investigation, computational results for both the heat exchanger (subjected to internal blast loading) and surrounding equipment (subjected to external blast loading) are in good agreement with the measured plastic deformations and failure modes that were actually observed in the field. Commentary on the likely detonation event that caused the significant damage observed is provided. Additionally, an advanced finite element failure criterion that is driven by plastic yielding is employed where portions of the computational model are removed from the simulation once a user-defined strain threshold is reached. This approach facilitates simulation of the gross heat exchanger pressure boundary failure actually observed in this case. The explicit finite element based analyses discussed in this study reasonably predict the structural response and damage characteristics corresponding to a recent, real-life industry failure.

Clamp Load Decay in Preloaded Dissimilar Lightweight-Material Joints due to Cyclic Temperature

Experimental and Finite Element methods are used for investigating the effect of cyclic thermal loading on the clamp load decay in preloaded single-lap bolted joints that are made of dissimilar-materials. Joint material combinations include steel and lightweight materials such as aluminum and magnesium alloys, with various different thicknesses. The range of cyclic temperature profile varies between −20°C and +150°C. A computer-controlled environmental chamber is used for generating the desired cyclic temperature profile and duration. Real time clamp load data is collected using high-temperature load cells. Percent clamp load decay is investigated for various combinations of joint materials, initial preload level, and test specimen thicknesses. Thermal and material creep finite element analysis is performed using temperature-dependent mechanical properties. FEA result has provided insight into interesting experimental observations regarding model predictions and the experimental data is discussed.

Stress Analysis and Sealing Performance Evaluation of Bolted Pipe Flange Connections With Smaller and Larger Nominal Diameter Under Repeated Temperature Changes

Pipe flange connections with gaskets in chemical plants, electric power plants and other industrial plants are usually exposed to elevated internal pressure with cyclic thermal condition. It is important to investigate the sealing performance of pipe connections under long term severe thermal exposure swings to ensure operational safety. In this study, the effects of cyclic thermal conditions on the sealing performance and mechanical characteristics in larger and smaller nominal diameter of pipe flange connection are examined using FEM calculations. Helium gas leakage is predicted using the contact gasket stress obtained from the FEM results. On other hand, the leakage tests using the smaller nominal diameter of pipe flange connection were conducted to measure the amount of helium gas leakage and to compare with the predicted amount of gas leakage. As the results, the contact gasket stress distributions were changed dramatically under cyclic thermal condition and elevated internal pressure. In the pipe flange connections with smaller nominal diameter, the contact gasket stress was the smallest in the restart condition. On other hand, the minimum contact gasket stress in the pipe flange connection with larger nominal diameter was depending on the materials of connection. In the pipe flange connection with larger nominal diameter, the contact gasket stress distributed and changed in the radial direction due to the flange rotation. A fairly good agreement was found between the experimental leakage result and predicted leakage results.

Other Factors Besides Anti-Seize That Affect Stud/Bolt Breakout and Assembly Torque (K-Factor)

This paper presents information about break out torque and several key elements to consider when specifying joint and disassembly procedures. These key elements include: (1) hardened washer material used, (2) penetrant selection for disassembly, and (3) penetrant application method. This paper also presents experimental K-factor data, including variation recorded from several hardened washer configurations and information from additional K-factor testing.

Overpressure Fragility Evaluation of a Mark I Drywell Using Thermal-Mechanical Finite Element Analysis

The overpressure fragility of a Mark I boiling water reactor drywell was performed by detailed finite element (FE) analysis. The drywell overpressure capacity is controlled by the onset of leakage in the bolted head flange connection once separation exceeds the capacity of the silicone rubber O-ring seals. The FE analysis was conducted at 6 discrete accident temperatures, ranging from 150 to 425°C. The overpressure evaluation used an axisymmetric model of the drywell head region for computational efficiency, and verified it by comparing to results from one FE model which used 3D solid elements. The mechanical properties of the steel materials were defined as temperature-dependent linear-elastic. The median overpressure capacity at each temperature was determined using a 2-step thermal-stress analysis procedure. First, a steady-state heat transfer analysis was conducted to map out the temperature distribution in the drywell wall, which is exposed to the accident temperature on the inside and ambient temperature on the outside. Second, a quasi-static multi-step stress analysis was performed. The vertical differential movement between the flange surfaces was monitored and compared to the O-ring rebound capacity to define the pressure at the onset of leakage. After leakage occurred, the relationship between leakage area and increased pressure was recorded. The evaluation predicted the median overpressure capacity and the lognormal standard deviation for uncertainty in O-ring rebound capacities, bolt preload, and model sophistication, in addition to the median pressure-leak area relationship.

Effect of Fastener Under Head Contact on the Early Stage of Self-Loosening of Preloaded Countersunk Fasteners Subjected to Cyclic Shear Loading

Three dimensional Finite Element model is used to investigate the loosening behavior of countersunk threaded fasteners subjected to cyclic shear loading applied through prescribed transverse excitation to the fastener head. Fasteners with conical head profile require precision machining of both the fastener head and the mating joint hole. Any mismatch between the head and the joint conical angles affects the torque tension relationship as well as the loosening performance. Investigation focuses on the loosening behavior in its early stages. Factors investigated include the effect of the bolt head/joint hole contact location, joint elastic modulus, and tapped hole clearance for different combinations of thread fit, on the loosening performance of preloaded countersunk-head bolts. The FEA model prediction of the self-loosening behavior is experimentally validated.